Abstract
Urban areas are expanding globally, and the impact of high human population density (HHPD) on bird species richness remains unresolved. Studies primarily focus on species richness along an urban-to-rural gradient; however, some studies have analyzed larger-scale patterns and found results that contrast with those obtained at smaller scales. To move the discussion beyond static species richness patterns, we analyzed the effect of HHPD on bird assemblage dynamics (year-to-year extinction probability, turnover, changes in species richness) across the United States over a 25-year period. We found that bird assemblages in both high and low human population density areas changed significantly over the period of record. Specifically, bird assemblages increased in species richness on average. Assemblage change in areas of HHPD was not significantly different from assemblage change in areas with LHPD. These results suggest that human population density alone does not alter the persistence of avian assemblage patterns.
Highlights
Urbanization is known to alter the species richness and diversity of many communities and/or assemblages [1, 2], and many researchers have chosen to focus on the response of bird species richness to urbanization [1, 3,4,5]
We studied bird assemblage dynamics in counties with high and low human population densities (LHPDs) across the U.S to determine if assemblage dynamics differ over a 25year period as a function of human population density
Mean turnover at high human population density (HHPD) and LHPD sites was slightly higher than extinction rates, which suggests that on average the colonization of a route by a species absent in a previous year is more likely than the local extinction of a species
Summary
Urbanization is known to alter the species richness and diversity of many communities and/or assemblages [1, 2], and many researchers have chosen to focus on the response of bird species richness to urbanization [1, 3,4,5]. Birds have been the focus of so many studies because they are sensitive to changes in habitat structure [1] and may serve as indicators of the ecological consequences that can accompany urban development. Several recent studies have suggested that many areas of high human population density (HHPD) are areas with high avian species richness [5]. This positive correlation is generally thought to result from the positive impact that high energy inputs (and high primary productivity) have on both human population density and avian richness. A more complete description of the impact HHPD has on bird assemblages can be achieved by examining assemblage dynamics over long time periods
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