A taste of space: Remote animal observations and discrete‐choice models provide new insights into foraging and density dynamics for a large subarctic herbivore

• Published in: The Journal of animal ecology Vol. 93; no. 7; pp. 891 - 905
• Main Authors: Ehlers, L., Palm, E., Herriges, J., Bentzen, T., Suitor, M., Joly, K., Millspaugh, J., Donnelly, P., Gross, J., Wells, J., Larue, B., Hebblewhite, M.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.07.2024
• Subjects: Animal behavior; Animal models; Biotic factors; Caribou; climate; competition; Density; density‐dependence; Eating; Food; Food availability; Food selection; Forage; Foraging behavior; functional response; Herbivores; insect harassment; Insects; Lichens; Probability; Rangifer tarandus granti; Reproductive behavior; Shrubs; summer diet; Wind effects; density‐dependence; summer diet; functional response; insect harassment; competition; climate; Caribou
• ISSN: 0021-8790; 1365-2656; 1365-2656
• DOI: 10.1111/1365-2656.14109

Competition for resources and space can drive forage selection of large herbivores from the bite through the landscape scale. Animal behaviour and foraging patterns are also influenced by abiotic and biotic factors. Fine‐scale mechanisms of density‐dependent foraging at the bite scale are likely consistent with density‐dependent behavioural patterns observed at broader scales, but few studies have directly tested this assertion. Here, we tested if space use intensity, a proxy of spatiotemporal density, affects foraging mechanisms at fine spatial scales similarly to density‐dependent effects observed at broader scales in caribou. We specifically assessed how behavioural choices are affected by space use intensity and environmental processes using behavioural state and forage selection data from caribou (Rangifer tarandus granti) observed from GPS video‐camera collars using a multivariate discrete‐choice modelling framework. We found that the probability of eating shrubs increased with increasing caribou space use intensity and cover of Salix spp. shrubs, whereas the probability of eating lichen decreased. Insects also affected fine‐scale foraging behaviour by reducing the overall probability of eating. Strong eastward winds mitigated negative effects of insects and resulted in higher probabilities of eating lichen. At last, caribou exhibited foraging functional responses wherein their probability of selecting each food type increased as the availability (% cover) of that food increased. Space use intensity signals of fine‐scale foraging were consistent with density‐dependent responses observed at larger scales and with recent evidence suggesting declining reproductive rates in the same caribou population. Our results highlight potential risks of overgrazing on sensitive forage species such as lichen. Remote investigation of the functional responses of foraging behaviours provides exciting future applications where spatial models can identify high‐quality habitats for conservation. We used an animal observation and modelling framework to test fine‐scale density‐dependent foraging in subarctic caribou.Caribou were more likely to eat shrubs as shrub cover and space use intensity of caribou increased in summer, but less likely to eat lichen. Insects reduced the overall probability of eating. Caribou also exhibited functional responses in foraging where they selected more of each food type as its availability increased. Remote investigations provide exciting applications to identify high‐quality habitats for conservation.