Plant phenology, migration and geographical variation in body weight of a large herbivore: the effect of a variable topography

Abstract

1. A central concept in ruminant foraging ecology is that even slight changes in plant quality affect body growth substantially, because ruminants not only gain more protein and energy but also use less time for rumination when eating high-quality forage. Increased access to highly nutritious forage is thus regarded as an important driving force in the evolution of migration in large herbivores, because the temporal and spatial variation in plant quality is huge. Body weight is in turn a major determinant of reproductive performance and survival in ungulates, and therefore important for population dynamics. 2. In the temperate region, the vertical movement of cervids from a low-elevation winter range to a high-elevation summer range is the most common pattern of migration. Migration to high elevations during summer is regarded as a strategy to increase energy intake among northern temperate ungulates. 3. It has been suggested that there is increased forage quality at high elevation. This leads to the prediction that body weights are positively correlated with the proportion of high-altitude habitat. Alternatively, cervids may benefit due to prolonged access to newly emerged forage as they migrate along an altitudinal gradient. If so, it can be predicted that body weights are highest in regions with the highest diversity of different altitudes. 4. The facing of slopes, i.e. the aspect, is also regarded as an important part of the habitat for deer. Access to north-facing slopes is regarded as favourable because plant quality may be higher on north-facing slopes; access to a variety of different aspects is also favourable because this may lead to a variable snow melt and thus a longer time period with access to high-quality forage. 5. In order to test the above predictions (under points 3 and 4), we analysed the spatial variability of body weight of 8452 female and 12 474 male red deer harvested during 1975-98 from 105 municipalities in Norway. 6. Body weight of red deer was positively related to the diversity of altitudes, and negatively related to the proportion of high-altitude habitat per se. This demonstrated that the altitudinal migration of cervids is not necessarily due to increased forage quality at high elevation, but rather that migrating cervids gain from prolonged access to newly emerging forage along an altitudinal gradient as they migrate to high elevation during early summer. 7. There was also no support for the hypothesis that access to a high proportion of north-facing slopes was favourable; rather, body weight of red deer was correlated with access to a diversity of aspects. There was thus clear evidence that a variable topography, measured as different altitude levels and aspects, was positively related to body weight of red deer.

Lynx Body Size in Norway is Related to its Main Prey (Roe Deer) Density, Climate, and Latitude

“…We used reported municipality roe deer bag size per km 2 forest area (as forested habitat near farmland is the preferred habitat of roe deer) in that municipality as a coarse proxy to which determine spatial and temporal variation in roe deer availability. This approach has been used by several researchers: Mysterud et al (2001) Information on density of semi-domestic reindeer was estimated from the information provided by the Norwegian reindeer management authorities (http://www.reindrift.no/, Anonymous 2003Anonymous , 2009. Almost all municipalities in the four northernmost counties in Norway (Nord-Trøndelag, Nordland, Troms, and Finnmark) have semi-domestic reindeer.…”

“…Variations in food availability during the growth period thus affect variation in growth rate and body mass (Bolton et al 1982). For example, body size of juveniles and/or adults was negatively related to population density in the red deer (Cervus elaphus; Mysterud et al 2001), roe deer (Pettorelli et al 2002), and brown bear Ursus arctos (Zedrosser et al 2006). Yom-Tov et al (2007) have shown that population density affected body size of the Canadian lynx (Lynx canadensis) in Alaska and suggested that this was due to food availability.…”

Warming, plant phenology and the spatial dimension of trophic mismatch for large herbivores

“…Invariably, however, those studies have used a regional landscape-scale approach, comparing patterns among populations of herbivores, and in this regard we believe our approach constitutes an important complement to such studies. Mysterud et al (2001), for instance, reported in a comparison of harvested red deer among 105 municipalities spanning hundreds of kilometres in Norway that body weight correlated positively with landscape heterogeneity, namely altitudinal variation. Mysterud et al (2001) concluded that this relationship reflected interactions between landscape heterogeneity, abiotic conditions and spatial patterns of plant phenology, but did not include actual measures of plant phenology in their study.…”

“…Mysterud et al (2001), for instance, reported in a comparison of harvested red deer among 105 municipalities spanning hundreds of kilometres in Norway that body weight correlated positively with landscape heterogeneity, namely altitudinal variation. Mysterud et al (2001) concluded that this relationship reflected interactions between landscape heterogeneity, abiotic conditions and spatial patterns of plant phenology, but did not include actual measures of plant phenology in their study. By contrast, Herfindal et al (2006), despite having conducted a similar comparison of variation in moose body weights among seven regions spanning the same spatial scale in Norway, documented a negative relationship between altitude and body weights.…”

“…Such observations suggest that any spatial constriction of the plant growing season might constrain the ability of migratory herbivores to prolong intake of high-quality forage during peak resource demand. Furthermore, such a constraint might negatively affect physical condition (Mysterud et al 2001) and offspring production and survival .…”