Mf. Wallisdevries, EFFECTS OF RESOURCE DISTRIBUTION PATTERNS ON UNGULATE FORAGING BEHAVIOR - A MODELING APPROACH, Forest ecology and management, 88(1-2), 1996, pp. 167-177
The food resources of forest ungulates typically are patchily distribu
ted. Research on foraging behaviour has often focused on habitat selec
tion but has rarely taken into account the influence of the spatial di
stribution of different food patches in two dimensions. However, espec
ially when travelling costs become significant, the pattern of resourc
e distribution is likely to be a major factor in determining foraging
behaviour and, hence, ungulate distribution. Using a modelling approac
h I examine the effects of group size and the effects of increasing in
ter-patch distance for various resource distribution patterns (random,
uniform and aggregated) on the spatial distribution of foraging time
for an ungulate in an hypothetical environment. The animal is faced wi
th two patch types: food and non-food. Food patches are loaded with a
similar initial forage quantity and productivity. They may be depleted
but regenerate by a constant production rate. Forage quality is assum
ed to decline with increasing standing crop. Young regrowth therefore
has the potential to attract ungulates by virtue of its high quality.
The foraging ungulate, represented by a large-bodied ruminant, is assu
med to follow an energy maximising strategy. It decides at regular int
ervals to stay or to leave for another patch by balancing potential en
ergy intake and travel costs. The results of the simulations reveal th
at travel costs can be an important factor in foraging decisions, even
though they constitute less than 10% of the daily energy intake. The
total number of exploited patches over a 100-day period was mainly det
ermined by forage depletion rate. The number of patches visited daily
was a function of both inter-patch distance and forage depletion rate.
By differences in the variation of inter-patch distance, the distribu
tion mode has important implications for the foraging route and the nu
mber of daily patch visits. With respect to grazing management the imp
ortant implication is that, aside from the relevance of forage quality
and abundance, the spatial distribution of food resources is another
factor determining concentrations of ungulates and, hence, their impac
t on the vegetation. Determination of the appropriate time scale of fo
raging decisions needs further study, as the role of travel costs incr
eases with a shorter time horizon and leads to a higher ungulate aggre
gation.