Upload
felicity-cynthia-garrison
View
218
Download
1
Tags:
Embed Size (px)
Citation preview
How Populations Grow
Learning Objectives Describe how ecologists study populations. Identify factors that affect population growth. Describe exponential growth. Describe logistic growth.
Essential Question
How can I explain the difference between exponential and logistic growth?
Growth Rate
Growth rate = 1
Population size is unchanged.
Growth rate > 0
Population size is growing.
Growth rate < 0
Population size is decreasing. Bacterial populationBacterial population
Population Growth
1. Births 3. Immigration
3. Emigration2. Deaths
# of individuals that enter or leave the population
Exponential Growth
Under ideal conditions with unlimited resources and protection from predators and disease, a population will grow exponentially.
Population is rapidly increasing at a constant rate.
J-shaped curve
Logistic GrowthWhen a population’s growth slows and then stops, following a period of exponential growth
S-shaped curve
Population growth may slow down when birthrate decreases, death rate increases, or both.
Growth rate equals zero at carrying capacity.
Most natural populations follow a logistic growth curve
Carrying Capacity
The maximum number of individuals of a particular species that a particular environment can support
Population stabilizes at carrying capacity.
Limits to Growth
Limiting Factors
Limiting factors determine the carrying capacity of an environment for a species.
Density dependent Density independent
Density-Dependent Factors
• Limiting factors that depend on a population size.
• Density-dependent limiting factors operate strongly when population density reaches a certain level.
Competition
• More individuals use up resources sooner.
• Individuals may compete for food, water, space, sunlight, shelter, mates, territories.
Predator–Prey Relationships
Parasitism and Disease
• Parasites and diseases can spread quickly through dense host populations.
• Stress from overcrowding can lead to lower birth rates, higher death rates, and higher emigration rates.
Density-Independent Factors
Density-independent limiting factors affect all populations regardless of population size and density.
Density-Independent Factors
• Limiting factor that DOES NOT depend on the density of the population.
•Examples: hurricanes, droughts, floods, wildfires
•May sometimes tie in with density-dependent factors
Canyon Lake, TX
Overview: Limits to Growth
Density dependent
Density independent
Flood waters cover a field of wildflowers.
Non-native snakes released into a wetland prey on native rodents.
Flu virus spreads quickly in schools.
Wildfires spread through a grassland.