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POPULATION BIOLOGY
Review: Population is a group of 1 species living in the same place at the same time.
A species is defined by reproduction (with each other, producing fertile offspring)
WHAT LIMITS A POPULATIONS GROWTH?
Answer: Limiting Factors
1. Density Dependent – increases as the population increases.
EXAMPLES OF DENSITY DEPENDENT
DISEASE SPREADS FASTER
MAD COW DISEASE
COMPETITION FOR FOOD
COMPETITION FOR WATER
PARASITES SPREAD EASIER
EXAMPLES OF DENSITY DEPENDENT
Diseases, competition, parasites, lack of food
All of these things increase pressure on the population as the population gets bigger.
WHAT LIMITS A POPULATIONS GROWTH?
Answer: Limiting Factors1. Density Dependent
2. Density Independent – affects the population regardless of the population size.
EXAMPLES OF DENSITY INDEPENDENT
STORMS
FLOODS
DROUGHT
POLLUTION
HABITAT DESTRUCTION
EXAMPLES OF DENSITY INDEPENDENT Storms, floods, drought, habitat
destruction, natural disasters, pollution
All of these things affect a population of 10 individuals or 10 million individuals. The size does not matter!
CARRYING CAPACITY
Definition: Number of organisms in the population (remember: just 1 species)
that the environment can support.
Populations may be over or under the CARRYING CAPACITY.
If a population is under the Carrying Capacity,
Then the population will increase (more births and survival because
there are enough resources like food, water, space)
If a population is over the Carrying Capacity,
Then the population will decrease (more deaths because of lack of
food, water, space,…)
POPULATION GROWTH CURVE POSSIBILITIES
J-Curve
Exponential Growth
Starts small
Rapid increase
POPULATION GROWTH CURVE POSSIBILITIES
S- Curve
Population growth adjusts to amount of resources.
POPULATION GROWTH CURVE POSSIBILITIES
Fluctuating Curve
Population oscillates above and under carrying capacity.
Ex. Lynx and snowshoe hare
ORGANISM INTERACTIONS THAT AFFECT POPULATION SIZE
Predator- Prey – prey pop. Goes up, then predator pop. Goes up, prey goes down, then predator pop. Goes down.
Competition - btwn organisms for food, space, light, water, mates,…
ORGANISM INTERACTIONS THAT AFFECT POPULATION SIZE
Crowding and Stress - Stress symptoms in a population:
Aggression Decrease in parental care Decrease in fertility Decreased resistance to disease
All of these things can lead to population decline!
HUMANS ARE ANIMALS TOO!
We are not exempt from limiting factors like
Natural disasters, disease, lack of food, water or space, overcrowding,
and competition.
HUMANS ARE ANIMALS TOO!
Humans have been able to exceed their carrying capacity by overcoming some
limiting factors.Ex. Medicine for diseases
Eliminating competition (wars, hunting,…)Increasing food production
Every second: 4-5 babies are born somewhere on Earth. Also in every
second, 2 people die.
Net growth: 2.5 people every second.9,000 people every hour.214,000 people per day.
HUMAN POPULATION
Vocabulary Alert!
Demography: study of human populations
Population Growth Rate= birth rate – death rate
In the U.S.: birth rates are down, but death rates are down as well.
People are having fewer children but life expectancy increases every year.
Vocabulary Alert!
Age Structure: number of individuals at each age group.
Histogram (or Population Pyramid): a graph of the age structure of a population (usually a country)
EXAMPLES OF HISTOGRAMS
HISTOGRAMS CAN HELP DEMOGRAPHERS PREDICT WHAT THE POPULATION WILL LOOK LIKE IN THE FUTURE.
If a pyramid shape – the population will grow.
If a rectangle shape – the population is steady.
If an inverted pyramid – the population will shrink.
Vocabulary Alert!
Mobility – movement of animals that affects population size and structure.
Immigration – movement of individuals INTO a population.
Emigration –individuals EXIT a population.