Seasonal and ontogenetic shifts in the diet of Arctic charr Salvelinus alpinus in a subarctic lake

Abstract

Arctic charr (Salvelinus alpinus (L.)) is a cold-adapted salmonid fish with a wide circumpolar distribution. Due to its wide fundamental trophic niche (i.e. diet and habitat use), Arctic charr can be used to study energy flow as well as competitive and predator-prey interactions in subarctic lakes. The objective of this thesis was to evaluate how the trophic niche of Arctic charr in subarctic lakes is influenced by various biotic (e.g. intra-and interspecific resource competition and predation) and abiotic (e.g. seasonality and lake morphometry) factors. Stomach contents and stable isotope analyses indicated marked between-lake and between-individual differences in Arctic charr diet and habitat use. In Saanajärvi, Arctic charr relied mainly on littoral production regardless of season or individual size, probably due to high primary production and lack of sympatric fish species in the littoral zone. In contrast, Arctic charr showed a reduced littoral reliance when the littoral trophic niche was dominated by brown trout, and an increased prevalence of piscivorous foraging when coexisting with planktivorous whitefish and benthivorous grayling. The final results from a total of 17 subarctic lakes indicated that Arctic charr shifted from littoral to a more pelagic trophic niche with increasing lake area and fish species richness. The shift of Arctic charr to a more pelagic piscivorous niche in large lakes was evidently promoted by the existence of small, planktivorous prey fish species and increased interspecific resource competition and/or predation in the littoral zone. The results demonstrate that littoral and pelagic food-web compartments in subarctic lakes can be integrated by generalist Arctic charr, but the energy flow pathways supporting this top consumer can be strongly influenced by prevailing intra-and interspecific interactions as well as by the morphometric characteristics of the lakes. The findings highlight that a comprehensive view of food-web structures is fundamental for predicting the likely responses of fish communities and subarctic lake ecosystems to potential environmental changes. Keywords: Energy flow; individual specialization; lake morphometry; littoral production; resource competition; stable isotope analysis; trophic niche. LIST OF ORIGINAL PUBLICATIONSThe thesis is based on the following original articles, which will be referred to in the text by their Roman numerals I-IV. I did most of the planning for each study and contributed to field work in I, III and IV, and to laboratory analyses in all the studies. I was responsible for the data analysis and wrote the first draft of all the papers. All co-authors made a significant contribution to planning and preparation of the final papers. IV Eloranta A.P., Kahilainen K.K., Amundsen P.-A., Knudsen R., Harrod C. & Jones R.I. 2013. Lake size and fish species richness determine resource use by top consumers in subarctic lakes. Manuscript. INTRODUCTION Food webs in lakesLakes are complex ecosystems, whose functioning is tightly connecte...

Diet of Leptobotia elongata revealed by stomach content analysis and inferred from stable isotope signatures

“…Therefore, we could only compare the data of the stomach content analysis to that of stable isotopic analysis conducted in the present study. We investigated diet shifts with a combination of stomach content and stable isotopic analysis, the results demonstrated that the diet shifts occurred when the body length of L. elongata was increased, which is consistent with findings for other fish species (Bacha and Amara 2009; Eloranta et al 2010;Santiago et al 2010). Metabolic rate directly impacts the food demand of fish (Moyle 2004) with metabolic rate of larger individuals slower than that of smaller individuals (Sims 1996).…”

“…N values of L. elongata were observed in this study, and this phenomenon has also been found in other fish (Eloranta et al 2010;Zhang et al 2013). The δ 13 C values were the highest in spring and the lowest in summer, and the δ 15 N values in autumn were higher than any other season and were lowest in winter, probably related to the diet shift of L. elongata.…”

“…Dietary shifts are a common phenomenon of the early life of many fish species (Eloranta et al 2010) and are usually the result of morphologic constraints, migration, or change in habitat (Grey 2001). Thus far, most studies of L. elongata have concentrated on its taxonomy and reproductive biology.…”

Lake size and fish diversity determine resource use and trophic position of a top predator in high‐latitude lakes

“…The sampling of fish muscle tissue for SIA was performed in the late open-water season to examine the main food sources assimilated during the main growth period (Perga and Gerdeaux 2005; Eloranta et al. 2010; Hayden et al. 2014b).…”

Seasonal Trophic Niche Shift and Cascading Effect of a Generalist Predator Fish

“…Fishes also show flexible feeding habits and sometimes undergo diet shifts that deviate from their presumed food sources [17], e.g., shifts between the benthic and planktonic food webs [18], [19]. Among fish, for instance, ontogenetic changes in resource use is a common feature during their life cycle [5], [20]. Diet shifts of fishes are usually due to migration, size-related morphological constraints, habitat use and other reasons [21], [22], and thus consequently affect species interactions and community structure [5].…”