Oecologia

, Volume 123, Issue 3, pp 425-435

First online:

Short-term dynamics of an acacia ant community in Laikipia, Kenya

  • T. M. PalmerAffiliated withDepartment of Environmental Horticulture and Graduate Group in Ecology, University of California, Davis, CA 95616, USA e-mail: tpyoung@ucdavis.edu Tel.: +1-530-7522667, Fax: +1-530-7521819
  • , T. P. YoungAffiliated withDepartment of Environmental Horticulture and Graduate Group in Ecology, University of California, Davis, CA 95616, USA e-mail: tpyoung@ucdavis.edu Tel.: +1-530-7522667, Fax: +1-530-7521819
  • , M. L. StantonAffiliated withDepartment of Evolution and Ecology and Center for Population Biology, University of California, Davis, CA 95616, USA
  • , E. WenkAffiliated withDepartment of Integrative Biology, University of California, Berkeley, CA 94720, USA

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Abstract 

In monospecific stands of Acacia drepanolobium in Laikipia, Kenya, virtually all but the smallest trees are occupied by one of four species of ants. Although trees are a limiting resource, all four ant species are maintained in this system. Three separate lines of evidence confirm a linear dominance hierarchy among these four ants: (1) experimentally staged conflicts, (2) natural transitions among 1773 tagged trees over a 6-month period, and (3) the average sizes of trees occupied by ants of different species. Short-term dynamics during a drying period reveal that many smaller trees (<1 m) occupied by dominant ants were subsequently abandoned, and that abandoned trees had grown more slowly than those that were not abandoned. Height growth increments over 6 months were generally independent of ant occupant, but increased with tree height. Among taller trees (>1 m), changes in ant occupation congruent with the dominance hierarchy (i.e., transitions from more subordinate ant species to more dominant ant species) occurred on trees that grew faster than average. In contrast, the (less frequent) changes in ant occupation ”against” the direction of the dominance hierarchy occurred on trees that grew more slowly than average. Observed correlations between tree vigor and takeover direction suggest that colony growth of dominant ant species is either favored in more productive microhabitats, or that such colonies differentially seek out healthier trees for conquest. Colonies of dominant species may differentially abandon more slowly growing trees during (dry) periods of retrenchment, or suffer higher mortality on these trees. Subordinate ant species appear to move onto these abandoned trees and, to a lesser extent, colonize new recruits in the sapling class. These data reveal that within a simple linear dominance hierarchy, short-term variations exist that may reveal underlying mechanisms associated with coexistence.

Key words Species coexistence Dominance hierarchy Acacia drepanolobium Crematogaster Tetraponera