Whether you call it the food web, food cycle, food chain or consumer-resource system, all life forms are lumped into two trophic (food, nourishment) types: autotrophs and heterotrophs.
Autotrophs are organisms that are able to produce their own food from inorganic substances like water and the sun, and have no need to consume other organisms. Most are plants but algae, phytoplankton and seaweed as well as some bacteria are also autotrophs.
Conversely, heterotrophs aka carnivores, herbivores and omnivores cannot produce their own food and therefore consume the nutrients of autotrophs. The National Geographic Society lays out a clear example: mule deer (herbivores) feed on grasses (autotrophs) for its nutrients and in turn mountain lions (carnivores) kill and consume deer for their nutrition. And while the food chain begins with autotrophs it closes with those that consume the wastes of both.
A death in nature is a call to action. Enter the clean-up brigade: decomposers, scavengers and detritivores. We look down on them without justification: they are the last link in the food chain and an important part of Nature’s ecosystem.
The majority of help comes from the decomposers, but I’ll start with the first responders: the scavengers and detritivores. There’s a fine line between the two, but simplistically speaking they both do the job of picking away at either dead plant and animal waste (carcass & faeces).
Scavengers are essential because they take nutrients away and spread the wealth to other areas. Those that consume both plants and carrion are called detritivores. The act of consuming dung or faeces is known as coprophagia.
Grouped by their animal worlds, we’ve got vultures, crows, ravens, gulls and eagles. Underwater we have crustaceans, sharks, eels, sea cucumbers, sea stars, catfish and some marine worms. The insect world has beetle larva, cockroaches, houseflies / blowflies (including their maggots), millipedes, mites, nematodes, slugs, springtails, termites, woodlice, worms and yellowjackets. In the mammalian world we’ve got bears, hyenas, jackals, raccoons, rats, and wild cats, large and small. And more, I’m sure.
When all the above have had their share, the last group – fungi and bacteria – aka the decomposers take care of what’s left.
This awesome image CC2.0 of “a natural community of bacteria growing on a single grain of sand” is courtesy of the Lewis Lab at Northeastern University and was created by Anthony D’Onofrio, William H. Fowle, Eric J. Stewart and Kim Lewis.
Fungi are eukaryotes, a complex multi-celled organism that grows its own host; they have a nucleus that contains their DNA. They’re also a food source for many invertebrates such as slugs, flies and beetles; and mammals such as various monkeys, gorillas and humans.
Bacteria on the other hand are prokaryotes, a single-celled organism without a nucleus and doesn’t require a host to grow. They’re found in just about all of Earth’s diverse and extreme ecosystems.
Fungi of course are visible as mushrooms, molds and such; whereas bacteria – that do the lion’s share of the work – are microscopic. Together they extract carbon, nitrogen and phosphorus and such from dead organic matter, revert them to their inorganic state and return them to the soil for the next generation of autotrophs.
And, as I mentioned in Little Buggers! regarding the symbiosis between termites needing protozoa to convert cellulose, plants have a similar relationship with fungi. In exchange for carbohydrates from the plant fungi share nitrogen and phosphorus for example that plants are unable to access on its own. This exchange is called Mycorrhiza.
For more information on this topic, check out Joseph West’s Why Are Bacteria Sometimes Called Nature’s Recyclers?; Kirsten Campbell’s 2017 How Are Bacteria a Part of Recycling & Biodegrading?; and Cara Bateman’s 2018 What Do Fungi Contribute to the Ecosystem? All three (and more) can be found on the same Sciencing.com website.
Recycling of organic matter is, to me, just one example of how remarkable nature is. And I don’t know about you, but the more I learn about the finer details of nature, the more it impresses me.
Just how important are scavengers? Ask India.
Chris Bowden’s 2018 article Asian Vulture Crisis – It’s Not Over Yet states within a 20 year period of India’s cattle farmers dosing their cattle with the pain killer diclofenac approximately 40 million vultures were killed. More than 10 years on since the link was made, India’s three indigenous vultures remain on the critically endangered list.
Despite its ban, diclofenac along with aceclofenac, carprofen, flunixin, ketoprofen – all toxic to vultures – are still in use. In their place, scavenging feral dog and rat populations have ballooned; neither are interested in cleaning a carcass to the bone but bring rabies and other diseases and leave air and water pollution to rise along with human health issues, including anthrax poisoning.
Steve Boyes Top 25 Birds that Scavenge
Bella Harris Scavengers: Nature’s Recyclers
Jessica Law 2017 New study: India may have even fewer vultures than we thought
Ken Thompson Detritivores and Decomposers