Coexistence on a Seasonal Resource

A model is presented giving conditions for competitive coexistence on a single resource with seasonal productivity. It is assumed that individuals can allocate time to foraging and remaining dormant and that dormancy is less costly than foraging. Coexistence requires a trade-off between foraging and maintenance efficiency. The species with the higher maintenance efficiency (ratio of harvest rate to cost of dormancy) can exploit periods of high resource abundance and then inexpensively remain dormant during periods of low abundance. The species with the higher foraging efficiency (ratio of harvest rate to the additional cost of foraging over remaining dormant) can continue to exploit profitably periods of low resource abundance. The optimal behavior of the foragers promotes coexistence. Furthermore, increasing variation in resource productivity increases the chances of adding to the community a species with a higher maintenance efficiency but lower foraging efficiency. Many ecological communities described in the literature have coexisting species with dissimilar body sizes or morphologies and a high degree of diet overlap. In many of these communities, perhaps, body size, wing morphology, or foraging tactics provide an evolutionary trade-off between maintenance and foraging efficiency. Coexistence mediated by variation in resource abundance may be a general ecological phenomenon that contributes to diversity in many feeding guilds.