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ANTSET: Studying local ant assemblages at a geographic scale |  |
| ant an | from "Energy, Density, and Constraints
to Species Richness: Ant Assemblages along a Productivity Gradient."
Michael Kaspari, Sean O'Donnell, and James Kercher. American Naturalist
155: 280-293
Species richness describes the number of species of a given taxon in a given time and space. The Energy Limitation Hypothesis links the species richness of consumer taxa to Net Primary Productivity (NPP) through two relationships: NPP limits a taxon's density, and taxon density limits species richness. We study both relationships with a survey of
15 ground ant assemblages along a productivity gradient from deserts to
rainforests. Ant density (colonies / m2) was a positive, decelerating
function of Net Aboveground Productivity (NAP).
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A stepwise regression suggests
that the efficiency with which NAP is converted to ant colonies increases
with maximum summer temperature and decreases with precipitation.
Ant species richness was a positive, decelerating function of density at three spatial scales. This supports the Energy Limitation Hypothesis' assumption that average population densities are higher in environments that are more productive. These two nonlinear functions (NAP-Density, Density-Species Richness) combine to create, at a variety of scales, positive, decelerating productivity-diversity curves for a common, ecologically dominant taxon across the terrestrial productivity gradient. However, variance in the density and diversity explained by NAP decreases with scale, suggesting that energy limitation of diversity predominates at small spatial scales (<1 ha). |
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| Updated 26July2000
Author Mike Kaspari |