COMPETITION ON A DIVIDED AND EPHEMERAL RESOURCE - TESTING THE ASSUMPTIONS .1. AGGREGATION

Tested the assumptions of the "aggregation model' of coexistence on a divided and ephemeral resource: 1) that the competing stage is aggregated; 2) that the distributions of individuals can be represented by a negative binomial distribution; and 3) that the degree of aggregation can be represented by a constant parameter. Tests are made on 360 datasets representing distributions of Diptera, particularly drosophilids, on a total of 7638 resource patches. For these data: 1) competing stages are strongly aggregated; 2) the negative binomial is not an exact description but may be adequate; and 3) aggregation varies with density. The authors relax the assumption of constant aggregation and develop a model of 2-species competition where aggregation varies with density. With observed estimates of parameters for drosophilids, coexistence between pairs of species with no resource partitioning remains likely despite strong local competition. -from Authors