Abstract ID
biodiv23
Type
Oral
Theme
biodiv
Full title
Determinants of ungulate biomass in grazing ecosystems: The importance of scale, floodpulses and habitat
connectivity
Abstract text
Maximizing the intake of protein and energy is critical for productive ungulate populations. Strong declines in
forage quality in the dry season means that ungulates need a high quality growing-season resource to put on as
much fat and protein in the wet season as possible to allow for sufficient body stores during the dry-season
protein and energy deficit. In addition, high quality forage is needed by lactating females during this period of
greatly increased nutrient demands. During the dry season ungulates have to find some quality forage to
minimize the rate of decline in their body stores. Significantly larger ungulate populations can be sustained in
regions where they are able to migrate into regions that provide green grazing during the late dry-season, such as
after the recession of floodwaters on floodplains or in areas that receive a large proportion of their total rainfall
during the dry-season. In addition, productive herbivore populations can only be sustained where lactating
females are able to track large-scale stochastic pulses in high quality forage during the growing season
associated with patchiness of fire and rainfall in regions of high soil fertility (the resource heterogeneity effect).
Owing to the ability to track stochastic pulses in quality forage at large scales, ungulates do not always return to
the same sites each year resulting in better resting of the forage resources (the trophic decoupling effect), which
combined with severe (but transient) grazing, trampling and dunging effects of large herds in large-scale
migratory systems, accelerates nutrient cycling and primary productivity, while improving grassland structure
and forage quality (the herd effect). Thus ungulates are able to increase their own carrying capacity at large
scales. In addition to forage quality, ungulates also have to consider predation risk. Migratory herbivores
experience greater decoupling from their predators than sedentary herbivores through the suppressive effects of
migratory movements on predator populations, lower dispersion amongst the regional predator population and
greater ability to select habitat that minimizes predation risk (the trophic decoupling effect). Loss of the ability
to select foraging sites at large scales often results in greater ungulate-predator coupling and a decline in the
ungulate population. This paper discusses the theory of angulate baiomass, raising research questions in the
context of the pulsed and stochastic nature of quality forage in the Okavango region as influenced by the flood
pulses, resource heterogeneity and the stochastic nature of rainfall in the outlying woodland regions.
Submission date
2009-09-30
Keywords
migration, adaptive foraging, resource heterogeneity, green forage
Will be submitting paper?
No