Describing PopulationsWhat is a population?

Members of a species that live in the same area at the same time

Determining Population

Population size

The number of individual organisms present in a given population at a given time

Population density

The number of individuals within a population per unit area

Differing densities

High population densities: can be susceptible to higher predation due to vulnerability, can spread diseases easier, can suffer from lack of space and resources due to increased competition

Low population densities: animals have more space and resources, harder to find mates

Population Distribution

Random

Organisms arranged in no particular pattern

Uniform

Organisms evenly distributed

Clumped

Organisms arrange themselves according to available resources

Population Changes

Immigration

Arrival of individuals from outside a given area

Emigration

Departure of individuals from outside a given area

Migration

Seasonal movement into and out of an area

Calculating Population Growth Rate

• (individuals added) – (individuals subtracted)

• Or

• (birth rate + immigration) – (death rate + emigration)

• Example: if birth rate is 18/1000 and death rate is 10/1000; immigration is 5/1000 and emigration is 7/1000, then:

(18+5) – (10+7) = 6. Multiplied by 100 to get a percent = 0.6%

How Populations Grow

Exponential Growth• When a population

undergoes a fixed percent of growth per year due to the right conditions

• A “J” shaped curve on a graph

Logistic Growth• Shows initial growth as

exponential but is then stopped or slowed by limiting factors

• Limiting factors: Determine carrying capacity; which is the largest population an environment can support

How populations grow cont.

• If birth rate exceeds death rate the population will increase

• If birth and death rate remain the same then population stays the same

• If death rate exceeds birth rate the population will decrease

Limiting Factors for Biotic Potential

Density-dependent factor

Limiting factors that are influenced by density:

• Predation

• Disease

• Competition

• Food

• Water

• Space

Density-independent factor

Limiting factors whose influence is not affected by density

• Climate change

• Natural disasters

• Cause a dramatic decrease in population size

Biotic Potential

• An organisms maximum ability to produce offspring in ideal conditions

2 types:

1. High biotic potential: cockroaches having 100s of babies

2. Low biotic potential: Orangutans, don’t reach sexual maturity for 10yrs and only have one baby every 8 years