Optimal foraging and community structure: implications for a guild of generalist grassland herbivores

A particular linear programming model is constructed to predict the diets of each of 14 species of generalist herbivores at the National Bison Range, Montana. The herbivores have body masses ranging over seven orders of magnitude and belonging to two major taxa: insects and mammals. The linear programming model has three feeding constraints: digestive capacity, feeding time and energy requirements. A foraging strategy that maximizes daily energy intake agrees very well with the observed diets. Body size appears to be an underlying determinant of the foraging parameters leading to diet selection. Species that possess digestive capacity and feeding time constraints which approach each other in magnitude have the most generalized diets. The degree that the linear programming models change their diet predictions with a given percent change in parameter values (sensitivity) may reflect the observed ability of the species to vary their diets. In particular, the species which show the most diet variability are those whose diets tend to be balanced between monocots and dicots. The community-ecological parameters of herbivore body-size ranges and species number can possibly be related to foraging behavior.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47765/1/442_2004_Article_BF00377109.pd

Different factors that modify anti-predator behaviour in guanacos (Lama guanicoe)

Animals optimize the trade-off between the cost of not fleeing and the benefits of staying because the factors that influence flight decisions and the disturbance level of a particular stimulus can vary both spatially and temporally. Different factors (human impact and habitat characteristics) likely to modify anti-predator behaviour in different types of guanaco social groups were analysed. We found that group size was conditioned by high poaching, vehicle traffic, predation risk and vegetation density. Solitary adult males showed shorter alert and flight initiation distances than bachelor and mixed groups. Alert distance was greater during the summer season, and assessment times were shorter when young were present in the groups. In high-predation-risk environments, guanacos detected threats at greater distances and flight initiation distance was longer. Alert distances were shorter on steeper sloped hills and assessment times were shorter in areas with irregular topography than on flat sites. In high traffic areas, flight initiation distance was longer and assessment times were shorter. And in areas with low poaching intensity, assessment times were greater than in those with high poaching levels. Therefore, guanacos may be able to evaluate a true threat. Social group and anti-predator responses were conditioned by habitat characteristics and human impact. We consider that plasticity of responses could be key to the survival of guanacos.Fil: Taraborelli, Paula Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mendoza. Instituto Argentino de Investigaciones de Zonas Aridas; Argentina. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Ovejero, R.. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Mosca Torres, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mendoza. Instituto Argentino de Investigaciones de Zonas Aridas; ArgentinaFil: Schroeder, Natalia. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mendoza. Instituto Argentino de Investigaciones de Zonas Aridas; ArgentinaFil: Moreno, Pablo Gastón. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias; ArgentinaFil: Gregorio, Pablo Francisco. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Marcotti, Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marozzi, Antonela Alejandra. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Carmanchahi, Pablo Daniel. Universidad Nacional del Comahue. Asentamiento Universidad San Martin de Los Andes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentin

The weather dictates the rhythms: Alpine chamois activity is well adapted to ecological conditions

Activity rhythms play an important role in the ecological relations of a species and form part of its evolutionary adaptation. Such rhythms are strongly synchronised with the annual cyclic changes by environmental stimuli, the so-called zeitgebers. Animals’ reliance on environmental stimuli is highly species-specific and allows behavioural adjustments to be made in preparation for the conditions expected in each season. We investigated daily and annual activity rhythms of Alpine chamois (Rupicapra rupicapra) by analysing high-resolution data of animals monitored with GPS collars. This first detailed field study of chamois activity showed that this species exhibited clear daily and annual activity rhythms entrained to the light-dark cycle. Chamois were more active during spring-summer and less active during winter, likely in response to the variation in the availability of food resources: both sexes appeared to maximise energy intake during the season offering the highest amount of food resources to compensate for poor food supply during winter. Daily activity was influenced by the climatic factors considered. We showed a negative correlation between daily activity and adverse climatic conditions (i.e. precipitation and, during winter, snow depth). As activity was strongly influenced by the interplay between temperature and wind throughout the year and by radiation and wind in winter, we conjectured that it was critically dependent upon animals’ thermal balance. In conclusion, our study highlighted that chamois is well adapted to the Alpine environment and seasonality but also raised questions about its ability to adapt to future climate change. Significance statement: In this study, we investigated the effects of ecological factors on Alpine chamois activity. Thanks to radio collars with accelerometers, we obtained highly detailed information on activity levels of wild animals. We found that chamois were more active during spring-summer (i.e. the seasons with the highest quality and quantity of food) and less active during winter. Our results showed that chamois activity was strongly influenced by such climatic factors as temperature, precipitation and wind speed. In winter time, chamois activity increased during the days with high solar radiation and decreased with high snow depth. Given their wide distribution in the Alps, chamois can be considered as a sentinel species of Alpine habitats. Thus, our results on the current relationship between climate and chamois behaviour may shed light on the animals’ ability to track and adapt to climate change