Download Ch 5 - Monmouth Regional High School

Chapter 5
POPULATIONS
Lab Biology CP
Red Crabs on Christmas Island in the Indian Ocean-
What assumptions can you make
about this population???
http://animal.discovery.com/videos/fooled-by-nature-christmas-island-crabmigration.html
What problems does this population
impose on other populations??
Chapter 5:
POPULATIONS
• 5.1: How Populations Grow
• 5.2: Limits to Growth
• 5.3: Human Population Growth
5.1
How Populations
Grow
What is a Population?
• A population is a group of organisms
of a single species that lives in a given
area
How do Ecologists Study Populations???
•
•
•
•
1.) Geographic Range
2.) Density and Distribution
3.) Growth Rate
4.) Age Structure
1. Geographic Range
• Geographic Range:
– The area inhabitated by a population
– Can vary in size
• Small - Bacteria in a rotting pumpkin (<1 cubic meter)
• Large - Cod in the Atlantic (hundreds of miles)
2. Density and Distribution
• Population Density:
– The number of individuals per unit area
– Vary in densities
• Distribution:
– How individuals in a population are spaced
out across the range of the population
• 1.) Randomly
• 2.) Uniformly
• 3.) Clumps (most concentrated)
3 Types of Population Distribution
3. Growth Rate
• Growth rate determines whether the size
of a population increases, decreases, or
stays the same.
• Examples:
– Zero growth rate:
• When the population size stays the same
– Positive growth rate:
• Population increases
– Negative growth rate:
• Population decreases
4. Age Structure
• Age structure:
– The number of males and females of
each age a population contains
– WHY?
• Because most plants and animals can’t
reproduce until a certain age
• Only females reproduce
What factors affect population growth?
•
•
•
•
1.) Birthrate
2.) Death rate
3.) Immigration
4.) Emmigration
Reasons for 3 & 4:
– Food shortage
– Overcrowding
– Looking for mates
Why does a population grow?
• Has food
• Has space
• Protection from predators
• Protection from disease
• Has removal of waste products
Exponential Growth
• Exponential Growth:
– The size of each
generation of offspring
will be larger than the
generation before it
– The larger the
population gets, the
faster it grows
– Under ideal conditions, a
population will grow
exponentially
Rates of Growth
• Reproduce Rapidly:
– Bacteria
• 1 day = 4,720,000,000,000,000,000 individual cells
• Reproduce Slowly:
– Elephants
• 1 offspring every 2-4 years
Logistic Growth
• Logistic Growth:
– Occurs when a population’s growth slows then
stops, following a period of exponential growth
– 3 Phases:
• Phase 1 – Exponential Growth
• Phase 2 – Growth slows down
• Phase 3 – Growth stops
– When birthrate and death rate are the same
– When emigration equals immigration
Carrying Capacity
• Carrying Capacity:
– The maximum
number of individuals
of a particular species
that a particular
environment can
support
5.2
Limits to Growth
Limiting Factors
• Limiting factors:
– A factor that controls the growth of a population
– Determine the carrying capacity of an
environment for a species
– Examples:
•
•
•
•
•
•
Competition
Predation
Parasitism
Disease
Natural disaster
Unusual weather
How might each of these factors increase the death rate in a
population?
Density Dependent Limiting Factors
• Operates strongly only when population
density reaches a certain level
• Examples:
–
–
–
–
–
–
1. Competition
2. Predation
3. Herbivory
4. Parasitism
5. Disease
6. Stress from overcrowding
1. Competition
• Organisms compete for:
–
–
–
–
Food
Space
Water
sunlight
2 & 3. Predation and Herbivory
• Predator-prey relationships
– Cycle up and down over time
• Herbivory effects
– Herbivores are predators to plants
– Cycle up and down
• Humans as predators
4 & 5. Parasitism and Disease
• Parasites make their hosts weak and may
cause disease or death
How does predation affect
population growth?
Density-Independent Limiting Factors
• Affect all populations
in similar ways,
regardless of
population size and
density
• Examples:
–
–
–
–
Hurricanes
Droughts
Floods
Wildfires
Controlling Introduced Species
• How to control runaway populations???
– Remove them
– Herbicides
• Problems:
– Only temporary solution
– Expensive
5.3
Human
Population
Growth
Has human population size changed over time?
• Tends to INCREASE
• Reasons:
– Medication
– Sanitation
Patterns of Human
Population Growth
• Demography:
– The scientific study of human populations
– Predicted by:
• Birthrates
• Deathrates
• Age structure
The Demographic Transition
• Demographic Transition:
– Dramatic change from high birthrates and
death rates to low rates
– 3 stages