Browsing by Author "Hill, Matthew P."

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    Divergent thermal specialisation of two South African entomopathogenic nematodes
    (PeerJ, 2015-07-02) Hill, Matthew P.; Malan, Antoinette P.; Terblanche, John S.
    Thermal physiology of entomopathogenic nematodes (EPN) is a critical aspect of field performance and fitness. Thermal limits for survival and activity, and the ability of these limits to adjust (i.e., show phenotypic flexibility) depending on recent thermal history, are generally poorly established, especially for non-model nematode species. Here we report the acute thermal limits for survival, and the thermal acclimation-related plasticity thereof for two key endemic South African EPN species, Steinernema yirgalemense and Heterorhabditis zealandica. Results including LT50 indicate S. yirgalemense (LT50 = 40.8 ± 0.3 ◦C) has greater high temperature tolerance than H. zealandica (LT50 = 36.7 ± 0.2 ◦C), but S. yirgalemense (LT50 = −2.4 ± 0 ◦C) has poorer low temperature tolerance in comparison to H. zealandica (LT50=−9.7±0.3 ◦C), suggesting these two EPN species occupy divergent thermal niches to one another. Acclimation had both negative and positive effects on temperature stress survival of both species, although the overall variation meant that many of these effects were non-significant. There was no indication of a consistent loss of plasticity with improved basal thermal tolerance for either species at upper lethal temperatures. At lower temperatures measured for H. zealandica, the 5 ◦C acclimation lowered survival until below−12.5 ◦C, where after it increased survival. Such results indicate that the thermal niche breadth of EPN species can differ significantly depending on recent thermal conditions, and should be characterized across a broad range of species to understand the evolution of thermal limits to performance and survival in this group.
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    Niche overlap of congeneric invaders supports a single- species hypothesis and provides insight into future invasion risk: implications for global management of the bactrocera dorsalis complex
    (PLoS, 2014-02) Hill, Matthew P.; Terblanche, John S.
    Background: The invasive fruit fly, Bactrocera invadens, has expanded its range rapidly over the past 10 years. Here we aimed to determine if the recent range expansion of Bactrocera invadens into southern Africa can be better understood through niche exploration tools, ecological niche models (ENMs), and through incorporating information about Bactrocera dorsalis s.s., a putative conspecific species from Asia. We test for niche overlap of environmental variables between Bactrocera invadens and Bactrocera dorsalis s.s. as well as two other putative conspecific species, Bactrocera philippinensis and B. papayae. We examine overlap and similarity in the geographical expression of each species’ realised niche through reciprocal distribution models between Africa and Asia. We explore different geographical backgrounds, environmental variables and model complexity with multiple and single Bactrocera species hypotheses in an attempt to predict the recent range expansion of B. invadens into northern parts of South Africa. Principal Findings: Bactrocera invadens has a high degree of niche overlap with B. dorsalis s.s. (and B. philippinensis and B. papayae). Ecological niche models built for Bactrocera dorsalis s.s. have high transferability to describe the range of B. invadens, and B. invadens is able to project to the core range of B. dorsalis s.s. The ENMs of both Bactrocera dorsalis and B. dorsalis combined with B. philipenesis and B. papayae have significantly higher predictive ability to capture the distribution points in South Africa than for B. invadens alone. Conclusions/Significance: Consistent with other studies proposing these Bactrocera species as conspecific, niche similarity and overlap between these species is high. Considering these other Bactrocera dorsalis complex species simultaneously better describes the range expansion and invasion potential of B. invadens in South Africa. We suggest that these species should be considered the same–at least functionally–and global quarantine and management strategies applied equally to these Bactrocera species.
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    Niche shift and resource supplementation facilitate an amphibian range expansion
    (Wiley, 2019) Davies, Sarah J.; Hill, Matthew P.; McGeoch, Melodie A.; Clusella-Trullas, Susana
    Aim: To determine whether recent range expansion of small- bodied arboreal frogs, Hyperolius marmoratus Rapp, is accompanied by changes in species–environment re- lationships and whether its historical range was constrained by climate, availability of water bodies or topographic variables. We test if artificial water bodies in the novel range have facilitated niche shift by increasing available habitats for frog establishment. Location: Western Cape Province, South Africa, with reference to the broader spe- cies range in southeastern Africa. Methods: We build species distribution models using occurrence data from the his- torical and novel ranges and reciprocally project them to highlight areas of putative niche change. We test for niche shift through ordination- based approaches to disen- tangle how species–environment relationships may have altered and whether climate or landscape features (artificial water bodies and topography) are more strongly as- sociated with the identified change. We further decompose niche change into areas of expansion and unfilling to quantify niche shift and describe potential future spread. Results: We observed niche expansion into novel environmental space, with 21% of niche space in the invaded range composed of environments that were not occupied in the native range. We also observed 16% niche unfilling, signifying range disequilib- rium and potential for further spread. Mean annual precipitation and proximity to water bodies were more influential in models constructed in the novel range than in historical or combined range models, suggesting that presence of artificial water bodies in the landscape ameliorates novel range conditions. Together, these metrics suggest that range expansion may be ongoing based on climate and water body availability. Main conclusions: Our analyses identify a realised niche shift that has allowed painted reed frogs to occupy drier and more thermally variable habitats in their novel (invaded) range. This shift may be mediated by artificial water bodies that provide additional buffered habitats, a key resource supplement for these small- bodied tropi- cal frogs.