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Ecology and People (BIOL 120)
Ecology an
Introduction
Critical Factors and Tolerance Limits
Lecture 3
!Von Liebig proposed the single factor in
shortest supply relative to demand is the
critical determinant in species distribution.
Today’s Outline
Critical Factors and
Tolerance Limits
Adaptation
Natural Selection = Evolution
Speciation
Ecological Niche
Species Interactions
Succession
Introduced Species and
Community Change
"Shelford later expanded by stating each
environmental factor has both minimum and
maximum levels, tolerance limits, beyond which
a particular species cannot survive.
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Critical Factors and Tolerance Limits
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Adaptation
! Interacting factors often determines
biogeographical distribution.
!For some organisms, there may be a
specific critical factor that mostly
determines abundance and distribution.
!Adapt is used in two ways:
"Range of physiological modifications available
to individual organisms.
"Inheritance of specific genetic traits allowing a
species to live in a particular environment.
!Explained by process of evolution.
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Natural Selection
Speciation
!Influences:
!Natural Selection - Members of a
population best suited for a particular set
of environmental conditions survive and
reproduce more successfully than
competitors.
"geographical isolation
"selective pressure
"Alternatively, isolation of population subsets,
preventing genetic exchange, can result in
branching off of new species that coexist with
the parental line.
"Acts on pre-existing genetic diversity.
"Limited resources place selective pressures on
a population.
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Evolution
Ecological Niche
Definition: The scientific theory that
explains how random changes in
genetic material and competition for
scarce resources cause species to
change over time.
!Divergent Evolution
! Habitat
" Place or set of environmental conditions where a
particular organism lives.
! Ecological Niche
" The total set of environmental factors that determines
species distribution.
! Fundamental Niche
!Look different - Act different
" Full range of resources or habitat a species could exploit
if there were no competition with other species.
!Convergent Evolution
! Realized Niche
!Look alike - Act alike…
but aren’t alike
" Resources or habitat a species actually uses.
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Resource Partitioning
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Species Interactions
!Law of Competitive
Exclusion
!A predator is an organism that feeds
directly upon another living organism,
whether or not it kills the prey in doing so.
!One will either migrate,
become extinct, or
partition the resource
and utilize a sub-set of
the same resource.
"Prey most successfully on slowest, weakest,
least fit members of target population.
!Reduce competition, population overgrowth, and
stimulate natural selection.
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Keystone Species
Competition
!Keystone Species
!Interspecific
!Intraspecific
"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.
"Often intense due to same space and nutritional
requirements.
!Territoriality - Organisms defend specific area
containing resources, primarily against members of
own species
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Symbiosis
Defensive Mechanisms
!Symbiosis - Intimate living together of
members of two or more species.
"Batesian Mimicry - Harmless species evolve
characteristics that mimic unpalatable or
poisonous species.
"Mullerian Mimicry - Two unpalatable species
evolve to look alike.
"Commensalism - One member benefits while
other is neither benefited nor harmed.
!(_+)
"Mutualism - Both members benefit.
!(++)
"Parasitism - One member benefits at the expense
of other.
!(-+)
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Abundance and Diversity
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Communities in Transition
!Ecological Succession
!Abundance
"Primary Succession
"Total number of organisms in a community.
!A community begins to develop on a site previously
unoccupied by living organisms.
!Diversity
"Secondary Succession
"Number of different species, ecological
niches, or genetic variation.
!An existing community is disrupted and a new one
subsequently develops at the site.
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Introduced Species and Community
Change
Ecological Succession
!If introduced species compete more
successfully than native populations, the
nature of the community may be altered!
! Ecological Development - Process of
environmental modification (facilitation) by
organisms.
! Climax Community - Community that develops
and seemingly resists further change.
"Human history littered with examples of
problematic introduced species.
" Equilibrium Communities (Disclimax Communities) Never reach stable climax because they are adapted to
periodic disruption.
!Can you think of examples?
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