Effects of habitat degradation on species interactions and reproductive success in an Ecuadorian bird community

Abstract

Interactions between species in groups are often ignored in studies of the effects of anthropogenic change on species' persistence. However, given their global ubiquity, mixed species groups have the potential to be models for community ecology. The purpose of my dissertation was to advance the understanding of the drivers of mixed species flocking behavior in birds, as well as how human disturbance affects these interactions and species' nest survival in a unique and highly threatened landscape in the Tumbesian region of Ecuador. I predicted that interspecific interactions would be disrupted and species would have lower nest survival in vegetation disturbed by small-scale livestock grazing and clearing of trees. Further, I predicted that perceived predation risk would be more important than feeding benefits in explaining flocking behavior. To obtain my results I employed line transect counts, mixed flock observations, foraging observations, vegetation plots, livestock abundance surveys, predatory raptor abundance surveys, arthropod traps, nest searching and monitoring. Based on observations of 431 mixed species flocks, I found habitat disturbance had little impact on these interspecific associations in arid scrub, but that there were large negative impacts in tropical dry forest vegetation. Further, based on observations of 805 nests, the nest survival of most species was more greatly negatively impacted by habitat disturbance in tropical dry forest than in arid scrub vegetation. I also determined that in this region birds are forming mixed flocks primarily to avoid predation rather than to accrue feeding efficiency benefits. However, participants were also able to forage at higher rates when in flocks than when alone or with conspecifics, suggesting that birds gain feeding benefits as a side effect of choosing to be with mixed flocks to avoid predation. My findings highlight the importance of examining multiple factors when attempting to predict species' long term persistence or creating conservation management plans. For example, determining how species richness, abundances, interactions, behavior and reproductive success varied across a landscape consisting of various levels of human disturbance allowed me to gain a more complete picture of species specific and community wide impacts of disturbance in this region.