Objectives:• To define and understand:

– Population biology – Characteristics of populationspopulations grow

• To estimate how pop’ns grow– initially w/ unlimited resources (exponential growth) – then as resources become limited (logistic growth)

• What limits growth?

– What are patterns in survivorship?– Trade-offs between growth, reproduction and

parental care– Human population growth

Definition of Pop’ns =

What are characteristics of the pop’n?

How is growth rate determined?

Measuring pop’n size (N). Census/count individuals

Δ N = (Δ B - D) + (Δ I - E) survival and reproduction are key factors that determine change in N

Growth of pop’n = change in # of individuals over time; G– Must calculate birth and death rates (b & d)

– Find the rate of increase = r

– Use r to estimate pop’n growth (G) for one time period = r N

• The biotic potential of pop’n

• Depends on:

Age structure

• Exponential growth implies unlimited resources• But, limits on pop’n growth exist

– Carrying capacity (= K)

– Environmental resistance

• Logistic growth; G= r N [(K-N)/K]– What happens when N > K, N = K, N < K?

Density-dependent and density independent limiting factors:

Pop’n may temporarily increase above carrying capacityOvershoot usually followed by a dramatic crash

Trade-off between births and density- as density increases births decrease

• Size of pop’ns may fluctuate with regularity.• Usually caused by multiple factors• Snowshoe hare-lynx example:

Three types of survivorship curvesType I –

Type III -

Type II –

Trade-offs between: 1) frequency of reproduction, 2) # of

offspring, and 3) parental care. • Big-bang reproduction

• Repeated reproduction

• Human pop’n growing exponentially

• Humans alter rate of increase; how?

• Humans alter environmental resistance; how?

• Largest countries: China, India, U.S.

• Worldwide >6 b. today (r = 0.013) – In 2050 ~10 b?

• Rapid growth in U.S. (1.8 % annually) – b and I– U.S. 300 m (~265 m 2003); now?– 2050, ~392 m