Ecologists are challenged to understand how factors at multiple scales interact to influence population abundance and community structure. At large scales, landscape composition and fragmentation influence recruitment and even population persistence. Fluctuating environmental conditions over time, such as ocean oscillations, snowfall, drought, and resource pulses are also strong drivers of animal populations, and it can take years for their effects to percolate up through the trophic web. Often, these large-scale processes act on populations and communities by influencing primary productivity, which elicits numerical responses in consumers. This in turn increases predator abundance, which can lead to density-dependent feedbacks and trophic web interactions such as buffering or apparent competition.
Avian nest survival is determined in part by a combination of large-scale environmental factors and local nest-site characteristics. Because predation is the primary cause of nest failure, those drivers likely operate by influencing predator abundance, behavior, and/or nest detectability. For example, fluctuations in landscape productivity can alter predator and prey abundance, whereas nest vegetation and patterns of nest spacing may influence predator behavior. We used 8 years of site-specific environmental data coupled with data collected from 11,547 duck nests to evaluate the relative importance of large-scale and local factors on nest survival.
Results/Conclusions
At larger spatial scales, we found that higher values of gross primary productivity, more wetland basins, and higher May pond counts were associated with higher nest survival in a given year, but were associated with lower nest survival the following two years. Taken in combination with previous research in this system, our interpretation is that productive environmental conditions can result in time-lagged increases in predator abundance, leading to higher levels of nest predation in subsequent years. Local factors measured at the nest site were generally less important than large-scale covariates in determining duck nest survival, but we found that nests laid earlier, in thicker vegetation, and with closer nearest neighbors had higher survival rates. However, as the season progressed, nests with closer nearest neighbors had lower survival rates (significant initiation date*distance interaction), suggesting predators may alter their behavior during the year and eventually aggregate in areas of higher nest density. Our results highlight the importance of both large-scale and local factors as they affect duck nest survival, and suggest several hypotheses about predator numerical and aggregative responses that are ripe for empirical testing.