Towards a mechanistic understanding of individual‐level functional responses: Invasive crayfish as model organisms

Stefan M Linzmaier,Jonathan M Jeschke

doi:10.1111/fwb.13456

Abstract

Abstract In novel communities, a rising number of new and emerging invasive species interact with resident species, some of which are non‐native themselves. We implemented an innovative trophic interaction framework for novel communities and quantified the interaction strength and impact potential of a truly novel species (marbled crayfish Procambarus virginalis) with a resident non‐native counterpart (spiny‐cheek crayfish Faxonius limosus). As prey, we used Dreissena mussels, which are non‐native as well and now hold a key position in many European and North American aquatic ecosystems. For both crayfish species, we predicted functional responses based on a mechanistic model that we parameterised with a set of experimental observations of foraging behaviour and satiation. We compared these predicted functional responses to empirically observed responses. In addition, we incorporated behavioural traits such as aggression, activity, and boldness in the comparisons between the species and individuals to determine their influence on functional responses. We tested individuals from aquarium stocks as well as naturalised individuals from invaded water bodies. Altogether, we performed 1,095 experiments with 26 individual crayfish. We found that per capita predation of spiny‐cheek crayfish exceeded that of marbled crayfish from aquaria and naturalised individuals. Functional responses differed between species and were mostly higher for spiny‐cheek crayfish males. Marbled crayfish, however, were more voracious and reached satiation more slowly. Consumption rates correlated with aggression for marbled crayfish and with an aggressive threat response for spiny‐cheek crayfish. We conclude that spiny‐cheek crayfish can reach higher short‐term consumption rates than marbled crayfish, but both species probably do not substantially affect Dreissena mussel populations in the field. For marbled crayfish, high long‐term consumption, interspecific aggression, and reproduction rates can promote their establishment and spread. Risk assessments of these invaders should be improved by considering numerical responses, and different prey organisms and predators.

Highlights

As the number of species invasions increases, the understanding of novel communities becomes increasingly pressing (Pacifici et al, 2015; Seebens et al, 2017)
We predicted functional responses based on a mechanistic model that we parameterised with a set of experimental observations of foraging behaviour and satiation
Marbled crayfish with higher aggression scores had higher h and higher functional responses at high prey densities compared to individuals with low aggression scores (Figure 2c), whereas a did not significantly differ

Summary

Introduction

As the number of species invasions increases, the understanding of novel communities becomes increasingly pressing (Pacifici et al, 2015; Seebens et al, 2017). These novel communities are often shaped by over-invasions, which take place when an invasive species is replaced by a functionally similar invader (Russell, Sataruddin, & Heard, 2014). When invasives and other novel organisms become part of native communities, they participate in predator–prey and other ecological interactions (Thuiller et al, 2010) Predicting these interactions would enable us to focus management efforts on the most impactful species (Jeschke, Keesing, & Ostfeld, 2013). Higher and more efficient resource utilisation is a common characteristic of successful invaders when compared to functionally similar species—it may be useful for predicting their impact (Dick et al, 2014, 2017)

Methods

Findings

Discussion

Conclusion