Top-down and Bottom-up Mechanisms of Urban Edge and Fragmentation Effects

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Bolger Abstract DEB-99-81758Top-down and bottom-up mechanisms of urban edge and fragmentation effectsHabitat fragmentation and edge effects due to urban and suburban development are among the principle threats to biological diversity. The effects of habitat fragmentation are complex, diverse and pervasive. They affect animal and plant populations through a number of interacting pathways. The PI's prior work has shown that predation and parasitism on Rufous-crowned sparrow do not increase along urban edges in coastal sage scrub habitat that is fragmented by urban development in coastal suouthern California. The research proposed here will investigate the generality of the previous findings by examining the rates of nest predation and brood parasitism in five focal species of birds that vary in nest placement (ground vs. shrub) and apparent sensitivity to fragmentation. Four landscape settings that vary in degree of exposure to edge and fragmentation effects will be considered. Rates of predation and parasitism will be compared across these landscape treatments. The proposed work will also address bottom-up (food-driven) effects on fragmentation and edge by quantifying foraging behavior, diet, and nestling provisinioning rates to determine if landscape-scale variation in arthropod (food) abundance affects higher trophic levels.