At first glance, the relationship between large, charismatic wildlife species and comparatively invisible carbon compounds is not abundantly clear. In terms of an ecosystem’s carbon dynamics, it’s more intuitive that soil microorganisms do a lot of the work by breaking down carbon compounds and respiring carbon dioxide; also intuitive is that plants draw carbon back down from the atmosphere through photosynthesis. This complimentary cycle is well-documented, and in fact, the idea that microbes and plants form the biological crux of the world’s carbon cycle is long-established. While they are undeniably key players, it would be too easy to ascribe all the credit for biological carbon dynamics to just plants and tiny organisms.
It is increasingly clear that in order to better understand ecosystem and global carbon dynamics, we need to consider the ways in which large wildlife contribute to them. Large herbivores can influence ecosystem carbon by, for example, consuming vast quantities in the form of plant matter. Large carnivores can control the number of large herbivores snacking on an ecosystem’s plant life by preying upon them. For both herbivores and carnivores, the next step after consuming carbon is, ahem, depositing the result (dung) into the environment, a source of nutrients both rich and essential for many photosynthesizing (and therefore carbon-dioxide consuming) organisms. For example, whale feces are circulated around the ocean and to its surface via upwelling in a process called the ‘whale pump’, where it stimulates primary production. While whale pump is clearly a fancy term for ‘whale poop plus ocean currents’, the process itself is fascinating when you consider its far-reaching impacts on carbon dioxide drawdown from the atmosphere.
Large wildlife species contribute to ecosystem carbon dynamics in myriad other ways: compacting soil, shaping plant community composition, influencing population densities of other large wildlife, and more. While traditional methods of constructing ecosystem carbon budgets do not incorporate them, understanding their role in local and global carbon dynamics becomes increasingly urgent in the face of continuing large wildlife loss. As the planet continues to advance into the Anthropocene, wildlife species continue to decline at unprecedented rates, with large-bodied species at the greatest risk of extinction; in addition, atmospheric carbon dioxide continues to climb. These interacting risks underscore the need to understand how large wildlife modulate ecosystem carbon, to better parameterize models for future wildlife, climate, and risk management scenarios.
The intersection of these phenomena is nuanced, socially relevant, and scientifically ‘sexy’. For those reasons, it’s where I’m pursuing my research as a graduate student at UC Santa Barbara in Santa Barbara, CA. I’ve been lucky to be able to start tackling this topic at Mpala Research Centre, in Laikipia County, Kenya. It’s an ideal location to study large wildlife loss, as the region is one of the last places on the planet to host intact communities of large wildlife. Alarmingly, the huge and hugely charismatic animals in central Kenya (elephants, giraffes, zebra, to name a few clearly awesome examples) are increasingly threatened with extinction.
To that end, this past year I’ve been working in the Kenya Long-term Exclosure Experiment (KLEE), established almost 20 years ago by Dr. Truman Young of UC Davis, to explore the long-term effects of large herbivore exclusion on the landscape. In the KLEE I have been, to put it simply, playing in the dirt. But what I’m really doing is sampling soil from different plots of land where large herbivores are present or absent, measuring the soil respiration rates from these samples both in the field and in the lab, exploring differences in rates of decomposition in the plots, incorporating landscape-level variation in soil like that from under trees and on termite mounds, and more. It may look like what I’m doing is crouching every ten meters holding a teeny spade and a sterile plastic baggie, ‘planting’ mesh bags full of leaf litter into the ground with stakes, or collecting syringe-fuls of air from the top of termite mounds…well, that is what I’m doing. But, it’s for science! And, in the end my goal is for the data I collect to plug into a larger picture of how carbon is exchanged between the ecosystem and the atmosphere in the savanna.
My questions about carbon exchange and wildlife definitely won’t end with dirt collecting. My interests balance on the divide between community ecology and ecosystems ecology, so my research will largely focus on how to connect the two using wildlife loss and carbon dynamics. I hope to predict how future extinctions will affect climate scenarios or regional carbon budgets, and perhaps how to mediate those impacts through better livestock management and conservation efforts. With luck I’ll get to keep exploring these subjects out in Kenya, and who knows? There are vulnerable communities of large wildlife the world over, and unanswered questions about the consequences of extinction in as many places; as an ecologist my goal is to be able to ask these questions anywhere.
Sources and additional information:
Dirzo et al. 2014. Defaunation in the Anthropocene. Science 345: 401-406.
Doughty et al. 2016. Global nutrient transport in a world of giants. Proceedings of the National Academy of Sciences 113: 868-873.
Holdo et al. 2009. A disease-mediated trophic cascade in the Serengeti and its implications for ecosystem carbon. PLoS Biology 7(9): e1000210.
Keesing and Young 2014. Cascading consequences of the loss of large mammals in an African savanna. Bioscience 64: 487-495.
Schmitz et al. 2014. Animating the Carbon Cycle. Ecosystems 17: 344-359.
Wilmers et al. 2012. Do trophic cascades affect the storage and flux of atmospheric carbon? An analysis of sea otters and kelp forests. Frontiers in Ecology and the Environment 10: 409-415.
Elizabeth Forbes is an ecology PhD student at UC Santa Barbara (department of Ecology, Evolution, and Marine Biology), in the lab of Dr. Hillary Young. While hailing from the Northeast US and beginning her career in coastal marine ecology, since moving to the west coast she has focused on the interactions between large wildlife communities and ecosystem carbon, as well as the dynamics of ecological networks like food webs. While she spends much of her time pursuing these topics, she is also passionate about science writing, science policy, environmental justice, and conservation. In her free time, she loves running in road races as well as moonlighting as an artist. As a National Geographic Young Explorer, Elizabeth does most of her research in Laikipia County, Kenya, at Mpala Research Centre; you can follow more stories from the field on her blog, at https://elizabethatmpala.wordpress.com/.