# LESSON 16 Population Characteristics

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Lesson #16:
POPULATION CHARACTERISTICS
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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A. CHARACTERISTICS: SIZE,
DENSITY, DISPERSION
1.
Population size (N) -estimated total
number of individuals
2.
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)
•
Ex. Table 1 pg. 651: Examples of
Population Densities
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Densities are sometimes inaccurate
due to unusable space within a habitat.
Crude
density –number of
individuals within a total area of the
entire habitat
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
•
Depends on environmental
conditions & social behaviour
•
3 main patterns among wild
populations
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i.
Clumped Dispersion
•
Individuals are more concentrated
in certain areas of a habitat
•
Most common in nature
•
ex. cattails, schools of fish
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i.
Uniform Dispersion
•
Individuals are equally spaced
throughout a habitat
•
Results from social competition for
territory (feeding, breeding, nesting)
•
Rare in nature
•
ex. King penguins on South Georgia
island
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iii.
Random Dispersion
•
Individuals are spread throughout a
habitat in an unpredictable/patternless
manner
•
Results from a consistent habitat
•
Rare in nature
•
ex. trees in the tropical rainforest
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•
Section14.1: Characteristics of
Populations
•
#1-3 pg.651
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B. MEASURING POPULATION
CHARACTERISTICS
Populations are “dynamic”; their numbers and
locations are constantly changing.
•
Makes an accurate count difficult! (i.e. counting
every individual only once)
•
Instead, count a “sample” population to estimate
total size & density
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1.
QUADRAT SAMPLING –technique used
for small, stationary species (plants, insects,
etc.)
•
•
Real or virtual counting frames are used
Figure 6 pg. 653
+ 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 1.0m2 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
•
Involves using numbered tags or bands, or
coloured dyes
•
Must not harm/restrict animal
•
Must remain visible for duration of study
•
Must not alter chances of being captured
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total # marked (M)
total population (N)
=
# of recaptures (m)
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
•
#5 pg. 657
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#3-6 pg. 659
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