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Biodiversity
Chapters 5 and 11 and not in exact
order
Striking gold in Costa Rica
• Golden toads were
discovered in 1964, in
Monteverde, Chile
• The mountainous cloud
forest has a perfect
climate for amphibians
• Unfortunately, they
became extinct within
25 years
– Due to global
warming’s drying
effect on the forest
Central Case: Saving the Siberian
tiger
• The largest cat in the world
• The Russian Far East
mountains house the last
remaining tigers
• Nearly became extinct due to
hunting, poaching and habitat
destruction
• International conservation
groups saved the species
from extinction
– Research, education,
zoos, and captive
breeding programs
Evolution: the source of Earth’s
biodiversity
• Biological evolution = genetic change
in populations of organisms across
generations
• May be random or directed by natural
selection
– Natural Selection = the process by
which traits that enhance survival and
reproduction are passed on more
frequently to future generations than
those that do not
New Species arise from old species
• It alters the genetic makeup of a
population
• It is important for understanding antibiotic
and pesticide resistance, agricultural
issues, production, medicines, etc.
• Organisms adapt to their environment
and change over time
Natural selection shapes organisms
•
In 1858, Darwin and Wallace both proposed
natural selection as the mechanism of evolution
– Organisms face a constant struggle to
survive and reproduce
– Organisms tend to produce more offspring
than can survive
– Individuals of a species vary in their
characteristics due to genes and the
environment
– Some individuals are better suited to their
environment and will survive and pass their
genes on in their offspring
Genetic variation
• Adaptive Trait (Adaptation) = a trait that
promotes reproductive success
• Mutations = accidental changes in DNA that
may be passed on to the next generation
– Non-lethal mutations provide the genetic variation
on which natural selection acts
• Sexual reproduction also leads to variation
Natural selection acts on genetic
variation
• Directional selection =
drives a feature in one
direction
• Stabilizing selection =
produces intermediate
traits, preserving the
status quo
• Disruptive selection =
traits diverge in two or
more directions
If the environment changes, a trait may no longer be adaptive
Evidence of natural selection is
everywhere
• It is evident in
every adaptation
of every organism
• Evident in bacteria
and fruit flies in
laboratories
• Selective breeding
of animals
Artificial selection
• Artificial Selection = the process of
selection conducted under human
direction
– For example, artificial selection has led to the
great variety of dog breeds
Evolution generates biodiversity
• Biological Diversity = An area’s sum total of all
organisms
– The diversity of species
– Their genes
– Their populations
– Their communities
• Species = a population or group of populations
whose members share characteristics and can
freely breed with one another and produce fertile
offspring
• Population = a group of individuals of a species
that live in the same area
Speciation produces new types of organisms
• The process of generating
new species
– A single species can
generate multiple
species
• Allopatric speciation =
species formation due to
physical separation of
populations
– Can be separated by
glaciers, rivers,
mountains
– The main mode of
species creation
Another type of speciation
• Sympatric speciation = species form from
populations that become reproductively
isolated within the same area
– Feed in different areas, mate in different seasons
– Hybridization between two species
– Mutations
•
Speciation results in diverse life
formspatterns of diversity
Speciation generates complex
above the species level
• Phylogenetic trees (Cladograms) = Represents the
history of species divergence
– Scientists can trace when certain traits evolved
– Show relationships between species
Extinction
• Species generally evolve from
simple to complex and small to
big, but the opposite can occur,
and some even disappear
• Extinction = the disappearance
of a species from Earth
– Occurs when a species
cannot adapt quickly enough
to a changing environment
– Speciation and extinction
affect species numbers
Extinction is a natural process
• Extinction is irreversible: once a species is
lost, it is lost forever
• Humans profoundly affect rates of
extinction
Some species are more vulnerable to
extinction
• Extinction occurs when the environment changes
too rapidly for natural selection to keep up
• Endemic species = a species only exists in a
certain, specialized area
– Very susceptible to extinction
– These species usually have small populations
• Many other factors also cause extinction
– Severe weather
– New species
– Specialized species
Earth has had several mass
extinctions
• Background extinction rate = extinction
usually occurs one species at a time
• Mass extinction events = five events in
Earth’s history that killed off massive
numbers of species at once
– 50-95% of all species went extinct at one time
• Humans are causing the sixth mass
extinction event
– Resource depletion
– Population growth
– Development
Biodiversity losses and species
extinction
• Extinction = occurs when the last member of a
species dies and the species ceases to exist
• Extirpation (local extinction) = the disappearance
of a particular population from a given area, but not
the entire species globally
– Can lead to extinction
• Mass depletion =occurs when the rate of extinction
is greater than usual background rate
• Commercial extinction =too few to make it worth
catching and sell
Extinction is a natural process
• Paleontologists estimate 99% of all species
that ever lived are now extinct
• Background rate of extinction = natural
extinctions for a variety of reasons
– 1 extinction per 1 to 10 million species for
mammals and marine species
– 1 species out of 1,000 mammal and marine
species would go extinct every 1,000 to 10,000
years
Earth has experienced five mass
extinctions
• In the past 440 million years, mass extinctions have
eliminated at least 50% of all species
• After every mass extinction the biodiversity returned to
or exceeded its original state
The current mass extinction is human
caused
• During this Quaternary period, we may
lose more than half of all species
– Hundreds of human-induced species
extinctions, and multitudes of others, teeter
on the brink of extinction
• The current global extinction rate is 100
to 1,000 times greater than the
background rate
– This rate will increase tenfold in future
decades due to human population growth
and resource consumption
People have hunted species to extinction for
millennia
Extinctions followed human arrival on islands and continents
Current extinction rates are higher
than normal
• The Red List = an updated list of species
facing high risks of extinctions
– 23% of mammal species
– 12% of bird species
– 31 - 86% of all other species
• Since 1970, 58 fish species, 9 bird species,
and 1 mammal species has gone extinct
– In the U.S., in the last 500 years, 236 animal and
17 plant species are confirmed extinct
– Actual numbers are undoubtedly higher
Ecology is studied at several levels
• Ecology and evolution are
tightly intertwined
• Biosphere = the total living
things on Earth and the
areas they inhabit
• Ecosystem = communities
and the nonliving material
and forces they interact
with
• Community = interacting
species that live in the
same area
Levels of ecological organization
• Population ecology = investigates the
quantitative dynamics of how individuals
within a species interact
• Community ecology = focuses on
interactions among species
• Ecosystem ecology = studies living and
nonliving components of systems to reveal
patterns
– Nutrient and energy flows
Organismal ecology: habitat
• Habitat = the environment in which an organism
lives
– Includes living and nonliving elements
– Scale-dependent: from square meters to miles
• Habitat use = each organism thrives in certain
habitats, but not in others
• Habitat selection = the process by which
organisms actively select habitats in which to live
– Availability and quality of habitat are crucial to an
organism’s well-being
– Human developments conflict with this process
Organismal ecology: niche
• Niche = an organism’s use of resources and its
functional role in a community
– Habitat use, food selection, role in energy and
nutrient flow
– Interactions with other individuals
• Specialists = species with narrow niches and
very specific requirements
– Extremely good at what they do, but
vulnerable to change
• Generalists = species with broad niches that
can use a wide array of habitats and resources
– Able to live in many different places
Population
characteristics
• All populations show
characteristics that help
scientists predict their
future dynamics
• Population size = the
number of individual
organisms present at a
given time
– Numbers can
increase, decrease,
cycle or remain the
same
Population characteristics
• Population density = the number of
individuals within a population per unit area
– High densities make it easier to find mates, but
increase competition, and vulnerability to
predation
– Low densities make it harder to find mates, but
individuals enjoy plentiful resources and space
Population characteristics
• Population distribution
(dispersion) = spatial
arrangement of
organisms within an area
– Random – haphazardly
located individuals,
with no pattern
– Uniform – individuals
are evenly spaced due
to territoriality
– Clumped – arranged
according to availability
of resources
• Most common in
nature
Birth and death rates
• Crude birth/death rates
= rates per 1000
individuals
• Survivorship curves =
the likelihood of death
varies with age
– Type I: More deaths at
older ages
– Type II: Equal number
of deaths at all ages
– Type III: More deaths
at young ages
Four factors of population change
• Natality = births within the population
• Mortality = deaths within the population
• Immigration = arrival of individuals from
outside the population
• Emigration = departure of individuals from
the population
• Growth rate formula =
– (Crude birth rate + immigration rate) - (Crude
death rate + emigration rate) = Growth rate
Exponential population growth
• Steady growth rates cause
exponential population
growth
– Something increases by
a fixed percent
– Graphed as a J-shaped
curve
• Exponential growth cannot
be sustained indefinitely
– It occurs in nature with a
small population and
ideal conditions
Limiting factors restrain growth
• Limiting factors = physical,
chemical and biological
characteristics that restrain
population growth
– Water, space, food, predators, and
disease
• Environmental resistance = All
limiting factors taken together
Carrying capacity
• Carrying capacity = the
maximum population
size of a species that its
environment can sustain
– An S-shaped logistic
growth curve
– Limiting factors slow
and stop exponential
growth
• Carrying capacity
changes
Humans have raised their carrying capacity by
decreasing the carrying capacity for other species
Perfect logistic curves aren’t often
found
Population density affects limiting
factors
• Density-dependent factors = limiting factors
whose influence is affected by population
density
– Increased risk of predation and competition for
mates occurs with increased density
• Density-independent factors = limiting
factors whose influence is not affected by
population density
– Events such as floods, fires, and landslides
Biotic potential and reproductive
strategies vary
• Biotic potential = the ability of an organism
to produce offspring
• K-selected species = animals with long
gestation periods and few offspring
– Have a low biotic potential
– Stabilize at or near carrying capacity
– Good competitors
• r-selected species = animals which
reproduce quickly
– Have a high biotic potential
K-selected vs. r-selected species
Population changes affect communities
• As population in one species declines, other
species may appear
• Human development now displaces other
species and threatens biodiversity
– As Monteverde dried out, species from lower,
drier habitats appeared
– But, species from the cloud-forest habitats
disappeared
Challenges to protecting biodiversity
• Social and economic factors affect species
and communities
– Nature is viewed as an obstacle to
development
– Nature is viewed as only a source of resources
– Human population growth pressures
biodiversity
Preserving biodiversity
• Natural parks and protected areas help
preserve biodiversity
– Often, they are underfunded
– Ecotourism brings jobs and money to
developing areas
Biodiversity encompasses several
levels
• Humans are reducing
Earth’s diversity of life
• Biodiversity – sum total of
all organisms in an area
– Split into three specific
levels:
• Species diversity
• Genetic diversity
• Ecosystem diversity
Species diversity
• Species Diversity = the number or
variety of species in the world or in a
particular region
– Richness = the number of species
– Evenness or relative abundance = extent
to which numbers of individuals of different
species are equal or skewed
– Speciation generates new species and
adds to species richness
– Extinction reduces species richness
The taxonomy of species
• Taxonomists = scientists
who classify species
– Physical appearance
and genetics
determines a species
– Genera = related
species are grouped
together
– Families = groups of
genera
• Every species has a twopart scientific name: genus
and species
Subspecies: the level below a species
• Subspecies = populations of species that occur in
different areas and differ slightly from each other
– Divergence stops short of separating the species
– Subspecies are denoted with a third part of the
scientific name
Bengal tiger =
Panthera tigris
tigris
Siberian tiger =
Panthera tigris
altaica
Genetic diversity
• Encompasses the differences in DNA among
individuals within species and populations
• The raw material for adaptation to local
conditions
• Populations with higher genetic diversity can
survive
– They can cope with environmental change
• Populations with low genetic diversity are
vulnerable
– To environmental change
– Disease
– Inbreeding depression = genetically similar
parents mate and produce inferior offspring
Ecosystem diversity
• Ecosystem diversity = the number and
variety of ecosystems
• Also encompasses differing
communities and habitats
• Rapid vegetation change and varying
landscapes within an ecosystem
promote higher levels of biodiversity
Some groups contain more species
than others
• Species are not evenly
distributed among
taxonomic groups
– Insects predominate over
all other life-forms
– 40% of all insects are
beetles
• Groups accumulate species
by
– Adaptive radiation
– Allopatric speciation
– Low rates of extinction
Insects outnumber all other
species
Measuring biodiversity is not easy
• Out of the estimated 3 - 100 million species
on Earth, only 1.7 - 2 million species have
been successfully catalogued
• Very difficult to identify species
– Many remote spots on Earth remain unexplored
– Small organisms are easily overlooked
– Many species look identical until thoroughly
examined
• Entomologist Terry Erwin found 163 beetle
species specialized on one tree species
Biodiversity is unevenly distributed
• Living things are
distributed unevenly
across Earth
• Latitudinal gradient
= species richness
increases towards the
equator
Canada has 30 - 100 species
of breeding birds, while
Costa Rica has more than
600 species
Latitudinal gradient has many
causes
• Climate stability, high plant productivity, and no glaciation
• Tropical biomes support more species and show more
species evenness
– Diverse habitats increase species diversity
• Human disturbance can increase habitat diversity
– But only at the local level
•
Biodiversity loss is more than
extinction
Decreasing numbers
are accompanied by
smaller species’
geographic ranges
• Genetic, ecosystem,
and species diversity
are being lost.
• The Living Planet Index
summarizes trends in
populations
– Between 1970 and
2003, the Index fell
by 30%
Biodiversity loss has many causes
• Reasons for biodiversity losses are multifaceted,
complex, and hard to determine
– Factors may interact synergistically
• Four primary causes of population decline are:
– Habitat alteration
– Invasive species
– Pollution
– Overharvesting
• Global climate change now is the fifth cause
Habitat alteration causes biodiversity loss
• The greatest cause of biodiversity loss
– Farming simplifies communities
– Grazing modifies the grassland structure and
species composition
– Clearing forests removes resources organisms
need
– Hydroelectric dams turn rivers into reservoirs
upstream
– Urbanization and suburban sprawl reduce natural
communities
– A few species (i.e., pigeons, rats) benefit from
changing habitats
Habitat alteration has occurred in
every biome
Particularly in tropical rainforests, savannas, and
tropical dry forests
Invasive species cause biodiversity
loss
• Introduction of non-native species to new environments
– Accidental: zebra mussels
– Deliberate: food crops
• Island species are especially vulnerable
• Invaders have no natural predators, competitors, or
parasites
• Cost billions of dollars in economic damage
Pollution causes biodiversity loss
• Harms organisms in many ways
– Air pollution degrades forest ecosystems
– Water pollution adversely affects fish and
amphibians
– Agricultural runoff harms terrestrial and
aquatic species
– The effects of oil and chemical spills on
wildlife are dramatic and well known
• The damage to wildlife and ecosystems caused
by pollution can be severe
– But it tends to be less than the damage
caused by habitat alteration or invasive
species
Overharvesting causes biodiversity
loss
• Vulnerable species are large, few
in number, long-lived, and have
few young (K-selected species)
– The Siberian tiger is hunted
without rules and regulations
– The early 1990s saw increased
poaching because of powerful
economic incentives
– Many other species affected:
Atlantic gray whale, sharks,
gorillas
Today the oceans contain only 10% of the large animals
they once did
Climate change causes biodiversity
loss
• Emissions of greenhouse gases warms
temperatures
– Modifies global weather patterns and
increases the frequency of extreme weather
events
– Increases stress on populations and forces
organisms to shift their geographic ranges
• Most animals and plants will not be able
to cope
Warming has been the greatest in the
Arctic
The polar bear is being
considered for the
endangered species list
It isn’t currently on list and
may not make the list
because part of the ESA,
endangered species act,
is habitat protection. For
polar bears this would
mean protecting sea ice
from melting-or reduction
in global warming.
Biodiversity loss has a variety of
causes
Biodiversity provides free ecosystem
services
• Provides food, shelter, fuel
• Purifies air and water, and detoxifies wastes
• Stabilizes climate, moderates floods, droughts, wind,
temperature
• Generates and renews soil fertility and cycles
nutrients
• Pollinates plants and controls pests and disease
• Maintains genetic resources
• Provides cultural and aesthetic benefits
• Allows us to adapt to change
The annual value of just 17 ecosystem services = $16 - 54
trillion per year
Biodiversity helps maintain
ecosystem function
• Biodiversity increases the stability and resilience of
communities and ecosystems
– Decreased biodiversity reduces a natural system’s
ability to function and provide services to our society
• The loss of a species affects ecosystems differently
– If the species can be functionally replaced by others,
it may make little difference
– Extinction of a keystone species may cause other
species to decline or disappear
• “To keep every cog and wheel is the first precaution of
intelligent tinkering” (Aldo Leopold)
Biodiversity enhances food security
• Genetic diversity within crops is enormously
valuable
– Turkey’s wheat crops received $50 billion
worth of disease resistance from wild wheat
• Wild strains provide disease resistance and
have the ability to grow back year after year
without being replanted
• New potential food crops are waiting to be used
– Serendipity berry produces a sweetener
3,000 times sweeter than sugar
Some potential new food sources
Organisms provide drugs and
medicines
• Each year
pharmaceutical
products owing their
origin to wild species
generate up to $150
billion in sales
– The rosy
periwinkle
produces
compounds that
treat Hodgkin's
disease and
leukemia
Biodiversity generates economic
benefits
• People like to experience protected natural
areas, creating economic opportunities for
residents, particularly in developing countries
– Costa Rica: rainforests
– Australia: Great Barrier Reef
– Belize: reefs, caves, and rainforests
• A powerful incentive to preserve natural areas
and reduce impacts on the landscape and on
native species
• But, too many visitors to natural areas can
degrade the outdoor experience and disturb
wildlife
People value and seek out nature
• Biophilia = connections that
humans subconsciously seek with
life
– Our affinity for parks and
wildlife
– Keeping of pets
– High value of real estate with
views of natural lands
• Nature deficit disorder =
alienation from the natural
environment
– May be behind the emotional
and physical problems of the
young
Do we have ethical obligations to
other species?
• Humans are part of nature and need
resources to survive
• But, we also have conscious reasoning ability
and can control our actions
– Our ethics have developed from our intelligence
and our ability to make choices
• Many people feel that other organisms have
intrinsic value and an inherent right to exist
Conservation biology responds to
biodiversity loss
• Conservation
biology = devoted
to understanding the
factors that
influence the loss,
protection, and
restoration of
biodiversity
– Arose as scientists
became alarmed at
the degradation of
Conservation scientists work at
multiple levels
• Conservation biologists integrate evolution and
extinction with ecology and environmental systems
– Design, test, and implement ways to mitigate
human impacts
• Conservation geneticists = study genetic
attributes of organisms to infer the status of their
population
• Minimum viable population = how small a
population can become before it runs into problems
• Metapopulations = a network of subpopulations
– Small populations are most vulnerable to
extinction and need special attention
Island biogeography
• Equilibrium theory of island biogeography
= explains how species come to be
distributed among oceanic islands
– Also applies to “habitat islands” – patches of one
habitat type isolated within a “sea” of others
– Explains how the number of species on an island
results from an equilibrium between immigration
and extirpation
– Predicts an island’s species richness based on
the island’s size and distance from the mainland
Species richness results from island size and
distance
• Fewer species colonize an island far from the mainland
• Large islands have higher immigration rates
• Large islands have lower extinction rates
The species-area curve
• Large islands contain more species than small
islands
– They are easier to find and have lower extinction
rates
Small “islands” of forest rapidly lose species
• Forests are fragmented
by roads and logging
• Small forest fragments
lose diversity fastest
– Starting with large
species
• Fragmentation is one of
the prime threats to
biodiversity
Should conservation focus on
endangered species?
• Endangered Species Act (1973) (ESA) =
forbids the government and private citizens
from taking actions that destroy endangered
species or their habitats
– To prevent extinction
– Stabilize declining populations
– Enable populations to recover
• As of 2007, the U.S. had 1,312 species listed
as endangered or threatened
Despite opposition, the ESA has had
successes
• Peregrine falcons, brown pelicans, bald
eagles, and others have recovered and
are no longer listed
• Intensive management has stabilized
other species
– The red-cockaded woodpecker
– 40% of declining populations are now
stable
• These successes occur despite
underfunding of the U.S. Fish and
The ESA is controversial
• Many Americans support protection of endangered
species
• Opponents feel that the ESA values endangered
organisms more than the livelihood of people
– Private land use will be restricted if an endangered
species is present
– “Shoot, shovel, and shut up” = landowners conceal
the presence of endangered species on their land
• But, the ESA has stopped few development projects
– Habitat conservation plans and safe harbor
agreements = landowners can harm species if they
improve habitat for the species in other places
Other countries have their own
version of the ESA
• Species at Risk Act (2002) = Canada’s
endangered species law
– Stresses cooperation between landowners and
provincial governments
– Criticized as being too weak
• Other nations’ laws are not enforced
– The Wildlife Conservation Society has to help pay
for Russians to enforce their own anti-poaching
laws
Protecting biodiversity
• Captive breeding – individuals are bred and raised with
the intent of reintroducing them into the wild
– Zoos and botanical gardens
• Some reintroductions are controversial
– Ranchers opposed the reintroduction of wolves to
Yellowstone National Park
– Some habitat is so fragmented, a species cannot
survive
Protecting biodiversity
• Cloning – a technique to create more
individuals and save species from extinction
– Most biologists agree that these efforts are not
adequate to recreate the lost biodiversity
• Ample habitat and protection in the wild are
needed to save species
Umbrella species
• Conservation biologists use particular species as
tools to conserve communities and ecosystems
– Protecting the habitat of these umbrella species
helps protect less-charismatic animals that would not
have generated public interest
• Flagship species – large and charismatic species
used as spearheads for biodiversity conservation
– The World Wildlife Fund’s panda bear
• Some organizations are moving beyond the single
species approach to focus on whole landscapes
International conservation efforts
• UN Convention on International Trade in
Endangered Species of Wild Fauna and Flora
(1973) (CITES) – protects endangered species
by banning international transport of their body
parts
• Convention on Biological Diversity (1992) –
– Seeks to conserve biodiversity
– Use biodiversity in a sustainable manner
– Ensure the fair distribution of biodiversity’s
benefits
– By 2007, 188 nations had signed on
– Iraq, Somalia, the Vatican, and the U.S. did
not join
Biodiversity hotspots
• Biodiversity hotspots –
prioritizes regions most
important globally for
biodiversity
– Support a great number of
endemic species = species
found nowhere else in the world
– The area must have at least
1.500 endemic plant species
(0.5% of the world total)
– It must have lost 70% of its
habitat due to human impact
There are 34 global biodiversity
hotspots
2.3% of the planet’s land surface contains
50% of the world’s plant species and 42%
of all terrestrial vertebrate species
Community- based conservation
• Protecting habitats makes good sense, but
this affects people living in and near these
areas
• Community-based conservation =
conservation biologists actively engage local
people in protecting land and wildlife
– Protecting land deprives people access to
resources
– But, it can guarantee that these resources will not
be used up or sold to foreign corporations and
can instead be sustainably managed
• Many projects have succeeded
– But, others have not, due mainly to funding
problems
Innovative economic strategies
• Debt-for-nature swap = a conservation
organization pays off a portion of a
developing country’s international debt
– In exchange for a promise by the country to
set aside reserves
– Fund environmental education, and
– Better manage protected areas
• Conservation concession = conservation
organizations pay nations to conserve,
and not sell, resources
Conclusion
• Loss of biodiversity will result in a mass
extinction
• Primary causes of biodiversity loss are:
– Habitat alteration, invasive species, pollution,
overharvesting of biotic resources, and
climate change
• Human society cannot function without
biodiversity’s benefits
• Science can help save species, preserve
habitats, restore populations, and keep
natural ecosystems intact