Sharing for science: High-resolution trophic interactions revealed rapidly by social media

Discrete, ephemeral natural phenomena with low spatial or temporal predictability are incredibly challenging to study systematically. In ecology, species interactions, which constitute the functional backbone of ecological communities, can be notoriously difficult to characterise especially when taxa are inconspicuous and the interactions of interest (e.g., trophic events) occur infrequently, rapidly, or variably in space and time. Overcoming such issues has historically required significant time and resource investment to collect sufficient data, precluding the answering of many ecological and evolutionary questions. Here, we show the utility of social media for rapidly collecting observations of ephemeral ecological phenomena with low spatial and temporal predictability by using a Facebook group dedicated to collecting predation events involving reptiles and amphibians in sub-Saharan Africa. We collected over 1900 independent feeding observations using Facebook from 2015 to 2019 involving 83 families of predators and 129 families of prey. Feeding events by snakes were particularly well-represented with close to 1,100 feeding observations recorded

Ecology of the Namaqua Dwarf Adder, Bitis schneideri

Ph.D., Faculty of Science, University of the Witwatersrand, 2011The loss of global biodiversity is exacerbated by the problem of trying to conserve species whose biology is not understood. The conservation of African snakes provides a striking example of this problem as many species remain entirely enigmatic. If we are to effectively manage or conserve these species, then we need to begin to describe and quantify their ecology. This project aimed to increase the body of knowledge regarding the ecology of Bitis schneideri, an arid-adapted African viperid, and as such, provide the basis for an informed critical assessment of the conservation status of the species. The improved understanding of the ecology of B. schneideri will contribute to the emerging study of African snake ecology, allowing scientists to compare and contrast the ecology of African snakes with those from northern temperate systems on which most of the global understanding of snake ecology is based. Bitis schneideri is a species of very small-bodied viperids that grow rapidly and reach sexual maturity within the first two years. They are sexually dimorphic for several traits, and evidence suggests that fecundity selection has played an important role in shaping their morphology. Moreover, I suggest that the selective advantage of being able to bury into sandy substrates has resulted in the extreme body size displayed in the species. Bitis schneideri is diurnally active, a state that is probably a derived condition, as B. caudalis (the sister species to B. schneideri) is reported to be nocturnal. Additionally, B. schneideri shows seasonal variation in activity, with increased activity during the spring mating season. Activity during winter is reduced, but not absent, and appears to be governed by the availability of suitable environmental conditions. Activity in B. schneideri is limited at all temporal scales by environmental conditions. Radio-telemetry and mark-recapture analysis showed that B. schneideri is highly sedentary, moving between 0.8 ± 6.5 m.d-1 and 47.3 ± 3.9 m.d-1, inhabiting small homeranges ( : 0.85 ± 0.09 ha; : 0.10 ± 0.09 ha). Moreover, juveniles show limited dispersal that, when combined with sedentary adult behaviour, could result in vulnerability to fragmentation by limiting gene-flow. Population densities are high ( 8 ha-1) and survival is low (39% and 56% per annum) compared to viperids from other parts of the world. Additionally, juveniles have higher survival rates than adults. Small litter sizes imposed by small-bodies, and low survival, means that B. schneideri must reproduce frequently, probably annually, in order for populations to persist. Such frequent reproduction is atypical, even among closely related species, and in B. schneideri, appears to be facilitated through the capacity to feed year-round in the aseasonal habitat in which they occur. Bitis 6 schneideri is a generalist that ambushes prey in proportion to encounter frequency. Also, I show that the capacity of B. schneideri to capture and consume relatively large prey items provides snakes with a large energetic advantage. Abundant generalist predatory birds are likely to be more important predators of B. schneideri than are rare specialist predatory raptors, although snakes are also vulnerable to other predators that include small mammals, other reptiles, and large invertebrates. Small body-size has two important implications for B. schneideri biology – reduced litter size, and vulnerability to a wide suite of predators. These attributes interact to result in low survival, reduced movement and dispersal, frequent reproduction, generalist foraging, and year-round feeding. Bitis schneideri is not at significant risk of facing extinction in the near future. The primary biological factor that ameliorates against extinction risk is large population size and high population density

The distribution and abundance of herpetofauna on a Quaternary aeolian dune deposit : Implications for strip mining

Exxaro KZN Sands is planning the development of a heavy minerals strip mine south of Mtunzini, KwaZulu-Natal, South Africa. The degree to which mining activities will affect local herpetofauna is poorly understood and baseline herpetofaunal diversity data are sparse. This study uses several methods to better understand the distribution and abundance of herpetofauna in the area. I reviewed the literature for the grid squares 2831DC and 2831 DD and surveyed for herpetofauna at the study site using several methods. I estimate that 41 amphibian and 51 reptile species occur in these grid squares. Of these species, 19 amphibian and 39 reptile species were confirmed for the study area. In all, 29 new unique, grid square records were collected. The paucity of ecological data for cryptic fauna such as herpetofauna is particularly evident for taxa that are difficult to sample. Because fossorial herpetofauna spend most of their time below the ground surface, their ecology and biology are poorly understood and warrant further investigation. I sampled fossorial herpetofauna using two excavation techniques. Sites were selected randomly from the study area which was expected to host high fossorial herpetofaunal diversity and abundance. A total of 218.6 m3 of soil from 311 m2 (approximately 360 metric tons) was excavated and screened for herpetofauna. Only seven specimens from three species were collected. All were within approximately 100 mm of the surface even though some samples removed soil 1 m below the surface. There was no detectable difference in fossorial herpetofaunal density (individuals.m-2) between methods or from areas under different land uses. Neither soil compaction nor land use nor soil texture predicted fossorial herpetofaunal density or abundance. The data suggest that fossorial herpetofauna occur at extremely low densities in the area. This finding has implications for population estimates and conservation measures for these species. In order to better understand the effects of land use on herpetofaunal diversity, I used sample-based rarefaction curves to compare the diversity of the herpetofaunal species assemblages occurring in each of the four main land uses on the study site. Forest areas hosted significantly higher diversity than grasslands and the two agricultural mono-cultures, Eucalyptus and sugarcane plantations. Additionally I demonstrated empirically that riparian woodlands host higher species richness and herpetofaunal abundance than non-riparian areas. Potential reasons for the apparently suppressed diversity of these areas include the use of pesticides and/or herbicides, harvesting regimes, and the reduction in habitat heterogeneity. The potential value of riparian woodlands as refugia and corridors that could facilitate recolonisation of revegetated areas post-mining is discussed. Negative influences of mining activities on local herpetofauna are of particular interest given the potential and verified presence of several threatened taxa in the area including Bitis gabonica, Python natalensis, Afrixalus spinifrons, Hemisus guttatus and Hyperolius pickersgilli. These, as well as the “conservation needy” species proposed in a specialist report on the impacts of the mine on local herpetofauna are discussed in the light of my fieldwork. Mitigatory measures are required to reduce the negative impacts likely to be experienced by certain threatened taxa. I discuss a proposal for the development of a wetland reserve targeting, among other amphibian species, H. pickersgilli

Scale-dependent orientation in movement paths: a case study of an African viper

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 schneideri (Namaqua dwarf adder) for evidence of broad-scale directional persistence and short-range avoidance of exposure. Although snakes clearly displayed directional persistence, they preferentially moved to nearby shrubs, thereby minimizing exposure to solar and thermal radiation and/or predation. Thus, snakes made decisions relating to orientation at a minimum of two scales, the interaction of which resulted in snakes moving ≈17% (mean straightness index = 0.85) further than the simple broad-scale straight-line distance. We assert that the actual path chosen by moving snakes represents a trade-off of various costs and risks that include risk of predation, exposure to the elements, time and energy expenditure. Our study highlights the need for cognizance of the possibility of the scale dependence of orientation and movement in studies of snake movement, and adds to a growing literature demonstrating previously unrecognized behavioural complexity in snakes

Serpientes depredadoras de huevos de aves: Una revisión y bibliografía

Snakes are frequent predators of bird nests and therefore potentially have an important impact on bird population dynamics. However, while many species are known to consume nestlings and chicks, few species have been recorded consuming bird eggs. To effectively quantify the effects of bird egg predation by snakes on bird demographics, a key first step is to identify which snake species consume bird eggs. Unfortunately, detailed information on the dietary habits of most snakes is scarce and feeding records are poorly cataloged, making it difficult to ascertain which species do and do not eat bird eggs. We reviewed the literature and online community science reports to compile a global list of confirmed snake predators of bird eggs. In total, we gathered 471 feeding records of 123 snake taxa consuming the eggs of at least 210 bird species from 238 individual data sources. Geographical locations of records disproportionately represented well-sampled regions, and we infer that many snake species not included on our list also consume bird eggs

Specialized morphology, not relatively large head size, facilitates competition between a small-bodied specialist and large-bodied generalist competitors

Interspecific competition for limited resources should theoretically occur between species that are morphologically similar to each other. Consequently, species that reduce competition by adapting to specialize on a specific resource should be morphologically disparate to sympatric contemporaries and show evidence of phenotypic specialization. However, few studies have compared the morphologies of specialist and generalist competitors. In this context, we compare the feeding morphology and diet of an obligate, specialist, bird-egg-eating snake to three sympatric generalists that only facultatively consume bird eggs. We measured and compared body and head morphology of preserved museum specimens of each of four, syntopic snake species from southern Africa: the obligate bird-egg-eating rhombic egg-eater (Dasypeltis scabra), and the facultative bird-egg-eating boomslang (Dispholidus typus), cape cobra (Naja nivea) and mole snake (Pseudaspis cana). Given the physical challenges of consuming bird eggs in snakes, we predicted that consumption of bird eggs would be facilitated by the evolution of relatively larger heads in the smaller bodied Dasypeltis. We found that head size was not phylogenetically conserved in the clades of these taxa and that contrary to our expectations, the specialist egg-eaters evolved to possess significantly smaller heads relative to body size than their competitors. We found a positive relationship between dietary niche breadth and head size within these species and their close relatives. Thus, relatively large-headed species have evolved diverse diets that overlap with the restricted diets of the small-headed specialist thereby producing this atypical competitive interaction. Our findings suggest that specialized adaptations can decouple typical body-size-constrained competition dynamics between sympatric snake species and highlight the complexity of the origins of dietary specialization

Identifying global priorities for the conservation of vipers

Vipers are among the most misunderstood and persecuted animals. They occupy most terrestrial ecosystems around the world, often at high population densities. However, certain aspects of their biology (e.g., low fecundity and slow growth) have resulted in vipers being disproportionately threatened by extinction. Despite increased extinction risk, relatively little is known about viper biology, severely limiting the development and implementation of conservation initiatives. Here, we review the conservation status of vipers globally, map species richness, and develop three indices (one reactive; one proactive; one combined index emphasising irreplaceable species facing severe threats) to identify species for which conservation action should be prioritised. Moreover, we map species richness weighted by each index to identify regions for conservation prioritisation. We ranked prioritisation scores for all species for which data were available. In doing so we identify species for which valuable data are missing and that should be prioritised for research. We additionally show that 17 species, currently listed as Not Assessed or Data Deficient by the IUCN, score sufficiently high on our Threat Index to be considered as Threatened in the future. We identify multiple regions for which viper conservation action should be prioritised. These areas broadly correlate with species richness patterns, suggesting that species richness may be an effective proxy for conservation planning. Finally, we discuss the major gaps in knowledge, as well as the major threats facing vipers

Snake body size frequency distributions are robust to the description of novel species

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 species have not yet been detected/described, also has the potential to influence BSFD shape and skew when missing species are disproportionately large or small. Missing species may thus influence the skew of a BSFD, misleading subsequent interpretations. In contrast to many vertebrate taxa, the BSFDs of snakes appears to be log-normal, with no significant skew. However, the influence of imperfect species sampling on these distributions has however not been previously evaluated. We collated body size data and date of description for 300 species of elapid, and 264 species of viperid snakes and assessed the shape and skew of the BSFD of each clade. Next we tested the hypothesis that date of description was related to body size in each clade. We show that the BSFDs of elapid and viperid snakes are both log-normal, with no significant skew. Moreover we demonstrate size-related differences in the probability of detection (as measured by year of description) among elapids and vipers: in both lineages, species with larger body size tend to have been described earlier. However, simulations testing the effect of the addition of novel, small-bodied species revealed that the distributions of elapids and vipers are not highly vulnerable to becoming significantly skewed in the future. Our results support current interpretations of BSFDs in snakes that suggest a lack of size-associated biases in the speciation and extinction rates of this clade

Sampling bias in reptile occurrence data for the Kruger National Park

To effectively conserve and manage species, it is important to (1) understand how they are spatially distributed across the globe at both broad and fine spatial resolutions and (2) elucidate the determinants of these distributions. However, information pertaining to the distributions of many species remains poor as occurrence data are often scarce or collected with varying motivations, making the resulting patterns susceptible to sampling bias. Exacerbating an already limited quantity of occurrence data with an assortment of biases hinders their effectiveness for research, thus making it important to identify and understand the biases present within species occurrence data sets. We quantitatively assessed occurrence records of 126 reptile species occurring in the Kruger National Park (KNP), South Africa, to quantify the severity of sampling bias within this data set. We collated a data set of 7118 occurrence records from museum, literature and citizen science sources and analysed these at a biologically relevant spatial resolution of 1 km × 1 km. As a result of logistical challenges associated with sampling in KNP, approximately 92% of KNP is data deficient for reptile occurrences at the 1 km × 1 km resolution. Additionally, the spatial coverage of available occurrences varied at species and family levels, and the majority of occurrence records were strongly associated with publicly accessible human infrastructure. Furthermore, we found that sampled areas within KNP were not necessarily ecologically representative of KNP as a whole, suggesting that areas of unique environmental space remain to be sampled. Our findings highlight the need for substantially greater sampling effort for reptiles across KNP and emphasise the need to carefully consider the sampling biases within existing data should these be used for conservation management decision-making. Modelling species distributions could potentially serve as a short-term solution, but a concomitant increase in surveys across the park is needed. Conservation implications: The sampling biases present within KNP reptile occurrence data inhibit the inference of fine-scale species distributions within and across the park, which limits the usage of these data towards meaningfully informing conservation management decisions as applicable to reptile species in KN

An ambusher’s arsenal: chemical crypsis in the puff adder (Bitis arietans)

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 attempted to demonstrate chemical crypsis. Field observations of puff adders (Bitis arietans) going undetected by several scent-orientated predator and prey species led us to investigate chemical crypsis in this ambushing species. We trained dogs (Canis familiaris) and meerkats (Suricata suricatta) to test whether a canid and a herpestid predator could detect B. arietans using olfaction. We also tested for chemical crypsis in five species of active foraging snakes, predicted to be easily detectable. Dogs and meerkats unambiguously indicated active foraging species, but failed to correctly indicate puff adder, confirming that B. arietans employs chemical crypsis. This is the first demonstration of chemical crypsis anti-predatory behaviour, though the phenomenon may be widespread among ambushers, especially those that experience high mortality rates owing to predation. Our study provides additional evidence for the existence of an ongoing chemically mediated arms race between predator and prey species