Basic Terms n Population: a group of individuals from the same species that all live in the same area at the same time. Ecology: the study of how populations interact with their environment.

Changes in whooping crane population at Wood Buffalo Park Number of cranes Year

Population Growth n Births and immigration add individuals to any population, while deaths and emigration remove them.

Population Growth n Basic models of population growth Continuous growth can be represented by the equation: N t = N 0 e r t

Discrete Growth (N t = N 0 t ) Population size (N) Continuous Growth (N t = N 0 e rt ) = 1.6 r = 0.47 Time (t)

Population Growth n Exponential growth Growth continues indefinitely and is density-independent. Can occur for short intervals, but cannot be sustained.

Population size (N) Generations High r Moderate r Low r Very low r Exponential growth

Population Growth n Exponential growth No population can continue to grow indefinitely. At high densities, growth becomes density-dependent. All populations eventually reach the carrying capacity of their habitat.

Population size Carrying capacity Time

Case Studies Explaining How Population Size Changes Over Time n Humans exhibiting density-dependent growth n Recovery from trauma: The Exxon Valdez oil spill

4–5 million 10,000 B. C Year : 6 billion 1900: 1.5 billion 1700: 600 million 1500: 400 million 1 A. D.: 150–200 million 2000 A. D. Human population (billions) Historical growth

1998 Projections Year Human population size (billions) Medium High Low Recent growth

1992 Projections Fertility rate High Medium Low Projected population in billion billion 7.8 billion The 1992 projections for 2050 are higher than those from 1998 primarily because the earlier projections did not account for the impact of AIDS.

Persistent oil in mussel beds…

…led to slow recovery in other species.

Population Structure n Age structure Developed nations have an age distribution that tends to be even. Developing nations have an age distribution that is bottom-heavy (mostly young individuals).

More-developed countries 1998 data 2050 projections (In millions) Males Females

Less-developed countries 1998 data 2050 projections (in millions) Males Females

Population Structure n Geographic structure Many species exist as a metapopulation. Small, isolated populations, even those on nature reserves, are unlikely to survive over the long term.

A metapopulation is made up of small, isolated populations. Individuals Habitat patches

Although some subpopulations go extinct over time...

…migration can restore or establish subpopulations.

Demography and Conservation n Demography: the study of factors that determine the size and structure of populations through time.

Demography and Conservation n Life tables Summarize the probability that an individual will survive and reproduce in any given year over the course of its lifetime.

Age Type lll Type ll Number of survivors (N x ) Low survivorship High survivorship Steady survivorship High survivorship Low survivorship Three general types of survivorship curves Type l

Demography and Conservation n Life tables Contain useful pieces of information, such as survivorship, fecundity, and net reproductive rate.

Life table Age (x)Survivorship (l x ) Fecundity (m x ) 0 (birth)

Demography and Conservation n Life tables Can be used to make population projections and guide conservation programs.

Demography and Conservation n Population viability analysis (PVA) A model that estimates the likelihood that a population will avoid extinction for a given time period.

Demography and Conservation n Population viability analysis (PVA) Populations are considered viable if they have a 95% probability of surviving for at least 100 years.

Demography and Conservation n Population viability analysis (PVA) Currently being used by natural resource managers.