Date of Award
Master of Science
The permeability of surrounding landcover types can influence the probability of animals leaving a patch and dispersing across the unsuitable matrix. The marsh rice rat (Oryzomys palustris) persists in wetlands that are often isolated by upland cover types. The goal was to quantify the permeability of three landcover types (grassland, agriculture, and forest) and calculate the landcover composition of home ranges for a population of rice rats in southern Illinois. Between March 2011 and January 2012, I trapped rice rats up to 95 m from wetlands into unsuitable cover and simultaneously followed individuals via radiotelemetry. I calculated the slope of capture rate (log-transformed) vs. distance from wetland as an inverse measure of permeability and also measured inundation, rice rat abundance, and matrix vegetation density as potential covariates explaining matrix use. I calculated mean home range size for males with the fixed kernel density method and compared landcover within home ranges to what was available in the surrounding landscape. Using generalized linear mixed models, I compared matrix capture rates and permeability levels among cover types, inundation, abundance, and vegetation density. After 13,610 trap-nights, I captured 43 rice rats in the matrix between March and September, with 24 in agriculture, 10 in grassland, and 9 in forest. I did not find permeability differed between landcover types, but did find that rice rats were captured further and more frequently in agriculture than grassland and forest cover. Both population abundance in wetlands and vegetation density < 0.5 m high had positive effects on matrix captures, while lowering water levels increased the permeability of the surrounding matrix. After radio-tracking 25 rice rats, home ranges were 3.01 ±0.57 ha and were the largest for individuals followed in early summer. Emergent vegetation was used proportionally more than would have been expected at random, indicating rice rats preferred emergent wetlands habitat at the home-range level. This study suggests that rice rats are more vagile and move through upland cover types more frequently than previously described in the literature.
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