Transcript 09Molles5e

Population Distribution and Abundance
Chapter 9
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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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Niches
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Niche: Summarizes environmental factors
that influence growth, survival, and
reproduction of a species.
 Grinnell’s definition focused on the effects
of the physical environment
 Elton’s definition included biotic and
abiotic factors
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Niches
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Hutchinson defined niche as:
 n-dimensional hyper-volume
 n equates the number of environmental
factors important to survival and
reproduction of a species.
 Fundamental niche - hypervolume
 Realized niche includes interactions such
as competition that may restrict
environments where a species may live.
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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 Distributions 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 Distributions 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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Review
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Distribution Limits
Distribution Patterns
Organism Size and Population Density
Commonness and Rarity
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