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Invasive predator-prey dynamics and monitoring in Guam forests




Hanslowe, Emma B., author
Bailey, Larissa L., advisor
Boone, Randall B., committee member
Wilson, Kenneth R., committee member
Yackel Adams, Amy A., committee member

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Managing invasive predators on islands is a global conservation priority because they are causally linked to the extinction and endangerment of hundreds of insular species. Sympatric invasive prey species further threaten native biota and complicate invasive predator management; top-down and bottom-up trophic forces following invasive predator management can negate costly control efforts and worsen invasive predator impacts. The growing possibility of landscape-scale suppression of the invasive brown treesnake (Boiga irregularis) on the island of Guam created the needs for 1) a cost-effective tool for monitoring brown treesnakes' invasive endothermic prey, and 2) improved understanding of the trophic dynamics between brown treesnakes and invasive small mammals. To address the first need, we tested the accuracy of chew-cards as a rat density index. Chew-card counts were correlated with rat capture-mark-recapture density estimates across a range of rat densities found in the region, and we thus consider chew-cards a suitable tool for indexing invasive rat density in these tropical island forests. To address the second need, we conducted systematic visual surveys targeting brown treesnakes and small mammals for up to three years during and after predator (snake) control treatments. There was strong support for site-specific treatment effects of predator control, but consistent top-down and bottom-up trophic effects on average small mammal and snake counts, respectively. This work adds to our growing understanding of invasive predator-prey dynamics on islands and has direct management implications for predator control and ecological restoration on Guam. Specifically, small mammal monitoring and control are likely critical components of a management strategy for long-term snake suppression to allow reintroduction of native vertebrates on Guam.


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count-based abundance indices
Mariana Islands
small mammals
invasive predator control
brown treesnakes


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