Preliminary investigation into anthropogenic and natural disturbance effects on the Nile crocodile (Crocodylus niloticus) in the Mutale river, Limpopo province

[摘要] My study investigated the significance of spatiotemporal heterogeneity on the Nile crocodile(Crocodylus niloticus), a long-lived, apex predator, occupying many African and some SouthAfrican riverine ecosystems. The scales of study included a long-term investigation of the(indirect) impacts of anthropogenic, landscape scale (100 km2) disturbances on the populationdemographics of C. niloticus, over 35 years. At the intermediate scale (15 km2), indirect anddirect impacts of flooding and seasonality on the health of the C. niloticus population wereinvestigated over a three-year period. This was performed by investigating preferred habitatavailability and river quality assessments, including physiochemical variables and rapid bioassessmentmeasures, which served as the 'smallest’ scale (with samples taken every 500 m).All scales were compared with long-term and short-term investigations into crocodilepopulation demographics. Total crocodile population size within the study river increasedover 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 anthropogenicallyaltered habitat increased over time from 24% total coverage attributable to farmland on thebanks of the Mutale River in 1977, to 66% land coverage in 2013. Increases in humaninducedhabitat alterations also created shifts in preferred crocodilian habitat availability.Investigations into the effects of natural disturbances revealed that physiochemistry wasseasonally variable, and changed drastically with changes in climate and runoff. Themacroinvertebrate communities in the Mutale River differed in time and space for a multitudeof reasons, including climate change and changes in habitat. The results of my study showedthat Nile crocodiles were affected by alterations to the environment on multiple scales. Thestudy concludes that the long-term population viability of C. niloticus is limited by acombination of these factors.

[发布机构] University of the Witwatersrand