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

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.

In a Pinch: Mechanisms Behind Potential Biotic Resistance Toward Two Invasive Crayfish by Native African Freshwater Crabs

“…Procambarus clarkii exhibit this pattern of niche breadth reduction when found in sympatry with P. loveni, where they affect leaf litter breakdown due to direct consumption (Jackson et al, 2016;Nishijima et al, 2017), possibly related to differences in chela morphology (Sibbing, 1991). Further, P. clarkii is capable of exerting predatory pressure on planktonic prey items which do not need strong crushing capacity to handle (South et al, 2019). Little work has been completed on the diet and trophic niche of C. quadricarinatus in either its invasive or native range.…”

“…The results presented here indicate that chelae closing force can be predicted by body mass and sex of the individual for all three decapod species but in order to correctly predict biotic resistance these must be validated further by assessing actual resource holding potential. Consequently, when trait based analysis should be complemented with other predictive assessments such as the comparative functional response and relative impact potential metrics (Dick et al, 2017;Dickey et al, 2018;South et al, 2019; but see Vonesh et al, 2017), but also with contest based experiments (Lopez et al, 2019;Zeng et al, 2019). Unfortunately, there is a severe paucity of data on the ecological impact of C. quadricarinatus but also on the basic ecology of Potamonautid crabs in southern Africa.…”

Invasive crayfish outperform Potamonautid crabs at higher temperatures

“…Invasion impacts are highly context dependent with regards to abiotic and biotic characteristics of the recipient environment; thus, FR provides a standardised method to compare resource consumption across contexts (Mofu et al., 2019; Strayer, 2020; Uiterwaal & DeLong, 2020). The parameter FRR [ a/h ] combines variables to elucidate potential intermediate impact (where previously distinguishing differences between FR curves was problematic) and may give a further mechanistic insight into the ultimate driver of impact (Cuthbert et al., 2019; Dickey et al., 2020; South et al., 2019).…”

Pushing the switch: functional responses and prey switching by invasive lionfish may mediate their ecological impact

“…Given that handling time increases concurrently with prey size, while attack rate is typically unimodal at intermediate relative predator-prey sizes (Brose 2010;McCoy et al 2011), lionfish likely consumed fewer G. oceanicus prey given the longer period of time required to subdue and digest such prey items (Black et al 2014;Pusack et al 2016;Davis 2018). Our assimilation of the attack rate and handling time parameters into the FRR (a/h) further demonstrates differential interaction strength between the prey species in a manner not immediately deductible from traditional FR curves alone (Cuthbert et al 2019b;South et al 2019). Whilst the FRR metric cannot distinguish between whether or not the attack rate or handling time drive differences in FRs, it allows for a simplified metric for practitioners to discern invader impact.…”

“…The handling time parameter was then used to determine maximum feeding rates (1/h) of lionfish across prey types. Furthermore, the functional response ratio (FRR; a/h) was calculated for each prey type to amalgamate information from these two FR parameters (Cuthbert et al 2019b;South et al 2019). The FRR metric allows for comparative insights through synthesis of both FR parameters, resolving issues of which should be selected when determining ecological impacts by practitioners.…”