Diet, Feeding Mode, Reproductive Biology
How Living Things Eat and Digest Food
The diets and feeding modes of organisms are as diverse as life itself, shaped by the forces of evolution and environmental opportunity. An understanding of what an organism consumes, how it acquires food, and how it digests its food informs us about what it does in an ecosystem.
Diet Classification
Living things can be classified by diet as:
- Autotrophs: Produce their own food through photosynthesis (e.g., plants) or chemosynthesis (e.g., deep-sea bacteria).
- Heterotrophs: Consume other living things for energy, further specialized as:
- Herbivores (plant consumers)
- Carnivores (meat consumers)
- Omnivores (consume both plants and animals)
Feeding Strategies
| Strategy |
Description |
Examples |
| Grazing |
Consumes plant material continuously |
Cows, grasshoppers |
| Predation |
Actively hunts and kills prey |
Wolves, lions |
| Filter-feeding |
Strains small food particles from water |
Baleen whales, clams |
| Parasitism |
Derives nutrients from a host without immediate killing |
Tapeworms, ticks |
Sharks have a spiral valve intestine to increase nutrient absorption surface area.
Digestive Specializations
To support varied diets, organisms evolved specialized digestive structures:
- Gizzards: Muscular stomach sacs in birds and some reptiles that grind hard food (compensating for lack of teeth).
- Ruminants (multi-chambered stomachs): Cattle, deer—harbor symbiotic microbes to break down cellulose.
- Symbiotic digestion: Common in herbivores (e.g., termites with gut microbes fermenting wood).
Biochemical Adaptations in Digestion
- Enzymes: Tailored to diet (e.g., cellulases for plant cell walls, proteases for proteins).
pH Variations:
- Carnivores: Highly acidic stomachs (aids protein digestion, kills pathogens).
- Herbivores: More neutral pH (supports microbial fermentation).
| Enzyme |
Optimal pH |
Found in |
Diet Adaptation |
| Pepsin |
1.5–2.5 |
Carnivores/Omnivores |
Protein digestion |
| Pancreatic lipase |
7–8 |
Most vertebrates |
Fat digestion |
| Salivary amylase |
6.7–7.0 |
Omnivores/Humans |
Starch breakdown |
| Cellulase |
6–7 |
Herbivores (microbial) |
Fiber fermentation |
| Lysozyme |
6.5 |
Ruminants |
Anti-bacterial |
Conclusion
Overall, feeding behavior, diet, and digestive biology all interlink an organism with its environment, affecting survival, reproduction, and ecosystem functioning.
Sources
- "Autotrophs and Heterotrophs." Khan Academy, https://www.khanacademy.org/science/biology/ecology/energy-flow-in-ecosystems/a/autotrophs-and-heterotrophs.
- "Herbivores, Carnivores, and Omnivores." National Geographic Education, https://education.nationalgeographic.org/resource/herbivores-carnivores-and-omnivores.
- "Feeding Strategies in Animals." Smithsonian National Museum of Natural History, https://naturalhistory.si.edu/education/teaching-resources/life-science/feeding-strategies-animals.
- "Parasitism." Encyclopedia Britannica, https://www.britannica.com/science/parasitism.
- "Gizzard." Britannica Kids, https://kids.britannica.com/kids/article/gizzard/631314.
- "Ruminant Digestion." Animal Science Extension, University of Illinois, https://ansci.illinois.edu/news/ruminant-digestion.
- "Symbiotic Digestion." Khan Academy, https://www.khanacademy.org/science/biology/ecology/community-ecology/a/symbiosis.
- "Digestive Enzymes." National Institute of Diabetes and Digestive and Kidney Diseases, https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-enzymes.
- "Stomach pH and Digestion." American Physiological Society, https://journals.physiology.org/doi/full/10.1152/ajpgi.00277.2010.