Abstract
Among spiders, taxonomically the most diversified group of terrestrial predators, only a few species are stenophagous and feed on ants. The levels of stenophagy and ant-specialisation vary among such species. To investigate whether stenophagy is only a result of a local specialisation both fundamental and realised trophic niches need to be estimated. Here we investigated trophic niches in three closely-related spider species from the family Gnaphosidae (Callilepis nocturna, C. schuszteri, Nomisia exornata) with different levels of myrmecophagy. Acceptance experiments were used to estimate fundamental trophic niches and molecular methods to estimate realised trophic niches. For the latter two PCR primer sets were used as these can affect the niche breadth estimates. The general invertebrate ZBJ primers were not appropriate for detecting ant DNA as they revealed very few prey types, therefore ant-specific primers were used. The cut-off threshold for erroneous MOTUs was identified as 0.005% of the total number of valid sequences, at individual predator level it was 0.05%. The fundamental trophic niche of Callilepis species included mainly ants, while that of N. exornata included many different prey types. The realised trophic niche in Callilepis species was similar to its fundamental niche but in N. exornata the fundamental niche was wider than realised niche. The results show that Callilepis species are ant-eating (specialised) stenophagous predators, catching mainly Formicinae ants, while N. exornata is an ant-eating euryphagous predator catching mainly Myrmicinae ants.
Highlights
Among spiders, taxonomically the most diversified group of terrestrial predators, only a few species are stenophagous and feed on ants
Specialised exploitation of a limited type of resources can be either due to local or global specialisation[1,2]. This can be resolved by comparing the fundamental and realised niches. While the former trophic niche is wide as it includes all prey types that the predator is capable of exploiting, the latter is obviously narrower as it is limited by prey availability
Our results from the prey DNA analysis show that both N. exornata and Callilepis spp. spiders hunt mostly ants in the field
Summary
Taxonomically the most diversified group of terrestrial predators, only a few species are stenophagous and feed on ants. Specialised exploitation of a limited type of resources (or stenophagy) can be either due to local (ecological) or global specialisation[1,2] This can be resolved by comparing the fundamental and realised niches. While the former trophic niche is wide as it includes all prey types that the predator is capable of exploiting, the latter is obviously narrower as it is limited by prey availability. Spiders are the most diversified and important terrestrial arthropod predators[3] but evidence of breadth of trophic niche is available only for less than 2% of species[4] Among these the majority of data exist for euryphagous species, i.e. feeding on wide variety of prey[5]. Drosophila melanogaster Meigen, 1830; Drosophila hydei Sturtevant, 1921 Callosobruchus maculatus (Fabricius, 1775)
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