Abstract
Understanding how to manage biodiversity in urban areas will become increasingly important as density of humans residing in urban centers increases and urban areas expand. While considerable research has documented the shifts in biodiversity along urbanization gradients, much less work has focused on how characteristics of dense urban centers, effectively novel environments, influence behavior and biodiversity. Urban bats in San Francisco provide an opportunity to document changes in behavior and biodiversity to very high-density development. We studied (1) the distribution and abundance of bat foraging activity in natural areas; and (2) characteristics of natural areas that influence the observed patterns of distribution and foraging activity. We conducted acoustic surveys of twenty-two parks during 2008–2009. We confirmed the presence of four species of bats (Tadarida brasiliensis, Myotis yumanensis, Lasiurus blossevillii, and M. lucifugus). T. brasiliensis were found in all parks, while M. yumanensis occurred in 36% of parks. Results indicate that proximity to water, park size, and amount of forest edge best explained overall foraging activity. Proximity to water best explained species richness. M. yumanensis activity was best explained by reduced proportion of native vegetation as well as proximity to water. Activity was year round but diminished in December. We show that although bats are present even in very densely populated urban centers, there is a large reduction in species richness compared to that of outlying areas, and that most habitat factors explaining their community composition and activity patterns are similar to those documented in less urbanized environments.
Highlights
Well-documented trends of increasing urbanization represent a major impact on most ecological systems: humans move to urban areas, as human density increases, urban biodiversity decreases and becomes more homogenous, and ecosystem services may decline [1]
We identified potential habitat-related explanatory variables for each park site based on those reported in other studies of urban bats, including park size (“Pk Size”) [22], amount of forest edge (“Edge”) [8, 36, 37], percent native habitat (“Native”) [70], distance to the nearest large park (“Lg Pk”) [22], and distance to nearest water (“Water”) [39, 40, 71]
Models containing proximity to water, amount of forest edge or park size best explained overall foraging activity, explaining 61, 55, and 49% of activity respectively (Tables 2 and 3), multimodel inference across all models of activity shows that no single variable was significant
Summary
Well-documented trends of increasing urbanization represent a major impact on most ecological systems: humans move to urban areas, as human density increases, urban biodiversity decreases and becomes more homogenous, and ecosystem services may decline [1]. Most research has focused on describing characteristics of urbanization gradients, documenting a common pattern of decreasing species richness and abundance with increasing urbanization
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