General Ecology BIOL 3700 – Lecture Notes
Lecture 2
Overview of Lectures 2 & 3:
• Lecture 2. The Biodiversity Crisis
– Extinction and current threats to species
• Lecture 3. The Ecology of Individuals
– Part I. Thermodynamics & the Niche
• The Laws of Thermodynamics and life’s functions
• Variation in metabolic rates
• The niche
– Part II. Physiological Ecology
• Temperature regulation
Lecture 2: The Biodiversity Crisis
Outline
• What is extinction?
• Extinction and the history of life on Earth
– Mass Extinction Events (MEEs)
– Holocene Mass Extinction
• Magnitude of the crisis
• Causes of extinction
• Why are some species naturally more vulnerable to extinction?
What is extinction?
• Definition: The irreversible loss of a species due to the cessation of its existence on
Earth
– Occurs when the last remaining individual dies
• “Functional extinction” – some individuals remain, but chances of sustaining viable
population are effectively zero
• Extinction is a natural phenomenon, but NOT at current rates
Natural extinction: pending case of the Tasmanian Devil
• “Recently, a deadly transmissible cancer has emerged in Tasmanian devils, the
largest existing marsupial carnivore. This disease, devil facial tumor disease (DFTD),
leads to the growth of large facial tumors that frequently metastasize to internal
organs. DFTD is thought to be transmitted by biting, and leads to death of affected
animals within months, usually by obstructing the animals' ability to feed.
Consequently, in the last 10 years Tasmanian devil numbers have dropped by about
60%. There are no genetic tests, vaccines, or treatments available for this disease,
and without intervention, models predict that DFTD could cause extinction of
Tasmanian devils in the wild within 50 years.”
– Science 327:84
We will lose the earth’s largest marsupial carnivore. This is an example of a natural cause…
with no known link to humans.
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General Ecology BIOL 3700 – Lecture Notes
Lecture 2
Mass extinctions have occurred throughout life’s history
We are living during the sixth MEE: the Holocene Mass Extinction (HME)
• Holocene
– Definition: geological epoch ~10,000 years before present (ybp) up til today
• Historical background extinction rate: average rate over 5 MEEs
• HME extinction rates: much greater than background rates
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General Ecology BIOL 3700 – Lecture Notes
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– >100, 1000, up to 10,000X historical rates, by some estimates (e.g. Chanson
2004)
Example of a human-caused Holocene extinction
Raphus cucullatus - Dodo bird, extinct by 1681
An unsolved Holocene extinction: probably multicausal (natural & human causes)
Incilius periglenes - Golden Toad… last seen in Costa Rica, May 1989.
• Hypothesized extinct due to:
– unfavorable El Niño climate patterns
– UV radiation
– fungal infections
– and/or pollution
Magnitude of the crisis
Global amphibian declines: 1 in 3 amphibian species is threatened with extinction
• 1,856 species threatened
• 4 confirmed extinct, 168 suspected extinct already
• Map: Distribution of endangered Neotropical amphibian species
Many mammals, amphibians and plants are threatened with extinction
“It is hardly news that the rich pageant of life, which inspired Darwin and his work,
is now suffering. According to data released this month by the International Union
for Conservation of Nature (IUCN) in its Red List of Threatened Species, one-fifth of
mammals and nearly one-third of amphibians are threatened with extinction, and
the situation is no better among plants: almost one-third of known gymnosperms,
the group that includes conifers, are threatened. Yet despite all the warnings from
scientists and environmentalists, nations have done little more than fret over the
problem.”
– An editorial on biodiversity, Nature 462, Nov. 19, 2009
20% of vertebrates are at risk of extinction in the wild
“Hoffmann et al. … draw on the results of five decades’ worth of data collection,
managed by the International Union for Conservation of Nature Species Survival
Commission. A comprehensive synthesis of the conservation status of the world's
vertebrates, based on an analysis of 25,780 species (approximately half of total
vertebrate diversity), is presented: Approximately 20% of all vertebrate species are
at risk of extinction in the wild, and 11% of threatened birds and 17% of threatened
mammals have moved closer to extinction over time. Despite these trends, overall
declines would have been significantly worse in the absence of conservation
actions.”
– Science 330, Dec. 10, 2010
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General Ecology BIOL 3700 – Lecture Notes
Lecture 2
Almost half of all primate species face extinction
The review, presented today at the 22nd International Primatological Society
Congress in Edinburgh, UK, shows that of the 634 known primate species and
subspecies, nearly 50% are threatened with extinction in the next decade. That
soars to more than 70% in Asia, with individual countries such as Vietnam and
Indonesia seeing at least 80% of their primate species threatened. Cambodia was at
the top of the list, with 90% of its primate species in imminent danger.
“We knew the situation was bad, but these numbers are shocking – particularly in
Southeast Asia,” says Mike Hoffman, a specialist in biodiversity assessment at the
non-profit environmental advocacy group Conservation International.
– Nature, August 2008
Vaquita: endemic to the northern Gulf of California
• Scientists are embarking on a last-ditch effort to help the world's most endangered
marine mammal—Vaquita (~150 left)—avoid the fate of its Chinese cousin, the
Baiji.
• Baiji was a freshwater dolphin found only in the Yangtze River, listed as extinct in
2007, example of “functionally extinct” species.
• Science 321:767, 2008
• [video]
What are the causes of extinction?
Discuss.
[HIPPO Slide]
Rates of habitat destruction in the tropics
HIPPO
• By 1989, tropical rain forests were reduced by half of pre-industrial cover… the area
of a football field was lost every second through the 80’s.
What about the last decade or so? [video]
Invasive species: devastation of Red Lionfish
HIPPO
The Red Lionfish (Pterois volitans), a stunning Indo-Pacific species, is central to an
invasive-species worst-case scenario that is playing out in the Atlantic Ocean.
A study shows that lionfish, with their voracious appetites, can reduce the survival
of young fish on experimental reefs by 80%. Eradicating the lionfish is now all but
impossible in the Bahamas. But conservationists in nearby regions in which lionfish
have been spotted in smaller numbers, such as the Dominican Republic, could take
steps to guard against the interlopers while there is still time.
– Nature 454, July 2008
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General Ecology BIOL 3700 – Lecture Notes
Lecture 2
The Axolotl: linking pollution and extinction
HIPPO
Axolotl… lives only in the polluted marshes and canals around Mexico City. Only 100
individuals per km2, or 16X lower density than in 1980
– Science 322:1456
Ambystoma mexicanum
IUCN 3.1 Critically Endangered species
• Used for neurological and evolutionary research because it can regenerate spinal
cord tissue.
Climate change and extinction
HIPPO
Torreya taxifolia
IUCN 3.1 Critically Endangered species
Torreya expert Mark Schwartz observes, “There are probably fewer than 1000 individuals
and the numbers are dwindling. At last count, there is a single known individual that is
producing seeds in the wild (personal observation). Aside from this one individual and the
approximately 8 seeds it has produced, there has been no observed seedling recruitment
for at least 20, and probably 40 years.”
• Hypothesized factors:
– Pre-reproductive mortality due to fungal pathogens
– Climate change
Over-exploitation
HIPPO
“Tragedy of the commons!” [ you should know this concept ]
Example: Current fisheries crisis
[can you explain this graph]
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General Ecology BIOL 3700 – Lecture Notes
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Over-exploitation
HIPPO
Example: American Bison
– 30-70 million in 1850’s
– nearly extinct by 1900’s
– now 350,000 and no migrations
Are we the “ultimate cause”?
“Human beings… have become a hundred times more numerous than any other land
animal in the history of life. Our species appropriates between 20 and 40 percent of
the Earth’s total resources. There is no way we can draw upon the resources of the
planet to such a degree without drastically reducing the state of most other species.”
• E. O. Wilson, 1992
• The world’s best-known ecologist, Harvard University.
Human demography and extinction
• The richest nations preside over the smallest and less diverse biotas.
• The poorest nations are stewards of the most diverse environments on Earth… the
tropics.
Example: Global amphibian species diversity is richest in tropical regions of the world with
the least resources [maps]
Why are some species naturally more vulnerable to extinction?
First, lets take a short diversion to make sure we are speaking the same language…
Traits
Adaptations
Fitness
What are traits?
• Definition: measurable phenotypic characteristics
• Types:
– Behavioral (e.g. nocturnal, or diurnal habit)
– Physiological (e.g. standard metabolic rate, SMR)
– Morphological (e.g. body size and shape)
– Ecological (e.g. life-history phenotypes)
What are adaptations?
• Definition: any heritable (genetically based) behavioral, morphological, or
physiological trait that affects the fitness of an organism.
• We will discuss many examples.
What is fitness?
• Definition: The ability of an individual to achieve representation in subsequent
generations through the survival of their offspring.
• Discuss.
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General Ecology BIOL 3700 – Lecture Notes
Lecture 2
Why are some species naturally more vulnerable to extinction?
Discuss.
Rarity
• Rarity has 3 components:
• geographic range
• habitat tolerance
• local population size
Small populations (rare taxa) are usually most vulnerable, but why?
Discuss.
Answer:
Three factors other than lower reproductive capacity / resiliency:
1. Reduced genetic variation
2. Demographic stochasticity
a. Fluctuations in population size due to random demographic events. Random
variation in the sequence of births and deaths.
3. Environmental stochasticity
a. Fluctuations in population size due to random environmental events.
Another reason:
Evolutionary/biogeographic isolation: island species are often very rare
[ Can you summarize all the reasons some species are naturally more vulnerable to
extinction than others? ]
The Passenger Pigeon, Ectopistes migratorius
• Distribution: eastern North America
• Most abundant bird species ever
– “biological storm”: 1 flock = 1 billion birds (Audubon: groups of 300 million),
40 miles long
• Over-exploited, hunted “to extinction” for meat
– 1 Michigan hunter shipped 3 million birds to east coast
• Respected by Native Americans,
• Killed mercilessly by colonists
• Went extinct after having >10,000 individuals in the wild
• Last individual died in captivity in Cincinnati Zoo, Sept. 1, 1914
• Reason for extinction unknown
•
Lessons from this species:
– Quick spiral to extinction under a threshold number the species
– It is not necessary to kill the last breeding pair to drive a species to extinction
– Why? Allee Effect
The Allee Effect
• Positive correlation between population size and mean individual fitness
There is no evidence for an Allee Effect in the near extinction of American Bison
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General Ecology BIOL 3700 – Lecture Notes
Example: American Bison
– 30-70 million in 1850’s
The End of the Biodiversity Crisis Lecture
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Lecture 2