ECR feature: Edmund Basham on tree-top frogs

Edmund Basham is a community ecologist and biogeographer who is currently studying toward his PhD at the University of Florida. He has deep love and interest in the frog communities of tropical rainforests. Edmund shares his recent research on the seasonal shifts and vertical stratification of tree-dwelling frog species in Panama.

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Institute. University of Florida

Academic life stage. PhD

Major research themes and interests. Amphibian community ecology, vertical stratification, biogeography, climate change.

Current study system. I am interested in the vast diversity of species that make up the amphibian communities found in the rainforests of Central Panama. Such species include fossorial caecilians that are found below the leaf litter, to the rare frogs that breed in tree holes found high in the canopy. Some of the trees at the site are upward of 50 m tall, and finding frogs at this height always gives a rush of wonder and excitement. Talking to non-ecologists about my research, a regular comment is an incredulous “do frogs really live up in tops of trees?!”. This is partially what I think makes this research so interesting, there is a hidden world above our heads that often goes amiss.

Recent paper in JBI. Basham, E. W. and Scheffers, B. R. 2020. Vertical stratification collapses under seasonal shifts in climate. Journal of Biogeography: 1–11. [Access here]

A Sylvias tree frog (Cruziohyla sylviae), found 23 m up sitting close to a tree hole filled with tadpoles and and overhanging eggs ready to drop in.

Study motivation. The canopies of rainforests still hold so many secrets. I wanted to be one of the few researchers who truly sampled across the whole range of habitats within the forest, including across the year to sample seasonal climatic variation. Looking at how animals respond to seasonal climates can also give us information about how climate change could affect them, which was a major motivator of this study. Furthermore, there is scant information on the lives of canopy dwelling frogs, so collecting data on where and how these species live is valuable in its own right.

Key methodologies. This paper is one of the very few amphibian focused papers that incorporates arborist tree access. To sample amphibians high in the tree tops, we would shoot a lead weight and line into the canopy, hooking it over a branch so that we could haul up a climbing rope. I would then climb up at night, searching for frogs on the leaves, moss, vines, epiphytes, and all the microhabitats occurring along the vertical transect. This meant that I could find many illusive species that may be missed during ground surveys. Indeed, many of the largest and most beautiful frogs are the rare tree frogs found only in the canopy.

Edmund ascending a huge Espavé (Anacardium excelsum) tree during a daytime survey, on the hunt for frogs.

Major results. We found that the species that normally live up into the canopy, descend towards the ground in the dry season. One striking example was the yellow-bellied poison frog, which shifted some 25 m from its home in the canopy down to the roots at ground level. The overall downward community shift left a canopy depauperate of frogs, where only a small number of individuals from select species are found toughing out the heat in the dry season. With frogs forced to live in a smaller area of habitat near the ground, there may be greater risk of disease, competition, and predation from ground-based hunters such as snakes.

Most importantly, climate change is set to lengthen and strengthen seasonal droughts across the tropics. This research suggests a change is coming in the vertical organisation of frogs in tropical forests, with species that require above-ground habitat to live and reproduce losing out.

A Rosenberg’s gladiator frog (Hypsiboas rosenbergi), found 12 m up calling from a large palm. 

A Palmers tree frog (Hyloscirtus palmeri), found 5 m up calling during a rain storm.

The very illusive tree-hole breeding Ecnomiohyla miliaria, the fringe-limbed treefrog, listed as Vulnerable on the IUCN Redlist. Found near the ground during the dry season in Sierra Llorona, Panama.

Challenges. Conducting field work in mountainous tropical forests is challenging, but when you add a climbing component it can become extra tough. Bullet ants and eyelash pit vipers abound, not to mention the physicality of climbing huge trees. Nonetheless, I wouldn’t have it any other way. The challenging nature of this field work means that there is still so much to explore and learn about these canopy environments. For example, I found that one species of poison frog only lived on the biggest wild cashew trees at the site in Central Panama, which led me to target this interesting relationship for further surveys.

I would implore budding scientists to immerse themselves in nature, because the best inspiration often comes from witnessing something that makes you scratch your head and wonder “what is going on?”.

Next steps. To fully understand the generality of these patterns across the tropics, further field seasons using the same method need to be conducted in forests representative of major ecoregions, for example, South-East Asia, Central Africa, and India. The communities of amphibians in these far-removed forests are only distantly related, for example, frogs in Madagascar have been isolated for ~80 million years. Thus, the processes of evolution and selection may have shaped communities to react to seasonal climate in unique ways. Equally, we may find that a downward descent during dry seasons is a convergent mechanism adopted by all communities. This would then suggest that climate change will affect communities similarly across the tropics. To answer these questions, we must climb more trees and find more frogs.

If you could study any organism on Earth, what would it be? Frogs, especially the colourful tree-frogs. They exist in such incredible variety and beauty, and they have an innocence and charisma which I think is so endearing (for the most part!).

Anything else to share? Only that all are welcome to contact me, whether it be to discuss science, have a friendly chat, or form ideas for future research collaborations.

If you want to see some of this tree climbing/frog catching/fun having field work, check out this short video I made about the research!

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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