Phenology and cover of plant growth forms predict herbivore habitat selection in a high latitude ecosystem.

Marianne Iversen,Per Fauchald,Nigel G Yoccoz,Knut Langeland,Rolf A Ims,Kari Anne Bråthen,John F Valentine

doi:10.1371/journal.pone.0100780

Marianne Iversen, Per Fauchald + Show 5 more

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https://doi.org/10.1371/journal.pone.0100780

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Abstract

The spatial and temporal distribution of forage quality is among the most central factors affecting herbivore habitat selection. Yet, for high latitude areas, forage quantity has been found to be more important than quality. Studies on large ungulate foraging patterns are faced with methodological challenges in both assessing animal movements at the scale of forage distribution, and in assessing forage quality with relevant metrics. Here we use first-passage time analyses to assess how reindeer movements relate to forage quality and quantity measured as the phenology and cover of growth forms along reindeer tracks. The study was conducted in a high latitude ecosystem dominated by low-palatable growth forms. We found that the scale of reindeer movement was season dependent, with more extensive area use as the summer season advanced. Small-scale movement in the early season was related to selection for younger stages of phenology and for higher abundances of generally phenologically advanced palatable growth forms (grasses and deciduous shrubs). Also there was a clear selection for later phenological stages of the most dominant, yet generally phenologically slow and low-palatable growth form (evergreen shrubs). As the summer season advanced only quantity was important, with selection for higher quantities of one palatable growth form and avoidance of a low palatable growth form. We conclude that both forage quality and quantity are significant predictors to habitat selection by a large herbivore at high latitude. The early season selectivity reflected that among dominating low palatability growth forms there were palatable phenological stages and palatable growth forms available, causing herbivores to be selective in their habitat use. The diminishing selectivity and the increasing scale of movement as the season developed suggest a response by reindeer to homogenized forage availability of low quality.

Highlights

The spatial and temporal distribution of forage quality is regarded as one of the most central factors affecting herbivore habitat use [1,2]
The importance of growth forms as a source of spatial variation in phenology is pronounced in arctic and alpine ecosystems, which are characterized by a broad spectrum of plant growth forms that shift their dominance relations according to environmental factors [16]
We found both forage quality and quantity assessed at the level of growth forms to predict habitat selection of a large ungulate at high latitude during summer

Summary

Introduction

The spatial and temporal distribution of forage quality is regarded as one of the most central factors affecting herbivore habitat use [1,2]. Forage quality is distributed spatially in terms of composition of species of differing palatability [3,4,5], and temporally in terms of plant phenology with plants being more palatable when younger [6,7,8,9]. Variability in plant phenology caused by local environmental factors and speciesspecific physiology and life history, are major contributors to spatial patterns in forage quality [10,11,12,13]. We ask to what extent plant phenology at the functional level of growth forms, is important for predicting large herbivore habitat selection across spatial and temporal scales

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