Spatiotemporal distribution and co-occurrence of Arctic herbivores in spring

Abstract

Biotic interactions play an important role in the structure and dynamics of food-webs and may drive the spatial distribution of species. In the Arctic, spring snow-cover limits the availability of resources at a critical time for resident and migratory herbivores, which could lead to resource competition. This study takes a first step towards understanding the potential for competition between the major Svalbard herbivores; Svalbard reindeer (Rangifer tarandus platyrhynchus), Svalbard rock ptarmigan (Lagopus muta hyperborea), pink-footed goose (Anser brachyrhynchus) and barnacle goose (Branta leucopsis) during spring when resources are limited. The behaviour of co-occurring herbivores was observed with the aim of describing behaviours that could indicate interference competition. Further, camera-trap data was used to quantify the effects of snow-cover extent, vegetation type and presence of potential competitors on the spatiotemporal distributions of reindeer and geese. Reindeer and geese in Svalbard were found to generally forage in the same areas, especially in moss tundra. Observations suggested that reindeer was the behaviourally dominant competitor, but even though geese were regularly disturbed by close encounters with reindeer, no direct interference interactions were observed. Quantitative analyses confirmed that their spatiotemporal distributions were mainly driven by snow-cover extent and vegetation type. While it was clear that reindeer did not avoid geese, the avoidance of reindeer by geese could not be rejected. Chasing of ptarmigans was observed from both reindeer and geese, however the potential for competition between these species is not further assessed in this study due to a low number of ptarmigan observations. Extensive snow-cover seemed to slightly increase the co-occurrence of reindeer and geese, and the effect is expected to be stronger in years of late snowmelt. The shared space use by these species could potentially lead to exploitative competition, however this should be further studied by assessing dietary overlap, especially in relation to timing of snowmelt which is predicted to change with climate warming. This study adds to the current knowledge of spatial ecology of reindeer and geese in Svalbard and gives insight to the potential for competition between these Arctic herbivores during spring.