Transcript Chapter 1 Notes

Chapter 52 Notes
Population Ecology
Characteristics of
Populations
Population: a group of individuals of a
single species that simultaneously
occupy the same general area
Two important characteristics of any
population are density and the spacing
of individuals
Density: the number of individuals per
unit area of volume
Characteristics of
Populations
Dispersion: the pattern of spacing
among individuals within the boundaries
of the population
The mark-recapture method can be
used to measure population density
N= number in 1st catch X total in 2nd catch
number of recaptures in 2nd catch
Characteristics of
Populations
3 Patterns of Dispersion
Clumped: the individuals are aggregated
into patches
ex. mushrooms, animals that move in
herds
Uniform: evenly spaced; may result from
direct interactions between individuals
ex. territorial behavior, competition
Characteristics of
Populations
Characteristics of
Populations
Random: occurs in the absence of
strong attractions or repulsions
Demography is the study of factors that
affect the growth and decline of
populations
- additions occur because of birth and
immigrations
Characteristics of
Populations
- eliminations occur because of deaths and
emigration
Life tables are used as a summary of the
survival patterns of a population
- survivorship curves plot the data for a
life table
- type 1 curve: low death rate during early
and middle ages; drops steeply with age
Characteristics of
Populations
- type 3 curve: high death rate among
young, then flattens out as death rate
declines for adults
ex. marine invertebrates
- type 2 curve: mortality is constant
over lifespan
ex. annual plants, grey squirrel
Characteristics of
Populations
Life History
Life histories are diverse, but they exhibit
patterns in their variability
- big-bang reproduction: some
plants and animals invest most of their
energy into growth and development,
and then expend their energy in 1 large
reproductive effort; also called
semelparity
Life History
Life History
- repeated reproduction: organisms
produce fewer offspring at a time, but
do so over many seasons; also called
iteroparity
- limited resources mandate trade-offs
between investments in reproduction
and survival
Population Growth
The exponential model of population growth
describes an idealized population in an
unlimited environment
Change in pop size = births – deaths
DN/Dt = B-D
Scientists use r to represent the difference
in per capita birth and death
r = b-d
Population Growth
Zero population growth (ZPG) occurs
when the birth rate equals the death
rate ( r = 0)
Intrinsic rate ( rmax) is the fastest
growth rate possible reproducing under
ideal conditions
Population Growth
Exponential growth is a population
increase under ideal conditions
dN/dt = rmaxN
- the population increases rapidly
- J shaped growth curve
Population Growth
The logistic model of population growth
incorporates the concept of carrying
capacity
Carrying capacity: the maximum
population size that an environment can
support
- symbolized as K
- when N = K, the growth rate = 0
Population Growth
Carrying capacity
Time (hours)
Population-limiting factors
Factors that limit growth are both densitydependent and density-independent
Density dependent: death rate will rise
as the population density rises
- predation-prey
- competition for food
Population-limiting factors
Population-limiting factors
Density independent: birth and death
rates do not change with density
- mainly caused by weather and climate
- not caused by negative feedback