title: Dietary niche constriction when invaders meet natives: evidence from freshwater decapods.
abstract: 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. 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. 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 3-year duration of the study, crab abundance declined at those sites invaded by the crayfish, becoming locally extinct at one. The invasive crayfish had a dramatic effect on ecosystem structure and functioning, halving benthic invertebrate densities and increasing decomposition rates fourfold 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. 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.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.|Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria, Hatfield, South Africa.
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Jackson
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.|Lancaster Environment Centre, Library Avenue, Lancaster University, Lancaster LA1 4YQ, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Grey
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Katie
authors.initials: K
authors.lastname: Miller
authors.affiliation: Centre for Conservation Ecology and Environmental Change, Christchurch House C238b, Talbot Campus, Bournemouth University, Fern Barrow, Poole, BH12 5BB, UK.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Britton
authors.affiliation: School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.|Trinity Centre for Biodiversity Research, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Ian
authors.initials: I
authors.lastname: Donohue
mesh_terms: D000818:Animals; D003400:Astacoidea / Q000502:physiology; D044822:Biodiversity; D033364:Decapoda / Q000502:physiology*; D004032:Diet; D017753:Ecosystem; D058865:Introduced Species; D007630:Kenya
keywords: Procambarus clarkii; community structure; diet breadth; ecosystem functioning; field experiment; interspecific competition; invasive species; stable isotopes