Competition for resources can be an important force in the determination of animal abundance, but is more often assumed than tested. In many cases, the importance of resource competition is context dependent and varies across abiotic gradients. This is especially true for mosquitoes (Diptera: Culicidae) where aquatic habitats range from large to small, and from permanent to ephemeral. For example, intraspecific competition is of clear relevance for many medically important container mosquitoes, but is of questionable relevance for species in large, permanent aquatic systems such as saltwater marshes. We investigated the role of intraspecific resource competition in the population dynamics of the widespread Arctic mosquito, Aedes nigripes. We conducted our research near Kangerlussuq in western Greenland, where A. nigripes is the only mosquito species and where interspecific competition from other aquatic invertebrates is also low. To estimate immature per capita mortality in field populations, we used larval count data across the immature development period from 8 ponds that we sampled for 2 years, and 4 ponds we sampled for 4 years that ranged in size, permanence, and presumably, productivity. For a subset of ponds, we calculated relative growth rate from larval mass data, and we measured the abundance and size of adults from emergence traps. We couple these field studies with a lab experiment where we manipulated the number of larvae and amount of detritus and tracked the survivorship and development of larvae.
Results/Conclusions
Across ponds, per-capita mortality rates were positively related to initial density. There was no evidence for overcompensation. Rather, ponds with higher abundance of hatching larvae typically produced the most pupae and adults. Furthermore, ponds with the highest larval densities often produced the largest adults, suggesting that density of larvae is positively associated with resource (microorganisms and fine particulate organic matter) abundance. Our lab experiment similarly showed evidence for resource competition, but not enough to produce overcompensation, even at very high densities. Our results show that negative density dependence does occur in field populations, but suggest that ponds with higher productivity and/or lower densities of larvae have lower levels of per-capita mortality. Female adults may tend to oviposit the most in these productive habitats that are most suitable for larval development.