Black Rhinoceros are browsers, feeding mainly on shrubs and trees. In Andries Vosloo Koedoe Reservaat (Provincie Oos Kaap, Grahamstad, South Africa), Rhinoceros have been introduced 15 years ago and have now attained a density of about 1 per square kilometre. Rhinoceros has specialised on large kandelaber Euphorbia trees, rhinos push the trees over and could therefore influence the population structure of these trees. Apparently smaller trees are not preferred, and larger trees are not easily pushed over, so that especially the intermediate size classes suffer most from rhino damage. The bark of the fallen Euphorbia trees is used by porcupines. Maintaining both the Rhinos and the Euphorbia trees is a conservation priority for the park.
The aim of this research project is to analyse the impact of rhinos on the Euphorbia trees, by quantifying damage on the different size classes and estimating the renewal and growth rate of the species. Data will be used to model future developments of the Euphorbia population and to estimate minimum viable population levels. Experiments will be carried out to simulate different levels of grazing pressure and measure the reaction of the Euphorbia.
Vegetation can regrow after grazing by herbivores. The quality of regrowth is generally high. Herbivores could return to these grazed patches after a certain time interval in such a way that they optimise (maximise?) their intake rate and ingested food quality on these regrown patches. The timing of the return visits of the herbivores is the most important variable that needs to be adapted to the specific responses of the vegetation. By optimising their return intervals, herbivores could benefit from a relatively large food intake of high quality. This "food manipulation" has been suggested for several herbivore species, but is still largely disputed.
In Andries Vosloo Koedoe Reservaat (Provincie Oos Kaap, Grahamstad, South Africa), Black Rhinoceros feed on dwarf Euphorbia trees (noors), succulent plants with one main stem. When this main stem is grazed, these Euphorbia trees resprout and form 4 stems. The rhinos can benefit from this regrowth pattern when they return and graze on these 4 regrowth stems. By returning after a certain interval and by grazing on certain stems, rhinos could increase the amount of food on offer.
The aim of this research project is to check whether rhinos manipulate their Euphorbia food resources in such a way that they increased long term food intake. Field methods will consist of registration of rhino feeding behaviour (food intake, Euphorbia stem preference, return time), and measuring the abundance and regrowth patterns of the Euphorbia shrubs (biomass, quality, regrowth velocity, plant physiognomy). Experiments will be carried out to simulate different grazing levels and measure the reaction of the Euphorbia.