Intermediate predator naïveté and sex-skewed vulnerability predict the impact of an invasive higher predator

Abstract

The spread of invasive species continues to reduce biodiversity across all regions and habitat types globally. However, invader impact prediction can be nebulous, and approaches often fail to integrate coupled direct and indirect invader effects. Here, we examine the ecological impacts of an invasive higher predator on lower trophic groups, further developing methodologies to more holistically quantify invader impact. We employ functional response (FR, resource use under different densities) and prey switching experiments to examine the trait- and density-mediated impacts of the invasive mosquitofish Gambusia affinis on an endemic intermediate predator Lovenula raynerae (Copepoda). Lovenula raynerae effectively consumed larval mosquitoes, but was naïve to mosquitofish cues, with attack rates and handling times of the intermediate predator unaffected by mosquitofish cue-treated water. Mosquitofish did not switch between male and female prey, consistently displaying a strong preference for female copepods. We thus demonstrate a lack of risk-reduction activity in the presence of invasive fish by L. raynerae and, in turn, high susceptibility of such intermediate trophic groups to invader impact. Further, we show that mosquitofish demonstrate sex-skewed predator selectivity towards intermediate predators of mosquito larvae, which may affect predator population demographics and, perversely, increase disease vector proliferations. We advocate the utility of FRs and prey switching combined to holistically quantify invasive species impact potential on native organisms at multiple trophic levels.

Alien Freshwater Fauna in South Africa

“…There has been no research into the impacts of G. affinis on native biota in South Africa, but their diet often overlaps with that of native fishes and there is potential for competition with native fishes when resources are limited (Pyke 2008). Experimental work by Cuthbert et al (2018), however, also highlighted that G. affinis select non-mosquito crustacean prey over mosquitos, highlighting their potential for impact on a broad range of invertebrate taxa.…”

Gimme Shelter: differential utilisation and propagule creation of invasive macrophytes by native caddisfly larvae

“…Functional responses and associated resource preferences/switching have been identified as powerful tools to quantify invasive species impacts and invasion success (Dick et al 2014;Cuthbert et al 2018b;Skein et al 2018), whereby Type II curves are thought to be resource destabilising due to high resource utilisation rates at low densities, whilst the converse is true for Type III FRs. However, whilst FRs are commonly applied to address consumer-resource interactions such as predation and herbivory (Dick et al 2014;Xu et al 2016a, b;Mu et al 2018;Cuthbert et al 2018a), there has hitherto been a lack of consideration for such per capita effects in shredder-herbivores, especially with regards to atypical resource utilisation behaviours, such as caddisfly case-building.…”

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

“…However, despite their significance for regional and global biodiversity, ephemeral wetlands have received relatively little attention due to spatial and temporal heterogeneity, which makes them difficult to detect and conserve during dry periods. The integrity of ephemeral wetlands is thus threatened in multiple ways, such as through land use changes driven by agricultural activity (Brock, Smith, & Jarman, ; Marty, ), species introductions (Cuthbert, Dalu, Wasserman, Dick, et al., ; Dalu, Wasserman, & Dalu, ), and climate change (Lu et al., ). Warming and salinisation are amongst the most pervasive stressors in ephemeral wetlands associated with ongoing environmental change (Dalu, Wasserman, & Dalu, ; Mabidi et al., ).…”

“…() often dominates ephemeral wetlands and belongs to the Paradiaptominae subfamily that is adapted to arid, temporary habitats. This species is large and predatory (Cuthbert, Dalu, Wasserman, Dick, et al., ; Suárez‐Morales et al., ; Wasserman, Alexander, Barrios‐O'Neill, et al., ), and occupies high trophic levels in ephemeral wetland ecosystems for much of the hydroperiod (Dalu, Wasserman, Froneman, & Weyl, ). Therefore, this species has the potential to have marked ecological impacts on lower trophic levels through biotic processes such as predation (Cuthbert, Dalu, Wasserman, Callaghan, et al., ).…”