Leopold’s “January Thaw,” reveals the importance of biodiversity in maintaining trophic structure. The hibernating skunk’s decision to uncurl himself and venture out to explore the wet droplets from post-blizzard conditions manifested a series of predator-prey relationships. When the skunk created tracks near the meadow mouse’s underground haystacks, the meadow mouse went out into plain sight and was eaten by the hawk (Leopold 2013). Similarly, the rabbit fearlessly darted out of the winter depths only to be eaten by an owl (Leopold 2013). The owl and hawk superiorly adapted to be able to respectively feed on the rabbit and mouse. However, if the latter two animals did not exist due to some source of biodiversity loss, neither would its owl and hawk predators. Even though Leopold did not observe the skunk as either a predator or prey, the skunk was a crucial factor in maintaining the area’s biodiversity as its mere presence jumpstarted a series of events revealing the ecosystem’s trophic structure.
The Serengeti’s degree of biodiversity definitely impacts its trophic structure. Similar to melting snow’s initiation of Leopold’s account, seasonal rainfall patterns that characterize the East African climate create annually fluctuating feeding opportunities for the large animals in the Serengeti (Dobson 2009). These consumers have the broadest diets that include species from a large variety of different habitats in the ecosystem (Dobson 2009). In contrast, species in only the longer grass areas often have smaller body size and more specialized diets than the migratory species (Dobson 2009). The net effect of this is a hierarchy of energy flow within the larger Serengeti food web. Sequential trophic levels interact with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web (Dobson 2009). If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem.
Dobson, Andy. 2009. “Food-Web Structure and Ecosystem Services: Insights from the Serengeti”. Philosophical Transactions: Biological Sciences. 364 (1524): 1665-1682.
Leopold, Aldo. 2013. Sand County Almanac & Other Writings on Conservation and Ecology. London: Penguin.
Comment by Professor Fenton Kay:
Great post, Mary. There is another series “Okavango: River of Dreams” that does a great job of demonstrating the trophic structure and its dependence on seasonal precipitation. It’s at PBS.org/nature, I think. I found the listing by Googling on PBS Nature, then clicking on Ep[isodes and clicking down until it came up. I think it’s streamable on your computer, and I think it’s available on Amazon Prime.
That sounds interesting. I just found a great article about the Okavango Delta linking the understanding of the trophic structure’s dependence on seasonal precipitation, as well as flooding from the rivers, with water allocation strategy within the watershed (Moyle et al. 2009). It also mentioned the fish depend on other members of the trophic structure (hippopotamuses, elephants, and termites) for creation and maintenance of habitats (Moyle et al. 2009).
The article brought up a fascinating concept called “ecological memory”. It entails imagining each region has a memory of the extent and size of past floods. The memory is longest in the seasonal swamp, where extensive flooding in one year may fill clay-bottomed pools and river channels with enough water to keep them watered through one or more drier years, and where swamp vegetation will persist for decades even if the flood regime changes (Moyle et al. 2009). The resilience of swamp vegetation is then going to impact the rest of the trophic structure. Do any other examples of ecological memory come to mind?
Moyle, Peter, Ketlhatlogile Mosepele, Belda Mosepele, Glenn S. Merron, David R. Purkey. 2009. “Fish, Floods, and Ecosystem Engineers: Aquatic Conservation in the Okavango Delta, Botswana”. BioScience. 59 (1): 53–64.
Response by Professor Fenton Kay:
I had not heard the term “Ecological Memory” before, but it makes good sense. When I was working in Nevada, we visited a gold mine in the north-central part of the state. The mine was located adjacent to an old, dried out wetland area. The mine started pumping their drainage water (seepage into the pit from groundwater) into the former wetland area. Much to everyone’s surprise, cattails and other emergent veg started growing around the resulting pond(s). I don’t know how long the area had been dried out, but clearly, the emergents were still there and still viable. I think that represents an example of ecological memory.
By-the-by, we got approval from the state for them to continue dumping the water and the ponds became a rather nice duck habitat. The water was not contaminated by heavy metals, so it was considered a safe thing to do. What I don’t know is when the mine closed or closes down what will happen to the marsh. I presume it will dry out again.
Comment by Bridget Clayton:
I appreciate your summary of “January Thaw.” I had not previously considered the skunk to be a catalyst to all of the events described. Ironically, the skunk itself is never seen, yet it leads Leopold to witnessing an array of biological processes/cycles. Thanks for your interpretation!
Original Post by Amanda Ruffini:
Biodiversity is crucial to the trophic structure of an ecosystem. The trophic structure is essentially the food change, showing how energy is dispersed as you move up the structure. At the base of the structure, are the plants that fuel the energy for the rest of the levels. These plants are consumed by primary consumers, who are consumed by secondary consumers, who are then consumed by tertiary consumers, which are then consumed by apex predators. Increasing species diversity then can influence ecosystem functions by increasing the possibility of species using complementary resources (Cleland 2011). If, for instance, biodiversity was not rich in an ecosystem, and only a few species existed at large numbers, there would be competition within that species for resources. This was a problem in Michigan where deer numbers significantly increased, while coyote populations, a natural predator, where not enough to keep population numbers in check. Too many dear, with not enough food, resulted in populations starving. Chapin et al. (2012) explains this as well, stating that intense herbivory from overstocking domestic livestock or removing predators from the ecosystem, has reduce the density and diversity of plants.
Leopold’s January Thaw also expresses the importance of biodiversity within the trophic structure. Following along the journey of a skunk, Leopold wonders what muskrat houses have been dug by the mink, the pines the deer have browsed, of the mouse eaten by the hawk or the rabbit caught by the owl. Each play a different role in the function of the ecosystem and this species richness allows the ecosystem to function accordingly without competition for resources or food. If the rabbit or mice were not present, neither wood the hawk or owl. And if the hawk or owl didn’t exist, the mice and rabbit population would explode.
When it specifically comes to the Serengeti of Africa, its degree of biodiversity equally impacts its trophic structure. The Serengeti grasslands are vital for the movement of millions of large animals, including wildebeests, zebras, and gazelle (WWF 2020). These large animals heavily impact their environment through grazing, moving cyclically as grasses dry out or are eaten away and nothing is left. These species do though complement each other by feeding on different grasses. Gazelles eat shrubs, while wildebeest eat short grasses, and topi eat long grasses. While these animals are big, they have natural predators, including cheetahs, lions, leopards, hyenas, and more. With that, only a third of deaths among the migratory herds are a result of predators, due to adaptions from thousands of years of predator-prey coexistence.
However, remove one of these predators, or one of vegetations from human development or climate change, the structure can cascade down. For example, in 1994, there was an outbreak of canine distemper through the lion population from domestic dogs, which resulted in the death of a 1/3 of the lions in the Serengeti NP (Mills 1999). Remove the lions and now, there is one less predator helping with population numbers. If, for instance less young is now killed, they grow up to continue impacting the region from grazing. A population increase can now put more stress on resources which are already pressed from encroaching agricultural development.
Chapin III, F. Stuart, Pamela A. Matson, and Peter M. Vitousek. 2012. Principles of Terrestrial Ecosystem Ecology. 2nd ed. New York, NY: Springer.
Cleland, E. E. (2011) Biodiversity and Ecosystem Stability. Nature Education Knowledge 3(10):14
Leopold, Aldo. 2013. Sand County Almanac & Other Writings on Conservation and Ecology. London: Penguin.
Mills, Cynthia. 1999. “The Wild, Wild Pest.” Sciences 39, no. 2(April): 10 – 13.
World Wildlife Fund (WWF). 2020. “Eastern Africa: The Greater Serengeti Grassland ecosystem in Northern Tanzania”. Accessed October 20, 2020. https://www.worldwildlife.org/ecoregions/at0714
Awesome post! Your explanation of the trophic structure is great as you outlined the progression from primary producers to top carnivores. I appreciate you mentioned a benefit of biodiversity being the use of complimentary resources. It is key to understanding how increased biodiversity is distinguished from increased population of a single species. Phenomenal application of the complimentary resources concept when explaining the Serengeti.
Considering apex predators are at the highest level, I decided to look into another example of how they are impacted by the material they consume from species in lower levels of the trophic structure. Bioaccumulation, the accumulation of chemicals up a food chain, is amplified within top predators such as orcas (Merrett 2018). Types of the harmful substances include heavy metals, pollutants, and micro-plastics. This too can lead to a loss of apex predators due to illness and mortality that can result from toxic contamination (Merrett 2018). Considering the importance of apex predators in the trophic structure, the problem would severely impact an entire ecosystem.
Merrett, Rachel. 2018. “Apex Predators and a Healthy Planet”. Georgia Strait Alliance. Accessed October 22. https://georgiastrait.org/2018/06/apex-predators-and-a-healthy-planet/
Response by Amanda Ruffini:
This is actually a very important concept! It goes back to the “We are what we eat”. If, toxins are consumed at the lower levels, it makes its way up the food chain until it is consumed by a top predator! Even then, if we are continuously eating it, it builds up into our system and can make us ill. We should be concerned with the pollution that occurs, because eventually, it can come back to us. Or, it can continue to disrupt ecosystems.