Three energy variables predict ant abundance at a geographical scale

Michael Kaspari, Leeanne Alonso, Sean O'Donnellkwd>

Abstract

Energy theory posits three processes that link local abundance of ectotherms to geographical gradients in temperature. A survey of 49 New World habitats found a two order of magnitude span in the abundance (nests m−2) of ground nesting ants (Formicidae). Abundance increased with net primary productivity (r2=0.55), a measure of the baseline supply of harvestable energy. Abundance further increased with mean temperature (r2=0.056), a constraint on foraging activity for this thermophilic taxon. Finally, for a given mean temperature, ants were more abundant in seasonal sites with longer, colder winters (r2=0.082) that help ectotherm taxa sequester harvested energy in non–productive months. All three variables are currently changing on a global scale. All should be useful in predicting biotic responses to climate change.

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