How has biodiversity changed through time?

                 The Earth is estimated to have formed, by the accretion through large and violent impacts of numerous bodies, approximately 4.5 billion years ago (Ga). Traditionally, habitable worlds are considered to be those on which liquid water is stable at the surface. On Earth, both the atmosphere and the oceans may well have started to form as the planet itself did so. Certainly, life is thought to have originated on Earth quite early in its history, probably after about 3.8–4.0 Ga, when impacts from large bodies from space are likely to have declined or ceased. It may have originated in a shallow marine pool, experiencing intense radiation, or possibly in the environment of a deeper water hydrothermal vent. Because of the subsequent recrystallisation and deformation of the oldest sediments on Earth, evidence for early life must be found in its metabolic interaction with the environment. 

                 The earliest, and highly controversial, evidence of life, from such indirect geochemical data, is from more than 3.83 billion years ago (Dauphas et al. 2004). Relatively unambiguous fossil evidence of life dates to 2.7 Ga (López-García et al. 2006). Either way, life has thus been present throughout much of the Earth’s existence. Although inevitably attention tends to fall on more immediate concerns, it is perhaps worth occasionally recalling this deep heritage in the face of the conservation challenges of today. For much of this time, however, life comprised Precambrian chemosynthetic and photosynthetic prokaryotes, with oxygen-producing cyanobacteria being particularly important (Labandeira 2005). Indeed, the evolution of oxygenic photosynthesis, followed by oxygen becoming a major component of the atmosphere, brought about a dramatic transformation of the environment on Earth. Geochemical data has been argued to suggest that oxygenic photosynthesis evolved before 3.7 Ga (Rosing and Frei 2004), although others have proposed that it could not have arisen before c.2.9 Ga (Kopp et al. 2005). 

                 These cyanobacteria were initially responsible for the accumulation of atmospheric oxygen. This in turn enabled the emergence of aerobically metabolizing eukaryotes. At an early stage, eukaryotes incorporated within their structure aerobically metabolizing bacteria, giving rise to eukaryotic cells with mitochondria; all anaerobically metabolizing eukaryotes that have been studied in detail have thus far been found to have had aerobic ancestors, making it highly likely that the ancestral eukaryote was aerobic (Cavalier-Smith 2004). This was a fundamentally important event, leading to heterotrophic microorganisms and sexual means of reproduction. Such endosymbiosis occurred serially, by simpler and more complex routes, enabling eukaryotes to diversify in a variety of ways. Thus, the inclusion of photosynthesizing cyanobacteria into a eukaryote cell that already contained a mitochondrion gave rise to eukaryotic cells with plastids and capable of photosynthesis. This event alone would lead to dramatic alterations in the Earth’s ecosystems. Precisely when eukaryotes originated, when they diversified, and how congruent was the diversification of different groups remains unclear, with analyses giving a very wide range of dates (Simpson and Roger 2004). The uncertainty, which is particularly acute when attempting to understand evolutionary events in deep time, results principally from the inadequacy of the fossil record (which, because of the low probabilities of fossilization and fossil recovery, will always tend to underestimate the ages of taxa) and the difficulties of correctly calibrating molecular clocks so as to use the information embodied in genetic sequences to date these events. Nonetheless, there is increasing convergence on the idea that most known eukaryotes can be placed in one of five or six major clades—Unikonts (Opisthokonts and Amoebozoa), Plantae, Chromalveolates, Rhizaria and Excavata (Keeling et al. 2005; Roger and Hug 2006). Focusing on the last 600 million years, attention shifts somewhat from the timing of key diversification events (which becomes less controversial) to how diversity per se has changed through time (which becomes more measurable). 

                  Arguably the critical issue is how well the known fossil record reflects the actual patterns of change that took place and how this record can best be analyzed to address its associated biases to determine those actual patterns. The best fossil data are for marine invertebrates and it was long thought that these principally demonstrated a dramatic rise in diversity, albeit punctuated by significant periods of stasis and mass extinction events. However, analyses based on standardized sampling have markedly altered this picture. They identify the key features of change in the numbers of genera (widely assumed to correlate with species richness) as comprising: 

(i) A rise in richness from the Cambrian through to the mid-Devonian (525–400 million years ago, Ma); (ii) a large
extinction in the mid-Devonian with no clear recovery
until the Permian (400–300 Ma); 

(iii) A large extinction in the late-Permian and again in
the late-Triassic (250–200 Ma)

(iv) A rise in richness through the late-Triassic to the present
(200–0 Ma; Alroy et al. 2008). 

                  Whatever the detailed pattern of change in diversity through time, most of the species that have ever existed are extinct. Across a variety of groups (both terrestrial and marine), the best present estimate based on fossil evidence is that the average species has had a lifespan (from its appearance in the fossil record until the time it disappeared) of perhaps around 1–10 Myr (McKinney 1997; May 2000). However, the variability both within and between groups is very marked, making estimation of what is the overall average difficult. The longest-lived species that is well documented is a bryozoan that persisted from the early Cretaceous to the present, a period of approximately 85 million years (May 2000). If the fossil record spans 600 million years, total species numbers were to have been roughly constant over this period, and the average life span of individual species were 1–10 million years, then at any specific instant the extant species would have represented 0.2–2% of those that have ever lived (May 2000). If this were true of the present time then, if the number of extant eukaryote species numbers 8 million, 400 million might once have existed. 

                The frequency distribution of the numbers of time periods with different levels of extinction is markedly right skewed, with most periods having relatively low levels of extinction and a minority having very high levels (Raup 1994). The latter are the periods of mass extinction when 75–95% of species that were extant are estimated to have become extinct. Their significance lies not, however, in the overall numbers of extinctions for which they account (over the last 500 Myr this has been rather small), but in the hugely disruptive effect they have had on the development of biodiversity. Clearly neither terrestrial nor marine biotas are infinitely resilient to environmental stresses. Rather, when pushed beyond their limits they can experience dramatic collapses in genetic, organismal and ecological diversity (Erwin 2008). This is highly significant given the intensity and range of pressures that have been exerted on biodiversity by humankind, and which have drastically reshaped the natural world over a sufficiently long period in respect to available data that we have rather little concept of what a truly natural system should look like (Jackson 2008). Recovery from past mass extinction events has invariably taken place. But, whilst this may have been rapid in geological terms, it has nonetheless taken of the order of a few million years (Erwin 1998), and the resultant assemblages have invariably had a markedly different composition from those that preceded a mass extinction, with groups which were previously highly successful in terms of species richness being lost entirely or persisting at reduced numbers.

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Measuring biodiversity

                 Given the multiple dimensions and the complexity of the variety of life, it should be obvious that there can be no single measure of biodiversity. Analyses and discussions of biodiversity have almost invariably to be framed in terms of particular elements or groups of elements, although this may not always be apparent from the terminology being employed (the term ‘biodiversity’ is used widely and without explicit qualification to refer to only some subset of the variety of life). Moreover, they have to be framed in terms either of “number” or of “heterogeneity” measures of biodiversity, with the former disregarding the degrees of difference between the occurrences of an element of biodiversity and the latter explicitly incorporating such differences. For example, organismal diversity could be expressed in terms of species richness, which is a number measure, or using an index of diversity that incorporates differences in the abundances of the species, which is a heterogeneity measure. 

                 The two approaches constitute different responses to the question of whether biodiversity is similar or different in an assemblage in which a small proportion of the species comprise most of the individuals, and therefore would predominantly be obtained in a small sample of individuals, or in an assemblage of the same total number of species in which abundances are more evenly distributed, and thus more species would occur in a small sample of individuals (Purvis and Hector 2000). The distinction between number and heterogeneity measures is also captured in answers to questions that reflect taxonomic heterogeneity, for example whether the above-mentioned group of 10 skipper butterflies is as biodiverse as a group of five skipper species and five swallowtail species (e.g. Hendrickson and Ehrlich 1971). In practice, biodiversity tends most commonly to be expressed in terms of number measures of organismal diversity, often the numbers of a given taxonomic level, and particularly the numbers of species. 

                 This is in large part a pragmatic choice. Organismal diversity is better documented and often more readily estimated than is genetic diversity, and more finely and consistently resolved than much of ecological diversity. Organismal diversity, however, is problematic inasmuch as the majority of it remains unknown (and thus studies have to be based on subsets), and precisely how naturally and well many taxonomic groups are themselves delimited remains in dispute. Perhaps most importantly it also remains but one, and arguably a quite narrow, perspective on biodiversity. Whilst accepting the limitations of measuring biodiversity principally in terms of organismal diversity, the following sections on temporal and spatial variation in biodiversity will follow this course, focusing in many cases on species
richness.

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Ecological diversity

                            The third group of elements of biodiversity encompasses the scales of ecological differences from populations, through habitats, to ecosystems, ecoregions, provinces, and on up to biomes and biogeographic realms. This is an important dimension to biodiversity not readily captured by genetic or organismal diversity, and in many ways is that which is most immediately apparent to us, giving the structure of the natural and semi-natural world in which we live. However, ecological diversity is arguably also the least satisfactory of the groups of elements of biodiversity. There are two reasons. First, whilst these elements clearly constitute useful ways of breaking up continua of phenomena, they are difficult to distinguish without recourse to what ultimately constitute some essentially arbitrary rules. For example, whilst it is helpful to be able to label different habitat types, it is not always obvious precisely where one should end and another begin, because no such beginnings and endings really exist.

                 In consequence, numerous schemes have been developed for distinguishing between many elements of ecological diversity, often with wide variation in the numbers of entities recognized for a given element. Second, some of the elements of ecological diversity clearly have both abiotic and biotic components (e.g. ecosystems, ecoregions, biomes), and yet biodiversity is defined as the variety of life. Much recent interest has focused particularly on delineating ecoregions and biomes, principally for the purposes of spatial conservation planning, and there has thus been a growing sense of standardization of the schemes used. Ecoregions are large areal units containing geographically distinct species assemblages and experiencing geographically distinct environmental conditions. Careful mapping schemes have identified 867 terrestrial ecoregions (Figure 2.1 and Plate 1; Olson et al. 2001), 426 freshwater ecoregions (Abell et al. 2008), and 232 marine coastal & shelf area ecoregions
(Spalding et al. 2007). 

                Ecoregions can in turn be grouped into biomes, global-scale biogeographic regions distinguished by unique collections of species assemblages and ecosystems. Olson et al. (2001) distinguish 14 terrestrial biomes, some of which at least will be very familiar wherever in the world one resides (tropical & subtropical moist broadleaf forests; tropical & subtropical dry broadleaf forests; tropical & subtropical coniferous forests; temperate broadleaf & mixed forests; temperate coniferous forests; boreal forest/taiga; tropical &
subtropical grasslands, savannas & shrublands; temperate grasslands, savannas & shrublands; flooded grasslands & savannas; montane grasslands & shrublands; tundra; Mediterranean forests, woodlands & scrub; deserts & xeric shrublands; mangroves). At a yet coarser spatial resolution, terrestrial and aquatic systems can be divided into biogeographic realms. 

                 Terrestrially, eight such realms are typically recognized, Australasia, Antarctic, Afrotropic, Indo-Malaya, Nearctic, Neotropic, Oceania and Palearctic (Olson et al. 2001). Marine coastal & shelf areas have been divided into 12 realms (Arctic, Temperate North Atlantic, Temperate Northern Pacific, Tropical Atlantic, Western Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Tropical Eastern Pacific, Temperate South America, Temperate Southern Africa, Temperate Australasia, and Southern Ocean; Spalding et al. 2007). There is no strictly equivalent scheme for the pelagic open ocean, although one has divided the oceans into four primary units (Polar, Westerlies, Trades and Coastal boundary), which are then subdivided, on the basis principally of biogeochemical features, into a further 12 biomes (Antarctic Polar, Antarctic Westerly Winds, Atlantic Coastal, Atlantic Polar, Atlantic Trade Wind, Atlantic Westerly Winds, Indian Ocean Coastal, Indian Ocean Trade Wind, Pacific Coastal, Pacific Polar, Pacific Trade Wind, Pacific Westerly Winds), and then into a finer 51 units (Longhurst 1998).

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Organismal diversity

                 Organismal diversity encompasses the full taxonomic hierarchy and its components, from individuals upwards to populations, subspecies and species, genera, families, phyla, and beyond to kingdoms and domains. Measures of organismal diversity thus include some of the most familiar expressions of biodiversity, such as the numbers of species (i.e. species richness). Others should be better studied and more routinely employed than they have been thus far. Starting at the lowest level of organismal diversity, little is known about how many individual organisms there are at any one time, although this is arguably an important measure of the quantity and variety of life (given that, even if sometimes only in small ways, most individuals differ from one another). Nonetheless, the numbers must be extraordinary. The global number of prokaryotes has been estimated to be 4–6 x 1030 cells—manymillion times more than there are stars in the visible universe (Copley 2002)—with a production rate of 1.7 x 1030 cells per annum (Whitman et al. 1998). The numbers of protists is estimated at 104 107 individuals per m2 (Finlay 2004).Impoverished habitats have been estimated to have 105 individual nematodes per m2, and more productive habitats 106 107 per m2, possibly with an upper limit of 108 per m2; 1019 has been suggested as a conservative estimate of the global number of individuals of free-living nematodes (Lambshead 2004). By contrast, it has been estimated that globally there may be less than 1011 breeding birds at any one time, fewer than 17 for every person on the planet (Gaston et al. 2003). Individual organisms can be grouped into relatively independent populations of a species on the basis of limited gene flow and some level of genetic differentiation (as well as on ecological criteria).

                  The population is a particularly important element of biodiversity. First, it provides an important link between the different groups of elements of biodiversity. Second, it is the scale at which it is perhaps most sensible to consider linkages between biodiversity and the provision of ecosystem services (supporting services—e.g. nutrient cycling, soil formation, primary production; provisioning services—e.g. food, fresh water, timber and fiber, fuel; regulating services—e.g. climate regulation, flood regulation, disease regulation, water purification; cultural services—e.g. aesthetic, spiritual, educational, recreational; MEA 2005). Estimates of the density of such populations and the average geographic range sizes of species suggest a total of about 220 distinct populations per eukaryote species (Hughes et al. 1997). Multiplying this by a range of estimates of the extant numbers of species, gives a global total of 1.1 to 6.6 x 109 populations (Hughes et al. 1997), one or fewer for every person on the planet. The accuracy of this figure is essentially unknown, with major uncertainties at each step of the calculation, but the ease with which populations can be eradicated (e.g. through habitat destruction) suggests that the total is being eroded at a rapid rate.

                  People have long pondered one of the important contributors to the calculation of the total number of populations, namely how many different species of organisms there might be. Greatest uncertainty continues to surround the richness of prokaryotes, and in consequence they are often ignored in global totals of species numbers. This is in part variously because of difficulties in applying standard species concepts, in culturing the vast majority of these organisms and thereby applying classical identification techniques, and by the vast numbers of individuals. Indeed, depending on the approach taken, the numbers of prokaryotic species estimated to occur even in very small areas can vary by a few orders of magnitude (Curtis et al. 2002; Ward 2002). The rate of reassociation of denatured (i.e. single stranded) DNA has revealed that in pristine soils and sediments with high organic content samples of 30 to 100 cm^3 correspond to c. 3000 to 11 000 different genomes, and may contain 104 different prokaryotic species of equivalent abundances (Torsvik et al. 2002). Samples from the intestinal microbial flora of just three adult humans contained representatives of 395 bacterial operational taxonomic units (groups without formal designation of taxonomic rank, but thought here to be roughly equivalent to species), of which 244 were previously unknown, and 80% were from species that have not been cultured (Eckburg et al. 2005).

                   Likewise, samples from leaves were estimated to harbor at least 95 to 671 bacterial species from each of nine tropical tree species, with only 0.5% common to all the tree species, and almost all of the bacterial species being undescribed (Lambais et al. 2006). On the basis of such findings, global prokaryote diversity has been argued to comprise possibly millions of species, and some have suggested it may be many orders of magnitude more than that (Fuhrman and Campbell 1998; Dykhuizen 1998; Torsvik et al. 2002; Venter et al. 2004). Although much more certainty surrounds estimates of the numbers of eukaryotic than prokaryotic species, this is true only in a relative and not an absolute sense. Numbers of eukaryotic species are still poorly understood. A wide variety of approaches have been employed to estimate the global numbers in large taxonomic groups and, by summation of these estimates, how many extant species there are overall. These approaches include extrapolations based on counting species, canvassing taxonomic experts, temporal patterns of species description, proportions of undescribed species in samples, well-studied areas, well-studied groups, speciesabundance distributions, species-body size distributions, and trophic relations (Gaston 2008). One recent summary for eukaryotes gives lower and upper estimates of 3.5 and 108 million species, respectively, and a working figure of around 8 million species. Based on current information the two extremes seem rather unlikely, but the working figure at least seems tenable. However, major uncertainties surround global numbers of eukaryotic species in particular environments which have been poorly sampled (e.g. deep sea, soils, tropical forest canopies), in higher taxa which are extremely species rich or with species which are very difficult to discriminate (e.g. nematodes, arthropods), and in particular functional groups which are less readily studied (e.g. parasites). A wide array of techniques is nowbeing employed to gain access to some of the environments that have been less well explored, including rope climbing techniques, aerial walkways, cranes and balloons for tropical forest canopies, and remotely operated vehicles, bottom landers, submarines, sonar, and video for the deep ocean.

                  Molecular and better imaging techniques are also improving species discrimination. Perhaps most significantly, however, it seems highly probable that the majority of species are parasites, and yet few people tend to think about biodiversity from this viewpoint. How many of the total numbers of species have been taxonomically described remains surprisingly uncertain, in the continued absence of a single unified, complete and maintained database of valid formal names. However, probably about 2 million extant species are regarded as being known to science (MEA 2005). Importantly, this total hides two kinds of error. First, there are instances in which the same species is known under more than one name (synonymy). This is more frequent amongst widespread species, which may show marked geographic variation in morphology, and may be described anew repeatedly in different regions. Second, one name may actually encompass multiple species (homonymy). This typically occurs because these species are very closely related, and look very similar (cryptic species), and molecular analyses may be required to recognize or confirm their differences. Levels of as yet unresolved synonymy are undoubtedly high in many taxonomic groups. Indeed, the actual levels have proven to be a key issue in, for example, attempts to estimate the global species richness of plants, with the highly variable synonymy rate amongst the few groups that have been well studied in this regard making difficult the assessment of the overall level of synonymy across all the known species.

                  Equally, however, it is apparent that cryptic species abound, with, for example, one species of neotropical skipper butterfly recently having been shown actually to be a complex of ten species (Hebert et al. 2004). New species are being described at a rate of about 13 000 per annum (Hawksworth andKalin-Arroyo 1995), or about 36 species on the average day. Given even the lower estimates of overall species numbers this means that there is little immediate prospect of greatly reducing the numbers that remain unknown to science. This is particularly problematic because the described species are a highly biased sample of the extant biota rather than the random one that might enable  more ready extrapolation of its properties to all extant species. On average, described species tend to be larger bodied, more abundant and more widespread, and disproportionately from temperate regions. Nonetheless, new species continue to be discovered in even otherwise relatively well-known taxonomic groups. New extant fish species are described at the rate of about 130–160 each year (Berra 1997), amphibian species at about 95 each year (from data in Frost 2004), bird species at about 6–7 each year (Van Rootselaar 1999, 2002), and terrestrial mammals at 25–30 each year (Ceballos and Ehrlich 2009).

                 Recently discovered mammals include marsupials, whales and dolphins, a sloth, an elephant, primates, rodents, bats and ungulates. Given the high proportion of species that have yet to be discovered, it seems highly likely that there are entire major taxonomic groups of organisms still to be found. That is, new examples of higher level elements of organismal diversity. This is supported by recent discoveries of possible new phyla (e.g. Nanoarchaeota), new orders (e.g. Mantophasmatodea), new families (e.g. Aspidytidae) and new subfamilies (e.g. Martialinae). Discoveries at the highest taxonomic levels have particularly served to highlight the much greater phyletic diversity of microorganisms compared with macroorganisms. Under one classification 60% of living phyla consist entirely or largely of unicellular species (Cavalier-Smith 2004). Again, this perspective on the variety of

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Genetic diversity

                       Some understanding of what the variety of life comprises can be obtained by distinguishing between different key elements. These are the basic building blocks of biodiversity. For convenience, they can be divided into three groups: genetic diversity, organismal diversity, and ecological diversity. Within each, the elements are organized in nested hierarchies, with those higher order elements comprising lower orderones. The three groups are intimately linked and share some elements in common.

Genetic diversity

                Genetic diversity encompasses the components of the genetic coding that structures organisms (nucleotides, genes, chromosomes) and variation in the genetic make-up between individuals within a population and between populations. This is the raw material on which evolutionary processes act. Perhaps themost basicmeasure of genetic diversity is genome size the amount of DNA (Deoxyribonucleic acid) in one copy of a species’ chromosomes (also called the C-value). This can vary enormously, with published eukaryote genome sizes ranging between 0.0023 pg (picograms) in the parasitic microsporidium Encephalitozoon intestinalis and 1400 pg in the free-living amoeba Chaos chaos (Gregory 2008).


                   These translate into estimates of 2.2 million and 1369 billion base pairs (the nucleotides on opposing DNA strands), respectively. Thus, even at this level the scale of biodiversity is daunting. Cell size tends to increase with genome size. Humans have a genome size of 3.5 pg (3.4 billion base pairs). Much of genome size comprises non-coding DNA, and there is usually no correlation between genome size and the number of genes coded. The genomes of more than 180 species have been completely sequenced and it is estimated that, for example, there are around 1750 genes for the bacteria Haemophilus influenzae and 3200 for Escherichia coli, 6000 for theyeast Saccharomyces cerevisiae, 19 000 for the nematode Caenorhabditis elegans, 13 500 for the fruit fly Drosophila melanogaster, and 25 000 for the plant Arabidopsis thaliana, themouseMusmusculus, brown rat Rattus norvegicus and human Homo sapiens.


                  There is strong conservatism of some genes acrossmuchof thediversityof life.Thedifferences in genetic composition of species giveus indications of their relatedness, andthus important informationas to how the history and variety of life developed. Genes are packaged into chromosomes. The number of chromosomes per somatic cell thus far observed varies between 2 for the jumper ant Myrmecia pilosula and 1260 for the adders-tongue fern Ophioglossum reticulatum. The ant species reproduces by haplodiploidy, in which fertilized eggs (diploid) develop into females and unfertilized eggs (haploid) become males, hence the latter have the minimal achievable single chromosome in their cells (Gould 1991). Humans have 46 chromosomes (22 pairs of autosomes, and one pair of sex chromosomes). Within a species, genetic diversity is commonly measured in terms of allelic diversity (average number of alleles per locus), gene diversity (heterozygosity across loci), or nucleotide differences.


                 Large populations tend to have more genetic diversity than small ones, more stable populations more than those that wildly fluctuate, and populations at the center of a species’ geographic range often have more genetic diversity than those at the periphery. Such variation can have a variety of population-level influences, including on productivity/ biomass, fitness components, behavior, and responses to disturbance, as well as influences on species diversity and ecosystem processes (Hughes et al. 2008).

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Biodiversity

                 Biological diversity or biodiversity (the latter term is simply a contraction of the former) is the variety of life, in all of its many manifestations. It is a broad unifying concept, encompassing all forms, levels and combinations of natural variation, at all levels of biological organization (Gaston and Spicer 2004). A rather longer and more formal definition is given in the international Convention on Biological Diversity, which states that “‘Biological diversity’ means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversitywithin species, between species and of ecosystems”. Whichever definition is preferred, one can, for example, speak equally of the biodiversity of some given area or volume (be it large or small) of the land or sea, of the biodiversity of a continent or an ocean basin, or of the biodiversity of the entire Earth.                  

                   Likewise, one can speak of biodiversity at present, at a given timeor period in the past or in the future, or over the entire history of life on Earth. The scale of the variety of life is difficult, and perhaps impossible, for any of us truly to visualize or comprehend. In this chapter I first attempt to give some sense of the magnitude of biodiversity by distinguishing between different key elements and what is known about their variation. Second, I consider how the variety of life has changed through time, and third and finally how it varies in space. In short, the chapter will, inevitably in highly summarized form, address the three key issues of how much biodiversity there is, how it arose, and where it can be found.

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Years of growth and evolution

                        Although conservation biology has been an organized field only since the mid-1980s, it ispossible to identify and summarize at least several salient trends that have shaped it since.

Implementation and transformation

                 Conservation biologists now work in a much more elaborate field than existed at the time of its founding. Much of the early energy and debate in conservation biology focused on questions of the genetics and demographics of small populations, population and habitat viability, landscape fragmentation, reserve design, and management of natural areas and endangered species. These topics remain close to the core of conservation biology, but the field has grown around them. Conservation biologists now tend to work more flexibly, at varied scales and in varied ways. In recent years, for example, more attention has focused on landscape permeability and connectivity, the role of strongly interacting
species in top-down ecosystem regulation, and the impacts of global warming on biodiversity (Hudson 1991; Lovejoy and Peters 1994; Soulé and Terborgh 1999; Ripple and Beschta 2005; Pringle et al. 2007; Pringle 2008; see Chapters 5
and 8).


                   Innovative techniques and technologies (such as computer modeling and geographic information systems) have obviously played an important role in the growth of conservation biology. The most revolutionary changes, however, have involved the reconceptualizing of science’s role in conservation. The principles of conservation biology
have spawned creative applications among conservation visionaries, practitioners, planners, and policy-makers (Noss et al. 1997; Adams 2005). To safeguard biological diversity, larger-scale and longer-term thinking and planning had to take hold. It has done so under many rubrics, including: adaptation of the biosphere reserve concept (Batisse 1986); the development of gap analysis (Scott et al. 1993); the movement toward ecosystem management and adaptive management (Grumbine 1994b; Salafsky et al. 2001; Meffe et al. 2002); ecoregional planning and analogous efforts at other scales (Redford et al. 2003); and the establishment of marine protected areas and networks (Roberts et al. 2001). Even as conservation biologists have honed tools for designing protected area networks and managing protected areas more effectively, they have looked beyond reserve boundary lines to the matrix of surrounding lands (Knight and Landres 1998). Conservation biologists play increasingly important roles in defining the biodiversity values of aquatic ecosystems, private lands, and agroecosystems.


                   The result is much greater attention to private land conservation, more research and demonstration at the interface of agriculture and biodiversity conservation, and a growing watershed- and community-based conservation movement. Conservation biologists are now active across the entire landscape continuum, from wildlands to agricultural lands and from suburbs to cities, where conservation planning now meets urban design and green infrastructure mapping (e.g. Wang and Moskovits 2001; CNT and Openlands Project 2004).

Adoption and integration

                  Since the emergence of conservation biology, the conceptual boundaries between it and other fields have become increasingly porous. Researchers and practitioners from other fields have come into conservation biology’s circle, adopting and applying its core concepts while contributing in turn to its further development. Botanists, ecosystem ecologists, marine biologists, and agricultural scientists (among other groups) were underrepresented in the field’s early years. The role of the social sciences in conservation biology has also expanded within the field (Mascia et al. 2003). Meanwhile, conservation biology’s concepts, approaches, and findings have filtered into other fields. This “permeation” (Noss 1999) is reflected in the number of biodiversity conservation-related articles appearing in the general science journals such as Science and Nature, and in more specialized ecological and resource management journals.


                  Since 1986 several new journals with related content have appeared, including Ecological Applications (1991), the Journal of Applied Ecology (1998), the on-line journal Conservation Ecology(1997) (now calledEcology and Society), Frontiers in Ecology and the Environment (2003), and Conservation Letters (2008). The influence of conservation biology is even more broadly evident in environmental design, planning, and decision-making. Conservation biologists are now routinely involved in land-use and urban planning, ecological design, landscape architecture, and agriculture (e.g. Soulé 1991; Nassauer 1997; Babbitt 1999; Jackson and Jackson 2002; Miller and Hobbs 2002; Imhoff and Carra 2003; Orr 2004). Conservation biology has spurred activity within such emerging areas of interest as conservation psychology (Saunders 2003) and conservation medicine (Grifo and Rosenthal 1997; Pokras et al. 1997; Tabor et al. 2001; Aguirre et al. 2002). Lidicker (1998) noted that “conservation needs conservation biologists for sure, but it also needs conservation sociologists, conservation political scientists, conservation chemists, conservation economists, conservation psychologists, and conservation humanitarians.” Conservation biology has helped to meet this need by catalyzing communication and action among colleagues across a wide spectrum of disciplines.

Marine and freshwater conservation biology

                    Conservation biology’s “permeation” has been especially notable with regard to aquatic ecosystems and marine environments. In response to long-standing concerns over “maximum sustained yield” fisheries management, protection of marine mammals, depletion of salmon stocks, degradation of coral reef systems, and other issues, marine conservation biology has emerged as a distinct focus area (Norse 1993; Boersma 1996; Bohnsack and Ault 1996; Safina 1998; Thorne-Miller 1998; Norse and Crowder 2005). The application of conservation biology in marine environments has been pursued by a number of non-governmental organizations, including SCB’s Marine Section, the Ocean Conservancy, the Marine Conservation Biology Institute, the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography, the Blue Ocean Institute, and the Pew Institute for Ocean Science. Interest in freshwater conservation biology has also increased as intensified human demands continue to affect water quality, quantity, distribution, and use. Conservationists have come to appreciate even more deeply the essential hydrological connections between groundwater, surface waters, and atmospheric waters, and the impact of human land use on the health and biological diversity of aquatic ecosystems (Leopold 1990; Baron et al. 2002; Glennon 2002; Hunt and Wilcox 2003; Postel and Richter 2003). Conservation biologists have become vital partners in interdisciplinary efforts, often at the watershed level, to steward freshwater as both an essential ecosystem component and a basic human need.

Building capacity

                At the time of its founding, conservation biology was little known beyond the core group of scientists and conservationists who had created it. Now the field is broadly accepted and well represented as a distinct body of interdisciplinary knowledge worldwide. Several textbooks appeared soon after conservation biology gained its footing (Primack 1993; Meffe and Carroll 1994; Hunter 1996). These are now into their second and third editions. Additional textbooks have been published in more specialized subject areas, including insect conservation biology (Samways 1994), conservation of plant biodiversity (Frankel et al. 1995), forest biodiversity (Hunter and Seymour 1999), conservation genetics (Frankham et al. 2002), marine conservation biology (Norse and Crowder 2005), and tropical conservation biology (Sodhi et al. 2007). Academic training programs in conservation biology have expanded and now exist around the world (Jacobson 1990; Jacobson et al. 1995; Rodríguez et al. 2005). The interdisciplinary skills of conservation biologists have found acceptance within universities, agencies, non-governmental organizations, and the private sector. Funders have likewise helped build conservation biology’s capacity through support for students, academicprograms, and basic research and field projects.


                  Despite such growth, most conservation biologists would likely agree that the capacity does not nearly meet the need, given the urgent problems in biodiversity conservation. Even the existing support is highly vulnerable to budget cutbacks, changing priorities, and political pressures.

Internationalization

                Conservation biology has greatly expanded its international reach (Meffe 2002; Meffe 2003). The scientific roots of biodiversity conservation are obviously not limited to one nation or continent. Although the international conservation movement dates back more than a century, the history of the science from an international perspective has been inadequately studied (Blandin 2004). This has occasionally led to healthy debate over the origins and development of conservation biology. Such debates, however, have not hindered the trend toward greater international collaboration and representation within the field (e.g. Medellín 1998).This growth is reflected in the expanding institutional and membership base of the Society for Conservation Biology.


                 The need to reach across national boundaries was recognized by the founders of the SCB. From its initial issue Conservation Biology included Spanish translations of article abstracts. The Society has diversified its editorial board, recognized the accomplishments of leading conservation biologists from around the world, and regularly convened its meetings outside the USA. A significant move toward greater international participation in the SCB came when, in 2000, the SCB began to develop its regional sections.

Seeking a policy voice

                 Conservation biology has long sought to define an appropriate and effective role for itself in shaping public policy (Grumbine 1994a). Most who call themselves conservation biologists feel obligated to be advocates for biodiversity (Odenbaugh 2003). How that obligation ought to be fulfilled has been a source of continuing debate within the field. Some scientists are wary of playing an active advocacy or policy role, lest their objectivity be called into question. Conversely, biodiversity advocates have responded to the effect that “if you don’t use your science to shape policy, we will.” Conservation biology’s inherent mix of science and ethics all but invited such debate. Far from avoiding controversy, Conservation Biology’s founding editor David Ehrenfeld built dialogue on conservation issues and policy into the journal at the outset.


                 Conservation Biology has regularly published letters and editorials on the question of values, advocacy, and the role of science in shaping policy. Conservation biologists have not achieved final resolution on thematter. Perhaps in the end it is irresolvable, a matter of personal judgment involving a mixture of scientific confidence levels, uncertainty, and individual conscience and responsibility. “Responsibility” is the key word, as all parties to the debate seemto agree that advocacy, to be responsible, must rest on a foundation of
solid science andmust be undertakenwith honesty
and integrity (Noss 1999).

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Consolidation: conservation biology secures its niche

                          In June 1987 more than 200 people attended the first annual meeting of the Society for Conservation Biology in Bozeman, Montana, USA. The rapid growth of the new organization’s membership served as an index to the expansion of the field generally. SCB tapped into the burgeoning interest in interdisciplinary conservation science among younger students, faculty, and conservation practitioners. Universities established new courses, seminars, and graduate programs. Scientific organizations and foundations adjusted their funding priorities and encouraged those interested in the new field.

                A steady agenda of conferences on biodiversity conservation brought together academics, agency officials, resource managers, business representatives, international aid agencies, and non-governmental organizations. In remarkably rapid order, conservation biology gained legitimacy and secured a professional foothold. Not, however, without resistance, skepticism, and occasional ridicule. As the field grew, complaints came from various quarters. Conservation biology was caricatured as a passing fad, a response to trendy environmental ideas (and momentarily
available funds). Its detractors regarded it as too theoretical, amorphous, and eclectic; too promiscuously interdisciplinary; too enamored of models; and too technique-deficient and data-poor to have any practical application (Gibbons 1992).
Conservation biologists in North America were accused of being indifferent to the conservation traditions of other nations and regions.

                  Some saw conservation biology as merely putting “old wine in a newbottle” and dismissing the rich experience of foresters, wildlife managers, and other resource
managers (Teer 1988; Jensen and Krausman 1993). Biodiversity itself was just too broad, or confusing, or “thorny” a term (Udall 1991; Takacs 1996). Such complaints made headlines within the scientific journals and reflected real tensions within resource agencies, academic departments, and conservation organizations. Conservation biology had indeed challenged prevalent paradigms, and such responses were to be expected. Defending the new field, Ehrenfeld (1992: 1625) wrote, “Conservation biology is not defined by a
discipline but by its goal to halt or repair the undeniable, massive damage that is being done to ecosystems, species, and the relationships of humans to the environment. . . . Many specialists in a host of fields find it difficult, even hypocritical, to continue business as usual, blinders firmly in place, in a world that is falling apart.” Meanwhile, a spate of new and complex conservation issues were drawing increased attention to biodiversity conservation. In North America, the Northern Spotted Owl (Strix occidentalis caurina) became the poster creature in deeply contentious debates over the fate of remaining old-growth forests and alternative approaches to
forest management; the Exxon Valdez oil spill and its aftermath put pollution threats and energy policies on the front page; the anti-environmental, anti-regulatory “Wise Use” movement gained in political power and influence; arguments over livestock grazing practices and federal rangeland policies pitted environmentalists against ranchers; perennial attempts to allow oil development within the Arctic National Wildlife Refuge continued; and moratoria were placed on  commercial fishing of depleted stocks of northern cod(Alverson et al. 1994; Yaffee 1994; Myers et al. 1997; Knight et al. 2002; Jacobs 2003).

                  At the international level, attention focused on the discovery of the hole in the stratospheric ozone layer over Antarctica; the growing scientific consensus about the threat of global warming (the Intergovernmental Panel on Climate Change was formed in 1988 and issued its first assessment report in 1990); the environmental legacy of communism in the former Soviet bloc; and the environmental impacts of international aid and development programs. In 1992, 172 nations gathered in Rio de Janeiro at the United
Nations Conference on Environment and Development
(the “Earth Summit”). Among the products of the summit was the Convention on Biological Diversity. In a few short years, the scope of biodiversity conservation, science, and policy had expanded dramatically (e.g. McNeely et al. 1990; Lubchenco et al. 1991). To some degree, conservation biology had defined its own niche by synthesizing scientific disciplines, proclaiming its special mission, and gathering together a core group of leading scientists, students, and conservation practitioners. However, the field was also filling a niche that was rapidly opening around it.

                  It provided a meeting ground for those with converging interests in the conservation of biological diversity. It was not alone in gaining ground for interdisciplinary conservation research and practice. It joined restoration ecology, landscape ecology, agroecology, ecological economics, and other new fields in seeking solutions across traditional academic and intellectual boundaries. Amid the flush of excitement in establishing conservation biology, it was sometimes easy to overlook the challenges inherent in the effort. Ehrenfeld (2000) noted that the nascent field was “controversy-rich.” Friction was inherent not only in conservation biology’s relationship to related fields, but within the field itself. Some of this was simply a result of high energy applied to a new endeavor. Often, however, this reflected deeper tensions in conservation: between sustainable use and protection; between public and private resources; between the immediate needs of people, and obligations to future generations and other life forms. Conservation biology would be the latest stage on which these long-standing tensions would express themselves.

                  Other tensions reflected the special role that conservation biology carved out for itself. Conservation biology was largely a product of American institutions and individuals, yet sought to address a problem of global proportions (Meffe 2002). Effective biodiversity conservation entailed work at scales from the global to the local, and on levels from the genetic to the species to the community; yet actions at these different scales and levels required different types of information, skills, and partnerships (Noss 1990). Professionals in the new field had to be firmly grounded within particular professional specialties, yet conversant across disciplines (Trombulak 1994; Noss 1997). Success in the practice of biodiversity conservation was measured by on-the-ground impact, yet the science of conservation biology was obliged (as are all sciences) to undertake rigorous research and to define uncertainty (Noss 2000). Conservation biology was a “value-laden” field adhering to explicit ethical norms, yet sought to advance conservation through careful scientific analysis (Barry and Oelschlager 1996).

                  These tensions within conservation biology were present at birth. They continue to present important challenges to conservation biologists. They also give the field its creativity and vitality.

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Establishing a new interdisciplinary field

                         In the opening of Conservation Biology: An Evolutionary Ecological Perspective, Michael Soulé and Bruce Wilcox (1980) described conservation biology as “a mission-oriented discipline comprising both pure and applied science.” The phrase crisis-oriented (or crisis-driven) was soon added to the list of modifiers describing the emerging field (Soulé 1985). This characterization of conservation biology as a mission-oriented, crisis-driven, problem-solving field resonates with echoes of the past. The history of conservation and environmental management demonstrates that the emergence of problem-solving fields (or new emphases within established fields) invariably involves new interdisciplinary connections, new institutions, new research programs, and new practices. Conservation biology would followhis pattern in the 1970s, 1980s, and 1990s. In 1970 David Ehrenfeld published Biological Conservation, an early text in a series of publications that altered the scope, content, and direction of conservation science (e.g. MacArthur and Wilson 1963; MacArthur and Wilson 1967; MacArthur 1972; Soulé and Wilcox 1980; CEQ 1980; Frankel and Soulé 1981; Schonewald-Cox et al. 1983; Harris 1984; Caughley and Gunn 1986; Soulé 1986; Soulé 1987a) (The journal Biological Conservation had also begun publication a year earlier in England).

                In his preface Ehrenfeld stated, “Biologists are beginning to forge a discipline in that turbulent and vital area where biologymeets the social sciences and humanities”. Ehrenfeld recognized that the “acts of conservationists are often motivated by strongly humanistic principles,” but cautioned that “the practice of conservation must also have a firm scientific basis or, plainly stated, it is not likely to work”. Constructing that “firm scientific basis” required—and attracted—researchers and practitioners from varied disciplines (including Ehrenfeld himself, whose professional background was in medicine and physiological ecology). The common concern that transcended the disciplinary boundaries was biological diversity: its extent, role, value, and fate. By the mid-1970s, the recurring debates within theoretical ecology over the relationship between species diversity and ecosystem stability were intensifying (Pimm 1991; Golley 1993; McCann 2000). Among conservationists the theme of diversity, in eclipse since Leopold’s day, began to re-emerge. In 1951, renegade ecologists had created The Nature Conservancy for the purpose of protecting threatened sites of special biological and ecological value. In the 1960s voices for diversity began to be heard within the traditional conservation fields. Ray Dasmann, in A Different Kind of Country (1968: vii) lamented “the prevailing trend toward uniformity” and made the case “for the preservation of natural diversity” and for cultural diversity as well. Pimlott (1969) detected “a sudden stirring of interest in diversity . . . Not until this decade did the word diversity, as an ecological and genetic concept, begin to enter the vocabulary of the wildlife manager or land-use planner.” Hickey (1974) argued that wildlife ecologists and managers should concern themselves with “all living things”; that “a scientifically sound wildlife conservation program” should “encompass the wide spectrum from one-celled plants and animals to the complex species we call birds and mammals.”

               Conservation scientists and advocates of varied backgrounds increasingly framed the fundamental conservation problem in these new and broader terms (Farnham 2002). As the theme of biological diversity gained traction among conservationists in the 1970s, the key components of conservation biology began to coalesce around it:

• Within the sciences proper, the synthesis of knowledge from island biogeography and population biology greatly expanded understanding of the distribution of species diversity and the phenomena of speciation and extinction.

• The fate of threatened species (both in situ and ex situ) and the loss of rare breeds and plant germplasm stimulated interest in the heretofore neglected (and occasionally even denigrated) application of genetics in conservation.

• Driven in part by the IUCN red listing process, captive breeding programs grew; zoos, aquaria, and botanical gardens expanded and redefined their role as partners in conservation.

•  Wildlife ecologists, community ecologists, and limnologists were gaining greater insight into the role of keystone species and top-down interactions in maintaining species diversity and ecosystem health.

•  Within forestry, wildlife management, range management, fisheries management, and other applied disciplines, ecological approaches to resource management gained more advocates.

• Advances in ecosystem ecology, landscape ecology, and remote sensing provided increasingly sophisticatedconcepts and tools for land use and conservation planning at larger spatial scales.

•  As awareness of conservation’s social dimensions increased, discussion of the role of values in science became explicit. Interdisciplinary inquiry gave rise to environmental history, environmental ethics, ecological economics, and other hybrid fields.

                As these trends unfolded, “keystone individuals” also had special impact. Peter Raven and Paul Ehrlich (to name two) made fundamental contributions to coevolution and population biology in the 1960s before becoming leading proponents of conservation biology. Michael Soulé, a central figure in the emergence of conservation biology, recalls that Ehrlich encouraged his students to speculate across disciplines, and had his students read Thomas Kuhn’s The Structure of Scientific Revolutions (1962). The intellectual syntheses in population biology led Soulé to adopt (around 1976) the term conservation biology for his own synthesizing efforts. For Soulé, that integration especially entailed the merging of genetics and conservation (Soulé 1980). In 1974 Soulé visited Sir Otto Frankel while on sabbatical in Australia. Frankel approached Soulé with the idea of collaborating on a volume on the theme (later published as Conservation and Evolution) (Frankel and Soulé 1981). Soulé’s work on that volume led to the convening of the First International Conference on Conservation Biology in September 1978.

                 The meeting brought together what looked from the outside like “an odd assortment of academics, zoo-keepers, and wildlife conservationists” (Gibbons 1992). Inside, however, the experience was more personal, among individuals who had come together through important, and often very personal, shifts in professional priorities. The proceedings of the 1978 conference were published as Conservation Biology: An Evolutionary- Ecological Perspective (Soulé and Wilcox 1980). The conference and the book initiated a series of meetings and proceedings that defined the field for its growing number of participants, as well as for those outside the immediate circle (Brussard 1985; Gibbons 1992). Attention to the genetic dimension of conservation continued to gain momentum into the early 1980s (Schonewald-Cox et al. 1983). Meanwhile, awareness of threats to species diversity and causes of extinction was reaching a broader professional and public audience (e.g. Ziswiler 1967; Iltis 1972; Terborgh 1974; Ehrlich and Ehrlich 1981). In particular, the impact of international development policies on the world’s species-rich, humid tropical forests was emerging as a global concern.

                 Field biologists, ecologists, and taxonomists, alarmed by the rapid conversion of the rainforests—and witnesses themselves to the loss of research sites and study organisms—began to sound alarms (e.g. Gómez-Pompa et al. 1972; Janzen 1972). By the early 1980s, the issue of rainforest destruction was highlighted through a surge of books, articles, and scientific reports (e.g.Myers 1979, 1980; NAS 1980; NRC 1982; see also Chapter 4). During these years, recognition of the needs of the world’s poor and the developing world was prompting new approaches to integrating conservation and development. This movement was embodied in a series of international programs, meetings, and reports, including the Man and the Biosphere Programme (1970), the United Nations Conference on the Human Environment held in Stockholm (1972), and the World Conservation Strategy (IUCN 1980). These approaches eventually came together under the banner of sustainable development, especially as defined in the report of the World Commission on Environment and Development (the “Brundtland Report”) (WCED 1987).

             The complex relationship between developmentand conservation created tensions within conservation biology from the outset, but also drove the search for deeper consensus and innovation (Meine 2004). A Second International Conference on Conservation Biology convened at the University of Michigan in May 1985 (Soulé 1986). Prior to the meeting, the organizers formed two committees to consider establishing a new professional society and a new journal. A motion to organize the Society for Conservation Biology (SCB) was approved at the end of the meeting (Soulé 1987b). One of the Society’s first acts was to appoint David Ehrenfeld editor of the new journal Conservation Biology (Ehrenfeld 2000). The founding of SCB coincided with planning for the National Forum on BioDiversity, held September 21–24, 1986 in Washington, DC. The forum, broadcast via satellite to a national and international audience, was organized by the US National Academy of Sciences and the Smithsonian Institution. Although arranged independently of the process that led to SCB’s creation, the forum represented a convergence of conservation concern, scientific expertise, and interdisciplinary commitment. 

                In planning the event, Walter Rosen, a program officer with the National Research Council, began using a contracted form of the phrase biological diversity. The abridged form biodiversity began its etymological career. The forum’s proceedings were published as Biodiversity (Wilson and Peter 1988). The wide impact of the forum and the book assured that the landscape of conservation science, policy, and action would never be the same. For some, conservation biology appeared as a new, unproven, and unwelcome kid on the conservation block. Its adherents, however, saw it as the culmination of trends long latent within ecology and conservation, and as a necessary adaptation to new knowledge and a gathering crisis. Conservation biology quickly gained its footing within academia, zoos and botanical gardens, non-profit conservation groups, resource management agencies, and international development organizations (Soulé 1987b). In retrospect, the rapid growth of conservation biology reflected essential qualities that set it apart from predecessor and affiliated fields:

• Conservation biology rests upon a scientific foundationin systematics, genetics, ecology, and evolutionary biology. As the Modern Synthesis rearranged the building blocks of biology, and new insights emerged from population genetics, developmental genetics (heritability studies), and island biogeography in the 1960s, the application of biology in conservation was bound to shift as well. This found expression in conservation biology’s primary focus on the conservation of genetic, species, and ecosystem diversity (rather than those ecosystem components with obvious or direct economic value).

• Conservation biology paid attention to the entire biota; to diversity at all levels of biological organization; to patterns of diversity at various temporal and spatial scales; and to the evolutionary and ecological processes that maintain diversity. In particular, emerging insights from ecosystem ecology, disturbance ecology, and landscape ecology in the 1980s shifted the perspective of ecologists and conservationists, placing greater emphasis on the dynamic nature of ecosystems and landscapes (e.g. Pickett and White 1985; Forman 1995).

• Conservation biology was an interdisciplinary, systems-oriented, and inclusive response to conservation dilemmas exacerbated by approaches that were too narrowly focused, fragmented, and exclusive (Soulé 1985; Noss and Cooperrider 1994). It provided an interdisciplinary home for those in established disciplines who sought new ways to organize and use scientific information, and who followed broader ethical imperatives. It also reached beyond its own core scientific disciplines to incorporate insights from the social sciences and humanities, from the empirical experience of resource managers, and from diverse cultural sources (Grumbine 1992; Knight and Bates 1995).

•  Conservation biology acknowledged its status as an inherently “value-laden” field. Soulé (1985) asserted that “ethical norms are a genuine part of conservation biology.” Noss (1999) regarded this as a distinguishing characteristic, noting an “overarching normative assumption in conservation biology. . . that biodiversity is good and ought to be preserved.” Leopold’s land ethic and related appeals to intergenerational responsibilities and the intrinsic value of non-human life motivated growing numbers of conservation scientists and environmental ethicists (Ehrenfeld 1981; Samson and Knopf 1982; Devall and Sessions 1985; Nash 1989). This explicit recognition of conservation biology’s ethical content stood in contrast to the usual avoidance of such considerations within the sciences historically (McIntosh 1980; Barbour 1995; Barry and Oelschlaeger 1996).

• Conservation biology recognized a “close linkage” between biodiversity conservation and economic development and sought new ways to improve that relationship. As sustainability became the catch-all term for development that sought to blend environmental, social, and economic goals, conservation biology provided a new venue at the intersection of ecology, ethics, and economics (Daly and Cobb 1989). To achieve its goals, conservation biology had to reach beyond the sciences and generate conversations with economists, advocates, policy- makers, ethicists, educators, the private sector,and community-based conservationists.

               Conservation biology thus emerged in response to both increasing knowledge and expanding demands. In harnessing that knowledge and meeting those demands, it offered a new, integrative, and interdisciplinary approach to conservation science.

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Historical foundations of conservation

                            Since conservation biology’s emergence, commentary on (and in) the field has rightly emphasized its departure from prior conservation science and practice. However, the main “thread” of the field the description, explanation, appreciation, protection, and perpetuation of biological diversity can be traced much further back through the historical tapestry of the biological sciences and the conservation movement (Mayr 1982;McIntosh 1985; Grumbine 1996; Quammen 1996). That thread weaves through related themes and concepts in conservation, including wilderness protection, sustained yield, wildlife protection and management, the diversity-stability hypothesis, ecological restoration, sustainability, and ecosystem health. By focusing on the thread itself, conservation biology brought the theme of biological diversity to the fore. In so doing, conservation biology has reconnected conservation to deep sources in Western natural history and science, and to cultural traditions of respect for the natural world both within and beyond the Western experience.

                 Long before environmentalism began to reshape “conservation in the old sense” in the 1960s prior even to the Progressive Era conservation movement of the early 1900s the foundations of conservation biology were being laid over the course of biology’s epic advances over the last four centuries. The “discovery of diversity” (to use Ernst Mayr’s phrase) was the driving force behind the growth of biological thought. “Hardly any aspect of life is more characteristic than its almost unlimited diversity,” wrote Mayr (1982:133). “Indeed, there is hardly any biological process or phenomenon where diversity is not involved.” This “discovery” unfolded as colonialism, the Industrial Revolution, human population growth, expansion of capitalist and collectivist economies, and developing trade networks transformed human social, economic, political, and ecological relationships ever more quickly and profoundly (e.g. Crosby 1986; Grove 1995; Diamond 1997). Technological change accelerated humanity’s capacity to reshape the world to meet human needs and desires. In so doing, it amplified tensions along basic philosophical fault lines: mechanistic/organic; utilitarian/reverential; imperialist/arcadian; reductionism/ holism (Thomas et al. 1956; Worster 1985). As recognition of human environmental impacts grew, an array of 19th century philosophers, scientists, naturalists, theologians, artists, writers, and poets began to regard the naturalworld within an expanded sphere of moral concern (Nash 1989).

                For example, Alfred RusselWallace (1863) warned against the “extinction of the numerous forms of life which the progress of cultivation invariably entails” and urged his scientific colleagues to assume the responsibility for stewardship that came with knowledge of diversity. The first edition of George Perkins Marsh’s Man and Nature appeared the following year. In his second chapter, “Transfer, Modification, and Extirpation of Vegetable and of Animal Species,” Marsh examined the effect of humans on biotic diversity. Marsh described human beings as a “new geographical force” and surveyed human impacts on “minute organisms,” plants, insects, fish, “aquatic animals,” reptiles, birds, and “quadrupeds.” “All nature,” he wrote, “is linked together by invisible bonds, and every organic creature, however low, however feeble, however dependent, is necessary to the well-being of some other among the myriad forms of life with which the Creator has peopled the earth.” He concluded his chapter with the hope that people might“learn to put a wiser estimate on the works of
creation” (Marsh 1864). Through the veil of 19th century language, modern conservation biologists may recognize Marsh, Wallace, and others as common intellectual ancestors. Marsh’s landmark volume appeared just as the post-Civil War era of rampant resource exploitation commenced in the United States.A generation later, Marsh’s book undergirded the Progressive Era reforms that gave conservation in the United States its modern meaning and turned it into a national movement. That movement rode Theodore Roosevelt’s presidency into public consciousness and across the American landscape.

                Conservationists in the Progressive Era were famously split along utilitarian-preservationist lines. The utilitarian Resource Conservation Ethic, realized within new federal conservation agencies, was committed to the efficient, scientifically informed management of natural resources, to provide “the greatest good to the greatest number for the longest time” (Pinchot 1910:48). By contrast, the Romantic Transcendental Preservation Ethic, overshadowed but persistent through the Progressive Era, celebrated the aesthetic and spiritual value of contact with wild nature, and inspired campaigns for the protection of parklands, refuges, forests, and “wild life.” Callicott (1990) notes that both ethical camps were “essentially human-centered or ‘anthropocentric’. . . (and) regarded human beings or human interests as the only legitimate ends and nonhuman natural entities and nature as a whole as means.”Moreover, the science upon which both relied had not yet experienced its 20th century revolutions. Ecology had not yet united the scientific understanding of the abiotic, plant, and animal components of living systems. Evolutionary biology had not yet synthesized knowledge of genetics, population biology, and evolutionary biology. Geology, paleontology, and biogeography were just beginning to provide a coherent narrative of the temporal dynamics and spatial distribution of life on Earth.

                Although explicitly informed by the natural sciences, conservation in the Progressive Era was primarily economic in its orientation, reductionist in its tendencies, and selective in its application. New concepts from ecology and evolutionary biology began to filter into conservation and the resource management disciplines during the early 20th century. “Proto-conservation biologists” from this period include Henry C. Cowles, whose pioneering studies of plant succession and the flora of the Indiana Dunes led him into active advocacy for their protection (Engel 1983);
Victor Shelford, who prodded his fellow ecologists to become active in establishing biologically representative nature reserves (Croker 1991); Arthur Tansley, who similarly advocated establishment of nature reserves in Britain, and who in 1935 contributed the concept of the “ecosystem” to science (McIntosh 1985; Golley 1993); Charles Elton, whose text Animal Ecology (1927) provided the foundations for a more dynamic ecology through his definition of food chains, food webs, trophic levels, the niche, and other basic concepts; Joseph Grinnell, Paul Errington, Olaus Murie, and other field biologists who challenged prevailing notions on the ecological role and value of predators (Dunlap 1988); and biologists who sought to place national park management in the USA on a sound ecological footing (Sellars 1997; Shafer 2001). Importantly, the crisis of the Dust Bowl in North America invited similar ecological critiques of agricultural practices during the 1930s (Worster 1979; Beeman and Pritchard 2001). By the late 1930s an array of conservation concerns soil erosion, watershed degradation, urban pollution, deforestation, depletion of fisheries and wildlife populations brought academic ecologists and resource managers closer together and generated a new awareness of conservation’ ecological foundations, in particular the significance of biological diversity. In 1939 Aldo Leopold summarized the point in a speech to a symbolically appropriate joint meeting of the Ecological Society of America and the Society of American Foresters:

The emergence of ecology has placed the economic biologist in a peculiar dilemma: with one hand he points out the accumulated findings of his search for utility, or lack of utility, in this or that species; with the other he lifts the veil from a biota so complex, so conditioned by interwoven cooperations and competitions, that no man can say where utility begins or ends. No species can be ‘rated’ without the tongue in the cheek; the old categories of ‘useful’ and ‘harmful’ have validity only as conditioned
by time, place, and circumstance. The only sure conclusion is that the biota as a whole is useful, and (the) biota includes not only plants and animals, but soils and waters as well (Leopold 1991:266–67).

                 With appreciation of “the biota as a whole” came greater appreciation of the functioning of ecological communities and systems (Golley 1993). For Leopold and others, this translated into a redefinition of conservation’s aims: away from the narrow goal of sustaining outputs of discrete commodities, and toward the more complex goal of sustaining what we now call ecosystem health and resilience. As conservation’s aims were thus being redefined, its ethical foundations were being reconsidered. The accumulation of revolutionary biological insights, combined with a generation’s experience of fragmented policy, short-term economics, and environmental decline, yielded Leopold’s assertion of an Evolutionary-Ecological Land Ethic (Callicott 1990). A land ethic, Leopold wrote, “enlarges the boundaries of the community to include soils, waters, plants, and animals, or collectively: the land”; it “changes the role of Homo sapiens from conqueror of the land-community to plain member and citizen of it” (Leopold 1949:204). These ethical concepts only slowly gained ground in forestry, fisheries management, wildlife management, and other resource management disciplines; indeed, they are contentious still. In the years following World War II, as consumer demands increased and technologies evolved, resource development pressures grew. Resource managers responded by expanding their efforts to increase the yields of their particular commodities.

                 Meanwhile, the pace of scientific change accelerated in disciplines across the biological spectrum, from microbiology, genetics, systematics, and population biology to ecology, limnology, marine biology, and biogeography (Mayr 1982). As these advances accrued, maintaining healthy connections between the basic sciences and their application in resource management fields proved challenging. It fell to a diverse cohort of scientific researchers, interpreters, and advocates to enter the public policy fray (including such notable figures as Rachel Carson, Jacques-Yves Cousteau, Ray Dasmann, G. Evelyn Hutchinson, Julian Huxley, Eugene and Howard Odum, and Sir Peter Scott). Many of these had worldwide influence through their writings and students, their collaborations, and their ecological concepts and methodologies. Working from within traditional disciplines, government agencies, and academic seats, they stood at the complicated intersection of conservation science, policy, and practice a place that would come to define conservation biology.

              More pragmatically, new federal legislation in the USA and a growing body of international agreements expanded the role and responsibilities of biologists in conservation. In the USA the National Environmental Policy Act (1970) required analysis of environmental impacts in federal decision making. The Endangered Species Act (1973) called for an unprecedented degree of scientific involvement in the identification, protection, and recovery of threatened species (see Chapter 12). Other laws that broadened the role of biologists in conservation and environmental protection include the Marine Mammal Protection Act (1972), the Clean Water Act (1972), the Forest and Rangeland Renewable Resources Planning Act (1974), the National Forest Management Act (1976), and the Federal Land Policy Management Act (1976). At the international level, the responsibilities of biologists were also expanding in response to the adoption of bilateral treaties and multilateral agreements, including the UNESCO (United Nations Educational, Scientific and Cultural Organization) Man and the Biosphere Programme (1970), the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (1975), and the Convention on Wetlands of International Importance (the “Ramsar Convention”) (1975). In 1966 the International Union for the Conservation of Nature (IUCN) published it first “red list” inventories of threatened species. In short, the need for rigorous science input into conservation decision-making was increasing, even as the science of conservation was changing. This state of affairs challenged the traditional orientation of resource managers and research biologists alike.

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