Population Ecology

• Population - group of individuals of the same species living in the same general area. – They must rely on the same resources, have a good chance of

interacting with each other, and have the similar environmental factors.

Factors affecting populations – Density - # of individuals per unit area

• counting & estimation • dynamic due to immigration, emigration, births & deaths

– Dispersion - how they are spread throughout their boundary area • clumped (most common) - maximizes reproduction • uniform (evenly spread) - maximizes survival in there are limited

resources – territoriality

Factors affecting populations

– Demography - study of the vital statistics of populations and how they change over time • life-tables - age specific summaries of life expectancy in a

population (sometimes called Quantitative demography) – built using cohorts - groups of similar aged individuals followed until death – graph is called a survivorship curve

– Reproductive rates - ignores males of a species • reproductive table - graphic representation of a cohorts

reproductivity during a lifespan

Life history• Life history - how an organism's

life begins and ends with particular emphasis on traits that affect an organism's schedule of reproduction.

• 3 basis variables: – when reproduction begins – how often the organism reproduces

• semelparity - reproduces once – big bang reproduction - many offspring

with low survival rate

• iteroparity - repeated reproduction – few offspring with high survival rate

– how many offspring are produced

Population growth and density• Population size is regulated by a complex interaction of

biotic and abiotic influences.• Density

– density independent growth - death rate is not influenced by birth rate

– density dependent growth - death rate increases with an increase in birth rate • factors

– Competition – territoriality – health – predation – intrinsic factors - births stop at a certain density regardless of the above factors

Growth • exponential model

– 1 -2-4-16-256-65536-4294967296... – cannot sustain itself due to the resources available. (example: a single E. coli

reproducing every 20 minutes would cover the world in less than 36hours) • most growth goes through stable and fluctuating periods • although the number of humans are still increasing the rate of growth slows

each year as we lose members to disease and choice – population dynamics is the study of biotic and abiotic factors that influence

population size • Carrying capacity - the amount of individuals that can be supported in one

system – it is estimated that the carrying capacity for humans is 10-15 billion (a number to be

reached by 2050 if there is not some global catastrophe) – can be further estimated by looking at the ecological footprint - the area a population

needs to gather resources and dispose of its waste • the US needs 8.4 ha/person but only has 6.2ha/person - over carrying capacity