Comments(0) Lauren Payne observed the waterbuck at Fossil Rim during the summer of 2008, when the vasectomized male, Lucifer, was replaced for two months by the young intact male, Douglas. This is a directed studies inquiry project for credit at Texas A&M University. In addition to the observations posted to this blog, Lauren produced:
Comments(9) Hofmann (1988 ) classified grazing ruminants into three basic categories along a continuum. These three categories are 1) the grass-roughage eater, 2) the intermediate feeder, and 3) the concentrate selector. Concentrate selectors are best illustrated by the white-tailed deer, the intermediate feeder by the goat, axis, and fallow deer, and the grass roughage eater by the cow.
The differences in the three categories of ruminants relates chiefly to the [change in] the rumen over evolutionary history. Grass-roughage eaters have the largest rumen relative to body size and have the most highly developed rumen relative to the other types. Because of the more highly developed rumen, grass-roughage eaters may subsist on lower quality diets that are less digestible. Digestibility rates are governed primarily by forage species and stage of maturity of the forage when consumed. Grasses, especially the C4, or warm-season, grasses are typically lower in nutritive value than are the diets selected by the concentrate selector. Concentrate selectors have a smaller rumen relative to body size and the least developed rumen relative to the other types. Concentrate selectors must choose diets that are highly digestible and have short residence times in the rumen. Typical diets include annual forbs and leaves, buds, and twigs or woody plants; these forage items are commonly referred to as browse. Intermediate feeders, as the name suggests, may subsist on either type of forage base.
Waterbuck are described in the literature as grass-roughage eaters. Thus, their forage base of choice will be the introduced (bermudagrass) and native grass species found at Fossil Rim. While the current population of waterbuck at Fossil Rim is low, [one hypothesis is that] exponential growth of the other species at Fossil Rim, in particular fallow deer, is creating increased competition for a decreasing amount of forage resources. [According to this hypothesis, t]he reason resources are decreasing is that woody species encroachment into the grassy meadows at Fossil Rim is reducing the forage base required by the waterbuck at the same time the number of competitors is increasing dramatically.
[If w]aterbuck calf mortality has increased recently [in the newborn age class, o]ne hypothesis for this [possible] increase might be that female waterbuck are not able to maintain adequate body condition during critical lactation periods, thus reducing the ability of the calf to adequately develop and successfully be recruited into the herd. Reduced forage availability could therefore affect either the female during gestation and post-parturition and subsequently impact the calf. An alternative to this hypothesis might be that the calf, post weaning, is unable to obtain adequate nutrition due to the intense competition for the decreasing levels of resources.
From a purely management standpoint, two recommendations would be made. The first would be to immediately implement a woody species management program. While certain levels of ash juniper will be required to maintain golden cheek warbler habitat, open areas must be maintained for the grass-roughage eaters such as the waterbuck. The other recommendation would be to reduce the number of animals at Fossil Rim. The current high population is not sustainable.
Larry
[For more scientific sources on this general topic of herbivore plant interactions, see Bibliography ]
[editorial changes in brackets by Jane 6/19/08]
Comments(1) We are thinking of three hypotheses:
1. the relation between neonatal calf survival and cold stress in the winter
2. the relation among weaning, survival and cold stress
3. the relation between mothers body condition and calf survival