population ecology
study of the biotic and abiotic factors that affect population size, density, distribution, and age structure
a group of individuals of a single species that occupy the same area at the same time
what are 2 important characteristics that a population includes
density (amount of individuals) and dispersion (how it's spread out)
number of individuals per unit area or volume
the density increases by; decreases by
births or immigration (organisms coming into a population); deaths or emmigration (organisms leave a population)
what is an example of density
Trees 5,000/km^2
pattern of spacing among individuals of the population
what are the 3 types of dispersion
clumped, uniform, and random
clumped dispersion
most common form of dispersion; individuals are found in patches, usually around a required resource; may increase the chances of survival
what are examples of clumped dispersion
trees along a stream and flocks of birds around a pond
uniform dispersion
often the result of antagonist interactions between individuals
what are examples of uniform dispersion
territories and spacing between desert plants
random dispersion
often the result of the absence of strong attractions or repulsions between individuals; these are not a common pattern
what is an example of random dispersion
dandelion or any kind of flower
the study of the vital statistics that affect population size
what are examples of demography
birth and death rates
survivorship curve
a graphic way to show birth and death rates in a population
what are the 3 curve types of survivorship
Type 1, Type 2, and Type 3
Type 1
low and early midlife deaths; high death rate in older age groups
what are examples of a Type 1 survivorship curve
humans and other large mammals (elephants)
Type 2
constant death rate over the life span
what are examples of a Type 2 survivorship curve
annual plants and many prey species (rodents/rabbits)
Type 3
high early death rates and low late deaths
what are examples of a Type 3 survivorship curve
trees, oysters, and frogs
life history strategies
traits that affect an organism's schedule of reproduction and survival make up it's life history
life histories have 3 variables:
when reproduction begins (age of sexual maturation), how often the organism reproduces, and the number of offspring in each reproductive event
what are the 2 types of life history strategies
1. "r" or opportunistic species and 2. "K" or equilibrial species
"r" species increase their fitness by
producing as many offspring as possible
"r" species can increase their fitness by doing this:
early maturation, many reproductive events, and many offspring
the result of "r" species would be to
maximize reproduction so that at least a few offspring survive to the next generation; however, most offspring die (TYPE 1 SURVIVORSHIP CURVE)
"k" species increase their fitness by
having the most offspring survive
"K" species can increase their fitness by doing this:
high parental care, late maturation, few reproductive events, and few offspring
the result of "K" species would be to
maximize survivorship of each offspring; they have few offspring, but the most survive (TYPE 1 SURVIVORSHIP CURVE)
population growth is where---list equation
(change in population)= N (change over time) = t === b (birth rate) - d (death rate)
rate of increase
r is equal to the difference between birth rate and death rate
exponential growth is a characteristic of the
"r" species; it produces a J-shaped growth curve; only holds for ideal conditions and unlimited resources
logistic growth
describes how a population grows more slowly as it nears it's carrying capacity where resources become limited when the population is too large; it is a characteristic of the "k" species
carrying capacity
carrying capacity of a population
the maximum population size that a certain environment can support at a particular time
K is not a
constant value
populations often oscillate around "K" as the
environment changes
populations often overshoot "K", then drop back to or below
what are the 2 types of regulation of population size
density-dependent and density-independent factors
density-dependent factors
affect is related to the number of individuals in a population (N); as N increases, morality increases
what are examples of density-dependent factors
competition for resources, territoriality, disease, and predation
density-independent factors
affect is not realted to N; mortality is not related to population size; things that could affect population whether big or small
what are examples of density-independent factors
weather and climate; natural disasters like naturally occurring fires
human population trends: our population is
no longer increasing exponentially, but it is still increasing rapidly
since about 1970. the rate of growth has
fallen by nearly 50% because of geographic transition--fewer people are having less kids
demographic transition occurs when
a population goes from high birth rates to high death rates to low birth rates to low death rates
the global carrying capacity for humans is
not known