I am studying dynamics and extinction risk in populations of the Bay checkerspot butterfly (Euphydryas editha bayensis), in collaboration with Paul Ehrlich and colleagues at Stanford University. This work demonstrates the utility of model systems in ecology, and of the Bay checkerspot butterfly as a model for the population concept. Populations are the basic functional unit for many ecological and evolutionary processes, including colonization, extinction, species range shifts, species interactions, evolution of adaptation, and maintenance of polymorphisms. Knowledge about populations thus provides a basis for understanding natural patterns ranging from the form of individual organisms to the composition of communities. The science of population biology seeks to explain how and why populations vary in size and structure through time and space. The central premise of population biology is that behavior of populations can be understood by studying factors affecting individual organisms and then summing their effects over all individuals. We have applied this premise to understand population responses to environmental change, including as plant succession, habitat loss, species invasions, and climate change. Recently, we showed that extinctions of the two longest studied populations were driven by climate change in the form of increasingly variable precipitation. Ultimately, habitat loss has been the greatest threat to most E. e. bayensis populations, but now climate change exacerbates habitat loss to hasten extinctions. Similar extinctions in other species are likely to occur as habitat loss, climate change, and other factors grow and interact.

Our work integrates field study of mechanisms causing population changes with mathematical modeling of population responses to those mechanisms. The result is a mechanistic understanding of checkerspot population dynamics. This is a primary goal in population biology, and a powerful tool for conservation. Results show that habitat characteristics can qualitatively affect population dynamics and quantitatively alter extinction risk. This work serves four purposes. First, it represents one of the few examples in which all major factors influencing the dynamics of a population have been analyzed. Second, it demonstrates relationships between habitat characteristics, population dynamics, and extinction risk. Third, it identifies conservation priorities for a particular threatened species. Fourth, it provides guidance for the conservation of lesser-studied populations, particularly invertebrates.

Abundances and distrubutions of butterflies and their food plants, spatial population structure, potential impacts of climate change ...
Details soon ... fieldwork to begin summer 2003.

This research program studies the status, distributions, and habitat relationships of forest carnivores. Researchers throughout western North America have recognized a need for basic and applied work on forest carnivores, especially marten, fisher, lynx, and wolverine. Apparent declines in the abundances and distributions of these species throughout the west have raised concern. These species are sensitive to habitat loss and degradation, due to their large area requirements, slow recovery from anthropogenically induced declines, and dependence on structural habitat features that take centuries to regenerate. This research program is a collaborative effort with the Mt. Baker-Snoqualmie National Forest and North Cascades National Park.

Habitat loss and fragmentation are the leading causes of species imperilment globally. Although effects of these processes on biodiversity are understood in general, thresholds of fragmentation causing extinction are known for few species. My work seeks to determine extinction thresholds for carnivores in the North Cascades. We rarely can say with confidence whether a given species persists via metapopulation processes or is doomed to extinction as a collection of isolated populations. Carnivore populations in the North Cascades offer an opportunity to answer the question of how much suitable habitat is needed to support a population. Old growth forest in the area is highly fragmented, including patches occupied by carnivores and others where carnivores are absent. My near-term research objective is to determine which habitat characteristics at levels of both forest stands and landscapes are necessary to support carnivore populations. Currently, we are analyzing the distribution of marten (Martes americana) relative to data on forest vegetation structure and landscape patterns.

I am working with North Cascades National Park Service Complex (NOCA) biologists to survey forest carnivores in the NOCA. We recently finished our second field season (winters 2002-2003 and 2003-2004). Our results will complement similar surveys that have been done recently at Olympic and Rainier National Parks and surveys conducted by the Washington Department of Fish and Wildlife and the U.S. Forest Service in the 1990s on other public lands in Washington.

This project was conducted by one of my graduate advisees, Peter Horne, in consultation with biologists in the National Park Service, US Forest Service, and US Fish and Wildlife Service. The first phase of the project was to map distribution of seasonal food sources in the North Cascades Grizzly Bear Recovery Zone. The second phase simulated movement of bears relative to seasonal food sources, boundaries of bear management units, and roads and trails.

Management decisions in the North Cascades Recovery Zone currently are based upon a policy of no net loss of core habitat, with core habitat defined by the absence of roads and high-use trails. Our work provides a more realistic approach, because it addresses spatial and temporal patterns in the distribution of grizzly food resources, movement of bears within those patterns, and risks of bear-human conflicts resulting from that movement. Results show that a policy based on core habitat differentiates well between landscapes with few vs. many roads and trails, but it does poorly with intermediate landscapes. Landscapes with intermediate amounts of roads and trails, which constitute most of the Recovery Zone, require an approach based on pattern and process. We now are analyzing alternatives to core habitat that are both easy to measure and that reliably discriminate between good and poor landscapes. This work contributes to the basic science of landscape ecology, and it has practical management applications for evaluating grizzly habitat, predicting effects of creating/removing particular roads and trails, and anticipating areas of likely bear-human conflict.

This project has two main goals. The first is to develop an understanding of avian-habitat relationships across diverse habitats in the North Cascades. The second is to develop and evaluate a design to inventory and monitor avian populations in areas with diverse habitats and limited access, including many National Parks. These goals also will support efforts to predict avian responses to anthropogenic and non-anthropogenic habitat changes.

This project is a collaboration with North Cascades National Park Service Complex (NOCA) and the Institute for Bird Populations (IBP) on a long-term program of avian research, inventory, and monitoring. The program promises to yield information valuable to basic science and applications to Park and Forest management. This work complements my Field Methods course (ENVR 408), which teaches methods used in avian research programs.

Preliminary Results: (Maps created by Stefan Freelan.)
American Robin
Winter Wren
Yellow Warbler

6 Trophic Interactions in Heterogeneous Environments

I am studying effects of spatial patterns on ecological communities with multiple trophic levels. This work applies mathematical models of linked predator-prey interactions in spatially variable environments. The simplest example would be interactions between plants, herbivores, and carnivores, in which plant productivity varies in space. The resulting models are multidimensional nonlinear systems of partial differential equations with heterogeneous coefficients. The usual mathematical approaches do not work in these cases. (Otherwise, the problem would have been solved long ago.) I am applying modern methods of applied mathematics to develop approximate solutions. Most environmental problems include nonlinear interactions among multiple components in spatially structured environments. This project represents a step toward developing analytical tools to address such problems in a quantitative way.

Collaboration among Wayne Landis, Leo Bodensteiner, Lynn Robbins, and myself produced an approach for conducting risk assessment at the scale of river basins. Our approach combines research methods from the social sciences, risk assessment, and quantitative ecology. It is an example of the kind of interdisciplinary work that is well served by Huxley's structure.

Wayne Landis and I expanded the approach to address sustainable management of ecological systems. We developed a decision theory for environmental sustainability. Our work quantifies formerly vague concepts of ecological integrity and sustainability. It will allow decision-makers to predict whether a given management program will be sustainable.