1. Lesson 3 – Interactions in Ecosystems

2. Ecological Niche
An ecological niche is the function a species serves in its ecosystem, including where it lives, what it eats, what eats it, and how it behaves
Consider a black bear:
They eat plant parts (nuts and berries), insects, other small animals
Few predators other than humans
Biting insects and parasites feed on them
Hibernate in winter

3. Types of Consumers
What each species eats has an important impact on an ecosystem
Consumers fit into the following types based on what they eat and how they behave
Herbivore – eats only plants or other producers
Carnivore – eats only other consumers
Omnivore – eats both producers and consumers
Scavenger and decomposer – feed on the remains of other, dead or decaying, organisms

4. Food Chains
Food chains show the feeding relationships among species in an ecosystem
Food chains illustrate what each species uses for food
Seeds of a pine tree (producer) are eaten by a red squirrel (herbivore)
Red squirrel is eaten by a weasel (carnivore)
Weasel is eaten by a goshawk (carnivore)

5. Food Chains
Carnivores linked in a food chain have a predator-prey relationship
The animal being eaten is the prey (the fish), the animal eating is the predator (the osprey)

6. Energy in the Food Chain
Chemical energy stored in pine seeds is passed to the red squirrel
Some energy passes to the weasel, and some of that to the goshawk
Food chains show how energy passes through an ecosystem

7. Energy in the Food Chain
The arrows show the direction of energy flow (always point at the organism that is eating)

8. Feeding Levels
The trophic level describes the position of an organism in a food chain
The first trophic level contains producers
The second contains herbivores or primary consumers
The third contains carnivores or secondary consumers
The fourth contains carnivores and are called tertiary consumers

9. Feeding Levels

10. Feeding Levels Organisms use energy to live and release thermal energy
Typically, only about 10 % of the energy taken in by organisms is passed on to the organism that consumes it

11. Food Webs Food chains show simple feeding relationships
A more complete model can be seen in a food web
Food webs show a series of interconnecting food chains
A consumer that feeds on many species is less affected if one of those populations decreases or becomes scarce
A newly introduced species can disrupt a food chain

12. Food Webs

13. Food Webs
The rusty crayfish invades this ecosystem and competes with native species for the same food