Abstract
Successful establishment of invasive species is often related to the existence of vacant niches. Competition occurs when invaders use the same limiting resources as members of the recipient community, which will be reflected in some overlap of their trophic niches. The concept of isotopic niche has been used to study trophic niche partitioning among species. Here, we present a two-year field study comparing isotopic niches of the deposit-feeding community in a naturally species-poor system. The isotopic niche analyses showed no overlap between a recent polychaete invader and any of the native species suggesting that it has occupied a vacant niche. Its narrow isotopic niche suggests specialized feeding, however, the high δ15N values compared to natives are most likely due to isotope fractionation effects related to nitrogen recycling and a mismatch between biological stoichiometry of the polychaete and the sediment nitrogen content. Notably, highly overlapping isotopic niches were inferred for the native species, which is surprising in a food-limited system. Therefore, our results demonstrate that invaders may broaden the community trophic diversity and enhance resource utilization, but also raise questions about the congruence between trophic and isotopic niche concepts and call for careful examination of assumptions underlying isotopic niche interpretation.
Highlights
Successful establishment of invasive species is often related to the existence of vacant niches
The total and relative abundance of species varied among stations, with densities of the invasive species Marenzelleria arctia ranging from 23 to 677 individuals m22 (Fig. 1)
In 2010 at stn Mörkö, the niche area overlap among the three native species was nearly complete (Fig. 2), with Monoporeia affinis overlapping by 98% with Pontoporeia femorata
Summary
Successful establishment of invasive species is often related to the existence of vacant niches. The isotope niche of a population integrates temporal (seasonal to multi-year) and – at least to some extent – spatial (population habitat) variations[14] This quantitative approach to describe trophic space by stable isotopes has been used to test ecological theories[15] including trophic ecology of invasive species in their novel environments[16,17], but has been criticized[18]. A recent experimental study using isotope enriched algae found little overlap in use of freshly deposited spring bloom material between M. arctia and the native species, suggesting that M. arctia is not a strong competitor for the nutritious diatom input during the experimental duration of three weeks[21]. The well-studied trophic ecology of the native species, especially the habitat and resource partitioning between the amphipods M. affinis and Pontoporeia femorata[20,26,27] provides a solid background for applications of isotope niche in ecological studies
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