This week’s seminar will be presented by Helen Sofaer, a PhD candidate studying orange-crowned warblers in Dr. Cameron Ghalambor’s lab.
Density dependence in two seasons: demographic effects of competition and climate
Abstract: Density dependence is central to our understanding of population dynamics. Theory predicts that populations must be regulated by density-dependent mechanisms during at least some time periods or life stages, but detecting and measuring the strength of density dependence is notoriously difficult. For example, population density is likely to interact with ecological conditions such as food availability to affect demographic rates, and these interactions may mask the signal of density dependence. Relatively simple ecological communities, such as those on islands, provide an opportunity to disentangle the effects of density dependence from demographic variation due to fluctuating ecological conditions. Here, we analyze the fecundity and apparent survival of Orange-crowned Warblers (Oreothlypis celata) breeding on Catalina Island, California to test for evidence of density dependence. We found that within the island’s mediterranean climate, rainfall was the primary driver of food abundance, and was positively correlated with fecundity. After accounting for variation in rainfall, fecundity showed a strong pattern of negative density dependence. In addition, apparent survival was negatively correlated with population density on the wintering grounds, providing a rare example of potential regulatory mechanisms acting in multiple seasons of a migratory bird.