08 Population Ecology

5/20/2018 08 Population Ecology

1/54

PopulationEcology


2/54

Population defined

Characteristics- density- dispersion- age structure

- birthrate- death rate

- growth rate


3/54

growth rate

Population

potentially interbreeding andinteracting individuals

same species living in the same place

living at the same time reproductively isolated fromother such groups


4/54

What are thecharacteristics of

a population?

?


5/54

Size of a population inrelation to a definite unit

of space (area, volume) e.g. # / km2

= crude density

1. Density


6/54

Ecological density

Number of individualsper unit of available living

space

e.g. # of ferns / cubicmeter of timber


7/54

number of individuals ina given area

?? Is density = toabundance??

Abundance


8/54

direct count

finite populations sampling

infinite populations

Techniques for determining

density


9/54

1 Schnabel method closed populations

multiple markings2 Jolly-Seber method

closed populations

multiple markings

Mark-and-Recapture Methods


10/54

1 Petersen method closed populations

single marking

N = C MR

N = population size estimate

C = total captured in 2nd

sampling

M = # of marked at 1st

sampling


11/54

population is closed N is constant during

sampling all animals have equal

chance of being caught none are trap-shy or trap

happy

Assumptions of Petersen Model


12/54

marking individuals doesnot affect their catchability

animals do not lose marksbetween sampling periods

all marks are reported on

discovery in the 2nd

sampling


13/54

Poisson confidence interval if R/C < 0.10 and R < 50

Normal approximation if R/C < 0.10 and R > 50

Normal distribution if R/C > 0.10

CI for the Petersen model


14/54

Density dependent population parametervaries with population

density

Density dependence


15/54

Density independent

population parameter

does not vary withpopulation density


16/54

In the absence of

immigration, a populationwill continue to increasein numbers unless either

the per capita birthrate ordeath rate is density

dependent


17/54

Maximal population growthmay occur at moderatedensities because at low

densities, location of matesmay be difficult, and anycooperation between

individuals of a species will becurtailed

Allee effect


18/54

death rates exactly balancesthe birth rate such that densityis neither increasing nor

decreasing only reached if B and/or Dare

density dependent = carrying capacity (K)

Equilibrium population density


19/54

exactly compensating

number of survivorswill be constant

regardless of thestarting density

Types of density

dependence


20/54

density-dependentprocesses exactly

compensate for

variation in startingnumber


21/54

Population size at time t

Nu

mberofsurvivorsatt+1

exact compensation

d ti


22/54

undercompensating

number of survivors risesas the starting density rises

density-dependentprocesses are failing to

match the population to theavailable resources


23/54


Nu


exact compensation

under compensation


24/54

overcompensating

number of survivorsfalls as the starting

density rises


25/54


Nu


exact compensation

under compensation

over compensation


26/54

distribution of organismswithin a population over anarea

2. Dispersion


27/54

probability that anotherindividual is nearby giventhe location of oneindividual

Patterns of dispersion

Cl d


28/54

if individuals areaggregated in scatteredgroups as a result of

responses to habitatdifferences, availability of

resources probability is increased

a. Clumped


29/54

if individuals are evenlyspaced

results from some form ofcompetition

e.g. territoriality probability is reduced

b. Uniform


30/54

if position of eachindividual is independentof the others

probability is unaffected

c. Random


31/54

3 A t t


32/54

number or proportion ofindividuals in each agegroup or classwithin a

population specific categories

life history stages

3. Age structure


33/54

1. Population Age Structure

Result of interaction between natality and

mortality showing the population profile

Population profile is the growth or declinein populations in various age classes

Divide population into age categories or

ecological age groups


34/54

Three ecological agegroups: Pre-reproductive Reproductive Post-reproductive

Populationsreproductive baseincludes members ofthe reproductive and

pre-reproductive agecategories

P l ti A P id


35/54

compare the percentagesof the population indifferent age groups

Population Age Pyramids


36/54


37/54

St bl di t ib ti


38/54

Ratio of one age group tothe next remains the same

shape of age pyramiddoes not change over timebecause birth and deathrates for each age classare constant

Stable age distribution


39/54

T pes of age dist ib tion


40/54

stationary

age structure is stable

and population size isconstant

Types of age distribution

i


41/54

growing

proportion of young islarger than the older

groups


42/54

d li i


43/54

declining

high proportion ofindividuals in the older

age groups

low production of young


44/54


45/54

Population Dynamics


46/54

Immigration (I) addsindividuals

Emigration (E)subtracts individuals Births (B) or natality

add individuals Deaths (D) or

mortality subtractindividuals

Changes in Population Size


47/54

Zero Population Growth

Interval in which number of births (B)

is balanced by number of deaths (D)

B = D Assume no change as a result of

migration

E + I = 0

Population size remains stable


48/54

Per Capita Rates

Rates per individual

Total number of events in a time

interval divided by the number of

individuals

Per capita birth rate per month =

Number of births per month

Population size


49/54

Population Growth and

Regulation

E ti l G th


50/54

Exponential Growth

Population size expands

by ever increasing

increments during

successive intervals The larger the

population gets, the

more individuals thereare to reproduce


51/54

Effect of Deaths

Population grows exponentially as long as per

capita death rates are lower than per capita

birth rates

25% mortality

between

divisions


52/54

Biotic Potential

Maximum rate of increase per

individual under ideal conditions

(meaning no environmental pressures

to the population)

Varies between species

In nature, biotic potential is rarelyreached


53/54

Logistic Growth

As size of the population increases, rate of

reproduction decreases

When the population reaches carrying capacity

(K), population growth ceases


54/54

Overshooting Capacity

Population may

temporarily increase

above carrying

capacity Overshoot is usually

followed by a crash;

dramatic increase indeaths

Reindeer on St. Matthews Island

08 Population Ecology

Documents

Transcript of 08 Population Ecology