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Population Ecology -the study of populations and how these populations interact with the environment
• Special methods are used to count, monitor, and model changes to populations
• Information is used to:
1. Assess health of species/entire ecosystems
2. Predict future trends of population growth
3. Develop plans & policies to prevent extinction

Habitat -the place where an organism/species normally lives
Species -organisms that are similar physically, behaviourally, genetically, and can interbreed under normal conditions to produce fertile offspring.

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1.
2.
Population size (N) -estimated total number of individuals
Population density (D) -number of individuals per unit area or volume
D = total # individuals (N) total area or volume (S)

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Population densities are highly variable between species.
• small organisms usually have higher densities (ex. bacteria)
• large organisms usually have lower densities (ex. elephants)
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Ex. Table 1 pg. 651: Examples of
Population Densities

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Densities are sometimes inaccurate due to unusable space within a habitat.
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Crude density –number of individuals within a total area of the entire habitat
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Ecological density –number of individuals within the useable area of the habitat

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Sample Problem a)
What is the population density of 480 moose living in a 600 hectare (ha) region of Algonquin Park?
b)
If 70ha of Algonquin Park is lake water, what is the ecological density?

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3.
Population Dispersion –the general pattern in which individuals are distributed throughout a specific area
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Depends on environmental conditions & social behaviour
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3 main patterns among wild populations

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Clumped Dispersion
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Individuals are more concentrated in certain areas of a habitat
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Most common in nature
• ex. cattails, schools of fish

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Uniform Dispersion
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Individuals are equally spaced throughout a habitat
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Results from social competition for territory (feeding, breeding, nesting)
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Rare in nature
• ex. King penguins on South Georgia island

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Random Dispersion
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Individuals are spread throughout a habitat in an unpredictable/patternless manner
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Results from a consistent habitat
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Rare in nature
• ex. trees in the tropical rainforest

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Section14.1: Characteristics of
Populations
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#1-3 pg.651

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Populations are “dynamic”; their numbers and locations are constantly changing.
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Makes an accurate count difficult! (i.e. counting every individual only once)
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Instead, count a “sample” population to estimate total size & density

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QUADRAT SAMPLING –technique used for small, stationary species (plants, insects, etc.)
Real or virtual counting frames are used
Figure 6 pg. 653

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Average sample density = total # individuals total sample area
Sample Problem.
To estimate the size of a slug population on a golf course with a total size of 100m X 100m, biology students randomly selected five 1.0m
2 quadrats in a 10m X 10m site. The numbers of slugs in each quadrat were 4, 8, 9, 5, and 1. Estimate the population density and size of slugs in this study site .

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2.
MARK-RECAPTURE METHOD –sampling technique used for mobile species
• a sample is captured, marked in some way, released, and another sample is captured…etc.
• compare the ratio of (unmarked:marked) individuals in the following samples
• accuracy of technique is based on the following assumptions:
 every organism has equal opportunity of being captured (ex. “trap happy mice”)
 between samples, the population remains constant (no migration, births, deaths)

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Marking/tagging
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Involves using numbered tags or bands, or coloured dyes
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Must not harm/restrict animal
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Must remain visible for duration of study
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Must not alter chances of being captured

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+ total # marked (M) = # of recaptures (m) total population (N) size of second sample (n)
Sample problem.
From a fish population of unknown size, 26 fish were captured, marked, and released.
A second sample of 21 fish were captured, in which 3 fish were found to be marked.
Estimate the total population size.

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Section 14.1
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#5 pg. 657
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#3-6 pg. 659