Nest Site Habitat Preference and Competition in Gasterosteus aculeatus and G. wheatlandi

Abstract

Gasterosteus aculeatus and G. wheatlandi are sympatric stickleback species that compete for suitable nest sites and nest material. Gasterosteus aculeatus, the dominant competitor, is a specialist species and will nest only in the presence of vegetation. Gasterosteus wheatlandi is a generalist species and nests success- fully in the absence of these materials. Gasterosteus wheatlandi may find a com- petitive refuge in this generalist behavior which allows for the coexistence of the two species in the estuaries. In competition with G. aculeatus in experimental pools, G. wheatlandi built significantly fewer nests, nested further away from its preferred nest site, and shifted its preference from Enteromorpha sp. to other nest habitats in combined species pools with G. aculeatus. The presence of G. wheatlandi in combined species pools had no measurable effect on G. aculeatus' nesting success.