Browsing by Author "Young, Hilary Catherine"

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    Animal Movement and Distribution at Habitat Edges
    (2015-02-02) Young, Hilary Catherine; Reid, Mary
    The response of organisms to habitat edges is a key factor affecting their distribution across the landscape. Resources are commonly expected to be the primary driver of edge responses, but additional processes may be important. Here I tested resource-based hypotheses and their alternatives by measuring the distribution of organisms and their resources at edges in laboratory and field settings. One non-resource-based process for animal accumulation at edges is a slowing of movement. I recorded the movement paths and distribution of Tribolium confusum beetles in an artificial arena devoid of resources. Beetles took smaller steps with larger turn angles near edges than in the arena’s centre, resulting in a distribution biased towards the edge. The proportion of time spent at edges also depended on the beetles’ propensity to cross the edge. These results suggest that proximate mechanisms such as movement behaviour should be explicitly considered when interpreting animal distributions. To investigate distribution at edges in nature, I examined the response of moose (Alces alces) and deer (Odocoileus hemionus and O. virginianus) to forest-clearcut edges of different ages. Moose responded to differences among habitat types studied but not to distance from edge within habitat types. Clearcuts > 15 years in age contained the most food and cover and were preferred to the adjacent forest and to clearcuts < four years in age. Conversely, differences in deer preferences were detected both among and within habitats. Deer were found more frequently in forest habitats than clearcuts of any age. They were also generally found closer to edges than far from them, although in old clearcuts and the adjacent forests, deer abundance dropped within 50 m of edges. I found evidence for the influence of food and cover availability on deer distribution among habitats, but it was weaker within habitats. These studies suggest that factors other than resources may affect the response of animals to habitat edges, although the field studies were largely consistent with resource tracking. To develop effective models predicting the impact of landscape heterogeneity, researchers should determine both the distribution patterns at habitat edges and the main mechanistic drivers behind these patterns.
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