2.6: Interactions in the Ecosystem pg. 42 Ecological Niche: the function a species serves in its ecosystem, including where it lives, what it eats, what eats it, and how it behaves. Trophic Level: the level of an organism in an ecosystem, depending on its feeding position along a food chain. Food Web: a representation of the feeding relationships within a community. Ecological Niches The Ecological niche is the role an organism plays within its ecosystem. The roles include what it eats, and what may eat it, where it lives and how it behaves. No two species have the same niche.
Types of Consumers What a species eats helps to define its niche. Consumers fit into the following types based on what they eat and how they behave. Herbivore is a first level consumer that eats only plants (producers) Carnivore are found in the second or higher consumer that eats only other consumers. Omnivore - are found throughout the levels of consumers, they eat both plants (producer) and animals (consumer). Scavenger and Decomposers are organisms that feed on the remains of other, dead or decaying, organisms. A Community of Eaters In an ecosystem there are populations of the same species, these populations make up the community of that ecosystem. The organisms of the community depend on each other for food and survival.
Food Chain A feeding relationship among species in an ecosystem that expresses a singular pathway is called a food chain. The food chain always begins with the producer which is eaten by the herbivore, followed by the first order consumer. The carnivores in the food chain represent a predator- prey relationship. Energy in the Food Chain The energy food (chemical potential energy glucose) in the producer is passed on directly to the first consumer (herbivore), the energy food in the herbivore is then passed onto the first order carnivore. Organisms continuously consume and release energy to survive. Figure 2: A food chain shows the feeding relationships in a forest ecosystem.
Feeding Levels The location where an organism is found within a food chain or food web, is known as a trophic level. First Trophic Level contains producers, such as grass or algae. Second Trophic Level contains herbivores, such as mice, rabbits and some insects. Third and Fourth Trophic Levels contains carnivores which eat other consumers, such as a snake eating a mouse and then a hawk eating the snake. Carnivores that eat other consumers are found in a predator prey relationship.
Beyond Food Chains The food chain is a single pathway indicating a feeding relationship. These food chains make up a complex system of relationships among different species. Food Web A food web shows many interconnecting food chains, showing various species feeding on many other organisms. When consumers feed on many different other species, then the impact on one specific species is lessened, which in turn maintains sustainability of the ecosystem. Figure 5: A food web is still not a complete model of every interaction in an ecosystem. A complete model would show thousands of species.
Effects of Changes to a Food Web Any change in an ecosystem can affect a food web. These changes can be natural increasing competition for food amongst other organisms. Human actions are one factor that may disrupt an ecosystem and its food web. If an organism in a lower trophic level decreases or is lost, it will affect organism further up the trophic levels. Energy Pathways All living organisms require energy for survival. They use chemical potential energy (glucose) for cellular respiration. One form of energy that is released is thermal energy (heat). When one organism eats another organism it gains its stored energy (Pyramid of Energy). Only 10% of the energy is passed on by an organism, from one trophic level to the next. In each trophic level the amount of energy is less as you move upward. Figure 6: A rusty crayfish invades the ecosystem and competes with native crayfish and minnows for many of the same foods.
Check Your Learning: Questions 1 5, pg. 47 Wrap Up: - Each species occupies a unique ecological niche. - Feeding relationships among organisms can be described by food chains and food webs. - Ecosystems can be disrupted by natural and human actions. - Only about 10 % of the energy available at any trophic level is transferred to the next higher level.