Snake population declines and conservation: a global synthesis, and perspectives from southern Africa, based on long-term field observations.

Abstract

Amphibian and reptile declines have been documented from across the globe in recent decades. This is a result of anthropogenically driven effects including transformation of the landscape, habitat destruction, environmental degradation, road mortality, leaching of chemicals and pollutants into the environment, genetic isolation and disease. More recently, several well-studied declines affecting snakes have been documented in the literature. Most studies emanate from North America and Europe, with a small percentage from Australia. Due to the absence of long-term site monitoring in Africa, the extent of snake population declines is mostly unknown and at best, speculative. My study aimed to provide baseline data on snakes from South Africa based on long-term field observation and accumulative data spanning a period of approximately 30 years, from 1988 – 2018. In my experience, I have noted perceived declines in several geographical regions, including species-specific declines. Whilst the primary focus of this study was on snakes, these declines extend to other amphibian and reptile species, and brief reference is made to these in the specific site studies. Firstly, in Chapter 1, I reviewed the published literature globally pertaining to snake conservation, population ecology and documented snake population declines and the contributing factors thereof. The causes of decline are complex and often interlinked, having a cascading effect. For example, a population of snakes isolated by roads and urban development will become genetically isolated, leading to weakened immunity and increased stresses, making them susceptible to disease and overloaded parasite burdens. Therefore, a population experiencing declines is affected by several interlinking causes. All contributing factors must be carefully analysed to initiate mitigation measures to prevent further decline. Secondly, in Chapter 2, I reviewed our current understanding of global snake diversity, conservation and systematics to quantify species diversity and conservation trends in extant snake species. We are far from understanding true snake species diversity with numerous new species being described by science annually. Systematics and taxonomy, including phylogenetic relatedness, are all crucial aspects required to facilitate and implement effective conservation measures if we are to conserve world snake diversity. Thirdly, in Chapter 3, I have presented snake data pertaining to road mortality based on a study undertaken along the R516 national road in Limpopo Province, South Africa. Road mortality has been identified as a contributing factor of snake population declines in many regions of the globe. The increasing network of roads and associated vehicular traffic is cause for concern, not only in protecting snakes, but other faunal species as well. In Chapters 4 and 5, I examined data from personal archived records taken at two different, well-defined, field study sites – one site situated in a former grassland habitat in Gauteng Province, which is now completely transformed, and a second site on the lower South Coast of KwaZulu-Natal Province, which has experienced relatively lower rates of anthropogenic habitat transformation. Both sites have been randomly surveyed for a period spanning approximately 30 years and may represent two of the longest-running site specific herpetological surveys undertaken in southern Africa. The impact of anthropogenic habitat transformation through ecological succession and urban development on species populations and diversity is discussed in detail. In the absence of consistent, methodologically robust surveys using trap arrays and mark-recapture studies, which are absent in South Africa, long-term field observation may be the only available option in identifying possible snake declines. This sentiment is echoed elsewhere across the globe where numerous seasoned herpetologists have indicated that snakes have declined in their respective field sites in recent decades. My data support this. In Chapter 6, I selected a common, widely distributed snake species, the rinkhals (Hemachatus haemachatus), as a species-specific candidate. These elapid snakes appear to have experienced dramatic declines in some parts of their range, i.e. the Western Cape and eastern Zimbabwe, but which are still thriving within a peri-urban environment on the eastern highveld in Gauteng. Factors contributing to its success or decline are discussed. In conclusion, our current lack of long-term monitoring is highlighted, as well as challenges and possible solutions and methods to gain better insight and understanding of snake population declines regionally and globally. The pros and cons of utilizing citizen science, virtual museums and social media data sets is discussed within the context of providing skewed data that may mask underlying population trends, providing a biased output which may in turn affect accurate conservation assessments. This thesis aims to be a qualitative study rather than a quantitative analysis. However, various population and ecological models are being researched for further statistical testing.