Transcript Nothing lasts forever. Species, too, become extinct. The

Fig. 14.8a
Horseshoe crab" fossil from the Ordovician Age.
This 450-million-year-old fossil is no different from
specimens living today.
Chapter 13 Extinctions
Nothing lasts forever. Species, too, become extinct.
The paleontologist G. G. Simpson estimated;
since the Cambrian 544 million years ago, more
than 99% are extinct today.
Evolution: speciation vs extinction
Had the dinosaurs not become extinct, mammals
may never have experienced the opportunity to
radiate
Survivors—Lingula
• A marine organism (brachiopod)
occupying vertical burrows in sand
and mud has survived
morphologically unchanged since the
Silurian.
Survivors—Horseshoe crabs
• The horseshoe crab, an inhabitant of marine
shores, has lived morphologically unchanged
since the Ordovician. A horseshoe crab in ventral
(underside) view is shown.
Species come and go
Some taxonomic groups are carried out as part of
large, wide-spread catastrophic or mass
extinctions.
In uniform or background extinctions, members
of taxonomic groups are lost gradually over long
time periods without abrupt loss of large numbers.
Most of the 99% of species now extinct were lost
not suddenly, but slowly,
Fig. 24.24
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Macroevolution is an
evolutionary event the
origin of species and
higher-level taxa.
注定
宿命絕後
六畜興旺
FIGURE 6.5 Morphological
Series
Why species become extinct
Horses arose in North America during the Eocene
and spread eventually to Asia, Africa, and South
America. As the most recent glacial ice sheet
went into retreat 15, 000 years ago, horses
became extinct in North and South America,
but survived in Europe and Asia, and in Africa as
zebras.
Change in habitat, and unfavorable horse perished
Four hundred years ago, the Spanish invaded
North America, bringing with them again.
Coevolution
Dodo bird (extinct)
Koala
• The koala lives in
Australia and feeds
exclusively on the
leaves of eucalyptus
trees whose toxic oils
are harmful to other
herbivores.
Co-evolution
extinction of the island dodo bird in the
seventeenth century endangered the Calvaria
tree.
The koala, an Australian marsupial, feeds
exclusively upon the leaves of eucalyptus trees,
whose toxic oils are harmful to other herbivores.
The koala’s digestive system neutralizes these
toxins.
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Eucalyptus alba
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Eucalyptus amygdalina
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Eucalyptus aromaphloia
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Eucalyptus baileyana
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Eucalyptus balladoniensis
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Eucalyptus bicostata
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Eucalyptus botryoides
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Eucalyptus brachyandra
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Eucalyptus brassiana
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Eucalyptus brevistylis
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Eucalyptus brockwayi
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Eucalyptus camaldulensis (Murray red gum)
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Eucalyptus ceracea
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Eucalyptus cloeziana (Queensland messmate)
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Eucalyptus coccifera
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Eucalyptus cordata
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Eucalyptus cornuta
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Eucalyptus corticosa
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Eucalyptus crebra
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Eucalyptus croajingolensis
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Eucalyptus curtisii
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Eucalyptus dalrympleana
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Eucalyptus deglupta
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Eucalyptus delegatensis
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Eucalyptus delicata
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Eucalyptus diversicolor
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Eucalyptus diversifolia
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Eucalyptus dives
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Eucalyptus dolichocarpa
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Eucalyptus dundasii
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Eucalyptus dunnii
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Eucalyptus elata
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Eucalyptus erythrophloia
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Eucalyptus eudesmoides
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Eucalyptus falcata
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Eucalyptus gamophylla
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Eucalyptus glaucina
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Eucalyptus globulus (blue gum)
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Eucalyptus globulus subsp. bicostata
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Eucalyptus globulus subsp. globulus
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Eucalyptus gongylocarpa
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Eucalyptus globulus subsp. globulus
Eucalyptus
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Eucalyptus
Eucalyptus
Eucalyptus
gongylocarpa
grandis
grandis x Eucalyptus nitens
grandis x Eucalyptus urophylla
guilfoylei
gunnii (cider tree)
haemastoma (scribbly gum)
hallii
houseana
jacksonii
lansdowneana
latisinensis
leucophloia
leucoxylon (white ironbark)
lockyeri
lucasii
maidenii
marginata
megacarpa
melliodora
michaeliana
microcorys (tallowwood)
microtheca
morrisbyi
muelleriana (yellow stringybark)
nitens
nitida
obliqua (messmate stringybark)
obtusiflora
occidentalis
optima
ovata
pachyphylla
pauciflora
pellita
perriniana
petiolaris
pilularis
piperita
platyphylla
polyanthemos
populnea
preissiana (bell-fruited mallee)
pseudoglobulus
pulchella
radiata
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regnans
risdonii
robertsonii
rodwayi
rubida
rubiginosa
saligna
salmonophloia
scoparia
sieberi
spathulata
staeri
stoatei
tenuipes
tenuiramis
tereticornis
tetragona (white-leaved marlock
tetrodonta
tindaliae
torquata
umbra
urophylla
vernicosa
viminalis
wandoo
wetarensis
willisii
Eucalyptus willisii subsp
Eucalyptus willisii subsp
Eucalyptus woodwardii
Species –Area relationships
The larger an island, the more species of plants
and animals the island supports. Conversely, the
smaller the area, the fewer the species.
Species –area relationship
One factor contributing to new species’ appearance
on this island is the immigration rate of new species
arriving on the island from the mainland.
A second factor, acting in opposition to
immigration rate, is the extinction rate.
We would likely find fewer total number of species
than the number present on the mainland.
A basic model of island equilibrium. Immigration
and extinction act in opposite ways, tending to add
or eliminate species, respectively.
FIG. 13.3 Immigration and Extinction on Islands
• (a) Immigration curve. As colonists fill the island,
the rate of arrival of new species drops. (b)
Extinction curve. As colonists fill up the island,
the rate at which species disappear increases.
(After MacArthur and Wilson 1967.)
FIGURE 13.4 Species Equilibrium
Where immigration and extinction curves cross, an equilibrium number of species is
reached. In this example, there are 10 species on the nearby mainland, making it possible
for up to 10 species to be on the island. However, in this example the equilibrium
sustainable by the island is 6.
The equilibrium number depends upon the
actual ecological hospitality and resource
richness of the particular island.
But the general principle will be the same.
Islands will reach an equilibrium number of
species that is below that of the larger mainland
nearby.
(Roderick and Gillespie, 1998)
Suppose we change the location of our island
relative to the mainland. What happens to the
equilibrium
Because it is the same island; so the extinction
curve remains unchanged. However, the
immigration curve adjusts. Located farther from the
mainland, the chance that new species will reach
the distant island decreases overall.
Distance affects the immigration rate.
Now suppose that we keep the island in the
same location relative to the mainland but
change the area of the island. What happens
now? If we make the island larger, the
immigration rate increases because the island
is a larger target,
the extinction rate, declines overall because a
larger island has more space and resources.
The reverse occurs if we make our island
smaller, and extinctions would follow.
Distance and Area Effects on Species Equilibrium
(a) Distance effect. If our island (from figure 13.4) were moved farther
from the mainland, the equilibrium would shift to the left, settling at 2, and
some species would become extinct on the island. (b) Area effect. A large
island reaches a higher equilibrium than a small island.
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It often produces many fragmented and isolated
groups out of the original, single population.
Because isolated groups are smaller,
Island Insights
From the standpoint of a species, alpine
mountaintops, separated bodies of water, or an
isolated tree can be “islands.”
What we have modeled on proper islands is also
applicable to a variety of other situations in nature,
where small parcels of habitat stand apart from
large enclaves of resources elsewhere.
Reducing area reduces the number of species
supported, and extinctions follow.
Red Queen
Leigh Van Valen expected extinctions to be
abrupt, the result of some sudden, unfavorable
change in the environment.
What he found instead was that most groups of
species became extinct gradually, at a constant
rate characteristic of their taxonomic group.
FIGURE 13.6
Phylogeny of a Group
FIGURE 13.7 Evolutionary
protists
deer
Survivorship Curves
ferns
•
horses
(a) Protists: foraminifera. (b) Mammals: artiodactyla—deer, elk, and
related species. (c) Pteridophyta: ferns and related species. (d)
Mammals: perissodactyla—horses and related species. M.Y.: millions
of years passed. (After Van Valen 1973.)
• Red Queen Hypothesis.--The "Red Queen"
hypothesis is used to describe two similar ideas,
which are both based on coevolution.
• The original idea is that coevolution could lead to
situations for which the probability of extinction is
relatively constant over millions of years (Van
Valen 1973).
• The gist of the idea is that, in tightly coevolved
interactions, evolutionary change by one species
(e.g., a prey or host) could lead to extinction of
other species (e.g. a predator or parasite.
• Van Valen named the idea "the Red Queen
hypothesis," because, under this view, species
had to "run" (evolve) in order to stay in the same
place (extant).
地球可以讓我
混 3000 萬年
可以混 200 萬
年就不錯了
Assessment of Uniform Extinctions
Among species of plants, mammals, insects, and
marine invertebrates, the typical survival time of a
species varies--marine invertebrates are the most
resilient, with an average species survival time of
around 30 million years, and mammal species
generally are the least durable, averaging about 2
or 3 million years per species.
Mass Extinctions
Select, at random, ten samples of genera
from a large data set of fossils, then plot the
maximum and minimum numbers becoming
extinct over available intervals of time.
Five common extinction peaks are noted-late in
or at the end of the Ordovician, Devonian,
Permian, Triassic, and Creatceous.
FIGURE 13.8 Extinction Episodes—Random
Sample
• Of more than 19,000 genera, 10 samples of 1,000 genera were
chosen at random and the percentage becoming extinct was
plotted. Major peaks of mass extinction are indicated.
Family in
Tetrapods
Based largely upon families of marine
vertebrates and invertebrates.
The total extinction rate can be determined
from the fossil record calculated as the
number of families becoming extinct per
million-year interval.
Mass extinctions –case studies
The first occurred at the end of Ordovician, with
85% of marine species becoming extinct within
about 10 million years.
The late-Devonian extinction, which lasted less
than 3 million years and took an estimated
83% of marine species.
At the end of the Permian, and saw a loss of
53% of marine invertebrate families.
At the end of the Triassic, lasted 4 million years,
and took many land vertebrates, but up to 80% of
all marine species.
At the end of the Cretaceous, taking all the
dinosaurs, many large marine reptiles, small
foraminifera, and many other marine species,
over a period of about 1 million years.
Several categories of extinction causes have
been proposed: plate tectonics , ice ages,
and cosmic collisions.
Collision zones
Continents and
extinctions
Mingling of species
The isthmus of Panama-the first land
connection between the two continents in more
than 60 million years.
Today, almost half of the medium to large
mammalian species in South America
originated in North America; and about onequarter of those in North America originated in
South America.
自然的
外來者 vs 入侵者
competition
On each of the separated continents, organisms
were accommodated to each other. But with the
sudden, on a geologic time scale, appearance of
new competitors arriving across the land bridge,
the co-evolutionary dynamics were suddeningly
changed. There were new competitors, and
little time to adapt.
Prediction:
We would predict that at moments in Earth history
when isolated continents made first contact, mass
extinctions should occur.
Test cases
1. At the end of the Permian, plate tectonics had
brought all the major continents of the world
together into a supercontinent called Pangaea.
2. At the end of the Cretaceous-the continents
were actually moving apart, separating them.
Trophic stability
The more stable the trophic resources, the
more species; conversely, the more unstable
the trophic resources, the fewer the species.
When continents come together, trophic
resources are unstable, leading to low numbers
of species
When the same landmass is broken up into
separate continents, trophic resources are more
stable and more species.
The reason is that when a large continent breaks
up into separate, smaller continents, the
surrounding ocean has more influence in
moderating the continental climate.
Predictions:
When plate tectonics bring continents together
into one supercontinent, mass extinctions
should occur.
Fragments into separate continents, mass
extinctions should be absent.
Test cases
1. the end of the Permian
2. the end of the Cretaceous fragmenting into
the smaller and more recognizable continents
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Changes in sea level
Sea-level changes may result from the
influence of plate tectonic activity.
If the ocean basins deepen, sea level along the
continental edges drops;
if the ocean basins be come more shallow, sea
level rises.
Glacial activity,
A drop in sea level has three consequences
First, shallow marine habitat is lost.
Second, a drop in sea level indirectly leads to
more severe terrestrial climates of the interior
continent.
Third, the groundwater table drops, indirectly
leading to dry, even drought, conditions within
the interior of the continent.
Drop
100-200
meters
Predictions:
Mass extinctions should correlate with a drop in
sea level. Conversely, a rise in sea level should
not coincide with mass extinctions.
1. at the end of the Permian, the sea level
dropped significantly
2. sea level also dropped at the end of the
Cretaceous, by some estimates by as much as
150 to 200 meters.
Ice ages we are currently, right now, in an ice
age.
One of at least three , during the Phanerozoic.
An ice age is made up of cycles wherein there is a
glacial phase (climate cools, ice sheets form and
spread) and an interglacial phase (climate
temporarily warms, ice sheets retreat).
A “wobbling” of the earth on its axis
plate tectonics that might move continents into
positions where they intercept and disrupt the flow
of warm tropical waters to polar regions.
Reflects more sunlight back into space, and the
climate cooling deepens.
Deep ice cores taken from old galciers in
Greenland and Antarctica give an almost annual
record of climate conditions over the last 252,000
years. Pollen and oxygen isotopes captured in
each annual cycle of the corer bear witness to the
annual flora and temperatures,
oxygen comes in several varieties, called isotopes:
oxygen-18(O18) and oxygen-16 (O16); The ratio
goes up or down with the temperature.
Each layer’s isotope ratios can be used to
calculate the successive climate temperatures,
The current ice age began about 30 to 40 million
years ago,
We are currently enjoying an interglacial phase
that began only about 12,000 years ago,
lasted about 100,000 years and was preceded by
an interglacial period lasting 20,000 years, and so
on back through vacillating cycles over the 30 to
40 million years of the current ice age.
Prediction:
glacial phases accompanied by a drop in average
temperatures, and deterioration of climate,
During interglacial phases, climate recovers and
warms, and galciers retreat. Such dramatic
environmental changes
Ice ages should correlate with mass extinctions.
Test Cases
Only the end of the Ordovician is roughly
correlated with an ice age.
Asteroid collision with the Earth
• This figure depicts events on the young
planet Earth when, still hot from its cosmic
birth, it endured a pummeling by rocky
debris 4 billion years ago. This
bombardment waned but did not cease
entirely. A similar strike by cosmic debris
(asteroid or comet) is thought by some
scientists to have caused the extinction of
dinosaurs 65 million years ago.
Until recently, convincing evidence supported the proposal
that earthly extinctions occurred on a regular schedule,
about every 26 million years.
Iridium spikes, big jumps in iridium concentration, were
documented in rocky formations at the very end of the
Cretaceous.
Mineral formed under high heat and pressure
An impact crater at this same time horizon and about 100
miles (150km)
The object that produced it is estimated to have been
almost 6 miles (10km) wide.
Cosmic collision
• At the end of the Cretaceous, an asteroid
or comet struck the Earth in the location of
present day Yucatan Peninsula in Mexico.
Although such a collision certainly
occurred, it is debated whether or not this
collision was directly responsible for the
dinosaur extinctions.
Critique of Collision Theory
First of all, it is too fast. The scenario of extinctions is
completed within years,
Second, dinosaur numbers were already dwindling several
million years before the asteroid impact occurred.
Third, the catastrophe was too selective.
Amphibians showed no; nor turtles or crocodiles or mammals,
Others have suggested that prolonged volcanism might be
the cause.
Adapting to changes
• As environment changes, the population at
“A” experiences a decline (bell-shaped
curve) through time and becomes extinct.
At “B,” the original population declines to
extinction, but before then a lineage
diverges via speciation to survive.
Applied island biogeography
• Principles of island biogeography applied
to the management of nature reserves
helps make decisions about survival of
organisms living in the reserve. In each
comparison, design A is superior to B.
Origin and extinction
• The rise and fall of various groups of
animals are shown relative to the geologic
time scale. The Permo-Triassic and
Cretaceous extinctions are evident.
Extinction of dinosaurs
• After their demise at the end of the
Cretaceous, dinosaurs were replaced as
dominant land vertebrates by birds and
mammals. [The geologic dates given here
are now revised, but provide a relative
picture of groups.]
After the dinosaurs
• Extinction of the dinosaurs left may
ecological niches empty. In part, the
subsequent flourishing of mammals and
birds represents an adaptive radiation into
many of these vacated life styles.