Aspects of the urban and rural ecology of Nile monitors (Varanus niloticus) in KwaZulu-Natal, South Africa.

Abstract

Changing land use, which is taking place globally at an unprecedented rate, generally has a negative impact on biodiversity. However, some species persist in or even exploit these anthropogenically modified environments. Little is known about how reptiles are affected by urbanisation, especially in the global South. Nile monitors (Varanus niloticus) are Africa’s largest lizard and are amongst the most exploited tetrapods on the continent, yet they can be found in highly urbanised and densely populated areas of KwaZulu-Natal, South Africa. They remain greatly understudied, with many gaps in even basic aspects of their ecology. They are projected to become threatened in parts of their range without successful management. This thesis focuses on two broad aspects of the ecology of Nile monitors in KwaZulu-Natal Province, South Africa. Namely, a) their distribution and persistence in a mosaic of land-use type and human population density in two focal areas and b) their population size and morphometrics in rural and urban areas. The aim was to fill important knowledge gaps in the ecology of this highly exploited, charismatic, and yet understudied species to make management recommendations and promote sustainable coexistence of people with Nile monitors in KwaZulu-Natal, South Africa. The first aim was to determine if Nile monitors occur in urban environments in KwaZulu- Natal and what land use types they are associated with. Using 419 Nile monitor sightings, two hotspots were found in the region, one dominated by protected land and the other dominated by mosaics of anthropogenic land use. They were found throughout regardless of human density. However, their use of residential areas was greater in the region with less available natural land. Increasing human density was positively associated with the use of more wooded habitats, except for planted forests, which were avoided systematically. Their association with water was confirmed; however, increased human density also increased their mean distance to rivers, likely reflecting their use of swimming pools, storm drains and other anthropogenic water features. Both managed and unmanaged green spaces (e.g., gardens, parks, golf courses) in urban mosaic landscapes are important features for the persistence of Nile monitors. The second aim was to estimate the Nile monitor population size using a mark-resight method with baited camera traps on a gradient of land use in three different specific sites and also compare urban and rural morphometrics throughout KwaZulu-Natal. Nile monitor limbs, body width, tail base, heads, and body mass were larger in rural areas but only marginally. Furthermore, we found greater population size estimates with increased habitat modifications (golf course > farmland > nature reserve), but the average estimated snout-vent length decreased. Reduced size may result from intraspecific or interspecific competition and different predation dynamics in urban and rural ecosystems. More independent trigger events of potentially competing diurnal mesocarnivores were recorded in the nature reserve and farmland than on the golf course. Despite the larger population size estimate of monitors, there was evidence of poaching at the golf course. One individual was stolen from a trap, and four instances of deployed snare traps were recorded. The inclusion of dead individuals for morphometrics has shed light on the added threats caused by domestic dogs (Canis lupus familiaris), people and vehicles for urban monitor populations. It is concluded that Nile monitors are successfully persisting in the mosaic urban landscapes of KwaZulu-Natal but are not as successful as some other urban varanids. The use of anthropogenic land-use, and thus conflict with people, will likely increase with continued land-use change. Future research should investigate Nile monitor interactions with people and pets as well as conflict mitigation strategies and both their urban and rural spatial ecology.