Browsing by Author "Cunningham, Susan"

Now showing 1 - 8 of 8
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    Are local range expansions in southerly populations of Aloidendron dichotomum early indicators of a future range shift?
    (2019) Grey, Kerry-Anne; Cunningham, Susan; Midgley, Guy; Foden, Wendy
    Aloidendron dichotomum is predicted to undergo a south and south-eastern range shift in response to anthropogenic climate warming. Despite this, its range is suggested to be limited by low temperature extremes at the cool range edge and no such range shift has yet been confirmed. However, eco-physiological knowledge necessary to predict and detect this range shift is lacking. This study aimed to determine whether physiological performance of A. dichotomum differs at a regional and local scale, and if so, whether regional and local temperatures explain physiological differences. Performance metrics and temperature data were collected during summer at 14 microsites in two sites at the cool range edge of A. dichotomum. Microsites were stratified by aspect and elevation. This study confirmed that A. dichotomum is performing CAM photosynthesis at its cool range edge. Further, the results provide evidence for the temperature dependence of A. dichotomum’s physiological performance. Higher performance was associated with warmer nights and the warmer north facing slopes. This is in keeping with our hypothesis that A. dichotomum individuals at the cool range edge would take advantage of higher temperatures more typical of their core range areas. Opposing this, higher carbon gain was found at Gannabos - the cooler of the two study sites. This may be due to the less variable rainfall pattern at Gannabos. Furthermore, performance was higher on the flats where temperatures were also cooler. This may be due to lower water runoff on the flats compared to the slopes. As a result, I suggest that the cool range edge of A. dichotomum is limited both by low temperatures and rainfall variability and that, with warming, constraints on these populations are being removed. This is substantiated by the observed high levels of juvenile recruitment in these populations relative to others, and in time, is likely to lead to range expansion in the region.
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    Assessing the climate change vulnerability of reptile and amphibian species found in Table Mountain National Park
    (University of Cape Town, 2020) Harper, Jack; Cunningham, Susan; Foden, Wendy; Van Wilgen, Nicola
    It is increasingly apparent that climate change and its associated impacts are a major threat to the rich biodiversity of the Cape floristic region. As the knowledge of the associations between biological traits and climate change impacts strengthens it has become clear that the assessment of climate change vulnerability is a key consideration in the management of biodiversity. This study is the first attempt to use a trait-based approach at the scale of a single national park, focusing on the climate change vulnerability of reptile and amphibian species found in Table Mountain National Park (including historically present species). The park and its immediate surrounding areas are home to a rich diversity of herpetofauna including the Critically Endangered Table Mountain ghost frog (Heleophryne rosei), Rose's mountain toadlet (Capensibufo rosei) and micro frog (Microbatrachella capensis), and the Endangered western leopard toad (Sclerophrys pantherina). Amphibian and reptile-specific assessment frameworks of biological and ecological traits were designed to identify the species most sensitive and least able to adapt to climate change pressures. Using a combination of a literature review and expert consultation, 18 species of amphibian and 41 species of reptile were assessed. The assessment highlighted that, in the worst-case scenario, 85% of the park's reptile species and 67% of the park's amphibian species are predicted to be highly vulnerable to climate change. The southern adder (Bitis armata), Cape long-tailed seps (Tetradactylus tetradactylus), Table Mountain ghost frog (Heleophryne rosei) and the Lightfoot's moss frog (Arthroleptella lightfooti) were identified as being the species most vulnerable to climate change within their respective taxa. All three of the Critically Endangered amphibian species were identified as having both high sensitivity and low adaptive capacity to climate change. Among the focal reptile species, climate change vulnerability was independent of current IUCN Red List status, highlighting that species currently not identified to be under threat by other anthropogenic pressures could imminently become threatened by climate change. Spatiallyexplicit presentation of the assessment output will help prioritise the management of areas within Table Mountain National Park that contain a high diversity of climate-vulnerable species. By reducing the threats from other human-associated impacts to these species, and by identifying when direct intervention is appropriate, the park's management can give these species the best opportunity of persistence in an uncertain climate future.
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    Fluctuating human activity and associated anthropogenic food availability affect behaviour and parental care of Red-winged Starlings
    (2018) Catto, Sarah; Cunningham, Susan; Amar, Arjun; Sumasgutner, Petra
    Increased food availability associated with urbanisation is widely recognised as one of the key factors influencing avian demography. Temporal fluctuations in food availability, tied to variation in human presence, are of particular interest as they occur frequently in urban environments, but their impacts on the survival and reproduction of birds have not been particularly well-studied. In this study, I explored whether breeding Red-winged Starlings at a university campus in Cape Town, South Africa alter their behaviour and parental care of nestlings in response to fluctuating numbers of people and associated food over a relatively short timescale. I used data from nest watches and behavioural observations collected during both incubation and nestling periods to test whether differences in food availability due to day status (week days with thousands of students present versus weekends with substantially fewer students) affected a number of behaviours related to parental care. I found that, with less available food on weekends, parent birds appeared to trade off feeding their offspring for maintaining their own energetic requirements, meaning that nestlings received less food on weekends. I also found that parents preferentially fed their nestlings natural food on week days, despite an increased availability of anthropogenic food. This suggests that, with increased food availability, birds in this system may use anthropogenic food to supplement their own diets, allowing them to prioritise the feeding of natural food to their chicks. These results provide evidence that fluctuating food resources impact the behaviour and parental care of starlings, but it is still unclear what effect they have on the individual health of adult birds and their developing young. To further enhance our understanding of some of the ecological implications of urbanisation, future research should prioritise understanding the potential health impacts such a variable urban diet may have on the birds exploiting it.
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    Heat tolerance of Southern Pied Babblers in the Kalahari Desert : how will they respond to climate change?
    (2011) Du Plessis, Katherine; Hockey, Phil A R; Ridley, Amanda; Martin, Rowan; Cunningham, Susan
    An increasing incidence of mass mortalities of birds in hot deserts suggests that birds may be appropriate candidates for assessing how natural selection, under the influence of climate change, drives adaptation. ... The effects of ambient temperature on daily weight gain, foraging effort and efficiency and the presence of heat-dissipation behaviours were assessed to determine the mechanisms by which increased temperature affect babbler body condition.
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    How common ravens (Corvus corax) exploit anthropogenic food sources through time and space in a semi-transformed, alpine environment
    (2021) Jain, Varalika; Sumasgutner, Petra; Cunningham, Susan; Bugnyar, Thomas; Loretto, Matthias
    From large-scale agriculture and farming to concentrated fishing discards, garbage dumps, game carcasses and bird feeders, human action has been increasingly affecting natural systems and animal species through the deliberate and unintentional provisioning of food resources. Anthropogenic food sources (AFSs) are often more spatially concentrated, easily accessible, abundant and stable than natural food sources. The common raven, Corvus corax, is a behaviourally flexible and ecologically adaptable species that has managed to thrive in human transformed landscapes by exploiting these anthropogenic sources of food. The aim of this research was to investigate how raven individuals vary in their use of different AFSs through space and time. I used data from a long-term GPS tracking initiative in the Upper Austrian Alps to investigate (1) the space-use of non-breeding raven individuals across this landscape to answer the questions: (2) what types of AFSs are most extensively used by ravens in this landscape, and what factors predict individual variation in AFS use (i.e., apparent reliance on and access to resources), specifically (3a) the number of AFSs visited and (3b) the probability of being at AFSs at any given point in time. Movement patterns can reveal information on the foraging decisions made by individuals, including how they use different AFSs. Non-breeding raven individuals exhibited great variation in how they moved around and used the landscape. The number of AFSs visited, but not the probability of being at an AFS (at any given point in time), varied among individuals with different ranging behaviour and of different age class (i.e., juvenile and adults) and origin (i.e., captive-bred-released and wild-caught), suggesting that experience affects AFS-use. Non-breeders differed in their use of AFSs by season, visiting the highest number of AFSs but having the lowest probability being present at an AFS in winter, potentially indicative of high foraging competition under stressful environmental conditions. They were also found to extensively exploit resources in spring, both visiting high numbers of AFSs and having a high probability of being present at an AFS, perhaps due to decreased competition (e.g., from breeders) and increases in food availability. The category (i.e., wildpark, refuse site, hut) of AFSs also influenced the probability of an individual being present at the site, likely because of differences in resource quality, quantity and replenishing rate. A very few foraging sites were highly popular, while over half attracted less than 5 individuals throughout the study. By exploiting AFSs, raven population numbers have increased across their range, raising conservation concerns (i.e., predation on threatened species and human-wildlife conflict). With a better understanding of the patterns of AFS-use and the factors influencing these patterns, I suggest that strategies to manage ravens in this semi-transformed, alpine environment should focus on controlling the supply of food at AFSs at a regional scale.
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    The influence of temperature on parental investiment in Common Fiscal and consequences for nestling growth
    (2014) Sadondo, Phenias; Cunningham, Susan; Martin, Rowan; Ryan, Peter G
    Global climate models project a 1.5-4oC increase in the Earth’s temperature by 2100. Africa, especially southern Africa, is expected to experience not only an increase in average temperatures but also an increase in the frequency and duration of extreme temperature events. Increasing temperatures will result in increased vulnerability to heat and drought stress to biodiversity. A recent paper by Cunningham et al. (2013) showed that temperature has a negative effect on daily mass gain in the nestlings of Common Fiscal (Lanius collaris) breeding in the southern Kalahari. This effect may be driven by parents modifying their provisioning rates at high temperature, but the mechanisms underpinning the relationship are not known. I investigate the influence of temperature on parental investment in Common Fiscal and the consequences of high temperatures for nestling growth using data from videos that were filmed in the Kalahari, Northern Cape, South Africa. Daily mass gain by nestlings increased with increasing provisioning rate and decreased in relation to the proportion of time chicks spent panting. Prey provisioning decreased with temperature in larger broods, however, there was no evidence to suggest that parents trade off provisioning and nest attendance. This might mean that prey availability is reduced at high temperatures, or that parents prioritise their own thermoregulation over provisioning.
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    Physiological tolerances of high temperatures in Fynbos birds: implications for climate change
    (2014) Milne, Robyn; Ryan, Peter G; Cunningham, Susan; Alan, Lee; Smit, Ben
    Climate change is a reality. Numerous biological systems have already responded to changes in climate, with range shifts towards higher latitudes and altitudes being one of the most common responses to climate warming. Bioclimatic envelope modelling provides a useful method for predicting a species, future distribution under a given climate change scenario. However, these models require verification with empirical evidence, including physiological information. Endotherm species (such as birds) have a thermal neutral zone (TNZ) which reflects the range of environmental temperatures over which minimal energy is required for thermoregulation. At temperatures above the TNZ, birds expend extra energy to facilitate evaporative water loss in order to maintain a stable body temperature, while some species increase their body temperature to conserve water. The increased costs of thermoregulation at temperatures above the TNZ can impair fitness, which could have implications for population persistence under climate change. The Fynbos biome of South Africa is a biodiversity hotspot and is home to a rich birdlife, including six endemic bird species. Climate change models predict an increase in temperature for this biome, which may alter the ranges of many of these species, resulting in a loss of species richness and diversity. Recent MaxEnt bioclimatic envelope modelling suggests that some Fynbos bird species may be range-restricted by temperature, while others are more likely limited by other bioclimatic variables (e.g. rainfall). These data require physiological verification.
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    The breeding ecology and behavioural adaptations of African black oystercatchers in light of climate change
    (2021) Azaki, Bukola Debola Aderewa; Underhill, Leslie; Cunningham, Susan
    This thesis examined how weather conditions and other environmental factors influence the vulnerability of nesting African Black Oystercatchers Haematopus moquini (oystercatchers) to climate and habitat change. I explore, for the first time, the behavioural adaptations used by the species to cope with breeding in a limited strip of beach, between high tides and terrestrial predators, and with little nesting shelter, and their breeding decisions to maximise breeding outcomes. Behavioural and breeding data were collected over three breeding seasons (2016—2018) on Robben Island, South Africa (a site with about 5% of the global population of the species) using time-lapse digital cameras and direct observations. Climate and environmental variables were obtained either through on-site iButton data loggers or from the relevant South African meteorological agencies. The results show that oystercatchers are vulnerable to increasing heat loads as temperature increases. However, oystercatchers used a suite of thermoregulatory behaviours to cope with a wide range of environmental temperatures and decreased the length of their incubation bouts as temperature increased. The proximity of the oystercatchers' breeding site to the ocean appears to contribute significantly to their capacity to cope with increasing heat loads. But such sites potentially expose the oystercatchers to the risk of nest losses to storm surges. Oystercatchers reduced this risk by using habitat selection to optimise the placement of their nests close to the midpoint of the beach, but some were constrained by the narrowness of their territories. Oystercatchers also used the biweekly semilunar spring tide cycle to synchronise the incubation start date of their clutches probably to minimise the number of spring tides that they experience during incubation. Predation was the main cause of oystercatcher nest failure. Surprisingly, Mole Snakes Pseudaspis cana were responsible in all cases where the predator identity was known rather than Kelp Gulls which have historically been suggested to be the main agent. Nest predation probability was influenced by temperature and distance to predator-concealing vegetation and increased as more nests became available, causing a seasonal decline of nest survival. Hence, oystercatcher pairs laying large clutches early in the season were more likely to produce one juvenile in a season. The average number of fledgelings per pair per season was 0.38 and close to that (0.35) required to maintain a stable population. These findings improve our understanding of the breeding ecology and behavioural adaptations of the oystercatchers which might help them to cope with climate change as well as provide new insights on which management decisions and further studies can be based.