Population Changes

Population changes happen when there is either an growth (increase) or a decline (decrease) in the number of organisms in an ecosystem.

Population Growth

2 main ways a population can grow

BIRTH-the most common method of growth
IMMIGRATION-when organisms move into a new habitat, joining the population that is already there.

Population Decline

2 main ways a population can decline

DEATH-the most common method of decline
EMIGRATION-when organisms out of a habitat.

Birth Rate

Birth Rate = Number of births / number of years

BIRTH RATE-the number of births in a certain amount of time.

Birth rate example: What is the birth rate (measured in births/year) if 20 cows are born in 4 years?

Death rate

DEATH RATE-the number of deaths in a certain amount of time.

Death rate example: What is the death rate if 8 cows die in 4 years.

Immigration

Organisms moving IN to a new area

Emigration

Organisms moving OUT or EXITING a habitat

Population Density

POPULATION DENSITY-the number of organisms in a given amount of space.
1. Each square has the same amount of space. But each square does not have the same number of ladybugs. The population density of the left square is higher than that of the right square because there are more ladybugs in the given amount of space.

Other important parts of population changes

LIMITING FACTORS- anything that prevents a population from growing larger.

1. Biotic examples: food, predators, mates
2. Abiotic examples: soil quality, water supply, temperature, wildfires

COMPETITION-the struggle between organisms within a population or a community for limited resources.

CLIMATE (the average temperature and amount of rainfall) will affect populations in an area.

1. As temperatures and rainfall increase (or decrease over LONG periods of time...not just seasonally), some organisms will become less suited to live in a region while other organisms will become more suited to live in that region. This can cause EMIGRATION and IMMIGRATION of populations.

NATURAL HAZARDS-can cause changes in populations. Generally we consider the negative effects of natural hazards, but there can be some unexpected positive benefits.

1. FLOODS-can deposit nutrient rich soil along the banks of the river.
  1. The banks of the Nile River and its delta (the triangle shape at the top) are green because the yearly flooding deposits nutrients into the soil.
2. LANDSLIDES-opens up new space for other organisms to immigrate and populate the area.
3. WILDFIRES
  1. Some plant species are unable to germinate (sprout from seed) unless they reach certain temperatures.
  2. Undergrowth is cleared out allowing for more space and for sunlight to penetrate to the forest floor (compare the left and right sides of the forest in the picture to the right).

Carrying Capacity

CARRYING CAPACITY-the maximum number of organisms that can survive in a particular ecosystem

1. Determined by limiting factors
2. Carrying capacity graphs

➢ Slow population growth (blue)

➢ Rapid/exponential population

growth (red)

➢ State of equilibrium (yellow)

➢ Carrying capacity (green)

Page updated

Report abuse