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

Rainfall extremes explain interannual shifts in timing and synchrony of calving in topi and warthog

We tested the hypothesis that ungulates time and synchronize births to match gestation and lactation with peak food availability and quality in seasonal environments, using ground counts of topi and warthog conducted over 174 months (July 1989-December 2003) in the Mara-Serengeti ecosystem. During this 15-year period, 2,725 newborn and 45,574 adult female topi and 933 newborn and 7,831 adult warthogs were recorded. Births were distinctly synchronized in both species but far less so than in ungulates in temperate regions. Extreme droughts delayed onset and reduced synchrony of calving and natality rates but high rainfall advanced onset and increased synchrony of calving and natality rates in both species, supporting the seasonality hypothesis. Annual shifts in birth peaks were significantly negatively correlated with the preceding wet season rainfall. Varying the timing and synchrony of births and natality rates are widespread but little understood adaptations of ungulates to climatic extremes. Climate change heightens the need for advancing this understanding because increasing frequency and severity of droughts is likely to decouple phenology of breeding in seasonally breeding ungulates from that in their food plants. Similar studies of African ungulates are either extremely rare or non-existent. New approaches to estimating the time of peak births and its confidence limits and the degree of synchrony of breeding are also presented