J. Quigley2012

• In 1850, about two dozen rabbits from Europe were introduced to Australia. The rabbits had plenty of vegetation to eat, no competition and no predators. Their numbers increased rapidly. By the 1950’s, there were 600 million rabbits!!! The rabbits ate so much vegetation that the numbers of native plants and animals declined and crops were damaged.

• As Australia learned, understanding populations is important in protecting ecosystems!

• A population is group of organisms of the same species that live together in the same place

• Understanding population grown is important because populations of different species interact and affect one another, including human populations

• How do populations grow and shrink?

• Biologists use population models to track population growth

• Population growth depends on: births, deaths, immigration and emigration

• Immigration is the movement of organisms INTO a population

• Emigration is the movement of populations OUT (Exit) of a population

• Exponential growth: occurs when number increase by a certain factor in each successive time period

Example: When a population is small, its growth is also small, but as it gets bigger… it grows even faster!

• Logistic Growth: A population growth that starts with a minimum number of individuals and reaches a maximum number of individuals depending on the carrying capacity of the habitat

• Populations do not grow unchecked forever. Factors such as food, predators and disease limit the growth size of a population.

• Carrying Capacity: the largest population that an environment can support at any given time

• Anything that limits the size of a population:• Availability of food

• Shelter• Space• Sunlight• Water• Mates• Disease

ABIOTIC FACTORS•Climate: temperature and rain•Sun exposure•Availability of water•Fertile soil•Earth factors: wind, tornadoes, volcanoes, earth quakes•Space and shelter

BIOTIC FACTORS•Food (plants and animals)•Predators (animals that eat other animals)•Finding a mate•Natural resources for living: nest making, trees for living, brush for hiding…)

• Today the world population is more than 6 billion people and increasing!

• Better sanitation and hygiene, medicine, disease control and agricultural technology have decreased the death rate of the human population

• For most of human history there has been fewer than 10 million people.

• In 1700 there were 10 million people but due to more modern technology… the population has grown to over 6 billion in 300 years!

• Scientists believe the world population will be 9 billion in another 50 years!

• How many people the earth can support depends on how humans take care of the earth, along with science and technology

• Interactions in communities take many forms. Predators and prey are locked in a struggle for survival. Organisms with the same needs compete for food. Parasites and hosts try to get ahead of one another and some organisms depend on other organisms for their own survival…

These two species of fish have These two species of fish have evolved a mutualistic evolved a mutualistic relationship: the grouper fish relationship: the grouper fish allows the cleaner fish to eat allows the cleaner fish to eat food trapped between its teeth: food trapped between its teeth: a free lunch in exchange for a free lunch in exchange for

some dental hygiene.some dental hygiene.

• Mutualism: a relationship in which both organisms benefit from one another (good/good)

• Example: A shark gets cleaned by cleaner fish. (shark gets parasites out of his gills, cleaner fish get food…good for both)

• Commensalism: a relationship in which two organisms live in a community, one organism benefits while the other is unharmed. (good/nothing)

• Example: Lion kills a zebra, when the lion is done eating, birds come and eat the rest (good for the birds, does not effect the lion)

• Parasitism: a relationship between two organisms in which one benefits and the other is harmed (good/bad)

• Example: Human Bot Fly needs to grow under the skin of the human stealing blood and nutrients and causing the human pain

A. Predator: An animal that hunts, kills and eats another animal

B. Prey: the animal that is hunted and killed by the predator