11.14

Life tables summarize the probability that an individual will survive and reproduce over the course of its lifetime.

Survivorship: the proportion of offspring that survive, on average, to a particular age.

Type I: High survivorship as youngs and low survivorship as olds. Humans

Type II: Steady survivorship. Birts

Type III: Low survivorship as young, high survivorship as old. Ants

Fecundity: the number of female offspring produced by each female in the population

Net reproductive rate: R_O. When it’s one, the population is not growing. Indicates whether the population is increasing or decreasing.

Fitness Trade-Offs

• Austrian common lizards have low fecundity and high survivorship, French common lizards have high fecundity and low survivorship. Austria has fewer and larger offspring, France has more and smaller offspring.

• You can’t be good at everything

• The low fecundity and high survivorship (Austrian) animals have higher resistance to diseases and predators

Change in population size = Births + Immigrants - Deaths - Emigrants

change in population size / change in time = birth rate - death rate

The difference between the birth rate and the death rate is called the per capita rate of increase ( r ). If r is zero, the population isn’t changing.

r = b - d

• Exponential population growth: if no immigration or emigration is occurring then:

• Change in population size / change in time = dN / dt = rN

• Exponential population growth is density independent

• As the value of r increases, the exponential growth curve gets steeper (dN/dt = 1.0N > 0.5N)

• Can be seen during colonization of a new habitat/recovery after a disaster

Ultimately, there is a limit to the number of individuals that can occupy a habitat.

Carrying capacity (K): maximum population size that a particular environment can sustain

• Logistic population growth: adds K.

• dN/dt = rN x (K-N) / K

• K-N is the number of additional individuals the environment can support

• The whole thing (K-N) / K is the fraction still available for population growth

• Logistic population growth is density dependent

• Graphs as an S shaped curve

• Initially growth is exponential, as resources are abundant. At carrying capacity, growth is 0, and the graph is flat

What density dependent factors limit population size?

• Competition for resources (food, water, territory, light, nesting sites, nutrients, oxygen)

• Disease and parasitism

• Predation

• Toxic wastes (ammonia, uric acid, alcohol, carbon dioxide)

• Social behavior (stress mediated behavior, dominance and mating behavior)