Browsing by Author "Tolley, Krystal A"

Now showing 1 - 8 of 8
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    The conservation genetics of a newly recognised Cape Peninsula endemic Rose's Mountain toad (Capensibufo rosei)
    (2012) Cressey, Emily R; Tolley, Krystal A; Measey, G John
    Declines and losses of amphibian populations are a global problem involving a complexity of interacting causes. Regardless of the fact that amphibians in Africa are among those predicted to be hit the hardest by anthropogenic global change, many species remain poorly studied. Capensibufo rosei, Rose's Mountain Toad, is a restricted range species that survives in a few small, isolated montane populations in the extreme south-western Cape of South Africa. A recent study of the genus revealed that C. rosei may in fact comprise several cryptic species, with a distinctive lineage potentially being confined to the Cape Peninsula. I test the hypothesis that breeding sites on the Peninsula form a single genetic lineage, but are distinct at a population level due to limited dispersal abilities and little if any gene flow.
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    Demographic and genetic variability in Cape Dwarf Chameleons, Bradypodion pumilum, withink a fragmented, urban habitat
    (2012) Katz, Eric Michael; Tolley, Krystal A; Bishop, Jacqueline M; Altwegg, Res
    Habitat fragmentation is recognized as a primary cause of biodiversity loss. To maximize biodiversity maintenance, researchers in the field of conservation biology often investigate population demography and genetic variability for species inhabiting fragmented landscapes. Findings from such work enable effective conservation management, maximizing viability for potentially imperiled populations. Previous research has relied predominately on spatial analysis when investigating population demography and genetic variability; however, temporal analysis is also important to species conservation. As of 2006, reptiles and amphibians had the highest threat status among small, terrestrial vertebrates, warranting continual investigation of herpetofaunal species inhabiting fragmented landscapes. Of the two, reptiles are the more poorly studied, though are suggested to be equally or more threatened than amphibians. The Cape Dwarf Chameleon, Bradypodion pumilum, exemplifies one potentially threatened reptile species which has suffered habitat loss, due to urbanization, inducing fragmentation and transformation among much of its habitat. As a result, many B. pumilum populations currently exist as a collection of isolated groups inhabiting critically endangered ecosystems.
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    The effects of environment and niche on the distributions of dwarf chameleons, present and future
    (2007) Houniet, Darren; Underhill, Les; Thuiller, Wilfried; Tolley, Krystal A; Midgley, Guy
    The niche and niche breadth of Dwarf Chameleons, Bradypodion, was assessed in terms of broad scale climatic factors. A niche-based modelling method was then used to construct present and future habitat suitability maps for 2050 and 2080, for species in the genus. Additionally, the relationship between environment and morphology was analysed for a representative Bradypodion species, the Cape Dwarf Chameleon, B. pumilum. The niche and niche breadth of species and phylogenetic clades were analysed and described via an ordination technique, the outlying mean index (OMI) analysis. Maxent (v2.3), a presence only niche modelling method, proved very useful in the construction of present and future habitat suitability maps for species within the genus. For analysis of the correspondence between environment and morphology for B. pumilum, regression trees were employed. Rainfall seasonality and maximum annual temperatures were shown to strongly effect the current distributions of the genus Bradypodion at both the species and clade level. Additionally, as closely related species inhabited similar environmental niches, the genus was shown to display a degree of niche conservatism. All species and clades were shown to respond to climate change scenarios for 2050 and 2080, but responses were individualistic. However, most demonstrated range contractions under predicted climate scenarios. Additionally, a strong correlation (p < 0.05) was found between the morphology of B. pumilum and its environment. Environmental factors explained over 40% of the variation in snout-vent length and tail length, and over 20% of the variation in head width and head height, thus supporting the hypothesis of a correspondence between vegetation and morphology in Bradypodion. These results have provided an understanding of the relationship between Bradypodion and their environments that could provide valuable information regarding their ecology. Additionally, the habitat suitability maps for 2050 and 2080 could prove useful in the construction of any future conservation plans for these species. Furthermore, the results support the hypothesis of a correspondence between environmental factors and morphological traits within the genus Bradypodion.
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    Movement of the Cape dwarf chameleon (Bradypodion pumilum): are they vulnerable to habitat fragmentation?
    (2014) Rebelo, Alexander Douglas; Tolley, Krystal A; Altwegg, Res
    Habitat fragmentation threatens the persistence of natural populations globally. Dispersal between populations can mitigate the negative impacts of habitat fragmentation. The Cape dwarf chameleon (Bradypodion pumilum) occupies heavily fragmented habitat and yet few studies have investigated their ability to disperse and thus persist. In this study I monitored chameleon movements and habitat use in the semi-transformed Noordhoek Wetlands, South Africa. Radio-telemetry was used to track adult chameleons (N=11) over 10 days during March 2010 and April 2014. Data were analysed using linear mixed effects models including relevant predictor variables. The chameleon habitat use, such as perch height, thickness and vegetation cover, including their GPS positions, was recorded hourly during the day. The increase in area used by chameleons over time increased at a relatively constant rate. Male and females showed similar areas of utilisation and daily displacement. However, males perched in higher, in less dense vegetation and on relatively thicker stems than females, although the latter two were not statistically supported. Additionally, chameleon vegetation use varied between day and night, but not between early morning, midday and late afternoon, where chameleons perched in higher and less dense vegetation at night than during the day. Habitats surrounded by wide spaces devoid of vegetation could isolate populations of Cape dwarf chameleons. However, the chameleon movement is unhindered by constraints of territory and by connecting habitat fragments together with corridors of suitable vegetation, the effects of fragmentation could be mitigated.
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    A multilocus phylogeny of the world Sycoecinae fig wasps (Chalcidoidea: Pteromalidae)
    (Public Library of Science, 2013) Cruaud, Astrid; Underhill, Jenny G; Huguin, Maïlis; Genson, Gwenaëlle; Jabbour-Zahab, Roula; Tolley, Krystal A; Rasplus, Jean-Yves; van Noort, Simon
    The Sycoecinae is one of five chalcid subfamilies of fig wasps that are mostly dependent on Ficus inflorescences for reproduction. Here, we analysed two mitochondrial ( COI , Cyt b ) and four nuclear genes (ITS2, EF-1α, RpL27a, mago nashi ) from a worldwide sample of 56 sycoecine species. Various alignment and partitioning strategies were used to test the stability of major clades. All topologies estimated using maximum likelihood and Bayesian methods were similar and well resolved but did not support the existing classification. A high degree of morphological convergence was highlighted and several species appeared best described as species complexes. We therefore proposed a new classification for the subfamily. Our analyses revealed several cases of probable speciation on the same host trees (up to 8 closely related species on one single tree of F. sumatrana ), which raises the question of how resource partitioning occurs to avoid competitive exclusion. Comparisons of our results with fig phylogenies showed that, despite sycoecines being internally ovipositing wasps host-switches are common incidents in their evolutionary history. Finally, by studying the evolutionary properties of the markers we used and profiling their phylogenetic informativeness, we predicted their utility for resolving phylogenetic relationships of Chalcidoidea at various taxonomic levels.
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    Phylogeny and codivergence in the fig-fig wasp mutualism : sycoecine and agaondid fig wasps (Chalcidoidea, Hymenoptera) associated with Ficus section Galoglychia (Moraceae)
    (2008) Underhill, Jenny G; Tolley, Krystal A; Hedderson, Terry A; Van Noort, Simon
    The interaction between figs and figs wasps is idealised as a classic example of coevolution through codivergence and cospeciation. Traditionally, the mutualism has been distinguished by a one-to-one ratio of host-specificity, whereby each species of fig tree (Ficlls, Moraceae) is pollinated by a unique species of fig wasp (Agaonidae, Chalcidoidea, Hymenoptera). Recent studies conclude, however, that extreme host-specificity is no longer as ubiquitous as previously considered. Nevertheless, there are many factors that are thought to constrain host-switching events and maintain, to some degree, the host specificity of both pollinating and non-pollinating fig wasps within the fig wasp community. This dissertation investigates the extent of codivergence between the host fig trees of Ficus section Galoglychia, associated agaonid pollinators and sycoecine non-pollinating fig wasps (Pteromalidae, Chalcidoidea, Hymenoptera) through cophylogenetic analysis.
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    The potential impact of climate change on the genetic diversity of the endangered western leopard toad, Sclerophrys pantherina
    (2017) Casola, Sarah; Tolley, Krystal A; Spottiswoode, Claire; Visser, Vernon
    Climate change is now considered to be one of the greatest threats to the persistence of biodiversity. Much work has focused on the potential for climatic shifts to alter species' ranges, phenology, physiology, and behaviour, addressing higher level units of biodiversity from populations to biomes. However, the potential effects of climate change on the most fundamental unit of biodiversity, intraspecific genetic diversity, has only recently received research attention. Studies to date suggest that the accelerated climatic changes we currently face could cause a loss of intraspecific diversity, hampering the ability of populations to respond to further environmental change. Amphibians are considered to be one of the most vulnerable taxa to climate change. The amphibians of the Western Cape of South Africa provide a powerful opportunity to study the impact of climate change on genetic diversity, as many are endemic, threatened, and generally considered to be poor dispersers, limiting their ability to respond to climatic changes through range shifts. This project had two aims: first, to explore the potential impact of climatic shifts on the genetic landscape of the endemic and Endangered western leopard toad, Sclerophrys pantherina, a species with a disjunct distribution on either side of the Cape Flats. Second, I aimed to test the hypothesis that climatic fluctuations drive genetic divergence, a mechanism which may explain the potential overlap of high diversity areas with areas of high climatic instability. Population genetic analyses supported the findings of previous genetic work on S. pantherina, that populations in the Cape Metropole and the Overstrand Municipality (to the west and east of the Cape Flats, respectively) are genetically distinct, and thus should be treated as separate conservation units. Higher haplotype diversity was identified in the populations in the Cape Metropole when compared with the Overstrand, highlighting the importance of urban habitat patches in harbouring diversity in the species. Distinct pockets of low haplotype diversity were identified at Observatory and Hout Bay, suggesting a lack of connectivity between these and adjacent breeding sites, likely due to urban-associated habitat fragmentation. Species distribution modelling revealed that the species could lose a substantial amount of climatically suitable space in its current area of occurrence by 2070. Furthermore, the degree of loss was not uniform across the species' distribution. The populations of the Cape Metropole were predicted to experience greater losses in climatically suitable space than populations in the Overstrand. Additionally, the change in climatic suitability between the mid-Holocene (6,000 years ago) and present as well as the change in suitability between future (2050 and 2070) and present were significant predictors of genetic diversity, where areas of the greatest change in suitability between time periods were associated with the highest genetic diversity. Future efforts to conserve the species should focus on establishing connectivity between breeding sites to allow for the rescue of genetically depauperate sites. Efforts to mitigate the drastic negative effects of climate change predicted by the species distribution models should prioritise the breeding sites in the Cape Metropole, which are both higher in diversity and at greater risk from climate change. Mitigation efforts will likely require the application of engineered solutions to promote the maintenance of suitable wetland habitat for the species.
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    Searching for answers to the silent decline: first estimates of survival and recruitment for the critically endangered Rose's mountain toadlet, Capensibufo rosei
    (2014) Becker, Francois Stephanus; Tolley, Krystal A; Altwegg, Res
    Capensibufo rosei, a critically endangered bufonid found only within Table Mountain National Park, has shown a silent decline over recent decades, despite being found within a protected area with apparently pristine habitat. I estimated the first survival and recruitment rates for the species, using Capture-Mark-Recapture (CMR) methods, over a 7-year period, in order to identify demographic trends over time. I also used covariate models to test whether any observed trends in these demographic parameters were significantly related to variation in rainfall or drought-stress. I found some evidence for an extreme rainfall-induced life-history plasticity, with both survival and recruitment rates covarying closely with rainfall parameters. Although recruitment rate showed a positive relationship with rainfall, the relationship between survival rate and rainfall, specifically during the start of breeding, was negative, with breeding season rainfall explaining 94% of the variability in survival rate over time. I also found evidence to suggest that higher adult survival during poorer breeding rainfall years may be a natural population buffering mechanism to a highly variable microclimate, and that variable rainfall during the start of the breeding season may elicit a variable response in breeding investment by adults. Finally, I found evidence to suggest that the population is small, range-restricted and highly unstable, and that disturbances at the breeding site during good breeding years may cause the population to crash.