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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 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
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
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
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of m
oo
se
100
90
80
70
60
50
40
30
20
10
01900 1910 1930 1950 1970 1990 2000
1999Year
Num
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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
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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