Ecology
Distribution & Occurrence
• Dispersal
• Behavior
• Biotic
– Competition
• Resource partitioning/niche differentiation
– facilitation
• Abiotic
– Tolerance/requirements
Factors Influencing Distribution and Occurrence of organisms
Expansion of cattle egret after arrival
to western hemisphere
Limiting Resources
Tolerance Range
minimum
Found in this range
• Intolerant (too little)
• required amount not present
• org. cannot survive
low
maximum
• Intolerant (too much)
• org. cannot survive
Environmental gradient
high
• Tolerance range is the range of a physical condition that the
organisms can survive in (between the minimum and maximum)
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Minimum = smallest amount the organism needs or can cope with
Maximum = largest amount the organism can cope with
Optimum = amount at which the organism does best
Populations can only become established in areas within the tolerance limit
Hibernation & dormancy are ways of avoiding periods of time where environment is
outside the tolerance limit
Tolerance range:
application of limiting resource
Limit due to requirement/tolerance
Limit due to tolerance
Tolerance range
for “grass”
too dry
too wet
water
wet
dry
Ecological Niche
• The totality of an organisms adaptations, its
use of resources, and the lifestyle to which it is
fitted
– Physical, chemical, biological factors needed to
survive
– Behavior
– Trophic level
– adaptations
– Habitat
– Abiotic components of the environment
A variety of definitions of “niche” just to show you it is an easy idea that is hard to create a good definition for
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How an organism survives and reproduces in an environment
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The place or function of a given organism within its ecosystem. Note : Different organisms may compete for
the same niche.
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For example, in a forest there may be a niche for an organism that can fly and eat nectar from blossoms.
niche is the sum of the habitat requirements and behaviors that allow a species to persist and produce
offspring
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How it does stuff and what resources it uses
habitat and behavior
The niche of an organism is its place in the biotic environment, its relations to food and enemies.
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Foraging/what it eats
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The environmental conditions and resources that define the requirements of an individual or a species to
survive and reproduce
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a niche is a term describing the relational position of a species or population in an ecosystem
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the role and position a species has in its environment; how it meets its needs for food and shelter, how it
survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic
factors of its environment.
Competition
• Interaction among organisms that vie for the
same resource in an ecosystem
• Intraspecific
– Competition between individuals in a population
• Interspecific
– Competition between individuals in 2 different
species
Interspecific Competition:
competition harms both organisms/species
Competitive Exclusion
• Two species cannot coexist permanently in the
same place if they compete for the same
resource (at the same time, in the same way)
– two species cannot coexist if they have the same
niche
• Over time, two competing species can either:
1. coexist, through niche differentiation (or other means)
2. compete until one species becomes locally
extinct.
Fundamental (Ecological) v. Realized Niche
• Green Anole (native to FL) and Brown Anole (introduced from Cuba)
Marshes and
tree canopies
Ghost of competition past
• The niche differentiation seen in the present is
the result of past competition.
• Past competition has resulted in:
– Similar species diverging (through selection) so
they do not directly compete (have different
niches)
– The extinction of poor competitors whose niches
overlapped with the existing organisms (who
outcompeted them).
Combined influence on distribution
• The range and distribution of species is due to
a combination of tolerance, competitive
exclusion, and dispersal ability/opportunity
Tolerance range/limiting factor + Competition
a simple schematic
Limit due to tolerance
Limit due to competition =
competitive exclusion
too dry
Tolerance range for
“grass”
Bush is better
competitor in this
area; excludes grass
water
wet
dry
Common Factors Determining Distribution
(i.e., where things are found)
Found in this range
• Intolerant (too much)
• Predation
• Out competed
• Intolerant (too little)
• Predation
• Out competed
Also dispersal: is the organism or its offspring able to get to an area. If the organism is incapable of reaching
an area (or has not yet reached an area) then it won’t be found there.
barrier to dispersal (no lizards here)
• Intolerant (too little)
• Predation
• Out competed
• disease/parasite
• Intolerant (too much)
• Predation
• Out competed
•Disease/parasites
The brownbarnacle competitively excludes the gray barnacle from the lower area
even though the gray barnacle could tolerate that area
Tolerance
ranges
Area
found
Character displacement
• Morphological divergence in sympatric populations of similar
species
• Evidence of niche differentiation that can be seen in present.
More character displacement
Stickle-back fish in lakes
Community Diversity, Disturbance, & Succession
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Diversity
Community Structure
Organismal Concept & Climax Communities
Individualistic Continuum
Non-equilibrium & intermediate disturbance
hypothesis
• Succession
Diversity = richness + relative abundance
Models of community composition
• EQUILIBRIUM=STABILITY=reach and maintain a
constant, stable species composition
• ORGANISMAL (interactive) CONCEPT
– Species co-exist because they have positive and necessary
interactions
• INDIVIDUALLISTIC CONTINUUM CONCEPT
– Associations due to similarity in tolerance and requirements
Intermediate disturbance hypothesis
• Wayne Sousa (1979) studied the effects of disturbance on the diversity of
marine algae and invertebrates growing on boulders in the intertidal zone.
• Small boulders high disturbance
• Large boulder  low disturbance
Succession
• change in species structure of community over
time
• one assemblage of species is gradually
replaced by another assemblage
– Each assemblage=sere
• Facilitation plays a role
Primary succession = bare mineral
(new substrate)
Secondary Succession = existing soil and community disturbed
• An example of Secondary Succession by stages:
1. A stable deciduous forest community
2. A disturbance, such as a wild fire, destroys the forest
3. The fire burns the forest to the ground
4. The fire leaves behind empty, but not destroyed, soil
5. Grasses and other herbaceous plants grow back first
6. Small bushes and trees begin to colonize the area
7. Fast growing evergreen trees develop to their fullest,
while shade-tolerant trees develop in the understory
8. The short-lived and shade intolerant evergreen trees
die as the larger deciduous trees overtop them. The
ecosystem is now back to a similar state to where it
began.
Secondary Succession of
an abandoned farm field in
North Carolina