Research Interests

Climate Change Impacts on Biodiversity

We develop and apply methods that link climate change models, species distribution or habitat suitability models, and metapopulation models with dynamic spatial structure, to predict the vulnerability of species to global climate change. Several recent workshops (in Adelaide, Australia, Silwood Park, UK and Madrid, Spain) explored the feasibility of such methods. The applications focus on:

• Plants in Australia
• Plants in South Africa
• Lagomorphs in Mexico and UK
• Reptiles and amphibians in Madagascar and North America (ongoing research supported by NASA)
• Shorebirds in Florida (ongoing research on effects of sea-level rise, supported by SERDP)
• Contributing to the development of Red List Guidelines for identifying species threatened by climate change.

Status and Trends of Biodiversity

Research to assess the vulnerability of species to extinction, and to quantify and analyze the threat status of species and trends in threat status involves

• Quantitative methods for estimating spatial and temporal uncertainties in parameters (such as extent of occurrence, EOO; area of occupancy, AOO; population reduction; extreme fluctuations; continuing decline) that are used in threatened species assessments based on the IUCN Red List Categories and Criteria;
• Methods for propagating parameter uncertainties through the IUCN Red List rules, in order to make consistent classifications under uncertainty;
• The impact of conservation on the status of the world's vertebrates
• The Red List Index, based on the IUCN Red List, is an indicator of the trends in biodiversity.
• Contributing to the National Red List of Butterflies in Turkey.

Species Conservation

We use habitat-based metapopulation models to estimate the risk of extinction or decline, and to evaluate the chances for recovery with different management and conservation options. Research in this area includes both the continued development of modeling platforms for population viability analysis, and case studies that apply these models to a variety of species, including

Population Dynamics

We are interested in developing new methods for modeling population dynamics, estimating model parameters, analyzing population declines, and validating extinction risk estimates. Research in this areas has involved

• Estimating variability in survival rates and fecundities due to environmental fluctuations, by removing variance due to demographic stochastricity from total observed variance;
• Showing that the theta-logistic model (used to describe how the growth rate of a population slows as abundance increases) is unreliable for modeling most census data;
• Establishing that scalar population models (also known as count-based models) overestimate variability and risks of decline and extinction;
• Demonstrating that the reddened spectra commonly seen in time series of population abundances can be due to measurement error and/or moderate density dependence;
• Determining the predictive accuracy of the probabilistic predictions of population viability analysis, with a retrospective analysis;
• Cataloging common mistakes in population modeling and suggesting ways to avoid them.

Demographic Toxicity

Currently, most assessments of the ecological impacts of pollutants use bioassays at the individual organism level. We are interested in developing standard methods that will allow ecotoxicological impacts to be assessed at the more relevant population and species levels. (Read about a recent book on methods and case studies of ecotoxicological risk assessment at the population level.)