Unit Three: Populations

Population

A group of individuals that belong to the same species and live in the same area

population size

the total number of individuals within a defined area at a given time

population density

the number of individuals per unit area at a given time

population distribution

a description of how individuals are distributed with respect to one another

Population sex ratio (PSR)

the ratio of males to females in a population

population age structure

a description of how many individuals fit into particular age categories

density dependent factors

limiting factor that depends on population size

limiting resource

a resource that a population cannot live without and that occurs in quantities lower than the population would require to increase in size (water, food supply, nest sites...)

carrying capacity (K)

the limit of how many individuals in a population the environment can sustain

density-independent factor

limiting factor that affects all populations in similar ways, regardless of population size

population growth models

mathematical equations that can be used to predict population size at any moment in time

population growth rate

the number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period

intrinsic growth rate

the maximum potential for growth of a population under ideal conditions with unlimited resources

exponential growth model (Nt=N0e^rt)

a growth model that estimates a population's future size (Nt) after a period of time (t), based on the intrinsic growth rate (r) and the number of reproducing individuals currently in the population (N0)

J-shaped curve

the curve of the exponential growth model when graphed

logistic growth model

a growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment

S-shaped curve

the shape of the logistic growth model when graphed

Overshoot

when a population becomes larger than the environment's carrying capacity

die-off

a rapid decline in a population due to death

K-selected species

a species with a low intrinsic growth rate that causes the population to increase slowly until it reaches carrying capacity

r-selected species

a species that has a high intrinsic growth rate, which often leads to population overshoots and die-offs

Traits of K-selected and R-selected species

survivorship curve

a graph that represents the distinct patterns of species survival as a function of age

corridor

strips of natural habitat that connect populations

metapopulation

a group of spatially distinct populations that are connected by occasional movements of individuals between them

competition

the struggle between organisms to survive in a habitat with limited resources

competitive exclusion principle

no two species can occupy the same niche in the same habitat at the same time

resource partitioning

when two species divide a resource based on differences in their behavior or morphology (temporal resource partitioning; spatial resource partitioning; morphological resource paritioning )

Predation

An interaction in which one organism kills another for food.

Parasitoids

organisms that lay eggs inside other organisms ( one specialized type of predator)

parasitism

A relationship in which one organism lives on or in a host and harms it.

Pathogen

a parasite that causes disease in its host

Mutualism

A relationship between two species in which both species benefit (pseudomyrmex ant and acacia tree)

Commensalism

A relationship between two organisms in which one organism benefits and the other is unaffected

keystone species

A species that influences the survival of many other species in an ecosystem

ecosystem engineers

a keystone species that creates or maintains habitat for other species

ecological succession

the predictable replacement of one group of species by another group of species over time

primary succession

An ecological succession that begins in an area where no biotic community previously existed

secondary succession

Succession following a disturbance that destroys a community without destroying the soil

pioneer species

a species that can colonize new areas rapidly and grow well in full sunshine

climax stage

communities in late-stage succession with more complex species; succession "ends"

succession occurs in a variety of aquatic ecosystems

over a time span of hundred to thousands of years, lakes are filled with sediments and slowly become terrestrial habitats

species richness of a community is influenced by many factors

latitude, time, habitat size, distance from other communities

Thomas Malthus

the human population could exceed Earth's carrying capacity

factors that influence human populations

population size, birth and death rate, fertility, life expectancy, and migration

Demography

The scientific study of population characteristics.

Immigration

the movement of people into one country from another for the purpose of settlement

Emigration

movement of individuals out of an area

doubling time

the time required for a population to double in size

the rule of 70

to find doubling time of pop, divide 70 by the percent of growth

Total Fertility Rate (TFR)

The average number of children a woman will have throughout her childbearing years.

Replacement level fertility

the total fertility rate required to offset the average number of deaths in a population in order to maintain the current population size

developed country

a country with relatively high levels of industrialization and income

developing country

a country with relatively low levels of industrialization and income

life expectancy

The average number of years an individual can be expected to live, given current social, economic, and medical conditions.

infant mortality

the number of deaths of children under 1 year of age per 1000 live birth

child mortality

the number of deaths of children under age 5 per 1,000 live births

Age-structure diagram

a visual representation of the number of individuals within specific age groups for a country, typically expressed for males and females

Population Pyramid

an age structure diagram that is widest at the bottom and smallest at the top, typical of developing countries

population momentum

continued population growth that does not slow in response to growth reduction measures

theory of demographic transition

the theory that as a country moves from a subsistence economy to industrialization and increased affluence it undergoes a predictable shift in population growth

family planning

the practice of regulating the number or spacing of offspring through the use of birth control

Affluence

wealth

IPAT equation

Impact = Population x Affluence x Technology

urban area

an area that contains more than 385 people per square kilometer (1,000 people per square mile)

The biotic potential of a population

is the maximum reproductive rate of a population

clumping

the most common dispersion pattern for populations, individuals flock together

cohort

a group of people from a given time period

Community

All the different populations that live together in an area

Dieback

A sudden population decline; also called a population crash.

fecundity

fertility

Generalist

Species that does not rely on a single source of prey

inbreeding depression

when individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce

uniform dispersion pattern

a pattern in which the individuals of a population are evenly distributed over an area

Crude Death Rate (CDR)

the number of deaths per 1,000 individuals per year

Crude Birth Rate (CBR)

the number of births per 1,000 individuals per year

post-industrialization

the shift from an industrial economy dominated by manufacturing jobs to an economy dominated by service-oriented information-intensive occupations.

Pre-Industrialization

Traditional, agrarian, rural, poor health, famine and disease

random dispersion pattern

a pattern in which the individuals of a population are spaced in an unpredictable way

sex ratio

The number of males per 100 females in the population.