Download Cons Biol apr 29 02

Raven and Johnson 1999
Conservation Biology
•Applied scientific discipline that seeks to
counter the current rapid decrease in the
diversity of life on Earth – biodiversity
•Human population size, and per capita
rates of resource use in particular, are
regarded as the “ultimate” (root, in this
sense) cause of the “Biodiversity Crisis”
•Components of biodiversity…what is it
we’re trying to save?
•genetic diversity, species diversity,
ecosystem diversity…
•integrity of ecological and
evolutionary processes; ecosystem
functions and processes
Population growth is highest in
tropical and subtropical
countries. Mexico City, the
world’s largest city, has well over
20 million inhabitants
A global perspective on the biodiversity
crisis
•~1.5 million species described; estimates of total
species diversity; 10 to 30-80 million species
•Many, perhaps up to half, of Earth’s species live
in tropical forest biome, which is being logged and
converted to cropland at a very high rate
•Globally the amount of human-altered land
surface is near 50%; we use over 50% of all
accessible surface fresh water
•Rates of diversity loss and ecosystem
degradation may now exceed the K-T asteroid
•Human activities are altering ecosystem
processes on a global scale
Deforestation rates are high in tropical forests.
Central America is a good example of the high
rate of destruction of tropical forest As the
forests are lost, so are the many species that
live in them
Viitousek et al 1997
HUMAN POPULATION
(Size and Resource Use)
INDUSTRY
AGRICULTURE
(forestry, grazing, ag-related commerce)
proximate causes of changes
human-caused global changes
CO2
ALTERED
PERSISTENT
CO
ALTERED
PERSISTENT
2
INCREASE
BIOGEOCHEMICAL ORGANIC
INCREASE BIOGEOCHEMICAL
ORGANIC
CYCLES
COMPOUNDS
CYCLES
COMPOUNDS
GLOBAL
CLIMATE
CHANGE
LAND USE AND HARVESTING
LAND
AND HARVESTING
LAND USE
COVER
NATURAL
LAND
COVER
NATURAL
CHANGE
POPULATIONS
CHANGE
POPULATIONS
LOSS OF
BIOLOGICAL
DIVERSITY
BIOLOGICAL
BIOLOGICAL
INVASIONS
INVASIONS
Greatest threat to biodiversity
globally are related to habitat loss
and degradation
The three principal forms of habitat loss and
degradation are:
•habitat destruction
•habitat alteration
•habitat fragmentation
•Fragmentation is often a consequence of
human land conversion activity; the
remaining patches are surrounded by areas
variously altered by humans
•Fragmentation has become a major subject
of research in conservation biology
Habitat fragmentation break up of extensive tracts of
habitat into small, isolated patches. Aerial photo of Mt.
Hood National Forest in the western U.S. shows common
result of ecosystem alteration; “islands” of coniferous
forest remain following logging
Biodiversity problems in the U.S.
Habitat destruction
and degradation is
the primary cause
of extinction and
endangerment for
freshwater aquatic
organisms
Small animals are
vulnerable to habitat
destruction because
they often have small
ranges and highly
specialized
requirements
Proportion of U.S. Species extinct or at risk. The
groups that are most endangered – mussels, crayfishes,
amphibians and fishes – live in freshwater, a habitat that
has been extensively destroyed and polluted
WHY SHOULD WE ATTEMPT TO CONSERVE
BIODIVERSITY?
•Conservation biology is driven by the value of
biodiversity
•instrumental values
•support anthropocentric, utilitarian rationales
that hold that biodiversity has value as a
means to human ends
•instrumental values include
•goods (actual and potential food,
medicine, fiber, fuel)
•services (pollination, nutrient recycling,
oxygen production
•information (practical scientific
knowledge, genetic library)
•psycho-spiritual satisfaction (natural
beauty, religious awe, pure scientific
knowledge)
•intrinsic values
•Support biocentric rationales that hold that
biodiversity has value simply because it exists
Meffe et al 1997
Cultural and Scientific History of Conservation of Biodiversity
•The “Conservation Movement” was born in the U.S.,
first half of the 20th Century; its roots can be traced
back to philosophical movements of the 19th and 20
centuries
•Romantic-Transcendental Conservation Ethic
•derived from writings of Thoreau, Emerson
(east) and Muir (west)
John Muir
•first prominent writers to argue in the mid
1800’s that nature has uses other than
economic gain; spoke of nature in a quasireligious sense
Preservationist movement,
advocating pure wilderness and
a spiritual appreciation for
nature
Gifford Pinchot
•Resource Conservation Ethic
•rooted in the utilitarian philosophy of John
Stuart Mill
•popularized by forester Gifford Pinchot, late
19th early 20th century
•stressed equity of resource use amongst
consumers; formed basis of the multiple-use
concept of USFS and BLM
http://sierraclub.org/john_muir_exhibit/index.html
Conservation movement,
advocating a resource-based,
utilitarian view of the world
Cultural and Scientific History of Conservation of Biodiversity
photo: http://www.naturenet.com/alnc/aldo.html
•The modern conservation movement was born in the
20th century, emerging with the development of
evolutionary ecology
Aldo Leopold
•Evolutionary-Ecological Land Ethic
•Developed by Aldo Leopold in his classic essays
in A Sand County Almanac (1949) and other
writings
•Leopold saw ecosystems in the context of
integrated systems and interdependent processes
and components – an equilibrium perspective
•Leopold’s equilibrium perspective has since been
replaced by a dynamic, nonequilibrium
perspective
It is inconceivable to me that an ethical
relation to land can exist without love,
respect, and admiration for land, and a high
regard for its value. By value, I of course
mean something far broader than mere
economic value; I mean value in the
philosophical sense.
Aldo Leopold 1949
•Nevertheless, the Leopold land ethic, rooted in
principles of ecology and evolution, remains as
the philosophical foundation for conservation
biology
Frances and Frederick Hamerstrom
Fragmentation and Metapopulations
•One common consequence of
fragmentation is the subdivision of a
formerly continuously distributed
populations into a metapopulation
•Typically, subpopulations exist in
patches of varying size and quality
•Larger patches with abundant, highquality resources tend to have more
persistent subpopulations – higher
reproduction and lower mortality rates –
that subpopulations in smaller patches
with poorer, fewer resources
Changes in wooded area of Cadiz
Township, Green County,Wisconsin,during
the period of European settlement.
Shaded areas represent the amount of
land in forest in each year
(Maffee et al 1997)
Sources and Sinks
•Persistent subpopulations may be a source
of new individuals that disperse to other
patches
•Source habitat = area where reproduction
exceeds mortality and from where
individuals disperse
•Subpopulations in small, poor patches may
persist in low numbers or be extinction prone
– sinks where dispersers either join the
existing population or recolonize the patch
•Sink habitat=area where mortality exceeds
reproduction
Florida Scrub Jays are cooperative
breeder, and an endangered species
with a metapopulation distribution
High quality oak scrub habitatat
Low quality oak scrub habitatat
•Population Modeling: Survival
probabilities of FSJ populations
“Monte Carlo” simulation techniques: natural
birth and death processes are allowed to
proceed each year indefinitely, until the
number of breeders is reduced to one or zero
(population extinct)
This is a stochastic, not deterministic,
approach to modeling (simulating) behavior of
populations
Repeat process for populations of different
initial sizes
•The process is repeated 100 times,
generating a frequency distribution of yearsto-extinction
•Assumptions include:
•each territory contains one pair of
breeding jays
•popul. is at carrying capacity to start
with – can not exceed initial size
•helpers per territory vary between 0-3
•yearlings don’t breed
Demographic (life history) values and their
annual variations used in computer simulation
of Florida Scrub Jay populations
Cumulative extinction probabilities versus
time for Florida Scrub Jay populations of
different maximum sizes measured in no.
of territories. Epidemic occur at random
intervals with a mean frequency of one
every twenty years
Same methods, but epidemic occur at
random intervals with a mean frequency of
of one every fifty years. Dashed lines
show analogous extinction curves for FSJ
pops. fragmented into 2,3 or 4 isolated
populations of 5 territories each