Monday, December 2, 2013

Journey Through the Center of an Elephant

As anyone who's spent even a few hours with an elephant will tell you, elephants spend most of their time (in fact, 12 to 18 hours every day) doing just one thing: eating.  From sugarcane to bananas, grass to ferns, Asian elephants eat over a hundred species of plants.  In order to support such a large body mass on plant matter alone, elephants need to eat up to 250 kilograms of food every day.  Although this number makes sense when considering their massive size, it is still a fairly high volume of food to need on a daily basis.  Why do elephants need such an impressive amount of food?  Well, elephants are actually not particularly good at digesting what they eat.  In order to process the nutrients from this endless stream of vegetative snacking, elephants have developed a massive, and massively inefficient, digestive system.

Photo by Rebecca Shoer

First, and most importantly, elephants are not what scientists refer to as "ruminants:" animals that digest their food by processing it through a combination of regurgitation (chewing cud) and passing the food through multiple stomach compartments.  This process is quite good at extracting nutrients from ingested vegetation.  Ruminants also depend on maintaining a steady population of bacteria in their stomachs, which break down the plant matter in such a way that the host animals can absorb the nutrients.  Elephants, along with all other "non-ruminant" herbivores, do not possess multiple stomach compartments, or chew their cud.  They do, however, utilize symbiotic bacteria to break down their food.

So what method do elephants use to extract nutrients from their food, other than hosting some friendly digestive bacteria?  Well, as you can imagine, elephants have a tremendously long digestive tract.   Food is first ground into oblivion by four massive molars, the only teeth that elephants possess (though they will have six sets of molars in a lifetime).  It is then passed through the esophagus to the stomach.  The stomach of an elephant is quite different from a human stomach--rather than being the primary site of digestion, it is mainly a large food-storage area.  The stomach is roughly cylindrical, and can store between 30 and 70 litres of food in a full-grown adult! 

The food is then passed along into the small intestine, or duodenum, which can grow to a spectacular 19 meters in length.  The food travels along to the spot where the small and large intestine meet, in an area called the caecum.  It is here that most digestion takes place, because a healthy population of bacteria break down the cellulose in plant matter to make it nutritionally available to the elephants (of course, the bacteria get to snack as well).  This process releases gases as a digestive side effect, and this is why elephants can let loose with some pretty spectacular flatulence.  Seriously, it's pretty amazing:

Sound provided by Buathong (via Lisa Barrett)

As food travels along the caecum, nutrients are absorbed into the bloodstream through its fairly thin walls.  After this, food travels through the large intestine, or jejunum, until all of the moisture is sucked out.  Finally, the food ends up as a nice pile of uniform dung.

Dung with accompanying mushrooms

Now, you might think that this lengthy process (almost 14 hours) would result in dung that has just about every nutritional particle sucked out of it.  In fact, just about the opposite is true.  Elephants digest barely one half of the nutritional value of their food, which means that their dung is nutrient rich.  This inefficiency in digestion is one of the reasons that elephants are an integral part of their ecosystem.  Just about anybody who's anybody uses this dung: baby elephants eat it, frogs live under it, mushrooms grow from it, and some plant species will only sprout once their seeds have been processed and deposited in elephant dung!  Elephants are an amazing and essential seed disperser, ensuring that trees and plant species are evenly and widely distributed throughout their habitat.  One survey of elephant dispersion refers to elephants as "megagardeners," so important are they to the ecosystem.

Of course, elephants are most likely not consciously deciding where to disperse their dung based on ecological needs.  Still, their importance, and the importance of their digestion, cannot be overstated.  Without elephants, these ecosystems will change in unknowable ways, possibly collapsing, and quite definitely threatening the survival of countless species that depend on this dung.  For elephants and their neighbors, an inefficient system has proven to be a very good thing.

References

Campos-Arceiz, A. and Blake, S. 2011. Megagardeners of the forest- the role of elephants in seed dispersal. Acta Oecologica. 37:542-553.



No comments:

Post a Comment