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 – – 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 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