Trophic niche overlap and abundance reveal potential impact of interspecific interactions on a reintroduced fish

Abstract

Conceptually trophic niche overlap and species abundance can describe the strength and number of interspecific trophic interactions to determine the competitive impact on reintroduced species or other ecosystem changes. We use an example with young-of-year (YOY) Atlantic salmon (<i>Salmo salar</i>) reintroductions to determine if trophic niche overlaps and abundances limit restoration success. Using seasonal stable isotopes and abundance estimates for invertivorous fishes in three Lake Ontario tributaries, we assessed community isotopic structure, trophic niche overlap, and the impact of the niche overlap by incorporating relative abundance. Brown trout (<i>Salmo trutta</i>) YOY could be a strong competitor with a high trophic niche overlap with Atlantic salmon YOY but at lower abundances relative to Atlantic salmon minimizes impact. Stream resident fish communities appeared to partition resources across seasons such that abundant species had low trophic niche overlap to minimize overall competition with Atlantic salmon YOY given available resources, indicating niche complementarity. Through joint consideration of trophic overlap and abundance using our conceptual model, the competitive impact of community composition on a reintroduced species could be assessed.

Predatory ability and abundance forecast the ecological impacts of two aquatic invasive species

“…4). These disparities in abundance are similar elsewhere regionally where the species are sympatric (Larocque et al 2020).…”

“…Abundance discrepancies may dampen the potential for interspecific competition and produce limited, but strong interactions between the two species, as evidenced by their overlapping isotopic niches (Larocque et al 2020). Furthermore, resource partitioning between Atlantic salmon and resident fish appears to reduce trophic interactions (Larocque et al 2020), which may further species' co-existence. These results support the need to disentangle density-mediated effects from per capita effects to better understand the processes driving impacts of individual invasive species.…”

Seasonality can affect ecological interactions between fishes of different thermal guilds

“…A high C:N ratio (Supplementary Figure 1) and large size of adult lake trout in Lake 1 compared to lakes without pelagic prey fish (Pazzia et al, 2002), indicates that cisco could buffer the impacts of smallmouth bass invasion on lake trout, as previously suggested (Vander Zanden et al, 2004;Sharma et al, 2009). Studies on the impact of smallmouth bass could include comparing lake trout diet and other factors like abundance (Larocque et al, 2021), bioenergetics, and growth rates in lakes with and without smallmouth bass, throughout an invasion, or through a historical reconstruction (e.g., Morbey et al, 2007).…”

Pulsed supplies of small fish facilitate short-term intraguild predation in salmon stocked streams

“…Diet niche partitioning is sometimes regarded as the outcome of interspeci c competition (e.g., one species mainly preys upon drifting terrestrial invertebrates, while another preys upon benthic invertebrates; Nakano et al 1999;Mookerji et al 2004). Although high diet-niche overlap is often indicative of intense interspeci c competition (Larocque et al 2021), it may also occur in systems where one type of food item is highly abundant, and sh prey upon them exclusively. In such systems, density-dependent competition may be lacking.…”