A temporally explicit investigation of the effects of habitat change on landbird population and community dynamics

Studying population and community dynamics through time provides a better understanding of the ecological impacts of increasing rates of anthropogenic change. Such investigations can (1) validate the tools we use to understand and predict the impacts of environmental dynamics, (2) identify dominant processes affecting populations and communities, and (3) provide insight into the mechanisms of population response to environmental change. Here, I use long-term data from the Palomarin Field Station in coastal California detailing three decades of landbird population and community dynamics at a site undergoing secondary plant succession to better understand the effects of environmental change on landbirds.;In Chapter 1, I compare the ability of a habitat suitability models (HSMs) to logistic population models to explain and predict trends in abundance of seven species. HSMs are increasingly used to predict species response to future climate and land-use scenarios. However, these models do not explicitly incorporate time-dependent processes such as population growth rates and the strength of density dependence. I compared HSMs to logistic population models in explaining and predicting landbird response to vegetation change at Palomarin. In the retrospective comparison, I found that HSMs performed well in explaining variation in trends of the seven species over a 23-year period from 1983--2005, explaining between 58 and 90% of deviance. However, for three of the species, Song Sparrow (Melospiza melodia), White-crowned Sparrow ( Zonotrichia leucophrys), and Wrentit (Chamaea fasciata), a logistic population model provided a better fit to the retrospective data. These three species have more localized dispersal, suggesting that incorporating population processes into habitat suitability modeling for species with similar dispersal patterns may improve projections. In the prospective evaluation, I used both model types to predict changes in abundance from 2006--2010, and I compared these predicted abundances to the observed abundances. Neither model type performed consistently better in predicting species trends over the five year period. In summary, I found that overall HSMs can explain and predict species' trends through time; however, for species with localized dispersal, incorporating population processes may improve understanding.;In Chapter 2, I applied a hierarchical approach and Bayesian inference to the times series of seven species used in my first chapter to partition variance in species trends between interspecific interactions, intraspecific processes and environmental forcing. I found that within-guild interspecific interactions were the least important contributor to variation in species trends, explaining between 0 and 5% of variation. Vegetation and rainfall variation, combined, explained 6 to 30% of variation in species trends. Intraspecific processes explained between 0 and 39% of variation. Between 27 to 90% of variation was attributed to unexplained variation. While these are not novel species interactions, as would be expected in communities resulting from anthropogenic change, these results suggest that within-guild interactions are not a major source of variation in landbird population trends.;In the third chapter of my dissertation, I investigated the underlying behavioral and demographic mechanisms of species' response to environmental dynamics. I focus on one species, White-crowned Sparrow, which has declined dramatically in density since 1980. I evaluate patterns in vegetation change, nest site selection, and three measures of reproductive success to understand the effect of habitat change on individuals and to provide insight into the degree to which White-crowned Sparrows are able to ameliorate the effects of habitat change through behavioral decisions. I found that White-crowned Sparrows prefer early successional habitat, and no evidence for an effect of the range of experienced habitat conditions on variation in nest survival, clutch size, or number of fledglings. These results provide evidence that through their strong habitat preference, individual White-crowned Sparrows are able to narrow the range of successional habitat they experience, and thus do not incur a demographic cost of habitat change on reproductive success. These results demonstrate the species' ability to adjust to habitat change through behavioral decisions. (Abstract shortened by UMI.).