Browsing by Author "Treurnicht, Martina"
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- ItemDemographic and functional determinants of large-scale population dynamics and ecological niches of 26 serotinous Proteaceae(Stellenbosch : Stellenbosch University, 2018-03) Treurnicht, Martina; Schurr, Frank M.; Pagel, Jorn; Esler, Karen J.; Slingsby, Jasper A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Understanding how organisms respond to the environment at large spatial scales is central to ecology, biodiversity research and conservation. Environmental variation affects the fitness (or performance), population dynamics and geographical distributions of species via morphological traits. Quantifying how demographic rates and functional traits vary across environmental gradients may thus yield insights into the underlying determinants of ecological performance and geographical distribution. However, studies of demographic and trait variation widely rely on observations from a few species, at small spatial scales and seldom include multiple abiotic and biotic drivers. A basic understanding of the drivers of large-scale demographic variation and how functional traits relate to population dynamics and species’ niches remains limited. Using the Hutchinsonian niche concept (i.e. the set of environmental conditions in which populations can grow), I investigated how environmental conditions and functional traits affect the demography, population dynamics and ecological niches of 26 serotinous Proteaceae species with fire-dependent life cycles from the Cape Floristic Region (South Africa). My objectives were to: (i) identify the environmental drivers of large-scale demographic variation, (ii) investigate whether plant functional traits explain demographic performance and Hutchinsonian niches, and (iii) study geographical variation in population sensitivity to wildflower harvesting. I addressed these objectives using data on key demographic rates and plant functional traits sampled across species’ entire geographical ranges. Environmental drivers (climate, fire disturbance, soil nutrient status and population density) explained variation in key demographic rates of reproduction and survival across species’ geographical distributions. The relative importance of these drivers varied throughout the life cycle of the study species: fecundity was mostly driven by fire interval whereas recruitment depended more on climate. A trade-off between survival and reproduction was also found where species with fire-protected buds (resprouters) had substantially higher fire survival compared to species without fire-protected buds (nonsprouters). Overall, intraspecific variation in fecundity and recruitment was greater than that of fire survival. I also investigated whether variation in functional traits (leaf, plant-architectural and seed traits) explains the Hutchinsonian niches of species. Results showed that interspecific trait variation explained considerable variation in global maximum population growth rates (rmax), as well as niche optima and widths along different environmental gradients. Intraspecific trait variation had positive effects on niche widths. Overall, relatively few individual traits stood out as predictors of species’ demographic niches. Finally, I integrated range-wide demographic data and dynamic population models to assess spatial variation in sensitivity to harvesting across species’ geographical distributions. I detected considerable variation in sensitivity to harvesting across species and populations. Range-wide intraspecific variation in sensitivity to harvesting showed distinct geographical and environmental relationships. Notably, sensitivity to harvesting was highest at the environmental limits of species’ ranges. Combined, these range-wide demographic and functional approaches on species niches provide fundamental and applied perspectives in ecology and conservation biogeography. These are necessary steps to understand how range dynamics emerge from variation in demography and functional traits, and how species may be affected by ongoing global change.
- ItemRange-wide population viability analyses reveal high sensitivity to wildflower harvesting in extreme environments(Wiley Online, 2021) Treurnicht, Martina; Schurr, Frank M.; Slingsby, Jasper A.; Esler, Karen J.; Pagel, JornAbstract 1. The ecological effects of harvesting from wild populations are often uncertain, especially since the sensitivity of populations to harvesting can vary across species’ geographical ranges. In the Cape Floristic Region (CFR, South Africa) biodiversity hotspot, wildflower harvesting is widespread and economically important, providing an income to many rural communities. However, with very few species studied to date, and without considering range-wide sensitivity to harvesting, there is limited information available to ensure the sustainability of wildflower harvesting. 2. We studied geographical variation in sensitivity to wildflower harvesting for 26 Proteaceae shrubs with fire-driven life cycles using population viability analyses. We developed stochastic, density-dependent population models that were parameterized from individual demographic rates (adult fecundity, seedling recruitment and adult fire survival) and local environmental conditions across the geographical ranges of the study species. We then simulated the effects of harvesting on populations in different environments across species ranges. Our model simulations predicted extinction risk per population, and we derived extinction probabilities over 100 years in response to different harvesting regimes. We used these population-level extinction probabilities to quantify inter- and intraspecific variation in sensitivity to wildflower harvesting, and to explore how geographical variation in sensitivity depends on environmental conditions (climate, soil fertility and fire disturbance). 3. We detected considerable inter- and intraspecific variation in sensitivity to wildflower harvesting for the 26 study species. This held for both ‘nonsprouters’ and ‘resprouters’ (species with low and high fire persistence ability, respectively). Intraspecific variation in sensitivity to harvesting showed varying geographical patterns and associated with environmental variation. Notably, sensitivity was high towards range edges and at the climatic extremes of species ranges, respectively. 4. Synthesis and applications: We show the importance of combining spatial demographic data, density-dependent population dynamics and environmental variation when assessing sensitivity to harvesting across species geographical ranges. Our findings caution against the application of general harvesting guidelines irrespective of species, geographical location or local environmental conditions. Our range-wide population viability analyses provide insights for developing species-specific, spatially nuanced guidelines for conservation management. Our approach also identifies species and areas to prioritise for monitoring to prevent the overexploitation of harvested species. Abstract 1. The ecological effects of harvesting from wild populations are often uncertain, especially since the sensitivity of populations to harvesting can vary across species’ geographical ranges. In the Cape Floristic Region (CFR, South Africa) biodiversity hotspot, wildflower harvesting is widespread and economically important, providing an income to many rural communities. However, with very few species studied to date, and without considering range-wide sensitivity to harvesting, there is limited information available to ensure the sustainability of wildflower harvesting. 2. We studied geographical variation in sensitivity to wildflower harvesting for 26 Proteaceae shrubs with fire-driven life cycles using population viability analyses. We developed stochastic, density-dependent population models that were parameterized from individual demographic rates (adult fecundity, seedling recruitment and adult fire survival) and local environmental conditions across the geographical ranges of the study species. We then simulated the effects of harvesting on populations in different environments across species ranges. Our model simulations predicted extinction risk per population, and we derived extinction probabilities over 100 years in response to different harvesting regimes. We used these population-level extinction probabilities to quantify inter- and intraspecific variation in sensitivity to wildflower harvesting, and to explore how geographical variation in sensitivity depends on environmental conditions (climate, soil fertility and fire disturbance). 3. We detected considerable inter- and intraspecific variation in sensitivity to wildflower harvesting for the 26 study species. This held for both ‘nonsprouters’ and ‘resprouters’ (species with low and high fire persistence ability, respectively). Intraspecific variation in sensitivity to harvesting showed varying geographical patterns and associated with environmental variation. Notably, sensitivity was high towards range edges and at the climatic extremes of species ranges, respectively. 4. Synthesis and applications: We show the importance of combining spatial demographic data, density-dependent population dynamics and environmental variation when assessing sensitivity to harvesting across species geographical ranges. Our findings caution against the application of general harvesting guidelines irrespective of species, geographical location or local environmental conditions. Our range-wide population viability analyses provide insights for developing species-specific, spatially nuanced guidelines for conservation management. Our approach also identifies species and areas to prioritise for monitoring to prevent the overexploitation of harvested species.
- ItemWildflower farming on the Agulhas Plain : fynbos management and conservation(Stellenbosch : University of Stellenbosch, 2010-12) Treurnicht, Martina; Esler, Karen J.; Gaertner, Mirijam; University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and EntomologyENGLISH ABSTRACT: The Agulhas Plain is a constituent of the Cape Floristic Region, internationally known as a global biodiversity hotspot. The species-rich Agulhas Plain consists mainly of fire-prone fynbos shrublands of which sandstone fynbos covers a significant surface area. This lowland region is characterised by mostly infertile soils yet has unique floristic complexity and contains a high amount of threatened lowland species. Natural vegetation on the Agulhas Plain has been prone to large scale land transformation activities, mainly attributed to the extent of alien plant invasions, urbanisation and agricultural expansion. Fynbos wildflower farming, specifically from natural vegetation, is an important economic activity and contributes to the region‟s agricultural sector. Farmers harvest large quantities of commercial fynbos species and supply these to the market in an attempt to sustain a livelihood. Certain wildflower farming practices (burning, ploughing and broadcast sowing) are applied to natural vegetation in an attempt to increase the abundance of commercial species (i.e. augmentation). Numerous farming practices are used in the industry and the application of these methods can be dynamic and divergent. Furthermore, the implementation of farming practices manifest as anthropogenically induced disturbance events and are a concern for conservation. Previous investigations suggest that farming practices could establish monocultures of commercial wildflower species by reducing species richness and plant diversity of wildflower vegetation. Although the impact of natural disturbance regimes (e.g. fire) and flower harvesting activities have been researched, the impact of farming practices on fynbos structure and composition remains largely unknown. This thesis reports on various aspects related to wildflower farming on the Agulhas Plain. Firstly, by administering a questionnaire, the extent and application of farming practices was investigated. Additionally, the opinion of wildflower farmers (referred to as landholders) about the impact of farming practices on wildflower populations was explored. Secondly, a vegetation survey aimed to assess the impact of farming practices on various structural (regeneration mode and growth form) and compositional attributes (plant family, dominant and rare species) of fynbos. Results from the questionnaire indicate that the application of farming methods are seasonally restricted, often used in varying combinations and relatively small in spatial extent. Furthermore, results show that wildflower farmers have an ecologically acceptable knowledge base and awareness of fynbos management and conservation. Secondly results, obtained from the vegetation survey, imply that natural vegetation subjected to particular farming practices differ from pristine fynbos vegetation by having both altered structural and compositional attributes. However, the impact of farming practices on rare species was less apparent. The conflict between commercial and conservation objectives are apparent from consultation with landholders. Nonetheless, landholders are optimistic about fynbos conservation and conservation can build upon these positive sentiments. Importantly, there is a need to communicate locally with landholders if a sustainable wildflower industry is a priority to stakeholders on the Agulhas Plain. Furthermore, fynbos ecosystems naturally entail complex ecological interactions. Wildflower farming practices reduce the ecological integrity (i.e. altered plant diversity, growth form and plant composition) of wildflower vegetation, at least at the local scale. These farming practices ultimately result both in distorted competitive interactions and disturbance regimes. Therefore, from a conservation perspective, the implementation of these farming practices (ploughing and broadcast sowing) should be cautioned against.