Predator-prey interactions in the canopy

Small mammal abundances are frequently limited by resource availability but predators can exert strong lethal (direct mortality) and non-lethal limitations (e.g. depressed site-level activity). Artificially increasing resource availability for small mammals provides a unique opportunity to examine predator-prey interactions. We monitored the 3-year response of arboreal rodents and their predators at nest platforms (n = 598; 23 young forest sites), using annual inspections and remote cameras (n = 168). One year after adding nest platforms we found a 2.9 to 9.2-fold increase in red tree vole (Arborimus longicaudus) use at the site-level, but little use by potential predators. Predator use of nest platforms began in year two and increased in year three of the study. Most potential nest predators were positively correlated with tree vole presence at nest platforms but effect size and direction varied with temporal grain considered (e.g. hour vs day time-bin widths). Flying squirrels (Glaucomys humboldtensis) were positively correlated with disturbances caused by digging birds. Using a Cormack-Jolly-Seber model and encounter histories produced from visual re-captures of marked tree voles, we estimated apparent annual survival to be 0.099 ± 0.057 (x̄ ± 1 SE) for females and 0.005 ± 0.014 for males. Weasels (Mustela spp.), an active seeking predator, preyed upon tree voles most frequently with 10% of weasel detections resulting in mortality of a tree vole (n = 8) whereas owls, an ambush predator, did not prey upon tree voles at nest platforms even though they were detected at similar frequencies as weasels. Weasels also exerted potential non-lethal effects and we observed a >10-fold reduction in the number of tree vole detections per week after weasel detection. Our evidence indicates that predators exert direct and indirect effects on tree vole populations with active seeking predators being the most important predators at nest sites.