Population dynamics and morphometrics of Nile monitors along a gradient of urbanization in KwaZulu-Natal, South Africa

Abstract

Globally, with the continuous increase in human populations, land use is changing at an unprecedented rate. Little is known about how African reptiles respond to urbanization. We used mark-resight and baited camera traps to compare population density and demographics of Nile monitors (Varanus niloticus) on a gradient of land use, namely a golf course, a farm and a nature reserve in KwaZulu-Natal, South Africa, during 2022–2023. We also collected detailed morphometrics on 112 Nile monitors throughout KwaZulu-Natal. We compared morphometric data on limbs, head, body and mass to establish whether the different ecological factors in urban and rural environments and associated behavioural shifts have resulted in unique phenotypes. No significant morphometric differences were found, but urban individuals were generally smaller and lighter than their rural counterparts. Population size estimates varied between sites. Overall, population size estimates increased with anthropogenic disturbance between our three focal sites, while the mean estimated snout-vent length decreased. The naïve presence of competing diurnal mammals did not follow a specific pattern. The overall insignificant variations in morphometrics in urban and rural areas of KwaZulu-Natal suggest that Nile monitors have adapted to urban mosaic landscapes with natural and managed (e.g. gardens, parks, golf courses, etc.) green spaces but are not as successful as some urban-exploiting varanids globally. Future research should investigate Nile monitor interactions with people and pets as well as conflict mitigation strategies.