Dung Cake and Feces Pie: Yum!

In architecture there is a stone upon which the whole structure depends.  It is known as the keystone.  More precisely keystone is a masonry term, and is the stone without which the structure collapses. 

Bison are a keystone species for the Great Plains. But specifically for the bison and the Great Plains what does this keystone look like? How does it work?  Perhaps a good place to start is where the poop hits the trail.  Usually when we hear “the chips are down,” we understand life is not going so well; but that is not true for the grasslands of the Great Plains.  When the chips are down, a veritable feast ensues.  Life is great for a host of microbes, insects, fungi and plants, which themselves present a delicious offering to other species.  Who would think dung could be so sweet?

We on the so-called upper echelon of the food chain look down on the unassuming dung pie.  Casting a disdainful glance on the heap, holding our noses as we pass, we hurry by to avoid further sensibility damage.  Our minds formulate a four-letter word, which, if spoken is a “naughty word.”  In our passing, though, we fail to see a dung beetle working feverishly on its claim.  It, in turn, has ignored us, so intent on its business; perhaps it is thinking in Cheech and Chong style: “This is some good shit man.” 

So what does the world of a bison dung pile entail? To understand this unique world its origin story must be told. In this case, the genesis of bison dung begins in the hidden regions of the bison digestive tract and in particular in its rumen, the first chamber of the bison’s four-chambered digestive system. In the rumen microbes aid the digestion of plant matter. The microbes provide enzymes which facilitate the breakdown and metabolism of the plant matter. These microbes and undigested plant matter, then, pass through the bison’s digestive system and deposit as feces on the soil. This is the fundamental means of nutrient flow for the grasslands. The average bison produces 10-12 quarts of dung in a day, providing a valuable source of nitrogen, phosphorus, calcium, sulfur and magnesium for microbes, plants and critters [1].

 In our walk by, and side-step of, the odious heap, we probably perceive the pile of blended nutrients to be just that: a static plop of poop.  However, we would be so wrong.  A diverse population of parasites, hosts, predators, prey, flies, dung beetles, wasps, earwigs, springtails, mites, etc. inhabit this aroma-rich world.  Not a static world, the dung world bustles with activity varying as it ages. The drying pile attracts different residents at different times.  Flies which may have been hovering around the bison hoping not to be snatched by a cowbird are ready to swoop down on the freshly dropped excrement as soon as it hits the ground, swarming over it like…well…like flies on poop.  The flies close to the herds literally have the drop on flies further away. Flies and other insects not close to the herds will come later following a spoor of wind-blown odors [2].  The flies test the surface of dung-world until it is dry enough to lay eggs.  The fly-infested bison chip can produce up to 3000 flies in over two weeks, providing a banquet for box turtles, bats and birds.

Dung beetles, bussing in flies and mites, come later, searching out bison dung. In our passing we probably did not consider that dung piles also vary in nature.  Poop is diverse, and dung beetles are selective.  Indeed the dung beetle populations have declined since the introduction of livestock because they cannot find just the right plop of poop.  The decline of the bison brought the decline of the industrious dung beetle.  This has reduced the ability of natural systems to cycle nutrients and decompose fecal matter, impacting the function of the Great Plains ecosystem [3].  Perhaps we should be required to go to Dung Diversity classes to address our dung-bias. 

During our next walk past a bison pile, after our Dung Diversity course, we pause and now notice our little Cheech and Chong  friend (Well, at this point it’s probably not the same beetle, but for the sake of this discussion we are pretending that it is).  We see it is perhaps a tunneler or roller  beetle working feverishly, burying the fresh manure into the soil.  From what we learned in our course, we realize what a great service these beetles offer.  Our little friend, by burying the excrement, moves nitrogen and carbon directly into the soil and activates microbial activity.  Microbes convert the nitrogen into ammonia which is essential to plants [4].

But dung-world is not a quaint, peaceful world of maggot nurseries, nutrient farms, ammonia factories and waste management facilities.  A ruthless insect-eat-insect environment exists.  Beetle and wasp larvae eat or kill maggots.  One kind of beetle can take away so much of the dung pile nothing is left for other insects.  The tumble bug will take a large mass of dung, roll it into a ball, deposit its eggs inside and then roll the ball of dung to a nesting site [5].

Insects, microbes and plant material are not alone in composing the fecal cake.  Seeds consumed during grazing, pass through the bison digestive tract and find a home in dung-world.  Bison feces contain an abundance and diversity of plant seeds, making bison an important dispersal agent [6].  Without the bison, the range and diversity of the grasses of the Great Plains and prairies is greatly reduced.

By providing crucial residence for invertebrate life, nutrient transformation processes for plants, and transportation means facilitating grass diversity, bison dung sustains the life of the Great Plains.  When the bison roamed the Great Plains and surrounding prairies in the millions, those ecosystems had an efficient means of replenishment and sustenance.  Now, without wild free-ranging bison grazing over vast stretches, without a keystone species, what will become of the Great Plains?  Not to mention: where will our little dung beetle friend find a home?

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[1] A Healthy Prairie Relies on Bison Poop. Bison Bellows. http://www.nps.gov.

[2] McHugh, T. 1972.  The Time of the Buffalo. 233.

[3] Bison Bellows

[4] McHugh, 234.

[5] McHugh 234.

[6] Rosas, Claudia A., Engle, David M., Shaw, James H. & Palmer, Michael W. See dispersal by bison bison in a tallgrass prairie. Journal of Vegetation Science 19: 769-778. 2008.