2.5: Food Webs and Ecological Pyramids pg. 42 Key Concepts: 3. Energy passes through ecosystems, whereas matter cycles within ecosystems. Evidence of Learning: Students can - make and use food chains, food webs, and trophic levels to show feeding relationships between organisms. - describe how living organisms lose energy to the environment, and explain why higher trophic levels have less energy than lower trophic levels. - use an ecological pyramid to describe energy, number, and biomass relationships. - Different species living in a forest is influenced and limited by its surrounding and the resources available to them. Ecological Niches Ecological Niche: the function a species serves in its ecosystem. Including what it eats, what eats it and how it behaves. - The way species interact with each other and their environment is their ecological niche. - The role in which an organism participates in its ecosystem is its niche, what it feeds on, what eats it, and it behaviour. - A key feature of any ecosystem is the feeding relationships between species. - Terms, such as; producer, consume, herbivore, carnivore, and omnivore are used to establish feeding relations hips. Table 1: Types of Consumers Feeding Role Definition Herbivore Animal that eats plants or other producers. Carnivore Animal that eats other animals. Omnivore Animal that eats both plants and animals. Scavenger Animal that feeds on the remains of another organism. Food Chains and Food Webs Food Chain: a sequence of organisms, each feeding on the next showing how energy is transferred from one organism to another. 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.
- Easiest way to present a feeding a relationship is through a linear food chain. - A food chain identifies who eats who as energy moves up the chain. - Food chain always starts with a producer, then herbivore, and then a carnivore. - Arrows are found between the organisms in the direction energy is moving up the trophic level. Figure 3: A simple food chain in a forest ecosystem. - Organisms use and release energy into their environment. - Energy is continuously lost into the environment as heat, a waste energy. - Trophic levels or feeding levels identify the position an organism processes in the food chain. - Producers are found in the 1 st. trophic level, herbivores (first order consumer) are found in the 2 nd trophic level. Carnivores (second, third, fourth order consumers) are found in sequential trophic levels. - Food chains arte artificial and are not found in nature, but are used to simplify feeding relationships being discussed. Figure 4: Species can be divided into trophic levels depending on how they obtain their energy.
- Food webs are used to show many different feeding relationships within an ecosystem. There are many paths expressed at once. - The more complex the food web, the more sustainable of the ecosystem. If one species is lost, there are still other organisms to feed from. - adding or subtracting organisms from a food web can either increase or decrease organism involved directly. Figure 5: A partial food web of the boreal forest. A complete model of the interactions in this ecosystem food web would show thousands of species including scavengers and decomposers which feed on dead organisms and wastes. Note that the food chain from figure 3 is embedded in this food web. What would happen of the lynx was removed from the food web? Figure 6: the invasive rusty crayfish (labeled in red) competes with native crayfish for many of the same foods. It also feeds on the eggs of bass and pickerel. Large fish feed on native crayfish but usually avoid eating the rusty crayfish.
Ecological Pyramids Ecological Pyramid: a representation of energy, numbers, or biomass relationships in ecosystems. Biomass: the mass of living organisms in a given area. - Pyramids display relationships between trophic levels. - There are three different types of pyramids. (Energy, numbers, and Biomass) - Energy pyramids show energy movement up the trophic levels, transfer and loss. - Each layer or trophic level identifies the amount of energy available. - Although energy is passed on from one organism to the next during feeding, a lot is lost to the environment as thermal energy. - The 10% rules is used to describe the amount of energy taken in by individuals at each trophic level, from the previous level. - Species found in the upper levels of a pyramid have less energy then these found in the lower levels. Figure 7: Only a small proportion of the total energy at any given trophic level is passed on to the next level. Energy is used in biological processes such as growth and reproduction and is lost as thermal energy (red arrows). - Biomass pyramid identifies the total mass of all organisms in a given trophic level. Figure 8: a) A simplified pyramid of numbers and b) a pyramid of biomass for a deciduous forest ecosystem. - Pyramid of Numbers identifies the number of individuals at a given trophic level.
BLM: 2.5-1: Try This Weaving a Food Web Check Your Learning Questions 1 8, page 47 Summary: - Every species occupies a unique ecological niche. - Feeding relationships between organisms can be represented by food chains, food webs, and trophic levels. - Energy is continuously being lost to the environment by all living organisms. - Higher trophic levels always have less energy available to them. - Ecological pyramids can be used to display energy, number, and biomass relationships.