Impacts of increasing isolation and environmental variation on Florida Scrub-Jay demography.

Isolation caused by anthropogenic habitat fragmentation and degradation can destabilize populations. Population demography is shaped by complex interactions among local vital rates, environmental fluctuations, and changing immigration rates. Empirical studies of these interactions are critical for testing theoretical expectations of how populations respond to isolation. We used a 34-year demographic and environmental dataset from a population of Florida Scrub-Jays ( Aphelocoma coerulescens ) that has experienced declining immigration to create mechanistic models linking environmental factors and variation in vital rates to population growth rates over time. We found that the population has remained stable despite declining immigration and increasing inbreeding, owing to a coinciding increase in breeder survival. We find evidence of density-dependent responses of immigration, breeder survival, and fecundity, indicating that interactions between vital rates and local density likely play a role in buffering the population against change. Our study elucidates the interactions between environment and demography that underlie population stability.