1. (CHAPTER 1 / SECTION 2) STUDYING POPULATIONS

2. A group of organisms from the same species occupying the same geographical area. This area may be difficult to define because: A population may be comprised of widely dispersed individuals which come together only infrequently, e.g. for mating. Populations may fluctuate considerably over time due to migration. Populations Migrating wildebeest population Tiger populations are comprised of widely separated individuals

3. Populations are dynamic (frequently changing). Populations can be measured or calculated: Population size: the total number of organisms in the population. Population density: the number of organisms per unit area. Population distribution: the location of individuals within a specific area. Features of Populations

4. The study of changes in the size and composition of populations, and the factors influencing these changes. Population growth rate: the change in the total population size per unit time. Natality (birth rate): the number of individuals born per unit time. Mortality (death rate): the number of individuals dying per unit time. Migration: the number moving into or out of the population. Population Dynamics Population size is influenced by births… …and deaths

5. Migration The movement of organisms into and out of a population affects the dynamics of a population. Populations lose individuals through deaths and emigration. Populations gain individuals through births and immigration. Migrating species may group together to form large mobile populations. Wildebeest Canada geese

6. The number of individuals per unit area. At low population densities, individuals are spaced well apart. Examples: territorial, solitary mammalian species such as tigers. At high population densities, individuals are crowded together. Examples: colonial animals, such as rabbits, corals, and termites. Population Density High density populations Low density populations

7. Competition Environmental resources are finite. Competition within species for resources increases as the population grows. At carrying capacity, the area can support its largest population. When the demand for a resource (e.g. water, food, space, light) exceeds supply, that resource becomes a limiting factor. Animals compete for resources such as water (left) or mates (right), especially when these are in short supply or access to them is restricted.

8. Physical (or abiotic) factors temperature precipitation Acidity Catastrophic events floods and tsunamis fire drought earthquake and eruption Limiting Factors

9. Population depends on the number of individuals added to the population from births and immigration, minus the number lost through deaths and emigration. This can be expressed as a formula: Population Growth Population growth = Births – Deaths + Immigration – Emigration (B)(D)(I)(E)

10. Calculating Population Change Births, deaths, and net migrations determine the numbers of individuals in a population. Emigration (E) Births (B) Immigration (I) Deaths (D)

11. Determining Population Size Direct observation - counting all the members within a population Indirect observation – observing signs of organisms ex. Nests Sampling – estimating the population size, counting the number of organisms in a small area and multiply to find the number in a larger area Mark and Recapture – capturing animals and marking them with a radio collar, or tag and releasing them to be recaptured later