The effect of habitat alteration by elephants on invertebrate diversity in two small reserves in South Africa.
Loading...
Date
2005
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Balancing increasing elephant numbers with biodiversity conservation in small reserves has
become a concern for many protected area managers. Elephants are considered important
agents of disturbance creating heterogeneity and thus contributing to the maintenance of
biodiversity. However elephants also damage vegetation through their destructive feeding
habits, and this has led to pressure to reduce elephant populations in many reserves.
Quantitative data on the impact of elephants on invertebrates, the main component of
biodiversity at the species level, are lacking.
The aim of this project was to assess the effect that habitat alteration by elephants has
on the diversity of selected ground-dwelling invertebrates (ants, centipedes, millipedes,
spiders, scorpions and termites) through the provision of logs and dung as a potential refuge
niche for these invertebrate communities, and to determine the effect of spatial (vegetation
types) and temporal (season and age of dung) variation on the invertebrates using these
refugia. Variation in impacts was considered important because savanna is not homogenous
and the impact of the refugia is likely to be dynamic in terms of seasonal trends in
invertebrate populations, and in terms of changes in the environmental conditions offered by
the refugia.
Elephant impact on vegetation, quantity of refugia (logs and dung) produced and
invertebrate diversity associated with refugia were determined for 115 transects within
Madikwe Game Reserve in the North Western Province, South Africa. Invertebrate
abundance, species richness and diversity were always higher under refugia than in areas
without refugia. Vegetation utilisation, frequency of refugia production and invertebrate
diversity showed strong temporal variation (seasonal); elephant impact and production of logs
were higher in winter than in summer because elephants are more likely to feed on woody
vegetation in winter when grass nutrient levels are low. Invertebrate diversity under the logs
was higher in summer than in winter, and this probably reflected the higher abundance and
diversity of invertebrates that are usually associated with the warmer, wetter summer months.
The effect of adding refugia to three vegetation types on invertebrate diversity was
tested experimentally at Makalali Private Game Reserve in the Limpopo Province, South
Africa. Logs and elephant dung were set out in five plots each measuring 20m x 20m within
Govender - iii
mixed bushveld, riverine and mopane woodland. Significant differences were observed in
invertebrate abundance, species richness and diversity between the refugia and control plots
that lacked refugia and between the three vegetation types sampled. Similarity between
invertebrate communities utilising the different refugia types and between the three different
vegetation types were tested using the Jaccard similarity coefficient. The three vegetation
types shared fewer than 50% of their species, as did the logs, dung and control sites. However
the results obtained do illustrate a higher degree of similarity between the refugia substrates
(logs and dung) than the control sites and between the more heterogeneous vegetation types
(mixed bushveld and riverine) than the mopane veld. This indicated that invertebrate
communities associated with refugia were not uniform, but were influenced by vegetation
type.
An experimental test of temporal changes in invertebrate community composition
illustrated the importance of elephant dung as a microhabitat for different invertebrate groups
over different ages of dung (three days, two, four, 12 and 32 weeks old). Colonisation of the
dung, by dung beetles was immediate but as the microclimate of the dung changed with time,
the new conditions were ideal for other invertebrate taxa. Over a period of eight months, the
change of invertebrate communities utilising the dung included dung beetles, followed by
millipedes and [mally ant and termite communities.
The results of this study illustrated the importance of refugia (logs and dung) produced
by elephants for ground-dwelling invertebrate species in the savanna environment. The extent
of the influence of the refugia varied both spatially and temporally and this should be
considered in future monitoring or in measuring impacts. While further research on a broader
range of organisms and at larger scales is necessary, elephants do have a positive impact on at
least some components of biodiversity, through the process of facilitation of refugia.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Elephants., Invertebrates., Biodiversity conservation., Habitat (Ecology), Vegetation dynamics., Insects., Dung beetles., Spatial ecology., Savanna ecology., Niche (Ecology), Space and time., Game reserves--South Africa., Invertebrate populations--Research--Methodology., Habitat conservation--Planning., Game reserves--Management., Species diversity., Faeces., Theses--Zoology.