The effect of inter‐ and intraspecific competition on individual and population niche widths: a four‐decade study on two interacting salmonids

Abstract

Competition is assumed to shape niche widths, affecting species survival and coexistence. Expectedly, high interspecific competition will reduce population niche widths, whereas high intraspecific competition will do the opposite. Here we test in situ how intra-and interspecific competition affects trophic resource use and the individual and population niche widths of two lacustrine fish species, Arctic charr and brown trout, covering a 40 year study period with highly contrasting competitive impacts prior to and following a large-scale fish culling experiment. Initially, an overcrowded Arctic charr population dominated the study system, with brown trout being nearly absent. The culling experiment reduced the littoral Arctic charr density by 80%, whereupon brown trout gradually increased its density in the system. Thus, over the study period, the Arctic charr population went from high to low intraspecific competition, followed by increasing interspecific competition with brown trout. As hypothesized, the relaxed intraspecific competition following the experimental culling reduced individual diet specialization and compressed population niche width of Arctic charr. During the initial increase of the brown trout population, there was a large dietary overlap between the two species. Over the subsequent intensified interspecific competition from the population build-up of brown trout, their trophic niche overlap chiefly declined due to a dietary shift of Arctic charr towards enhanced zooplankton consumption. Contrary to theoretical expectations, the individual and population niche widths of Arctic charr increased with intensified interspecific competition. In contrast, the diet and niche width of brown trout remained stable over time, confirming its competitive superiority. The large-scale culling experiment and associated long-term research revealed pronounced temporal dynamics in trophic niche and resource use of the inferior competitor, substantiating that intra-and interspecific competition have large and contrasting impacts on individual and population niches.

Invader abundance and contraction of niche breadth during replacement of a native gammarid amphipod

“…In recent times, the latter has become much more tractable using stable isotopes (Jackson et al, 2011) and thus there has been an upsurge in interest particularly with regard to the relationships between trophic niche breadth and abundance and range, and predicting success and impacts of invasive species. Prati et al (2021) used more conventional methods to track changes in diet of Arctic char in response to increased abundance of brown trout. There has been less attention as to how spatial niche breadth might be affected by abundance of conspecifics and potential competitors.…”

Environmentally Modulated Repeat Evolution of Polymorphic Arctic Charr Life History Traits

“…The narrow niches occupied by each morph leave little to no opportunities for individual specialists within the PB/PZ and PP population's niche (Amundsen, 1995) resulting in very similar energy acquisition potential among lakes. These results suggest that Arctic charr can specialize within various niches (Prati et al, 2021) even within what we consider comparable morphs. However, the constraints put on by the narrowed niche seem to influence the reproductive tradeoffs in a similar manner within the morph types.…”

“…The limnological descriptions of the studied lakes are relatively comparable, however, it is likely that the LO morphs within the different lakes focus their realized niche differently related to environmental heterogeneity as Arctic charr is known to have specialist individuals who restrict themselves to narrow realized niches (Amundsen, 1995). The lakes studied here contain differing number of species, including brown trout which is a competitor and predator of Arctic charr, therefore imposing varying pressures on Arctic charr niche (Prati et al, 2021). Of interest would be to assess the growth of the morphs in relation to environmental variables, such as lake size (Eloranta et al, 2015), latitude (Chavarie et al, 2010), temperature (Knudsen et al, 2015), and/or competition (Prati et al, 2021), to assess the contribution of the environment to the realized niche of Arctic charr morphs.…”

“…The lakes studied here contain differing number of species, including brown trout which is a competitor and predator of Arctic charr, therefore imposing varying pressures on Arctic charr niche (Prati et al, 2021). Of interest would be to assess the growth of the morphs in relation to environmental variables, such as lake size (Eloranta et al, 2015), latitude (Chavarie et al, 2010), temperature (Knudsen et al, 2015), and/or competition (Prati et al, 2021), to assess the contribution of the environment to the realized niche of Arctic charr morphs. Among the pairwise comparisons examining the LO morph's investment in reproduction few similarities (4 of 10) were found, highlighting the breadth in the LO morphs life history strategy.…”

Niche partitioning and individual specialisation in resources and space use of sympatric fur seals at their range margin

“…In contrast, at their range margin where population sizes are still small, these male fur seals continued to display a broad dietary niche (δ 15 N values) and movement niche (horizontal and vertical behaviour), and this is consistent with an earlier dietary analysis of fur seal scats (Hardy et al 2017). Alternatively to enhanced intraspecies competition, individuals may expand their foraging niche in response to interspecific competition or decreased availability of most valuable food resources (Chiaradia et al 2003;Moleón et al 2009;Prati et al 2021) and both these alternatives typically characterise a species' range margins (MacArthur 1984;Case et al 2005;Guo et al 2005). Therefore, individuals may need to maintain a broad niche when moving between their range core and margins to mitigate different types of competition (intra and interspecies) and variable abundance of favourable prey throughout a species' distribution.…”