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 DispersionClumped: the individuals are

aggregated into patchesex. mushrooms, animals that move in herds

Uniform: evenly spaced; may result from direct interactions between individualsex. 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 – deathsDN/Dt = B-D

Scientists use r to represent the difference in per capita birth and deathr = 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 conditionsdN/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 GrowthN

u mbe

r of

Yea

st C

ell s

Time (hours)

Carrying capacity

Population-limiting factors

Factors that limit growth are both density-dependent 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