Graham J. Alexander

University of the Witwatersrand | wits · School of Animal, Plant and Environmental Sciences

Urbanisation creates novel environments, not only through (abiotic) microhabitat alterations, but also due to changes in (biotic) inter- and intraspecific interactions. Where sheltering sites in urban habitats are limited, intra or interspecific interactions may increase, resulting in increased competition and changes in predation risk in urban are...

A complete and high-quality reference genome has become a fundamental tool for the study of functional, comparative, and evolutionary genomics. However, efforts to produce high-quality genomes for African taxa are lagging given the limited access to sufficient resources and technologies. The southern African dwarf chameleons (Bradypodion) are a rel...

Time from birth or hatching to the first shed (postnatal ecdysis) in snakes ranges from about an hour to several weeks depending upon the species. We assessed patterns in time to postnatal ecdysis in 102 snake species for which we could source appropriate information, covering 2.6% of all extant snake species, and related measures to various biolog...

The North West Province, South Africa, is centrally situated in southern Africa and is characterised by savannah with a mesic, temperate climate in the east and a hot, arid climate in the west. While the eastern region is fairly well-documented for herpetofauna, the arid central and western regions are poorly surveyed. Given that the Province has b...

Comprehensive assessments of species’ extinction risks have documented the extinction crisis and underpinned strategies for reducing those risks. Global assessments reveal that, among tetrapods, 40.7% of amphibians, 25.4% of mammals and 13.6% of birds are threatened with extinction. Because global assessments have been lacking, reptiles have been o...

The Great Karoo is an ecologically fragile, poorly studied arid region in central South Africa. With the discovery of shale gas as a potential resource in the Great Karoo, it is expected that a substantial footprint will be left in this region if gas extraction proceeds. This highlights the need for biodiversity surveys of the Great Karoo of taxono...

Comprehensive assessments of species’ extinction risks have documented the extinction crisis and underpinned strategies for reducing those risks. Global assessments reveal that, among tetrapods, 40.7% of amphibians, 25.4% of mammals and 13.6% of birds are threatened with extinction. Because global assessments have been lacking, reptiles have been o...

Windhoek-born Wulf Dietrich Haacke’s career as a herpetologist while associated with the Transvaal Museum in Pretoria spanned more than 50 years. He passed away on 30 June 2021 at the age of 84. This tribute summarises various aspects of his life and achievements, and their significance to African herpetology, including his involvement with the Her...

Viviparity has evolved independently multiple times within squamate reptiles. In the Lacertidae, two genera and several species from the Northern Hemisphere are known to be viviparous. However, although viviparity is present in many African reptiles, all African lacertids were considered exclusively oviparous. The lacertid genus Tropidosaura is res...

It is commonly recognised that natural history datasets contain locality errors that can compromise the utility of those datasets. However, another source of error in these datasets is taxonomic misidentifications, and this type of error is potentially common, particularly with regards to morphologically conservative species. For example, in the Af...

Climate change is causing the geographical ranges of some species to track suitable conditions. Habitat specialists, range-restricted species and species with limited dispersal abilities may be unable to track changing conditions, increasing their extinction risk. In response to changing conditions and species movement patterns, there is a need to...

The Great Karoo and Namaqualand of South Africa are home to a species complex of morphologically conserved lizards that occur in allopatry (Karoo: Cordylus aridus, Cordylus cloetei, Cordylus minor; Namaqualand: Cordylus imkeae). However, there are negligible morphological differences and a lack of obvious physical or climatic barriers, particularly...

Measures of activity patterns in relation to environmental conditions provide insights into ecologically driven requirements and climate preferences of species, particularly for ectotherms, due to the strong relationship between body temperature (Tb) and environmental temperatures. Lygodactylus incognitus (cryptic dwarf gecko) and Lygodactylus sout...

Identifying the traits of ancestral organisms can reveal patterns and drivers of organismal diversification. Unfortunately, reconstructing complex multistate traits (such as diet) remains challenging. Adopting a ‘reconstruct, then aggregate’ approach in a maximum likelihood framework, we reconstructed ancestral diets for 298 species of elapid snake...

Identifying the traits of ancestral organisms can reveal patterns and drivers of organismal diversification. Unfortunately, reconstructing complex multistate traits (such as diet) remains challenging. Adopting a 'reconstruct, then aggregate' approach in a maximum likelihood framework, we reconstructed ancestral diets for 298 species of elapid snake...

Characterising species-landscape associations is relevant for conservation planning and management in response to environmental transformation. The occurrence of reptiles is linked to landscape structure that allows for thermoregulation, shelter and feeding, but the relative importance of these factors is unknown for many tropical and subtropical s...

Fencing, including electric fencing, is widely used across South Africa for livestock and game ranching practices. Leopard tortoises (Stigmochelys pardalis) are particularly prone to being killed by electric fences, but no published studies have assessed the impact of fence structure or quantified tortoise mortality along non-electric fences. This...

The Colubroidea includes all venomous and some nonvenomous snakes, many of which have extraordinary dental morphology and functional capabilities. It has been proposed that the ancestral condition of the Colubroidea is venomous with tubular fangs. The venom system includes the production of venomous secretions by labial glands in the mouth and usua...

Sexual selection studies often focus on morphological traits that are important only in the later stages of mate acquisition. Comparatively little is known about traits that lead to mate acquisition, such as mate-searching activities. We experimentally manipulated body condition (i.e., the energy reserves) in male puff adders (Bitis arietans) prior...

The authors would like to correct the error in table 4 which was incorrectly published in original version. Correct version of Table 4 is updated here.

Correction to article: Male energy reserves, mate‑searching activities, and reproductive success: alternative resource use strategies in a presumed capital breeder

Body size is a key selected trait in many animal systems: larger size is sexually selected for in males because it confers a reproductive advantage during contest competition for access to females, and larger females are naturally selected for fecundity. Herein, we used radio‐telemetry to gather a large dataset of male–female interactions and DNA p...

Syntopic species often exhibit evolutionary mechanisms that reduce competition. A common mechanism facilitating coexistence is niche separation, which may manifest through spatial, temporal or trophic dimensions. Species that are morphologically similar, such as congeners, are likely to compete directly and thus separate their niche spatially. The...

Understanding the role of climatic and ecological factors in limiting species to their distributions is becoming ever more important in a world where anthropogenic activities are increasingly threatening species persistence. Species with restricted distributions are often poorly known even though they may be most vulnerable to extinction. We invest...

A horizon scan was conducted to identify emerging and intensifying issues for biodiversity conservation in South Africa over the next 5–10 years. South African biodiversity experts submitted 63 issues of which ten were identified as priorities using the Delphi method. These priority issues were then plotted along axes of social agreement and scient...

The mole snake (Pseudaspis cana) is capable of inflicting unusual bites in defence and during male combat that present as two parallel lacerations. We investigated the dental morphology of the mole snake by making SEM images, and by CT-scanning and digitally reconstructing the skulls of 14 specimens comprising both sexes. The lengths, volumes, shap...

Foraging modes (ambush vs. active foraging) are often correlated with a suite of morphological, physiological, behavioural and ecological traits known as the "adaptive syndrome" or "syndrome hypothesis." In snakes, an ecological correlate often reported in the literature is that ambush‐hunting snakes have a higher relative meal size compared to act...

Compared to the global average, extinction risk for mainland African reptiles, particularly for South Africa, appears to be relatively low. Despite this, African reptiles are under threat primarily due to habitat loss as a result of agriculture, resource extraction, and urbanisation, and these pressures are expected to increase into the future. Sou...

It is incredibly challenging to study the natural feeding habits of snakes. Snakes are themselves secretive and rarely observed in the wild, and they feed relatively infrequently, making observations of feeding scarce. As a result, scientific understanding of snake dietary ecology (beyond simple prey lists) remains remarkably superficial outside of...

The African green and bush snakes of the genus Philothamnus currently comprises 21 species and three subspecies and occurs throughout sub-Saharan Africa. The genus has been the subject of previous taxonomic revisions based on traditional morphological characters and limited genetic assessment, and may not reflect their evolutionary history. Indeed,...

Body temperature (Tb) is one of the most influential factors affecting physiological processes in ectothermic animals. Reptiles use behaviours such as shuttling, and postural and orientation adjustments to ensure that Tb remains close to a target. It is thought that target body temperature (Ttarget) is aligned to the physiological and behavioural t...

Reproductive strategies such as parental care have been pivotal in evolutionary innovations such as endothermy in birds and mammals. The diversity of reproductive biology across the squamates provides a unique opportunity for elucidating the selective forces responsible for the evolution of various reproductive strategies. Here, I report on the rep...

Examination of the gastrointestinal contents of museum specimens is routinely used as a method for assessing diet in a wide variety of reptiles. However, this method might be biased toward detecting prey items that are less digestible and larger in size because these food items are digested more slowly. In this study, we used fixed videography on f...

The dangerous prey hypothesis predicts that when predators can discriminate between harmless and dangerous prey, they should alter their predatory behavior according to the risk. Venomous snakes, which rely on an envenomating strike to kill prey, often feed on potentially dangerous prey such as rodents, and have the choice between two alternative s...

The Sungazer (Smaug giganteus) is a threatened lizard species endemic to the Highveld grasslands of South Africa. The species faces risks from habitat loss and fragmentation, and illegal harvesting for traditional medicine and the pet trade. Despite these threats, the current conservation status of the species was poorly validated. We visited 79 Su...

The scales of the African Viper Bitis arietans were tested for optical effects. Spectral intensity was recorded at incident angles over the visible spectrum for dark, pale, and ventral scale regions. The lowest spectral intensity recordings were associated with scales which have the greatest level of micro-structuring. Our results indicate that sca...

The effect of food availability on the spatial ecology of animals varies within and across study systems because a multitude of factors can affect the spatial activity of organisms. Low-energy specialists, such as ambush-foraging snakes, feed infrequently and can endure long periods without food. Because they have low-energy requirements, one possi...

Aggressive mimic species use signals typically resembling an attractive or harmless model to deceive other organisms in order to increase foraging success. With the exception of a few brood parasitic birds that combine two signals, most known cases of aggressive mimicry involve only a single signal. Here, we used fixed videography, a technique whic...

The potential economic and energy security opportunities of a medium to large shale gas resource could be substantial for South Africa; as are both the potential social and environmental risks associated with a domestic gas industry in the Central Karoo. The development of shale gas using vertical and horizontal drilling and hydraulic fracturing or...

Zootherapy plays a role in healing practices in Mozambican society. Although several studies have focused on ethnobotany and traditional medicine in the country, little research has been conducted on the use of reptiles in zootherapy. The aim of this study was therefore to fill this gap by assessing the reptile species traded for traditional medici...

Snake farming in Asia has increased over the past decade, and conservationists have expressed concerns that farms may foster overexploitation of wild populations and create legal conduits for illegally harvested wild individuals. We conducted face-to-face interviews with snake farmers in Viet Nam and China, with the aim of describing the basic mode...

The accurate interpretation of body size frequency distributions (BSFDs) has important implications for understanding large-scale ecological and evolutionary patterns because they are shaped by ecological and evolutionary processes. However incomplete species sampling resulting either from a paucity of reliable body size data or because those speci...

 Ambush foragers use a hunting strategy that places them at risk of predation by both visual and olfaction-oriented predators. Resulting selective pressures have driven the evolution of impressive visual crypsis in many ambushing species, and may have led to the development of chemical crypsis. However, unlike for visual crypsis, few studies have...

Decisions relating to the orientation of movement by animals and how this translates into movement patterns can occur at multiple spatial scales simultaneously, but this interaction is poorly understood for many groups of animals. Using the tracks left by moving snakes in their sandy habitat, we studied the movement paths of the African snake Bitis...

Movement patterns in animals have been studied extensively, but differences in sampling frequencies produce datasets that are not always directly comparable. Because information is collected as point coordinates, measures of movement generally underestimate actual distances moved, especially when sampling frequency is low. Many animals, including m...

Changes in the size and location of species ranges are a recognized response to environmental changes. We assessed recent range dynamics of South African amphibians using data consolidated by the South African Frog Atlas Project, which provided both historical (1905–1995) and recent distribution data (1996–2003). Sampling differences were accounted...

Ambush foragers use a hunting strategy which places them at risk of predation by both visual and olfactory-oriented predators. Resulting selective pressures have driven the evolution of impressive visual crypsis in many ambushing species, and may have lead to the development of chemical crypsis. However, unlike visual crypsis, chemical crypsis is d...

We present data from gut content analyses of Varanus albigularis (savanna monitor) and V. niloticus (water monitor) in South Africa. Both species are generalist, opportunistic feeders. We did not detect any sex-based differences in the diet of V. albigularis, and there were relatively high levels of dietary overlap between the species, although the...

We present data from gut content analyses of Varanus albigularis (savanna monitor) and V. niloticus (water monitor) in South Africa. Both species are generalist, opportunistic feeders. We did not detect any sex-based differences in the diet of V. albigularis, and there were relatively high levels of dietary overlap between the species, although the...

Habitat fragmentation and transformation arising from urbanisation are leading causes of frog population declines. Artificial wetlands are sometimes used in remediation to minimise biodiversity loss in urban landscapes, but little is known about the specific habitat requirements of frog species for breeding. The aim of our study was to identify pan...

Prey items vary greatly in the total amount of energy they provide and the costs associated with their location, capture, consumption and assimilation. As a result not all prey types are of equal value, and the relative frequency with which different prey types are consumed can strongly influence an organism's fitness. In order to understand foragi...

Stress levels in organisms provide a rapid measure for assessing population health. Handling and capture stress, however, cause error in blood measures, so this method is rapidly being replaced by assessing levels of stress metabolites in faeces. This eliminates the source of error because there is a lag period between stress perception and the res...

Aim Small range size often increases a species’ susceptibility to decline. A narrow ecological niche is one factor that may cause species to inhabit a small range. We investigated whether specialized niches have made S outh A frican amphibians more vulnerable to range contractions. Location S outh A frica. Methods The S outh A frican F rog A tlas...

Habitat fragmentation and destruction arising from urbanisation are leading causes of frog population declines. Artificial wetlands are frequently used in remediation to minimize biodiversity loss in urban landscapes, but little is known about the specific requirements of frog species for breeding habitat. The aim of our study was to identify pan c...

Reproductive frequency is a key component of reproductive output, and has important influences on organismal fitness and population persistence. Viperid snakes, like many other ectothermic vertebrates, generally exhibit a low frequency of reproduction (LFR), as females only reproduce every second year, or even less frequently. However, for small‐bo...

Moving from one location to another provides animals with obvious benefits, but also incurs costs. When and how far an animal chooses to move is thus of fundamental importance to all aspects of its biology. We investigated movement patterns in a population of Namaqua Dwarf Adders (Bitis schneidert) in southern Africa through the use of radio teleme...

Although estimates of survival and population density are available for several snake populations, most of these are for populations in northern temperate environments. Here we present the results of a 3-yr mark—recapture study for an African species, the Namaqua Dwarf Adder (Bitis schneideri). We estimated survival, recapture probability, and popu...

We measured apparent assimilation efficiency (AAE) and gut passage time in the African elapid snake Hemachatus haemachatus under laboratory conditions. AAE was dependent on food type, being 89.8% when snakes were fed frogs and 82.8% when fed mice. Differences in AAE for different meal types could be ascribed to the indigestible hair in mouse meals...

Namaqua Dwarf Adders (Bitis Schneider!) are small vlperids that inhabit sandy coastal habitats within the Succulent Karoo Biome in southern Africa. Their ecology, and the faunal ecology within the region in general, is poorly documented, hampering effective conservation planning for this biodiversity hotspot. We used radio telemetry to investigate...

Quality conservation planning requires quality input data. However, the broad scale sampling strategies typically employed to obtain primary species distribution data are prone to geographic bias in the form of errors of omission. This study provides a quantitative measure of sampling bias to inform accuracy assessment of conservation plans based o...

We investigated the thermoregulatory abilities and behavior of Pseudocordylus melanotus melanotus (Drakensberg crag lizard) in terms of the relationship between the operative temperature (Te), selected temperature (Tsel), set-point range (Tset) and field active body temperature (field Tsel), exposure to low temperature, body posture and activity. T...

Basic ecological data are lacking for many species of herpetofauna, particularly fossorial species. Quantitative analyses of the factors that may influence the occurrence of fossorial herpetofaunal species are rare, with minimal work conducted in southern Africa. We mapped the absolute and relative fossorial herpetofaunal species richness across So...

Habitat transfonnation is the primary anthropogenic threat to global biodiversity. Fragmentation of reptile populations following habitat transfonnation within a landscape can lead to the extirpation of species. We investigated the effects of land-use on the species richness and abundance of reptile assemblages in three habitat types (two natural a...

Developmental plasticity results from environmental influences on the phenotype of an organism during its development, and its effects are irreversible. The phenomenon of phenotype-genotype uncoupling (plasticity) causes problems in species delineations, and has been suggested as a cause underlying a mismatch between morphology and genetics between...

Developmental plasticity results from environmental influences on the phenotype of an organism during its development, and its effects are irreversible. The phenomenon of phenotype–genotype uncoupling (plasticity) causes problems in species delineations, and has been suggested as a cause underlying a mismatch between morphology and genetics between...

Fire is a frequent feature of African grasslands and is commonly used in the management of conservation areas. We studied the herpetofaunal richness and composition of 10 sites to determine the effects of a 30-year fire management regime on the herpetofaunal assemblage in a reserve in South Africa. We trapped amphibians and reptiles during March an...