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Abstract
(1) Diffuse competition affects per capita rates of population increase among species that exploit similar resources, and thus can be an important structuring force in ecological communities. Diffuse competition has traditionally been studied within taxonomically similar groups, although distantly related intraguild species are likely also to compete to some degree. (2) We assessed diffuse competition between mammalian and reptilian predators at sites in central Australia over 24 years. Specifically, we investigated the effect of dasyurid marsupial abundance on the diet breadth of three groups of lizards (nocturnal dietary generalists, diurnal dietary generalists and dietary specialists). (3) Nocturnal generalist lizards had progressively narrower diets as dasyurid abundance increased. The diet breadth of diurnal generalist lizards was unaffected by overall dasyurid abundance, but was restricted by that of the largest dasyurid species (Dasycercus blythi). Ant- and termite-specialist lizards were unaffected by dasyurid abundance. (4) Diffuse competition, mediated by interference, between dasyurids and nocturnal generalist lizards appears to have strong effects on these lizards, and is the first such between-class interaction to be described. Diffuse interactions may be widespread in natural communities, and merit further investigation among other disparate taxon groups that occur in the same ecological guilds.
Highlights
Diverse ecological communities of different species that exploit similar resources in similar ways are likely to experience some degree of competition [1]
We investigated the effect of dasyurid marsupial abundance on lizard diet breadth, focusing in particular on the diets of skinks and geckoes, the two most species-rich groups in Australia’s central deserts
Our results suggest that diffuse competition occurs between desert lizards and dasyurids, and that competition is stronger between some components of this taxonomically disparate guild of small predators than others
Summary
Diverse ecological communities of different species that exploit similar resources in similar ways are likely to experience some degree of competition [1]. If these communities comprise largely predators, competitive interactions are likely to be mediated primarily by antagonism or interference, which, in extreme forms, may be manifest as intraguild killing or predation [2,3,4]. Competition and predation in multi-species communities have received some theoretical attention [5,6], with both direct and indirect trophic interactions emerging as important structuring forces [7,8]. A species’ per capita rate of population increase is predicted to decline with increasing numbers of competitors, such that a constellation of species will
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