Between‐lake variation in the trophic ecology of an invasive crayfish

Abstract

The trophic ecology of invasive species has important implications for their impacts on recipient ecosystems, with omnivorous invaders potentially affecting native species and processes over multiple trophic levels. The trophic ecology of invaders might be affected by both their body size and the characteristics of their habitat due to variation in energy requirements and resource availability. Here, using stable-isotope analysis, we investigated the trophic ecology of the invasive crayfish Procambarus clarkii in 15 populations in southwest France over a gradient of individual (crayfish body size), population (crayfish abundance) and ecosystem (lake size, productivity and predation pressure) characteristics. We predicted that population niche width, level of omnivory and trophic position of individuals would change with abiotic and biotic conditions, but that these relationships would vary with lake size. The trophic position of individual crayfish increased with body size in lakes with low productivity, but decreased with body size in more productive lakes. As crayfish abundance increased (and therefore potential intraspecific competition), individual trophic position and population niche width decreased. This was most apparent in smaller lakes, suggesting it related to an increase in encounter rates with conspecifics. Body size, population abundance, lake size and lake productivity influenced the trophic ecology of invasive crayfish, which can affect their interactions with native species. Our results demonstrated that the trophic ecology of invasive species can be variable across invaded landscapes, with implications for their ecological impacts on native communities. This emphasizes the importance of characterising the diet of invasive species across their non-native range and environmental gradients to better predict and manage their impacts

Stable resource polymorphism along the benthic littoral–pelagic axis in an invasive crayfish

“…There was, however, no significant difference in trophic position between littoral and pelagic individuals. Trophic positions of 3 indicated that P. clarkii feed on more than one trophic level and are thus omnivorous, as observed previously in the studied ecosystems (Jackson et al, ). This omnivorous diet was likely composed of a mixture of primary producers, invertebrates, and fish (eggs and larvae or carrion) in both habitats (Gutiérrez‐Yurrita et al, ).…”

“…On the same day as crayfish sampling, putative trophic resources of P. clarkii were collected in three different locations in each habitat of each lake to capture potential spatial heterogeneity in their stable isotope values. Specifically, periphyton and leaf litter were collected from the littoral, as they represent important components of P. clarkii's diet (Alp et al, ; Jackson et al, ), while pelagic zooplankton was collected using a 200‐µm mesh net as we assume that pelagic individuals on muddy bottoms could consume detritus including zooplankton debris (Ruokonen, Kiljunen, Karjalainen, & Hämäläinen, ; Smart et al, ). Periphyton and zooplankton samples were freeze‐dried (−50°C for 5 days) and oven‐dried (60°C for 48 hr), respectively (further details available in Jackson et al, ).…”

“…Specifically, periphyton and leaf litter were collected from the littoral, as they represent important components of P. clarkii's diet (Alp et al, ; Jackson et al, ), while pelagic zooplankton was collected using a 200‐µm mesh net as we assume that pelagic individuals on muddy bottoms could consume detritus including zooplankton debris (Ruokonen, Kiljunen, Karjalainen, & Hämäläinen, ; Smart et al, ). Periphyton and zooplankton samples were freeze‐dried (−50°C for 5 days) and oven‐dried (60°C for 48 hr), respectively (further details available in Jackson et al, ). Samples of crayfish and putative prey were collected in September–October (i.e., at the end of the growing season) to ensure that stable isotope analyses were representative of the trophic interactions occurring during this period.…”

“…The study was conducted in 16 gravel pit lakes ranging from 0.7 to 27.1 ha and located along the Garonne River in southwestern France (Alp, Cucherousset, Buoro, & Lecerf, 2016;Jackson et al, 2017) (Appendix S1). Created between 1963 and 2007, these lakes are characterized by different environmental conditions arising from various levels of maturity and management practices (Zhao, Grenouillet, Pool, Tudesque, & Cucherousset, 2016).…”

Within‐individual trophic variability drives short‐term intraspecific trait variation in natural populations

“…On the other hand, differences observed over time within an individual represent trait variation emerging from environmental variability or biological processes, such as phenology or sexual maturity (van de Pol & Wright, ). Between‐individual variability in traits has been found across a wide range of species, including arthropods (Jackson et al, ), amphibians (Araújo, Bolnick, Martinelli, Giaretta, & Reis, ), reptiles (Vander Zanden, Bjorndal, & Bolten, ), birds (Cherel, Quillfeldt, Delord, Weimerskirch, & Inger, ), mammals (Novak & Tinker, ) and fish (Litz et al, ). However, little is known on the respective contribution and temporal consistency of between‐ and within‐individual effects on the variability of trophic traits at the level of population and species (Novak & Tinker, ).…”