Hudson Bay Population and Community Ecology - As the numbers of lesser snow geese in the breeding colonies along Hudson and James Bays have increased, these herbivores have outstripped their resources and begun a trophic cascade - a pattern of run-away consumption that impacts all levels and members of the simple food chain typical of arctic coastal ecosystems. While degradation of the habitat results in a reduction in local reproductive success for the snow geese, they escape the control of density-dependent population regulation by dispersing to adjacent, less degraded areas. In doing this, their geographically expanded population continues to increase and the trophic cascade spreads along the coast as an ever-expanding wave of habitat destruction. We have assembled a research team that is studying the population and community ecology of the plants and animals sharing this coastal tundra ecosystem. My primary contributions to the effort center on long-term monitoring of the snow geese and common eiders as well as studying their foraging, nesting and brood rearing behavior. I am also monitoring the success and dynamics of the region's avian community, especially in relation to potential impact by the snow goose induced trophic cascade. A detailed account of all aspects of our collaborative work can be accessed at the Hudson Bay Project . The site is under construction.
Population Dynamics - Using both individual based models and matrix projection models, we are examining the population dynamics of several species of migratory waterfowl including snow geese, emperor geese, northern pintails and spectacled eiders. One goal of the work is to develop accurate models of both short- and long-term population growth of these species for management purposes. Another goal centers on understanding the relative impacts of the underlying demographic parameters (e.g. breeding propensity, nesting success, adult survival) on population dynamics - especially under conditions of density-dependence, non-linear interaction among demographic parameters and environmental stochasticity. We have begun expanding both data collection and modeling efforts to structured assemblages of the species with dispersal connecting the subpopulations. Source-sink systems are of particular interest. Much of this work is in collaboration with Barry Grand and Paul Flint of The Alaska Science Center, Biological Resources Division, US Geological Survey. Progress can be found at http://www.absc.usgs.gov/research/speimod/
Lifetime Reproductive Success - The mean and variance of lifetime reproductive success (ELRS and VLRS, respectively) are key parameters influencing the evolutionary dynamics of species. They also play a critical role in the shorter-term dynamics of species being managed for conservation purposes. While the meaning of these parameters is conceptually obvious, their estimation from real populations is fraught with difficulties. For birds, these range from our inability to precisely monitor survival of individually marked hatchlings to confusion between mortality and permanent emigration to issues of determining true paternity and maternity in mating systems that are seldom purely definable. Using both mathematical approaches and individual based modeling, we have been developing procedures to estimate ELRS and VLRS with less than complete data and have been testing them with data from several long-term studies including our work with lesser snow geese and work on emperor geese that has been carried out by Joel Schmutz and Margaret Petersen of The Alaska Science Center, Biological Resources Division, US Geological Survey. We are also developing procedures with which these incomplete data estimators of ELRS and VLRS can be used to generate estimates of other important parameters such as effective population size (Ne). In all cases, we attempt to provide tests to ascertain whether field data conform to the assumptions of our procedures.
Genetic Structure and Gene Flow - Few species are distributed continuously. Rather, they exist as disjunct populations connected by gene flow. Inferences regarding the evolutionary dynamics of such assemblages and decisions regarding their conservation and management require estimates of genetic structure and gene flow. Many of the current estimation procedures using direct examination of genetic variation in field situations appeal to often untested or untestable assumptions regarding selection, equilibrium and the pattern and stability of patterns of genetic exchange among the populations. Our work in this area centers on 3 main areas: 1) development of models that use demographic data to predict the genetic structure that is (or can be) then tested for conformity; 2) examination of the robustness of measures of genetic structure and gene flow to departures from underlying assumptions; 3) development of topological approaches to the estimation of genetic structure and gene flow using gene trees and coalescence theory. Our initial applications involve the Pacific black brant in collaboration with Mark Lindberg.
These images can be accessed on the US Fish and Wildlife Service Federal Duck Stamp Homepage
revised - October 06, 2000