Lesson 4.2 Describing Populations 1900 to 2000- NY white-tailed deer population grew from 20,000 to over 1 million Metropolitan areas have densities of over 100 deer per sq mi

Population Size Number of individuals in a population at a given time Lesson 4.2 Describing Populations Population Size Number of individuals in a population at a given time Sudden, dramatic decrease in population size can indicate an unhealthy population headed toward extinction Ecologists use sampling techniques to estimate population size Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years. Counting Laysan Albatross Nests

Population Density How crowded a population is Lesson 4.2 Describing Populations Population Density How crowded a population is Larger organisms; lower population densities Low population density: More space, resources; finding mates can be difficult High population density: Finding mates is easier; more competition; more infectious disease; more vulnerability to predators Northern pintail ducks

Population Distribution Lesson 4.2 Describing Populations Population Distribution How organisms are arranged within an area: Random distribution: no particular pattern Uniform distribution: evenly spaced Clumped distribution: grouped near resources; most common in nature

Age Structure Number of organisms of each age group Lesson 4.2 Describing Populations Age Structure Number of organisms of each age group Used to predict future population growth

Sex Ratios Proportion of males to females Age structure diagrams Lesson 4.2 Describing Populations Sex Ratios Proportion of males to females Age structure diagrams For a monogamous species, the ideal sex ratio is 50:50.