A dissertation submitted to the Faculty of Science, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. 30 October 2014. / My study investigated the significance of spatiotemporal heterogeneity on the Nile crocodile
(Crocodylus niloticus), a long-lived, apex predator, occupying many African and some South
African riverine ecosystems. The scales of study included a long-term investigation of the
(indirect) impacts of anthropogenic, landscape scale (100 km2) disturbances on the population
demographics of C. niloticus, over 35 years. At the intermediate scale (15 km2), indirect and
direct impacts of flooding and seasonality on the health of the C. niloticus population were
investigated over a three-year period. This was performed by investigating preferred habitat
availability and river quality assessments, including physiochemical variables and rapid bioassessment
measures, which served as the ‘smallest’ scale (with samples taken every 500 m).
All scales were compared with long-term and short-term investigations into crocodile
population demographics. Total crocodile population size within the study river increased
over time (from 18 in 1981 to 35 in 2013), but the number of adults decreased (from 9 to 3).
Human population size increased at a rate of 3300 individuals per year and anthropogenically
altered habitat increased over time from 24% total coverage attributable to farmland on the
banks of the Mutale River in 1977, to 66% land coverage in 2013. Increases in humaninduced
habitat alterations also created shifts in preferred crocodilian habitat availability.
Investigations into the effects of natural disturbances revealed that physiochemistry was
seasonally variable, and changed drastically with changes in climate and runoff. The
macroinvertebrate communities in the Mutale River differed in time and space for a multitude
of reasons, including climate change and changes in habitat. The results of my study showed
that Nile crocodiles were affected by alterations to the environment on multiple scales. The
study concludes that the long-term population viability of C. niloticus is limited by a
combination of these factors.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/16827 |
| Date | 30 January 2015 |
| Creators | Gibson, Myfannwyn |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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