Population Density, Dispersion, Demographics Chapter 36.1 – 36.3

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

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

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

You try it! 1.50 rabbits are captured and tagged on the first visit. Two months later, 45 rabbits are captured and 14 of them are tagged from the previous visit. Approximately, how large is the population? 2.24 Polar Bears are captured and tagged on the first visit. On the second visit, 1 month later, only 11 are captured and 10 of them are tagged from the first visit. 3.In a different environment, 24 polar bears were captured on the first visit. On the second visit, 12 are captured, but only 3 were previously tagged. 4.Complete the following statement: The larger the percentage of tagged individuals in the second capture, the ___________ the population.

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)

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

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