PBIO 100 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 37 - BIODIVERSITY & SPECIES EXTINCTION
REQUIRED
READING
I. Biodiversity
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Definition: [REQUIRED
READING] The variety and variability of life-forms, both contemporary and
extinct, including genetic and ecosystem diversity, in a defined area at
and over time.
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Global
patterns [REQUIRED READING]
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Approximately 90 phyla of extant
organisms
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Most have few species and are marine
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Plants
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Bryophyta (bryophytes, mosses & hornworts): 24000 sp
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Polypodiophyta (ferns): 8500 sp
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Lycopodiophyta (club mosses): 1225 sp.
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Equisetophyta (horsetails): 29 sp.
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Psilotophyta (whisk ferns): 4 sp.
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Cycadophyta (cycads): 105 sp.
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Pinophyta (conifers): 600 sp.
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Ginkgoophyta (ginkgo): 1 sp.
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Gnetophyta (gnetops): 70 sp.
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Magnoliophyta (flowering plants): 245000 sp.
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Plant and animal diversity is critical to habitat preservation
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Concepts of
biodiversity
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Hypotheses:
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"Rivet popper": Each species is important in its own small way, lose one
(like a rivet in a plane) and little happens but the ecosystem weakens. Lose
several species and at some point the whole system fails.
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"Redundancy": Most species are superfluous as only a few are critical to
the survival of the ecosystem. Species are like passengers on the plane,
even with only a few, the plane can still fly
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Evidence
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Crop production increases with diversity, e.g., greater production of corn
if other plants are intercropped than increasing the number of corn plants
per acre
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Increased ecosystem resilience to stress with increase species diversity
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Full productivity can be reached by a few select species in terms of biomass
but most ecosystems have far more species than necessary, thus random loss
will not cause system collapse
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Levels of diversity
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Rates of
speciation [See also examples of
recent
speciation]
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Rapid speciation occurs in
tropical and arid (especially
desert)
regions; less so in temperate regions
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Rate of speciation low in aquatic habitat yet individual species tend to
survive for much longer periods of time; rates much higher in areas of
environmental stress (desert)
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Individual species survive for long periods of geological time in tropical
regions where more species per unit area can exist and where even marginally
successful species can survive a library filled with numerous books, even
those with numerous error
-
Individual species do not survive for long periods of time in areas of
environmental stress a library of only a few books, all essentially in perfect
condition
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Species diversity
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About 2800 species of vascular plants (ferns, fern allies, gymnosperms and
flowering plants) in Alaska; about the same number in Maryland
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About 5000 species in eastern United States; about 4800 species in Nevada
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About 22000 species in North America north of Mexico; about 25000 species
in Costa Rica
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Threats to diversity
- an essay by E.O. Wilson
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Humans: Current major cause of species loss and habitat degradation
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Human-caused habitat destruction is often wanton and thorough; widespread
and often concentrated
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Native species often lost and habit invaded by exotic weeds
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Alien plants tend to be short-lived and aggressively weedy
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Non-random, naturally occurring species losses
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Selective and random; infrequent and widely scattered
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Native species reduced in numbers but not locally extirpated; habitat locally
disrupted but not thoroughly destroyed
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Re-colonization is by native species even if area initially invaded by alien
species
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Different habitats have different kinds of threat and different causes of
those threats
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Coastal ecosystems
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Marine
ecosystems
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Significance
of biodiversity {REQUIRED READING]
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Long the study of biologists
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Public now aware that as a global resource, biodiversity is the underpinning
of the healthy functioning of the earth's many ecosystems
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Persons involved with decision-making affecting the environment require knowledge
of the origin and extent of biodiversity, and how it might be maintained
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Without a biologically viable world, humans will not exist
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Biodiversity provides an array of services that maintain life on earth
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Biodiversity provides humans with substantial economic benefits
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1) crops
2) domestic animals
3) medicines
4) natural products: wildlife, fish, timber
5) some 10000 species of plants and animals are exploited industrially
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Biodiversity provides humans with esthetic benefits
II. What is known about the biota?
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Far more organisms to discover than have been found and studied scientifically
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The number of plants thought to exist now is about 350,000 of which only
some 256,000 have be described
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Of the estimated 30 million animals, only some 1.1 million are known
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Mere discovery is not enough
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Described and classified
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Role in the environment evaluated
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Potential value
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Conservation critical to maintaining currently available biodiversity
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Critical habitat: The area required to maintain not only one species but
the suite of species that make up the population structure in which the species
is found
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Germplasm preservation: Natural populations of species critical to human
survival must be preserved with their population structure to provide future
germplasm for human survival in a changing environment
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Conservation is successful only when large areas are maintained
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Future of the biota
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Responsibility of all people
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Effective only at national and international level; impetus for action at
local level.
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People make decisions to destroy the environment; people can also make the
decision not to abuse the environment
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Maryland Natural Heritage
Program: What is being done here? Check out the
teaching program
in California
III. Extinction
![](6617a.jpeg)
The small franklinia tree (Franklinia alatamaha), named for Benjamin
Franklin in 1785,
is known today only from garden specimens, being last seen in the wild in
1803
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Definitions:
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Extinction: The loss of a species from the biota; the failure of a taxonomic
group to produce direct descendants, causing its worldwide disappearance
from the record at a given point.
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Extirpation: The loss of a species from a significant portion of its range
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Endemic: A species restricted to a defined geographic area
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Extinction as a natural process
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Each species has a finite lifetime probably 99% of all organisms that have
existed are now extinct
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Most species exist 2-5 million years
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Extinction can result in an available ecological niche (where an organism
lives and its behavior in that place) to be occupied by other species
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Kinds of extinction
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Background extinction: The continuous, low-level rate of extinction
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Mass extinction: A large loss of species in a brief geological period of
time
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Cretaceous
extinction when the
dinosaurs
disappeared some 65 million years ago (mya) -- see
this site and
especially the
pictures
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Numerous major extinctions have occurred (5 or 6) each resulting in a fundamental
change of the biota (e.g., rise of flowering plants at the end of the Jurassic
some 130 mya)
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Significant extinctions occur about every 26 million years
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Causes of mass extinction
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Climate: Changes in the climate always results in changes in the biota; sudden
(in geologic time) and profound changes nearly always result in mass extinction
events. Gradual changes usually result in a displacement of the biota but
not necessarily mass extinction
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Pleistocene
glaciation [good but slow to load!] (over the last 2.5 my) resulted in
significant extinction of grazing animals in North America and Eurasia, but
not in Africa and portions of South America
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Eastern deciduous forests pushed into eastern Mexico so that most of the
flora survived; montane forests in southern California and Arizona were
extirpated during the Holocene (last 10,000 y) as the climate warmed after
the glacial era
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Geologic events: Dramatic flooding, extensive volcanic activity, major tetonic
shifts (e.g., continental drift, widespread volcanic eruptions), etc. can
all resulted in global or near-global extinction events
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Increases or decrease in sea levels
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Volcanic
and fire-induced high altitude air pollution
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Continental
drift and
island
formation
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Meteorite: Impact of large or numerous meteorites. [See
When the Sky Fell by Philippe Claeys, a thorough summary]
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Meteorite: Impact with earth can cause increase in dust at high elevations
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End of Cretaceous probably caused by meteorite hitting the earth near Yucatan;
iridium layer found at same level all around the earth
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Human:
The single largest cause of extinction presently [REVIEW this paper,
"The Current State of Biodiversity" by E.O. Wilson]
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About 2400 species disappear daily
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About 10000 new species described annually
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Extinction
rate now greater than that at the end of the Cretaceous Period
Other sites of interest
Biodiversity:
An overview: An excellent and thorough review from
Biodiversity Internet
Sites
Biodiversity Conservation Information
System
Biodiversity: The most fundamental issue a speech by Thomas Lovejoy
Natural Heritage Network Central
Server: Biodiversity sites in the New World
The case for saving
species
Why species
are important
Extinctions
past and present
Diversity Special:
By Dr. Veron Heywood - A major summary of global biodiversity efforts
Centre for Plant
Biodiversity: An example of a national biodiversity program
Protecting
biodiversity: from Greenpeace
Greenpeace Biodiversity
Page
Teaching
Biodiversity: A Unit Study for Elementary Teachers
The Stochastic
Extinction Model: Technical but interesting
The
Biophilia Hypothesis: Read the introduction by E.O. Wilson
All about
asteroids
An
excellent review of dinosaurs!
Last revised: 23 Aug 1998 - Reveal