Date of Award
Master of Science
Spatiotemporal heterogeneity in predator activity can generate and influence the availability of refugia to prey. In eastern forests, white-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) are abundant generalist rodents, and large-scale removal experiments have confirmed they are important predators of gypsy moth (Lymantria dispar) pupae and songbird nests and eggs. Models predict the extinction of gypsy moth populations when confronted with abundant mouse populations, but small-scale (10s of m) heterogeneity in rodent activity may allow for the persistence of moth populations. I quantified the magnitude, variability, temporal persistence, and spatial structure of white-footed mouse and eastern chipmunk activity, and evaluated the effects of small-scale (30 x 30 m "spots") rodent removal, on 3 pairs of oak-dominated plots for 3, 2-week periods in summers 2008 and 2009 at the Cary Institute of Ecosystem Studies, Millbrook, NY, USA. Small-mammal track activity (1/check) was best fit by a beta-binomial distribution, and the mean and CV ranges of mouse and chipmunk track activity were similar between years. Disattenuated correlations of mouse and chipmunk activity were similar between sampling periods, as well as between years. I found little evidence of spatial structure in rodent activity at the scales sampled (15-250 m). Mean local track activity counterintuitively increased in removal spots compared to control spots for mice in 2008 and chipmunks in 2009. Local, between-year track activity was more strongly correlated and of greater magnitude in persistent removal spots than in non-persistent removal spots for both mice and chipmunks Environmental factors like abundant alternative food sources can influence predator foraging behavior by concentrating predator space use and altering predation rates on incidental prey items. However, the spatial scale of this aggregative effect, and impact on consumption rates on incidental prey items, are not well understood. In spring 2010, I conducted live-trapping, measured local rodent track activity, and quantified consumption rates on two incidental prey items (almonds [Prunus dulcis] and maple [Acer saccharum] seeds) on 6 plots provided with 3 supplemental food treatments (control, corn, and sunflower seeds) at Touch of Nature Environmental Center, Carbondale, IL, USA. A half-normal, cosine detectability function best fit our live-trapping data in both pre- and post-experiment trapping sessions, but considerable support remained for other models. Overall mean track activity was greater in control treatments than in sunflower and corn treatments. I found a significant interaction effect of treatment and distance, and significantly increased activity in control treatments at distances of 0, 10, and 40 m. Overall mean almond and maple seed consumption was greater in control treatments than in sunflower and corn treatments, but was greater in corn than sunflower treatments and increased from period 1 to period 3 at all distances. Mean almond consumption by mouse only and mouse + unknown predator groups was greater in control treatments than in sunflower and corn treatments. Mean maple seed consumption by mouse only and mouse + unknown predator groups was greater in control treatments than in sunflower and corn treatments.
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