ECR feature: Mekala Sundaram on the climatic influence of conifers biodiversity

Mekala Sundaram is a postdoc at the University of Georgia in the USA. She is an ecologist interested in unveiling macroecological patterns. Here, Mekala shares her recent work on the influence of current and past climate on the global biodiversity of conifers.

Mekala Sundaram is an ecologist working on the global diversity of conifers.

Personal links. Research Gate

Institute. Center for Ecology of Infectious Diseases, University of Georgia

Academic life stage. Postdoc

Major research themes. Species occurrence, Community assembly and Macroecology

Current study system. My recent research focuses on understanding how conifers are distributed across the globe, where biodiversity hotspots occur, and where they may be expected to occur in the future under different climate change scenarios. Conifers are an interesting study system because there are over 600 species globally that occur in a wide variety of biomes, from tropical forests to boreal biomes. Conifers are also an ancient taxonomic group, first appearing in the fossil record in the Carboniferous period (~300 million years ago).

Recent JBI paper. Sundaram, M., & Leslie, A. B. (2021). The influence of climate and palaeoclimate on distributions of global conifer clades depends on geographical range size. Journal of Biogeography, 48(9): 2286-2297

Motivation behind this paper. In this paper, we explore the reasons underlying conifers’ distributions. As conifers are an old lineage, current distributions of conifers may be related to current climate patterns or could result from past climatic responses. Regions with stable past climates are hypothesized to be refugia for conifer biodiversity. Therefore, we tested if restricted conifers occur in areas with stable past climates when compared to widespread conifers.

Thuja occidentalis is a widespread conifer found in North America (Photo credit: Dr. Andrew Leslie).

Key methodologies. We gathered geographic ranges of conifers from previous works, modern climate information, and GIS layers of past climates reconstructions for the last 2 million years. We used a novel modelling framework of zeta diversity to disentangle which climate variables explain distributions of restricted conifers versus distributions of widespread conifers. We also employ ensemble species distribution modelling methods to further explore how climate drivers explain distributions of widespread and range-restricted conifers. Both modelling methods provide robust and consistent conclusions.

Unexpected challenges. We faced some computational challenges while analyzing the global distributions of 606 conifer species! Quantitatively combining distributions of 606 species with climate layers in an ensemble modelling framework required lots of computational memory. Also, gathering past climate records from the last 2 million years was difficult, as reconstructing past climates for the entire globe is a challenging endeavour by its nature. To solve the computational problems, we were able to break down modelling into smaller pieces to be completed separately. For past climate information, we were able to gather suitable datasets after an extensive search for paleoclimate records.

Agathis australis is a restricted conifer found in New Zealand, but this specimen was photographed in the Christchurch Botanic Gardens (Photo credit: Dr. Andrew Leslie).

Major results. Our paper advances the field as we directly test how climate patterns from the last 2 million years influence the distributions of a major plant group nowadays. We conclude that geographically restricted conifers are best predicted by past climate patterns, meaning that fluctuations in climate over the last 2 million years have led to some species being restricted in refugial areas or places that have experienced relatively stable climates. Meanwhile, the more widespread conifers are best predicted by modern climates, with several large range species occupying regions with inhospitable climates. Conifer biodiversity hotspots occur in refugial areas where range-restricted species tend to occur, therefore, historical climate patterns may play a role in the formation of these biodiversity hotspots. Our unique methodological approaches have allowed us to disentangle how past climates influence distributions of conifers of different geographic range sizes. These findings and methods have allowed us to test long-standing theories on how plants are distributed and how biodiversity hotspots are formed.

Next steps for this research. The next step is to ask whether species restricted to stable refugial areas are likely to survive in the future. Under a warming climate, species currently restricted to climatically stable biodiversity hotspot regions may be threatened in the future. Therefore, field and modelling studies are needed to test whether taxa can survive under future climate conditions.

Callitris pancheri is a restricted conifer endemic to New Caledonia (Photo credit: Dr. Andrew Leslie).

If you could study any organism on Earth, what would it be? I would like to study a rare species that very little is known about or a non-charismatic species that gets little attention, e.g., aardvark or the rare Wollemia nobilis conifer.

Anything else to add? I have recently switched from studying conifers to studying infectious disease outbreaks to shed light on how humans’ interaction with biodiversity might lead to infectious disease outbreaks. With the ongoing pandemic, there has been great interest in studying how biodiversity should be conserved and understanding how to maintain a healthy environment that minimizes the risk of disease transmission. I am now using methods similar to those described in the conifer paper to examine how biodiversity relates to infectious disease outbreaks.

Published by jbiogeography

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

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