Population Characteristics: * all species occur in groups called populations * pop. Density * spatial distribution * growth rate * used to classify pops of org * bacteria * animals * plants
Population density: * Population Density: is the number of orgs per unit area
Spatial Distribution: * Dispersion: the pattern of spacing of a population within an area * One of the primary factors in the patter of dispersion for all orgs is the availability of resources such as food
Population ranges: * Pop. is huge * Orgs adapt to biotic and abiotic factors * Species might not be able to expand if abiotic might not be bearable * Change in temp., humidity, rainfall, or sunlight might make a new geographic area uninhabitable for species. * Biotic factors such as predators, competitors, parasites, present threats that might make new location difficult for survival.
Population-Limiting Factors: * Limiting factors are biotic and abiotic factors that keep a pop from increasing indefinitely * Decreasing a limiting factor like food, often changes the number of orgs to survive
Density-independent factors: * Two types * Density independent * Density dependent * Density-independent: any factor in the environment that does not depend on the # of members in a pop. Per unit of area. * Events that limit pop * Drought or flooding, extreme heat or cold, tornados, and hurricanes * Ground fires * Pops can be limited by the unintended results of human alterations of landscape * Air and water land pollution affect the results of human activity that also can limit pops. * Pollution reduces the available resources by making some of the resources toxic.
Density-dependent factors: * Density dependent factor: any factor in the environment that depends on the number of members in a pop. Per unit area * Often biotic factors such as predation, disease, parasites, and competition
* Tend to occur when pop has increased and pop density is high * Diseases are transmitted more easily when pop is high * Contact between two is more frequent * True for human pop. * protists, plants, and other species of animals
* increases when density increases * when pop increases to a size that resources such as food or space become limited, orgs in pop must compete * competition might reduce the pop. Size due to starvation or need of more resources * as pop decreases, competition decreases
* as pop density decreases pop can be effected * the presence is a density-dependent factor that can negatively effect pop growth
Population growth rate: * impt is growth rate * population growth rate: (PGR) explains how fast a pop grows * the natality of a pop is the birthrate: or the number of individuals born in a given time period * Morality: the number of deaths that occur in the pop during a given time period. * More important are natality and morality * Emigration: is the term ecologists use to describe the # of individuals moving away from the pop * Immigration: is the term ecologists use to describe the number of individuals moving into a pop. * Mostly immigration and emigration are = * Some pops remain one size others change
Exponential growth model: * If all offspring survive to breed, the pop grows slowly at first * Slow graph period is defined as a lag phase * The rate pop growth soon begins to increase rapidly due to the total # of orgs that are able to reproduce *