Browsing by Author "Mokhatla, Mohlamatsane McDonald"

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    Evaluating the effects of changing global climate on amphibian functional groups of southern Africa: an ecophysiology modelling approach
    (Stellenbosch : Stellenbosch Univesity, 2018-12) Mokhatla, Mohlamatsane McDonald; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Global climate change is suggested to be one of the leading threats to anuran diversity by the end of the century. This is largely because, compared to other vertebrates, anurans have characteristically small distribution ranges and limited dispersal abilities, making them particularly vulnerable to climate change. To predict how climatic changes may impact species, biologists have used correlative-based species distribution models (SDMs). However, correlative-based SDMs have been criticised for their simplistic approach of correlating known distributions with climatic variables, and thus not accounting for other process-based variables that determine distributions such as physiology, performance and morphology. Using a multi-disciplinary approach, the aim of this study is to synergise data from multiple lines of evidence and incorporate them into SDMs to aid in accurately predicting the responses of southern African amphibians with different life-history traits to climate change. In chapter two, I used correlative-based SDMs to determine the impact of past (LGM: Last Glacial Maximum, HGM: Holocene Glacial Minimum) and future (2080) climate change on species distribution ranges of 37, narrowly distributed Cape Floristic Region (CFR) anuran fauna. I found that the biotic velocity at which the CFR anuran community is expected to shift North and East far exceeds historical rates. These models further suggest that the CFR anuran community has already lost ≈ 56% of suitable climate space since the LGM and this is expected to accelerate under future emission scenarios. Chapter three assessed the impacts of climate change on the distribution ranges of three widely distributed anuran species with different ecological specialisations: Xenopus laevis, Amietia delalandii and Sclerophrys capensis. Although all three species have lost suitable climate since the LGM, the models further suggest that A. delalandii is expected to gain suitable climate space by 2080, at least under two GCMs namely, CCSM (25%) and MPI-ESM (7%), while S. capensis and X. laevis are expected to lose suitable climate space by 2080. In chapter four, I examined how changes in ambient temperature (Ta) and body mass (Mb) affect body temperature (Tb), standard metabolic rates (SMR) and evaporative water loss (EWL). I found that Tb, whole-animal EWL and whole-animal SMR increased with an increase in temperature. Body temperature increased with an increase in Mb in A. delalandii and S. capensis but not in X. laevis. Wholeanimal SMR increased with an increase in Mb in S. capensis only. Chapter five examined the impact of temperature on i) burst swimming and hopping (velocity and acceleration) and hoppping endurance (distance and time) in the same three frog species. Here, I show that temperature changes affect thermal reaction norms only in terrestrial performance traits. Furthermore, A. delalandii outperformed X. laevis in both speed and acceleration traits in both burst swimming and hopping experiments, despite X. laevis being adapted to an aquatic lifestyle. Lastly, I implemented ecophysiology models using the results of the temperature-trait relationships obtained in chapter four and five by constructing spatially explicit surface models which were used as input layers in Maxent. Following the same methods as in chapter three, I found that ecophysiology modelling techniques accurately predict current distributions of these widely distributed African anurans. Although species have lost suitable climate space in the past, models predict that A. delalandii will gain thermally suitable space by the year 2080 while X. laevis is also expected to gain suitable thermal space only under MPI-ESM GCM. Sclerophrys capensis is expected to lose suitable climate space in the same period under all GCMs. In conclusion, I showed that although correlative-based SDMs are useful, bottom-up trait-based techniques such as ecophysiology models improves our understanding on how large-scale climate variables affect key physiological traits in shaping what we observe at species distribution level. In addition to biological traits and ecological specialisations, the incorporation of climate variation in modelling processes is also a necessary aspect, given that we have no clear understanding of how climate change will eventually take place.