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Population Distribution and
Case Study: From Kelp Forest to Urchin Barren
Waters surrounding
the Aleutian Islands
have abundant
marine life,
including the sea
Figure 8.1 Key Players in the Forests of the Deep
Figure 8.2 Do Sea Urchins Limit the Distribution of Kelp Forests?
Distribution: Geographic area over
which individuals of a species occur.
Abundance: The number of individuals in
a specific area.
Figure 8.3 Abundances Are Dynamic (Part 1)
Concept 8.1: Populations are dynamic
entities that vary in size over time and space.
Population: Group of individuals of the
same species that live within a particular
area and interact with one another.
Abundance can be reported as
population size (# individuals), or
density (# individuals per unit area).
Figure 8.3 Abundances Are Dynamic (Part 2)
Figure 8.4 Fragmentation of Dorset Heathlands
Figure 8.5 Aspen Groves—One Tree or Many?
Figure 8.6 Plants and Animals That Form Clones
Individuals can be defined as products of
a single fertilization: The aspen grove
would be one individual, a genet.
Members of a genet may be
independent physiologically, so
members of a genet are called ramets.
Distribution and Abundance
Concept 8.2: The distributions and
abundances of organisms are limited by
habitat suitability, historical factors, and
Abiotic features of the environment include
moisture, temperature, pH, sunlight,
nutrients, etc.
Some species can tolerate broad ranges
of physical conditions, others have
narrow ranges.
Figure 8.7 The Distributions of Two Drought-Tolerant Plants
Figure 8.8 Herbivores Can Limit Plant Distributions
Figure 8.9 Joint Effects of Temperature and Competition on Barnacle Distribution
Figure 8.10 Continental Drift Affects the Distribution of Organisms
Figure 8.11 Populations Can Expand after Experimental Dispersal
Distribution and Abundance
Dispersal limitation can prevent
species from reaching areas of suitable
Example: The Hawaiian Islands have
only one native mammal, the hoary bat,
which was able to fly there.
Figure 8.12 Desert Pupfish Habitat
Geographic Range
Concept 8.3: Many species have a patchy
distribution of populations across their
geographic range.
There is much variation in the size of
geographic ranges—the entire
geographic region over which a species
is found.
Figure 8.13 Monarch Migrations
Table 8.1
Geographic Range
Other species, such as the coyote, have
very large geographic ranges.
Some species are found on several
Few species are found on all continents
except humans, Norway rats, and the
bacterium E. coli.
Figure 8.14 Populations Often Have a Patchy Distribution (Part 1)
Figure 8.14 Populations Often Have a Patchy Distribution (Part 2)
Figure 8.15 Abundance Varies Throughout a Species’ Geographic Range
Figure 8.16 Dispersion of Individuals within Populations
Dispersion within Populations
Concept 8.4: The dispersion of individuals
within a population depends on the location
of essential resources, dispersal, and
behavioral interactions.
Figure 8.17 Territorial Behavior Affects Dispersion within Populations (Part 1)
Figure 8.17 Territorial Behavior Affects Dispersion within Populations (Part 2)
Estimating Abundances and Distributions
Concept 8.5: Population abundances and
distributions can be estimated with areabased counts, mark–recapture methods, and
niche modeling.
Estimating Abundances and Distributions
Quadrats are sampling areas (or
volumes) of specific size, such as 1 m2.
Individuals are counted in several
quadrats; the counts are used to
estimate population size.
Figure 8.18 Estimating Absolute Population Size
Estimating Abundances and Distributions
40, 10, 70, 80, and 50 chinch bugs are
counted in five 10 cm × 10 cm (0.01 m2)
(40 + 10 + 70 + 80 + 50) / 5
= 5000/m 2
Estimating Abundances and Distributions
Estimating Abundances and Distributions
Mark–recapture methods are used for
mobile organisms.
Example: 23 butterflies are captured and
marked (M).
A subset of individuals is captured and
marked or tagged in some way, then
Several days later, 15 are captured (C), 4
of them marked (R for recaptured).
At a later date, individuals are captured
again, and the ratio of marked to
unmarked individuals is used to
estimate population size.
To estimate total population size (N):
M / N = R/C
N = (M × C ) / R
N = (23 × 15) / 4 = 86
Figure 8.19 Causing the Outbreak? From Rain to Plants to Mice
Estimating Abundances and Distributions
These data can be compared from one
time period to another, allowing an
estimate of relative population size.
Figure 8.20 Predicted Distributions of Madagascar Chameleons
Estimating Abundances and Distributions
The ecological niche: The physical and
biological conditions that a species
needs to grow, survive, and reproduce.
Figure 8.21 The Effect of Otters on Urchins and Kelp (Part 1)
Figure 8.21 The Effect of Otters on Urchins and Kelp (Part 1)
Figure 8.22 Orca Predation on Otters May Have Led to Kelp Decline (Part 1)
Figure 8.22 Orca Predation on Otters May Have Led to Kelp Decline (Part 2)
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