Data from: Dietary niche constriction when invaders meet natives: evidence from freshwater decapods

1. Invasive species are a key driver of global environmental change, with
frequently strong negative consequences for native biodiversity and
ecosystem processes. Understanding competitive interactions between
invaders and functionally similar native species provides an important
benchmark for predicting the consequences of invasion. However, even
though having a broad dietary niche is widely considered a key factor
determining invasion success, little is known about the effects of
competition with functionally similar native competitors on the dietary
niche breadths of invasive species. 2. We used a combination of field
experiments and field surveys to examine the impacts of competition with a
functionally similar native crab species on the population densities,
growth rates and diet of the globally widespread invasive red swamp
crayfish in an African river ecosystem. 3. The presence of native crabs
triggered significant dietary niche constriction within the invasive
crayfish population. Further, growth rates of both species were reduced
significantly, and by a similar extent, in the presence of one another. In
spite of this, crayfish maintained positive growth rates in the presence
of crabs, whereas crabs lost mass in the presence of crayfish.
Consequently, over the three year duration of the study, crab abundance
declined at those sites invaded by the crayfish, becoming locally extinct
at one. 4. The invasive crayfish had a dramatic effect on ecosystem
structure and functioning, halving benthic invertebrate densities and
increasing decomposition rates four-fold compared to the crabs. This
indicates that replacement of native crabs by invasive crayfish likely
alters the structure and functioning of African river ecosystems
significantly. 5. This study provides a novel example of the constriction
of the dietary niche of a successful invasive population in the presence
of competition from a functionally similar native species. This finding
highlights the importance of considering both environmental and ecological
contexts in order to predict and manage the impacts of invasive species on
ecosystems.