SUNScholar - Browsing by Author "Vimercati, Giovanni"

Browsing by Author "Vimercati, Giovanni"

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Exploring the invasion of the guttural toad Sclerophrys gutturalis in Cape Town through a multidisciplinary approach
(Stellenbosch : Stellenbosch University, 2017-03) Vimercati, Giovanni; Measey, John; Davies, Sarah J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Invasive populations of amphibians may have considerable ecological and socio-economic impacts; reconstructing their invasion dynamics is essential to perform adaptive management. Investigating these populations is also an opportunity to address eco-evolutionary questions; it helps to improve our comprehension of biological systems and define in greater detail invasion potential. This study explores the invasion of the guttural toad Sclerophrys gutturalis in Cape Town through a multidisciplinary approach that integrates physiology, evolutionary biology, ecological modelling and environmental economics. The species is domestic exotic in South Africa, being native in most of the country but not in Cape Town, where an invasive population established in 2000. Although an extirpation program (started in 2010) removed some thousand adults, tadpoles and eggs until 2016, the population is still spreading. Invasion dynamics emerging from traits of the invader and characteristics of the invaded landscape are unknown. Additionally, efficacy and efficiency of the current mode of removal as well as the possibility to implement more effective extirpation strategies have not been investigated. Since the winter rainfall environment of Cape Town is drier and colder than that of the source population (Durban), especially during the summer breeding season, the species’ ability to spread is remarkable. Currently it is not clear how the abiotic conditions of Cape Town constrain this species and whether invasive toads adaptively respond to reduce phenotypic mismatch in the novel environment. Firstly, I built an age structured model that can be utilized to simulate population dynamics of invasive pond-breeding anurans. The model follows a metapopulation approach and simulates change in survival and dispersal behaviour as a function of age. It also integrates dispersal with landscape complexity through least cost path modelling to depict functional connectivity across the pond network. Then I applied the model to my case study; parameterization was conducted through field and laboratory surveys, a literature review and data collected during the extirpation. I found a lag phase in both demographic and spatial dynamics. Also, I found that the spatial spread fits an accelerating trend that causes the complete invasion of the network in six years. Such dynamics match field observations and confirmed patterns previously detected in other invaders characterized by high dispersal abilities. The age structured model was further employed to explore efficacy and efficiency of the current management. I investigated how a scenario incorporating the demographic effects of the current removal differs from a no-extirpation scenario. I also asked which limitations might impede the management from being successful and whether alternative strategies may determine better results. I found that the current management does not sufficiently take into consideration non-linear population dynamics and it reduces the efficiency; moreover the removal started during the spread phase of the invasion. Spatial limitations linked to the social dimension of the landscape severely reduce efficacy of the current removal; other management countermeasures such as control or containment should thus be considered. To explore how the species phenotype is constrained in the invaded environment during the breeding period and whether invasive toads underwent any adaptive response, I performed a comparison between the invasive population of Cape Town and the native source population of Durban. Field data and physiological traits such as evaporative water loss, water uptake, sensitivity of locomotion to desiccation and critical thermal minimum were collected. In accordance to the more desiccating and colder environment of Cape Town, invasive guttural toads responded physiologically and behaviourally on short time scale (less than two decades) to reduce sensitivity to lower conditions of hydration and temperature. The species is still constrained in the novel environment but its invasion potential is higher than I could infer from the source population. To confirm that the colder environment of Cape Town constrains invasive toads also during the non-breeding season, I investigated post-breeding energy storage in populations from Cape Town (high latitude), Durban (intermediate latitude), Mauritius and Reunion (low latitude) where the species is also invasive. Although post-breeding energy storage should be high (capital breeding strategy) at high latitudes and low (income breeding strategy) at low latitudes, guttural toads unexpectedly shifted energy storage strategy from capital to income breeding when introduced from lower to higher latitude. The invaded environment is therefore less severe during the non-breeding season; winter rainfall promotes, and does not reduce, toads’ activity. In summary, I showed that the invasion success of the guttural toad in Cape Town may be attributable to several factors such as initial lag that delayed management, accelerating spread, rapid adaptive response and less severe non-breeding season. The spatial dimension of the invaded landscape strongly limited the efficacy of the current management program. My work has relevant management implications; it shows that the invasion potential of the species is already higher than that I could infer from the source population and only tackling social limitations could have promoted effective extirpation.
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.
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.
The importance of assessing positive and beneficial impacts of alien species
(Pensoft, 2020-10-15) Vimercati, Giovanni; Kumschick, Sabrina; Probert, Anna F.; Volery, Lara; Bacher, Sven
ENGLISH ABSTRACT: Extensive literature is available on the diversity and magnitude of impacts that alien species cause on recipient systems. Alien species may decrease or increase attributes of ecosystems (e.g. total biomass or species diversity), thus causing negative and positive environmental impacts. Alien species may also negatively or positively impact attributes linked to local human communities (e.g. the number of people involved in a given activity). Ethical and societal values contribute to define these environmental and socio-economic impacts as deleterious or beneficial. Whilst most of the literature focuses on the deleterious effects of alien taxa, some recognise their beneficial impacts on ecosystems and human activities. Impact assessment frameworks show a similar tendency to evaluate mainly deleterious impacts: only relatively few, and not widely applied, frameworks incorporate the beneficial impacts of alien species. Here, we provide a summary of the frameworks assessing beneficial impacts and briefly discuss why they might have been less frequently cited and applied than frameworks assessing exclusively deleterious impacts. Then, we review arguments that invoke a greater consideration of positive and beneficial impacts caused by alien species across the invasion science literature. We collate and describe arguments from a set of 47 papers, grouping them in two categories (value-free and value-laden), which span from a theoretical, basic science perspective to an applied science perspective. We also provide example cases associated with each argument. We advocate that the development of transparent and evidence-based frameworks assessing positive and beneficial impacts might advance our scientific understanding of impact dynamics and better inform management and prioritisation decisions. We also advise that this development should be achieved by recognising the underlying ethical and societal values of the frameworks and their intrinsic limitations. The evaluation of positive and beneficial impacts through impact assessment frameworks should not be seen as an attempt to outweigh or to discount deleterious impacts of alien taxa but rather as an opportunity to provide additional information for scientists, managers and policymakers.
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.
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.
Understanding uncertainty in the Impact Classification for Alien Taxa (ICAT) assessments
(Pensoft, 2020-10-15) Probert, Anna F.; Volery, Lara; Kumschick, Sabrina; Vimercati, Giovanni; Bacher, Sven
ENGLISH ABSTRACT: The Environmental Impact Classification for Alien Taxa (EICAT) and the Socio-Economic Impact Classification of Alien Taxa (SEICAT) have been proposed to provide unified methods for classifying alien species according to their magnitude of impacts. EICAT and SEICAT (herein “ICAT” when refered together) were designed to facilitate the comparison between taxa and invasion contexts by using a standardised, semi-quantitative scoring scheme. The ICAT scores are assigned after conducting a literature review to evaluate all impact observations against the protocols’ criteria. EICAT classifies impacts on the native biota of the recipient environments, whereas SEICAT classifies impacts on human activities. A key component of the process is to assign a level of confidence (high, medium or low) to account for uncertainty. Assessors assign confidence scores to each impact record depending on how confident they are that the assigned impact magnitude reflects the true situation. All possible sources of epistemic uncertainty are expected to be captured by one overall confidence score, neglecting linguistic uncertainties that assessors should be aware of. The current way of handling uncertainty is prone to subjectivity and therefore might lead to inconsistencies amongst assessors. This paper identifies the major sources of uncertainty for impacts classified under the ICAT frameworks, where they emerge in the assessment process and how they are likely to be contributing to biases and inconsistency in assessments. In addition, as the current procedures only capture uncertainty at the individual impact report, interspecific comparisons may be limited by various factors, including data availability. Therefore, ranking species, based on impact magnitude under the present systems, does not account for such uncertainty. We identify three types of biases occurring beyond the individual impact report level (and not captured by the confidence score): biases in the existing data, data collection and data assessment. These biases should be recognised when comparing alien species based on their impacts. Clarifying uncertainty concepts relevant to the ICAT frameworks will lead to more consistent impact assessments and more robust intra- and inter-specific comparisons of impact magnitudes.
Why have a pet amphibian? insights from youtube
(Frontiers, 2019-03-04) Measey, John; Basson, Annie; Rebelo, Alexander D.; Nunes, Ana L.; Vimercati, Giovanni; Louw, Marike; Mohanty, Nitya Prakash
The desire to own a pet amphibian is growing, and with it a growth in amphibian trade and in negative impacts on native populations, including disease transmission and invasive amphibian populations. We know very little about how or why people choose amphibians as pets, but amphibian owners share large numbers of videos on freely accessible platforms, such as YouTube. We aimed to use videos of captive amphibians to determine which species are kept, their life-history stage and the types of videos uploaded. We watched and categorized 1,162 videos by video type, type of amphibian behavior and amphibian taxonomy (superfamily, family, and species). We used data on the amphibian trade from the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), on conservation status from the International Union for Conservation of Nature (IUCN) red list, and on potential environmental impact from published Environmental Impact Classification of Alien Taxa (EICAT) records, to determine potential conflicts of owning pet amphibians. We recorded 173 captive species in 847 videos with a taxonomic overrepresentation of salamandroids and pipoids, and an underrepresentation of ranoids and plethodontoids. When compared to videos of wild amphibian species, videos of captive animals featured disproportionate amounts of adults feeding, being handled and moving. The videos watched had a smaller proportion of threatened amphibian species, but a higher proportion of invasive species, than would be expected by chance, with the proportion present in CITES appendices (18%) being non-significant. We suggest that such data can be used to profile potential pets for trade and attempt to avoid conflicts with threatened and highly impacting alien species.

Browsing by Author "Vimercati, Giovanni"

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