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Unit 4
Chapters 4 and 5
The American Alligator-
ecological niche- species way of life in a
community
• What job does it do or role does it fulfill?
• The Alligator is a:
• Keystone species- A species in an ecosystem that plays a
central role in the health of that ecosystem, and whose removal
may cause the collapse of the ecosystem
Biodiversity or Biological diversity
• The variety of the Earth’s species, the genes they
contain, the ecosystems in which they live, and the
ecosystem processes such as energy flow and nutrient
cycling that sustain all life
• Interaction between speciation and extinction
Why is biodiversity important?
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Food
Wood
Fibers
Energy
Medicines
Preserving air, water, and fertile soil
Natural selection- independently proposed
by:
• Charles Darwin
• Alfred Wallace
Observations that led to concept of evolution
• Organisms struggle
• Some individuals have advantages that help them
survive
• The ones that survive, pass these traits down to
offspring
• Natural selection
• A change in the genetic characteristics of a population
from one generation to another is biological evolution
Genetic variability is the first step
• Occur through mutations
• Only mutations in reproductive cells are passed down
• Mutagens are external agents that cause mutations, but
mutations can occur randomly( examples: chemicals, UV
light, radioactivity, Xrays)
• Adaptation or adaptive trait- any heritable trait that
enables an individual to survive
• In order for natural selection to occur, a trait must be
heritable, meaning that it can be passed down from one
generation to another. The trait must also lead to
differential reproduction.
Summary of biological evolution
• Genes mutate, individuals are
selected, and populations
evolve that are better adapted
to survive and reproduce
under existing environmental
conditions.
Possible futures
• Adapt
• Migrate
• Become extinct
Adaptations of humans that have made
them successful
• Strong opposable thumbs
• Walk upright
• Complex brain
Limits to natural selection
• Adaptations only occur for traits already
present in a populations gene pool.
• Even if a beneficial heritable trait is
present in a population, the population's
ability to adapt may be limited by
reproductive capacity
Common myths
• Survival of the fittest- does not mean survival of the
strongest- ****** fitness is a matter of reproductive
success*****
• Organisms do not develop traits because they need or
want them
• Grand plan of nature
Effects of plate tectonics
• 1. Locations of continents influences
climate which helps determine where
plants and animals can live
• 2. The movement of continents has
allowed species to move, adapt and form
new species through natural selection
speciation
• Geographic isolation
• Reproductive isolation
Extinction is forever
• Golden toad- endemic to costa rica
• Extinction due to climate change
Background and mass extinction
• Background rate of extinction- normal low rate of
extinction throughout history- 1 to 5 species per million
species
• Mass extinction- loss of many species in a short amount
of time
• 25%-70%
• 5 mass extinctions have occurred in the last 500 million
years.
Species richness- number of different
species
Species evenness- abundance of individuals
of each species
Geographical location
• Terrestrial- higher diversity in tropics
• Most diversity in rainforest, coral reefs, the ocean bottom
zone and large tropical lakes
• Species rich ecosystems are more productive and stable
due to higher numbers of different producers with more
feeding relationships
Each species has a distinct role to play in in
an ecosystem
• ecological niche- species way of life in a community
Generalist vs. Specialist species
• A generalist species has a broad niche(live
in many places, eat a variety of food,
tolerate a wide range of conditions)(Ex.
Flies, roaches, mice, rats, white-tailed
deer, raccoons, and humans)
• A specialist species has a narrow
niche(one types of habitat, one or few
types of food)(tiger salamanders, giant
pandas)
• Which is better? It depends, When
conditions are stable, generalists are
better off. When conditions are
rapidly changing, specialists do better
Cockroaches: nature’s ultimate survivor
• 3,500 species, eat almost anything, live
almost anywhere, avoid predators, High
reproductive rates, quick genetic
resistance,
Non-native species
• A.K.A.- invasive, alien, exotic
• They can spread rapidly if they do not
have predators and diseases they faced
before, or they may be able to outcompete native species
Biological smoke alarms
• They provide early warnings of damage to a community
or an ecosystem.
factors that can affect frogs and other amphibians at
various points in their life cycles
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Habitat loss and fragmentation
Prolonged drought
Polution
Increases in UV radiation
Parasites
Viral and fungal diseases
Climate change
Overhunting
Natural immigration of, or introduction of nonnative
predators and competitors
Why should we care about amphibians?
• Sensitive biological indicators
• Important ecological roles in biological
communities
• Genetic storehouse of pharmaceutical products
waiting to be discovered.
Keystone species
• Pollination
• Top predator
Foundation species• Examples- elephants, beavers
• What’s the difference between a keystone and a
foundation species?
• Foundation species help to create habitats and
ecosystems
• Keystone species do this and more
Ch 5 notes
• Sea otters generate millions of dollars in tourism.
• Keystone species that helps maintain kelp forests to
maintain biodiversity.
• 5 types of species interactions• Interspecific competition
• Predation
• Parasitism
• Mutualism
• Commensalism
Illustrates the principle of
population control
Competitive exclusion principle
• No two species can occupy exactly the same ecological
niche for very long
• Methods of capturing prey
• Carnivores- pursuit and ambush
• Camouflage
• Chemical warfare
How prey avoid predators
• Speed, developed sense of sight or smell, protective
shells, thick bark, spines, thorns, camouflage, bright
coloring, chemical warfare, warning coloration,
E.O. Wilson
• If it’s small and strikingly beautiful, it’s probably
poisonous.
• If it’s strikingly beautiful and easy to catch, it’s probably
deadly.
Coevolution
• Predators and prey constantly exert intense natural
selection pressures on each other.
Parasitism- one benefits the other is harmed
parasitism
Mutualism- both benefit
mutualism
Commensalism- one benefits, the other is
not helped or harmed
Reducing niche overlap
• Resource partitioning- when
species competing for similar
scarce resources evolve
specialized traits that allow them
to use shared resources at
different times, in different ways,
or in different places.
Population distribution
• Even
• Random
• Clumped
• Clumped is the most common because resources are
often found in patches
Population change
• Population change = (births + immigrations) – (deaths +
emmigration)
• Intrinsic rate of increase- reproduce early in life, have
short generation times, can reproduce many times, and
have many offspring each time
• When a population exceeds carrying capacity, the
population can crash.
• Overshoot occurs because of reproductive lag time.
K- selected and r-selected
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r-selected species have a capacity for a high rate of
population increase, they produce many offspring to try
to overcome huge losses when offspring are young
(they have boom and bust cycles of population growth)
• K-selected- long life spans, reproduce later in life, small
number of offspring, cared for by parents
Genetic factors that play a role in loss of
genetic diversity
• Founder effect- occurs when a few
individuals in a population colonize a new
habitat that is geographically isolated from
other members of the population.
• Demographic bottleneck- when only a few
individuals survive a catastrophe such as
a fire or hurricane
• Genetic drift- random changes in the gene
frequencies in a population that can lead
to unequal reproductive success
• Inbreeding- when individuals in a small
population mate with one another
Density dependent population
controls
• Competition for resources, disease,
predation, parasitism
Density independent
• Floods, fire, hurricanes, pollution,
drought, habitat destruction
Four general patterns of variations in
population size?
• 1. Stable- fluctuates near carrying capacity
• 2. Irruptive- grows to a high peak and then
crash to a more stable lower level
• 3. Cyclic(boom and bust)- populations rise
and fall every so many years
• 4. Irregular- no recurring pattern
Ecological succession
• The gradual change in species composition in a given
area.
• Primary succession- happens where no previous
ecosystem has existed (exposed rock from a receding
glacier)
resilience
• The ability of a living system to be restored after a period
of moderate disturbance
Tipping point
• Ecosystems and global systems have limits to the stresses they
can take. The level beyond which any additional stress will
cause an abrupt and unpredictable change