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

自上而下和自下而上的城市边缘和破碎化效应机制城市和郊区发展导致的栖息地破碎化和边缘效应是对生物多样性的主要威胁之一。生境破碎化的影响是复杂、多样和普遍的。它们通过许多相互作用的途径影响动物和植物种群。PI先前的工作表明，在南加州沿海城市发展破碎的沿海鼠尾草灌丛栖息地，沿城市边缘，对红冠麻雀的捕食和寄生并没有增加。本研究将通过研究五种不同筑巢地点（地面与灌木）和对破碎化的明显敏感性的鸟类的巢捕食率和雏鸟寄生率来调查先前研究结果的普遍性。将考虑四种不同程度暴露于边缘和碎片效应的景观设置。将比较这些景观处理的捕食率和寄生率。该研究还将通过量化觅食行为、饮食和雏鸟供应率来解决自下而上（食物驱动）对碎片化和边缘的影响，以确定景观尺度上节肢动物（食物）丰度的变化是否会影响更高的营养水平。

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.