Transcript INTRODUCTION

Population Distribution and Abundance
Chapter 7
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Outline
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Distribution Limits
Distribution Patterns
Organism Size and Population Density
Commonness and Rarity
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Introduction
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Ecologists usually define a population as a
group of individuals of a single species
inhabiting a specific area.
 Characterized by the number of
individuals and their density.
 Additional characteristics of a population
include age distributions, growth rates,
distribution, and abundance.
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Distribution Limits
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Physical environment limits geographic
distribution of a species.
 Organisms can only compensate so much
for environmental variation.
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Kangaroo Distributions and Climate
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Caughley found a close relationship between
climate and distribution of the three largest
kangaroos in Australia.
 Macropus giganteus - Eastern Grey
 Eastern 1/3 of continent.
 Macropus fuliginosus - Western Grey
 Southern and western regions.
 Macropus rufus - Red
 Arid / semiarid interior.
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Kangaroo Distributions and Climate
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Kangaroo Distributions and Climate
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Limited distributions may not be directly
determined by climate.
 Climate often influences species
distributions via:
 Food production
 Water supply
 Habitat
 Incidence of parasites, pathogens and
competitors.
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Tiger Beetle of Cold Climates
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Tiger Beetle (Cicindela longilabris) lives at
higher latitudes and elevations than most
other species in NA.
 Schultz et. al. found metabolic rates of C.
longilabris are higher and preferred
temperatures lower than most other
species.
 Supports generalization that the
physical environment limits species
distributions.
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Tiger Beetle of Cold Climates
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Distributions of Plants along a MoistureTemperature Gradient
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Encelia species distributions correspond to
variations in temperature and precipitation.
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Distributions of Barnacles along an
Intertidal Exposure Gradient
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Organisms living in an intertidal zone have
evolved to different degrees of resistance to
drying.
 Barnacles show distinctive patterns of
zonation within intertidal zone.
 Connell found Chthamalus stellatus
restricted to upper levels while Balanus
balanoides is limited to middle and
lower levels.
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Distributions of Barnacles along an
Intertidal Gradient
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Balanus appears to be more vulnerable to
desiccation, excluding it from the upper
intertidal zone.
 Chthamalus adults appear to be excluded
from lower areas by competition with
Balanus.
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Distributions of Barnacles along an
Intertidal Gradient
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Distribution of Individuals on Small Scales
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Random: Equal chance of being anywhere.
 Uniform distribution of resources.
Regular: Uniformly spaced.
 Exclusive use of areas.
 Individuals avoid one another.
Clumped: Unequal chance of being
anywhere.
 Mutual attraction between individuals.
 Patchy resource distribution.
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Distribution of Individuals on Small Scales
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Distribution of Tropical Bee Colonies
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Hubbell and Johnson predicted aggressive
bee colonies would show regular distributions
while non-aggressive species would show
random or clumped distributions.
 As predicted, four species with regular
distributions were highly aggressive.
 Fifth was non-aggressive and randomly
distributed.
 Prospective nest sites marked with
pheromones.
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Distributions of Desert Shrubs
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Traditional theory suggests desert shrubs
are regularly spaced due to competition.
 Phillips and MacMahon found distribution
of desert shrubs changes from clumped to
regular patterns as they grow.
 Young shrubs clumped for (3) reasons:
 Seeds germinate at safe sites
 Seeds not dispersed from parent areas
 Asexual reproduction
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Distributions of Desert Shrubs
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Phillips and MacMahon proposed as plants
grow, some individuals in clumps die,
reducing clumping.
 Competition among remaining plants
produces higher mortality.
 Eventually creates regular distributions.
Brisson and Reynolds found competitive
interactions with neighboring shrubs appear
to influence distribution of creosote roots,
Larrea tridentata.
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Distributions of Individuals on Large Scales
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Bird Populations Across North America
 Root found at continental scale, bird
populations showed clumped distributions
in Christmas Bird Counts.
 Clumped patterns occur in species with
widespread distributions.
 Brown found a relatively small proportion
of study sites yielded most of records for
each bird species in Breeding Bird Survey.
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Plant Abundance along Moisture Gradients
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Whittaker examined distributions of woody
plants along moisture gradients in several
North American mountain ranges.
 Documented moisture gradient from moist
canyon bottoms up to the dry southwestfacing slopes.
 Tree species showed a highly clumped
distribution along moisture gradients,
with densities decreasing substantially
toward the edges of their distribution.
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Plant Abundance Along Moisture Gradients
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Organism Size and Population Density
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In general, population density declines with
increasing organism size.
 Damuth found the population density of
herbivorous mammals decreased with
increased body size.
 Peters and Wassenberg found aquatic
invertebrates tend to have higher
population densities than terrestrial
invertebrates of similar size.
 Mammals tend to have higher population
densities than birds of similar size.
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Organism Size and Population Density
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Plant Size and Population Density
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Plant population density decreases with
increasing plant size.
 Underlying details are very different.
 Tree seedlings can live at very high
densities, but as the trees grow, density
declines progressively until mature trees
are at low densities.
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Commonness and Rarity
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Rabinowitz devised commonness
classification based on (3) factors:
 Geographic Range of Species
 Habitat Tolerance
 Local Population Size
Populations that are least threatened by
extinction, have extensive geographic
ranges, broad habitat tolerances, and some
large local populations.
 All seven other combinations create some
kind of rarity.
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Rarity
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Rarity I
 Extensive Range, Broad Habitat
Tolerance, Small Local Populations
 Peregrine Falcon
Rarity II
 Extensive Rage, Large Populations,
Narrow Habitat Tolerance
 Passenger Pigeon
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Rarity
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Rarity III
 Restricted Range, Narrow Habitat
Tolerance, Small Populations
 California Condor
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Applications and Tools
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Estimating abundance
Estimating Whale Population Size
Lincoln-Peterson index:
M/N=m/n
Where:
M=the number of individuals marked and Released
N=the actual size of the study population
M=the number of marked individuals in a sample of the
population.
n=the total number of individuals in a sample.
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N.Bailey proposed a corrected formula
N=M(n+1)/m+1
Some of the assumptions of mark and
recapture studies.
All individuals have an equal probability of being captured.
The population is not increased by births or immigration
between marking and recapture.
Marked and unmarked individuals die and emigrate at the
same rate.
No marks are lost.
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The Relative Abundance of Corals, Algae and
Sponges
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1 m² maped
Measured area for each species
Calculate percentage of coverage
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