population
group of organisms that belong to the same species and live in a particular place at the same time.
population density
measures how crowded a population is, always expressed as the number of individuals per unit of area or volume.
dispersion
the spatial distribution of individuals within the population.
birth rate
the number of births occurring in a period of time
death rate
the number of deaths in a period of time, aka mortality rate
life expectancy
how long on average an individual is expected to live.
age structure
the distribution of individuals among different ages in a population.
survivorship curves
show the probability that members of a population will survive to a certain age.
growth rate
the amount by which a population's size changes in a given time.
immigration
the movement of individuals into a population
emigration
the movement of individuals out of the population
exponential model
a model of population growth in which a constant and unlimited growth rate results in geometric increases in population size.
limiting factor
any factor, such as space, that restrains the growth of a population.
logistic model
a model of population growth that assumes the finite resource levels limit population growth
carrying capacity
the number of individuals the environment can support over a long period of time. (symbolized by K)
density-independent factors
factors such as weather, floods, and fires, reduce the population by the same proportion, regardless of the population's size.
density-dependent factors
factors such as resource limitations, like shortages of food or nesting sites, and are triggered by increasing population density.
inbreeding
the crossing or mating of plants or animals with close relatives
hunter-gatherer lifestyle
way of life in which people obtain their food by hunting and gathering wild animals and plants.
agricultural revolution
when humans began to domesticate animals and cultivate certain plants for food.
developed countries
the world's modern, industrialized countries, about 20% of the population
developing countries
about 80% of the world's population lives in these poorer countries with rapidly growing populations
demographic transition
the general pattern of demographic change from high birth and death rates to low birth and death rates, as observed in the history of more developed countries.