apes ch. 4, part 2
TRANSCRIPT
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Biodiversity & Evolution, part 2
Miller & Spoolman, 16th ed
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Big Idea #4
◊ Human activities decrease biodiversity
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What is a “species”?
◊ A species is a group of the same type of organism that can breed with each other and produce fertile offspring.
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How do we get new species?
◊ Speciation - the formation of new species
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◊ Most common mode of speciation:◊ Geographic isolation - members of a
population physically separated (due to migration, mountain range, road) - over time they may become separate species
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◊ Geographic isolation may lead to reproductive isolation - the two groups can no longer reproduce or produce fertile offspring
◊ When groups are reproductively isolated, they are different species
◊ Geographic isolation may lead to reproductive isolation - the two groups can no longer reproduce or produce fertile offspring
◊ When groups are reproductively isolated, they are different species
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Reproductive isolation ◊ Takes a long time
• In fastest breeding organisms - 10s - 100s of years
• In slower breeding organisms - 1000s to millions of year
Gestation 660-760 days, 5 years between births Gestation 12-13 days,
births every year
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Extinction is Forever :’(
◊ Extinction - an entire species ceases to exist
http://aso.gov.au/titles/historical/tasmanian-tiger-footage/clip1/
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Who is vulnerable to extinction?◊ Endemic species - found in only one place◊ Resource specialist species - eat a limited
food range or live in only one type of habitat
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Types of extinction
◊ Background extinction - low rate of species extinction that occurs all the time - on average 1-5 species/million/year
Does it really matter?
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◊ Mass extinction = significant rise in extinction rate where large groups of species are wiped out
◊ ~ 250 mya about 95% of all species went extinct (dinosaurs)
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Extinction and biodiversity
◊ When species go extinct, it opens new habitat and resources for other species - possibly leading to the formation of new species
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Quick Think◊ How would you respond to someone
that says that because extinction is a natural process, we should not worry when a species becomes endangered due to human activities?
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Big Idea #5
◊ Biodiversity increases the sustainability to ecosystems
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How do we measure species diversity? ◊ 2 major components:
• Species richness - the number of different types of species
• Species evenness (aka species number) - the relative abundance of each species
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Simple example
◊ High School A has 1000 students• 350 white students• 400 black students• 250 Hispanic
students
◊ High School B has 1000 students• 950 white students• 20 black students• 30 Hispanic students
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More “real” example
◊ Tropical rain forest• 10,000s of different
species, but low numbers of each type
◊ Deciduous forest• Only a few
dozen different species, but high numbers of each one
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Where is it most diverse?◊ It varies with the
geographic location◊ On average, there are
more plants and animals near the equator, and the numbers decline as you move toward the poles (plus ocean bottom)
Most diverse
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◊ Four MOST species rich environments:• Tropical rain forests• Coral reefs• Ocean bottom• Large tropical lakes
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High species richness
◊ Areas that have high species richness also have higher primary productivity and tend to be more stable ecosystems• More plants support more consumers• More consumers and plants means more
connections
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Islands
◊ Theory of island biogeography - the number of species on an island is determined by 2 things: immigration rate and extinction rate
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2 Things about the island affect these rates:◊ 1. Size of the island
• Smaller islands have less species because it is a smaller target out there for colonizers
◊ So lower immigration rate
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◊ Smaller islands also have higher extinction rates• Have fewer resources and less ecosystem
diversity
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◊ 2. Distance from the mainland• Closer to the mainland tends to have
higher immigration rate and thus more species
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This work is important because◊ We create islands
when we develop land◊ Scientists use this
theory to determine how big the island needs to be to maintain biodiversity
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Quick Think◊ If you could design a healthy,
sustainable ecosystem, but you had to choose between high species richness and low evenness, or the opposite, which would you choose and why?
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Big Idea #6
◊ Each species plays an important role in its ecosystem
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Ecological Niche ◊ The role that a species plays in the
ecosystem• It includes everything that affects its
survival and reproduction• Water, sunlight needs• Space requirements• Temperature tolerance• Food, resource needs
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Habitat
◊ Where a species lives◊ (Niche is the WAY it lives)
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2 main types of niches
◊ Generalists - broad niche• Can live in many places• Eats a variety of foods• Can tolerate a range of conditions• Examples: mice, deer, raccoons, humans,
flies
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◊ Specialists - narrow niche• Only live in one type of habitat• Use one or just a few food types• Tolerate a small range of environmental
conditions• Examples: tiger salamanders, Giant
pandas, flamingos, koalas
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Pros and Cons of each type
◊ Generalist -• More competition• More adaptable to
change
◊ Specialist• Little or no
competition• Not adaptable to
change
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5 especially important niches
◊ Native species◊ Nonnative species
◊ Keystone species◊ Indicator species◊ Foundation species
(aka ecosystem engineers)
Muskrat - invasive in CA
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Native species◊ Species that normally live in a given
area• They have evolved along with the other
native species and have intricate connections with them
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Nonnative species
◊ Aka alien, invasive, exotic◊ Accidentally or deliberately introduced
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◊ Not always bad - most crops and livestock are nonnative species
◊ Sometimes they ARE bad - in 1957 Brazil introduced wild African bees (aka “killer bees”) to increase honey bees. These bees out-competed native bees and led to a decrease in honey production
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More on nonnative species
◊ Sometimes - an introduces species just dies out • The new area is not favorable to it
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◊ Sometimes, the nonnative species flourishes, but with no harm to other organisms• Habitat is favorable• Native species peacefully coexist with it
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◊ Sometimes - nonnative species takes over• Often there are no predators for this
species, since it hasn’t evolved alongside them
• This gives the nonnative a competitive advantage
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Indicator Species
◊ Provide ecologists with an early warning system for damage to the ecosystem
◊ They are the canaries in a coal mine
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Examples:◊ Birds - found almost everywhere,
heavily affected by environmental damage, especially chemical pesticides
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Examples◊ Amphibians - breathe partially through
skin, so very sensitive to changes in water quality
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Keystone species
◊ Have a large effect on the number and type of other species in the ecosystem
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Examples:
◊ Top predators - feed on and help regulate the size of of other species
◊ Pollinators - control the size of plant populations
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Effects of losing a keystone species◊ When a keystone species is lost - it
leads to population crashes and extinctions of other species
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Foundation Species◊ Aka ecosystem engineers◊ Play a major role in creating the
ecosystems in which they live
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Examples:◊ Elephants pull out or break small trees
in the African savannah◊ This allows grass to grow and benefits
other grazers and open plains predators
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Examples:
◊ Beavers - build dams to create ponds that other species benefit from
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Quick Think◊ Should we devote more of our budget
to protecting keystone and foundation species, perhaps at the peril of other species? Explain your reasoning.