POPULATION DYNAMICSCARRYING CAPACITY

CHAPTER 9

APES 12/2006

Figure 9-1Page 190

Population Dispersion

Fig. 9-2 p. 191Fig. 9-2 p. 191

Factors Affecting Population Growth

• Births

• deaths

• immigration

• emigration

The Biotic Potential

• Population potential capacity to grow

• Intrinsic rate of increase(r ) - rate with unlimited resources– reproductive age– reproduce many times– many offspring

• Two houseflies, ten years, several meters over entire earth - yuck :-(

Population Growth Rate

• Birth Rate: births/popn at beginning • Death rate: deaths/popn at beginning • Growth rate = birthrate-deathrate• Example

– Population of 5000 on Jan 1– Births 400 throughout year– Deaths 100 throughout year– What is Birthrate and deathrate?– How many added to this population this year

• Calculate number added if population were 100,000 at beginning of year instead of 5000

• Answers: BR=8%; DR =2%; GR=6%• Popn 100000 added is 6000

Rate of Growth – Births

• What would affect number of births in a population?– Number of young in each “litter”

• Examples of high and low number??

– How often have young• Examples of seldom vs. often

– Age at which females start having young• Rodents vs. elephants

• Biotic potential for a population

Rate of Growth – Deaths

• What would affect number of deaths in a population?– Lifespan– Outside environmental factors – limiting factors

• density dependent – examples

• density independent– examples

Environmental Resistance• Limits population growth• Population size - interplay between biotic

potential and environmental resistance• Carrying capacity (K) - number individuals of a

given species that can be sustained - expressed as in a given area (say sq. m)

• Minimum viable population– locate mates

– sufficient genetic diversity

POPULATION SIZE

Growth factors(biotic potential)

Favorable light & temperature & foodchemical environment (optimal level of critical factors)

Abiotic

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and and adapt to environmental change

Decrease factors(environmental resistance)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment

Abiotic

© 2004 Brooks/Cole – Thomson Learning

Low reproductive rate

Specialized niche

Changing food supply

Too many competitorsInsufficient ability to hide from or defend against predatorsInability to migrate and live in other habitats

BioticBiotic

Exponential vs. Arithmetic Growth

• Arithmetic: constant amount per time unit– Independent of population size

• Exponential: increases by constant fraction, or exponent, by which current population multiplied– Dependent on population size – Power of biological reproduction– Compound interest

The J Curve

The Rule of Seventy

• At 1% per year, population doubles in 70 years (Table 6.1)

• Doubling time = 70 / % increase

• So, if 4% growth (interest) rate, what is doubling time?

Logistic Strategies• Exponential or J-phase

• Followed by S-phase

• Do not overshoot carrying capacity

• As populations increases, birthrate decreases

• Intrinsic: Territoriality, decreased fertility

• Extrinsic: predators, parasites, resources - may overshoot, then return to carrying capacity

Logistic Growth

Carrying Capacity

Factors Regulating Population Growth

• Extrinsic vs. Intrinsic

• Biotic vs. Abiotic

• Density-Dependent vs. Density-Independent– Interspecific: predation, parasitism, competition– Intraspecific: Competition, territoriality– Stress Related factors

Malthusias or Irruptive Growth

• May go through repeated cycles

• Early successional species

• Opportunists

Malthusian or Irruptive Growth

• Rapid exponential growth (J curve) followed by population crash

• Population surpasses carrying capacity

• Deathrate exceeds birthrate

• Thomas Malthus: human populations tend to grow until resources exhausted, death by famine, disease, war

Malthusian or Irruptive Growth

Moose and Wolves of Isle Royale

Slide 12Slide 12Slide 12Slide 12Slide 12Slide 12Slide 12Slide 12

5,000

4,000

3,000

2,000

1,000

500

Num

ber

of m

oo

se

100

90

80

70

60

50

40

30

20

10

01900 1910 1930 1950 1970 1990 2000

1999Year

Num

ber o

f wolv

es

Moose populat ion

Wolf population

In-text f igurePage 197

Isle Royale - Wolves and Moose

• What caused 1930 crash in moose popn.?

• Why did the moose not decrease their population before the crash occurred?

• Why did the predators not exterminate the moose population?

• What happened when the wolf population declined in the 1980s?

© 2004 Brooks/Cole – Thomson Learning

Nu

mb

er o

f in

div

idu

als

Time

Cyclic

Irregular

Figure 9-7Page 194

Irruptive

Stable

K-Strategists

Few but large young, protect young, lower infant mortality

• Long lifespan

• Later reproductive age

• Less energy on reproduction

• Later successional environments

• More specialized niches

R-Strategist Species

Prolific reproduction, up unprotected young, high mortality rate of young

• Low in trophic levels• Early succession• Opportunists• Populations regulated by extrinsic environmental

effects• Insects, parasites, algae, annual plants, many fish

Survivorship Curves

Percent of population surviving at different ages

Deer in PA

• DCNR and State Forest– Deer browsing studies

The Cats Dropped In !

• What - cats parachuted into North Borneo?

• What lessons can be learned?

• What are the ecological connections?

• (“Ecological Surprises” - page 200)