The Role of Conservation in Expanding Biodiversity Research
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FORUM is intended for new ideas or new ways of interpreting existing information. It FORUM provides a chance for suggesting hypotheses and for challenging current thinking on FORUM ecological issues. A lighter prose, designed to attract readers, will be permitted. Formal research reports, albeit short, will not be accepted, and all contributions should be concise FORUM with a relatively short list of references. A summary is not required. The role of conservation in expanding biodiversity research Diane S. Sri7asta7a, Dept of Zoology, Uni7. of British Columbia, 6270 Uni7ersity Bl7d, Vancou7er, B.C. Canada V6T 1Z4([email protected]). It has been suggested that current reductions in global biodiver- tween community ecology and conservation. Tradition- sity may impair the functioning of ecosystems. This biodiversity- ally, conservation biologists have been quick to adapt ecosystem function (BD-EF) hypothesis represents a new avenue of ecological research originating from conservation concerns. general ecological theories to particular applied issues. However, the subsequent evolution of BD-EF research has A classic example is the application of island biogeog- reflected academic concerns more than conservation priorities. I raphy theory to the design of nature reserves. Commu- suggest three questions for BD-EF research, which would benefit nity ecologists, by contrast, have been slow to convert both ecological theory and conservation. (1) Is biodiversity the main driver of ecosystem function? Several experiments show conservation issues into new areas of ecological theory. that biodiversity loss is a minor link between habitat change and Given the importance of conservation for the origin ecosystem function. (2) How will extinction patterns change of the BD-EF hypothesis, one would imagine that as BD-EF relationships? Biased extinctions may have additional impacts on ecosystem function, which can be deduced by com- BD-EF research evolved, it would expand along lines parison with random-loss models. (3) Will conserving regional relevant to conservation. This has been only partially biodiversity conserve local ecosystem function? The answer to true. In the last decade, BD-EF research has expanded this question may differ between saturated and unsaturated in three main areas: methodology, measures of ecosys- communities, and may depend on whether the magnitude or stability of ecosystem function is measured. tem function, and modeling of mechanisms. Vigorous debates around experimental methodology, especially regarding spurious results, have resulted in increasingly The world is currently experiencing exceptionally high sophisticated experiments and analysis (Huston 1997, rates of species extinctions, largely because of human Loreau 1998a, 1998b, Wardle 1999, Huston et al. 2000). activity (Lawton and May 1995). While the loss of The original rather vague concept of reduced function- biodiversity is in itself a tragedy, there may be more ing has been replaced by a more precise understanding practical consequences for humankind. Approximately of the key components of ecosystem functioning: mag- a decade ago, several ecologists proposed that reduc- nitude, resilience and resistance to disturbance, con- tions in current species diversity would lead to reduc- stancy in space and time, and resistance to invasions by tions in the functioning of ecosystems; that is, in the exotic species (Case 1990, Tilman 1996, Doak et al. biogeochemical processes carried out by the Earth’s 1998, Naeem 1998). The theoretical foundation for the biota (di Castri and Younes 1990, Ehrlich and Wilson BD-EF hypothesis, once meager, has been buttressed 1991, Lubchenco et al. 1991, Walker 1992, Schulze and and expanded by recent modeling studies (Tilman et al. Mooney 1993). The motivation for this biodiversity- 1997, 1998, Ives et al. 1999, Loreau 2000, McCann ecosystem function (‘‘BD-EF’’) hypothesis is clearly 2000). While all of these areas are academically impor- rooted in conservation concerns. For example, the Eco- tant, and indeed essential for the development of the logical Society of America, in launching its Sustainable discipline, few have direct relevance to conservation (a Biosphere Initiative, urged researchers to examine bio- notable exception being interest in stability benefits of diversity effects on ecosystem function because ‘‘ecolo- biodiversity: Schwartz et al. 2000). Nor has BD-EF gists are increasingly asked to justify the benefits of research crossed over to any degree into the conserva- biological diversity compared to the human benefits tion literature (as evidenced by the concentration of this that might be derived from economic development’’ research in academic ecology journals: see reference list (Lubchenco et al. 1991, p. 390). of this paper). The purpose of this paper is to suggest The role of conservation in formulating the BD-EF several new directions for BD-EF research that would hypothesis is a reversal of the usual relationship be- make it more useful to conservation. However, making OIKOS 98:2 (2002) 351 BD-EF research more useful for conservation need not to assess the relative contribution of different mecha- come at the expense of ecological generality. Indeed, nisms to an overall biodiversity effect. Once these goals the research questions outlined in this paper also point are recognized as distinct from each other, conflict the way to how existing ecological theory can be inte- disappears (as has recently been witnessed: Hughes and grated into a BD-EF framework. I begin by discussing Petchey 2001, Loreau et al. 2001). how applied goals can be accommodated within aca- I now turn to several specific examples of how BD- demic ecology. EF research could be expanded in ways that satisfy both academic and applied goals. In these examples, academic goals are met by linking current BD-EF theory with other ecological theory, such as species Are academic and applied goals compatible saturation theory or life history correlates of extinction in biodiversity research? risk. Applied goals are met by asking questions about the importance of biodiversity effects in the context of Conservation and community ecology have different other environmental changes, and by linking local bio- goals for biodiversity research (Takacs 1996). The eco- diversity effects with regional conservation policies. logical or academic goal for BD-EF research is to determine the presence of biodiversity effects on ecosys- tem function. The conservation or applied goal for Is biodiversity the main driver of ecosystem BD-EF research is to determine the importance and function? predict the likelihood of such a biodiversity effect. These academic and applied goals are occasionally in conflict, Many BD-EF experiments have shown that biodiversity as illustrated by a recent debate in the literature. The has some effect on ecosystem function (reviewed by ‘‘sampling effect’’ debate can be summarized brieflyas Schwartz et al. 2000). It is not clear, however, whether follows. In many BD-EF experiments, communities of this biodiversity effect is important in comparison to differing diversity are randomly assembled from a spe- the more direct effects of habitat change on ecosystem cies pool. As diversity increases, the probability of any function (Hughes and Petchey 2001). given species occurring in the community also increases. Habitat change is generally agreed to be the primary If one particular species has a disproportionate effect reason for the current wave of species extinctions (Dia- on the ecosystem function being measured, any increase mond 1989, Lawton and May 1995). Close on its heels in ecosystem function with diversity could simply reflect are species invasions and over-exploitation (Diamond the increasing the probability of including this species 1989). Climate change is poised to become a fourth (a ‘‘sampling’’ or ‘‘selection probability’’ effect) rather major cause of contemporary extinctions (Sala et al. than a true biodiversity effect (Aarssen 1997, Huston 2000). Clearly, the only way to prevent further biodi- 1997, Wardle 1999). This is an academic argument, versity loss is by ameliorating these factors. At some which questions the presence of a biodiversity effect point, therefore, BD-EF research needs to explicitly once external, non-ecological mechanisms (sampling examine whether changes in human action (e.g. con- probability) are accounted for. The most common serving intact habitat) intended to protect biodiversity counter-argument, by contrast, is based in applied con- will also preserve ecosystem function. cerns and is as follows. Even if the underlying mecha- The links between habitat change, biodiversity loss nism behind BD-EF correlations turns out to be and ecosystem function are surprisingly complex. Con- probability rather than ecology, this does not invalidate sider the case of habitat fragmentation. There would the conclusion that declining biodiversity will affect appear to be a solid case for reducing habitat fragmen- ecosystem function. The experiments mimic how hu- tation if it is conclusively shown both that habitat mankind is reducing biodiversity: randomly, without fragmentation leads to lower local diversity, and that regard to any particular species’ effect on ecosystem lower local diversity leads to reduced ecosystem func- function (Lawton et al. 1998, van der Heijden 1999, tion. However, this argument is not logically complete Hector et al. 2000). Although sampling probability is as it assumes that there is no direct (i.e.,