Predicting the competitive interactions and trophic niche consequences of a globally invasive fish with threatened native species.

Josie South,Victoria Dominguez Almela,J. Robert Britton

doi:10.1111/1365-2656.13571

Josie South, Victoria Dominguez Almela

Open Access

https://doi.org/10.1111/1365-2656.13571

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Abstract

Novel trophic interactions between invasive and native species potentially increase levels of interspecific competition in the receiving environment. However, theory on the trophic impacts of invasive fauna on native competitors is ambiguous, as while increased interspecific competition can result in the species having constricted and diverged trophic niches, the species might instead increase their niche sizes, especially in omnivorous species. The competitive interactions between an omnivorous invasive fish, common carp Cyprinus carpio, and a tropically analogous native and threatened fish, crucian carp Carassius carassius, were tested using comparative functional responses (CFRs). A natural pond experiment then presented the species in allopatry and sympatry, determining the changes in their trophic (isotopic) niche sizes and positions over 4 years. These predictive approaches were complemented by assessing their trophic relationships in wild populations. Comparative functional responses revealed that compared to crucian carp, carp had a significantly higher maximum consumption rate. Coupled with a previous cohabitation growth study, these results predicted that competition between the species is asymmetric, with carp the superior competitor. The pond experiment used stable isotope metrics to quantify shifts in the trophic (isotopic) niche sizes of the fishes. In allopatry, the isotopic niches of the two species were similar sized and diverged. Conversely, in sympatry, carp isotopic niches were always considerably larger than those of crucian carp and were strongly partitioned. Sympatric crucian carp had larger isotopic niches than allopatric conspecifics, a likely response to asymmetric competition from carp. However, carp isotopic niches were also larger in sympatry than allopatry. In the wild populations, the carp isotopic niches were always larger than crucian carp niches, and were highly divergent. The superior competitive abilities of carp predicted in aquaria experiments were considered to be a process involved in sympatric crucian carp having larger isotopic niches than in allopatry. However, as sympatric carp also had larger niches than in allopatry, this suggests other ecological processes were also likely to be involved, such as those relating to fish prey resources. These results highlight the inherent complexity in determining how omnivorous invasive species integrate into food webs and alter their structure.

Highlights

Ongoing globalization is driving increases in biological invasions (McNeely, 2001)
Considerable progress has been made in predicting the trophic impacts of aquatic invasive species in recent years using comparative functional responses (CFRs), where relatively simple aquarium experiments using alien species and their native analogues have successfully predicted high impacting invaders (e.g. Paterson et al, 2015, Laverty et al, 2017)
Predicting outcomes of trophic interactions between native and invasive species is a prerequisite for invasive species risk assessment and subsequent management

Summary

Introduction

Ongoing globalization is driving increases in biological invasions (McNeely, 2001). Besides driving biological homogenization, invasive species can have substantial consequences upon the receiving communities, including the transmission of novel pathogens, habitat degradation and hybridization with native species (Hitt et al, 2003; Matsuzaki et al, 2009; García-Vásquez et al, 2017). Predicting the ecological impacts of alien species is an important aspect of invasion risk assessment, it remains highly challenging (Dick et al, 2017b). Considerable progress has been made in predicting the trophic impacts of aquatic invasive species in recent years using comparative functional responses (CFRs), where relatively simple aquarium experiments using alien species and their native analogues have successfully predicted high impacting invaders Scaling-up experimental approaches for predicting the trophic impacts of alien freshwater fishes to mesocosms and pond enclosures have provided considerable insights into their trophic interactions with native species (Britton, 2018), with suggestions that rather than share and potentially compete for similar prey resources, functionally analogous native and alien fishes often demonstrate strong patterns of trophic niche partitioning (Britton et al, 2018, Raby et al, 2020)

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