Date of Award

5-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Wildlife and Fisheries Biology

Advisor

McFadden, Katherine W

Committee Member

DeWalt , Saara

Committee Member

Loeb , Susan

Committee Member

Bridges , William

Abstract

Oak trees (Quercus species) are a foundation species that influence the population dynamics of other organisms by stabilizing ecosystem processes. Globally, oak-dominated forests have experienced widespread mortality due to the fungal pathogen, Phytophthora ramorum, which causes the disease Sudden Oak Death (SOD). I investigated the impact of a simulated pathogen attack such as SOD on the small mammal assemblage of an oak forest in Cornwall, New York. Specifically, I tested the hypothesis that specialist species are most impacted by the loss of foundation species and that they would decline in abundance because of changes in food and habitat resources. In 2008, oaks were girdled to cause mortality and mimic the symptoms of SOD. Four treatments were established, with three replicates of each: 100% oaks girdled, 50% oaks girdled, 100% non-oaks girdled, and control. From 2008 to 2012, small mammals were live captured, individually marked, and released in each of the four treatments. In addition, environmental variables hypothesized to influence small mammal abundance were collected, including coarse woody debris, leaf fall, canopy openness, soil moisture and temperature. Six small mammal species were captured, resulting in 5,135 total small mammal capture events. A total of 576 white-footed mice (Peromyscus leucopus) and 412 eastern chipmunks (Tamias striatus) were captured. These two species composed more than 97% of all animals captured. Small mammal species diversity, as measured by Shannon-Wiener diversity index, did not differ by treatment across years, but diversity was significantly lower in 2011 and 2012 across treatments. Decreased species diversity in the fourth and fifth years after treatment suggests that the small mammal assemblage, specifically the resource specialist species, may be negatively impacted by landscape-level forest disturbances. Full likelihood closed capture models indicated that abundance of the generalist white-footed mice and eastern chipmunks as well as their capture and recapture probabilities were not driven by the treatment conditions. Abundance did significantly vary by year for both white-footed mice and eastern chipmunks. White-footed mouse abundance was significantly higher in 2011and 2012 than all other years. Eastern chipmunk abundance was significantly higher in 2009 and 2012 and significantly lower in 2011. Northern short-tailed shrew (Blarina brevicauda) abundance significantly varied by year, but not treatment. Northern short-tailed shrew abundance was significantly higher in 2008 and 2009 compared to 2010-2012. Red-backed vole (Clethrionomys gapperi) abundance did not significantly differ by year, but it was significantly higher on control and 100% non-oak girdled plots compared to 50% oak girdled and 100% oak girdled plots. Meadow vole (Microtus pennsylvanicus) abundance varied significantly by year, but not by treatment, with abundance significantly higher in 2009 compared to all other years of the study. Environmental conditions significantly varied by treatment, with coarse woody debris and soil moisture being greater in 100% oak and 50% oak girdled treatments. These habitat changes did not appear, however, to impact the generalist small mammal species. Relationships between these measured environmental variables and small mammal abundance did not follow expected patterns, which may have been due to the relatively short duration of the study. Based on my findings and due to their sensitivity to the altered environmental conditions, resource specialists such as northern short-tailed shrews and red-backed voles may be more appropriate biological indicators of ecosystem health following large-scale forest disturbance events. As the movement of pathogens globally accelerates, it will be increasingly important for ecologists to understand the bottom-up cascade of impacts related to the loss of foundation tree species.

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