ECR feature: Bornean birds and elevational limits with Ryan C. Burner

Ryan Burner is currently a postdoc at the Norwegian University of Life Sciences. He is a community ecologist with an interest in the birds and insects harboured in tropical ecosystems. His recent work in the Journal of Biogeography has investigated the range limits of birds inhabiting Bornean mountains. Ryan shares his findings on temperature gradients and the “fine-tuning” effects of competition in structuring these montane bird communities from South East Asian.

(left) Ryan Burner with a Banded Broadbill (Eurylaimus harterti) mist-netted in Danum Valley, Sabah, Malaysian Borneo. (right) Oriental Paradise-flycatcher (Terpsiphone affinis) mist-netted on Mt. Mulu, Sarawak.

Personal links. Research Gate | Google Scholar

Institute. Norwegian University of Life Sciences (NMBU)

Academic life stage. Postdoc

Research interests. Community ecology, Tropical ecology, Ornithology, Entomology, Bayesian modeling.

Current study system. Much of my work takes place in Borneo in Southeast Asia – one of the largest islands in the world – with a focus on birds. Borneo has more endemic bird species than any of the surrounding islands and also has some of the most intact remaining tropical forest. It is also a place with a lot of conservation challenges, however, and more forest is being cut down every day to make forest-derived products and clear space for plantations. The biodiversity in the tropics is incredible, and the basic life history of so many species unknown. For example, my co-authors and I have been able to describe the nests of several bird species for the first time, and many remain to be discovered. Louisiana State University (where I completed my PhD) and University of Montana and The Evergreen State College (homes of several collaborators) are leading the way in understanding the birds of this fascinating region!

Recent paper in Journal of Biogeography. Burner, R., A. Boyce, D. Bernasconi, A. Styring, S. Shakya, C. Boer, M. Rahman, T. Martin, F. Sheldon. 2020. Biotic interactions and temperature gradients contribute to differences in bird range limits on Bornean mountains. Journal of Biogeography 47: 760-771.

Research motivation. As ecologists, we are interested in why species occur where they do. This is particularly interesting on tropical mountains, where you can walk uphill for a few hours and pass into almost entirely new bird communities. What stops all these species from living farther down (or up) than they do? Is it climate? Habitat? Competition with other species? This is particularly important as we think about climate change. Will some of these species change their ranges, or lose their homes entirely as they are forced onto tiny mountain tops?

One way to answer this is to compare the current distributions of a group of species to their distributions in the past and see whether any differences are correlated to changes in the habitat or climate. The problem is that there are few historic data sources of sufficient quality to do this. What we did instead was compare the ranges and relative abundance of a group of over 100 bird species on three different mountains in Borneo. These mountains differed in their habitat, climate, and the abundances of potentially competing bird species, letting us test which of these factors is most important.

Key methodologies. When looking for the effects of competition, ecologists often test whether a given species is less common when another similar (but potentially competing species) is more abundant. If so, this is taken as evidence that the two species may compete. Theory predicts, though, that in many cases competition won’t just occur between pairs of species but rather will be among larger groups of species. But it is harder to test for this ‘diffuse’ competition. What we did was add together the abundances of entire groups of potentially competing species – basically species that ate similar foods in similar ways – and test whether these total abundances could be used to predict the abundances of other species.

Unexpected challenges. I love working in remote areas and it is a priority in my research, but it does have its challenges. There were times during the fieldwork for this project, hiking steep slopes in the rain before sunrise, that we questioned the sanity of what we were doing. But in exchange for a bit of discomfort there are incredible rewards – the huge trees, beautiful streams, strange sights and sounds.

Another challenge was a bit more mundane – listening to and transcribing many hours of recordings after returning home to identify difficult bird species. But even this can take you back to the forest. Listen to this Crimson-headed Partridge (Haematortyx sanguiniceps).

(left) A typical small stream from the steep montane forest of Borneo. Much of Borneo receives more than 3 m of rainfall per year. (right) Poison-tipped blowgun darts carried by a local hunter near Mt. Mulu. Several Penan villages are located near the park, and they are expert at living in the forest.

Major results. The changes in bird communities as you go up a tropical mountain are largely due to climatic differences, and the resulting changes in habitat that result from them. This is generally expected and was true in our study as well. Our main contribution, however, was to find evidence of diffuse competition (between groups of similar species) in ‘fine-tuning’ the ranges of individual species. This was particularly noticeable for bird species that live near the base of the mountain – they lived further up on mountains where fewer potential competitors were present on the upper slopes. This effect was less important in setting the lower range limits for birds living near the mountain tops, indicating that these mountain species may be stronger competitors than the lowland species (although others have found the opposite – we need to keep investigating the nuances of these interactions).

Next steps. Recent advances in Bayesian joint species distribution models now make it possible to combine many sources of information about these birds in a single modeling framework – traits, phylogenetic relationships, and environmental characteristics. My collaborators and I are in the process of combining our datasets of bird surveys across the island of Borneo with trait measurements from museums and forest information from remote sensing to better understand how the environment and species interactions shape bird communities.

Anything else? A description of the process, motivation, and rewards of this research wouldn’t be complete without a mention of the many local Indonesians and Malaysians who guided me through the forest and taught me so much. They have such a wealth of knowledge from a life spent in the forest and are a true highlight of time spent in Borneo.

Regarding myself, I’ll just say that my interests span beyond Borneo to a wide variety of questions in community ecology. Some other current projects include examining the effects of forest management practices on wood-living beetles in Scandinavia, and analyzing long-term time series of birds and moths from Africa, South America, and Europe.

If you could study any organism on Earth, what would it be and why? As an ecologist, I prefer to answer with a system rather than a single organism. Different taxonomic groups, whether birds, insects, plants, are often studied in relative isolation for practical reasons – just researching a single species is difficult enough! And yet we know that nature knows no such boundaries. Think of a tropical forest – fruit-eating bats, birds, and mammals are all relying on the same resources, and the lives of predatory insects and insectivorous bird and bats are closely linked as well (to give a very simplistic example). My ideal research program then would be to examine the interactions among plants, insects, birds, and mammals in the tropics – these areas are hyper-diverse, under-represented in the literature, and in immediate danger from rapid land use changes.

Published by jbiogeography

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

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