Predicting the ecological impacts of an alien invader: Experimental approaches reveal the trophic consequences of competition

Abstract

Ecological theory on the trophic impacts of invasive fauna on native competitors is equivocal. Whilst increased interspecific competition can result in coexisting species having constricted and diverged trophic niches, the competing species might instead increase their niche sizes to maintain energy intakes. Empirical experiments can test invasion theory on competitive interactions and niche sizes across different spatial scales and complexity. The consequences of increased interspecific competition from a model alien fish Leuciscus idus were tested on two taxonomically and trophically similar native fishes, Squalius cephalus and Barbus barbus. Competitive interactions were tested in tank aquaria using comparative functional responses (CFRs) and cohabitation trials. The consequences of these competitive interactions for the trophic niche sizes and positions of the fishes were tested in pond mesocosms. Comparative functional responses revealed that compared to B. barbus, L. idus had significantly higher attack and consumption rates; cohabitation trials revealed B. barbus growth rates were depressed in sympatry with L. idus. For L. idus and S. cephalus, differences in their functional response parameters and growth rates were not significant. Pond mesocosms used stable isotope metrics to quantify shifts in the trophic niche sizes of the fishes between allopatry and sympatry using a substitutive experimental design. Isotopic niches were smaller and more divergent in sympatric paired species than predicted by their allopatric treatments, suggesting trophic impacts from interspecific competition. However, an all‐species sympatric treatment revealed similar niche sizes with allopatry. This maintenance of niche sizes in the presence of all species potentially resulted from the buffering of direct competitive effects of the species pairs by indirect effects. Experimental predictions from tank aquaria assisted the interpretation of the constricted and diverged trophic niches detected in the paired‐species sympatric treatments of the pond mesocosms. However, the all‐species sympatric treatment of this experiment revealed greater complexity in the outcomes of the competitive interactions within and between the species. These results have important implications for understanding how alien species integrate into food webs and influence the trophic relationships between native species.

Biological and trophic consequences of genetic introgression between endemic and invasive Barbus fishes

“…Indeed, the highest fish density was in TL i , in large part caused by the high density of the Arno goby P. nigricans (Table S2), an invertivore (Pompei et al 2014 ). However, experimental studies have shown decreased trophic niche sizes in relation to interspecific competition in B. barbus and other cyprinids (Britton et al 2019 ; De Santis et al 2021 ), which contrasts with the findings of this study. Specialization and subsequent reduction in trophic niche breadth have also facilitated the coexistence between other omnivorous fishes when resources are limited (e.g.…”

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)

“…Invasive alien species (IAS) are nowadays recognized as a major component of the global decline in biodiversity. 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].…”

Trophic consequences of competitive interactions in freshwater fish: Density dependent effects and impacts of inter‐specific versus intra‐specific competition

“…trophic niche size and position) of a model species is altered by the increased abundance of a co‐existing species, and how these impacts relate to those from increased intra‐specific competition. The model animals were freshwater fishes, as these are adaptable and tractable animals that provide excellent model systems for experimental competitive studies with, for example, their indeterminate nature of growth enabling correlation with competitive success (Britton et al., 2019; Ward et al., 2006). The model species was chub Squalius cephalus , a fish of the Cyprinidae family that is found throughout much of north‐west Europe.…”