Chapter 4: Biological Communities and Species Interactions

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Chapter 4 Biological Communities and Species
Interactions

• Understand the fundamental factors driving
  community development

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I. Who Lives Where and Why?

• A. Critical Factors and Tolerance Limits
• Examples of limiting conditions are temperature,
  moisture levels, nutrient supply, and soil
• Liebigs principle (law) states, the single
  factor in shortest supply relative to demand is
  the critical determinant to species distribution
• Called the principle of limiting factors

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I. Who Lives Where and Why?

• A. (cont)
• Shelford used Liebigs principle to formulate
  that there are maximums and minimums for
  environmental factors (resources)
• Called tolerance limits
• Zones of intolerance are areas of species
  extinctions in that habitat
• The factor closest to the zone of intolerance
  determines where an organism can survive
• Sometimes called Shelfords Law

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I. Who Lives Where and Why?

• A. (cont)
• Some variations of the 2 rules exist
• Could be multiple factors working together to
  limit distribution
• Some organisms have a specific critical factor
• Passenger Pigeons (land), Saguaro Cacti (cold)
• Some limitations may occur during a specific
  portion of the life cycle
• Desert Pupfish (temperature and salinity levels
  for juveniles only)

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I. Who Lives Where and Why?

• A (cont)
• Indicator species are species with defined
  tolerance limits and are used to indicate the
  health of the habitat
• For some, if missing there is a problem
• For some, if present there is a problem
• Environmental indicators are species of organisms
  which can give specific information about a
  habitat
• May indicate specific nutrients present or
  missing
• May indicate pollution

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I. Who Lives Where and Why?

• B. Natural Selection, Adaptation, and Evolution
• 1. General Information
• Organisms adapt to special conditions
• One form of adaptation is acclimation
• Organisms experiences physiological modifications
  or changes
• Non-permanent, reversible
• Another form is genetic, part of evolution
• Will change the population
• Inheritance of specific traits
• Natural selection allows the organism best
  suited for an environment to reproduce

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Darwins Finches
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I. Who Lives Where and Why?

• B. (cont)
• Acts on pre-existing genetic diversity
• Mutations can add to the genetic diversity
• Genes that suit the environment will become the
  dominant trait over time
• Darwins finches is a good example
• Common, general ancestor becoming specialized
  multiple current species
• Also called selective pressure

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I. Who Lives Where and Why?

• B. (cont)
• Factors affecting selective pressure are
• Physiological stress due to inappropriate levels
  of some critical factors
• Predation, parasitism and disease
• Competition
• Luck?
• Geologic isolation can aid in different gene
  expression
• Possibly leading to speciation

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I. Who Lives Where and Why?

• B. (cont)
• Natural Selection and Adaptation can cause
  similar species or 2 groups of the same species
  to drift genetically apart
• Called Divergent Evolution
• Natural Selection and Adaptation can cause 2
  different species to drift genetically together
  (considered the same species)
• They look and act alike
• Called Convergent Evolution

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I. Who Lives Where and Why?

• C. The Ecological Niche
• 1. General Information
• Habitat is the place where an organism lives
• Ecological niche is a description of the role of
  a species in a biological community
• Niches can change as physical characteristics
  change

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I. Who Lives Where and Why?

• C. (cont)
• 2. Law of competitive exclusion
• States that no two species will occupy the same
  niche and compete fro exactly the same resources
  in the same habitat (for a long period of time)
• Creates niche specialization, which creates
  behavioral separation, when two niches overlap

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Paramecium Graph
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Resource partitioning and niche specialization
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I. Who Lives Where and Why?

• C. (cont)
• 2 (cont)
• The number of niches is determined by the
  resources and the extent by which they can be
  separated
• Some animals can share resources, but use them at
  different times
• Ex. Owls and Hawks, Bats and Mockingbirds
• Some animals can use the same resources, but use
  different portions of the same resource
• Ex. Finches, MacArthur's Warblers, Flickers and
  Woodpeckers

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MacArthur's Warblers Splitting the same resource
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Left to right Cape May, Yellow-rumped,
Black-throated Green, Blackburnian, and
Bay-breasted Warblers. Black areas in stylized
conifers show where feeding is concentrated.
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II. Species Interactions and Population Dynamics

• A. Predation
• An organism that feeds directly on another
  organism (living)
• Yes, Herbivores are predators!
• Scavengers, detritovores and decomposers (that
  feed on dead organisms) are NOT predators
• Parasites? , pathogens
• Predation is an influence on population balance
  in a community

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II. Species Interactions and Population Dynamics

• A. (cont.)
• Involves 3 scenerios
• 1. Influences all stages of the life cycle for
  both predators and prey
• 2. influences food obtaining mechanisms
• Influences prey- predator adaptations to resist
  or encourage predation
• As prey species mature, the predators change
• As predators mature, the prey species change
• Tend to be the most successful with the old and
  the young (book says least fit)
• Some prey have created defenses
• Spines, thorns, thicker bark, poisonous chemical
  mimicry, speed, etc

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II. Species Interactions and Population Dynamics

• B. Keystone Species
• A species or group of species whose impact on its
  community is much larger and more influential
  than would be expected from mere abundance
• At one time they were thought to be top predators
• May be a species that has a significant impact on
  other organisms
• Ex tropical figs, sea otters, prairie dogs

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Keystone Species Prairie Dogs
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Keystone Species Sea Otters
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Keystone Species American Beaver
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II. Species Interactions and Population Dynamics

• B. (cont.)
• In some conditions microscopic organisms may be
  the keystone species
• Ex mycorrhzae (root fungus)
• C. Competition
• When organisms compete over resources
• 2 types
• Interspecific between organisms of different
  species
• Intraspecific- between organisms of the same
  species

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Interspecific Competition
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Intraspecific Competition Territories
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II. Species Interactions and Population Dynamics

• C. (cont.)
• Interspecific competition is responsible for
  niche specificity
• Physically designed to tolerate conditions,
  acquire foods, and reproduce at a time different
  from competitors
• Animal kingdoms arms race
• Bigger, stronger, faster, and smarter
• Avoids fighting as much as possible
• Where 2 different species that occupy the same
  niche compete in a habitat, one species will out
  compete the other

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II. Species Interactions and Population Dynamics

• C. (cont)
• Described as the Lotka-Volterra Competition Model
• Mathematical equations to predict which species
  will out compete the other
• Depends on 2 factors
• 1. The number of individuals of species 2
  present and (2) the intensity of the
  interference with species 1s growth or the
  intensity of the competition of species 2 on
  species 1
• It will be a negative factor

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Lotka-Volterra Competition Model
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II. Species Interactions and Population Dynamics

• C. (cont.)
• Intraspecific competition is more intense
• Battling with organisms with the exact same set
  of needs
• Plants have to battle with mature adults
• Adaptive tendencies lead to greater dispersal of
  seeds
• Territories are a direct result of intraspecific
  competition

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II. Species Interactions and Population Dynamics

• C. (cont.)
• Battle for an area with all of the needs of the
  organism at all stages of the life cycle
• Those animals without all either dont reproduce
  or dont reproduce successfully
• D. Symbiosis
• Interactions between species
• Not always antagonistic
• Intimate living together of members of two or
  more species

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II. Species Interactions and Population Dynamics

• D. (cont.)
• 4 types of symbiosis
• Commensalism- one benefits while another has no
  apparent effect
• Mutualism- both organisms benefit
• Predator/Prey- one benefits while the other dies
• Parasitism- one benefits the other has no effect
  or bad effect

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II. Species Interactions and Population Dynamics

• E. Defensive Mechanisms
• Toxic chemicals, body armor, similar coloration,
  and others to defend against predation
• Poison ivy, thorns
• Batesian mimicry
• Mullerian mimicry, 2 different species
  unpalatable and dangerous looking very similar

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III. Community Properties

• General Information
• Try to understand the factors which make up the
  properties involving communities
• Productivity, diversity, complexity, resilience,
  stability, and structure
• A. Productivity
• Photosynthetic rates are regulated by light
  levels, temperature, moisture, and nutrient
  availability.

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III. Community Properties

• A. (cont.)
• Corn and sugar cane under ideal conditions, in
  the tropics can approach productivity as high as
  the rain forest
• A very small amount of available sunlight is
  captured by photosynthetic communities
• B. Abundance and Diversity
• Abundance is the total number of organisms of a
  species in an area

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III. Community Properties

• B. (cont.)
• Diversity is the number of different species in
  an area
• Abundance and diversity are inversely related
• High abundance means low diversity
• High diversity means low abundance
• Diversity decreases away from the equator and
  toward the poles

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III. Community Properties

• B. (cont.)
• Abundance increases away from the equator and
  toward the poles
• Diversities decreases moving upward in attitude
• C. Complexity and Connectedness
• Complexity is the number of species at each
  trophic level and the number of trophic levels in
  a community

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III. Community Properties

• C. (cont.)
• A diverse community may not be a complex
  community
• Tropical rainforests have many trophic levels
  that are compartmentalized
• Called guilds
• Species that occupy the same trophic level
• Fruit enters, leaf nibbles, seed gnawers, etc

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III. Community Properties

• D. Resilience and Stability
• 3 Types
• 1. constancy, lacks fluctuations in composition
  and function
• 2. inertia, which indicates resistance to
  perturbations
• 3. renewal, which is the ability to repair damage
  after disturbances

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III. Community Properties

• D. (cont)
• MacArthur believed the more complex a community
  the more stable and resilient the community will
  be when disturbed (studies show no real
  consistency with this conclusion)
• Disturbances are based on the organism
• Ex. Earthquakes, flooding, traveling, spitting,
  etc.

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III. Community Properties

• E. Edges and Boundaries
• Areas between 2 adjacent and different
  communities
• Edge effect is the relationship of communities
  and the organisms that inhabit the edge of the 2
  communities or habitats
• Considered secondary habitats
• Some boundaries are sharp and distinct, called
  edges

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III. Community Properties

• E. (cont)
• When the 2 habitats or communities blend
  together, it is called a boundary
• Edges and boundaries are also called Ecotones
• Sharp divisions are called closed communities
• Boundary divisions where many species cross are
  called open communities
• Adjacent communities may be important for species
  that need both types during different stages of
  development in the life cycle

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IV. Communities in Transition

• A. Ecological Succession
• Transition of communities in an area over time
• 2 types
• Primary Succession development starts with a
  site that is newly broken rock or an area
  unoccupied previously by organisms
• Starts with pioneer species, such as lichens and
  bacteria

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IV. Communities in Transition

• A. (cont)
• Secondary Succession an existing community is
  disrupted and a new, previous, community
  redevelops in the habitat or community
• Caused by wildfires, or farmland restoration
• Starts with weeds or grasses, when dealing with a
  fire (depends on the severity of the fire)
• Starts with grasses and shrubs when dealing with
  overgrown farmland

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IV. Communities in Transition

• A. (cont)
• Typical primary succession
• Rocks, lichens, weeds, grasses, shrubs, conifers,
  deciduous trees (TDF)
• Typical secondary succession
• Climax community, fire, weeds, grasses, shrubs,
  coniferous trees, deciduous trees
• May be much faster and may skip some steps,
  depending on what community surrounds the fire
  area and what plants are ready to spread seeds
  into the open area

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IV. Communities in Transition

• B. Introduced Species and Community Change
• Introduced species are non-native species
• They can replace existing organisms or (by out
  competing them for the same resources) or
• They can wipe out an unintended species
• Ex. Mongooses in Hawaii