Abstract
The increasing evidence of coexistence of cryptic species with no recognized niche differentiation has called attention to mechanisms reducing competition that are not based on niche-differentiation. Only sex-based mechanisms have been shown to create the negative feedback needed for stable coexistence of competitors with completely overlapping niches. Here we show that density-dependent sexual and diapause investment can mediate coexistence of facultative sexual species having identical niches. We modelled the dynamics of two competing cyclical parthenogens with species-specific density-dependent sexual and diapause investment and either equal or different competitive abilities. We show that investment in sexual reproduction creates an opportunity for other species to invade and become established. This may happen even if the invading species is an inferior competitor. Our results suggests a previously unnoticed mechanism for species coexistence and can be extended to other facultative sexual species and species investing in diapause where similar density-dependent life-history switches could act to promote coexistence.
Highlights
Maintenance of species diversity is a central topic in ecology, a critical issue being the limiting similarity of competing species allowing coexistence [1]
We propose another mechanism for stable coexistence of ecologically equivalent species based on density-dependent investment in sexual reproduction and/or dormancy
Model analysis Density-dependent sexual/diapause investment can be described by a sharp sigmoid function accounting in a continuous fashion for the occurrence of a population growth phase with negligible sexual or diapause investment and a population growth phase with both sexual and asexual reproduction (Fig. 1)
Summary
Maintenance of species diversity is a central topic in ecology, a critical issue being the limiting similarity of competing species allowing coexistence [1]. A necessary condition for stable coexistence is population growth from low densities (i.e. invasibility criterion) [7] For this to happen, the species with the highest density should affect their own growth more negatively than that of the rare species. Zhang and Hanski [8] showed that negative feedback could arise through features of sexual reproduction and recognized three mechanisms that could promote stable coexistence of identical competitors: density-dependent adjustment of sex ratio, sexual conflict, and sexually transmitted diseases. We propose another mechanism for stable coexistence of ecologically equivalent species based on density-dependent investment in sexual reproduction and/or dormancy. This mechanism may be especially important in facultatively sexual species (e.g., cyclical parthenogens), and species with diapause stages
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