Seasonal and habitat-related changes in bird assemblage structure: applying a diversity/dominance approach to Mediterranean forests and wetlands

Abstract

In this work, we quantified the differences in the bird assemblage structure between seasons in two Mediterranean habitat types (small wetlands and oak forests) using a diversity/dominance approach (Whittaker plots). Small wetland assemblages showed the higher slopes in Whittaker plots for breeding species; oak forest assemblages showed the higher slope for wintering species. When we compared seasonal assemblages between the two habitat types, only the breeding species showed significant differences in the slopes of lines. When we compared the three seasonal-related assemblages (migrants, wintering and passage species) inside each habitat type, we observed significant differences in small wetlands, but not in oak woodlands. Our data suggest that season associated to habitat type could be considered an important factor affecting the structure of bird assemblages. Small Mediterranean wetlands are characterized by seasonally specific structural disturbances and changes in resource and niche availability that may be more abrupt when compared to forest habitats. These changes allow the coexistence of a higher number of individuals and species, so significantly affecting the line slopes between seasonal-related assemblages. During the spring, breeding species are less represented in small wetlands due to their less stratified vegetation, when compared to oak forests. Instead, oak forests are resource poor and less dynamic environments, especially in winter (high slope in tendency line) where only sedentary generalist species could persist. We stimulate the use of diversity/dominance approaches to detect seasonal and habitat differences among animal assemblages.