POPULATION ECOLOGY

HOW DO POPULATIONS CHANGE?

What is a population? All members of a species living in the same place at the same time They usually breed with organisms in their own population

The daisy’s in a field in Ohio won’t mate with daisy’s in a field in Maryland

Generally a person in Nutley won’t mate with someone in Brazil

PROPERTIES OF POPULATIONS

Size Density – the number of individuals per unit area/volume

10,500 people per square mile in Washington D.C. 1.3 people per square mile in Alaska

Dispersion – the distribution or arrangement of individuals within a given space

POPULATION DYNAMICS

Birth rate – numbers of births in a population in a given period of time

Death rate – number of deaths in a population in a given period of time

Life expectancy – how long, on average, a person will live

Change in population size = births - deaths

POPULATION GROWTH

Exponential Growth – maximum growth in ideal conditions Ideal conditions would be plenty of food, unlimited resources and no

predators What would happen if populations grew like this? Is this realistic?

This would never happen because of limiting

factors – factors that prevent a population from

growing (space, food, resources, predators) What are some other limiting factors?

POPULATION GROWTH

Logistic Growth – growth that accounts for limiting factors

Populations that have limiting factors reach a carrying capacity Carrying capacity is the max number of organisms an

environment can support indefinitely.

POPULATION REGULATION

Population size can be limited in ways that may OR may not depend on the density of the population...

Density dependent – when deaths occur more quickly in a crowded population The cause may be disease

Density independent – when a proportion of the population dies regardless of the density The cause is usually natural disaster

HOW SPECIES INTERACT

What is the difference between lions in the zoo and lions in the wild?

Niche – the role of a species in an ecosystem This includes: physical home, environmental

factors needed for survival and all interactions

A LIONS NICHE

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WAYS SPECIES INTERACT

Symbiosis – Two species live closely together in an ecosystem

There are 5 major interactions: Competition Predation Parasitism Mutualism Commensalism

COMPETITION

When different organisms or populations try to use the same limited resource

Competition can occur within or between species

Competitive Exclusion Principal – this says that two species that compete for the exact same resources cannot stably exist together

PREDATION

When an organism feeds on another organism Predator – hunter Prey – hunted

PARASITISM

An organism that lives in or on another organism

Fleas, ticks etc + -

MUTUALISM

A close relationship between two species in which each species provides a benefit to the other

Bacteria in your intestines Shark and pilot fish + +

COMMENSALISM

A relationship in which one species benefits and the other species is unaffected

Sea anemone and clown fish Barnacles and whales + 0