Weather-dependent changes in habitat use by Alpine chamois

BACKGROUND

Alterations in weather patterns due to climate change are accelerated in alpine environments, but mountains also provide a wide range of niches and potential refuge areas. In order to identify future critical habitat for mountain ungulates for effective protection, it is important to understand their spatial responses to changing weather conditions without movement constraints by human disturbance.

METHODS

Using integrated step selection functions, we investigated fine-scale changes in seasonal habitat use in response to weather and time of day for 55 GPS-collared adult Alpine chamois in summer and 42 individuals in winter in a strictly protected area.

RESULTS

Chamois reacted to increasing precipitation and wind speeds primarily by moving to lower elevations in summer and winter. However, reactions to high summer temperatures predominantly involved preferences for increasing tree cover density and northerly slopes. Snow depth had little effect on habitat choice, and southerly slopes were preferred in winter regardless of temperature. At night, chamois moved to steeper slopes and lower elevations than during daytime in both seasons, and to more open areas in summer. Steeper slopes were also preferred with increasing tree cover density.

CONCLUSIONS

Chamois employ adaptive fine-scale adjustments in their habitat choice consistent with respect to efficient thermoregulation and protection from both weather extremes and predation risk in summer and winter. Movement responses to climate change are therefore expected to be far more complex than simple altitudinal changes in distribution. Particularly the role of forest cover must not be underestimated, as it appears to provide important thermal refuge habitat from high summer temperatures.

Multi-event capture-recapture analysis in Alpine chamois reveals contrasting responses to interspecific competition, within and between populations

Understanding components of interspecific competition has long been a major goal in ecological studies. Classical models of competition typically consider equal responses of all individuals to the density of competitors, however responses may differ both among individuals from the same population, and between populations. Based on individual long-term monitoring of two chamois populations in sympatry with red deer, we built a multi-event capture-recapture model to assess how vital rates of the smaller chamois are affected by competition from the larger red deer. In both populations, mortality and breeding probabilities of female chamois depend on age and in most cases, breeding status the preceding year. Successful breeders always performed better the next year, indicating that some females are of high quality. In one population where there was high spatial overlap between the two species, the survival of old female chamois that were successful breeders the preceding year (high-quality) was negatively related to an index of red deer population size suggesting that they tend to skip reproduction instead of jeopardizing their own survival when the number of competitors increases. The breeding probability of young breeders (ages 2 and 3) was similarly affected by red deer population size. In contrast, in the second site with low spatial overlap between the two species, the vital rates of female chamois were not related to red deer population size. We provide evidence for population-specific responses to interspecific competition and more generally, for context-, age- and state-dependent effects of interspecific competition. Our results also suggest that the classical assumption of equal responses of all individuals to interspecific competition should be relaxed, and emphasize the need to move towards more mechanistic approaches to better understand how natural populations respond to changes in their environment.

Joint effects of weather and interspecific competition on foraging behavior and survival of a mountain herbivore

Weather variations have the potential to influence species interactions, although effects on competitive interactions between species are poorly known. Both weather and competition can influence foraging behavior and survival of herbivores during nursing/weaning, a critical period in the herbivore life cycle. We evaluated the joint effects of weather and competition with red deer Cervus elaphus on the foraging behavior of adult female Apennine chamois Rupicapra pyrenaica ornata in summer, and on winter survival of chamois kids. High temperature and low rainfall during the growing season of vegetation had negative effects on bite rate. Effects of weather were greater in forb patches, including cold-adapted, nutritious plants of key importance to chamois, than in graminoid ones. Our results confirm previous indications of a negative effect of competition on bite rate of female chamois and on kid survival. Furthermore, harsh weather conditions and competition with deer had additive, negative roles on foraging behavior and survival of chamois. Growing temperatures are expected to influence distribution, growth, and/or nutritional quality of plants; competition would reduce pasture quality and food availability through resource depletion. Both factors would limit food/energy intake rates during summer, reducing survival of the youngest cohorts in winter. We suggest that interspecific competition can be an important additive factor to the effects of weather changes on behavior and demography.

Plastic adaptations of foraging strategies to variation in forage quality in Alpine chamois (Rupicapra rupicapra)

Foraging efficiency strongly affects individual fitness and is influenced by diverse factors such as food quality and quantity, as well as intra- and inter-specific interactions. We investigated whether Alpine chamois (Rupicapra rupicapra (Linnaeus, 1758)) in a protected area in the Swiss Alps adapted their foraging behaviour to forage availability and quality by modeling the bite and step rates of individuals on vegetation nitrogen content, relative plant cover, sex, daytime, air temperature, and slope. Vegetation characteristics were derived using remote sensing data from airborne imaging spectroscopy data sets and feeding locations determined using a theodolite. Chamois increased their bite rates with decreasing forage nitrogen content, decreasing slope, and increasing temperature. Step rates were higher at high temperatures and decreased with increasing relative plant cover. Males showed higher bite rates and lower step rates than females. Daytime had no influence on either bite or step rates. An increase in bite rate may represent a plastic adaptation of foraging behaviour to compensate for lower nutritional quality of the available vegetation. Our results show variability in foraging behaviour according to both vegetation characteristics and physical environment and emphasize the use of remote sensing data to investigate relationships between habitat and subtle behavioural adaptations in ungulates.

Heterogeneity in Primary Productivity Influences Competitive Interactions between Red Deer and Alpine Chamois

Habitat heterogeneity can promote coexistence between herbivores of different body size limited to different extents by resource quantity and quality. Red deer (Cervus elaphus) are known as superior competitors to smaller species with similar diets. We compared competitive interactions and habitat use between red deer and Alpine chamois (Rupicapra rupicapra) in two adjacent valleys in a strictly protected area in the Central Alps. Red deer density was higher in the valley with higher primary productivity. Only here was horn growth in kid and yearling chamois (as a measure for body condition) negatively correlated with red deer population size, suggesting interspecific competition, and chamois selected meadows with steeper slopes and lower productivity than available on average. Conversely, red deer selected meadows of high productivity, particularly in the poorer area. As these were located mainly at lower elevations, this led to strong altitudinal segregation between the two species here. Local differences in interspecific competition thus coincided with differences in habitat preference and–segregation between areas. This suggests that spatial habitat and resource heterogeneity at the scale of adjacent valleys can provide competition refuges for competitively inferior mountain ungulates which differ from their superior competitor in their metabolic requirements.