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 quantityTakes 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