Collaborative Research: Testing for Cascading Effects of Habitat Fragmentation

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Collaborative Research: Testing for Cascading effects of Habitat FragmentationDiffendorfer, James, F.San Diego State UniversityFood web theory provides a useful framework for management of ecosystems, and compliments well the more traditional population-level approach. However, the applicability of food web concepts, including keystone species and top-down cascades, to ecosystems of conservation concern is unclear. This project will study changes in predator-prey interactions in the coastal sage scrub ecosystem of southern California cause by habitat fragmentation, associated with urban development. This project focuses on four landscape treatments in coastal San Diego County that vary in the degree of exposure to urban edge and fragmentation: interior of large habitat blocks (1000ha), urbanized edge of large blocks, large habitat fragments (50-100 ha) and small fragments (5-20 ha). The proposed research will expand previous work by continuing demographic studies on birds, but with simultaneously estimation of mesocarnivore, snake, and raptor abundance and activity to estimate their impacts and examine how these vary with habitat fragmentation. The work will determine if nest predation, juvenile and adult bird survival, as well as small mammal abundance and survival vary with fragment size and predator composition. In addition, it will investigate the role of snakes, and raptors and determine their impact relative to mammalian predators by comparisons across experimental treatments and by path analysis. By comparing bird responses to small mammals this project will address the question of whether all primary consumers are vulnerable to cascades, or if the biological differences between taxa make one group more susceptible to top-down regulation than another. Overall, this project will train 18-25 undergraduates, 3 graduate students and a post-doctoral student, and will creating research opportunities for underrepresented students participating in an NSF Undergraduate Mentoring in Environmental Biology teaching program. In addition, this research will directly benefit ongoing management and reserve design objectives of local wildlife agencies and nonprofit, land management organizations.