Context-dependent differences in the functional responses of conspecific native and non-native crayfishes

Abstract

Invasive species are proliferating globally and cause a range of impacts, necessitating risk assessment and prioritization prior to management action. Experimentally derived estimates of per capita effects (e.g. functional responses) have been advocated as predictors of field impacts of potential invaders. However, risk assessments based on estimates from single populations can be misleading if per capita effects vary greatly across space and time. Here, we present a large-scale, multi-population comparison of per capita effects of the American spinycheek crayfish, Faxonius (formerly Orconectes) limosus—a species with an extensive invasion history in eastern North America and Europe. Functional responses were measured on individuals from six geographically disparate populations of F. limosus in its native and invaded ranges on two continents. These revealed inter-population differences in both the maximum feeding rate and functional response type that could not be explained by the biogeographic origin of the population nor by time since the invasion. We propose that other differences in source communities (including the presence of competitors) impose selective pressures for phenotypic traits that result in dissimilar per capita effects. We also compared functional responses of the congeners F. limosus and F. virilis in the presence and absence of potential competitors to examine indirect competitive effects on feeding behaviour. The maximum feeding rate of F. limosus, but not F. virilis, was suppressed in the presence of heterospecific and conspecific competitors, demonstrating how the per capita effects of these species can differ across biotic contexts. In the competitor-presence experiments, individuals from the invasive population of F. limosus consistently had a higher maximum feeding rate than those of the native F. virilis, regardless of treatment. Our results caution against invasion risk assessments that use information from only one (or a few) populations or that do not consider the biotic context of target habitats. We conclude that comparative functional responses offer a rapid assessment tool for invader ecological impacts under context dependencies when multiple populations are analyzed.

Invasive crayfish outperform Potamonautid crabs at higher temperatures

“…Nonetheless, P. perlatus had a low and high FRs under the high and low temperatures respectively, which suggests a cooler thermal range than the other species that may be a result of adaptation to the cooler Eastern Cape water bodies (Dallas, 2008). While the native range of P. perlatus is large and overlaps with regions that have been invaded by the two crayfish species in South Africa, as well as spreading into Namibia (Barnard, 1950; Cumberlidge & Daniels, 2007; Gouws et al., 2002), it should be emphasized that FRs can be population specific (Boets et al., 2019; Grimm et al., 2020). Similar results (i.e.…”

Differences in the functional responses of four invasive and one native crayfish species suggest invader‐specific ecological impacts

“…Third, the data were non-parametrically bootstrapped to generate bias-corrected and accelerated (BCa) 95% confidence intervals (CI) for the a and h estimates using the bootstrap function of the frair-package (N = 999; Pritchard et al, 2017). Non-overlapping 95% BCa CI for a or h were considered as significant differences (Grimm et al, 2020;South et al, 2019). Bootstrapping was also used to generate empirical 95% CI around the fitted FR curves for visual inspection of differences among crayfish species, whereby a lack of overlap indicates statistical differences in FR (South et al, 2019).…”

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large, and Oligotrophic Lake (Lake Maggiore, North Italy)

“…Great efforts have been spent to find general patterns able to predict the invasiveness, introduction paths, and impacts [1][2][3][4][5][6], with the aim to better allocate resources toward the management of the most problematic IAS [7]. Nevertheless, the impacts of biological invasions are highly context-dependent [8][9][10], triggering the predictions of the consequences of successful invasions [11]. This may be particularly true when the invader colonizes habitats that are different than those that are usually occupied both in the native and invaded ranges (i.e., novel habitats).…”