Feeding Among Heterotrophs

All life needs energy, and since infinite free energy breaks the known laws of physics, this energy must be acquired from an outside source. The ways organisms acquire fuel and energy can be separated into two general feeding types: autotrophs and heterotrophs. Today, we’ll specifically be looking at the feeding traits among heterotrophs.

So, what is the difference between an autotroph and a heterotroph? Simply put, autotrophs obtain their energy directly from the sun through photosynthesis, or from the accumulation of chemical components, which is called chemosynthesis. Autotrophs are also known as producers since they produce their own food. In contrast, organisms that depend on other organisms for food and energy are called heterotrophs. Since they do not create their own food like autotrophs, heterotrophs are known as consumers. The way we categorize the different heterotrophic organisms is determined by their place in the food web, beginning with primary consumers, and moving through secondary, tertiary, etc., depending on what organisms they generally eat. Let’s take a look at the seven diverse eating habits that we use to separate them into their specific subcategories.

1. Herbivore
Generally seen as the lowest rung of heterotrophs in the trophic ladder, organisms that feed solely off vegetation and other plant matter are known as herbivores. Herbivores are primary consumers that typically have complex digestive systems enabling them to break down the cellulose found within the structure of most plants. This allows access to greater quantities of static, renewable resources than many other feeding types have. Some herbivores you are familiar with include horses, sloths, sheep, and elephants.

2. Carnivore
When organisms without the ability to consume plant materials require energy, they must get it from other sources in the environment. As vegetation is off the menu, the only thing left is the other heterotrophs around them, which puts carnivores in the “higher levels” of the trophic ladder. Some recognizable carnivores are wolves, lions, ferrets, alligators, and sharks. Some plants are also carnivorous, but they still get their energy from the sun and use insects for nutrients like nitrogen and phosphorus.

3. Omnivore
Organisms that utilize a combination of both plant- and animal-based diets for fuel are known as omnivores. Omnivores have a natural benefit over other feeding types in that they have a wider variety of food sources available to choose from at any given time. Humans, pigs, raccoons, and badgers are excellent examples of omnivores since our diets often include both plant and animal matter incorporated into a single meal. Not only can omnivores eat both plants and animals, but we can eat many things that are poisonous to herbivores or carnivores, such as chocolate, caffeine, and some peppers.

4. Coprovore
Due to the inefficiencies of biological systems, much of the matter that heterotrophs consume remains undigested after passing through their digestive tracts. Because of this, many species have developed tendencies to consume fecal matter in a process known as coprophagy. Some coprophagic heterotrophs, such as certain species of rabbits, eat their own fecal matter to regain gut bacteria, or to utilize nutrients inaccessible until after initial digestion4. Dung flies, termites, butterflies, and many species of beetles are common coprophagic insects.

5. Detritivore
A detritivore is a heterotrophic organism that obtains its nutrition by feeding on detritus. Detritus is the organic matter made up of dead plant and animal material that exists in the environment. Due to their ability to process and digest dead matter, many detritivores also practice coprophagy as a supplement to their diet. Some of the most well-known detritivores are the various species of worms found in soil and used in composting. Examples of other detritivores include sea anemones, sea cucumbers, and many species of crabs that are known to feed substantially on aquatic detritus.

6. Scavenger
While similar to detritivores in the process of feeding on dead matter, scavengers feed on dead animals and break them into smaller pieces, thus keeping an ecosystem free of bodies of dead animals.6. To support this feeding method, many scavenger heterotrophs possess specialized digestive processes and/or bacteria that facilitate the consumption of decomposing matter without toxicity to the consumer. Heterotrophs iconically associated with scavenging behaviors are hyenas, vultures, and raccoons, but also include lions, wolves, and a large percent of the organisms in aquatic environments.

7. Decomposer
Eventually all the organic matter accumulated in the environment dies off and needs to be recycled back into the food web. To fulfill this role, decomposers are the final step in the trophic system, where even the smallest and least accessible bits of material are broken down and utilized. Decomposers are distinguished from other heterotrophic feeding methods in their saprotrophic method of nutrient ingestion6. What does that mean? Saprotrophic means that instead of swallowing matter, they perform extracellular digestion on the environment around them before they absorb available nutrients. The result of this is the deposition of humus into the soil, a key nutrient source for primary producers. Common decomposers include fungi, bacteria, and other microorganisms found in most environments.
Okay, now that we’ve covered everything, let’s go over a couple of review questions.

Review Questions

1. Which of the following describes a detritivore?

1. Keeps the ecosystem free of the bodies of dead animals
2. Eats their own fecal matter to regain gut bacteria
3. Feeds on organic matter made up of dead plants and animals
4. The final step of the trophic system where the smallest bits of material are broken down

2. Which of the following describes an omnivore?

1. Keeps the ecosystem free of the bodies of dead animals
2. Utilizes a combination of both plant- and animal-based diets
3. Obtains energy using photosynthesis or chemosynthesis
4. Uses saprotrophic feeding methods

3. Dung flies, termites, and butterflies are all examples of…

1. Herbivores
2. Omnivores
3. Coprovores
4. Scavengers

That’s all for this review of heterotrophs! Thanks for watching, and happy studying!