Chapter 4:
Evolution, Biological Communities,
and Species Interactions
Advanced Environmental Science
Section 4.1
EVOLUTION PRODUCES SPECIES DIVERSITY
Summary:
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artificial selection
natural selection
adaptation in ecosystems
speciation
evolution still at work
Artificial Selection
Artificial Selection
Natural Selection
adaptation:
the acquisition of traits that allow a species to
survive in its environment
natural selection:
the process of better-selected individuals
passing their traits on to the next generations
selection pressures:
factors in the environment that favor successful
reproduction of individuals possessing heritable
traits and that reduce viability/fertility of
individuals not possessing those traits
(examples…)
critical factor:
the single factor in shortest supply relative to
demand
tolerance limits:
minimum and maximum levels for each
environmental factor
Adaptation in Ecosystems
habitat vs. niche
competitive exclusion principle:
no two species can occupy the same niche for
long (the more successful will exclude the other)
resource partitioning:
allows several species to utilize the same
resource and coexist
(examples…)
Speciation
speciation:
development of new species
allopatric speciation:
geographic barriers cause reproductive isolation
sympatric speciation:
biological or behavioral barriers cause
reproductive isolation
(once isolation occurs species diverge genetically)
Evolution is still at work…
• Galapagos island finches
• pesticide resistant insects
• drug-resistant pathogens
Section 4.2
SPECIES INTERACTIONS SHAPE
BIOLOGICAL COMMUNITIES
Competition
intraspecific
interspecific
Predation
• Predator-prey relationships exert selection
pressures that favor evolutionary adaptation.
• Predators become more efficient at searching
and feeding, and prey become more effective
at escape and avoidance.
coevolution:
species exert selective pressures on each other
and gradually change as a result
Predator Avoidance
Batesian mimicry:
species that are harmless resemble poisonous or
distasteful ones
Müllerian mimicry:
two unpalatable or dangerous species look alike
Batesian mimicry
Symbiosis
mutualism
Symbiosis
commensalism
Symbiosis
parasitism
keystone species:
a species that plays a critical role in a biological
community that is out of proportion to its
abundance
Section 4.3
COMMUNITY PROPERTIES AFFECT
SPECIES POPULATIONS
primary productivity:
rate of biomass production
abundance:
total number of organisms in a community
diversity:
number of different species, niches, or genetic
variation present in a community
complexity:
the number of species at each trophic level and
the number of trophic levels in a community
Stability and Resiliency in Ecosystems
constancy:
lack of fluctuations in composition or functions
inertia:
resistance to perturbations
renewal:
ability to repair damage after disturbance
edge effects:
changes encountered at the boundary between
two ecosystems
ecotone:
a boundary between two types of biological
community
*interior area is significant*
Section 4.4
COMMUNITIES ARE DYNAMIC AND
CHANGE OVER TIME
Ecological Succession
primary succession:
succession that occurs in an area where no
community existed before
secondary succession:
succession that occurs in an area where the
existing community is disturbed
pioneer species:
the first species to colonize a new area
climax community:
the community that develops last and stays the
longest
• represents the maximum complexity and
stability possible
• depends on climate and soil
disturbance:
any force that disrupts the established patterns
of species diversity and abundance, community
structure or community properties
disturbance-adapted species:
species that depend on disturbances to succeed