The effect of prey identity and substrate type on the functional response of a globally invasive crayfish

Takudzwa C Madzivanzira,Dumisani Khosa,Josie South,Jaimie T A Dick,Olaf L F Weyl,Monica Mccard,Lubabalo Mofu

doi:10.3897/neobiota.52.39245

Abstract

Biological invasions threaten biodiversity on a global scale, therefore, developing predictive methods to understand variation in ecological change conferred is essential. Trophic interaction strength underpins community dynamics, however, these interactions can be profoundly affected by abiotic context, such as substrate type. The red swamp crayfish (Procambarus clarkii) has successfully invaded a number of freshwater ecosystems. We experimentally derive the Functional Response (FR) (density dependent predation) of the red swamp crayfish preying upon both a benthic prey; chironomid larvae, and a pelagic prey; Daphnia magna, on a no substrate control, sand, and gravel substrates to determine whether (1) there is a higher impact on prey that are benthic, and (2) whether the presence of different substrate types can dampen the interaction strength. We apply and demonstrate the utility of the Functional Response Ratio (FRR) metric in unravelling differences in ecological impact not obvious from traditional FR curves. Procambarus clarkii is capable of constantly utilising high numbers of both benthic and pelagic prey items, showing a Type II functional response under all scenarios. The presence of gravel and sand substrate each independently decreased the magnitude FR upon D. magna. Though, with regards to chironomid larvae the FR curves showed no difference in magnitude FR, the FRR reveals that the highest impact is conferred when foraging on sand substrate. This reinforces the need for impact assessments to be contextually relevant.

Highlights

Aquatic biological invasions are increasing at an alarming rate driven by increased connectivity due to new trade routes and ongoing climatic change (Davis and Darling 2017; Carlton and Fowler 2018; Seebens et al 2017; Meyerson et al 2019)
We looked to address this by investigating whether there was a difference in the rate of resource utilisation over time by P. clarkii preying upon a benthic prey and a pelagic prey (Daphnia magna) under three different substrate types
Substrate type significantly interacted with prey species to affect number of prey consumed (Table 1) where there was no difference in number of chironomid larvae consumed between substrate type, but there were more D. magna consumed on no substrate and sand compared to on gravel and more consumed on no substrate compared to sand (p < 0.001)

Summary

Introduction

Aquatic biological invasions are increasing at an alarming rate driven by increased connectivity due to new trade routes and ongoing climatic change (Davis and Darling 2017; Carlton and Fowler 2018; Seebens et al 2017; Meyerson et al 2019) Such invasions can result in substantial loss of biodiversity and homogenisation of communities (Bellard et al 2016; Courchamp et al 2017), which is often quantified and defined as “ecological impact” (Ricciardi et al 2013; Blackburn et al 2014; Dick et al 2017a, b). By determining impact under different environmental contexts, both mechanistically and phenomenologically, it is possible to identify the drivers of ecological impact exerted by a particular species on resources and incorporate preventative or mitigation measures into management policies (Wasserman et al 2016; South et al 2017; Dick et al 2017a, b)

Methods

Results

Conclusion