Browsing by Author "Crous, Casparus J."

Now showing 1 - 5 of 5
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    Conserving a geographically isolated Charaxes butterfly in response to habitat fragmentation and invasive alien plants
    (AOSIS Publishing, 2015-08) Crous, Casparus J.; Pryke, James S.; Samways, Michael J.
    In South Africa, much of the forest biome is vulnerable to human-induced disturbance. The forest-dwelling butterfly Charaxes xiphares occidentalis is naturally confined to a small forest region in the south-western Cape, South Africa. Most of the remaining habitat of this species is within a fragmented agricultural matrix. Furthermore, this geographical area is also heavily invaded by alien plants, especially Acacia mearnsii. We investigated how C. x. occidentalis behaviourally responds to different habitat conditions in the landscape. We were particularly interested in touring, patrolling and settling behaviour as a conservation proxy for preference of a certain habitat configuration in this agricultural matrix. Remnant forest patches in the agricultural matrix showed fewer behavioural incidents than in a reference protected area. Moreover, dense stands of A. mearnsii negatively influenced the incidence and settling pattern of this butterfly across the landscape, with fewer tree settlings associated with more heavily invaded forest patches. This settling pattern was predominantly seen in female butterflies. We also identified specific trees that were settled upon for longer periods by C. x. occidentalis. Distance to a neighbouring patch and patch size influenced behavioural incidences, suggesting that further patch degradation and isolation could be detrimental to this butterfly. Conservation implications: We highlight the importance of clearing invasive tree species from vulnerable forest ecosystems and identify key tree species to consider in habitat conservation and rehabilitation programmes for this butterfly. We also suggest retaining as much intact natural forest as possible. This information should be integrated in local biodiversity management plans.
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    The darker side of quantitative academic performance metrics
    (Academy of Science of South Africa, 2019-07-30) Crous, Casparus J.
    No abstract available
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    Ecological disequilibrium drives insect pest and pathogen accumulation in non-native trees
    (Oxford University Press on behalf of the Annals of Botany Company, 2017) Crous, Casparus J.; Burgess, Treena I.; Le Roux, Johannes J.; Richardson, David M.; Slippers, Bernard; Wingfield, Michael J.
    Non-native trees have become dominant components of many landscapes, including urban ecosystems, commercial forestry plantations, fruit orchards and as invasives in natural ecosystems. Often, these trees have been separated from their natural enemies (i.e. insects and pathogens) leading to ecological disequilibrium, that is, the immediate breakdown of historically co-evolved interactions once introduced into novel environments. Long-established, non-native tree plantations provide useful experiments to explore the dimensions of such ecological disequilibria. We quantify the status quo of non-native insect pests and pathogens catching up with their tree hosts (planted Acacia, Eucalyptus and Pinus species) in South Africa, and examine which native South African enemy species utilize these trees as hosts. Interestingly, pines, with no confamilial relatives in South Africa and the longest residence time (almost two centuries), have acquired only one highly polyphagous native pathogen. This is in contrast to acacias and eucalypts, both with many native and confamilial relatives in South Africa that have acquired more native pathogens. These patterns support the known role of phylogenetic relatedness of non-native and native floras in influencing the likelihood of pathogen shifts between them. This relationship, however, does not seem to hold for native insects. Native insects appear far more likely to expand their feeding habits onto non-native tree hosts than are native pathogens, although they are generally less damaging. The ecological disequilibrium conditions of non-native trees are deeply rooted in the eco-evolutionary experience of the host plant, co-evolved natural enemies and native organisms from the introduced range. We should expect considerable spatial and temporal variation in ecological disequilibrium conditions among non-native taxa, which can be significantly influenced by biosecurity and management practices.
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    Evolutionary dynamics of tree invasions : complementing the unified framework for biological invasions
    (Oxford University Press on behalf of the Annals of Botany Company, 2017) Zenni, Rafael D.; Dickie, Ian A.; Wingfield, Michael J.; Hirsch, Heidi; Crous, Casparus J.; Meyerson, Laura A.; Burgess, Treena I.; Zimmermann, Thalita G.; Klock, Metha M.; Siemann, Evan; Erfmeier, Alexandra; Aragon, Roxana; Montti, Lia; Le Roux, Johannes J.
    Evolutionary processes greatly impact the outcomes of biological invasions. An extensive body of research suggests that invasive populations often undergo phenotypic and ecological divergence from their native sources. Evolution also operates at different and distinct stages during the invasion process. Thus, it is important to incorporate evolutionary change into frameworks of biological invasions because it allows us to conceptualize how these processes may facilitate or hinder invasion success. Here, we review such processes, with an emphasis on tree invasions, and place them in the context of the unified framework for biological invasions. The processes and mechanisms described are pre-introduction evolutionary history, sampling effect, founder effect, genotype-by-environment interactions, admixture, hybridization, polyploidization, rapid evolution, epigenetics and second-genomes. For the last, we propose that co-evolved symbionts, both beneficial and harmful, which are closely physiologically associated with invasive species, contain critical genetic traits that affect the evolutionary dynamics of biological invasions. By understanding the mechanisms underlying invasion success, researchers will be better equipped to predict, understand and manage biological invasions.
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    Foliar nitrogen dynamics of an invasive legume compared to native non-legumes in fynbos riparian zones varying in water availability
    (South African Water Research Commission, 2019) Crous, Casparus J.; Drake, Deanne C.; Jacobsen, Anna L.; Pratt, R. Brandon; Jacobs, Shayne M.; Esler, Karen J.
    The legume Acacia mearnsii invades South Africa’s fynbos riparian zones and may alter the nitrogen (N) dynamics and supply in these areas that typically support few native N fixers. Nitrogen uptake by A. mearnsii may also be influenced by water availability, potentially affecting riparian-specific performance and impact estimations. We expected to find functional differences between the invasive legume and the two co-occurring but non-leguminous native species Brabejum stellatifolium and Metrosideros angustifolia. We also wanted to examine whether in-situ water availability affected N source or uptake in the invasive species. We found A. mearnsii was indeed functioning differently from non-N-fixing native species, and had considerably higher foliar %N. Interestingly, 15N abundance and uptake were associated with site hydrology, meaning water availability should be scrutinised when assuming N-fixing in A. mearnsii using δ15N. Nonetheless, higher water availability to A. mearnsii in fynbos riparian ecosystems did increase foliar N uptake. This has implications for prioritizing clearing of sites with increased nutrient deposition, such as dense stands in relatively moist riparian zones.