The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Quantifying edge effects using stable isotopes


1Geology, University of Cincinnati, 2Anthropology, University of Cincinnati, 3Anthropology, University of Toronto

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Forest fragmentation creates abrupt boundaries between intact forests and matrix habitats. Edge effects occur when abiotic and biotic conditions from the matrix penetrate into the forest interior. Such effects are relevant to the lemurs of Madagascar, which are severely threatened by forest loss and fragmentation. Traditionally, abiotic and biotic variables are measured separately. However, these factors are intrinsically linked. Stable isotope values in leaves provide an integrated measure of both abiotic and biotic edge effects. We surveyed and quantified carbon and nitrogen isotope values in tree leaves eaten by resident lemurs that were growing along a savannah-dry forest edge at Ankarafantsika National Park, northwest Madagascar.

We predicted that both carbon and nitrogen isotope values would be highest close to the savannah border, where trees are exposed to more sun, drier air and higher temperatures, and that they would decrease with increasing distance from the savannah border. Instead, we found (i) a negligible relationship between carbon isotope values and distance from the edge, and (ii) a strong positive relationship between nitrogen isotope values and distance from the edge. We attribute these patterns to a gradient in soil chemistry between the savannah and the forest interior. Whereas forest soils are nutrient-deprived sands, savannah soils may have a higher nutrient and moisture content. These patterns will be useful for tracking consumption or avoidance of edge resources by resident lemurs.

This project was supported by a NSERC Discovery Grant to SML.

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