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An Incidental-Effect Hypothesis Explaining Aggregation of Males in a Population of Euphydryas anicia

1988; University of Chicago Press; Volume: 132; Issue: 5 Linguagem: Inglês

10.1086/284885

1537-5323

F. J. Odendaal, Peter Turchin, Frank R. Stermitz,

Animal Behavior and Reproduction

We suggest that male aggregation in Euphydryas may be a side effect of their mate-finding behavior. Euphydryas males investigate any flying object that resembles a female and, as a result, spend much of their time chasing each other. Under some circumstances, this male-male chasing behavior can lead to the "incidental" formation of male aggregations. We tested our "incidental aggregation" hypothesis with a population of E. anicia that occurs on a flat plain, thereby eliminating topographical factors that may bias male movement. In three of four years the distribution of males was significantly aggregated. Observations of male movements indicate that when their flight is uninterrupted by encounters with other butterflies, males tend to follow highly directional straight paths. However, when they encounter other males, females, or even non-conspecifics, the directionality of their movement breaks down; that is, the direction of the flight after a chase is not correlated with the direction of the flight before the chase. Using a computer simulation, we show that the tendency of males to chase each other results in a clumped distribution of males. A behavior that is presumably adaptive-namely, to investigate all possible mates-therefore has an incidental effect on the pattern of male movement, resulting in the formation of male aggregations.