|
BIOL 4140
Contemporary Problems
in Environmental Science
Phil Ganter
302 Harned Hall
963-5782 |
|
This Scrub Pine Ecosystem
in southern Florida prompts the question of how much and with
what methodology do we value such rare ecosystems |
Natural Resources III Biodiversity
Lecture 08
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me
Unit
Organization:
Reading:
Textbook: Chapter 11
Ancillary Reading:
Biodiversity
We
have already described biodiversity and its measurement (see lecture 3),
and so we will use that material as our starting point for this chapter
- Please
briefly review the lecture and pay close attention to the way in which
biodiversity is measured
Lecture
3 was a description of the biodiversity on Earth but this chapter will focus
on three things:
- The
value of biodiversity
- The
threats to biodiversity
- efforts to conserve biodiversity
Biodiversity
losses have spurred the birth of a new sub-discipline within environmental
science: Conservation Biology
interdisciplinary
field that draws from ecology, evolution, genetics, physiology, and other
fields to develop methods of conserving species and larger biological systems
Value of Biodiversity
As
scientists, we should always be explicit about our assumptions and be willing
to examine them for their validity
- Conservation
of species and habitats can be costly (however one measures it), so we need
to ask if biodiversity has value to offset the costs of preserving it
- Biodiversity's
value is hard to assess, as are all values
Is
there value to biodiversity? Consider this:
Value of Biodiversity
Assessing
biodiversity's value must involve examining what the term "value" means
- Most
definitions seem fuzzy but all might be boiled down
- Value
is
the regard or importance that something is held to deserve
by an individual or group of individuals
Thus,
it always involves a subjective component, no matter how exactly it might
be defined for a specific situation
- Would
you stop and pick up a single penny? Dime? Quarter? Dollar?
Here,
we will consider the ways in which at least some people have placed value
on biodiversity
- Intrinsic
Value (value independent of humans) - non-use value
- Whether
or not other living things have value simply by their existence is
a matter of Ethics
- Some
cultures value all life but few put other living forms on an
equal basis with humans
- Ethical
evolution - extending "personhood" or intrinsic value to others
- Those who believe that ethical systems
"evolve" believe in orthogenesis - the
idea that evolution follows a pre-set path (not a popular idea
among modern evolutionary
biologists, but the idea of evolution, like all ideas, belongs
to all of us)
- The idea behind ethical evolution is that
our history has been that of admitting a wider and wider circle into
the inner group: those who have equal status (or near equal)
with ourselves
- members
of family (nuclear, extended)
- members
of local group (clan, tribe, etc.)
- members
of larger political units (e.g. nationalism)
- members
of Homo sapiens
- members
of other species
- Is
mankind a part of the natural world, master of the natural world or apart
from it?
- Anthropomorphic
Value (direct and indirect use value) is biodiversity's value to humans
- Economic
Benefits
- Direct
- exploitation
of wild populations of plants, fungi, and animals (value of these goods)
- tourism
- Indirect
- Services
to human society provided by natural systems
- water
purification
- climate
regulation
- regeneration
of oxygen, humidification of the atmosphere, and removal of CO2
- regeneration
of nutrients needed for soil productivity
- decomposition
of wastes
- Aesthetic
and Psychological benefits
- Scientific
Knowledge and Innovation
- Storehouse
of unknown, future benefits
Biodiversity Loss
Loss of Biodiversity
Biodiversity
is affected by population and species loss and by the founding of new populations
and species
- Extinction is the total loss of a species
- Extirpation is the loss of local population
- Ecological
Extinction is the loss of a species function in the larger community or ecosystem
due not to extinction or extirpation but to the reduction of a population
to a size so small that it no longer performs its role in the larger unit
- Mass
Extinctions are widespread extinctions that result in the loss of many species
in all habitats
- Background
Extinctions are the extinctions that occur for reasons other than those that
produce mass extinctions
- Biological
Impoverishment is the loss of biodiversity in an area through extinctions,
extirpations, and the reduction in population size of many other species
(without their extinction or extirpation)
Data
on extinctions is best for vertebrates and plants
- In
the last 400+ years, 2% of all known mammal species have gone extinct
- At
that rate, all mammals will be extinct in 10,000 years (just a moment in
geologic time)
- For
birds and mammals, the extinction rate has increased through time, so the
10,000 year estimate is to long
- If
you look at the number of threatened species, the numbers are much worse
(25% of mammals, 12% of birds, 2% of plants)
- Estimated
rates of extinction show that, in all groups, between 1 and 11 % of species
are lost per decade
Causes of
Extinction
There
is no easy way to separate all of the causes of extinction into natural versus
man-made causes, although some causes are clearly due to human activity
- Natural
causes can be due to changes in the physical or biological environment of
the species
- Humans
can alter the rate of change in either of these causes, so we can accelerate
or decelerate losses due to natural causes
- Extinctions
are more common on islands (as are invasions)
- Islands
are often recent and unstable communities with small populations and so,
are prone to both invasion and extinction
Extinction
through Human Activity
Habitat
Disruption causing loss of species dependent on the habitat
- Deforestation
of both tropical and temperate forests
- Urbanization
(and Suburbanization) - housing, commercial property, industry
- Conversion
of land to agricultural use
- Dam
building
- Removal
of bosque removes shading of streams, warming them and increasing available
light
- Eutrophication of lakes, rivers, estuaries, and neritic seas
- Habitat
Fragmentation - breakup of continuous biome area
- Fragmentation
of a biome means that islands surrounded by hostile habitat are formed
- Organisms
must disperse across the hostile habitat and, if they can't, the islands
be come isolated and local extinctions can't be undone by colonization
- Fragmentation
makes many edges and edges have numerous effects on the habitat
(Edge Effects)
- Edge is the portion of the biome that is altered by contact with the hostile habitat
- Core is the portion not affected
- Edges
reduce the core habitat, making conserved areas less effective
- Example: Compare
the following situations
- Unfragmented: 10
km by 10 km area of biome in which edge
effects extend 1 km from boundary of the biome
- Fragmented:
Four 5 km by 5 km areas of biome
- Unfragmented
Biome - 100 sq km total area, 64% unaffected by edges (core), 36% affected
by edges
- Fragmented
Biome - 100 sq km total area, 36% unaffected by edges (core), 64% affected
by edges
- Edges
allow extremes of temperature, moisture, etc. to penetrate more of the core
areas of the biome
- Edges
are stressful environments for "core" species individuals that happen to
be close to a new edge
- Circular
areas lose least to edge effects and edges become more and
more important as the shape becomes more and more irregular
Introduction
of New Species causing loss of species already there and/or reduction in
value of the system
- Introductions
occur when a small number of individuals of a non-native (exotic) species
successfully colonize new territories
- Introductions
may cause reductions in native (endemic) species
- When
an introduced species spreads widely and replaces native species, it is
called invasive
- Introductions
may be
- Deliberate
- Horses
in North America, rabbits in Australia and New Zealand, fresh water game
fish, striped bass in impoundments, many flowering plants for household gardens,
kudzu to stabilize steep roadsides
- Inadvertent
- Freshwater
species in ship's ballast, insects on horticultural plants, seeds
and animals clinging to shipped goods, escape of the gypsy moth
- Introduced
species may:
- out
compete
natives for resources
- not
be food for native herbivores, parasites, or carnivores
- alter
the habitat with harmful effects on native species
- Melaleuca
quinquenervia, Paperbark Trees or Punktrees, introduced to Florida to
dry up swampland, spread through 1500 sq km of south Florida and used so
much
water
that it
lowered
the
water table and caused economic loss (agricultural and real estate) and
the loss
of
native
species
- The
Tea Tree is a member of this genus and produces an oil found in many cosmetic
products. The oil has anti-bacterial and anti-fungal properties
- act
as reservoirs for
parasites that are more harmful to native species than to the introduced
species
- Introduced
species can be costly
- Loss
of income from native species
- Loss
of agricultural land or land for housing
- Cost
of eradication or control
Over-Exploitation
causing loss of exploited species
- Large,
slowly reproducing, small population, and valuable are all characteristics
of species at risk of eradication directly through human activity
- Over-fishing
of commercial fish stocks
- Dozens
of commercially valuable marine species are threatened with extinction
due to over-fishing
- Despite
regulatory intervention in the 1970's, by 1992 the north Atlantic cod fishery
had collapsed
- Two
bass species have collapsed (the barred sand bass and kelp bass) in California
under the nose of watchful resource managers
- Spawning
caused many bass to collect in a few places favored by recreational fishermen
and the numbers convinced many that there were plenty of both species
- Aggregation
behavior means that, the density of fish remains great, even as the population
shrinks (the total area occupied by the breeding swarms shrinks, not the
density of fish in the remaining spawning area)
- Commercial
harvest has been illegal since 1953 but recreational fishing was never stopped
- Plants
- wild medicinal plants, showy or rare orchids (which often have very low
population densities)
- Birds
- Wikipedia lists 190 species of extinct birds, many due to over exploitation
(covers only extinctions since 1500 AD)
- Mammals
- bison, wolf, eastern populations of mountain lion, mountain sheep, many
baleen whale species
- Many
mammals are hunted for food (wild meat) in poorer countries and this can
lead to drastic population reductions
- Whales
are over exploited by industry and many species are on the endangered
or threatened list
- Some
are simply over exploited by sport hunters
Secondary
(Indirect) Effects causing extinction of species not directly affected by
human activity
- Species
lost by over exploitation may be replaced by species of no value or not replaced
at all
- Example
- Lyme
disease is a zoonosis (human disease with another animal as a reservoir)
caused by a bacterium (three species of Borrelia) and first described
in 1975 from cases in Lyme, Connecticut. It
is associated with a wider range of symptoms. It starts a local
infection (bullseye rash, flu-like symptoms), can become a disseminated
infection (spread
to many
parts of body and associated with migrating pain in joints and muscles
and facial palsy, headaches, shooting pains, memory loss, sleep disturbances
and heart problems in 10% of those infected) and may become a persistent
infection (with rare symptoms of loss of use of legs, depression, many
mental
problems and severe arthritis). Thus,
some symptoms may not present for months or years after infection. Rodents
are the animal host and ticks are the means of transmission
- Loss
of predators of Eastern Whitetail Deer has resulted in much larger deer
populations, which
increases
the population
of
deer ticks,
which
results
in more ticks
transferring lyme disease from white-footed mice to humans
- So,
do those deer along the roadside seem so cute now?
Minimal Viable
Population Size
- All
populations have a maximum size but it is also true that populations
have a minimum size, although what that size is depends much on the biology
of the species
- When
the minimum number is crossed the population collapses (called, very
dramatically, an extinction vortex in
the book)
- Causes
are
- Loss
of genetic variation leading to inbreeding and the expression of
unfit recessive alleles and linkage of unfit alleles
- This
can cause infertility or early mortality in inbred individuals
- Loss
of reproduction opportunities (no mates, finding mate too costly)
Ecosystem and Community Degradation
Extinctions are more likely when the entire system in which a species is
embedded is under stress from human-caused disturbances
- Much
of conservation legislation focuses on saving individual species
- This
has historical roots and is linked to feelings aroused by the loss of "attractive"
species
- American
eagle, panda bear, humpbacked whale, etc.
- Many
biologists argue that it is a mistake to focus
legislation on the species and argue that we should focus on conservation
of habitats
- Extinction
of species is a natural, ongoing process as well as a man-made process
- Elimination
of habitats is mostly man-made in the present (geological upheaval in the
past has also caused elimination of habitats)
- No
species will persist if it's habitat is eliminated
- Focus
on habitat conservation may save many more species than individual target
species
- It
is systems, not species, that deliver ecosystem services
- Stressed
systems may provide degraded services long before collapse of the system
- Ecosystem
simplification through human-caused disturbance may reduce the ability of
a system to provide service
- Ecosystem
health may be assessed through the use of a subset of the species in the
system
- Indicator
species - a set of species that show population
declines or extirpations as ecosystem stresses increase
- more
pollution
- changes
in physical parameters due to human activities
- changes
in composition of producer communities
- loss
of predators
Disturbance,
biodiversity and stability
- stability
for our purpose is
a measure of the ability of a system to provide services
- Not
a simple relationship
- Lowest
diversity systems are usually least stable and most affected by disturbance
- Agricultural
monocultures
- Moderate
levels of diversity are often the most stable and least affected by disturbance
- Very
diverse communities often do not show parallel increases in stability
compared to intermediate levels of diversity
- Responses
may be tied to Keystone species, so degree of response is tied to which species
is lost, not number of species lost
Biodiversity
Conservation and Recovery
Determining
Risk of Extinction
All
species are not equally likely to go extinct
- Some
species are characterized by multiple risk factors
Factors
affecting probability of extinction
Ecological
Factors
- Low
population size
- Small
populations are closer to the minimal viable size and therefore, at greater
risk
- Small
populations are less likely to send out successful colonists
- Small
populations take longer to recover from sudden reductions
- Low
population sizes are expected for
- Rare
Species
- Species
at the top of trophic pyramids
- Island
populations
- Species
with narrow habitat requirements
- Species
with restricted geographical ranges
- Species
with large ranges
- Eastern
mountain lion (last left is the Florida panther)
- California
condor
- Polar
bear
- Florida
manatee
- Species with low reproductive rates
- blue whale
- valuable hardwood trees (mahogany, ebony, etc.)
- Species with behaviors unfit for human contact
- Manatees attraction to fresh water sources
(like drainage pipes)
- Bird migration at night when it is difficult
to spot towers, wires, and windmills
Physiological
Factors
- Species
that are susceptible to human-caused environmental changes
- Frogs
and reproductive hormone mimics
- Plants
with narrow temperature or drought tolerances and climate change
- Stream
vertebrates and invertebrates with high oxygen demands and stream heating
post bosque removal
- Non-target
insects and widespread insecticide applications for both agriculture and
home use
Direct
Anthropogenic Factors
- Species
with commercial value
- Species
dependant on commercially valuable lands
- Species
killed for sport (conservation efforts to increase these populations
are more and more common in the US and Europe, less common elsewhere)
Which species
to preserve
This
type of question is usually approached through the tripartite-answer devised
by Napoleon's army to cope with battlefield causalities (the "tri" in triage
does not mean three; the word derives from the French "trier", to sort)
- If
not all species at risk can be saved then one must sort them into three categories
- Species
that will persist without any intervention
- Species
that will not persist no matter what intervention is made
- Species
that might persist if intervention is attempted
- Triage
can end there if there are sufficient resources to intervene on the behalf
of all species in the third category.
- If
not, then a second round of triage must be done but the criteria are more
complex than those used in
the first round
- Which
of the species that might be saved will actually be
the target of conservation efforts depends assessing several factors
- The
relative cost of intervention
- The
relative likelihood of the intervention's
success
- The
role that the species plays in its community and ecosystem
- Keystone
species (from the keystone of an arch) are species that, if removed from
the system, result in other species loss as well
- A
keystone predator may lower the size of its prey populations and, if removed,
the competitive dominant among the prey species may then eliminate it competitors
from the system, leading to a greater biodiversity loss than just the loss
of the predator
- There
are also keystone food resources or keystone species that provide habitat
for many other species (corals are keystone species on coral reefs)
- How unusual is the species in terms of its phylogeny
or phenology
- Pandas are bears but represent a very divergent
clade
- Pandas are also phenotypically unusual
in their dietary adaptations and behaviors
- The Nashville Crayfish lives only in Mill Creek
- Membership in a very diverse assemblage of related
organisms can contribute to perceived species value (members of a "biodiversity
hotspot" for a type of organism)
- The river systems in the Eastern US are home
to the most diverse set of freshwater clams and mussels in the world
- The Appalachian Mountains are home to
a diverse set of plethodontid salamanders
- Membership in a favored group
- Birds are more likely to receive intervention
than moles
- Favoritism may get a species special
status and separate resources, which may increase the total resources
available for conservation
Means of Preserving
Biodiversity
- Much
attention has gone into protection of species but other approaches may be
more effective in preserving biodiversity
- Protecting
larger biological entities than species may be necessary (communities, ecosystems)
- No
species can be successfully conserved in the wild if it's habitat disappears
- Establishment
of protected areas
- Establishment
of "zoos" for species that have lost their habitat in nature or have dipped
below the minimal viable population size
- These
"zoos" (in quotes because the approach can be applied to plants and other
organisms not in the Animalia) can be useful as a bridge between immanent
loss and successful restoration
- Whooping
Crane - one of two crane species in North America, up to 5 feet tall with
a wingspan over 7 feet, about 500 individuals in the wild (some in declining
populations) and 180 in zoos
- California
Condor
- Wollemi
Pine
Legislative
Approaches to Preserving Biodiversity
The
International Union of Conservation of Nature, a non-profit organization,
establishes criteria for extinction risk and maintains the Red List, the
larges list of species conservation status
- Extinct -none known to exist
- Extinct
in the Wild - none known to exist outside of captivity
- Critically
Endangered - extremely high risk of extinction
- Endangered - high risk of extinction
- Vulnerable - high risk of becoming listed as endangered
- Near
Threatened - likely to be listed as endangered in the near future
- Least
Concern - not likely to be listed as endangered in the near future
- Data
Deficient - Not enough data to make a risk assessment
- Not
Evaluated - self explanatory
The
US government has established legal definitions for conservation status
- Placement
of a species in the endangered category triggers protection for that species
- US
Endangered Species Act of 1973
- Administered
by the US Fish and Wildlife Service and the National Oceanic and
Atmospheric Administration
- Categories
- Endangered - any species which is in danger of extinction throughout all or a significant
portion of its range other than a species of the Class Insecta determined
by the Secretary to constitute a pest
- Threatened -
any species which is likely to become endangered throughout all
or a significant portion of its range in the foreseeable future
- Candidate - species under consideration for listing as threatened or endangered
- Endangered
due to Similarity of Appearance - any species which would pose difficulties
in separating it from an Endangered species
- Experimental
Essential Population - any population of an endangered
or threatened species released outside of the species current
range but within the historical range
deemed essential for the species continued existence by the Secretary
of the Interior
- Experimental
Non-essential Populations - any population of
an endangered or threatened species released outside of the species
current range but within the historical
range
deemed non-essential for the species continued existence by the
Secretary of the Interior (populations are treated
as threatened species)
- There
is a formal listing process for a species to receive an ESA designation
but the delisting process is not well defined
- Listed
species are to be protected and, if possible, restored
to a condition that would result in their being delisted
- How
protection of a specie is to be done has been the object of several
rounds of amendments, some designed to strengthen the ability to accomplish
the
goal and
others designed to weaken it by making cost a factor in decision making
- The
act gives the federal government, through the administering agencies,
broad powers to limit activity that would further endanger listed
species, whether
or not the land occupied is publicly or privately owned
- The
agencies must protect critical habitat and must develop and implement a recovery
plan
- This
power has bruised many landowners, making the act controversial in the particular
while enjoying broad, general support
- Tennessee
has a fully functional dam on the Duck River that was never filled (the famous
snail darter was the species involved) but no better way of species preservation
has been suggested
- Some
criticize the act on it ineffectiveness, noting that far more
species are listed as endangered or threatened (over 2000 as of
2012, 1400 native)
than de-listed (40, 33 native to the US)
- NOAA's
National Marine Fisheries Service lists 88 species or populations (sub species)
of whales, turtles, seals, fish and invertebrates (4 total) as endangered
or threatened but only 2 delisted species, one delisted because it went extinct
- Related
Acts and Treaties:
- The
1973 act replaced earlier acts, which have been rescinded and won't
be mentioned here
- The
Lacy Act of 1900 (not to be confused with the Lacey
Act of 1907, which pertains to the disbursement of federal funds to
various tribes) - penalties for
those
who traffic in illegally taken plants, wildlife, and fish
- Convention
on the International Trade in Endangered Species (CITES,
also called the Washington Convention, which is a bit ironic) - a framework
of protections
which signers of the convention, drawn up by the ICUN, agree to implement
in their domestic legislation
- Signers
who violate CITES are liable to some sanctions (suspension of trade in CITES-listed
species, formal warnings, visits from convention secretariat, and others)
- As
of Sept 2012, 176 of the 193 UN countries are signatories of CITES
- Species
are listed in one of three Appendices:
- I
- 1200 species -at risk of extinction in the near future and affected by
trade
- II
- 21,000 species - threatened by extinction unless trade is controlled
- III
- 170 specie - special status for individual species that a
signatory nation has asked for assistance in their attempts
to preserve the species
Sustainable
Exploitation
- Conservationists
often promote sustainability as a goal that will preserve biodiversity
- Sustainability
means that man must not disturb, introduce, exploit, or indirectly affect
(the four causes of human-caused extinction - see above) natural systems
beyond the point at which the systems begin to sustain the loss of species.
- If
this is an achievable goal, then some questions arise before we can begin
to move toward it
- Do
we accept the current state of already-stressed systems when modelling sustainability?
- Do
we accept temporary unsustainable practices in the transition from
over-exploitation to sustainability?
- How
much of the cost of achieving sustainability is to be born by individuals
versus the government?
- How
do we balance the goal of sustainability with the additional pressures on
natural systems that come from population increase and an increase in the
standard of living?
Moratoria,
Breeding Programs, and Reintroductions
Conserving
biodiversity will mean taking direct action to do so
- The
ESA gives the government the power to protect listed species but, so far,
that power has not resulted in many species being delisted
- Because
the ESA is reactive and not proactive, there is no legal authority to stop
practices that lead species to be listed (the ESA only takes effect after
listing)
So,
what is being done to recover species
- Moratoria
on exploitation (most commonly used for directly exploited species such
as commercial fisheries)
- Preservation
of habitat
- Reintroductions
where local extirpation has occurred
- Captive
breeding programs when the population has fallen below the minimum viable
size
The Role of
Non-Governmental Organizations
- Almost all industries have a trade
association made up of commercial entities (timber, fishing, cattle [Beef,
it's what's for dinner], etc.)
- Numerous public organizations of individuals
exist that have an interest in conservation efforts
- Sport hunting associations, sport fishing associations
- conservation organizations (WWF, Sierra Club,
Nature Conservancy, Green Peace, and many others), international, national
and local
- Many organizations with interests outside
of conservation may advocate on specific conservation issues (Rotary
clubs with positions on wolf reintroduction efforts in the western
US, etc.)
- These groups may impact conservation efforts
by
- acting as advocates for conservation,
applying pressure to the government and sometimes through public education
- using their resources to help
conserve species of interest
- attempting self-regulation of
member activities
- acting as political pressure groups
resisting regulation
- engaging in public advocacy (both pro and con)
on specific conservation efforts
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Last updated October 4, 2012