Abstract

Coprophagous insect communities play a critical role in the decomposition of vertebrate dung and provide ecosystem functions fundamental to modern agriculture. While the ecology of dung beetles is rather well understood, niche differentiation in coprophagous flies is poorly studied. Sepsid flies (Diptera: Sepsidae) are a vital part of the European community of coprophages, with 6-7 widespread species of Sepsis often found co-occurring in the same pasture. To advance our ecological understanding of the mechanisms that enable species to coexist, we investigated the oviposition preferences and larval performance of 7 common species of Sepsis in the dung of different large domestic and wild mammals. Substrate preferences and subsequent performance of larvae in laboratory experiments did not vary greatly. All species did very well on cow dung, the most common substrate in Central Europe, but also on dung of horse and wild boar. In contrast, flies did not prefer or grow well in dung of red and roe deer, two of the most common wild vertebrates. Thus there were only minor differences among the species tested along the specialist-generalist (dung) gradient, indicating that differences in the choice of oviposition sites by the adults of the different fly species and larval performance do not constitute a major axis of ecological differentiation. Nevertheless, there was a positive correlation between substrate choice and larval performance indicating the preference of gravid females for particular oviposition sites is adaptive. We conclude that sepsids are common in Europe because they are well adapted to the dung of herbivorous livestock rather than wild animals. Nevertheless, specialization on particular types of dung does not define the niche of Sepsis dung flies and hence plays a minor role in mediating their species diversity.

Highlights

  • According to the principle of competitive exclusion, species that inhabit identical or very similar ecological niches should not be able to coexist

  • Given that diversity is often linked to ecosystem function (Oehri et al, 2017), understanding the mechanisms mediating diversity and abundance of coprophages could be vital for agricultural management

  • The foraging niches of the closely-related species investigated seem to overlap greatly, indicating that specialization on different kinds of dung contributes little to the avoidance of direct competition in the larval habitat. Despite this rather slight interspecific variation, we found a positive correlation between a mother’s choice of substrate and subsequent larval performance across the 9 taxa (Fig. 5). This follows the expectation that natural selection should align adult oviposition preference and larval performance

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Summary

Introduction

According to the principle of competitive exclusion, species that inhabit identical or very similar ecological niches should not be able to coexist. Species that are dependent on the same physiologically non-substitutable resource are expected to only co-occur if they manage somehow to evade direct competition (Holt, 2009). Such niche differentiation can be explained as an evolutionary result of competitive divergence by which competition for the same resource leads to ecological character displacement, niche shifts and eventual competitive exclusion of one species by another (Abrams, 1987). In practice, niche differentiation is inferred post-hoc by comparing closely related species that do, or do not, coexist in space or time This typically starts with an assessment of the spatio-temporal distribution of organisms belonging to a particular guild in nature

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