BIOL 4120: Principles of Ecology
Lecture 8: The Distribution
and Spatial Structure of
Populations
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Chapter 10
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Population and Subpopulations (or local
populations)
Due to
environmental
heterogeneity
and mosaic of
different
habitats, many
populations are
divided into
smaller
subpopulations.
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Properties of Population
Most important property is abundance of
population which is determined by its
distribution and density.
Populations have
• Distribution: population extent, geographic area occupied
by a population (also called geographic range)
• Population size: Number of individuals in a population
(varies with food supplies, predation rates etc.)
• Population Structure: encompasses a number of
attributes, including density and spacing of individuals
within suitable habitat and proportions individuals of each
sex and age class (Spatial structure)
 Density: How to determine population density?
 Age structures and Different sex ratios along time
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Topics
10.1 Populations are limited to ecologically
suitable habitats
10.2 Ecological niche modeling predicts the
distributions of species
10.3 The dispersion of individuals reflects habitat
heterogeneity and social integrations
10.4 The spatial structure of populations parallels
environmental variation
10.5 Three types of models describe the spatial
structure of populations
10.1 Populations are limited to
ecologically suitable habitats
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Distribution
• Spatial location, Area over
which a species occupies
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Geographic range
• Area that encompasses
the entire population of a
species
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Limited by
• Climate: temperature,
precipitation…
• And other factors
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Food production
Water supply
Habitat
Incidence of parasites,
pathogens and
competitors
Geographic barriers
All these factors together are called
ecological niche
The distribution of a species is related
to ecological niche
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Fundamental niche: The range of
physical conditions over which
species can persist
Realized niche: Within the range of
conditions, predators, pathogens and
competitions limit the distribution of
a species to a smaller place
Barnacles
Distribution of a species varies at
different spatial scales
Distribution of moss Tetraphis
Continental scale: climate
suitability
Particular area: microclimate
and stream banks (coniferous
trees and abundance)
Within a particular locality:
occupy stumps of conifer trees
(pH is acidic)
Local subpopulations
BIOL 4120: Principles of Ecology
Lecture 8: The Distribution
and Spatial Structure of
Populations
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu

Recap
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Population & Metapopulation
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Populations properties
Distribution, size, and structure (density,
spacing, age, sex etc)
Niche: Fundamental niche
Realized niche
Distribution patterns at different scales
Distribution of the perennial shrub
Clematis
Only in Jefferson county, Missouri
Dry and rocky soils
Further confined to suitable soil
structure, moisture and nutrients
Individual fitness is highest
within the natural distribution
of a species
A transplant study by Amy
Angert et al. of Michigan State
University
Two species of monkeyflower,
one grows in low and one in
high elevations
Other factors influence species
distributions
•Dispersal limitation
•Migration
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Dispersal limitation
Dispersal: movement of individuals in space.
Dispersal limitation: the absence of a population from
suitable habitat because of barriers to dispersal
Methods of dispersal
Passive dispersal (gravity, wind, water, animal) seeds of
plants, small animals, fish, shrimp. fruits and seeds ate and
carried by animals (long distances)
Active dispersal: animal movement.
Barriers to long-distance dispersal often limit geographic
ranges are overcome by human intervention
Move plants and animals around the world (invasive
species)
Migration
Geographic range of a
population includes all
the areas of its
members occupy during
their entire life history
Migration – A round trip,
perhaps involving
mating
Red-necked ducks:
Breeding in the northeast
Winter in South Carolina
and Florida
Gray whale:
Winter in California,
Summer in Arctic
Migratory pathways of Ring-necked ducks and
gray whale.
Atlantic bluefin tuna range across the breadth of the Atlantic
Ocean (A 5 year record of the movement of a single individual
using electronic tag)
Some fish
(Actic
Terns)
travel
30,000 km
per year
Tuna:
Tagged in
1999 and
captured
in 2003
Wildebeests in
East Africa
migrate long
distances following
the geographic
pattern of
seasonal rainfall
and fresh
vegetation
Some migratory movements are a response of occasional failure or
depletion of local food supplies (Somalia, Africa, 1962)
e.g.: migratory locusts
10.2 Ecological niche modeling predicts the
distributions of species
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How to predict the species distribution?
For ecological management purposes (species
protection, conservation, new species introduction), we
need to understand and predict species distribution
Ecological niche modeling: Using exist species
distribution knowledge and the related climatic factors to
predict actual or potential species distribution under
future climate conditions
Ecological niche modeling
The catalog of ecological
conditions is a species’
ecological envelope.
Mostly involve “training”
and “test” sites.
Also called Climatic
Envelope Modeling
Ecological envelopes of three species of Eucalyptus trees across
6,080 plots in southeastern New South Wales, Australia
Ecological envelopes can be used to predict the distributions of
invasive species
Aquatic plant (Hydrilla) and Chinese bush clover (Lespedeza)
Native
regions in
Asia and new
location in
US
Global warming on the distribution of Anchovies: expanding their
geographic ranges northward increased species richness in North Sea
Hiddink and ter Hofstede 2008
Increased
species
diversity,
but
decreased
some
commercial
species.
10.3 The dispersion of individuals reflects
habitat heterogeneity and social integrations
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Dispersion
• The spacing of individuals within respect to one
another within the geographic range of a
population
Not dispersal
Distribution patterns
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Distribution patterns
1. Random: Equal chance of being anywhere. Neutral interactions.
2. Uniform (spaced) distribution of resources.
Regular: Uniformly spaced.
Exclusive use of areas. Antagonistic interaction
individuals avoid one another.
3. Clumped: Unequal chance of being anywhere.
Mutual attraction between individuals.
Patchy resource distribution.
Clumped distribution of Aspen trees
Different clones of aspen trees, distinguished by
timing of leaf fall. Each clone from one seed
10.4 The spatial structure of
populations parallels environmental
variation
Population density
Number of individuals per unit of area
Variation in population density
Population density of a
small songbird of prairies
and grasslands: dickcissel
Highest at the center of a
species’ geographic range
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Influenced by available habitat
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Carolina wren:
Northwards -7oC; Westward>52mm
• When all environmental factors within its range of
tolerance, the organism can live in its habitat
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Horned lark
• Avoids forests
• Available territory
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Recap
Populations are limited to ecologically suitable
habitats
Dispersal and migration
Spatial patterns
Ecological niche modeling predicts the
distributions of species
Ecological niche model
The spatial structure of populations parallels
environmental variation
Ideal free distribution hypothesis
All individuals seek good
patch and good patch filled
up quickly and eventually,
becomes less favorable than
poor patch.
The quality of these good
patches decreases until poor
patches become equally
good choices.
In the end, individuals move
from better to poorer
patches until each patch has
the same value for individual
fitness, regardless of the
intrinsic patch quality.
Dispersal from high-density to
low density patches
Population distribution rarely reach Ideal Free
Distribution
1. individuals do not know which patches are
good patches
2. dominant individuals may forces
subordinates to leave high-quality patches
Results: individuals in best habitats produce surplus
individuals whereas in poor habitats, deaths exceeds
births and populations can’t maintain their numbers
Dispersal from high-density to
low density patches
Immigration from good to poor patches
One example: Blue tit (Parus caeruleus), a small songbird
Two habitats:
Deciduous downy oak, more caterpillars as food, high density (90
pairs/100 ha), high reproduction (5.8/pair)
Everygreen holm oak, low density (10 pairs/100 ha), low
reproduction (3.6 /pair)
Immigration maintain poor patch subpopulations (otherwise,
13% decrease).
Even with dispersal, population distribution
can not move to very poor habitat
10.5 Three types of models describe
the spatial structure of populations
10.6 Dispersal is essential to the
integration of populations
When individuals disperse throughout a population, they link
different subpopulations together and make the whole population
function and evolve as a single structure. When dispersal is limited,
different subpopulations behave independently to each other.
Measurements of dispersal: Method: mark and recapture
Life time dispersal distance: how far an individuals move, on
average, from their birthplace to where they reproduce.
Life time dispersal area:
Neighborhood size: number of individuals, defined by the life
time dispersal area times the population density.
An example, 8 small songbird species:
Life time dispersal distances: 344 to 1,681 meters
Population densities: 16 to 480 individuals per sq. km
Neighborhood size: 151 to 7,697 individuals
Neighborhood size= lifetime
dispersal area * population
density
Since the average dispersal
distance bears a constant
relationship to population
density, neighborhood
sizes are rather more
similar than one expect
from either dispersal
distance or population
density alone:
land snails: 1,800 to 7600;
songbirds: 151 to 7679;
lizard: 225 to 270.
Introduced population can spread rapidly outside their established
range
European starling in the US (shade area: breeding range; dots:
records of birds, young individuals)
Invasive species
Gypsy moth
caterpillars
$764 M loss in 1981
Defoliated oak
forest
Invasive species
Kudzu, an invasive species
Native to Asia, introduced to US
as an ornamental vine in 1876
Used to control soil erosion in
1930s and 1940s
1950s, recognized as pest
Cover southeastern US, 2 million
to 7 million acres
10.7 Macroecology addresses
patterns of range size and
population density
Macroecology: study of relationships
between organisms and environments
at large spatial scales; to determine
and explain the distribution patterns
and population size of a particular
species by large samples of species.
Macroecology addresses patterns
of range size and population
density
James Brown, University of New Mexico
Distribution and population size of a species
reflects the distribution of conditions to which
individuals of the species were well adapted.
If these conditions are common and widespread,
then the population should be common and widespread.
Range size and population density
Birds with large ranges tend to have higher maximum abundances
(457 species of North American birds) (McGill and Collins, 2003)
Body size, distribution, and abundance
Population density to body size, a matter of size relative to space
Sample of herbivorous mammals, slope is -0.73. (Gaston and
Blackburn 2000)
One example: Population density in carnivores is closely
related to their body size
The density of
population
decreases as the
-2/3 power of
body mass of
predator.
(Carbone and
Gittleman 2002)
Energy Equivalent Rule
Concept: Populations tend to consume the same amount of food
per unit of area regardless of the size of individuals
Metabolic rate of organisms and therefore, their food
requirements, increase with body mass, to a power of 3/4.
Since the population density decreases with the body mass at
the same rate that food requirement increases.
The total food consumption of a population per unit of area is
equal to the average consumption per individual multiplied by
the local population density (M3/4 * M-3/4=1).
Therefore, elephants and mice would have about the same food
requirement per hectare, and by implication, they would have
similar effects on population and ecosystem processes.
10.8 Variation in populations
over space and time
Distribution of crop damage caused by
chinch bugs in Illinois varied dramatically
over the period between 1840 and 1939.
Yellow: low density of chinch bugs
Blue: high density
Reasons: climate change, resources,
predators and pathogens?
Population density change over time and
space
The END
Tiger Beetle of Cold Climates
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Recap
Populations are limited to ecologically suitable
habitats
Distribution
Factors (niche)
Spatial patterns
Ecological niche modeling predicts the
distributions of species
Ecological niche model