Resource Partitioning in Food, Space and Time between Arctic Charr (Salvelinus alpinus), Brown Trout (Salmo trutta) and European Whitefish (Coregonus lavaretus) at the Southern Edge of Their Continuous Coexistence

Abstract

Arctic charr and European whitefish are considered to be strong competitors in lakes, with the latter usually being the superior species. However, high niche plasticity and lake morphometry may suggestively facilitate resource partitioning and coexistence between charr and whitefish. Here, we explore the trophic niche utilization (diet and habitat use) of charr and whitefish co-occurring with brown trout in the deep and oligotrophic Lake Fyresvatnet, southern Norway (59°05’N, 8°10’E). Using CPUE, stomach contents and stable isotope analyses, a distinct resource partitioning was revealed between brown trout and the other two species. Brown trout typically occupied the littoral zone, feeding on benthic invertebrates, surface insects and small-sized whitefish. In contrast, charr and whitefish were predominantly zooplanktivorous, but diverged somewhat in habitat utilization as charr shifted seasonally between the profundal and the littoral zone, whereas whitefish were found in the upper water layers (littoral and pelagic habitats). Accordingly, the stable isotope values of carbon (δ13C) reflected a pelagic orientated prey resource use for both charr and whitefish, whereas brown trout had elevated carbon and nitrogen (δ15N) signatures that reflected their benthivore and piscivore diet, respectively. The findings suggest that charr may not rely upon the profundal zone as a feeding habitat but as a refuge area, and may coexist with whitefish if a third competitive and predatory species like brown trout co-occur in the lake. The study indicates that a general high habitat plasticity of Arctic charr may be essential in the presently observed coexistence with a competitively superior fish species like whitefish, and that a third fish species like brown trout may facilitate this particular fish community structure.

Non‐native species and lake warming negatively affect Arctic charSalvelinus alpinusabundance; deep thermal refugia facilitate co‐existence

“…However, the use of air temperature ignores the important effects of lake morphology when modelling climatic effects on species distribution (Hayden et al ., ). Temperature effects become apparent when thermal gradients within waterbodies with sympatric populations are considered (Jensen et al ., ; Langeland et al ., ; Sandlund et al ., ) with deep thermal habitat providing an important refuge from interspecific interactions during hot periods (Jensen et al ., ).…”

“…Typical effects of eutrophication are increased primary productivity with decreased dissolved oxygen (Smith & Schindler, ; Vonlanthen et al ., ). Therefore, it is expected that eutrophication and species introductions currently pose a greater threat to southern S. alpinus populations than predicted increases in temperature, as S. alpinus typically occur in deep lakes that provide a thermal refuge from negative interspecific interactions (Jensen et al ., ; Sandlund et al ., ).…”

“…The introduction of species to waterbodies previously uninhabited by them ( i.e ., non‐native species) can cause significant change in fish community structure and ecosystem functioning (Gozlan & Newton, ; Toussaint et al ., ). Interspecific interactions, temperature and productivity are important factors that affect the geographical distribution and lake habitat use of S. alpinus in both co‐evolved and recently formed ( e.g., introduced species) fish communities (Finstad et al ., ; Jensen et al ., ; Langeland et al ., ). Recent evidence suggests that S. alpinus may be considered under threat from climate change in co‐evolved fish communities, as brown trout Salmo trutta L. 1758 (superior competitors at higher temperatures) may exclude S. alpinus from shallow lakes as productivity and temperatures rise (Finstad et al ., ).…”

“…Salvelinus alpinus and S. trutta overlap in their thermal tolerances and have similar optimal temperatures for growth (Elliott & Elliott, ; Elliott & Hurley, ; Larsson & Berglund, ). Nevertheless, temperature can facilitate resource segregation in co‐evolved S. alpinus and S. trutta populations (Finstad et al ., ; Jensen et al ., , ; Langeland et al ., ). In allopatry, S. alpinus occupy all habitats (Langeland et al ., ).…”

Climate Change and Monitoring of Temperate Lakes

“…They can all feed on zoo-plankton, but with different efficiency, due to different body size, population density and not least, different density of the gillrakers that filter food items from the water. The dense gill rakers of most of the cyprinids filter small zooplankton species that slip through the gill rakers of coregonids, not to mention those of Arctic charr and brown trout (Salmo trutta) [28]. This again affects the zooplankton grazing capacity, as the most important herbivorous species are large and more catchable than the smaller species, and algae blooms become more probable [29,30].…”