We are investigating the interaction of large grazing herbivores with their seasonal forage resource. In our model, grasslands show strong seasonal variation in forage quality and production. In the beginning of the growing season, forage mass is low, but is increasing fast because production is high. At this time, forage quality, which is a negative function of forage mass, is high, too, because of the high quality of young plant material and little differentiation between plant parts. In the course of the growing season forage mass increases continuously while the production slows down. Plant tissue aging causes forage quality to decline and progressive differentiation of plant parts causes an increase in the variation of quality between plant parts. In the dormant season forage production ceases. The variation in quality between plant parts lessens as all plant material turns moribund and forage quality becomes low. The density of resident herbivores in our model is limited by the low dormant season forage availability and therefore is too low to check overall growing season biomass build-up. Herbivores select for plant parts of a minimum quality. The functional response has the shape of an asymptotic Holling’s type II curve. The slope and maximum of the response curve depend on the density of the preferred plant parts. Feeding sites are selected by the herbivores on the basis of a nutrient intake maximising trade-off between quality and quantity of ingested forage. Our findings show seasonal dynamics in the spatial aggregation of herbivores. These dynamics are the result of intra-specific facilitation being the temporally limited benefits of herbivore co-operation in controlling forage resource quality.
|Journal||African Journal of Range and Forage Science|
|Publication status||Published - 2003|