Chapter 6 Population Biology
6.1 Dynamics Of Population Growth
• Isle Royale
– moose
– wolves
– carrying capacity
– population balance.
Species and Population
• Organism
• Species: genetically similar organisms that
reproduce
• Population: all members of a species in an
area
Dynamics Of Population Growth
• Exponential Growth Growth at a constant
rate of increase per
unit time.
(Geometric)
• Arithmetic Growth Growth at a constant
amount per unit time.
Population Growth
• Growth rate =
birth – death rates
• Doubling time
– Rule of 70
– Tdbl = 70/ann % incr.
Table 6.1
Feedback
• Positive: Change leads to more change
– More Offspring = More Future Parents
– Exponential Growth
– Positive = Mathematically, not Necessarily in
terms of Desirability
• Negative: Change opposes More Change
– Rate of increase lessens
– More Output = Less Competition for Product =
Less Profit = Less Output
Nothing Can Grow Forever
• One cent @ 1% interest in 1 AD:
– Would now be $4.9 million
• One cent @ 2% interest in 1 AD:
– Would now be $1,972 trillion
– 328 million tons of Gold
– Total Gold Production to data: 150,000 tons
• Offsetting Growth
– Money: Inflation, Devaluation, Default
– Population: Epidemics, Famine, War
Population Oscillations and Irruptive
Growth
• Irruptive or
Malthusian growth
• Overshoot
• Dieback
Malthusian Growth
• Malthusian Growth (Irruptive Growth) Population explosions followed by population
crashes.
– Thomas Malthus concluded unchecked
populations tend to grow until they reach carrying
capacity and are vulnerable to crashes.
– To get land's fruit in quantity
Takes jolts of labour ever more,
Hence food will grow like one, two, three....
While numbers grow like one, two, four....
Growth to a Stable Population
Logistic Growth
• Logistic Growth - Growth rates regulated by
internal and external factors until they come
into equilibrium with environmental
resources.
– Growth rate slows as population approaches
carrying capacity.
– S-Shaped curve
• Environmental Resistance - Any environmental
factor that reduces population growth
• Environmental Resistance = Negative
Feedback
J and S Curves
• Initial Phase (J or Exponential)
– No practical limits
– Growth leads to more growth
• Inflection Point: Opposing Forces Kick In
• Later Phase (Top of the S Curve)
– Growth has Costs
– Costs Inhibit Growth
• Final Outcomes
– Stable Limit (Best Case)
– Overshoot, Crash, Oscillations
– Overshoot and Catastrophic Crash (Worst Case)
Growth to a Stable Population
• Logistic growth
• Environmental
resistance
(Negative
Feedback)
6.2 Strategies of Population Growth
• Malthusian Strategies (r-selected species)
– High Reproduction rates offset high
mortality
– Population limited by external factors
• Logistic Strategies (K-selected species)
– Low reproduction rates, usually don’t reach
carrying capacity
– intrinsically controlled growth
r-selected species
• Typically Small, Short Life Span
– Insects
– Rodents
– Marine Invertebrates
– Parasites
– Annual Plants
– Tribbles
K-selected species
• Low Reproduction Rates, Usually Don’t Reach
Carrying Capacity, Longer Life Span, Bigger
– Wolves
– Elephants
– Whales
– Primates
Growth Factors
• Natality = new
individuals
•
•
•
•
•
– often related to
Environmental
Conditions
Mortality
Immigration
Emigration
r = (b – d) + (i – e)
Survivorship:
number that survive
• Life expectancy
6.3 Regulation of Population
• Density-Independent
– Affect natality or mortality
independently of population density
– Often abiotic (weather and climate,
geologic hazards, fire…)
Regulation of Population
• Density-Dependent (competition)
– Decrease natality or Increase mortality as
population increases
– Interspecific (Different Species):
• predator-prey, parasites, symbiosis
• Example: hare - lynx
– Intraspecific (Same Species)
• Territoriality
• Stress and crowding (e.g. mouse)
6.4 Conservation Biology
• Island biogeography describes
isolated populations
• Conservation genetics is important
in survival of endangered species
• Population viability analysis
calculates chances of survival
• Metapopulations connected
Island Biogeography
• Single islands always have fewer species than
similar size areas on the mainland.
• Because islands are isolated, it will be harder
for species to immigrate to them, lowering the
rate of immigration.
• Limited resources on islands mean lower
carrying capacity.
• Applies to isolated habitats on land, also