Time budgets of grassland herbivores: body size similarities

Abstract

The summer (May-September) time budgets of 14 generalist herbivore species living in the same grassland environment are presented in terms of various component activities (e.g., walking, feeding, resting, etc.). All the species exhibit a decrease in activity as average daily air temperature increases. Greater body size and variety of habitats used by a species lead to increased time spent active. Use of a greater variety of habitats may increase activity time because different habitats provide suitable thermal conditions for activity at different times of the day. Body size affects sn herbivore's thermal balance through metabolism, body surface area and thermal inertia. The time spent feeding, exclusive of time spent searching for foods, is less for large than small herbivores. This may arise because large species must spend more time walking in the search for food to satisfy their energy requirements. The observed feeding time differences for species composing a common trophic level in a single environment may help to explain their diet choice because feeding time constrains the variety of foods an herbivore can select. Diet differences, in turn, can explain the potential competition for food if food is in short supply.

Activity rhythms and the influence of some environmental variables on summer ungulate behaviour in Ordesa-Monte Perdido National Park

“…The present study was developed in a multigrazing system where all the herbivores fed only on grass, and the results suggest that grazing time increases as body size decreases (Figure 1), in agreement with BELOVSKY & SLADE (1986) and BUNNELL & GILLINGHAM (/. c).…”

“…A possible relationship between body size and grazing time in ruminants has been pointed out (BUNNELL & GILLINGHAM, 1985;BELOVSKY & SLADE, 1986;MYSTERUD, 1998), although some other factors (physiological constraints, biting rate, food availability, etc) may also be responsible for the variations on feeding time (NORTON, 1981). The present study was developed in a multigrazing system where all the herbivores fed only on grass, and the results suggest that grazing time increases as body size decreases (Figure 1), in agreement with BELOVSKY & SLADE (1986) and BUNNELL & GILLINGHAM (/.…”

“…However, as the number of individuals surveyed at hourly intervals was not simñar, we used the proportion of individuals involved in each activity type and hourly interval to estimate the proportion of observations imdertaken in different activities during daylight hoLirs. This avoids the bias of oversampling certain times of the day (BELOVSKY & SLADE, 1986).…”

Climate warming and predation risk during herbivore ontogeny

“…I also examined the effect of T max on grasshopper and spider average vertical height with linear regressions. I estimated total daily feeding time in minutes for each individual grasshopper by making the assumption that each time I observed a grasshopper feeding, that individual had been feeding during the entire 30-min observational interval (Belovsky and Slade 1986). I multiplied the number of observed feeding bouts by 30 minutes to determine total daily feeding time.…”

Weasels and Martens — Carnivores in Northern Latitudes

“…Smaller herbivores spend proportionally more time active and are more nocturnal than large herbivores (Belovsky and Slade 1986); a relationship that may apply to mammalian carnivores as well. In a review of 146 species in the Carnivora, nocturnal species were significantly smaller than those that were not nocturnal, a pattern that was exhibited in the Mustelidae as well (Zielinski, unpubl.…”