Determining Population Size Answers

The sampling method involves counting the total number of organisms in a certain area and then using that number to determine the total number of organisms in a larger area.

A number of members of a population are capture, tagged, and released. At a later time, the sampler returns and captures a set number of members of the population and determines the ratio of tagged to untagged individuals. The ratio of tagged to caught individuals is then approximately equal to the ratio of originally tagged individuals to the total population.

A logistic growth curve is S-shaped. Populations that have a logistic growth curve will experience exponential growth until their carrying capacity is reached, at which point their growth begins to level. An exponential growth curve is J-shaped. Exponential growth is more common in R-selected species, which have a short life span and a high rate of reproduction.

New Zealand’s population density = 4,326,380 people /103,736 mi^2 = 42 people/mi^2. Australia’s population density = 21,905,140 people / 2,967,909 mi^2 = 7 people/mi^2.

Even though New Zealand has a smaller population than Australia, it has a greater population density because it covers a much smaller area. Australia’s population is approximately five times larger than New Zealand’s while the area Australia covers is approximately 30 times larger than the area New Zealand covers.

Select representative portions of the habitat and count the organisms in them, often using quadrats or transects. Calculate the average number of organisms per unit area from the samples, then use that density to estimate the population across the entire habitat.

Capture a sample of organisms, mark them harmlessly, and release them. After they have had time to mix back into the population, capture a second sample and count how many are marked. Use the proportion of marked organisms in the second sample to estimate the total population: (number marked initially × size of the second sample) ÷ number of marked organisms recaptured.

New Zealand: 42 people per square mile. Australia: 7 people per square mile.

Population density is the number of people per unit of area. New Zealand has about 41.7 people per square mile, while Australia has about 7.4 people per square mile. New Zealand has a smaller total population, but its area is much smaller relative to its population, so more people live in each square mile.

An exponential growth curve continues to increase rapidly without leveling off, forming a J shape. A logistic growth curve grows rapidly at first, then slows as resources become limited and levels off near carrying capacity, forming an S shape.