Biodiversity and Ecosystem Function

               The role of biodiversity in providing ecosystem services is actively debated in ecology. The diversity of functional groups (groups of ecologically equivalent species (Naeem and Li 1997)), is as important as species diversity, if not more so (Kremen 2005), and in most services a few dominant species seem to play the major role (Hooper et al. 2005). However, many other species are critical for eco system functioning and provide “insurance” against disturbance, environmental change, and the decline of the dominant species (Tilman 1997; Ricketts et al. 2004; Hobbs et al. 2007). As for many other ecological processes, it was Charles Darwin who first wrote of this, noting that several distinct genera of grasses grown together would produce more plants and more herbage than a single species growing alone (Darwin 1872). Many studies have confirmed that increased biodiversity improves ecosystem functioning in plant communities (Naeem and Li 1997; Tilman 1997). Different plant species capture different resources, leading to greater efficiency and higher productivity (Tilman et al. 1996). Due to the“sampling-competition effect” the presence of more species increases the probability of having a particularly productive species in any given environment (Tilman 1997). Furthermore, different species’ ecologies lead to complementary resource use, where each species grows best under a specific range of environmental conditions, and different species can improve environmental conditions for other species (facilitation effect; Hooper et al. 2005). Consequently, the more complex an ecosystem is, the more biodiversity will increase ecosystem function, as more species are needed to fully exploit the many combinations of environmental variables (Tilman 1997). More biodiverse ecosystems are also likely to be more stable and more efficient due to the presence of more pathways for energy flow and nutrient recycling (Macarthur 1955; Hooper et al. 2005; Vitousek and Hooper 1993; Worm et al. 2006). Greenhouse and field experiments have confirmed that biodiversity does increase ecosystem productivity, while reducing fluctuations in productivity (Naeem et al. 1995; Tilman et al. 1996). 

               Although increased diversity can increase the population fluctuations of individual species, diversity is thought to stabilize overall ecosystem functioning (Chapin et al. 2000; Tilman 1996) and make the ecosystem more resistant to perturbations (Pimm 1984). These hypotheses have been confirmed in field experiments, where speciesrich plots showed less yearly variation in productivity (Tilman 1996) and their productivity during a drought year declined much less than species poor plots (Tilman and Downing 1994). Because more species do better at utilizing and recycling nutrients, in the long-term, species-rich plots are
better at reducing nutrient losses and maintaining soil fertility (Tilman et al. 1996; Vitousek and Hooper 1993). Although it makes intuitive sense that the species that dominate in number and/or biomass are more likely to be important for ecosystem function (Raffaelli 2004; Smith et al. 2004), in some cases, even rare species can have a role, forexample, in increasing resistance to invasion (Lyons and Schwartz 2001). A keystone species is one that has an ecosystem impact that is disproportionately large in relation to its abundance (Hooper et al. 2005; Power et al. 1996;). Species that are not thought of as “typical” keystones can turn out to be so, sometimes in more ways than one (Daily et al. 1993). Even though in many communities only a few species have strong effects, the weak effects of many species can add up to a substantial stabilizing effect and seemingly “weak” effects over broad scales can be strong at the local level (Berlow 1999). Increased species richness can “insure” against sudden change, which is now a global phenomenon (Parmesan and Yohe 2003; Root et al. 2003). Even though a few species may make up most of the biomass of most functional groups, this does not mean that other species are
unnecessary (Walker et al. 1999). 

              Species may act like the rivets in an airplane wing, the loss of each unnoticed until a catastrophic threshold is passed (Ehrlich and Ehrlich 1981b). As humanity’s footprint on the planet increases and formerly stable ecosystems experience constant disruptions in the form of introduced species, pollution , climate change, excessive nutrient loads, fires, and many other perturbations, the insurance value of biodiversity has become increasingly vital over the entire range of habitats and systems, from diverse forest stands sequesterin CO2 better in the long-term (Bolker et al. 1995; Hooper et al. 2005; but see Tallis and Kareiva 2006) to forest-dwelling native bees’ coffee pollination services increasing coffee production in Costa Rica (Ricketts et al. 2004;). With accelerating losses of unique species, humanity, far from hedging its bets, is moving ever closer to the day when we will run out of options on an increasingly unstable planet.

Read More

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).

Read More