1. Population Density, Dispersion, Demographics Chapter 36.1 – 36.3

2. What you need to know!  How density, dispersion, and demographics can describe a population.

3. Population  A group of organisms of the same species that live in the same place at the same time  2 nd level of organization  3 defining characteristics:  Density  Dispersion  Demographics

4. Density  The number of individuals of a species per unit area or volume  Ex: 100 oaks/km 2  NOT 100 oaks! Counting methods:  Count individuals in a given area (usually too difficult)  Count a small area and multiply based on size ratios (plants)  Mark-recapture method: N=(MC)/R  N = Estimate of total population size  M = Total number of animals captured and marked on the first visit  C = Total number of animals captured on the second visit  R = Number of animals captured on the first visit that were then recaptured on the second visit

5. Dispersion  How individuals are organized within their geographic area  Clumped: organisms live closely together in groups (most common)  Uniform: organisms are evenly spaced out usually due to interactions between individuals (i.e. territorial disputes)  Random: unpredictable (rarest type)

6. Demographics Vital statistics:  Birth rates  Death rates  Life tables show relationships between age and death  Survival curves graphically represent life tables

7. Life Tables and Survivorship Curves  Life tables allow ecologists to study the dynamics of population growth  Survivorship curves are graphic representations of life tables Analysis of curves:  Type I: die at old age; larger species; provide good care to offspring, but have few of them; humans, elephants  Type II: intermediate graph with relatively constant death rates across all ages; rodents, lizards, invertebrates  Type III: massive death of the young; with long lives for the survivors; “lay-‘em and leave-‘em”; fish, plants