Browsing by Author "Vimercati, G."
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- ItemDoes restricted access limit management of invasive urban frogs?(Springer, 2017) Vimercati, G.; Davies, S.J.; Hui, C.; Measey, J.Management recommendations that target urban invaders should consider environmental and socio-economic aspects peculiar to the urban landscape. Urbanization often leads to the fragmentation of the invaded landscape into subunits inaccessible to managers (restricted access) or for which detailed information is lacking. Using models to explore impact of these limitations on management success provides a useful approach to propose effective counter measures. Here we deploy a spatially explicit age-structured model applied to a pond network to investigate how restricted access and lack of detailed information may affect management of three invasive anuran species across a peri-urban landscape. The target species, the guttural toad Sclerophrys gutturalis, the African clawed frog Xenopus laevis and the painted reed frog Hyperolius marmoratus, belong to different ecotypes (terrestrial, aquatic and arboreal, respectively) and have different life history traits. We show that restricted property access significantly constrains management success in two of the three species (the guttural toad and the painted reed frog), while lack of detailed information around the invaded landscape impedes successful management in only one species (the guttural toad). The species-dependent response we detected is due to contrasting demographic and spatial invasion dynamics linked to the different anuran ecotypes. Our work highlights the necessity to adopt a context-dependent approach when proposing management recommendations in urban environment.
- ItemA global meta-analysis of the ecological impacts of alien species on native amphibians(The Royal Society Publishing, 2019) Nunes, A.L.; Fill, J.M.; Davies, S.J.; Louw, M.; Rebelo, A.D.; Thorp, C.J.; Vimercati, G.; Measey, J.The exponential increase in species introductions during the Anthropocene has brought about a major loss of biodiversity. Amphibians have suffered large declines, with more than 16% considered to be threatened by invasive species. We conducted a global meta-analysis of the impacts of alien species on native amphibians to determine which aspects of amphibian ecology are most affected by plant, invertebrate, fish, amphibian, reptile, or mammal introductions. Measures of fitness were most strongly affected; amphibian performance was consistently lower in the presence of alien species. While exposure to alien species caused a significant decrease in amphibian behavioural activity when compared with a no species control, this response was stronger towards a control of native impacting species. This indicates a high degree of prey naivete´ towards alien species and highlights the importance of using different types of controls in empirical studies. Alien invertebrates had the greatest overall impact on amphibians. This study sets a new agenda for research on biological invasions, highlighting the lack of studies investigating the impacts of alien species on amphibian terrestrial life-history stages. It also emphasizes the strong ecological impacts that alien species have on amphibian fitness and suggests that future introductions or global spread of alien invertebrates could strongly exacerbate current amphibian declines.
- ItemHow repeatable is the Environmental Impact Classification of Alien Taxa (EICAT)? Comparing independent global impact assessments of amphibians(John Wiley & Sons Ltd., 2017) Kumschick, S.; Measey, G.J.; Vimercati, G.; de Villiers, F.A.; Mokhatla, M.M.; Davies, S.J.; Thorp, C.J.; Rebelo, A.D.; Blackburn, T.M.; Kraus, F.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.
- ItemThe importance of assessing positive and beneficial impacts of alien species(2020) Vimercati, G.; Kumschick, S.; Probert, A.F.; Volery, L.; Bacher, S.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.
- ItemIntegrating age structured and landscape resistance models to disentangle invasion dynamics of a pond-breeding anuran(Elsevier B.V., 2017) Vimercati, G.; Hui, C.; Davies, S.J.; Measey, G.J.Modelling population dynamics of invasive species may help to propose effective management countermeasures. Invasion dynamics generally show recursive patterns across species and regions, where initial lag is followed by spread and eventual dominance phases. However, timing and modes of these phases are highly variable, emerging from the interplay between traits of the invader and characteristics of the invaded landscape. Disentangling this interplay is particularly arduous in species with complex life-histories, where an individual passes through different life stages that alter physiology, behaviour and interactions with the environment. Here, we describe an age structured model that can be utilized to simulate population dynamics of invasive pond-breeding anurans. The model follows a spatially structured population approach, each pond representing a discrete habitat patch that exchanges individuals with other similar patches, and simulates change in survival and dispersal behaviour as a function of age.It also integrates dispersal with landscape complexity through landscape resistance modelling to depict functional connectivity across the pond network. Then we apply the model to a case study, the invasion of the guttural toad Sclerophrys gutturalis in Cape Town, first detected in 2000. Age-structured demographic and spatial dynamics of the focal population are reconstructed in a network of 415 ponds embedded in a heterogeneous landscape. Parameterization is conducted through field and laboratory surveys, a liter-ature review and data collected during an ongoing extirpation from 2010. We use the model to explore:i) occurrence and duration of lag phase; ii) whether the spatial spread fits an accelerating or a lineartrend; iii) how simulated dynamics match field observations. Additionally we test model sensitivity to demographic and behavioural traits. We found a lag phase in both demographic and spatial dynamics;however the lag duration of these dynamics does not coincide, where invaders start to spread across thepond network five years before the demographic explosion. Also, we found that the spatial spread fits an accelerating trend that causes complete invasion of the network in six years. Such dynamics noticeably match field observations and confirmed patterns previously detected in other invaders characterized by high dispersal abilities. Sensitivity analysis suggests that it would have been preferable to quantify initial propagule size and post-metamorphic survival in the field; both timing and modes of invasion are par-ticularly sensitive to these parameters. We conclude that the model has potential to forecast amphibian invasion dynamics and test management countermeasures.
- ItemUnderstanding uncertainty in the Impact Classification for Alien Taxa (ICAT) assessments(2020) Probert, A.F.; Volery, L.; Kumschick, S.; Vimercati, G.; Bacher, S.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.