Complex competitive interactions in four species of Lucilia blowflies

Abstract

Abstract. The effects of intraspecific and interspecific larval competition on larval survival, adult size, adult longevity and fecundity were quantified in four species of coexisting Lucilia blowflies: illustris, silvarum, sericata and caesar. There was a general negative effect of increasing density on larval and adult survival, size and fecundity. Additionally, complex species‐specific and frequency‐dependent responses were identified, which were not expected in these biologically and morphologically closely similar species. Lucilia illustris, the numerically dominant species in the natural community, was a superior competitor to L.silvarum at intermediate densities but an inferior competitor at high density. Such nonlinear responses may be related to differences in the life histories and larval behaviour of the species (bigger eggs and more contest‐type outcome of competition in L.silvarum). We parameterized a model of interspecific competition on a subdivided resource in an attempt to reconcile the conflicting results on larval competitive abilities and the abundances of the species in the field. Using laboratory and field‐estimated parameter values the model predicted coexistence of L.illustris and L.silvarum and the observed numerical dominance of the former species. The average densities of flies in the field are limited to relatively low levels, apparently preventing L.silvarum (the superior competitor at high density) from dominating and excluding L. illustris.