Year: 2011
Type: dissertation
Abstract: MaxEnt modelling uses only the known locations of a species to predict the overall \ndistribution of a species. Large trees are important for the functioning of savanna ecosystems, \nbringing nutrients to the surface, providing shelter to animals and providing a number of \necological functions. Large trees have been identified as declining in density in many \nsouthern African reserves, making the conservation of large trees within reserves an issue in \npark management, such as in Kruger National Park (KNP) and Hluhluwe iMfolzi Parks \n(HiP). Two species of primary concern are Acacia nigrescens and Sclerocarya birrea, which \nhave similar distributions in Southern Africa. Effective management of large trees requires \nunderstanding their distribution within reserves and any potential distribution changes. By \ndetermining the current locations of a species, and using GIS layers of environmental \nvariables to predict the extent of habitats that could support the species, niche models can \npredict species distribution. Maximum Entropy techniques evaluate the probability of finding \nthe species in raster squares, with values for environmental factors controlling distribution. \nFor this study, the locations of A. nigrescens and S. birrea trees higher than 5 m were \nrecorded in KNP and HiP, and were used in conjunction with MaxEnt to produce distribution \nprobability maps for both species in each reserve. In HiP, the distribution map was compared \nwith an independent existing data set to determine if the predicted distributions were \naccurate. The factors effecting their distribution were compared between HiP and KNP to \ndetermine why the species were found together in KNP but not in HiP. MaxEnt could predict \nthe locations of the species within HiP, but predictions were better for A. nigrescens than S. \nbirrea. In both Reserves, rainfall was the best predictor of tree location, along with elevation. \nThe niche overlap was higher in KNP, where both species are well within their total species \nrange, than in HiP where A. nigrescens was at the edge of its distribution. These variables \nthat are limiting distribution at a reserve scale will have an influence on the overall \ndistribution of the species. Niche models can be used to inform the establishment of \nbotanical reserves or other management strategies that can help preserve large trees within \nreserves.
Author: Alain Smith
Language: English
Subfield: Ecological Modeling
Field: Environmental Science
Domain: Physical Sciences
SDG: Life on land
Open Access status: green
Award: G8008708590
OpenAlex ID: W1600584069