Population Dynamics SBI4U

Characteristics of Populations Habitat: the place where an organism or species normally lives Species: organisms that resemble each other and have the ability to interbreed

Population Size and Density Population Size: the number of individuals of a species occupying a given area at a given time Population Density: the number of individuals of the same species that occur per unit area

Population Density population density (D) total number counted (N) area occupied (S) D= N S e.g. = 480 moose = 0.8 moose/ha 600 ha

Sometimes, parts of a certain area are unusable (e. g Sometimes, parts of a certain area are unusable (e.g. river, mountain), so ecologists measure: Crude density: # of individuals of the same species within the total area of the entire habitat Ecological density: # of individuals of the same species per unit area actually used

Patterns of Dispersion

Patterns of Dispersion Clumped: organisms are densely grouped in areas of habitat with favourable conditions Uniform: individuals are evenly distributed throughout the habitat Random: individuals are minimally influenced by interactions with other individuals, and habitat conditions are virtually uniform

Sampling Techniques Every once in a while, biologists make an exact count of population numbers (e.g. in a lab, large animals in a small area) Normally, biologists count a sample of the population then estimate a total size This is important for many reasons – e.g. estimating the population density and size of tree species in the forestry industry to determine allowable harvest rates

Quadrats A common technique for stationary or small organisms (such as plants and insects) A large area can be sampled using small, selected plots A sampling frame (quadrat) on the ground, and the # of individuals of one or more species are counted

Quadrats continued Average estimates of population size and density for the entire area can then be extrapolated average sample density = total number of individuals total sample area

Mark-Recapture Sampling A common sampling technique for estimating the size and density of mobile wildlife populations, such as fish A sample of animals is captured, marked in some way, and released Fisheries scientists base management programs (such as restocking) on data

Mark-Recapture continued Large animals, such as moose or polar bears, may be tranquilized, captured, then marked with tags, bands or dye Technicians may also use such opportunities to weigh, measure and examine tranquilized individuals

Mark-Recapture continued After a period of time that allows marked animals to mix randomly with unmarked animals in the population, researchers capture a second sample Proportion of marked to unmarked animals provide a basis for estimating the size of the entire population

Mark-Recapture stipulations The chances for each individual to be caught must be equal (i.e. random) Marking techniques must not harm the organism or restrict its normal activities During the time period before recapture, no individuals can enter the population, no marked animal can die or leave

Mark-Recapture formula total # marked (M) = # of recaptures (m) total population (N) size of 2nd sample (n) N = Mn m Try this: In a wetland, 80 wood ducks are captured in traps, marked with bands and released. Two weeks later, 110 wood ducks are captured, of which 12 are marked. Estimate the total wood duck population in the survey area.

Modern Technology When tagging individuals, researchers can also attach radio collars or satellite-linked devices to track migration and behaviour patterns This information can be mapped in geographic information systems (GIS) This is especially useful for open-ocean predators, who don’t tend to stay in one area

Ethical Questions What are the effects on animals of being pursued, captured and marked? Will animals behave differently after being released? Does tranquilization have long-term effects? The Canadian Council on Animal Care (CCAC) suggests reducing use of animals in studies, refining techniques to minimize pain and distress, and replacing the trapping of animals whenever possible with computer models.