Introducing aSCR to the San Diego Zoo

While in California this July, I was asked to give a talk on some of my work for a weekly meeting of the San Diego Zoo staff. I chose to talk about aSCR because of the relevance it has to monitoring threatened species. 

There was a good turnout and some great questions after the talk. The zoo has a great presentation room with a nice sound system on which we could listen to the calls of South African frogs. 

It was great to give a talk on aSCR again and reflect on how much we have achieved with this technique over the last 10 years. 

Measey, J. Counting chirps. Acoustic monitoring of threatened frogs in South Africa's fynbos. San Diego Zoo. 13 July 2023

A big step toward conservation of Rough Moss Frogs

Ten years is a relatively short period of monitoring data, yet it can reveal important ecological interactions that can inform conservation managers about on the ground decisions. In this study, published today, we show the clear synergistic relationship between fire and the invasion of pine trees on populations of moss frogs on the Klein Swartberg. 

In the figure below, you can see how the density of calling male Rough Moss Frogs increases in the absence of invasive pine trees, but declines in their presence. In addition, our analyses indicated that this decline was manifest when fire interacted with the invasion.  

We obtained the density estimates of calling frogs in this study from a microphone array using the aSCR methodology (described here). We employed this approach at 12 sites on the Klein Swartberg over 10 years with 35 recordings. This included the initial work undertaken by Debra Stark (see here). Debra's work is published in a book chapter (see here). Currently, the invasion of pines on the Klein Swartberg is incredible, but undergoing control through block burning. 

A picture of Oliver Angus among the pines on the Klein Swartberg in June 2021. 

Further reading:

Angus, O., Turner, A.A. & Measey, J. (in press) In a Rough Spot: Declines in Arthroleptella rugosa calling densities are explained by invasive pine trees. Austral Ecology https://doi.org/10.1111/aec.13273

Getting a reporter's view

When I got an email from Wendell Roelf, Reuters news agency, asking for information about invasive trees and any frogs that they may impact, there was one clear example that sprung to mind. We have been monitoring the rough moss frog on the Klein Swartberg near Caledon for around 10 years now. In that time the invasion from pine trees on the massif has been spectacular. Since a fire in 2011, we have seen the mountain turn from blackened earth to a carpet of pine seedlings, and now thick sways of pines that are so dense that individuals are as thin as sticks but have reached 3 to 4 m in height. 

In amongst all this the Rough Moss Frog, Arthroleptella rugosa, can be found in fewer spots on the mountain. Where it is still present among the pines the calls are far fewer. Oliver Angus, Honours student in the MeaseyLab, has been using aSCR to determine the density of the remaining populations of the Rough Moss Frog. Stay tuned to see the outcome of his findings here.

The MeaseyLab (myself, Oliver Angus and Andrea Melotto) took Wendell Roelf and cameraman Mike Hutchins up the Klein Swartberg where we introduced him to Andrew Turner from CapeNature, Lampie Fick chairman of the Klein Swartberg nature conservancy, and a team of contractors who are cutting fire breaks that will form the basis of a rotational burn on the mountain that should see it free of pines in the future. After getting the full picture, Wendell took himself off into the pines to jot down notes for his story.

It was a fun day and great to see that Wendell wrote a great article that has been syndicated all over the world.

To read Wendell's article, click the image below:

They also put together a neat video that shows what it takes to remove invading pine trees:

The southwestern Cape is getting warmer and drier - bad news for frogs

Many of you will be aware that the extreme southwestern Cape of South Africa is a frog biodiversity hotspot. There are four endemic genera and 36 endemic species that occur in the fynbos alone (see Colville et al.2014). It is also a hotspot where many species are threatened, as shown in the following image from Angulo et al. (2011). Reasons for the threats include habitat transformation and invasive species, but new data from the IPCC suggest what many of us have been thinking that the climate is getting worse for amphibians in this area.

Frogs from this area breed in seasonal temporary vernal pools, puddles or have direct-developing tadpoles that rely on seepages and moist environments. A combination of reduced rainfall and increased temperatures in this region is therefore bad news for frogs. 

This area of the world is also under high anthropogenic pressure. The City of Cape Town has expanded to include ~4.6 million people, all of whom require food grown in the lowland areas North and East of the city. Species in the mountains are generally impacted by invasive plants such as pines and acacias. 

The new IPCC WGI interactive Atlas (https://interactive-atlas.ipcc.ch/) with regional information allows users to plot mean temperatures and mean precipitation per decade from 1980 to 2015. The trended data demonstrates that this region of the world is getting warmer and drier. This is within living memory, and chimes with comments from the community that frogs are becoming generally less abundant when walking in the mountains. According to Barry Rose, who as a boy in the 1950s collected frogs for his grandfather, when walking in the mountains of the Cape peninsula he saw an abundance of frogs that would jump out of his path as he moved through the fynbos. Now they seem to be far fewer.

We have also seen this trend in our research on toadlets from the genusCapensibufo. Cressey et al. (2015) that are no longer in many of the places where they were found in the 1970s. We have also seen general analyses on the assemblage frogs in this area from Mokhatla et al. (2015).

Is climate to blame for enigmatic declines?

It is very hard to know whether climate change alone is reducing the overall numbers of frogs in the fynbos. But this does underline the importance of monitoring populations of the species that remain. Very few areas are being monitored, but we appreciate that there is a need for long term support for initiatives that are collecting data (Measey et al.2019). 

See the recent blog posts (hereandhere) to find out more about how the MeaseyLab is attempting to monitor populations of frogs by usingaSCRto quantify the density of calling males.

Literature

Angulo, A., Hoffmann, M. & Measey, G.J. (2011). Introduction: Conservation assessments of the amphibians of South Africa and the world. In: Ensuring a future for South Africa’s frogs: a strategy for conservation research. (ed. G.J. Measey), pp. 1-9. SANBI Biodiversity Series 19. South African National Biodiversity Institute, Pretoria. 

Colville, J.C., Potts, A.J., Bradshaw, P.L., Measey, G.J., Snijman, D., Picker, M.D., ProcheŞ, S., Bowie, R.C.K. and Manning, J.C. (2014) Floristic and faunal Cape biochoria: do they exist? In: Fynbos: ecology, evolution, and conservation of a megadiverse region. (eds. Allsopp, N., Colville, J.F., Verboom, G.A.) pp 73-93. Oxford University Press. 

Cressey, E.R., Measey, G.J., & Tolley, K.A. (2015). Fading out of view: the enigmatic decline of Rose’s mountain toad Capensibufo rosei. Oryx, 49, 521–528.https://doi.org/10.1017/S0030605313001051 

Measey, J., Tarrant, J., Rebelo, A.D., Turner, A.A., Du Preez, L.H., Mokhatla, M.M., Conradie, W. (2019) Has strategic planning made a difference to amphibian conservation research in South Africa? African Biodiversity & Conservation - Bothalia  49(1), a2428.https://doi.org/10.4102/abc.v49i1.2428

Mokhatla, M. M., Rödder, D. & Measey, G.J. (2015) Assessing the effects of climate change on distributions of Cape Floristic Region amphibians. South African Journal of Science;111, 2014-0389.https://doi.org/10.17159/sajs.2015/20140389

10 years of monitoring the Rough Moss Frog

It was 2011 when I first visited the Klein Swartberg, near Caledon, to carry out aSCR recordings to measure density of calling male Rough Moss frogs, Arthroleptella rugosa, with Andrew Turner from CapeNature. Some of you will remember the visit of Debra Stark in 2015. Debra also conducted recordings of Rough Moss frogs on the mountain (see here).

Since then, the mountain burned and recovered, and we have been back most years to measure density of the frogs. In 2013, the mountain looked the best I've ever seen it. The fire that went through in February 2012 had taken out most of the large pines, and the seepage where the frogs call was free of invaders (see top image below). 

Last week we were back with Oliver Angus (lower image) who is looking at the aSCR data from all years for his Honours project in the MeaseyLab. That same seep was not only invaded by pines, Pinus pinaster, but the frogs were no longer calling from what had been a stronghold for them. 

Happily, they are still calling at other sites on the mountain. 

In this image you see a male Rough Moss Frog that was ~20 mm long (SVL). For their small size they make quite a good noise that we can use to measure their population size.

Stay tuned for more news on this project...