THE INFLUENCE OF HABITAT STRUCTURE UPON DIVERSITY AND EVENNESS OF ABUNDANCE

This study examined the relationship between habitat heterogeneity and species diversity in a transitional zone between temperate and tropic al America. Additionally, the relationship between habitat heterogenei ty and evenness of abundance (EA) was examined, as measured by both ab undance and flock size. Sampling of avian community diversity, as well as flock size and abundance of three sympatric Neotropical species wi th different breeding strategies (Green Jay Cyanocorax yncas, Groove-b illed Ani Crotophaga sulcirostris and Plain Chachalaca Ortalis vetula) took place along the Rio Grande River in southern Texas. Sampling occ urred during nine months of an annual cycle, at four different habitat s representing different degrees of heterogeneity. Diversity and habit at heterogeneity exhibited the typical positive relationship. The thre e species in this study varied in abundance at different sites due to different microhabitat preference. Flock sizes of the three species be came more similar with increasing habitat heterogeneity due to more mi crohabitats within a mosaic selected by the suite of species.