How Populations Grow

Welcome to Class!
9-14 and 9-15
Complete the following:
 Pick two different biomes, discuss how are their biotic
and abiotic factors different in your journal
 New entry “Population Grow and Limiting Factors”
 Check A-Day Students Foodweb and Bean Pyramids
 Go to restroom? Define a vocabulary before go
 Tutoring hours:
 Wednesdays afterschool 4-5pm
 Mondays, Wednesdays, Fridays morning 7:30am
 Lecture notes on Population and limiting factor
 Concept Maps
 Online Population Growth Lab
 Homefun:
 Study for your Test
 Next Friday 9-18 is our Unit One Test!!! Study!
How Populations Grow
Learning Objectives
Describe how ecologists study populations.
Identify factors that affect population growth.
Describe exponential growth.
Describe logistic growth.
Describing Populations
• Geographic range
• Density and distribution
• Growth rate
• Age structure
Geographic Range
Density and Distribution
Growth Rate
Growth rate = 0
Population size is unchanged.
Growth rate > 0
Population size is growing.
Growth rate < 0
Population size is decreasing.
Bacterial population
Age Structure
• Only certain age groups
can reproduce.
• Only females produce
Population Growth
Exponential Growth
Under ideal conditions with unlimited resources, a population will
grow exponentially.
Population is rapidly
Logistic Growth
When a population’s growth slows and then stops, following a
period of exponential growth
Phase II
Phase III
Phase I
Carrying Capacity
The maximum number of individuals of a particular species that a
particular environment can support
Population stabilizes at
carrying capacity.
Overview: How Populations Grow
1. “Ten individual per square hectare” is a description
of population
2, When resources are limited, a population will grow
3. When growth rate is greater than zero , the population is
Limits to Growth
Learning Objectives
 Identify factors that determine carrying capacity.
 Identify the limiting factors that depend on population
 Identify the limiting factors that do not depend on
population density.
Limiting Factors
Limiting factors determine the carrying capacity of an environment
for a species.
Density dependent
Density independent
Density-Dependent Factors
Density-dependent limiting factors operate strongly when
population density reaches a certain level.
• More individuals use up
resources sooner.
• Individuals may compete
for food, water, space,
sunlight, shelter, mates,
Predator–Prey Relationships
Herbivore Effects
Populations of herbivores and plants cycle up and down like
populations of predators and prey.
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
• Examples: hurricanes,
droughts, floods, wildfires
• Density-independent factors
may actually vary with
population density.
Canyon Lake, TX
Controlling Invasive Species
Density-independent measures?
• Herbicides, mechanical removal
Density-dependent measures?
• Predation
Another invasive
Overview: Limits to Growth
Flood waters cover a
field of wildflowers.
Density dependent
Non-native snakes
released into a wetland
prey on native rodents.
Density independent
Flu virus spreads quickly
in schools.
Wildfires spread through
a grassland.