Biodiversity and Ecosystem Dynamics in Human-Dominated Landscapes

Global demand for food is expected to double, roughly, over the coming three decades. Whatever course is taken to try to meet this demand, it is fair to expect that growing anthropogenic pressures will put biodiversity at great risk. Food production is arguably humanity's most important activity, and ecosystems and their biodiversity supply critical benefits to agriculture. Yet the conversion of native habitats to agricultural uses is also the most important proximate cause of biodiversity loss and ecosystem disruption worldwide.

The tradeoffs involved here are complex; they are fraught with uncertainty, non-linearity, and vexing dilemmas, both practical and ethical in nature. The fact is that ecosystems are changing with ever greater rapidity, and with consequences that feed into economic, political, climatological, epidemiological, and other important systems. My focus is on extinction. Of the many dimensions of global change, none has problems of irreversibility more serious than extinction. What are the societal impacts of biodiversity loss and other ecosystem changes? Which merit the most attention? What levels and types of changes are acceptable? And what institutions and policies will be effective in sustaining both agricultural productivity and the delivery of ecosystem services?

To refine our approach to such questions, we must recognize that ecosystems are capital assets: if properly managed, they yield a flow of vital services. Ecosystem services include the production of goods, such as seafood, timber, and precursors to many industrial and pharmaceutical products. They also include basic life-support processes (such as pollination, water purification, and climate regulation), life-fulfilling conditions (such as serenity, beauty, and cultural inspiration), and preservation of options (such as conserving genetic and species diversity for future use). Proper accounting would value the flow of ecosystem services while costing out the depreciation of the underlying asset, just as for physical capital, for example. Unfortunately, relative to other forms of capital, ecosystem capital is poorly understood, scarcely monitored, and, in many important cases, undergoing rapid degradation and depletion. These circumstances demand urgent attention.

My research is aimed at answering three fundamental questions. First, what sorts of species and ecosystems will be with us (remain extant or assemble / evolve) over the coming decades and centuries? Second, what sorts do we want to retain? And, third, how can we achieve what we desire? Clearly these are complex questions, each having many important dimensions in the natural and social sciences, and outside of academia in the real world of human activity and policy. I am presently working with a diverse array of collaborators on aspects of each.

The focus of my research program in Costa Rica, and the subject of this grant application, is the ecological aspects of the first two questions. On the question of the ecosystems of the future, I am trying to characterize the dynamics of biodiversity and ecosystem change in human-dominated, "countryside" habitats in the tropics, a topic which has received relatively little attention to date. The organisms that can take advantage of countryside - rural and suburban landscapes devoted primarily to human activities - deserve more attention, for a series of reasons. First, it is unlikely that many large, undisturbed tracts of natural habitat will remain in the face of projected growth in the size and environmental impacts of the human population. Second, the conservation potential for many species may rest on preserving or enhancing certain aspects of rural landscapes containing remnants of native habitat, in lieu of protecting large tracts of undisturbed habitat. Third, the supply of important ecosystem system services, such as pest control and pollination, will depend in many instances on the biodiversity that occurs locally, in agricultural, or countryside, habitats. Finally, a growing interest in restoration in some regions will require comparing the potential of alternative sites for reestablishing desired ecosystems.

With a group of collaborators, I am documenting and analyzing patterns of occurrence, movement, and resource use of different groups of organisms in native and agricultural habitats embedded within landscapes of varying land-use intensity. The aim is to use changes in land use as a basis for forecasting changes in biodiversity and ecosystems. At the same time, we are attempting to determine the utility of different groups of organisms as indicators of change. We have ongoing studies of birds, butterflies, moths, beetles, and mammals and are presently planning to investigate floristic aspects of change. Our findings suggest that (i) different groups of organisms respond quite differently to changes in land use, and therefore do not serve well alone as indicators of other groups at the local scale (<1000ha); (ii) generally speaking, about 50% of the species in these major groups occur in some agricultural habitats; (iii) the relationship between biodiversity and land-use intensity (using various measures) is highly non-linear for most groups.

We are now in the process of testing the generality of these initial findings in four biogeographically and ecologically distinct regions of Costa Rica, using birds - the best known and most readily sampled part of the fauna. We are also testing the utility of Landsat satellite images in predicting the occurrence of species across complex, human-dominated landscapes. Postdoctoral fellow Sallie Bailey and I are applying the latest techniques in land classification and image interpretation to see whether we can predict patterns of biodiversity across broader regions of the tropics. Together these efforts are yielding insights to the ecosystems of the future.

On the second question, Which species and ecosystems do we want to retain?, I am beginning to investigate the ecological function of particular landscape elements and species. I am doing this in part by researching (in the literature) the ecological roles known to be played by the different groups that we are studying (birds, mammals, etc.). In addition, postdoctoral fellow Taylor Ricketts is launching a project to assess the value of native habitats in supplying pollinators to coffee plantations. Preliminary data suggest that, although the most commonly grown coffee varieties are self-pollinated, the bean is larger and longer-lived if it results from cross-pollination. Moreover, local farmers claim that the principal pollinators (bees and wasps) nest in forest.

We are now poised to put our initial observations, and those of other researchers, into a theoretical framework. The development of theory is critical to predicting future changes in biodiversity and ecosystem functions. It will allow us to clarify, contrast, and test alternative assumptions about the mechanisms underlying the patterns we see. It would thereby also inform the future course of the empirical work on these issues. While much theory exists that could be usefully applied to this work, I also hope to develop some new approaches. With graduate student Henrique Pereira, I have initiated the development of simple models relating land-use intensity to species richness and composition. The work is promising but there is a great deal of room for exploration. I propose to apply a McDonnell Award to hiring a postdoctoral fellow to expand and intensify efforts on this front.

In summary, our findings so far suggest that there is considerable potential for conserving or enhancing biodiversity and ecosystem services in countryside habitats. The next major step is to develop a predictive framework for interpreting these findings over the long term and over broader geographic regions.