Populations and Communities Holt Ch. 5.1 Glencoe Ch. 4.1 Holt Ch. 5.1 Glencoe Ch. 4.1

Population: a group of organisms of the same species that live together in one place at one time and interbreed. Population growth is important because populations of different species (including humans) interact in communities Population: a group of organisms of the same species that live together in one place at one time and interbreed. Population growth is important because populations of different species (including humans) interact in communities

Population growth depends on 4 factors: 1.Births 2. Deaths 3. Immigration (movement of individuals into a population) 4. Emigration (movement of individuals out of a population) 1.Births 2. Deaths 3. Immigration (movement of individuals into a population) 4. Emigration (movement of individuals out of a population)

Two kinds of population growth:  Exponential  logistic  Exponential  logistic

Exponential growth  Numbers increase by a certain factor in each time period  J-shaped graph  Numbers increase by a certain factor in each time period  J-shaped graph

Logistic growth  Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat  S - shaped graph  Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat  S - shaped graph

Carrying capacity  The maximum population an environment can support at any given time

Actual logistic growth

Logistic growth curve

Factors affecting population size  Abiotic factors: Weather, climate  Biotic factors: food predators disease parasites humans

Density-dependent factors limiting growth number of individuals  Variables that are affected by the number of individuals present  Ex: availability of nest sites, food, water,competition, migration number of individuals  Variables that are affected by the number of individuals present  Ex: availability of nest sites, food, water,competition, migration

Density-independent factors affecting growth regardless of population size  Variables that affect a population regardless of population size  Ex: weather, flood, fire regardless of population size  Variables that affect a population regardless of population size  Ex: weather, flood, fire

Human population  Demography: the study of human population  Size  Density  Distribution  Movement (immigration/emigration)  Births and deaths  Demography: the study of human population  Size  Density  Distribution  Movement (immigration/emigration)  Births and deaths

Human population  Slow growth in the past  > 7 billion now  Industrial revolution increased growth  Better sanitation, hygiene, vaccines, nutrition, agricultural technology  Slow growth in the past  > 7 billion now  Industrial revolution increased growth  Better sanitation, hygiene, vaccines, nutrition, agricultural technology

Population Clock

Can the Human Population keep increasing forever? Can the Human Population keep increasing forever?

Humans can alter the environment and change the carrying capacity

Exponential Growth Dr. Albert A. Bartlett  The Most Important Video pt. 1 The Most Important Video pt. 1  The Most Important Video pt. 2 The Most Important Video pt. 2  3:36  The Most Important Video pt. 1 The Most Important Video pt. 1  The Most Important Video pt. 2 The Most Important Video pt. 2  3:36

Demographic Transition Model Demographic Transition Model  A geographical model used to explain the change from high birth rates and high death rates to low birth rates and low death rates as part of the economic development of a country from a pre-industrial to an industrialized economy.

Population pyramid  A graph used to show the population distribution over gender and age of a population

The Lynx and the Snowshoe Hare

Canadian lynx only eat meat. Snowshoe hares are a very important food for these cats, and when there are fewer hares to eat, the number of lynx decreases. In some areas lynx eat only hares, but in other areas they also eat rodents, birds, fish, or sick or weak deer. They also eat carcasses left by human hunters. Fox, D. and T. Murphy 2002"Lynx canadensis" (On- line), Animal Diversity Web Canadian lynx only eat meat. Snowshoe hares are a very important food for these cats, and when there are fewer hares to eat, the number of lynx decreases. In some areas lynx eat only hares, but in other areas they also eat rodents, birds, fish, or sick or weak deer. They also eat carcasses left by human hunters. Fox, D. and T. Murphy 2002"Lynx canadensis" (On- line), Animal Diversity Web

Snowshoe hares are famous for their seasonal molts. In the summer, the coat of the hare is reddish brown or gray, but during the winter, the coat is snowy white. Snowshoe hares are famous for their seasonal molts. In the summer, the coat of the hare is reddish brown or gray, but during the winter, the coat is snowy white.

snowshoe hares eat green grasses, forbs, brome, wild strawberry, dandelions, clovers, and daisies. During the winter, snowshoe hares forage on buds, twigs, bark, and evergreens. At all times, it is important for hares to re-ingest certain feces. Because much of the digestion of food occurs in their hindguts, in order to extract all of the available nutrients from their food, they must cycle it through their digestive system a second time. (Kurta, 1995; Wilson and Ruff, 1999)

An adult Hare  can travel up to 27 miles per hour  can cover up to 10 feet in a single bound  change direction and leap vertically An adult Hare  can travel up to 27 miles per hour  can cover up to 10 feet in a single bound  change direction and leap vertically