Population: a group of members of the same species living in an area

Community: populations of different species living together in an area

Population growth: change in population

• Equilibrium: births + immigration are equal to    deaths + emigration

• Often, population growth is not zero

(Births + Immigration) – (Deaths + Emigration) = Change in population number

Population growth rate: amount the population has

changed divided by the time it had to change

Population growth curves: graph how populations grow;

used to find:

• How fast a population could grow

• How many individuals there are now

• What the future population size could be

Constant growth: adds a constant number of individuals

over each time period

Calculated as the population number at the start + (A constant * Time) = Population number at the end

Exponential growth: each species can increase its population two fold in each growth period

Logistic growth: some process slows growth so it levels off near carrying capacity (population grows and then levels off)

Carrying capacity (K): the maximum population of a species that a given habitat can support without being degraded

Logistic growth: some process slows growth so it levels off near carrying capacity (population grows and then levels off)

Density dependent population growth-depends on the # of individuals at a given point in time

Biotic potential: the number of offspring (live births, eggs, or plant seeds and spores) produced under ideal situations

• Measured by r (the rate at which organisms   reproduce)

• Varies tremendously from less than 1 birth/year   (some mammals) to millions/year (plants,   invertebrates)

Recruitment: survival through early growth stages to become part of the breeding population

• Young must survive and reproduce to have any   effect on population size

Life history: the progression of changes in an organism’s life that focuses on reproduction (passing on your genes to your offspring

• Age at first reproduction, length of life, etc.

• Visualized in a survivorship graph

• Type I survivorship: low mortality in early life

• Most people survive (e.g., humans)

• Type III survivorship: many offspring that die   young

• Few live to the end of their life (oysters,   dandelions)

• Type II survivorship: intermediate survivorship   pattern (squirrels, coral)

Environmental resistance: the biotic and abiotic factors that may limit a population’s increase

• Biotic: predators, parasites, competitors, lack of   food

• Abiotic: unusual temperatures, moisture, light,   salinity, pH, lack of nutrients, fire

r-strategists (r-selected species): produce lots of young, but leave their survival to nature (Type III)

Life history traits: are any characteristic that helps a species overcome environmental stress and reproduce

K-strategists (K-selected species): lower biotic potential (Type 1)

• Care for and protect young

• Live in a stable environment already populated by   the species

• Larger, longer lived, well-adapted to normal   environmental fluctuations

• Their populations fluctuate around carrying   capacity

• For example, elephant, California condor

Predation: one benefits, the other is harmed (+−)

• Includes parasitism, herbivory

Competition: both species are harmed (−−)

• Interspecific competition: between different   species

• Intraspecific competition: between the same   species

Mutualism: both species benefit (++)

Commensalism: One species benefits, the other is not affected (+0)

Herbivores: plant eaters

Parasite: an organism (plant or animal) that feeds on its “prey,” usually without killing it

Keystone species: are species that if removed creates a cascade of effects (usually predators)

• Impacting far more than just the other species   they interact with

Niche: the position of a population or species within its ecosystem and describes how an organism or population respond to the distribution of resources and competitors

Intraspecific competition: competition between members of the same species

Territory: an area defended by an individual or group

Amensalism: one species is harmed; the other is unaffected

Resource partitioning: the division of a resource and specialization in different parts of it