Transcript Understanding Our Environment

Biological Communities and Species Interactions
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Why is Earth "just right" for life?
• Distance from sun
• Size
• Rotation
• Orbit around sun
• Atmospheric evolution
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Who lives where and why?
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Interaction of several factors determines
biogeographical distribution.
 determine abundance and distribution
Species requirements and tolerances can also be
used as useful indicators.
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Tolerance Limits
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Adaptation
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Adapt is used in two ways:
 Limited range of physiological modifications
 Inheritance of specific genetic traits allowing a
species to live in a particular environment.
 Evolution
 Microevolution
 Macroevolution
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Evolution & Adaptation
• Microevolution- change in gene
frequency within a population
• Macroevolution- formation of new
species from ancestral species
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Genes mutateindividuals selectedpopulations evolve
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Microevolution
Four processes drive microevolution:
1. Genetic variability
2. Natural selection
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Microevolution
Four processes drive microevolution, cont:
3. Gene flow
4. Genetic drift:
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Natural Selection
Directional selection favors individuals with traits that
are at one end of a distribution
• giraffe example
• "It pays to be different.”
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Natural Selection
Stabilizing selection eliminates individuals at both ends
in the spectrum of variation
• the average remains the same.
• "It pays to be average.”
•Ex. Plant height
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Natural Selection
Disruptive (diversifying) selection eliminates average
individuals, but favors individuals at either extreme of
the spectrum of variation.
"It doesn't pay to be normal.“
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Convergent Evolution
Species from different evolutionary branches may come to
resemble one another if they live in very similar environments
Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
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Coevolution
•
1.
2.
Evolutionary change

Competitive relationships lead to coevolution.
Example:
Cheetah and gazelle
Insects and flowers
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Macroevolution
Speciation-Evolution of a new species-geographical
isolation or selective pressure can create an
entirely new species.
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Speciation
Geographic
isolation can
lead to
reproductive
isolation,
divergence and
speciation.
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Community Relationships
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Habitat
Niche
 Includes:
 range of tolerance for various physical conditions
(temp and water)
 types and amounts of resources it uses
 interactions with abiotic and biotic components
 the role it plays
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Niche
Fundamental niche: theoreticaly use
if there were no competition
Realized niche: actually uses
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Resource Partitioning
•
Law of Competitive Exclusion
 One will either migrate, become extinct, or
partition the resource
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Types of Species
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Generalist
broad niches
 tolerate wide range of environmental variations

•
Specialist
narrow niches
 more likely to become endangered
 do better under consistent environmental conditions

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r and k strategists
The r-strategists
1.
High biotic potential – reproduce very fast
2.
Are adapted to live in a variable climate
3.
Produce many small, quickly maturing offspring = early
reproductive maturity
4.
“Opportunistic” organisms
The K-strategists
1.
Adaptations allow them to maintain population values around
the carrying capacity
2.
They live long lives
3.
Reproduce late
4.
Produce few, large, offspring
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What Different Roles Do Various Species Play in
Ecosystems?
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Native
Nonnative
Indicator species
Keystone species
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Non-native Species
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Nonnative/Exotic/Alien Species
- Examples: Zebra Mussels in the Great Lakes,
Snakehead fish in MD, Mongoose in Hawaii,
Cane Toads in Australia
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Keystone Species


Strong interactions with other species which affect the
health and survival of those species
If a keystone species is removed from a system
- the species it supported will also disappear
- other dependent species will also disappear
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SPECIES INTERACTIONS
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Predator
- Reduce competition, population overgrowth,
and stimulate natural selection.
o Coevolution
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Predator Adaptations
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Prey Adaptations
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Competition
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Interspecific -different species
 Results in: migration, population declines
Intraspecific - same species
 Intense due to direct competition for same
resources
- Territoriality
 Disadvantages?
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Symbiosis
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Symbiosis
 Mutualism - Both members benefit.
- Insects and flowers
 Ex. Yucca plant and moth
Yucca’s only pollinator is the
yucca moth. Hence entirely
dependent on it for dispersal.
Yucca moth caterpillar’s only
food is yucca seeds.
Yucca moth lives in yucca and
receives shelter from plant.
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Mutualism
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Symbiosis Cont…

Commensalism
- Sharks and remora
- Whales and barnacles
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Symbiosis Cont…

Parasitism –
 Humans and Tapeworms
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Ecological Processes
• Ecological Succession
•Primary Succession
•Secondary Succession
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Primary Succession
• Gradual establishment of biotic
communities in an area where no life
existed before
• No preexisting seed bank
•newly formed islands (i.e. volcanic
origin)
•retreat of a glacier
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Primary Succession
Glacier Retreat
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Secondary Succession
• Gradual reestablishment of biotic
communities in an area where one was
previously present.
• Preexisting seed bank
•"old field succession"
•forest fire
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