Abstract
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.