Abstract
Foraging strategies and range use in wild female Svalbard reindeer (Rangifer tarandus platyrhynchus) were studied in two areas where the historical grazing pressure differed. We mapped vegetation where the reindeer were seen grazing, and related forage availability to characteristics such as home range size, activity budgets and reproductive status. There were significant differences in quantity of forage available between the two areas and the utilization of vegetation types differed between the sites. However, we found no difference in home range size between the two sites, and individual home range sizes were not related to forage quantity, possibly a result of a skewed and small sample size. Even though significant differences in availability of plant species and groups were found, no variation in home range size was found between reproductive and non-reproductive females on Brøggerhalvøya. Neither did we find any differences between areas or between reproductive groups within or between areas in how female reindeer allocated use of time, or in number of steps taken. However, a significant three way interaction indicated that some variance existed between reproductive groups within or between areas, but we do not conclude that this indicate different grazing strategies. Thus, even though variation in the duration of previous grazing has evidently resulted in rather different foraging conditions in our two areas, we detected no differences in present-day foraging behaviour. Thus, our analyses suggest no relationship or feedback between past grazing and current foraging behaviour in these reindeer.
Highlights
Herbivores in the high Arctic live in an environment with large seasonal variations in grazing conditions and where food of high quality is available only for a short period of the year (Sørmo et al, 1999)
A significant three way interaction indicated that some variance existed between reproductive groups within or between areas, but we do not conclude that this indicate different grazing strategies
The present study showed that reindeer females in the less grazed area at Sars had better foraging conditions than females on Brøgger, which had a longer grazing history
Summary
Herbivores in the high Arctic live in an environment with large seasonal variations in grazing conditions and where food of high quality is available only for a short period of the year (Sørmo et al, 1999). The most common hypotheses to explain differences in grazing strategies are the forage abundance hypothesis (FAH) (MacArthur & Pianka, 1966), minimum area hypothesis (MAH) (Harestad & Bunell, 1979) and selective quality hypothesis (SQH) (Jarman & Sinclair, 1979). An opportunistic grazing strategy enables herbivores to maximize net intake of energy or some nutrient per unit time by minimizing the time used to search for food (Sæther & Andersen, 1990). The increased searching effort as a consequence of improved grazing conditions can result in higher movement rates (Vivås & Sæther, 1987; Sæther & Andersen, 1990; Kohlmann & Risenhoover, 1994), which in turn may lead to a larger home range size (Predavec & Krebs, 2000). If the FAH applies to the Svalbard reindeer (Rangifer tarandus platyrhynchus), we would expect to see higher movement rates (e.g. take more steps) in the area with better foraging conditions
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