Download Chapter04 - Duluth High School

Biological Communities
and Species Interaction
Chapter 4
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Outline:
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Critical Environmental Factors
Ecological Niche
Population Dynamics
Community Properties
Succession
Introduced Species
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Critical Environmental Factors
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The nutrient in the shortest supply is the
critical factor or critical determinant
Analogous to limiting reactant in chemistry
 Shelford - each environmental factor has
both minimum and maximum levels,
tolerance limits, beyond which a particular
species cannot survive.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Tolerance Limits
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Critical Environmental Factors
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For many species, the interaction of several
factors, rather than a single limiting factor,
determines biogeographical distribution.
 For some organisms, there may be a
specific critical factor that mostly
determines abundance and distribution.
Environmental indicators are organisms or
physical factors that serve as a gauge for
environmental changes/conditions.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Natural Selection
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Natural Selection - Members of a population
best suited for a particular set of
environmental conditions survive and
produce offspring more successfully than
their competitors.
 Acts on pre-existing genetic diversity.
 Limited resources place selective
pressures on a population.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Ecological Niche
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Habitat - Place or set of environmental
conditions where a particular organism lives.
Ecological Niche - Description of the role a
species plays in a biological community, or
the total set of environmental factors that
determines species distribution.
 Generalists - Broad niche
 Specialists - Narrow niche
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Competition
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Resource Partitioning
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Law of Competitive Exclusion - No two
species will occupy the same niche and
compete for exactly the same resources for
an extended period of time.
 One will either migrate, become extinct, or
partition the resource and utilize a sub-set
of the same resource.
- Given resource can only be partitioned a
finite number of times.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Resource Partitioning
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
POPULATION DYNAMICS
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Predation - A predator is an organism that
feeds directly upon another living organism,
whether or not it kills the prey in doing so.
 Prey most successfully on slowest,
weakest, least fit members of target
population.
- Reduce competition, population
overgrowth, and stimulate natural
selection.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Keystone Species
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Keystone Species - A species or group of
species whose impact on its community or
ecosystem is much larger and more
influential than would be expected from mere
abundance.
 Often, many species are intricately
interconnected so that it is difficult to tell
which is the essential component.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Competition
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Interspecific - Competition between members of different
species
Snake and owl competing for mice
Bears and eagles for salmon
Intraspecific - Competition among members of the same
speices
Bears competing for salmon
Both are in the same community
Often intense due to same space and nutritional
requirements.
- Territoriality - Organisms defend specific area
containing resources, primarily against members of
own species.
 Resource Allocation and Spacing
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Symbiosis
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Symbiosis - Intimate relationship among members of
two or more species.
 Commensalism – relationship in which one
member benefits and the other is neither harmed
nor helped
 Moss on trees
Mutualism –both species benefit
Bird and hippo; bacteria (e. coli) and humans
 Parasitism - One species benefits at the others
expense.
 Humans and ringworm, tapeworm
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Defensive Mechanisms
Batesian Mimicry - Harmless species
evolve characteristics that mimic
unpalatable or poisonous species.
 Coral snake and King snake
 Mullerian Mimicry –both are unpalatable or
poisonous or some other defense
mechanism and they resemble each other.
 Brightly colored frogs are poisonous
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
COMMUNITY PROPERTIES
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Primary Productivity - Rate of biomass
production. Used as an indication of the rate
of solar energy conversion to chemical
energy.
 Net Primary Productivity - Energy left after
respiration.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Abundance and Diversity
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Abundance -Total number of organisms in a
community.
Diversity - Number of different species,
ecological niches, or genetic variation.
 Abundance of a particular species often
inversely related to community diversity.
 As general rule, diversity decreases and
abundance within species increases when
moving from the equator to the poles.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Complexity and Connectedness
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Complexity - Number of species at each
trophic level, and the number of trophic
levels, in a community.
 Diverse community may not be complex if
all species are clustered in a few trophic
levels.
 Highly interconnected community may
have many trophic levels, some of which
can be compartmentalized.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Edges and Boundaries
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Edge Effects –boundary between two
habitats
Ecotones –boundaries between two
communities
Forests/grassland
Sharp boundaries - Closed communities
 Indistinct boundaries - Open communities
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Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
COMMUNITIES IN TRANSITION
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Ecological Succession
 Primary Succession – the ecological
succession that begins in an area where
no biotic community previously existed
- Pioneer Species lichens, mosses
 Secondary Succession –on a site where
an existing community has been disrupted
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Terrestrial Primary Succession
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Ecological Succession
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Ecological Development - Process of
environmental modification (facilitation) by
organisms.
Climax Community - Community that
develops and seemingly resists further
change.
 Equilibrium Communities (Disclimax
Communities) - Never reach stable climax
because they are adapted to periodic
disruption.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Invasive (Introduced) Species
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If introduced species prey upon or compete
more successfully than native populations,
the nature of the community may be altered.
 Human history littered with examples of
introducing exotic species to solve
problems caused by previous
introductions.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Summary:
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Critical Environmental Factors
Ecological Niche
Population Dynamics
Community Properties
Succession
Introduced Species
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.