Conservation endocrinology: a noninvasive tool to understand relationshipsbetween carnivore colonization and ecological carrying capacity

Reproductive technology, especially the diagnosis of pregnancy by radioimmu noassay of focal steroid metabolites, is an important component of captive propagation, but its role in our understanding of ecological interactions a nd in situ biological restoration has been more limited. Where large herbiv ores have been "released" from predation by the extirpation of carnivores, controversy often exists about possible detrimental effects at the ecosyste m level. A related concern is that the reestablishment of large carnivores may decrease the availability of prey populations for human subsistence. We suggest that pregnancy assays can be a valuable tool to help distinguish b etween the roles of predation versus food-imposed limitations on population size and their effects on juvenile recruitment in wild species. We explore d this issue through analyses of fecal progestagen concentration (FPC) leve ls to document pregnancy in moose (Alces alces) in the southern Greater Yel lowstone Ecosystem, a site where wolves (Canis lupus) and grizzly bears (Ur sus arctos) are recolonizing former habitats after an absence of more than 60 years. Pregnancy was clearly discernible (mean FPC for pregnant and nonp regnant females, respectively: 10.60 vs. 2.57 mu g/g; p < 0.0001). Among th e potential confounding variables that need to be considered if FPC is appl ied to ecological and demographic questions are whether baseline values are affected by handling, whether neonate survival has been assessed, and whet her sampling efforts are directed at both pregnant and nonpregnant animals. With these issues accounted for, the local moose population experienced ju venile survival rates among the highest in North America. Pregnancy rates, however, dropped from 90% in 1966 to about 75% today, rendering them in the lowest fifteenth percentile among moose populations in North America. Our findings suggest that a relatively low frequency of juvenile moose is not t he likely results of predation, and they illustrate how endocrinology can b e applied to issues involving reproductive events within an ecological cont ext. They also affirm that noninvasive and generally inexpensive endocrinol ogical procedures will be applicable to understanding interactions between recolonizing predators and prey, an issue that will continue to arise becau se of global restoration efforts, and to the study of rare ungulates in rem ote systems where data on reproductive events are difficult to obtain.