Name ____________________________
Lakeland High School
Date ____________________________
Biology/Mrs. Cropsey – packet #55
Populations and communities
Population –
All the organisms of one species that live in one place at a particular time.
Community –
All of the populations that interact with each other at a particular time.
Examples:
A field can be called a “community” with populations of mice, insects,
flowers, etc.
Growth rate – The increase or decrease in the density of a population over a specific
period of time
Things that affect population growth –
Reproduction rate
Availability of food, water, shelter, etc.
Death rate
Carrying capacity – The size of a population that can be supported by an
ecosystem. (where it levels off is the carrying capacity.)
1
Community interactions
No organism lives alone – no population lives alone. Organisms that live in the same
environment are always interacting with each other.
Competition is one of the main interactions between organisms.
Competition can be interspecific, meaning two different species competing for the same
resources (food, shelter, etc.) or intraspecific, meaning between members of the same
species. Both types of competition result in only the most fit individuals surviving and
passing on their genes
 What is this process called, where only the most fit individuals survive?
Natural selection. Survival of the fittest
Predation is another basic relationship that occurs in nature
Prey
An organism that is hunted or seized for food
Predator-
An organism that lives by preying on other organism
An organism can be both in a food chain
Over time, certain species have evolved certain adaptations to help them avoid becoming
prey
Mimicry -
An organism pretends to be something else
2
Camouflage – An organism is difficult to see because it blends in with its
environment.
Why is this beneficial ? ---hide from predators
Symbiosis –
One type of organism lives near or in another organism
The organism can either help, harm or have no effect on the other
Parasitism
One organism is helped, the other is hurt
Parasite / host
Commensalism
One organism is helped – the other is neither harmed nor helped
3
Mutualism
-
Both organisms benefit
Changing communities – succession
Succession – the orderly change in the inhabitants of an area through time
Pioneer community-
First plants in an are – usually lichens, algae
Climax community
Everything in balance – stability is reached
No changes in the community
4
Primary succession
Occurs in areas where there was no life before
Secondary succession
Succession in areas where there was life before
Example: a forest fire destroys a forest
The forest will eventually rebuild following secondary succession
5
Summary Questions
1. What is the difference between a population and a community?
2. What are some factors that would influence the rate of population growth?
3. How would a population’s growth rate be affected once it reaches carrying
capacity?
4. Why are mimicry and camouflage use adaptations in nature?
5. Fleas live on a dog and drink its blood, causing itchy bites that make the dog
miserable. This is an example of what type of relationship?
6
6. Many corals have algae that live inside their tissues. The algae are protected by
the coral, and the coral need the algae to survive. This is an example of what type
of relationship?
7. The regrowth of an environment after a fire would be considered which type of
succession?
7