Species interactions are disrupted by habitat degradation in the highly threatened Tumbesian region of Ecuador

Abstract

Interactions between species in groups are often ignored in studies of the effects of anthropogenic change on species' persistence, and yet, given their global ubiquity, mixed-species groups have the potential to be models for community ecology. In this paper we examine the impacts of rural community activities that are pervasive in tropical regions on mixed-species flocks of birds in a unique coastal tropical dry forest ecosystem, with the aim of advancing both our understanding of mixed-species associations and how best to conserve them. We examined the effects of small-scale clearing of trees and livestock grazing on mixed flocks in two vegetation types in the highly threatened Tumbesian region of Ecuador. Because the fitness benefits of flocking come from a reduced risk of predation or enhanced feeding efficiencies, or both, habitat degradation could lead to changes in the benefits of flocking and thus flock characteristics. We predicted that, in more disturbed vegetation, flocks would have fewer species and individuals and that species would show lower flocking propensities and feeding efficiencies. Based on observations of 431 flocks, we found that these predictions were supported in tropical dry forest but not always in arid scrub vegetation. Less disturbed tropical dry forest had greater mean species richness per flock than more disturbed tropical dry forest, but mean species richness per flock did not differ between more and less disturbed arid scrub. Flock species richness and composition differed across the disturbance levels in tropical dry forest, but not in arid scrub. Many species had their highest flocking propensities and greatest foraging efficiencies in less disturbed, compared to more disturbed, vegetation. We show that existing park management, which allows community development and livestock grazing within national park borders, leads to degradation of the vegetation and disrupts species' interactions in tropical dry forest. We provide specific conservation recommendations to mitigate these disruptive influences. Examining intraspecific associations across diverse communities is of the utmost importance to both answering basic theoretical questions in community ecology and conserving species diversity in the face of anthropogenic landscape change.