Foraging flexibility in changing environments – Stable isotope perspectives on generalist diets
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
OP-Pohjola Auditorium (L6)
Topic of the dissertation
Foraging flexibility in changing environments – Stable isotope perspectives on generalist diets
Doctoral candidate
Master of Science in Biology (Ecology) Tamara Ann Hiltunen
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Ecology and Genetics Research Unit
Subject of study
Biology
Opponent
Professor Anna Skarin, Swedish University of Agricultural Sciences
Custos
Professor Jouni O. Aspi, University of Oulu
Foraging flexibility in changing environments – Stable isotope perspectives on generalist diets
Global environmental change is altering the structure and dynamics of northern ecosystems, with significant consequences for herbivores, carnivores and their trophic interactions. These changes affect the conditions under which animals acquire food, making foraging flexibility a crucial factor for survival. This thesis applies stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) to investigate how generalist species from different trophic levels respond to environmental variability across seasonal, decadal and centennial timescales. Three studies were conducted: (1) Svalbard reindeer (Rangifer tarandus platyrhynchus) winter diets (1995–2012), (2) Finnish wolverine (Gulo gulo) diets from historical (1905–1999) and modern (2000–2020) specimens, and (3) seasonal shifts in diet and habitat selection of semi-domesticated reindeer (R. t. tarandus) in northern Finland during 2019.
In Svalbard, the winter diets of reindeer over a 17-year period shifted towards graminoids and away from mosses, reflecting the combined influence of climate variability and population density. Finnish wolverines have maintained a broad yet flexible carnivorous diet over the past century, with only subtle shifts in prey composition, indicating resilience through opportunistic foraging and the consumption of carrion. In northern Finland, semi-domesticated reindeer exhibited marked seasonal shifts: early summer diets, dominated by lichens and shrubs, transitioned to late-summer consumption of grasses, sedges, and fungi, accompanied by corresponding changes in habitat selection as revealed by GPS tracking.
Collectively, these studies demonstrate that dietary plasticity enables generalist species to buffer themselves against environmental variability. However, reliance on a limited subset of resources may increase their vulnerability under accelerating environmental change. By integrating stable isotope data with movement records and historical collections, this thesis demonstrates the potential of these tools to reveal long-term dietary trends and the ecological strategies animals employ to cope with changing environments. The findings emphasise the need to preserve diverse prey and forage communities in order to support the resilience of northern ecosystems in the face of accelerating climate and land-use change.
In Svalbard, the winter diets of reindeer over a 17-year period shifted towards graminoids and away from mosses, reflecting the combined influence of climate variability and population density. Finnish wolverines have maintained a broad yet flexible carnivorous diet over the past century, with only subtle shifts in prey composition, indicating resilience through opportunistic foraging and the consumption of carrion. In northern Finland, semi-domesticated reindeer exhibited marked seasonal shifts: early summer diets, dominated by lichens and shrubs, transitioned to late-summer consumption of grasses, sedges, and fungi, accompanied by corresponding changes in habitat selection as revealed by GPS tracking.
Collectively, these studies demonstrate that dietary plasticity enables generalist species to buffer themselves against environmental variability. However, reliance on a limited subset of resources may increase their vulnerability under accelerating environmental change. By integrating stable isotope data with movement records and historical collections, this thesis demonstrates the potential of these tools to reveal long-term dietary trends and the ecological strategies animals employ to cope with changing environments. The findings emphasise the need to preserve diverse prey and forage communities in order to support the resilience of northern ecosystems in the face of accelerating climate and land-use change.
Created 6.1.2026 | Updated 7.1.2026