SUNScholar - Browsing by Author "Davies, Sarah J."

Browsing by Author "Davies, Sarah J."

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Emerging infectious diseases and biological invasions : a call for a One Health collaboration in science and management
(Royal Society, 2019) Ogden, Nick H.; Wilson, John R. U.; Richardson, David M.; Hui, Cang; Davies, Sarah J.; Kumschick, Sabrina; Le Roux, Johannes J.; Measey, John; Saul, Wolf-Christian; Pulliam, Juliet R. C.
The study and management of emerging infectious diseases (EIDs) and of biological invasions both address the ecology of human-associated biological phenomena in a rapidly changing world. However, the two fields work mostly in parallel rather than in concert. This review explores how the general phenomenon of an organism rapidly increasing in range or abundance is caused, highlights the similarities and differences between research on EIDs and invasions, and discusses shared management insights and approaches. EIDs can arise by: (i) crossing geographical barriers due to human-mediated dispersal, (ii) crossing compatibility barriers due to evolution, and (iii) lifting of environmental barriers due to environmental change. All these processes can be implicated in biological invasions, but only the first defines them. Research on EIDs is embedded within the One Health concept—the notion that human, animal and ecosystem health are interrelated and that holistic approaches encompassing all three components are needed to respond to threats to human well-being. We argue that for sustainable development, biological invasions should be explicitly considered within One Health. Management goals for the fields are the same, and direct collaborations between invasion scientists, disease ecologists and epidemiologists on modelling, risk assessment, monitoring and management would be mutually beneficial.
Frog eat frog : exploring variables influencing anurophagy
(PeerJ, 2015) Measey, G. John; Vimercati, Giovanni; De Villiers, F. Andre; Mokhatla, Mohlamatsane M.; Davies, Sarah J.; Edwards, Shelley; Altwegg, Res
Background - Frogs are generalist predators of a wide range of typically small prey items. But descriptions of dietary items regularly include other anurans, such that frogs are considered to be among the most important of anuran predators. However, the only existing hypothesis for the inclusion of anurans in the diet of post-metamorphic frogs postulates that it happens more often in bigger frogs. Moreover, this hypothesis has yet to be tested. Methods - We reviewed the literature on frog diet in order to test the size hypothesis and determine whether there are other putative explanations for anurans in the diet of post-metamorphic frogs. In addition to size, we recorded the habitat, the number of other sympatric anuran species, and whether or not the population was invasive. We controlled for taxonomic bias by including the superfamily in our analysis. Results - Around one fifth of the 355 records included anurans as dietary items of populations studied, suggesting that frogs eating anurans is not unusual. Our data showed a clear taxonomic bias with ranids and pipids having a higher proportion of anuran prey than other superfamilies. Accounting for this taxonomic bias, we found that size in addition to being invasive, local anuran diversity, and habitat produced a model that best fitted our data. Large invasive frogs that live in forests with high anuran diversity are most likely to have a higher proportion of anurans in their diet. Conclusions - We confirm the validity of the size hypothesis for anurophagy, but show that there are additional significant variables. The circumstances under which frogs eat frogs are likely to be complex, but our data may help to alert conservationists to the possible dangers of invading frogs entering areas with threatened anuran species.
Geographic range, spread and potential distribution of the painted reed frog Hyperolius marmoratus in the Western Cape Province, South Africa
(Stellenbosch : Stellenbosch University, 2014-12) Davies, Sarah J.; Clusella-Trullas, Susana; McGeoch, Melodie A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Amphibian populations are among the most seriously threatened by global environmental change. Nonetheless, a few species have expanded their ranges to become globally invasive. In southern Africa, several anuran species are undergoing extra-limital range expansion on a regional scale and one of them, the painted reed frog (Hyperolius marmoratus Rapp.), is now invasive across the south-western Cape of South Africa. To answer the question of how this tropical, summer-breeding anuran has made such a successful transition into the temperate, winter rainfall region, I investigated several important aspects of the invasion process using a range of approaches from range ecology, physiology and niche modelling. Reconstruction of the painted reed frog’s invasion history allowed the date of introduction to be identified as 1997 or early 1998. The novel range was defined as extending from the Tsitsikamma Forest in the east to the Cape Peninsula in the west. Patches and gaps in the range structure and disparate rates of spread indicated that human-assisted jump dispersal and diffusion-based dispersal dominate in different parts of the novel range. A significant gap in the novel range distribution is formed by the Riviersonderend Mountains, a section of the Cape fold mountain range, that acts as a barrier to spread. To identify physiological range limiters, I investigated the plasticity of key physiological traits that influence thermoregulation, energetics and evaporative water loss. After thermal acclimation at three temperatures commonly encountered in their historical and novel ranges, frogs exhibited a broad thermal tolerance range and higher plasticity in CTmax than in CTmin. Resting metabolic rates were lowest in cold-acclimated animals, partially supporting the ‘colder is better’ hypothesis over beneficial acclimation. Active metabolic rates were lowest in warm-acclimated frogs, suggesting compensation for energy conservation. Notably, evaporative water loss was not significantly altered by acclimation in resting or active frogs, demonstrating a lack of plasticity in this trait. Plasticity of thermal tolerance and metabolic rate suggests that painted reed frogs efficiently conserve energy in a range of thermal environments and can withstand seasonal cooling by minimising the costs of resting metabolism. These characteristics could play a beneficial role in the novel range, which has a temporally and spatially variable climate. Together with their significant warming tolerance, they may facilitate spread into more extreme thermal environments north of their current range. On the other hand, the lack of plasticity in water loss rates, combined with reliance on the water-conserving posture to limit evaporative water loss could constrain further expansion to new sites. To form an integrated picture of the forces facilitating and constraining painted reed frog spread, reciprocal niche modelling was used to investigate the relationship between range shift and niche shift. I tested whether the niche of the painted reed frog has been conserved during recent range expansion or whether spread has been facilitated by a niche shift by using a modelling framework comprising both climatic and landscape variables. Niche models trained in the historical and novel ranges and projected in the reciprocal range revealed that H. marmoratus has undergone a niche shift between its historical range in the northern and eastern coastal regions and its novel range in the Mediterranean ecosystems of the south-western Cape. The niche shift corresponds with a climatic gradient towards higher summer aridity and generally lower precipitation in the novel range than the historical range, but is likely mediated by landscape transformation in the form of artificial water bodies that provide additional buffered habitats. I conclude that the niche shift accompanying range expansion has allowed painted reed frogs to occupy drier and more variable habitats in the novel range, while on a finer scale, access to permanent water bodies in the landscape is limiting. Artificial water bodies provide a key resource supplement for these invasive tropical frogs, which can be recognised as ‘urban exploiters’. Unspecialised habitat requirements, rapid spread and significant phenotypic plasticity suggest that they could continue to spread further within the matrix of suitable habitat available to them. In summary, this study found that availability of water in the landscape and the physiological capabilities of the frogs in relation to water loss are key determinants of the distribution and niche of painted reed frogs in their novel range. The work highlights the importance of broadscale climatic variables, landscape transformation in the form of artificial water bodies, and synergistic interactions between physiology and behaviour in determining invasion success. Om die beperkings op fisiologiese verspreiding te bepaal, is navorsing onderneem oor die plastisiteit in die vernaamste fisiologiese kenmerke wat termoregulering, energetiek en waterverlies deur verdamping beïnvloed. Ná termiese akklimatisasie by drie temperature wat algemeen in die historiese en nuwe verspreidingsgebiede van die spesie voorkom, het die paddas ’n groot termiese toleransiebestek en hoër plastisiteit by CTmax as by CTmin getoon. Rustende metaboliese tempo’s was die laagste by diere wat by lae temperature geakklimatiseer is, wat die ‘kouer is beter’-hipotese eerder as voordelige akklimatisasie ondersteun. Aktiewe metaboliese tempo’s was die laagste by die paddas wat by hoë temperature geakklimatiseer is, wat weer op kompensasie vir energiebehoud dui. Akklimatisasie het geen beduidende verskil aan waterverlies deur verdamping by rustende of aktiewe paddas gemaak nie, wat ’n gebrek aan plastisiteit in hierdie kenmerk aandui. Plastisiteit in termiese toleransie en metaboliese tempo gee te kenne dat die gestreepte rietpadda in ’n verskeidenheid termiese omgewings energie kan behou, en seisoenale afkoeling kan weerstaan deur die eise van rustende metabolisme te beperk. Hierdie kenmerke kan voordelig wees in die nuwe verspreidingsgebied, wat oor ’n temporeel en ruimtelik veranderlike klimaat beskik. Tesame met ’n beduidende toleransie vir hitte, kan hierdie
How repeatable is the Environmental Impact Classification of Alien Taxa (EICAT)? Comparing independent global impact assessments of amphibians
(Wiley Open Access, 2017) Kumschick, Sabrina; Measey, G. John; Vimercati, Giovanni; De Villiers, F. Andre; Mokhatla, Mohlamatsane M.; Davies, Sarah J.; Thorp, Corey J.; Rebelo, Alexander D.; Blackburn, Tim M.; Kraus, Fred
The magnitude of impacts some alien species cause to native environments makes them targets for regulation and management. However, which species to target is not always clear, and comparisons of a wide variety of impacts are necessary. Impact scoring systems can aid management prioritization of alien species. For such tools to be objective, they need to be robust to assessor bias. Here, we assess the newly proposed Environmental Impact Classification for Alien Taxa (EICAT) used for amphibians and test how outcomes differ between assessors. Two independent assessments were made by Kraus (Annual Review of Ecology Evolution and Systematics, 46, 2015, 75-97) and Kumschick et al. (Neobiota, 33, 2017, 53-66), including independent literature searches for impact records. Most of the differences between these two classifications can be attributed to different literature search strategies used with only one-third of the combined number of references shared between both studies. For the commonly assessed species, the classification of maximum impacts for most species is similar between assessors, but there are differences in the more detailed assessments. We clarify one specific issue resulting from different interpretations of EICAT, namely the practical interpretation and assigning of disease impacts in the absence of direct evidence of transmission from alien to native species. The differences between assessments outlined here cannot be attributed to features of the scheme. Reporting bias should be avoided by assessing all alien species rather than only the seemingly high-impacting ones, which also improves the utility of the data for management and prioritization for future research. Furthermore, assessments of the same taxon by various assessors and a structured review process for assessments, as proposed by Hawkins et al. (Diversity and Distributions, 21, 2015, 1360), can ensure that biases can be avoided and all important literature is included.
Impact assessment with different scoring tools : how well do alien amphibian assessments match?
(Pensoft Publishers, 2017-01-27) Kumschick, Sabrina; Vimercati, Giovanni; De Villiers, F. Andre; Mokhatla, Mohlamatsane M.; Davies, Sarah J.; Thorp, Corey J.; Rebelo, Alexander D.; Measey, G. John; Rabitsch, W.
Classification of alien species’ impacts can aid policy making through evidence based listing and management recommendations. We highlight differences and a number of potential difficulties with two scoring tools, the Environmental Impact Classification of Alien Taxa (EICAT) and the Generic Impact Scoring System (GISS) using amphibians as a case study. Generally, GISS and EICAT assessments lead to very similar impact levels, but scores from the schemes are not equivalent. Small differences are attributable to discrepancies in the verbal descriptions for scores. Differences were found in several impact categories. While the issue of disease appears to be related to uncertainties in both schemes, hybridisation might be inflated in EICAT. We conclude that GISS scores cannot directly be translated into EICAT classifications, but they give very similar outcomes and the same literature base can be used for both schemes.
Invasion science for society : a decade of contributions from the Centre for Invasion Biology
(Academy of Science of South Africa, 2014) Van Wilgen, Brian W.; Davies, Sarah J.; Richardson, David M.
Biological invasions are a growing problem worldwide. In 2004, the South African Department of Science and Technology, through the National Research Foundation, established a Centre of Excellence for Invasion Biology, with the primary goal of providing scientific understanding and building capacity in the field of biological invasions. South Africa is an extraordinary natural laboratory for the study of biological invasions, and the Centre for Invasion Biology (C·I·B) has capitalised on this situation. During its first decade, the C·I·B generated over 800 publications, and produced almost 200 graduates at honours, master’s and doctoral levels. The C·I·B has therefore made a considerable contribution to building human capacity in the field of biological invasions. Substantial advances have been made in all aspects of invasion science, which is not limited to biology and ecology, but includes history, sociology, economics and management. The knowledge generated by the C·I·B has been used to inform policy and improve management practices at national and local levels. The C·I·B has emerged as a leading institute in the global field of invasion biology, with several unique features that differentiate it from similar research institutes elsewhere. These features include a broad research focus that embraces environmental, social and economic facets, leading to a diverse research programme that has produced many integrated products; an extensive network of researchers with diverse interests, spread over a wide geographical range; and the production of policy- and management-relevant research products arising from the engaged nature of research conducted by the C∙I∙B.
Invasive amphibians in southern Africa : a review of invasion pathways
(AOSIS Publishing, 2017) Measey, John; Davies, Sarah J.; Vimercati, Giovanni; Rebelo, Alex; Schmidt, Warren; Turner, Andrew
Background: Globally, invasive amphibians are known for their environmental and social impacts that range from poisoning of local fauna and human populations to direct predation on other amphibians. Although several countries on most continents have had multiple introductions of many species, southern Africa appears to have escaped allochthonous introductions. Instead, it has a small number of domestic exotic species that have rapidly expanded their ranges and established invasive populations within South Africa. Objectives & methods: We used the literature to provide a historical overview of dispersal by some of the world’s major invasive amphibians, give examples of species that are commonly moved as stowaways and discuss historical and current amphibian trade in the region. In addition, we give an overview of new South African legislation and how this is applied to amphibian invasions, as well as providing updates on the introduced populations of three domestic exotics: Hyperolius marmoratus, Sclerophrys gutturalis and Xenopus laevis. Results: We show that frogs are mainly moved around southern Africa through ‘jump’ dispersal, although there are a number of records of ‘cultivation’, ‘leading-edge’ and ‘extreme long-distance’ dispersal types. Important pathways include trade in fruit and vegetables, horticultural products and shipping containers. Conclusion: We suggest that southern Africa is becoming more vulnerable to amphibian invasions because of an increase in trade, agricultural and domestic impoundments as well as global climate change. Increasing propagule pressure suggests that preventing new introductions will become a key challenge for the future. Currently, trade in amphibians in the region is practically non-existent, suggesting potential for best practice to prevent importation of species with high invasion potential and to stop the spread of disease.
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.
Opening the floor for discussion : a perspective on how scholars perceive attitudes to science in policymaking in South Africa
(ASSAf, 2021-01-29) Czachur, Molly V.; Todd, Melvi; Goncalves Loureiro, Taina; Azam, James M.; Nyeleka, Siphokazi; Alblas, Amanda; Davies, Sarah J.
Policymakers are a vital group with whom scientific research should be communicated, especially when the reason for many research projects is linked to relevance for socio-political and economic management. Science communication has a vital role in transforming research into policy, and a core element of this process is understanding the target group, namely policymakers. Science and policy influence each other deeply, so researchers and policymakers should improve their understanding of each other and of the processes involved in both fields in order to better collaborate. Accordingly, an in-depth understanding of how scholars perceive policymakers is a precondition for scientists to achieve any desired management and policy impacts. In December 2019, six researchers and one research manager from Stellenbosch University, South Africa, gathered to discuss their understanding of policymakers. The discussion was part of a Science Communication Masterclass hosted by the South African Research Chair in Science Communication and Econnect Communication, Australia. The purpose of the group discussion was to develop a science communication strategy that would enhance the sharing of scientific research outputs with policymakers in South Africa. We explored five questions to help us record our perception of policymakers: (1) Who do we think the policymakers are? (2) How do we think that policymakers perceive research? (3) What concerns do we believe that policymakers have about research? (4) What information do we think policymakers are interested in? (5) What forms of communication do we think policymakers prefer? This Commentary presents our view on how we think researchers perceive policymakers, as discussed in the Science Communication Masterclass. We hope to initiate a discussion around science communication with policymakers, and improve current practices.
Rapid adaptive response to a Mediterranean environment reduces phenotypic mismatch in a recent amphibian invader
(Company of Biologists, 2018) Vimercati, Giovanni; Davies, Sarah J.; Measey, John
Invasive species frequently cope with ecological conditions that are different from those to which they adapted, presenting an opportunity to investigate how phenotypes change across short time scales. In 2000, the guttural toad Sclerophrys gutturalis was first detected in a peri-urban area of Cape Town, where it is now invasive. The ability of the species to invade Cape Town is surprising as the area is characterized by a Mediterranean climate significantly drier and colder than that of the native source area. We measured field hydration state of guttural toads from the invasive Cape Town population and a native source population from Durban. We also obtained from laboratory trials: rates of evaporative water loss and water uptake, sensitivity of locomotor endurance to hydration state, critical thermal minimum (CTmin) and sensitivity of CTmin to hydration state. Field hydration state of invasive toads was significantly lower than that of native toads. Although the two populations had similar rates of water loss and uptake, invasive toads were more efficient in minimizing water loss through postural adjustments. In locomotor trials, invasive individuals noticeably outperformed native individuals when dehydrated but not when fully hydrated. CTmin was lower in invasive individuals than in native individuals, independent of hydration state. Our results indicate that an invasive population that is only 20 years old shows adaptive responses that reduce phenotypic mismatch with the novel environment. The invasion potential of the species in Cape Town is higher than we could infer from its characteristics in the native source population.
The unknown underworld : understanding soil health in South Africa
(Academy of Science of South Africa, 2014-05) Louw, Schalk v. d. M.; Wilson, John R. U.; Janion, Charlene; Veldtman, Ruan; Davies, Sarah J.; Addison, Matthew
The need to provide food security to a growing human population in the face of global threats such as climate change, land transformation, invasive species and pollution is placing increasing pressure on South African soils. South Africa is losing an estimated 300–400 million tonnes of soil annually, while soil degradation is a major threat to agricultural sustainability. In spite of these problems, treatment of soil health in biodiversity assessment and planning in South Africa has been rudimentary to date.

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