Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Zanette, Liana Y.


Predators not only kill prey, but through the 'fear' of predation, predators induce costly anti-predatory responses in prey. Anti-predatory costs may scale up to effects on prey populations, through effects on prey reproduction and survival. This thesis aimed to quantify the net effect of predation risk effects on a prey population in a terrestrial vertebrate system for the first time. I manipulated the perceived risk of predation in multiple study years by exposing song sparrows (Melospiza melodia) to playbacks of either predator or non-predator calls. Females exposed to predator playbacks laid fewer eggs, had more eggs fail to hatch, and had more nestlings die, replicating past studies. However, my thesis differentiated from past work by assessing predation risk effects on the survival of free-living juveniles using radio-telemetry. From egg-laying to juvenile independence females exposed to predator playbacks produced 53 % fewer offspring. Using mark-recapture methods I found that this 53 % reduction to juvenile independence was maintained to juvenile recruitment into the breeding population, effectively halving the number of new breeders to join the population. Predation risk effects further affected the breeding population by disproportionally reducing female survival in recruits and older adults. The annual survival for females in the predator playback treatments was 42 % compared to 69 % in the non-predator treatment. Observed differences between treatments appeared to be differences in true survival values because mark-recapture histories and natal dispersal comparisons suggested that juveniles and adults did not differ in emigration rates between treatments. Incorporating the observed effects on all life-history stages of my study species into Leslie matrices revealed that the cumulative cost of predation risk effects caused a 25 % difference in population growths rates between playback treatments. Overall, predation risk effects were strong enough to predict population declines (24 % per year) suggesting that predation risk effects do indeed scale up to population level effects. Thus, predation risk effects should be taken into consideration for future conservation and wildlife management decisions pertaining to the control or reintroduction of species.