Variation in functional trait composition of benthic invertebrates across depths and seasons in a subarctic lake

Smalås

et al. 2021

Oikos

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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.

Section: Methodsmentioning

confidence: 99%

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

Prati

Smalås

et al. 2021

Oikos

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“…Interannual variation in prey availability (i.e., temporal variations in prey communities) has frequently been observed in aquatic systems (e.g., Løvik and Kjellberg 2003;Hämäläinen et al 2003;Frainer et al 2016;Prati et al 2021), likely shaping foraging and diet composition of predators (e.g., Ringler 1985;Baudrot et al 2016). In the present study, even though most interannual variation observed with the singleand two-year time scales could be ascribed to bias from low sample sizes of certain ontogenetic stages, there were a few dietary changes that were consistent also for the five-and ten-year time scale approaches, supporting that these represent valid temporal variation.…”

Section: Discussionmentioning

confidence: 99%

Exploring temporal patterns in fish feeding ecology: Are ontogenetic dietary shifts stable over time?

Sánchez‐Hernández

Prati

Rev Fish Biol Fisheries

et al. 2022

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Disentangling the causes and consequences of ontogenetic niche shifts has been a pivotal challenge in ecology, aiming to enhance the understanding of biological processes that function at the individual, population, and community levels. Studies on ontogenetic dietary shifts have traditionally focused on short time scales, mostly including sampling covering just one or a few consecutive years, thus neglecting possible aspects of temporal variation and ecosystem stability that can only be revealed on long-term scales. We address ontogenetic dietary shifts of two fish predators in an intraguild system (Arctic charr and brown trout) using a long-term dataset spanning 20 consecutive years. Our study revealed distinct ontogenetic niche shifts of the two intraguild predators and demonstrated that these patterns were stable over time, suggesting large stability in prey acquisition and resource partitioning despite changes in their abundances and relative species composition. Some interannual variation was observed, but this was primarily due to sampling bias from low observation numbers for some ontogenetic stages, reflecting a common methodical challenge for ontogenetic niche shift studies. The persistent patterns in the trophic ontogeny of intraguild predators likely facilitate population and community stability by reducing inter- and/or intraspecific competition, thereby having important consequences for ecosystem functioning and resilience. Our study provides a strong rationale for performing ontogenetic niche shift studies over several consecutive years, enabling important insights into temporal variation, enhancement of observation numbers by merging data from multiple years, and the facilitation of a less intrusive sampling scheme for more vulnerable populations.

“…Takvatn (69°07′N, 19°05′E) is a subarctic, oligotrophic, and dimictic lake in northern Norway that has been the focus of intensive ecological and food web studies for more than 30 years (details in Amundsen et al., 2009, 2013, 2019). The lake is situated 214 m above sea level with a surface area of 15 km 2 and a maximum depth of ca 80 m. There is little macrovegetation in the lake, but the littoral zone (3–10 m depth) has dense beds of the grass‐like macroalgae Nitella sp., which contain the highest abundances of G. lacustris (Frainer et al., 2016).…”

Section: Methodsmentioning

confidence: 99%

High parasite diversity in the amphipodGammarus lacustrisin a subarctic lake

Shaw

Knudsen

et al. 2020

Ecology and Evolution

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There is often more than meets the eye when examining food web ecology. Network concepts such as connectance (Lafferty et al., 2006) and robustness (Lafferty & Kuris, 2009) have been well described for several food webs, including webs that consider infectious agents. Here, we look at a key species in the consumer dynamics of the Norwegian subarctic lake Takvatn (hereafter "Takvatn"; "vatn" means "lake" in Norwegian), the amphipod Gammarus lacustris, and reveal that it plays a central role in parasite transmission to the main predators in the lake, including several birds and three abundant fish species.