Niche theory, species distributions, and conservation planning in a changing climate
Conservation planning is the process of identifying areas that will, if protected or managed in a specific way, conserve biodiversity. Such planning requires a basic understanding of where the various elements that compose biodiversity are—and equally importantly, where those elements will be in the future. Therein lies the challenge. We know relatively little of the whereabouts of most species today, much less where they will be in the future. Conservation biologists do, however, have several tools at their disposal to address this challenge. One of the most often used—the species distribution or niche model—uses empirical relationships between species and their environments to predict potential occurrences through space.
The origins of species distribution models can be traced back to the basic ecological theory of the niche. Grinnell, Elton, and Hutchinson all posited that there are sets of conditions (e.g., the availability of resources, the presence of predators) that determine where a species can exist and hence where it will be found. The diverse array of species distribution models reflects the various formulations of the niche concept. I will review the basic theory behind, the multiple uses of, and the potential future of species distribution modeling for conservation planning.
Species distribution models have been used to guide survey and monitoring efforts, as the foundation for conservation plans, and in large-scale conservation assessments. More recently, they have been used to project the potential effects of climate change on future species distributions. These projections have been used to assess the future effectiveness of reserve networks, the relative impact of climate change and land-use change, and to identify potential corridors to facilitate climate-driven species movements. I will give examples of each of these uses.
Although there are limitations to species distribution models used in any context, the limitations are perhaps the most numerous when these models are used to project future distributions. These limitations have driven research in two distinct directions—employing more sophisticated models to try to capture more of the mechanisms that define the realized niche of a species and forgoing projections altogether and relying on even more basic ecological concepts. I will briefly describe these approaches (e.g., integrating population and distribution models and mapping geophysical settings). Although species distribution models will likely remain a tool in the conservation planner’s toolbox, as the field advances, they will be just one tool of several available to address climate change.