SUNScholar - Browsing by Author "Measey, John"

Browsing by Author "Measey, John"

Now showing 1 - 20 of 23

Anti-predator strategies of the invasive African clawed frog, Xenopus laevis, to native and invasive predators in western France
(Regional Euro-Asian Biological Invasions Centre, 2019) Kruger, Natasha; Measey, John; Herrel, Anthony; Secondi, Jean
ENGLISH ABSTRACT: When species are translocated to a novel environment, individuals become exposed to new predators against which they may not express very efficient defences at least at an initial stage. The strength of anti-predator defence is an important parameter that may determine the ability of local communities to control the expansion of invasive populations. The African clawed frog, Xenopus laevis, is a globally invasive amphibian that has successfully established invasive populations on four continents. In its invasive distribution in western France, X. laevis encounters novel aquatic predators. Some may be related to the predators in the native range but others may belong to different taxonomic groups and not be functionally or ecologically equivalent. We tested whether naïve X. laevis tadpoles from the invasive French population exhibit anti-predator response to local predators, and whether the response depends on the degree of relatedness with predators encountered in the native range of the frog, or whether individuals may express generic neophobia to any cue they are not familiar with. We exposed naïve lab-reared tadpoles to a native non-predatory water snail, Planorbarius corneus, a native predatory beetle, Dytiscus dimidiatus, and an invasive predatory crayfish, Procambarus clarkii. We found that X. laevis tadpoles innately reduce their activity when exposed to beetle and crayfish stimulus cues, but not to snails. Reducing activity can decrease the probability of being detected by predators. This demonstrates that invasive tadpoles respond to known and novel predators regardless of the evolutionary history. Whether the produced response is always effective against a totally novel predator remains to be tested.
Are invasive populations characterized by a broader diet than native populations?
(PeerJ, 2017) Courant, Julien; Vogt, Solveig; Marques, Raquel; Measey, John; Secondi, Jean; Rebelo, Rui; De Villiers, Andre; Ihlow, Flora; De Busschere, Charlotte; Backeljau, Thierry; Rodder, Dennis; Herrel, Anthony
Background. Invasive species are among the most significant threats to biodiversity. The diet of invasive animal populations is a crucial factor that must be considered in the context of biological invasions. A broad dietary spectrum is a frequently cited characteristic of invasive species, allowing them to thrive in a wide range of environments. Therefore, empirical studies comparing diet in invasive and native populations are necessary to understand dietary requirements, dietary flexibility, and the associated impacts of invasive species. Methods. In this study, we compared the diet of populations of the African clawed frog, Xenopus laevis in its native range, with several areas where it has become invasive. Each prey category detected in stomach contents was assigned to an ecological category, allowing a comparison of the diversity of ecological traits among the prey items in the diet of native and introduced populations. The comparison of diets was also performed using evenness as a niche breadth index on all sampled populations, and electivity as a prey selection index for three out of the six sampled populations. Results. Our results showed that diet breadth could be either narrow or broad in invasive populations. According to diet and prey availability, zooplankton was strongly preferred in most cases. In lotic environments, zooplankton was replaced by benthic preys, such as ephemeropteran larvae. Discussion. The relative proportions of prey with different ecological traits, and dietary variability within and between areas of occurrence, suggest that X. laevis is a generalist predator in both native and invasive populations. Shifts in the realized trophic niche are observed, and appear related to resource availability. Xenopus laevis may strongly impact aquatic ecosystems because of its near complete aquatic lifestyle and its significant consumption of key taxa for the trophic relationships in ponds.
Assessing water conditions for Heleophryne rosei tadpoles and the conservation relevance
(AOSIS, 2020-08-11) Ebrahim, Zishan; De Villiers, Atherton; Measey, John
ENGLISH ABSTRACT: The Table Mountain Ghost Frog (Heleophryne rosei) is endemic to the Table Mountain massif and is Critically Endangered. Other than clear, clean perennial stream flow, the optimal aquatic conditions required by their larvae are unknown. Dissolved oxygen, temperature, pH, electro-conductivity, aspect and permanence of flow are the independent variables measured seasonally at two sampling altitudes at 12 rivers of the massif. Using a logistic regression model we found that a permanence of water flow and lower water temperature were significant predictors of tadpole presence. Streams with mean summer temperature above 17.2 °C, at 300 m – 400 m above sea level, do not have tadpoles. Summer and autumn abstraction should be avoided, while a summer water temperature above an average of 17.2 °C is a threshold of potential concern for management authorities responsible for biodiversity conservation, threat mitigation efforts, and bulk-water supply and abstraction. Conservation implications: The Environmental Water Reserve has not been determined for streams of Table Mountain. The requirements of the Critically Endangered Table Mountain Ghost Frog (Heleophryne rosei) can be adopted as the minimum conditions to support this species and associated communities. Perennial flow, an average January water temperature of 17.2 °C or lower.
Competition and feeding ecology in two sympatric Xenopus species (Anura: Pipidae)
(PeerJ, 2017) Vogt, Solveig; De Villiers, F. Andre; Ihlow, Flora; Rodder, Dennis; Measey, John
The widespread African clawed frog (Xenopus laevis) occurs in sympatry with the IUCN Endangered Cape platanna (Xenopus gilli) throughout its entire range in the south-western Cape, South Africa. In order to investigate aspects of the interspecific competition between populations of X. laevis and X. gilli, an assessment of their niche differentiation was conducted through a comprehensive study on food composition and trophic niche structure at two study sites: the Cape of Good Hope (CoGH) and Kleinmond. A total of 399 stomach contents of X. laevis (n = 183) and X. gilli (n = 216) were obtained together with samples of available prey to determine food preferences using the Electivity index (E*), the Simpson’s index of diversity (1 − D), the Shannon index (H′), and the Pianka index (Ojk). Xenopus gilli diet was more diverse than X. laevis, particularly in Kleimond where the Shannon index was nearly double. Both species were found to consume large amounts of tadpoles belonging to different amphibian species, including congeners, with an overall higher incidence of anurophagy than previously recorded. However, X. laevis also feeds on adult X. gilli, thus representing a direct threat for the latter. While trophic niche overlap was 0.5 for the CoGH, it was almost 1 in Kleinmond, suggesting both species utilise highly congruent trophic niches. Further, subdividing the dataset into three size classes revealed overlap to be higher in small frogs in both study sites. Our study underlines the importance of actively controlling X. laevis at sites with X. gilli in order to limit competition and predation, which is vital for conservation of the south-western Cape endemic.
The cost and complexity of assessing impact
(Pensoft, 2020-10-15) Measey, John; Wagener, Carla; Mohanty, Nitya Prakash; Baxter-Gilbert, James; Pienaar, Elizabeth F.
ENGLISH ABSTRACT: The environmental and socio-economic impacts of invasive species have long been recognised to be unequal, with some species being benign while others are disastrous. Until recently there was no recognised standard impact scoring framework with which to compare impacts of species from very different taxa. The advent of the Environmental Impact Classification for Alien Taxa (EICAT) and Socio‐Economic Impact Classification of Alien Taxa (SEICAT) schemes allows for the possibility of assessing impact through a standard approach. However, both these schemes are still in their infancy and the associated costs of the research that informs them is unknown. We aimed to determine the study costs and complexity associated with assessing invasive species’ socio-economic and environmental impacts. We used amphibians as a model group to investigate papers from which EICAT and SEICAT scores could be drawn up to 2019. Our analysis shows that studies that resulted in higher impact scores were more costly. Furthermore, the costs of studies were best predicted by their complexity and the time taken to complete them. If impact scores from EICAT and SEICAT are allowed to inform policy, then we need to carefully consider whether species with low scores represent true impact, or require more research investment and time. Policy makers needing accurate assessments will need to finance larger, more complex, and rigorous studies. Assessing impacts in low and middle income countries may need investment using international research collaborations and capacity building with scientists from high income areas.
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.
An established population of African clawed frogs, Xenopus laevis (Daudin, 1802), in mainland China
(Regional Euro-Asian Biological Invasions Centre, 2019) Wang, Supen; Hong, Yufeng; Measey, John
ENGLISH ABSTRACT: Reports of amphibian invasions are increasing, although it seems likely that there are more extant populations of alien species than we are currently aware of, and we are far from understanding their full environmental and economic impact. Here we provide data on another established population of African clawed frogs, Xenopus laevis (Daudin, 1802); from Yunnan Province in mainland China. The site is an aquaculture area immediately adjacent to the northern shores of Lake Kunming. This report is significant as it is the first known alien population of an albino form of this species, the form that is most prevalent in the pet trade. We call for urgent surveys using eDNA to determine the extent of the invasion of this cryptic amphibian invader around Lake Kunming, as well as studies to determine the environmental and economic impacts at this site, which is already known for an invasion of American bullfrogs, Lithobates catesbeianus (Shaw, 1802).
Has strategic planning made a difference to amphibian conservation research in South Africa?
(South African National Biodiversity Institute (SANBI), 2019-09-25) Measey, John; Tarrant, Jeanne; Rebelo, Alex; Turner, Andrew; du Preez, Louis; Mokhatla, Mohlamatsane; Conradie, Werner
Background: Conservation relies on the strategic use of resources because monies for conservation action are limited, especially in developing countries. South Africa’s Frog Atlas project established a baseline for the country’s amphibian data and threat levels in 2004, and in 2009 a prioritisation exercise developed a strategy for conservation research. Objectives: In this article, we assess this strategy for conservation research. Method: We conducted a quantitative and qualitative assessment of research undertaken since the strategy was developed. Results: The strategy has produced a lasting impact on taxonomy, ecological studies, monitoring and capacity building. Publications in all areas have increased, but particularly in conservation ecology. Other indicators are increases in the numbers of locality records for target taxa, species descriptions and postgraduate degrees with amphibians as the principal topic. We document important milestones for South African amphibian conservation, including the first Biodiversity Management Plan for Species (BMP-S) for Hyperolius pickersgilli, a smart device app that uploads locality data to an open access database, 15 years of monitoring data and new amphibian identification books for adults and children. The Red List Index calculated for South African amphibians shows that the country’s species are becoming more threatened (a 1% reduction in 10 years), but a hindcasting exercise suggests that most of the damage was already done by 1990. We provide a checklist for 131 amphibian species in South Africa, of which 82 species are endemic. Conclusion: A strategy for conservation research was found to greatly augment the focus of research on South African frogs. A new strategy should focus on fewer taxa over meaningful time spans.
The implications of the reclassification of South African wildlife species as farm animals
(ASSAf, 2020-01-29) Somers, Michael J.; Walters, Michele; Measey, John; Turner, Andrew A.; Venter, Jan A.; Nel, Lizanne; Kerley, Graham I. H.; Taylor, W. Andrew; Moodley, Yoshan; Strauss, W. Maartin
The Government Gazette No. 42464 dated 17 May 20191 amended Table 7 of the Animal Improvement Act (Act no. 62 of 1998), which lists breeds of animals, to include at least 32 new wild animal species, including 24 indigenous mammals. The list includes threatened and rare species such as cheetah, white and black rhinoceros, and suni. Some alien species such as lechwe, various deer species and rabbits are also included. The cornerstone of the original Act is ‘To provide for the breeding, identification and utilisation of genetically superior animals to improve the production and performance of animals in the interest of the Republic; and to provide for matters connected therewith.’ By declaring these wild animals as landrace breeds (in Table 7 of the regulations), the Act implies that they are locally developed breeds. The Act typically provides for landrace breeds to be bred and ‘genetically improved’ to obtain superior domesticated animals with enhanced production and performance. Similarly, provision is made for the Breeders Association to lay claim to the breed and to establish specific breed standards for animals to be included in stud books. Animals declared as landrace breeds can also be used for genetic manipulation, embryo harvesting, in-vitro fertilisation and embryo transfers. As indigenous species of wildlife are included in the recent amendment to the Act, the amendment is flawed. Here we point out numerous concerns in the new legislation, including the process of consultation, and argue that the law will not improve the genetics of the species mentioned but will have considerable negative genetic consequences and pose ecological and economic risks. We also suggest that this new law is in direct conflict with other biodiversity laws in South Africa.
In a pinch : mechanisms behind potential biotic resistance toward two invasive crayfish by native African freshwater crabs
(Frontiers, 2020-03-27) South, Josie; Madzivanzira, Takudzwa C.; Tshali, Ntombizanele; Measey, John; Weyl, Olaf L. F
It is essential to incorporate mechanisms of biotic resistance into predictions of ecological impact conferred by invasive species. Trophically and functionally analogous native species have high potential to confer biotic resistance or to be susceptible to competitive exclusion by the invading species. In species with dominance hierarchies and high aggression the role of weapons, such as chelae, is emphasised and selected for. Differences in traits such as crushing capacity can indicate prey handling capabilities, while correlations between closing force and morphology can be used to understand the role of signaling in agonistic contests. Closing force strength can be used to infer the outcomes of both direct (predation) and indirect (competition) trophic interactions. Southern Africa has been invaded by two freshwater crayfish species (Cherax quadricarinatus and Procambarus clarkii). Biotic resistance of freshwater crabs toward crayfish invasions varies between geographic location and co-evolutionary history, thus comparing invasion histories without incorporating geographic context can produce unequivocal conclusions. We compared the closing force and chelae morphology of both crayfish species with a native trophically analogous freshwater crab, Potamonautes perlatus. Closing force increased significantly with mass for all species. There was significant interaction between sex and species on closing force. Potamonautes perlatus females showed significantly stronger maximum chela closing force than male P. perlatus, both sexes of P. clarkii and female C. quadricarinatus. Contrastingly, male C. quadricarinatus had significantly higher closing forces than both sexes of P. clarkii and female C. quadricarinatus, however, there was no difference between female P. perlatus. Native P. perlatus has the capacity to hold a competitive mechanical advantage over both invaders, but this varies with sex. Chelae length was not a significant predictor for closing strength in any of the species, which may be related to dishonest signaling in decapod species. This makes it imperative to assess whether factors such as closing force actually translate to resource holding potential in a contest scenario. We thus provide evidence that African freshwater crabs may exhibit biotic resistance toward invasion and the first measurements for C. quadricarinatus closing force strength.
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.
Invasive frogs in Sao Paulo display a substantial invasion lag
(European Geosciences Union, 2018) Toledo, L. Felipe; Measey, John
ENGLISH ABSTRACT: The first report of the invasion of the Robber frog Eleutherodactylus johnstonei Barbour, 1914 in the municipality of São Paulo was made in 2014. However, we report here that sound records of this species in the same area of São Paulo, and deposited in a Brazilian sound archive, date back to 1995. Therefore, we expand the timeframe of the presence of this invasive population in the city, and provide information on its pathway of introduction, which is not accidental as previously suggested, but intentional. These data improve the knowledge on this invasion and indicate the urgent actions to avoid the expansion of this invasive species to other sites where its impact could be higher.
Mechanistic reconciliation of community and invasion ecology
(Ecological Society of America, 2021-02) Latombe, Guillaume; Richardson, David M.; McGeoch, Melodie A.; Altwegg, Res; Catford, Jane A.; Chase, Jonathan M.; Courchamp, Franck; Esler, , Karen J.; Jeschke, Jonathan M.; Landi, Pietro; Measey, John; Midgley, Guy F.; Minoarivelo, Henintsoa O.; Rodger, James G.; Hui, Cang
Community and invasion ecology have mostly grown independently. There is substantial overlap in the processes captured by different models in the two fields, and various frameworks have been developed to reduce this redundancy and synthesize information content. Despite broad recognition that community and invasion ecology are interconnected, a process‐based framework synthesizing models across these two fields is lacking. Here we review 65 representative community and invasion models and propose a common framework articulated around six processes (dispersal, drift, abiotic interactions, within‐guild interactions, cross‐guild interactions, and genetic changes). The framework is designed to synthesize the content of the two fields, provide a general perspective on their development, and enable their comparison. The application of this framework and of a novel method based on network theory reveals some lack of coherence between the two fields, despite some historical similarities. Community ecology models are characterized by combinations of multiple processes, likely reflecting the search for an overarching theory to explain community assembly and structure, drawing predominantly on interaction processes, but also accounting largely for the other processes. In contrast, most models in invasion ecology invoke fewer processes and focus more on interactions between introduced species and their novel biotic and abiotic environment. The historical dominance of interaction processes and their independent developments in the two fields is also reflected in the lower level of coherence for models involving interactions, compared to models involving dispersal, drift, and genetic changes. It appears that community ecology, with a longer history than invasion ecology, has transitioned from the search for single explanations for patterns observed in nature to investigate how processes may interact mechanistically, thereby generating and testing hypotheses. Our framework paves the way for a similar transition in invasion ecology, to better capture the dynamics of multiple alien species introduced in complex communities. Reciprocally, applying insights from invasion to community ecology will help us understand and predict the future of ecological communities in the Anthropocene, in which human activities are weakening species’ natural boundaries. Ultimately, the successful integration of the two fields could advance a predictive ecology that is urgently required in a rapidly changing world.
Motivations and contributions of volunteer groups in the management of invasive alien plants in South Africa’s Western Cape province
(South African National Biodiversity Institute, 2021-07-08) Jubase, Nolwethu; Shackleton, Ross T.; Measey, John
ENGLISH ABSTRACT: Background: Research and management of biological invasions traditionally focuses on state operated large scale control initiatives, with little emphasis on volunteers. Volunteering can, however, contribute to detection, eradication and containment of invasive alien plant species (IAPS). Understanding the extent of involvement of volunteers in invasive alien species management is important. Similarly, understanding volunteers’ motivations to volunteering is important to improve the success of invasive alien species management. Objective: In this study we aimed to: 1) identify volunteer groups controlling IAPS in the Western Cape province of South Africa, 2) understand their practices and contributions towards detecting and controlling IAPS, 3) examine volunteer’s motivations for controlling IAPS, and, 4) identify the challenges individual volunteers and groups face. Methods: The data were collected using online questionnaires. Results: In total, we identified 52 volunteer groups. We broadly estimate that these groups clear nearly 8000 ha of land with estimated labour costs of ZAR 6.5 million annually (equivalent to USD 0.38 million) when aligned with formal state management cost estimates. Most volunteer groups raise their own funds to facilitate their work, however, many suggest support from government entities, landowners and Non-Government Organisations would help. Most volunteers (82%) detect and report invasive species to their team leaders, citizen science platforms and relevant authorities. Volunteers themselves gain physical and psychological fulfilment and build their social capital by meeting new people. Conclusion: Our findings point to the valuable contribution of these groups, but also the need for better co-ordination and engagement between volunteer groups and mandated authorities on science, policy and management
Overland movement in African clawed frogs ( Xenopus laevis ) : a systematic review
(PeerJ, 2016) Measey, John
African clawed frogs (Xenopus laevis) are often referred to as ‘purely aquatic’ but there are many publications which suggest extensive overland movements. Previous reviews which considered the topic have not answered the following questions: (1) is there evidence for overland dispersal in native and invasive ranges; (2) what is the range of distances moved overland; (3) when does overland movement occur; and (4) is there evidence of breeding migratory behaviour? A systematic review was chosen to synthesise and critically analyse all literature on the overland movement in Xenopus laevis. Database searches resulted in 57 documents which revealed a paucity of empirical studies, with 28 containing no data, and 19 having anecdotal content. Overwhelming evidence shows that both native and invasive populations of X. laevis move overland, with well documented examples for several other members of the genus (X. borealis, X. gilli, X. muelleri, X. fraseriand X. tropicalis). Reports of distances moved overland were from 40 m to 2 km, with no apparent difference between native and invasive ranges. Overland movements are not confined to wet seasons or conditions, but the literature suggests that moving overland does not occur in the middle of the day. Migrations to temporary water-bodies for breeding have been suggested, but without any corroborating data
Public awareness and perceptions of invasive alien species in small towns
(MDPI, 2021-12-14) Jubase, Nolwethu; Shackleton, Ross T.; Measey, John
Invasive alien species (IAS) are a growing threat globally and cause a variety of ecological, economic, and social impacts. People can introduce IAS and facilitate their spread, and can also implement, support, or oppose their management. Understanding local knowledge, awareness, and perceptions are therefore crucial if management and policy are to be effective. We administered questionnaires to members of the public in eight small towns along the Berg River Catchment in the biodiverse fynbos biome of South Africa. We aimed to assess: (1) awareness of IAS by the general public, (2) local perceptions of the impacts associated with IAS, (3) whether awareness of IAS is correlated with demographic covariates and IAS density, and (4) people’s willingness to detect, report, and support IAS management. Overall, 262 respondents participated in the survey. Most respondents (65%) did not know what IAS are, and 10% were unsure. Many respondents also perceived IAS as beneficial. Using a logistic regression, we found that IAS density, educational level, and gender influenced people’s knowledge and perceptions about IAS in the region. There were a small number (4%) of respondents currently detecting and reporting IAS, but many respondents were interested to learn more. We concluded that people living in small towns in the Western Cape of South Africa remain largely unaware of IAS and their impacts. It is crucial to increase awareness-raising initiatives, and build support and engagement in management of IAS in small towns.
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 role of ambient temperature and body mass on body temperature, standard metabolic rate and evaporative water loss in southern African anurans of different habitat specialisation
(PeerJ, 2019) Mokhatla, Mohlamatsane; Measey, John; Smit, Ben
Temperature and water availability are two of the most important variables affecting all aspects of an anuran’s key physiological processes such as body temperature (Tb), evaporative water loss (EWL) and standard metabolic rate (SMR). Since anurans display pronounced sexual dimorphism, evidence suggests that these processes are further influenced by other factors such as vapour pressure deficit (VPD), sex and body mass (Mb). However, a limited number of studies have tested the generality of these results across a wide range of ecologically relevant ambient temperatures (Ta), while taking habitat use into account. Thus, the aim of this study was to investigate the role of Ta on Tb, whole-animal EWL and whole-animal SMR in three wild caught African anuran species with different ecological specialisations: the principally aquatic African clawed frog (Xenopus laevis), stream-breeding common river frog (Amietia delalandii), and the largely terrestrial raucous toad (Sclerophrys capensis). Experiments were conducted at a range of test temperatures (5–35 °C, at 5 °C increments). We found that VPD better predicted rates of EWL than Ta in two of the three species considered. Moreover, we found that Tb, whole-animal EWL and whole-animal SMR increased with increasing Ta, while Tb increased with increasing Mb in A. delalandii and S. capensis but not in X. laevis. Whole-animal SMR increased with increasing Mb in S. capensis only. We did not find any significant effect of VPD, Mb or sex on whole-animal EWL within species. Lastly, Mb did not influence Tb, whole-animal SMR and EWL in the principally aquatic X. laevis. These results suggest that Mb may not have the same effect on key physiological variables, and that the influence of Mb may also depend on the species ecological specialisation. Thus, the generality of Mb as an important factor should be taken in the context of both physiology and species habitat specialisation.
Size-dependent functional response of Xenopus laevis feeding on mosquito larvae
(PeerJ, 2018-10-26) Thorp, Corey J.; Alexander, Mhairi E.; Vonesh, James R.; Measey, John; Kramer, Donald
Predators can play an important role in regulating prey abundance and diversity, determining food web structure and function, and contributing to important ecosystem services, including the regulation of agricultural pests and disease vectors. Thus, the ability to predict predator impact on prey is an important goal in ecology. Often, predators of the same species are assumed to be functionally equivalent, despite considerable individual variation in predator traits known to be important for shaping predator–prey interactions, like body size. This assumption may greatly oversimplify our understanding of within-species functional diversity and undermine our ability to predict predator effects on prey. Here, we examine the degree to which predator–prey interactions are functionally homogenous across a natural range of predator body sizes. Specifically, we quantify the size-dependence of the functional response of African clawed frogs (Xenopus laevis) preying on mosquito larvae (Culex pipiens). Three size classes of predators, small (15–30 mm snout-vent length), medium (50–60 mm) and large (105–120 mm), were presented with five densities of prey to determine functional response type and to estimate search efficiency and handling time parameters generated from the models. The results of mesocosm experiments showed that type of functional response of X. laevis changed with size: small predators exhibited a Type II response, while medium and large predators exhibited Type III responses. Functional response data showed an inversely proportional relationship between predator attack rate and predator size. Small and medium predators had highest and lowest handling time, respectively. The change in functional response with the size of predator suggests that predators with overlapping cohorts may have a dynamic impact on prey populations. Therefore, predicting the functional response of a single size-matched predator in an experiment may misrepresent the predator’s potential impact on a prey population.
A taxonomically and geographically constrained information base limits non-native reptile and amphibian risk assessment : a systematic review
(PeerJ, 2018-11-08) Van Wilgen, Nicola J.; Gillespie, Micaela S.; Richardson, David M.; Measey, John; Roberts, David
ENGLISH ABSTRACT: For many taxa, new records of non-native introductions globally occur at a near exponential rate. We undertook a systematic review of peer-reviewed publications on non-native herpetofauna, to assess the information base available for assessing risks of future invasions, resulting in 836 relevant papers. The taxonomic and geographic scope of the literature was also compared to a published database of all known invasions globally. We found 1,116 species of herpetofauna, 95% of which were present in fewer than 12 studies. Nearly all literature on the invasion ecology of herpetofauna has appeared since 2000, with a strong focus on frogs (58%), particularly cane toads (Rhinella marina) and their impacts in Australia. While fewer papers have been published on turtles and snakes, proportionately more species from both these groups have been studied than for frogs. Within each herpetofaunal group, there are a handful of well-studied species: R. marina, Lithobates catesbeianus, Xenopus laevis, Trachemys scripta, Boiga irregularis and Anolis sagrei. Most research (416 papers; 50%) has addressed impacts, with far fewer studies on aspects like trade (2%). Besides Australia (213 studies), most countries have little location-specific peer-reviewed literature on non-native herpetofauna (on average 1.1 papers per established species). Other exceptions were Guam, the UK, China, California and France, but even their publication coverage across established species was not even. New methods for assessing and prioritizing invasive species such as the Environmental Impact Classification for Alien Taxa provide useful frameworks for risk assessment, but require robust species-level studies. Global initiatives, similar to the Global Amphibian Assessment, using the species and taxonomic groups identified here, are needed to derive the level of information across broad geographic ranges required to apply these frameworks. Expansive studies on model species can be used to indicate productive research foci for understudied taxa.

Browsing by Author "Measey, John"

Results Per Page

Sort Options