1,721,181 research outputs found
Reply to O’Sullivan: Wicked problems demand sophisticated understandings of complexity and feedbacks, not focus on a single variable
No full text[Extract] O’Sullivan (1) both misunderstands and misrepresents our analysis (2). We tested, and found support for, the hypothesis that national economies tend toward one of two attractors because of complex feedbacks among ecosystem services, economic growth, and population growth. We then explored the possible consequences of alternative feedback loops for global sustainability. O’Sullivan seeks to simplify and reframe our analysis as a debate on population growth, ignoring both the thesis of our article and our empirical analysis. While human population growth is an important component of social–ecological sustainability, our analysis also demonstrates empirically that there are other important forces at play, such as changing consumption patterns. Reducing population growth is not a panacea for everything
Linking economic growth pathways and environmental sustainability by understanding development as alternate social-ecological regimes
No full textScientists understand how global ecological degradation is occurring but not why it seems to be so difficult to reverse. We used national-level data and a mathematical model to provide an empirical test of the hypothesis that national economies display two distinct economic regimes that are maintained by self-reinforcing feedbacks between natural resources and society. Our results not only support previous findings that two distinct groups exist, but also show that countries move toward one of these two different equilibrium points because of their different patterns of natural resource use and responses to population growth. At the less economically developed equilibrium point maintained by "green-loop" feedbacks, human populations depend more directly on ecosystems for income. At the more economically developed equilibrium point maintained by "red-loop" feedbacks, nonecosystem services (e.g., technology, manufacturing, services) generate the majority of national gross domestic product (GDP), but increasing consumption of natural resources means that environmental impacts are higher and are often exported (via cross-scale feedbacks) to other countries. Feedbacks between income and population growth are pushing countries farther from sustainability. Our analysis shows that economic growth alone cannot lead to environmental sustainability and that current trajectories of resource use cannot be sustained without breaking feedback loops in national and international economies
A multi-scale study on the movement ecology of Afrotropical waterbirds
No full textUnderstanding the processes and mechanisms governing animal movement is a fundamental goal in ecology. Processes driving movement can occur across multiple spatiotemporal scales and have important consequences for the structure and dynamics of populations, communities and ecosystems. The study of movement provides insights into the ecological resources and habitats necessary for persistence of species and communities. It also provides a theoretical and applied basis from which to formulate informed conservation plans. Waterbirds in semiarid southern Africa are an ideal study group for understanding interactions between movement and environmental factors because they exhibit a wide range of movement strategies and are located within a landscape in which resources are characterised by high levels of spatiotemporal variability. Emphasis has been placed on understanding movement phenomena from individually-tracked animals, but cases which consider this approach in conjunction with traditional community ecology perspectives are rare. In this thesis I explored questions of movement in both individuals and communities, and argue that an integrated multi-scale approach is necessary to advance our broader understanding of movement in waterbirds. In the first part of the study I addressed an individual-level movement perspective. I used fine-scale telemetry data from 35 individually tracked Egyptian Geese Alopochenaegyptiaca and Red-billed Teal Anas erythrorhyncha with novel analytical techniques to explore questions of trade-offs in habitat selection, functional responses and whether movement responses to landscape resources are reactive or prescient. My findings suggested that, at the home-range scale, both forage optimisation and predation risk were limiting factors of movement and habitat selection of Egyptian Geese. I also showed for the first time that waterbirds exhibit functional responses in relation to changes in the availability of habitat types. I subsequently showed that the proximate drivers of waterfowl movement are the dynamics of rainfall and primary productivity. Egyptian Geese and Red-billed Teal were able to perceive and respond to temporal shifts in resource conditions prior to habitat patch occupation. This in turn suggested that their movements in semi-arid landscapes are underpinned by an intimate knowledge of the local environment and that waterfowl exhibit a complex behavioural movement strategy. In the second part of the study I used waterbird count data collected from wetlands in KwaZulu-Natal, South Africa, to address the community-level movement perspective
Using real-time forest loss alerts and global deforestation maps to assess the effectiveness of Africa's tropical protected areas
No full textTropical rainforests harbor a significant portion of the world's remaining biodiversity. Having undergone rapid changes in forest cover over the last two decades, a large amount of irreplaceable biodiversity has been lost. The establishment of protected areas has been a key strategy to hinder the loss of tropical forests and biodiversity. However, the effectiveness of designating protected areas has been called into question, particularly in regions such as tropical Africa where widespread conditions of poverty, rapid population growth and political instability are evident. Quantitative measurements of park effectiveness for forest conservation are urgently needed, however accurate inferences concerning park effectiveness across broad regions is difficult. Whilst remote sensing techniques have been proposed as a practical solution, the intensity of data processing has made it untenable until recently. Here, I use remote-sensing methods to analyze high-resolution satellite imagery of tropical forest loss (as a proxy for tropical deforestation) within and outside 224 parks across 23 countries in Africa. I compare the extent of tropical forest loss inside parks to outside of them to show that the majority of African parks in the Subtropical and Tropical Moist Broadleaf forest biome are effective in curbing forest loss within park boundaries. However, certain parks were more effective in forest conservation than others. Whilst smaller parks were less effective at preventing forest loss inside park boundaries than larger parks, older parks were less effective than younger parks. Furthermore, parks of varying IUCN management categories exhibited negligible differences in forest loss between one another. Lastly, significant geographical variations in park effectiveness existed: West African parks exhibited the most forest loss within park boundaries and Central African parks exhibited the least. My results demonstrate the complexity of factors which influence a park's ability to curb forest loss within its boundaries. Furthermore, this study is the first bioregional-wide assessment of park effectiveness using remote sensing. These results supplement scarce literature on tropical deforestation in Africa and demonstrate the potential of using remote satellite imagery for measuring the relative impact of park establishment on forest conservation in this region
The influence of location on the structure and functioning of private land conservation networks in the Western Cape province of South Africa
No full textProtected areas are an important tool for biodiversity conservation. Statutory protected areas are, however, perceived to currently be insufficient in extent and functioning for achieving conservation goals. Conservation action on privately owned land plays an increasingly vital role in expanding the global conservation estate. Private Land Conservation Areas (PLCAs) exist with internal properties and external contexts and do not occur isolated in space and time. They can thus best be described as linked social-ecological systems. Little comprehensive work has yet been done concerning the structure and functioning of PLCAs. However, an understanding of their emergence, long-term persistence and contribution to conservation is highly relevant. How can PLCAs maintain their identity against disturbances in order to be resilient into the future? Spatial patterns and relationships determine the answer to this question. Geographical location influences the private conservation estate through different drivers, namely biophysical conditions, network connections and membership, as well as socio-economic conditions. I thus used a comparative, spatially explicit and holistic approach to better understand spatial resilience of PLCAs in the Western Cape Province of South Africa as case study region. The approach was based on assessing representative measures for four elements of system identity (being components, relationships, sources of continuity, and sources of innovation). I expected that geographical location and spatial variation in social-ecological factors strongly influence PLCA types, socio-economic interaction networks among protected areas and other stakeholders, contribution to conservation by PLCAs and their ecotourism performance. Information and data for this research were obtained from personal interviews conducted with owners and managers of 70 PLCAs across the province. Additional data were derived via conservation authorities and online tools. My findings show that the identity and resilience of PLCAs are strongly dominated by the influence of spatial location and heterogeneity in factors such as ecological features or socioeconomic context. I was able to verify existing PLCA types, namely game and habitat reserves, which strongly depended on the biophysical context. Visitation rates were influenced by location which determined the adopted corporate model of PLCAs. Clear neighbourhood effects emerged in socioeconomic interaction networks, which further highlighted great potential to enhance collaboration across scales. PLCAs provided a substantial contribution to conservation targets in terms of importance (covering critical biodiversity areas) and urgency (protecting ecosystems of threatened status). My findings will be valuable to highlight opportunities for more effective conservation in the study region, and to advance insights into the spatial resilience of social-ecological systems
The role of waterbirds in the dispersal of aquatic organisms in southern Africa
No full textDispersal is a fundamental process with far-reaching ecological and evolutionary consequences. Not all organisms are capable of dispersing on their own and instead produce propagules that must be transported to new habitat by a vector. Propagule dispersal by frugivorous bird species is well researched, but only very recently has the capacity of highly mobile waterbirds to disperse aquatic organisms received similar attention in the dispersal literature. Dispersal is important for the organisation of communities, and therefore understanding the frequency and scale of waterbird-mediated dispersal provides insight into the structure of wetland communities. Additionally, the study of waterbird-mediated dispersal in arid southern Africa provides an opportunity to expand our knowledge on the persistence of populations of aquatic organisms in heterogeneous environments. Recently, field and laboratory studies have demonstrated the remarkable ability of waterbirds to disperse the propagules of both plants and aquatic invertebrates. However, these studies have largely been based in the northern hemisphere and many have focussed on long-distance dispersal by migratory waterbirds. Therefore, it is difficult to generalise how waterbird-mediated dispersal plays out in different landscapes and throughout the annual cycle. Furthermore, there is still little knowledge of the spatial patterns of propagule dispersal and the mechanisms that cause these patterns to vary in space and over time. This thesis aims to addresses several of these knowledge gaps in waterbird-mediated dispersal and presents the first detailed study of propagule dispersal by waterbirds anywhere in Africa. In Chapters 2 - 5, I adopt a field- and experimental-based approach to develop a general understanding of waterbird-mediated dispersal in southern Africa. Firstly, making use of faecal samples and feather brushings collected from several waterfowl (duck) species at three locations in South Africa, I determine the quantity and viability of propagules transported via endozoochory and ectozoochory. I then assess the relative contributions of each dispersal mode to the dispersal of plants and aquatic invertebrates in the field. I show that endozoochory is the dominant dispersal mechanism, but it may be complementary to ectozoochory as different propagules are transported via this mode. Secondly, by making use of an experimental feeding trial with two captive waterfowl species, Egyptian Goose and Red-billed Teal, I explore how seed traits mediate a trade-off in recoverability and germinability against gut retention times. I show that small, hard-seeded species are retained for longer and therefore may be dispersed further. Thirdly, I incorporate gut retention time data and Egyptian Goose and Red-billed Teal movement data, acquired from GPS satellite transmitters across five study populations in southern Africa, into a mechanistic model to explore spatial patterns of seed dispersal. The model demonstrates that waterfowl generally facilitate dispersal on the local scale of below 5 km, but on occasion can transport seeds as far as 500 km from a seed source. There was variation in dispersal distances between the vectors and across the study populations and the results indicate that dispersal is affected by both intrinsic and extrinsic drivers of animal movement. In Chapters 6 and 7, I apply the concept of waterbird-mediated dispersal more broadly to address (1) the role of waterbirds in the dispersal of aquatic invaders; and (2) the determination of seed dispersal functional groups amongst a waterfowl community. I conducted a literature review to objectively describe the role of waterbirds in the dispersal of aquatic weeds. Waterbirds are important vectors of aquatic invasive species and consideration of the spatially explicit manner in which birds move is imperative to our understanding of invasive spread. In the second case, I used diet data from the 16 waterfowl species indigenous to southern Africa to explore whether finer level seed dispersal functional groups were evident. I found support for several functional groups of seed disperser based on unique plant families in the diet and suggest that important functional differences do occur between groups of waterfowl species
Human networks of tetrapod translocations in the Western Cape, South Africa: trends and potential impacts on biodiversity
No full textIncludes abstract.Includes bibliographical references.Global trends show an increase in wildlife trade associated with the process of globalisation and increased international trade. In addition, biodiversity managers are increasingly turning to species translocations to achieve conservation goals. These human induced movements of wildlife have a number of potential impacts, one being the introduction of non-native species that may establish and become invasive. Although the underlying mechanisms are debated, it is accepted that invasive species are having detrimental effects on biodiversity worldwide
Using stable isotopes to trace the movements of ducks in southern Africa
No full textIncludes bibliographical references.Despite the importance of movement ecology studies, the field faces a prevailing challenge of methodological limitations in tracking individual organisms. This research investigated the utility of the stable isotope technique to trace movements of ducks in southern Africa. I sampled and analysed feathers of ten duck species for stable isotope proportions of Carbon (δ13C), Nitrogen (δ15N) and Hydrogen (δD), from five wetlands (Strandfontein and Barberspan in South Africa, the Manyame catchment in Zimbabwe, Lake Chuali in Mozambique, and Lake Ngami in Botswana) as test cases.Sampling was carried out at different seasons to account for seasonal isotope signature variations. Isotope signatures of feathers grown at different moulting locations were compared to test whether southern Africa shows stable isotope spatial patterns (distinct isotopic regions). Feathers grown at different life-phases were compared to test whether different sites had been used and if more mobile species showed more and stronger isotope distinctions. Finally, growing flight feathers grown at moulting locations were compared across species to query how much information on diet and foraging behaviour can be inferred from southern African duck feather stable isotopes.Feather isotope signatures were distinct by site in at least one of the tested isotopes, for the majority of ducks tested. Strandfontein had more and stronger distinctions of isotope signatures between feathers grown at different life phases. This site is the closest to the sea and most likely to have marine-influenced isotope signatures especially in δ15N, it falls within the Mediterranean climatic conditions experiencing winter rainfall unlike all the other sites. Vegetation compositions (C3 and C4 plant distributions) therefore vary across sites influencing δ13C patterns. More mobile species (only Egyptian Goose Alopochen aegyptiacus from Strandfontein, and Cape Shoveler Anas smithii from Barberspan; determined by mobility scores from other studies) had more and stronger distinctions between flight and body feathers. All the other species did not comply with mobility scores. They showed weaker and fewer tissue signature distinctions than their mobility scores suggested. There were high isotopic signature overlaps in δ13C and δ15N across and within feeding guilds at each moulting site implying dietary overlaps during moulting. More overlaps occurred during the dry seasons (summer in Strandfontein and winter in Lake Chuali, Manyame catchment site, and Lake Ngami). Higher isotopic variances (higher dietary flexibility) were associated with isotope signature divergence to mobility scores especially in Cape Teals and Yellow-billed Ducks.The isotope technique is flawed with uncontrollable sources of variation which potentially confound movement inferences. It is best used when accompanied by conventional methods to detect and counter against species specific biology and dietary behaviour imposed biases in tissue isotope signatures. Further research on how species specific biological processes affect the reflection of spatial patterns of isotopes in feathers is recommended. Multi-isotope time explicit approaches and trace element analysis were also recommended. Scientists should be wary about basing management strategies or building theory about movement patterns of species based on the technique at least in stochastic environments such as southern Africa. My results provide empirical evidence that the technique is unreliable at this scale of analysis. In particular, the majority of ducks in this region are not good candidates for use of isotopic signatures in distinguishing movement patterns of southern African ducks.498
Implications of agricultural transitions and urbanization for ecosystem services
No full textHistorically, farmers and hunter-gatherers relied directly on ecosystem services, which they both exploited and enjoyed. Urban populations still rely on ecosystems, but prioritize non-ecosystem services (socioeconomic). Population growth and densification increase the scale and change the nature of both ecosystem- and non-ecosystem-service supply and demand, weakening direct feedbacks between ecosystems and societies and potentially pushing social-ecological systems into traps that can lead to collapse. The interacting and mutually reinforcing processes of technological change, population growth and urbanization contribute to over-exploitation of ecosystems through complex feedbacks that have important implications for sustainable resource use
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