Lesson 3:Interactions among

Living ThingsGrade 7 Science

Interactions in the Environment

Interaction among Living Things

O Learning Goals:O Explain how an ecosystem if limited in the

number of living things it can support.

O Success Criteria:O I can explain how abiotic factors limit the

number of organisms in a given area.O I can explain how predation and competition

limit the number of organisms in a given area.O I can describe and give examples of

mutualism.

Recall that a population is all the members of a particular species found in one area.

Populations can vary in size. They can be large, such as an ant colony, or small, such as a

single pair of breeding woodpeckers in a woodlot.

What determines the size of these populations?

Abiotic Factors

OAbiotic factors limit the number of organisms that can live in an ecosystem. Let’s discuss some examples of this:

Biotic Factors related to Abiotic Factors

OHow organisms interact within an ecosystem also limits the number of organisms in an ecosystem.

OTwo important biotic interactions are competition and predation.

Competition: occurs when more than one

organism tries to obtain the same basic

resources in the same habitat

Competition is the struggle that happens when organisms in the same habitat try to

use the same resources. Can anyone think of an example???

Competition Examples:1. plants that grow close together in one area compete for the same

water, sunlight, and nutrients.

2. When farmers grow crops, they spray pesticides on the crops to

stop other organisms from eating them. Farmers are able to control,

or even eliminate, competing organisms.

Predation

OPredator: an organism that hunts other living things for food

OPrey: an animal that is hunted by a predator

OExample: A wolf (predator) eating a moose (prey) is an example of a predator-prey relationship

OA moose eating grass is not an example of a predator-prey relationship because the moose does not need to hunt the grass

PredationO The population of predators is affected by the

population of prey and vice versa. The number of predators can only increase if there is enough food to eat. If a predator population is increasing in size, the prey population will decrease in size because more predators are eating prey.

O However, if the prey population gets too low, there is not enough for the predators to eat. The predator population decreases; some die from starvation and others may be too weak to produce young.

PredationO This video gives more examples of

predation. Notice the other factors that are mentioned that are necessary for organisms to live. Be ready to discuss some examples from this video:

O Predators and Prey in an Ecosystem

MutualismOMutualism: an interaction between

individuals of different species that benefits both individuals

O Example: When a bee visits a flower. The bee takes nectar from the flower for food, and picks up pollen from the flower while doing so. The pollen is that transferred to the next flower the bee visits. This transfer of pollen allows plants to reproduce. The nectar benefits the bee and the transfer of pollen benefits the flower.

Interactions among Living Things

O The following video illustrates the concepts we have talked about in this lesson. Be ready to discuss some examples after watching the video:

O Competition, Predation and Symbiosis (Mutualism)

O Competition and other Interactions (skip first 1min)

Let’s play with some simulations.

Gizmo time!