EXTINCTION DYNAMICS IN THE AMERICAN MARTEN (MARTES AMERICANA)

We constructed a model of marten population dynamics and used it to in vestigate extinction processes across a wide range of parameter values . The model was based on rules governing the behavior and physiology o f individual martens and focused on energy balance. Spatial dynamics a nd demographic and environmental stochasticity were in corporated. The outcome was the probability of extinction and quasiextinction (20 fem ales remaining) over 500 years. Three qualitative forms of extinction were delineated. The first was deterministic extinction, associated wi th those parameter combinations leading to a negative population growt h rate. The second was probabilistic extinction in systems with a stro ng positive growth rate but restricted population size due to habitat constraint. The transition from 100% persistence to 100% quasiextincti on, as the input habitat size was decreased, was abrupt. The final for m of extinction was in systems with a growth rate of approximately zer o. Prey availability maintained an upper limit on these populations, b ut otherwise fluctuations in population size were essentially random, leading to nontrivial probabilities of extinction in even relatively l arge populations. A number of issues requiring further empirical resea rch were identified. These included the relationship between habitat q uality and marten reproduction, dispersal patterns and dispersal morta lity, the effect of habitat edge on marten reproduction and mortality, and the characterization of the severity and frequency of catastrophi c mortality as experienced by marten populations.