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Retrieving loggers from KZN

14 March 2022

Downloading data from Hobo loggers

Sometimes you have to take a leap of faith and leave expensive equipment in the field in order to get much needed long-term data. This is what we did last February in a trip to KZN where we made an elevational transect while collecting African clawed frogs for Laurie (see Blog Post here). We placed four loggers at sea level, 1000 m, 2000 m and 3000 m asl. Sadly, the logger at 3000 m asl disappeared very soon after we placed it in a deluge of floods that hit Lesotho in March 2021. That meant that there were still three more loggers out in the field that needed to be retrieved. 

Happily, the logger from 2000 m asl at the Fat Mulberry was retrieved by Marggie and she brought it to Stellenbosch where we could download the data.

This month I made a trip back to KZN to retrieve the outstanding loggers from near Dalton and at Bonamanzi:

The temperature of the water in a dam near Dalton never went below freezing, but it did get quite cold (as well as getting hot in the summer). 

Meanwhile at Bonamanzi, the temperature was nearly always above 10 C, and even went above 40 C!

You may remember that Bonamanzi was where we had our traps vandalised by crocodiles. Happily though, you can see that the logger (right) didn't come to the same fate. The logger near Dalton (left) was still tied to the same stone sunk in the dam. 

Thanks to friends in Lesotho, we redeployed one of these Hobo devices there. Because you can replace their batteries, they are fantastic and just carry on working. We are hoping that the new logger won't go AWOL!

Sam defends his MSc thesis from a comfy chair in Mauritius

12 February 2022

An unusual MSc defence setting

Defending your MSc with an oral presentation can be a harrowing experience. The assembled crowd is anticipating the results of your research study, you are aware that your presentation counts as 20% of your final mark (in South Africa at least). It is time for your best performance. However, with COVID comes challenges and also opportunities. For Sam Peta, being able to present his MSc thesis defence online allowed him not to miss the opportunity of a lifetime with fieldwork in Mauritius. With the island closed to visitors (from South Africa) for nearly two years, Sam's only opportunity to go came around the same time that he needed to defend his thesis. 

An hour before the defence, the heavens opened and torrential rain fell on Mauritius. Undeterred, Sam continued to prepare to give his talk. The, about 30 minutes before the defence was due to start, the power to the house failed and we were thrown into the gloomy darkness of a power-cut in a storm on a tropical island. Quickly we devised a plan, we could use the mobile network and hope that the laptop battery would continue to work for the full talk. Just as we got it all set up, around 10 minutes before the start, the power popped back on again and we breathed a sigh of relief.

Sam settled into presentation mode, making himself comfortable as much as he could while he talked to the congregated academics. The talk went well but now it was time for the inquisition. Sam responded to all questions in his usual detailed response, and after nearly an hour the defence was over.

I took Sam out for dinner at the Flying Dodo to celebrate this final hurdle of his MSc studies. We will remember this MSc defence for a long time to come.

Fieldwork for Sam in Mauritius

11 February 2022

Sam Peta - In Mauritius at long last

The COVID-19 restrictions have been tough on most people, but for MSc student Sam Peta they turned his international fieldwork for his MSc studies into a very local affair. Sam was supposed to be investigating diet and trophic levels of invasive and native populations of the Guttural Toad (Sclerophrys guttuarlis) using a suite of quantitative methods. Those invasive populations include Cape Town, and the Indian Ocean islands of Mauritius and Reunion. 

However, the COVID lockdowns started only 3 months into Sam's thesis, when he had only managed a single trip to the native range in Durban. At the time, we thought that we'd still get Sam into the field to work on the island populations before the end of his thesis. But back then we were not familiar with the course of the pandemic, the waves and the variants that would see those in southern Africa become the new pariahs of the rest of the world. 

Although the trip was postponed, happily for Sam he managed to make it to Mauritius and conduct the planned field work on their tiny toads. Sadly, this work is too late for his thesis, but it'll be a great addition to his existing work on Guttural Toad diet. Reunion remains closed.

Eggs, toads or tadpoles & the hydra effect

22 December 2021

All toads are equal, but some are more equal than others

When conducting an eradication campaign, it seems obvious that you should go out and collect all the individuals you can find. But could collecting some individuals be more important than others? This question is especially important when it comes to animals with complex life-cycles where the larvae and adults inhabit different parts of the ecosystem. We asked this question of the Guttural toad eradication in Cape Town, and received some surprising answers. 

Guttural toads lay large numbers of eggs, and their tadpoles inhabit garden ponds in the low-density, high-income suburb of Constantia. Meanwhile, the adults cruise around the gardens looking for insects and snails to snack on. For the people charged with their control, they can either spend their time cruising in the shrubberies looking for adult toads, or go to the ponds with nets and scoop up tadpoles and strings of eggs. Or of course, they could do both. But what is the best strategy?

Giovanni Vimercati built a mathematical model of the Guttural toad population in Constantia to answer this problem (see also Vimercati et al. 2017a,b). Recently, Gio used this same model to answer the question of which life-history stage of these toads should be targeted by people trying to control the population. Because there is strong competition between tadpoles and metamorphs, Gio found that any attempts to remove these aquatic life-history stages resulted in an increased number of toads in the population. The counter-intuitive result is known as the ‘hydra effect’ - where cutting off some heads simply makes more grow. In the case of the Guttural toad, the removal of some of the aquatic stages increases the rate of survival and fitness of those that remain. 

The model has the advantage that it can be run forwards to see what happens to the population given different control regimes. The mathematical model results told us that to maximise the impact of time spent controlling toads, concentrate on collecting adults. Adult removal has a far greater impact on the total population. 

To read more:

Vimercati G, Davies SJ, Hui C, Measey J (2021) Cost-benefit evaluation of management strategies for an invasive amphibian with a stage-structured model. NeoBiota 70: 87–105. 

Other publications on this model are:

Vimercati, G., Davies, S.J., Hui, C. & Measey, J. (2017) Does restricted access limit management of invasive urban frogs? Biological Invasions19: 3659-3674.

Vimercati, G., Davies, S.J., Hui, C. & Measey, J. (2017) Integrating age structured and landscape resistance models to disentangle invasion dynamics of a pond-breeding anuran. Ecological Modelling 356: 104–116 

Another online CIB-ARM

19 November 2021

Centre for Invasion Biology - Annual Research Meeting - online again

By May 2021 it seemed that we could have started planning for an in-person Annual Research Meeting (ARM) for the Centre for Invasion Biology (CIB), but decided to err on the side of caution and keep it online only. That turned out to be the best plan as the third wave of COVID hit us in July and still hadn't entirely left by September. 

We managed to fit all CIB students into 4 pods led by all remaining post-docs, and had some great presentations from all members of the MeaseyLab. Below you will find images of everyone giving their talks. 

Sam Peta, M.Sc. An army marches on its stomach: diet composition and prey preference of guttural toad (Sclerophrys gutturalis) populations along a native-invasive and natural-urban gradient. 

John Measey How to write a PhD in Biological Sciences - book launch

SESSION 03: Distribution, spreading and impacts of invasive species Introduced and chaired by
Dr Andrea Melotto

Dan Van Blerk, M.Sc. Impacts of invasive fish on amphibians in lentic and lotic systems: a meta-analysis 

Laurie Araspin, Ph.D. Temperature dependence of locomotor performance across an altitudinal gradient in an invasive frog, Xenopus laevis

Of course, you can watch the full meeting (only 7.5 hours) on YouTube (below) if you want!

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