Differences in trophic niches and life-history traits between brook trout and brown trout in alpine lake food webs

Abstract

Trophic ecology of lacustrine salmonid populations is well-documented in North America and northern Europe, highlighting their role in aquatic ecosystems. However, there is a notable gap in comparative studies on the trophic niches and life-history traits of salmonids in Iberian alpine lakes, which are increasingly impacted by introduced fishes. We compared the trophic ecology and life-history traits of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) in two alpine lakes of central Spain, providing insights into their ecological roles and potential responses to environmental pressures. Compared to brown trout, brook trout displayed a broader dietary niche (based on isotopes and stomach contents), higher reliance on terrestrial food resources, higher delta 13C values and higher trophic position. Thus, the higher trophic position of top predator salmonids suggests a slightly longer food chain in the lake with brook trout. Brook trout showed a higher trophic plasticity indicated by an ontogenetic dietary shift from zooplanktivory to more generalist foraging on terrestrial prey. Brook trout displayed life-history traits such as early maturation, which likely facilitate successful establishment in alpine lakes. Our study suggests that the trophic plasticity and adaptive life-history traits likely support the successful establishment of non-native salmonids in alpine lake food webs.