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# Food Chains and Relationships Between Species Species can be herbivores (only eating plants), carnivores (only eating meat), or omnivores (eating both). Most herbivores don't have to put a lot of effort into finding their food, because plants don't move and usually grow abundantly. They also surv...

# Food Chains and Relationships Between Species Species can be herbivores (only eating plants), carnivores (only eating meat), or omnivores (eating both). Most herbivores don't have to put a lot of effort into finding their food, because plants don't move and usually grow abundantly. They also survive and grow back after being eaten, so the food supply gets replenished. Carnivores, on the other hand, are predators who need to catch their prey. Carnivores have a predator-prey relationship with the animals they eat. ## Predator-Prey Relationship * **Predator:** Organism that eats another organism. (Graphed in dark gray) * **Prey:** Organism that is eaten. (Graphed in light gray) If there are few prey animals, the young of the predators will starve. This will lead to less predators, which means the prey population can grow. When the prey population is large again, the predators can raise a lot of young. This causes the predator population to grow, and the prey population to decrease again. ## Food Chains and Food Webs Organisms are connected to each other in a food chain. For instance, grass → cow → human. However, food chains rarely exist on their own. Within an ecosystem, food chains are connected to each other in a food web. (refer to image 9). * **Producers:** The bottom of a food chain is called the first trophic level and always have a producer. Producers are autotrophs, organisms who can make their own food (thus energy) from inorganic resources, and can be plants or certain kinds of bacteria. * **Consumers:** All other levels in a food chain are consumers. Consumers are heterotrophs (meaning an organism that needs to eat another organism for energy. The first consumer is called a primary consumer and is on the second trophic level. * **Trophic Levels:** Within a food web, organisms can be on several different trophic levels at the same time. ## Energy Transfer Each step up in a food chain (going up a trophic level) will lose energy. Only producers capture energy (most often from the sun through photosynthesis, but it could also be from chemical reactions in chemosynthesis). But from all the energy that producers captured, only about 10% will end up in the next trophic level. This is true for each trophic level you go up. Therefore, food chains cannot be too long, for there would be very little energy left over for the top levels. (refer to image 10) ## Graph Description A graph displays the predator and prey population densities over time. The graph shows cyclical patterns of predator and prey populations which seem to be correlated to each other's densities.