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BRICS countries call for invasion networks

19 September 2019

Brazil, Russia, India, China and South African (BRICS) authors all call for action to build capacity in invasion science

BRICS (Brazil, Russia, India, China and South African) countries are rapidly developing economies, with a large proportion of their populations having subsistence livelihoods. Their rapid development means that they are exporting ever increasing amounts of goods to the rest of the world, and with them are likely to be propagules of invasive species. Not only this, but these countries are increasingly importing goods from around the world, and are suffering from an ever growing list of similar invasive species. 

When problems are shared, such as invasive species in BRICS countries, a network is an attractive solution to share experiences and solutions in a meaningful way. South Africa already has an exemplary example of a facilitated network in invasion biology: the DSI-NRF Centre of Excellence for Invasion Biology (or CIB as we are more commonly called). 

Last November, the CIB hosted a workshop on facilitated networks in Invasion Science (see blogpage here). As was said back then, we were formulating a policy piece, which is now published as a perspective piece in PLoS Biology.

Measey, J., Visser, V., Dgebuadze, Y., Inderjit, Li, B., Dechoum, M.S., Ziller, S.R. & Richardson, D.M. (2019) The world needs BRICS countries to build capacity in invasion science. PLoS Biology

  Lab  meetings

What's the big idea?

17 September 2019

What’s the big idea?

In previous blog posts (see here), I’ve talked about the importance of having a hypothesis, and building that hypothesis in a logical framework within the introduction (see here). The introduction serves to inform the reader about why this particular hypothesis was chosen, introducing both the response and determinate variables, as well as the presumed mechanism by which the hypothesis can be falsified (or upheld).

In this post, I take the lead from my recent talk for the Herpetological Association of Africa (see blog post here), in which I talked about the need for herpetologists to respond to bigger theories in biological sciences.

This message was the result of work done in the MeaseyLab (but not yet completed!) on invasion hypotheses, where we (Nitya, James, Sarah, Natasha and I) checked 850+ papers on alien herps to see which of 33 common invasion hypotheses they had tested. The answer was disappointing, with <1% having used an invasion hypothesis.

In my talk, I suggested that this might not be true only of papers on herpetological invasions, but also of herpetology in general (although I concede that some areas, such as herp physiology are actually quite good). Further, I contend that using these wider hypotheses or theories would actually be good for the authors concerned, as it would likely garner them a wider audience. Moreover, a greater number of biologists might come to realise how valuable reptiles and amphibians are as models in biology.

So where would we find all of these big ideas?

There are quite a few papers that synthesise hypotheses in various areas of biology. Here I provide two, but I will endeavour to add more as I come across them… so watch this space (although not too keenly).

The first is by Mark Velland on theories in community ecology

The next is by Jane Catford on hypotheses in invasion biology, but I encourage you to look for more up to date versions (the newest is by Enders et al 2018, but this’ll change in time).

Each of these papers will give you a list of big ideas, together with the citations for seminal papers that have built them. You will note that many of these theories are very old with many dating back to Darwin.

Of course, there are many ways to approach and test these theories, but if you don’t know about them, then your work may actually make a considerable contribution to upholding or refuting them, but go totally unrecognised. When the significance of your work isn’t realised, it’s unlikely that it’ll be widely read and used.

Let’s face it, if all the effort of the work that we put into papers is just going to get buried, then is it really worth it? The work that we do is also really expensive, so making it as relevant as we can to a wide an audience possible is something that we should be concerned about.

So, I encourage you to stand on the shoulders of giants by using big ideas in your introduction. Make sure that the data that you collect can actually be used to respond to some of these big ideas. Then make sure that you cite them, giving them the importance that they deserve (yes, even as key words) so that others can find your work, and you might even find that one day, your work has shoulders that are broad enough for others to stand on!

A useful structure for thinking about how hypotheses are structured was presented by Heger & Jeschke (2018) in what they termed the 'Hierarchy of Hypotheses'.

The take home message:

1. As herpetologists we are not engaging with theories from ‘the literature’

2. Herps are great models [even snakes]

3.We have a lot to donate to many areas of biology, but we need to engage

Reading the literature can really expand your mind and horizons. When undertaking a literature review [or when reviewing a paper], take the time to think about not only what has been tested, but what could have been.

Further Reading

Catford, J.A., Jansson, R. and Nilsson, C., 2009. Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework. Diversity and Distributions15(1), 22-40.

Enders, M., Hütt, M.T. and Jeschke, J.M., 2018. Drawing a map of invasion biology based on a network of hypotheses. Ecosphere9(3), p.e02146.

Vellend, M., 2010. Conceptual synthesis in community ecology. The Quarterly review of biology85(2), 183-206.

Heger, T. and Jeschke, J.M., 2018. The Hierarchy-of-hypotheses Approach Updated – a Toolbox for Structuring and Analysing Theory, Research and Evidence. In Invasion Biology: Hypotheses and Evidence. J. Jeschke and T. Heger eds. CABI. pp 38-45.

  Lab  Writing

The HAA meeting 2019

13 September 2019

The HAA meeting at Cape St. Francis, Eastern Cape

Only 8 hours drive from Cape Town, and we arrived at Cape St. Francis in the Eastern Cape to attend the Herpetological Association of Africa's 14th conference.

Of course, once we were there, we all gave stunning talks from many members of the MeaseyLab, both those based at Stellenbosch University and elsewhere. Nitya got a special surprise when the paper on which his talk was based was accepted in the session before he talked! Very welcome news indeed!

It was good fun to get to the beach, meet up with plenty of herpers that we knew and meet new ones that we didn't know. A special mention to Alan Channing who received the HAA's highly prized life-time achievement award for his contribution to southern African frog taxonomy. More than 20 years ago (1998), I worked with Alan at UWC during my first Royal Society post-doc (see here). 

Here are some of the abstracts of the talks:

Kruger, N, Vimercati, G, Herrel, A, Secondi, J & Measey, J Spatial sorting on dispersal traits are stage dependent in the invasive amphibian Xenopus laevis in western France

Organisms are exposed to trade-offs constraining their anatomy, physiology, and behavior between dispersal and life-history traits. The spatial sorting theory predicts the enhancement of dispersal traits due to resource re-allocation at the periphery of expanding populations. A more nuanced view of spatial sorting emerges when one considers organisms with complex life cycles in which dispersal usually occurs at a particular ontogenic stage. It is currently not known if enhancement of dispersal traits in organisms with complex life cycle emerges only at the dispersal stage. In amphibians, larval development can influence life-history traits that directly influence dispersal in post-metamorphic juveniles. Spatial sorting for dispersal traits occurs in adults of the invasive African clawed frog, Xenopus laevis, in western France. Individuals have been expanding from a single introduction point since the 1980s colonizing an area of ~2000 km2. The mass of reproductive organs is reduced at the range periphery while the dispersal rate, probability and distance are increased. In X. laevis all stages are aquatic and dispersal is terrestrial. We predict that the enhancement or adaptation of dispersal traits due to spatial sorting occurs at the onset of their development regardless of dispersal ability of tadpoles. To test this, we conducted experiments in outdoor mesocosms and in microcosms in the lab. We surveyed tadpole development for 10 weeks from hatching to metamorphosis. We observed no effect of site position (core vs. periphery) on morphology, development, and survival of tadpoles. This study shows that spatial trait variation in pre-dispersal and dispersal stages are decoupled to a large extent in species with complex life cycles. In amphibians, tadpole development is constrained by factors such as initial density, food availability, and predation whereas in adults, resource allocation to dispersal can be enhanced at the dispersing stage and not at the pre-dispersal stage.

Measey, J, Baxter-Gilbert, J, Davies S, Kruger, N, Mohanty N How do herpetologists study invasions?

Invasion Biology is a young discipline, Charles Elton only coined the term in 1958. Although the subject was generally ignored by most people for 40 years, the last 20 years has seen a near exponential rise in papers by herpetologists on alien reptiles and amphibians (and not only by Rick Shine!). But how do herpetologists go about studying invasions? In this study, we reviewed 836 publications on alien herps and compared their objectives with 30 well known hypotheses from invasion biology. We found that although the field is rapidly expanding, very few researchers had specified any of the invasion hypotheses, but 26% had the data to test one or more. The most commonly tested hypothesis resembled the concept of the ‘ideal weed’, that invasion success of a non-native species depends on its specific traits (3.8%). Other popular hypotheses referred to habitat filtering (1.7%), preadaptation through human commensalism (1.8%), novel weapons (1.3%), novel associations (1.4%) and invasion meltdown (1.5%). Perhaps more excitingly, are the new hypotheses that herpetologists can donate to invasion biology, including spatial sorting, invasion hubs and hybridisation. We conclude that herpetologists need to pay more attention to existing hypotheses in invasion biology, many of which stem from classical questions in ecology. Better transdisciplinary communication will likely lead to increased impact of studies which could teach invasion biologists more about reptiles, amphibians and their amazing invasions.

Mohanty, N & Measey, J The global pet trade in amphibians: Species traits, taxonomic bias, and future directions

The burgeoning global pet trade in vertebrates has multi-pronged conservation implications, including overexploitation of native populations, spread of diseases, and invasions. The majority of amphibian invasions are due to the pet trade pathway and current lists of extra-limital amphibians (including those in trade) suggest that future invasions will encompass a broader taxonomic diversity than is known. Given that trade is dynamic, it is essential to move beyond currently traded species and understand which species are likely to be traded in the future and serve as candidates for invasions. In this study, we systematically assess amphibian species in the pet trade, i) characterising taxonomic bias, ii) evaluating species-traits as predictors of traded species and trade volume, and iii) forecasting likely future pets. We collated a global list of 443 traded amphibians and a regional dataset (USA) on trade volume. Species-traits (body size, native range size, clutch size, and breeding type) and conservation status, were considered as predictors of traded species and volume. Six Families contributed disproportionately to the amphibian pet trade; the likelihood for species to be traded was positively associated with body size, range size, and a ‘larval’ breeding type. However, species-traits performed poorly in predicting trade volume, suggesting an overriding effect of socio-economic aspects of the trade. The identified species-traits and taxonomic bias of the trade were then used to predict species likely to be traded as pets in the future. This study formalizes the knowledge on amphibian species that are traded as pets. We found a strong bias for certain Families, along with a preference for large-bodied and widely distributed species with a larval phase. Our results pave way for more trait-based approaches to forecast amphibians entering the trade. Such understanding of the pet trade can help pre-emptively tackle the pathway responsible for most invasions and disease spread in amphibians.

Peta, STP, Engelbrecht, GD & Measey, J Reptile and avian assemblage along a gradient of invasive alien plants in the critically endangered Woodbush Granite Grassland

Invasive alien plants species (IAPs) are a significant problem in South Africa and can pose complex and far-reaching challenges to biodiversity, with impacts on fauna poorly understood. The study aimed for multi-site comparison of reptile and bird assemblages between pristine grassland, alien plant invaded and plantation habitats. Reptiles and birds were surveyed using standard Y-shape trap array and fixed-point counts respectively. Vegetation structure and invasion intensity was determined using point-intercept method. Five IAPs were identified: Acacia mearnsii, Eucalyptus grandis, Pennisetum clandestinum, Pinus patula and Solanum mauritianum. Reptiles (23 individuals from 5 species) were recorded, with highest abundance and diversity in the grassland. Birds (2113 individuals from 67 species) showed the greatest abundance, diversity and richness in the invaded habitat. Trachylepis varia was a common reptile species, showing overlap between grassland and invaded habitat. Lygodactylus methuen was the only identified endemic reptile species. Grassland bird specialists (i.e. Anthus similisCisticola lais, and Sphenoeacus afer) were observed in more open and moderately invaded habitat but absent in denser and heavily invaded habitat. The study demonstrated that reptiles and birds respond differently to alien plants invasion. Reptiles were mostly supported by low vegetation cover, availability of microhabitats e.g. rocks and bare ground for thermoregulation while birds responded to rich vegetation stratification. Clearing of invasive alien plants can be considered as management strategy if it is to promote biodiversity. Clearing can create more thermal opportunities for reptiles and accommodate open habitat bird species.

Telford, N, Channing, A & Measey, J Origin of invasive populations of the Guttural Toad, Sclerophrys gutturalis

The Guttural toad, Sclerophrys gutturalis, has three established invasive populations on Mauritius, Reunion and in Constantia, a peri-urban area of Cape Town, South Africa. The native range of this toad covers much of central and southern Africa. Here we use mitochondrial DNA (mtDNA) to sample across the range of the natural distribution (from Kenya to South Africa) and compare ND2 and 16S sequences to those from animals sampled from each of the three invasive populations. We show that all invasive populations refer to the same mtDNA clade, which is naturally distributed in north-eastern South Africa, but not from adjoining Mozambique or southernmost Eastern Cape areas. Our findings corroborate previous reports of deliberate introductions from South Africa to Mauritius, and from Mauritius to Reunion. Similarly, our results suggest a single accidental translocation within South Africa from the northeast to Constantia. Our findings highlight the combination of anthropophilic behavior, and extreme long-distance dispersal occurring with accidental translocation for this species. We caution that accidental pathways are likely to continue into the future, with increasing numbers of invasive populations of this species.

Wagener, C, Kruger, N & Measey, J Xenopus laevis progeny display local adaptation of physiological performance to environmental extremes

Altitudinal variation of environmental temperatures is expected to shape the evolution of physiological functions of widespread populations. Adaptation to thermal extremes can create altitudinal differentiation in ectotherm physiological performance. In this study, a common garden experimental approach was employed to determine whether thermal adaptations to contrasting environmental regimes are heritable and how these thermal adaptations affect performance. To address this, we compared the critical thermal limits and swimming performance of African clawed frog (Xenopus laevis) tadpoles bred from two adult populations captured from high (~ 2000 m above sea level) and low (~ 5 m above sea level) altitudinal extremes. Parental-origin significantly affected tadpoles’ critical thermal minima (CTmin), maximum velocity, maximum acceleration, total distance and distance travelled in the first 200 m.s-1. Tadpoles with low-altitude parental-origins had a higher optimal temperature (Topt) for swimming performance and CTmin than tadpoles with high-altitude parental-origins. Performance of tadpoles bred from high-altitude adults was significantly higher at cooler temperatures and lower at the highest test temperature, in comparison with tadpoles bred from low-altitude adults. These results suggest that thermal performance curves of X. laevis tadpoles have adapted in response to contrasting local environmental conditions experienced by adults. Future studies should focus on whether similar thermal performance trait variations are present in other populations of the widely distributed African clawed frogs (X. laevis).

Jordaan, PR, Measey, J, Hanekom, CC, Greend, AN, Woolcocke, AB, Combrink, X Grassland and savanna fossorial herpetofaunal densities

Ecological data on soil living amphibians and reptiles are largely lacking. Specialised methods relying on substrate excavation are required to adequately quantify fossorial herpetofaunal densities as surveying techniques which rely on surface movement (e.g. pitfall or funnel trap surveys) are biased against soil-living species which infrequently move over the soil surface. As part of a larger study, we quantified baseline densities for fossorial herpetofauna in grassland at Sileza Nature Reserve and in savanna at Tembe Elephant Park. All sites were underlain by aeolian sand. Grassland surveys were conducted at two adjoining sites, one during summer, and one in winter while both savanna sites were only surveyed during winter. Quadrats of 4 m2 (2 m x 2 m) were excavated to a mean depth of 0.25 m (volume of 1 m3) as most species of fossorial herpetofauna are considered to live at shallow soil depths. The excavated substrate was momentarily stored in 20 litre buckets before being sifted through a 2 mm x 2 mm (4 mm2) metal mesh, exposing soil living reptiles and amphibians. Grassland fossorial herpetofaunal densities were marginally lower during winter (0.56 individuals.m-2) compared to the summer (0.67 individuals.m-2) survey. Grassland species richness consisted of a single amphibian, Breviceps mossambicus, as well as five reptile species. Although amphibian species richness was considerably lower in grassland compared to reptiles, densities were higher especially during summer. Inter-seasonal demographic variability was observed in the grassland amphibian population with higher numbers of juveniles present during the summer. Herpetofaunal fossorial densities at savanna sites were on average more than four times lower (0.11 and 0.14 individuals.m-2 respectively) compared to grassland. Once again, the only amphibian present was B. mossambicus, but in much lower densities (0.01 and 0.02 individuals.m-2). It is hoped that the outcomes of this study will contribute to a better ecological understanding of soil megafauna in grassland and savanna ecosystems.

Plenary talk for SEH20

06 September 2019

The future of our planet’s amphibians and reptiles: a view from invasion science

I was asked to deliver a plenary to the 20th meeting of the Society for European Herpetology back in October 2018. This gave me a very long time to think about what soap box I wanted to get onto. This plenary invitation came with no strings, so I had the full gambit of subjects to consider. Given my current position and my recent reviews of the herp literature, it was clear to me that I wanted to give herpetologists more background and ideas about why invasion science is particularly important subject to be involved with.

I started my presentation with a reflection on the writing workshop of editors we had back in March 2019. It was John Wilson who suggested that for the last chapter of the book “Biological Invasions in South Africa” we should consider long-term trajectories of invasions, following the lead of Baum et al (2019). This gave us 4 outcomes for 2000 years’ time, and I began the plenary by describing each one and then explaining how we might expect invasion profiles to look in order to reach the outcomes.

In this slide, you’ll only see 3 outcomes as I ditched the ‘end of humanity’ trajectory as the planning for this is too similar to ‘pangea’.

You’ll be able to read more about the outcomes of this exercise in the forthcoming book chapter (Wilson et al 2019), but for the purposes of this blog post, the idea in both the plenary and the book chapter was to help people see how short-term planning needs to be in line with long-term thinking. This seems to be especially relevant now that we’ve lost the ability to think in the ‘long now’ that we had in the past.

This framework allowed me to place the Seebens et al (2017) revelation that there’s no saturation to alien introductions into the context of both alien reptiles and amphibians, and those other invasive populations that damage them (cf Nunes et al 2019).

I then continued by explaining the importance of the pet trade in future amphibian and reptile invasions (cf  Measey et al 2019; Mohanty & Measey in press), and especially the relevance of invasion debt in this; such that we should not expect to see invasive populations of all of these newly traded species, but that they will come in time.

I finished off the talk, by giving a few highlights of why studying invasive species is such fun. Special shout-outs were given to studies by Nick Telford, Nitya Mohanty, Gio Vimercati, Nicola van Wilgen and Carla Madelaire (among others).

If you’ve helped and are reading this blog, but didn’t get a chance to see the plenary, here’s the acknowledgement slide at the end, in which should be your pic!


Baum SD et al. (2019) Long-term trajectories of human civilization Foresight 21:53-83 doi:10.1108/fs-04-2018-0037

Measey J et al. (2019) Why have a pet amphibian? Insights from YouTube. Front. Ecol. Evol. 7: 52. doi: 10.3389/fevo.

Nunes AL et al. (2019) A global meta-analysis of the ecological impacts of alien species on native amphibians. Proceedings of the Royal Society B286(1897), p.20182528.

Seebens H et al. (2017) No saturation in the accumulation of alien species worldwide. Nature Communications8, p.14435.

Wilson JR et al. (2019) Potential Futures of Biological Invasions in South Africa. In van Wilgen et al. Biological Invasions in South Africa. Springer.

Other MeaseyLab talks at SEH20 were:

Ginal, P. Herrel, A., Measey, J., Mokhatla, M., Rodder, D. Ecophysiology predicts the fundamental niche of native and invasive populations of the African clawed frog Xenopus laevis. XX European Congress of Herpetology, Milan 2-6 September 2019

One main threat promoting the worldwide amphibian decline is the introduction of non-indigenous amphibians, like the African Clawed Frog Xenopus laevis, which is now one of the widest distributed amphibians occurring on four continents with ongoing expansion including large parts of Europe. Species Distribution Models (SDM’s) and the concept of ecological niche are essential to predict the invasive risk of those species. Previous efforts to predict distributions of invasive amphibians have mainly focussed on correlative approaches but these can be vulnerable to extrapolation errors when projecting species’ distributions in non-native ranges. Recently, more robust process-based models, which use physiological data like critical thermal limits, or hybrid models of both approaches were used for this purpose. Previous correlative SDM’s for Europe predict different patterns in the potential distribution but it is likely that these models do not access the full invasive potential. Based on physiological performance trials we calculated size and temperature depending response surfaces, which were scaled to the species’ range matching the critical thermal limits. These ecophysiological performance layers were used in a standard correlative SDM framework to predict the potential distribution in South Africa and Europe. We found thermal performance differed significantly among native and invasive populations indicating some degree of fundamental niche change, which lead to different potential distribution patterns for the native and invasive populations in the respective ranges. Our hybrid-SDMs revealed that X. laevis has a much higher invasive potential than previous correlative models predicted for Europe.

Measey, J. The future of our planet’s amphibians and reptiles: a view from invasion science XX European Congress of Herpetology, Milan 2-6 September 2019

In 2000 years, the future of our planet could have one of four potential outcomes: end of humanity, Pangea, use some/preserve others, and conservation earth. While we have already started along the trajectory toward Pangea, our actions in the near future will determine whether we can achieve a future where we retain areas that are preserved and herpetologically distinct. Among the global change drivers, invasion science is increasing in importance because of a continuing and near exponential increase in trade. We need all herpetologists to help generate the data needed to prevent the Floridarisation of herpetology. In this presentation, I outline a number of ways in which herpetologists can push back against herpetological Pangea: (i) characterising current invasive species, (ii) determining the breadth of invasion debt, and (iii) scoping the traits of all species to establish a rational basis for future trading. Although it was only conceived in the 1950s, invasion science now draws on almost all disciplines in biology, including phylogenetics, population biology, evolutionary ecology and modelling, to name but a few. However, our best chances of preventing herpetological Pangea may come from social science studies of what drives the trade in reptiles and amphibians. The challenge for us is to retain the potential for inspiring reptile and amphibian pets for coming generations, without peppering our environment with propagules of invasive species.

Vimercati, G., Davies, S. & Measey, J. Invasive subtropical toads allocate more resources to growth and maintenance over reproduction and storage in a mediterranean environment. XX European Congress of Herpetology, Milan 2-6 September 2019

Amphibians living in cold and seasonal environments allocate more resources to growth, maintenance and storage than do conspecifics from warmer and less seasonal environments. This sustained resource allocation may be obtained at the expense of reproduction, especially when low conditions of temperature and rainfall restrict breeding season length. Invasive populations act as experiments to explore how resources are allocated in novel environments. We studied the guttural toad Sclerophrys gutturalis, a synanthropic species which naturally inhabits subtropical areas of central and southern Africa. Guttural toads were introduced in the early 2000s to Cape Town, where they rapidly became invasive. Since Cape Town experiences a mediterranean climate, the species has been exposed to an environment that is cooler and presents a different rainfall pattern from that of the native range. We targeted the Cape Town invasive population and a native source population from Durban (South Africa). After dissection, lean structural mass (bones and muscles), gonadal mass, liver mass and body fat % were measured in 161 native and invasive animals sampled at the beginning and the end of the breeding season. As expected, male and female toads from the invaded range allocate more resources to growth and maintenance than their native counterparts, whereas invasive female toads direct fewer resources to reproduction than native ones. Unexpectedly, energy storage of guttural toads does not consistently differ between invaded and native ranges. Such allocation shift may be a response to the low temperature, reduced rainfall and heightened seasonality encountered by the invasive population.

Another Guttural Toad revelation

03 September 2019

Capital Breeding in Cooler Cape Town

A new study suggests that guttural toads are changing their breeding patterns to accommodate the cooler, drier Cape Town climate.

In this study, Giovanni Vimercati compared the mass of different organs from guttural toads from their native population in Durban (see post here) and the invasive population in the peri urban area of Constantia, near Cape Town. The relative masses of the different organs provide information about how these toads invest their energy. 

Native frogs in Cape Town save up much more energy in their storage organs prior to breeding, because of the inhospitable dry summers. Whereas the guttural toad in its native Durban, uses energy as they generate it during the breeding period. These two strategies are known as capital- and income-breeding, respectively. 

Giovanni's study suggests that even though they have only been in Cape Town for less than 20 years, they have already started moving toward a capital breeding strategy, typical of the native species in the area. However, he only found this difference in females and not males.

The MeaseyLab is conducting lots of interesting work on invasive populations of Guttural Toads at the moment. To see more blog posts about this work, click here.

Vimercati, G., Davies, S. & Measey, J. (2019) Invasive toads adopt marked capital breeding when introduced to a cooler, more seasonal environment. Biological Journal of the Linnnean Society pdf

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