Biology 5C ~ Lecture 8 ~ Density Demographics

What is a population?

-A population is a group of individuals of a single species living in the same general area

-members of a population rely on the same resources, are influenced by similar environmental factors and are likely to breed and interact with one another

Populations have four key emergent properties:

-size
-density
-dispersion
-rate of change in size over time

Size:

N=the total number of individuals in the population

Density:

the number of individuals per unit area or volume

Dispersion:

the distribution of individuals in the population over space or volume

Rate of change in size over time:

growth, decline or stability

Patterns of Dispersion:

-random distributions
-clumped distributions
-uniform distribution

Random distributions:

Every point in space has an equal and independent probability of containing an individual

Clumped distributions:

- Individuals are more aggregated than in a random distribution
- Individuals are more likely to be found in close proximity to other individuals

Uniform distributions:

- individuals are more evenly spaced than in a random distribution
- individuals are less likely found near other individuals

population size, density, growth and dispersion are influenced by:

-the ecological needs of the species
-the distribution and abundance of resources
-the interactions among individuals in the population (attraction & repulsion)

Attraction:

mating, parenting, herding, and schooling

Repulsion:

territoriality, competition for resources

populations are dynamic

-births and immigration add individuals to a population
-deaths and emigration remove individuals from a population

Demography:

study of the vital statistics of a population and how they vary with age

Life table:

list of the vital statistics of a population

-the data from life tables can be presented graphically as survivorship curves

Cohort:

a group of individuals in a population born about the same time

Survivorship (I_x):

proportion of individuals born that survives to age x

A life history is the schedule of an organism's life:

-age/size at reproductive maturity
-allocation of energy to reproduction
-number and size of offspring
-number of reproductive events
-life span

The central trade-off: reproductive strategy

-time of maturation
-relative number offspring
-lifespan
-number reproductive events
-offspring survivorship

Why do r-selection and K-selection exist?

Finite (limited) resources --- principle of allocation

Principle of allocation:

resources that an organism has to partition among life history functions (growth, maintenance, and reproduction) are limited

SLIDES THAT WILL BE ON THE EXAM

-population and the four key emergent properties
-population dispersions and what influences them
-four factors that influence change in population numbers
-life table
-survivorship curves
-life history