Performance, morphology, dispersal and habitat-type of the southern African Pyxicephalidae
For my MSc I am studying the Pyxicephalidae, the frog family that has undergone the largest frog radiation in South Africa and accounts for nearly half of the region’s frog species. This group exhibits high morphological diversity, extreme variation in area of range and different habitat preferences. This provides the opportunity to study the correlations of morphology and locomotory performance with the extent of geographic range and habitat-type. The first aim of my study is to uncover the common morphological and performance traits of pyxicephalid frogs that are correlated with extralimital range expansion, habitat specificity and geographic range. The second aim of my study is to determine whether ecologically relevant morphology and locomotory performance are the result of adaptation to novel habitats, or dispersal and conservatism within lineages of the pyxicephalid frogs. This study will determine whether morphology and dispersal, in combination with habitat, plays a major role in the extra-limital expansion or reserved distribution of some pyxicephalid frogs. In addition, the morphological and performance traits could indicate what ecological function these traits benefit. Finally, this study hopes to shed light on the evolutionary history of this family and recognise their potential to adapt with further habitat and climatic change imminent.
Xenopus laevis: Its invasive impact on other Xenopus species
For my MSc I will be looking at the functional response (relationship between resource consumption and resource availability) between the African clawed frog (Xenopus laevis) and three Xenopus species found in southern Africa. The African clawed frog is an invasive species and has spread extensively across southern Africa, often as a result of their ability to exploit artificial water bodies. Another possible suggestion as to why they have been so successful in invading is due to their ability to utilize available resources. This may have a significant negative impact on local Xenopus populations, especially on the Cape platanna (X. gilli) which is considered endangered by the IUCN . I will also be looking at the role of cannibalism in Xenopus ecology, specifically looking at X. gilli and X. laevis. By identifying the predator-prey relationships of each Xenopus species, I will be able to provide insight into the ecological impact that each species has in their habitat as well as determine the invasive potential of X. laevis.
James Vonesh & Mhairi Alexander
Amphibian conservation in an urban park: A spatial approach to qualifying threats to Anura in Table Mountain National Park
Seven amphibian species which are endemic (or near-endemic) and threatened to the Cape peninsula are the focus of my MSc study. Past assessments have highlighted general threats to these species e.g.: the threat of alien invasive plants. However, the spatial extent of multiple and cumulative threats has not been assessed or analysed. To do this I am taking a spatial analytic and modelling approach, using a Geographical Information Systems. This analysis will be used to create a cumulative proximity-to-threat layer for each species. Additionally, threats observed in field (fine-scale mapping, near breeding habitats) will also be spatially analysed. SANParks’ Table Mountain National Park places Heleophryne rosei as its top ranked animal species of special concern (SSC), and listed as Critically Endangered by the IUCN. The threats to this species are generalizations and assumptions based on the precautionary principle; while in reality, threats are different within different sub-populations. I am to explain the observed variation in habitat (tadpole) productivity by examining the water chemistry at each sub-population. In-so-doing define an ‘optimal’ ecological envelope for H. rosei tadpoles.
With this MSc, I aim to evaluate how populations of a frog species endemic to the Cape Peninsula, Arthroleptella lightfooti, are affected by invasions of exotic woody vegetation. The Fynbos Biome contains more invasions of alien plants compared to any other vegetation type in South Africa. The presence of invasive woody species such as Pinus pinaster and Acacia saligna in the mossy seepage habitat of these frogs may have an effect on the population densities of the frog. Higher degrees of invasion by the plants may result in lower population densities of A. lightfooti. This hypothesis will be explored using an acoustic Spatially Explicit Capture Recapture method (aSECR). An array of microphones arranged around a recording device can capture the chirp-like calls emitted by male A. lightfooti. These calls can be analysed using aSECR (noting which microphones did and did not capture a particular call). Together with information such as the differences between the time of arrival (TOA) and signal strength (SS) of each call across the different microphones, the density of calling frogs can be estimated. With the current global decline of amphibian populations, mastering effective means to evaluate or monitor amphibian populations is quintessential for conservation efforts.