1. Populations and Communities
Chapter 5
Populations and Communities

2. 5-1: Populations Why is it important to study populations?
What is the difference between exponential growth and logistic growth?
What factors affect population size?
How have science and technology affected human population growth?
Understanding how populations grow and shrink is
critical to managing agricultural pests and
diseases and also for knowing how to
protect ecosystems.

3. What is a Population?
Population  a group of organisms of the same species that live in a specific geographical area, at the same time and are able to interbreed
Small populations
Herd of zebra
Large populations
Rabbits in Australia
Steady – fairly unchanging numbers
Increasing – exponentially or logistically
Rabbits in Australia from 24 to 600 million in 100 years
Decreasing – exponentially or logistically

4. Population Growth Birth rate  babies born per time
Death rate  deaths per time
Immigration  movement of individuals into a population
Emigration  movement of individuals out of a population
Carrying capacity the largest population that the environment can support at a given time

5. Growth Patterns
Exponential growth  numbers increase by a certain factor in each successive period of time
Bacteria
rabbits
Logistic growth  starts with a minimum number of individuals and reaches a maximum depending on the carrying capacity of the habitat
Most animals are contained by competition for food, shelter, mates and other resources

6. Factors Affecting Population Size
Abiotic – plants limited by amount of sunlight and soil nutrients like nitrogen
Biotic – populations can be limited by number of pollinators and predator-prey relationships
Density-Dependent – something like a disease can impact a population and be worse if there are more individuals
Density-Independent – something like a tornado can impact a forest but hits no matter how many trees there are

7. Human Population Historic Science and Technology
Hunter-gatherer societies
Cities (near resources)
Industrial revolution and westward expansion
Science and Technology
Medicine; when ill and/or wounded
Health care; especially preventative like vaccines
Clean water
Enough food

8. 5-2: Interactions in Communities
How do predator-prey interactions influence both predator and prey?
What are two other types of interactions in a community?
Interactions between organisms are
the basis of communities and are
shaped by changes in the environment
and the evolution of organisms

9. Predator - Prey Interactions
Predation  one organism kills another for food
Lion eats zebra
Shark eats fish
Also at microscopic level (daphnia eat amoebas)
Very few organisms have no predator (killer whales) and most are both predator and prey

10. Other relationships
Coevolution  two or more organims have developed responses to one another due to mutual influence
Faster zebras will require faster cheetahs…. Genetic basis occurs over many generations (of a population), evolution does not occur in the lifetime of an individual
Parasitism  fleas, tick, tapeworms; host provides food and home; parasite has adaptations like the cuticle (skin) of tapeworm that keeps it from being digested
Herbivory  defenses like thorns so that a plant isn’t eaten (grazed). Also includes chemical defenses…..monarch eat milkweed that is toxic to many herbivores – and then the monarch also becomes toxic!

11. Symbioses
Symbiosis is a relationship between two species in close association with each other.
Mutualism  both species benefit
Cleaner fish get meal and protection while predator is freed from potential parasites
Pollinators are a great example of this interaction
Commensalism  one species benefits and the other is neither harmed or helped
Orchids are epiphytes, plants that grow attached to other plants…helps them get to sun and doesn’t hurt tree they are on.