EFFECTS OF RESOURCE DISTRIBUTION PATTERNS ON UNGULATE FORAGING BEHAVIOR - A MODELING APPROACH

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.