Independent Study, Spring 2019
• ANIMALS •
Animal life is a nearly negligible pool in the global carbon cycle, but it does have some effect on flows between carbon pools. The amount of carbon stored in living animal tissue is minute, but the behavior of animals moves carbon through the cycle. Animals are constantly breathing, respiring CO2 into the atmosphere with every exhale. Because the food web is grounded largely in plant tissues, animals are essentially eating plant-captured carbon and moving it back to the atmosphere. Grazing animals and termites also release substantial amounts of methane (CH4), a more potent but shorter-lived greenhouse gas, from their digestive tracts (Schlesinger and Bernhardt).
Aside from human fossil fuel emissions and land use changes, animals’ largest impact on carbon cycles may be their ability to affect ecosystems. In an ecosystem each species is interconnected, so the behavior and abundance of each affects the others. For example, herbivory on vegetation at optimal levels (not too high or too low for a given ecosystem) raises plants’ net primary productivity (NPP) in many cases. Even predatory animals have a role here because they keep populations of herbivores at reasonable levels. Animals also move nutrients through the landscape in their droppings, increasing deposition of carbon to the soil, and in some cases they allow higher levels of plant productivity over broader areas than would otherwise be possible (Oswald et al).
Credit: Nicole Fuller/Sayo-Art; Oswald et al., Science.
Oswald J. Schmitz, Christopher C. Wilmers, Shawn J. Leroux, Christopher E. Doughty, Trisha B. Atwood, Mauro Galetti, Andrew B. Davies, Scott J. Goetz (2018) Animals and the zoogeochemistry of the carbon cycle. Science.362: 6419 DOI: 10.1126/science.aar3213
Schlesinger W.H. and Bernhardt E.S. (2013)Biogeochemistry: An Analysis of Global Change, 3e.Academic Press.
The Yale Review on animals as carbon cycle mediators. https://environment-review.yale.edu/animals-carbon-cycle-mediators-0