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5 Evolution and Community Ecology C
HA
PT
ER
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Lesson 5.1 Evolution
Scientists have identified and described over 1.5 million species. Millions more have yet to be discovered.
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Evolution (change over time) and Natural Selection
• Gene: Sequence of DNA that codes for a particular trait
• Gene pool: All the genes present in a pop
• Biological evolution: change in a pop’s gene pool over time
Lesson 5.1 Evolution
A starting population of fish. Genes control
the color and pattern of the fish’s scales.
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Mechanisms of Biological Evolution: Mutation and Migration
Mutation
Lesson 5.1 Evolution
Change in DNA that can
give rise to variation among
indivs
Migration (gene flow)
Movt of individuals into
(immigration) or out of (emigration)
a pop—changes gene pool (gene
flow)
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Mechanisms of Biological Evolution: Genetic Drift and
Natural Selection
Lesson 5.1 Evolution
Genetic Drift Natural Selection
Evolution that occurs by chance Process by which traits useful for survival & reprod are passed on more frequently than those that are not
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Conditions of Natural Selection
Lesson 5.1 Evolution
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(1) Organisms
produce more
offspring than
can survive—
struggle for
existence
(2) Indivs vary in
characteristics, some
of which are heritable.
(3) Indivs vary in
fitness, or reproductive
success. (adaptations
increase org fitness
level) Did You Know? Darwin privately researched natural selection for two decades before publishing On the Origin of Species.
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Artificial Selection
Lesson 5.1 Evolution
• Selection under human direction
• Chosen & bred animals & plants with beneficial
traits.
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Speciation Lesson 5.1 Evolution
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• Process by which
new species are
generated
• Can occur in a
number of different
ways; the most
important way is
called allopatric
speciation
(geographic sep of
pops)
• Has resulted in every
form of life on Earth—
today & in the past
Allopatric Speciation
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Extinction
Lesson 5.1 Evolution
• Disappearance of species
from Earth
• Generally occurs gradually,
1 species at a time, when
envtal conditions change
more rapidly than species
can adapt
• 5 known mass extinction
events, each of which
wiped out a large
proportion of Earth’s
species.
Did You Know? During the Permo-Triassic
extinction 250 million years ago, 70% of all land species and 90% of all marine species went extinct.
Trilobites
Marine arthropods that went extinct at the end of the Permian period.
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Lesson 5.2 Species Interactions
The zebra mussel has completely displaced 20 native mussel species in Lake St. Clair.
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The Niche
Lesson 5.2 Species Interactions
• Describes org’s use of resources & functional role in a
community
• Affected by an organism’s tolerance—its ability to survive &
reproduce under changing environmental conditions
• Often restricted by competition
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Competition • Organisms compete when
they seek the same limited resource.
• In rare cases, one species can entirely exclude another from using resources.
• To reduce competition, species often partition resources, which can lead to character displacement.
Lesson 5.2 Species Interactions
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Predation (+/–)
• Predator hunts, kills, & consumes prey
• Causes cycles in predatory & prey population sizes
• Defensive traits: camouflage, mimicry, & warning coloration have evolved in response to predator-prey interactions.
• Some predator-prey relationships are ex of coevolution, the process by which 2 species evolve in response to changes in each other.
Lesson 5.2 Species Interactions
Did You Know? A single rough-skinned newt contains enough poison to kill 100 people. Unfortunately for the newt, its predator, the common garter snake, has coevolved resistance to the toxin.
Rough-Skinned Newt
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Parasitism and Herbivory (+/–)
Lesson 5.2 Species Interactions
Did You Know? One study of Pacific estuaries suggests that parasites play an important role in keeping these ecosystems healthy by controlling host populations.
Hookworm (a parasite)
• Parasitism: 1 org (the
parasite) relies on
another (the host) for
nourishment or for some
other benefit
• Herbivory: An animal
feeding on a plant
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Mutualism (+/+) and Commensalism (+/0)
Lesson 5.2 Species Interactions
Did You Know? Symbiosis describes a long-lasting and physically close relationship between species in which at least one species benefits.
• Mutualism: a
relationship in which 2 or
more species benefit
• Commensalism: a
relationship in which 1
species benefits while
the other is unaffected Lichen: a symbiotic relationship
between a fungus and a photosynthetic partner, such as an alga
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Lesson 5.3 Ecological Communities
The sun provides the energy for almost all of the ecological communities and species interactions on Earth.
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Primary Producers (Autotrophs) • Capture NRG from
sun/chemicals & store it in the bonds of sugars, making it available to rest of community
• NRG from the sun is captured by plants, algae, or bacteria thru photosynthesis.
• NRG from chemicals captured by some bacteria thru chemosynthesis.
Lesson 5.3 Ecological Communities
Did You Know? Deep-sea vents, far from sunlight, support entire communities of fish, clams, and other sea animals, which depend on energy converted through chemosynthesis.
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Consumers (Heterotrophs) •Rely on other organisms for NRG & nutrients
• Herbivores: plant-eaters
• Carnivores: meat-eaters
• Omnivores: combo-eaters
• Detritivores and decomposers: recycle nutrients w/in the ecosystem by breaking down nonliving organic matter
•Use oxygen to break bonds in sugar & release its NRG thru cellular respiration (primary producers do this, too)
Lesson 5.3 Ecological Communities
California Condor
Did You Know? Scavengers, such as vultures and condors, are just large detritivores.
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Energy in Communities
• Organism’s rank in a feeding hierarchy is its trophic level.
• Primary producers always occupy 1st trophic level of any community.
• In general, only about 10% of the NRG avail at any trophic level is passed to the next; most of the rest is lost to the envt as heat.
Lesson 5.3 Ecological Communities
Pyramid of Energy
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Numbers & Biomass in Communities
• A trophic level’s biomass = mass of living tissue it contains.
• In general, there are more orgs & greater biomass at lower trophic levels than higher ones.
Lesson 5.3 Ecological Communities
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Food Chains
and Webs
• Food chain: Linear series of feeding relationships
• Food web: Shows the overlapping and interconnected food chains present in a community
Lesson 5.3 Ecological Communities
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• Species that have strong and/or wide-reaching effects on a community
• Removal of keystone species can significantly alter the structure of community.
Keystone Species
Lesson 5.3 Ecological Communities
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Lesson 5.4 Community Stability
A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages.
Invasive kudzu
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Ecological Disturbances
Lesson 5.4 Community Stability
• Community in equilibrium is generally stable & balanced, w/ most populations at/or around carrying capacity.
• Disturbances/changes in envt can throw a community into disequilibrium.
• Severe disturbances cause permanent changes to a community & initiate a predictable series of changes = succession.
Forest fire
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Primary Succession
Lesson 5.4 Community Stability
• No traces of the original community remaining, including vegetation and soil
• Pioneer species (lichens):1st to colonize.
• Envt changes as new species move in, adding nutrients & generating habitat.
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Secondary Succession
Lesson 5.4 Community Stability
• Occurs when disturbance dramatically alters a community but does not completely destroy it
• Common after disturbances such as fire, logging, or farming
• Occurs significantly faster than primary succession
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Succession in Water
Lesson 5.4 Community Stability
• Primary aquatic succession occurs when an area fills w/ water for the 1st time.
• Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession.
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Climax Communities
Lesson 5.4 Community Stability
• Ecologists once thought succession leads to stable “climax” communities.
• Today, ecologists see communities as temporary, ever-changing associations of species.
• Communities influenced by many factors & constant disturbances.
Beech-maple forest, a classic “climax community”
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Invasive Species
Lesson 5.4 Community Stability
• Nonnative organisms that spread widely in a community
• A lack of limiting factors such as predators,
parasites, or competitors enables their
population to grow unchecked.
• Not all invasive species are harmful.
Did You Know? Although the European honeybee is
invasive to North America, it is beneficial because it pollinates our agricultural crops.