The distribution of nutrients across a landscape is critical in determining primary productivity (i.e. plant growth) and organism survival. Historically, ecologists have focused on larger-scale environmental forces that affect this distribution, like wind, current, gravity, and erosion. However, in 2019, researchers at UC Davis developed a theoretical framework outlining that animal behavior is another critical force influencing nutrient transport that should be considered as we try to understand how different ecosystems function.
Animals can be a source of nutrients in a variety of ways; for instance, they serve as prey for other organisms, their bodies decay into the ground, and they poop. Several studies have already demonstrated that nutrient input by organisms can be necessary to the organization of certain ecosystems. In this study, a team of UC Davis behavioral ecologists including Alexandra McInturf, Lea Pollack, Dr. Louie Yang and Dr. Orr Spiegel, build on these findings to suggest that animals may also serve a unique role in how nutrients are distributed. Specifically, through their behavior, animals provide different pathways through which nutrients can move. This study highlights three major features that allow them to do so.
First, animals can move in ways unachievable by passive forces. For instance, different organisms exhibit behaviors that take them up hills, opposite winds and currents, and against gravity. Spawning salmon (Oncorhynchus spp.) swim upstream from the ocean hundreds of kilometers to spawn, which can double or triple the amount of nitrogen and phosphorous (key nutrients) in upstream habitats [1, 2, 3]. Similarly, deep-diving whales in areas like the Gulf of Maine have to surface (move against gravity) in order to breathe. Once at the top of the water column, these animals will often poop. In doing so, they bring nutrients acquired from prey they find at depth to the upper layers of the ocean .
Second, animals actively respond to the patterns of nutrients that they generate. By continuing to occupy a certain area where they defecate and feed, they can create ecological “hotspots” and actively improve their own habitat. The nutrient input into the ground from their food remnants and feces allows plants to grow. These plants can either feed the organism itself (if it’s an herbivore), or attract other organisms to the area that may serve as prey. The cycle then continues through a positive feedback loop. Similarly, negative feedback loops can occur when organisms actively avoid certain areas and limit the amount of nutrients those areas are getting. Because those habitats do not have sufficient nutrient input, other organisms and species then also avoid those areas, and the negative feedback loop continues. In sum, organisms are able to cultivate or avoid certain areas or habitats. In doing so, they affect where nutrients will be transported.
Third, animals interact with each other. Those interactions also affect nutrient distribution. Animals that are social or tend to gather, like wildebeest, deer, and seabirds, deposit vast amounts of nutrients in the same location at the same time. However, the presence of predators may determine the areas that potential prey species can safely occupy, which in turn would also affect where those species can deposit nutrients.
Generally, this study concludes that the role of animal behavior in nutrient distribution remains underappreciated. The authors suggest that ecologists continue to integrate behavior into future empirical studies. This may be particularly important if human-induced environmental change begins to affect animal movement patterns, as such alterations could lead to dramatic and unexpected consequences for how ecosystems continue to function in the future.
For more information:
McInturf, A. G.*, Pollack, L.*, Yang, L. H.*, & Spiegel, O.* (2019). Vectors with autonomy: what distinguishes animal‐mediated nutrient transport from abiotic vectors?. Biological Reviews, 94(5), 1761-1773.
*Stars denote authors currently or previously affiliated with UC Davis.
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Cover Photo Citation: Wikimedia Commons