title: The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better?
abstract: In patchy habitats, the relationship between animal abundance and cover of a preferred habitat may change with the availability of that habitat, resulting in a functional response in habitat use. Here, we investigate the relationship of two specialized herbivores, willow ptarmigan (Lagopus lagopus) and mountain hare (Lepus timidus), to willows (Salix spp.) in three regions of the shrub tundra zone-northern Norway, northern European Russia and western Siberia. Shrub tundra is a naturally patchy habitat where willow thickets represent a major structural element and are important for herbivores both as food and shelter. Habitat use was quantified using feces counts in a hierarchical spatial design and related to several measures of willow thicket configuration. We document a functional response in the use of willow thickets by ptarmigan, but not by hares. For hares, whose range extends into forested regions, occurrence increased overall with willow cover. The occurrence of willow ptarmigan showed a strong positive relationship to willow cover and a negative relationship to thicket fragmentation in the region with lowest willow cover at landscape scale, where willow growth may be limited by reindeer browsing. In regions with higher cover, in contrast, such relationships were not observed. Differences in predator communities among the regions may contribute to the observed pattern, enhancing the need for cover where willow thickets are scarce. Such region-specific relationships reflecting regional characteristics of the ecosystem highlight the importance of large-scale investigations to understand the relationships of habitat availability and use, which is a critical issue considering that habitat availability changes quickly with climate change and human impact.
authors.affiliation: Department of Arctic and Marine Biology, University of Tromsø, Tromso, Norway. dorothee.ehrich@uit.no
authors.forename: Dorothée
authors.initials: D
authors.lastname: Ehrich
authors.forename: John-André
authors.initials: JA
authors.lastname: Henden
authors.forename: Rolf Anker
authors.initials: RA
authors.lastname: Ims
authors.forename: Lilyia O
authors.initials: LO
authors.lastname: Doronina
authors.forename: Siw Turid
authors.initials: ST
authors.lastname: Killengren
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lecomte
authors.forename: Ivan G
authors.initials: IG
authors.lastname: Pokrovsky
authors.forename: Gunnhild
authors.initials: G
authors.lastname: Skogstad
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Sokolov
authors.forename: Vasily A
authors.initials: VA
authors.lastname: Sokolov
authors.forename: Nigel Gilles
authors.initials: NG
authors.lastname: Yoccoz
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D017753:Ecosystem; D046094:Galliformes; D034621:Hares; D060434:Herbivory; D009664:Norway; D011157:Population Dynamics; D012426:Russia; D032108:Salix; D012800:Siberia; D013045:Species Specificity