Species distribution models must balance the need for model generality with that for precision and accuracy. This is critical when modelling range-expanding species such as invasive species. Given the increased use of species distribution models to study invasive species-landscape relationships, a better understanding of the effect of spatial scales, sampling biases, model transferability and discrepancies between different models’ future predictions is necessary. This dissertation addresses these knowledge gaps using mute swans (Cygnus olor) as a case study species. I specifically examine mute swan’s distributions in parts of their native range of Britain and their non-native range of Ontario, Canada. I first investigate which environmental variables at which spatial scales best explain mute swan’s distribution in its non-native range. Second, I perform a sample selection bias study to examine predictive accuracy when species distribution models are built using varying ranges of environmental variables and applied to broader spatial extents. Third, I examine the potential for, and limitations of model transferability between native and non-native regions. Finally, I use two different modelling approaches and three different climate change and land use change scenarios to predict future mute swan habitat suitability. The results indicate that (1) models with better predictive accuracy include environmental variables from multiple ecologically-meaningful scales and measured at spatial extents that include a broad range of environmental variable values; (2) models can exhibit asymmetrical transferability; (3) climate change will facilitate mute swan range expansion in the future more than land use change; and (4) mute swans are often found near urban waterbodies. When modelling invasive species distributions, I suggest that ecologists consider: (I) spatial scale of the underlying landscape processes and species’ use of the landscape; (II) variability and range of each environmental variable used for building models; and (III) stage of establishment of the invasive species.

Species distribution models must balance the need for model generality with that for precision and accuracy. This is critical when modelling range-expanding species such as invasive species. Given the increased use of species distribution models to study invasive species-landscape relationships, a better understanding of the effect of spatial scales, sampling biases, model transferability and discrepancies between different models’ future predictions is necessary. This dissertation addresses these knowledge gaps using mute swans (Cygnus olor) as a case study species. I specifically examine mute swan’s distributions in parts of their native range of Britain and their non-native range of Ontario, Canada. I first investigate which environmental variables at which spatial scales best explain mute swan’s distribution in its non-native range. Second, I perform a sample selection bias study to examine predictive accuracy when species distribution models are built using varying ranges of environmental variables and applied to broader spatial extents. Third, I examine the potential for, and limitations of model transferability between native and non-native regions. Finally, I use two different modelling approaches and three different climate change and land use change scenarios to predict future mute swan habitat suitability. The results indicate that (1) models with better predictive accuracy include environmental variables from multiple ecologically-meaningful scales and measured at spatial extents that include a broad range of environmental variable values; (2) models can exhibit asymmetrical transferability; (3) climate change will facilitate mute swan range expansion in the future more than land use change; and (4) mute swans are often found near urban waterbodies. When modelling invasive species distributions, I suggest that ecologists consider: (I) spatial scale of the underlying landscape processes and species’ use of the landscape; (II) variability and range of each environmental variable used for building models; and (III) stage of establishment of the invasive species.

In order to predict future range shifts for invasive species it is important to explore their ability to acclimate to the new environment and understand physiological and reproductive constraints controlling their distribution. My dissertation studied mechanisms by which temperature may affect the distribution of two of the most aggressive plant invaders in North America, Bromus tectorum and Bromus rubens. While Bromus tectorum is dominant in the “cold desert” steppes of the Intermountain region of western North America, B. rubens is one of the severe grass invaders in the “hot deserts” of southwestern North America. I first evaluated whether winter freezing tolerance is the mechanism responsible for the distinct northern range limits of Bromus species. Bromus rubens has a slower rate of freezing acclimation that leads to intolerance of sudden, late-autumn reductions in temperature below -12°C, Bromus tectorum, by contrast, cold hardens rapidly and is not impacted by the sudden severe late-autumn cold. Photosynthetic response to temperature does not explain their current range separation. Bromus species differ little in their photosynthetic temperature responses and the acclimation pattern of photosynthesis. Both species acclimated to a broad range of temperature through the amelioration of Pi regeneration limitation at sub-optimal temperatures and improved carboxylation capacity above the thermal optimum which probably resulted from increased thermostability of Rubisco activase. The effect of elevated temperatures during flowering on the seed yield of Bromus species demonstrates that neither species produces seed at 36°C and above. These thresholds are close to temperatures encountered during flowering in their natural environment. In summary, climatic changes will cause northward range expansion of Bromus species due to less severe autumn and winter, while reproductive failure could cause range contraction at their southern margins.

No description available.

No description available.

Conservation frequently requires immediate responses to prevent further declines of imperilled populations, often in the absence of detailed information. Consequently, population distribution patterns are often used to guide conservation decisions. However, distribution patterns may be misleading if threats have restricted species to low quality habitat. This issue means it is not always apparent where management efforts should be concentrated for maximum conservation gain. My aim was to improve the effectiveness of threatened species conservation by investigating this issue in whio (blue duck - Hymenolaimus malacorhynchos), a New Zealand riverine duck that has undergone serious declines. I used population and spatial modelling to answer three questions: (1) what are the threats to whio, (2) how can these threats be managed, and (3) managing which whio habitats will give the greatest conservation gain? A spatial analysis of contemporary whio habitat using boosted regression trees revealed whio are only secure in 1 % of their historical range, with predation likely causing significantly greater range contraction (83 %) than habitat modification (29 %). In that analysis, I identified 39,000 km of occupiable whio habitat, providing extensive opportunities to expand their contemporary range through management. Intensive monitoring identified stoats (Mustela erminea) as the primary cause of whio population declines, with stoat predation severely reducing whio nest survival (10 % and 54 % in the absence and presence of stoat control, respectively). Population viability analyses indicated whio populations in the absence of stoat control were at high risk of extinction (λ = 0.74) but large-scale, low-intensity predator control was useful for short-term whio conservation. However, whio populations with stoat control still had a declining population growth rate (λ = 0.95) and further intervention may be required to prevent whio extinctions. Such management needs to target high quality habitat to ensure the greatest conservation value. Analyses of habitat quality revealed whio fitness was highest in warm, low gradient rivers, although fitness gradients differed between North and South Islands. Comparisons of fitness relationships with spatial model predictions showed that South Island whio occurred more frequently in poorer habitat, indicating they may occupy a relict distribution. Limited resources for conservation mean identifying effective management techniques is critical for species persistence. My modelling approach enabled the effectiveness of whio management to be assessed and areas of high quality habitat where such management should provide the greatest benefit to be identified. These tools are directly applicable to the conservation management of many threatened species by quickly informing managers in situations where distributions may not follow habitat quality.

South Africa is a megadiverse country, and its biodiversity is endangered by population pressure and the development needs of a developing country. In order to address the rapid decline in biological diversity, biodiversity planning has become a key focus area that aims at identifying priority areas for species and ecosystem conservation within and outside of formally protected areas. Plant conservation hotspots are identified by the quantification of indicator taxa such as plant taxa richness, rarity and endemism. But the urgent and enormous task of biodiversity assessment for conservation planning requires that we make most of what we know. Therefore, this study seeks to make a contribution by finding new ways of biodiversity pattern estimation from the extrapolation of incomplete sets of plant species distribution data at the Quarter Degree Grid level. Incomplete sampling across the grids of a study area results in false records of species absence and thus a biased biodiversity estimation. As a possible solution, plant distribution data for the western Central Bushveld Bioregion has been standardized using two profiles, namely the ‘Centroid Grid’ and ‘Integrated Grid’ profile. The former involves the strengthening of under-sampled grids by extrapolating species occurrences from three adjacent grids with the most similar vegetation units, whereas the latter integrates phyto-diversity data for the four grids intersecting at each grid reference point. Standardized data has proved to provide a means to counter the bias in plant diversity data linked to Quarter Degree Grids by a) strengthening of under-sampled grids and b) visibly smoothing out the gaps between under- and well-sampled grids, which resulted in improved biodiversity estimation for more representative spatial biodiversity modelling. Interpolation created geo-referenced polygons for more explicit use in the identification of areas of conservation concern at bioregional scale. However, well-sampled grids still dominate the outcomes of the analysis by creating spatial sampling bias. Therefore, this approach to calibrate Quarter Degree Grid resolution of spatial data is an additional attempt to achieve more representative mapping of biodiversity patterns, which is a prerequisite for strategic conservation planning for ‘living landscapes’. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012

South Africa is a megadiverse country, and its biodiversity is endangered by population pressure and the development needs of a developing country. In order to address the rapid decline in biological diversity, biodiversity planning has become a key focus area that aims at identifying priority areas for species and ecosystem conservation within and outside of formally protected areas. Plant conservation hotspots are identified by the quantification of indicator taxa such as plant taxa richness, rarity and endemism. But the urgent and enormous task of biodiversity assessment for conservation planning requires that we make most of what we know. Therefore, this study seeks to make a contribution by finding new ways of biodiversity pattern estimation from the extrapolation of incomplete sets of plant species distribution data at the Quarter Degree Grid level. Incomplete sampling across the grids of a study area results in false records of species absence and thus a biased biodiversity estimation. As a possible solution, plant distribution data for the western Central Bushveld Bioregion has been standardized using two profiles, namely the ‘Centroid Grid’ and ‘Integrated Grid’ profile. The former involves the strengthening of under-sampled grids by extrapolating species occurrences from three adjacent grids with the most similar vegetation units, whereas the latter integrates phyto-diversity data for the four grids intersecting at each grid reference point. Standardized data has proved to provide a means to counter the bias in plant diversity data linked to Quarter Degree Grids by a) strengthening of under-sampled grids and b) visibly smoothing out the gaps between under- and well-sampled grids, which resulted in improved biodiversity estimation for more representative spatial biodiversity modelling. Interpolation created geo-referenced polygons for more explicit use in the identification of areas of conservation concern at bioregional scale. However, well-sampled grids still dominate the outcomes of the analysis by creating spatial sampling bias. Therefore, this approach to calibrate Quarter Degree Grid resolution of spatial data is an additional attempt to achieve more representative mapping of biodiversity patterns, which is a prerequisite for strategic conservation planning for ‘living landscapes’. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012

In order to predict future range shifts for invasive species it is important to explore their ability to acclimate to the new environment and understand physiological and reproductive constraints controlling their distribution. My dissertation studied mechanisms by which temperature may affect the distribution of two of the most aggressive plant invaders in North America, Bromus tectorum and Bromus rubens. While Bromus tectorum is dominant in the “cold desert” steppes of the Intermountain region of western North America, B. rubens is one of the severe grass invaders in the “hot deserts” of southwestern North America. I first evaluated whether winter freezing tolerance is the mechanism responsible for the distinct northern range limits of Bromus species. Bromus rubens has a slower rate of freezing acclimation that leads to intolerance of sudden, late-autumn reductions in temperature below -12°C, Bromus tectorum, by contrast, cold hardens rapidly and is not impacted by the sudden severe late-autumn cold. Photosynthetic response to temperature does not explain their current range separation. Bromus species differ little in their photosynthetic temperature responses and the acclimation pattern of photosynthesis. Both species acclimated to a broad range of temperature through the amelioration of Pi regeneration limitation at sub-optimal temperatures and improved carboxylation capacity above the thermal optimum which probably resulted from increased thermostability of Rubisco activase. The effect of elevated temperatures during flowering on the seed yield of Bromus species demonstrates that neither species produces seed at 36°C and above. These thresholds are close to temperatures encountered during flowering in their natural environment. In summary, climatic changes will cause northward range expansion of Bromus species due to less severe autumn and winter, while reproductive failure could cause range contraction at their southern margins.

Conservation frequently requires immediate responses to prevent further declines of imperilled populations, often in the absence of detailed information. Consequently, population distribution patterns are often used to guide conservation decisions. However, distribution patterns may be misleading if threats have restricted species to low quality habitat. This issue means it is not always apparent where management efforts should be concentrated for maximum conservation gain. My aim was to improve the effectiveness of threatened species conservation by investigating this issue in whio (blue duck - Hymenolaimus malacorhynchos), a New Zealand riverine duck that has undergone serious declines. I used population and spatial modelling to answer three questions: (1) what are the threats to whio, (2) how can these threats be managed, and (3) managing which whio habitats will give the greatest conservation gain? A spatial analysis of contemporary whio habitat using boosted regression trees revealed whio are only secure in 1 % of their historical range, with predation likely causing significantly greater range contraction (83 %) than habitat modification (29 %). In that analysis, I identified 39,000 km of occupiable whio habitat, providing extensive opportunities to expand their contemporary range through management. Intensive monitoring identified stoats (Mustela erminea) as the primary cause of whio population declines, with stoat predation severely reducing whio nest survival (10 % and 54 % in the absence and presence of stoat control, respectively). Population viability analyses indicated whio populations in the absence of stoat control were at high risk of extinction (λ = 0.74) but large-scale, low-intensity predator control was useful for short-term whio conservation. However, whio populations with stoat control still had a declining population growth rate (λ = 0.95) and further intervention may be required to prevent whio extinctions. Such management needs to target high quality habitat to ensure the greatest conservation value. Analyses of habitat quality revealed whio fitness was highest in warm, low gradient rivers, although fitness gradients differed between North and South Islands. Comparisons of fitness relationships with spatial model predictions showed that South Island whio occurred more frequently in poorer habitat, indicating they may occupy a relict distribution. Limited resources for conservation mean identifying effective management techniques is critical for species persistence. My modelling approach enabled the effectiveness of whio management to be assessed and areas of high quality habitat where such management should provide the greatest benefit to be identified. These tools are directly applicable to the conservation management of many threatened species by quickly informing managers in situations where distributions may not follow habitat quality.