Abstract
SummaryLarge herbivores gain nutritional benefits from following the sequential flush of newly emergent, high‐quality forage along environmental gradients in the landscape, termed green wave surfing. Which landscape characteristics underlie the environmental gradient causing the green wave and to what extent landscape characteristics alone explain individual variation in nutritional benefits remain unresolved questions. Here, we combine GPS data from 346 red deer (Cervus elaphus) from four partially migratory populations in Norway with the satellite‐derived normalized difference vegetation index (NDVI), an index of plant phenology. We quantify whether migratory deer had access to higher quality forage than resident deer, how landscape characteristics within summer home ranges affected nutritional benefits, and whether differences in landscape characteristics could explain differences in nutritional gain between migratory and resident deer. We found that migratory red deer gained access to higher quality forage than resident deer but that this difference persisted even after controlling for landscape characteristics within the summer home ranges. There was a positive effect of elevation on access to high‐quality forage, but only for migratory deer. We discuss how the landscape an ungulate inhabits may determine its responses to plant phenology and also highlight how individual behavior may influence nutritional gain beyond the effect of landscape.
Highlights
Migration between separate seasonal home ranges is a common phenomenon across animal taxa in many ecosystems all over the globe (Bauer & Hoye, 2014; Bolger, Newmark, Morrison, & Doak, 2008; Fryxell, Greever, & Sinclair, 1988)
There has been limited effort to relate the individual variation in access to newly emergent plants to the landscape characteristics that cause environmental gradients in the onset and development of plant growth, such as latitude, distance to coast, elevation, slope, and aspect
Several of the landscape characteristics were significantly related to the cumulative IRG (CIRG) (Table 3), providing overall support for P2, which suggests that variation in landscape characteristics in summer home ranges causes variation among individuals in their access to high-quality forage (CIRG)
Summary
There are several studies providing empirical support of the forage maturation hypothesis, demonstrating that herbivores utilize spatial variation in the onset of plant growth to enhance the duration of access to newly emergent, high-quality plants (Bischof et al, 2012; Hebblewhite et al, 2008; Merkle et al, 2016; Searle, Rice, Anderson, Bishop, & Hobbs, 2015). We may expect delayed phenology at sites with a more northerly aspect and along flat terrain; such sites allow snow to accumulate, delaying plant growth in the spring It remains largely an open question which landscape variables other than elevation underlie the most beneficial phenological gradient for ungulates, yielding the highest access to high-quality forage. We further tested whether the effects of landscape characteristics affected resident and migratory deer in the same way (i.e., if there were interactions)
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