populations

populations

groups of individuals of the same species in the same place

population size (N)

the total number of individuals

population density

the number of individuals within a specific area or volume

3 characteristics of population ecology

1. population range (area throughout which a population occurs)

2. pattern of spacing individuals

3. how population changes in size through time

population range

ranges change through time

environment changes

dispersal to new areas

humans have expanded and reduced ranges

pattern of spacing individuals (uniform)

allelopathic plants, territorial animals

pattern of spacing individuals (random)

wind dispersed plants (dandelion)

pattern of spacing individuals (clumped)

plants that drop their seeds straight to the ground, and animals that live in groups

may be a function of habitat heterogeneity

population demography

quantitative study of populations

how population size changes through time

whole population

birth and death rates of a specific age

age structure

determined by the numbers of individuals in each different age group

cohort

group of individuals of the same age

fecundity

number of offspring produced in a standard time

mortality

death rate in a standard time

population growth can be influenced by

population’s sex ratio

generation time

average interval between birth of an individual and birth of its offspring

population with short generations can

increase in size more quickly than populations with long generations

larger organisms have

longer generation times

survirorship

percent of an original population that survives to a given age

2 factors that affect natural selection

how long an individual lives

how many young it produces each year

fecundity is inversely related to

the amount of parental care given to an individual offspring

semelparity

a species that reproduces only once during its lifetime and then dies

iteroparity

species that reproduce repeatedly during their lives

exponential growth

occurs when the individuals in a population reproduce at a constant rate

the rate of population increase is defined as

r = (b-d) + (i-e)

biotic potential

r = r max

carrying capacity

symbolized by K

the maximum number of individuals that the environment can support

logistic growth model

applies to populations as they reach K

dN/dt = rN(K-N)/K

density-dependent

factors that affect the population and depend on population size

density-independent

other factors, such as natural disasters, affect populations regardless of size

density dependent negative feedback

reduce population size

density dependent positive feedback

allee effect

growth rates increase with population size

density independent effects

rate of growth of a population is limited by something unrelated to the size of the population

cold, drought, storm

k-selected populations

adapted to thrive when population is near its carrying capacity

r-selected populations

selection favors individuals with the highest reproductive rates

characteristics of k-selected species

mature late

greater longevity

increased parental care

increased competition

fewer offspring

larger offspring

characteristics of r-selected species

mature early

lower longevity

decreased parental care

decreased competition

more offspring

smaller offspring