Transcript - Catalyst

TESC 211
The Science of Environmental Sustainability
Autumn Quarter 2011 UWT
The tectonic plates “drift” on the planets mantle, consequently:
• The movement of the continents has allowed species to
migrate, adapt to new environments and form new species.
• The location of the continents and the World’s oceans
greatly effects its climate.
• Climate can be defined as the long term weather in a
particular location over at least 30 years.
• Over the Earth’s history its climate has varied
significantly and has been a driving force for evolution
When the process of evolution leads to an entirely new species
this is referred to as speciation.
Most commonly this is a result of:
• Geographic isolation
• a portion of the population becomes physically
separated
• Reproductive isolation
• genetic mutations operate differently in
geographically isolated populations
• eventually, may give rise to individuals so different
they cannot successfully reproduce.
While speciation serves to increase the number of species,
extinction serves to decrease the number.
Endemic species (those that exist in a single location) are
especially vulnerable to extinction.
It is estimated that the “back ground extinction” rate has been
1-5 species per year for every 1 million species on Earth.
Periodically there have been events that result in mass
extinctions in which 25-90% of all species became extinct over a
few million years.
These mass extinctions have occurred at intervals of 20-60
million years apart of the last 500 million years.
There is evidence that the rate of extinction is higher now than at
any time in the past 65 million years. Many scientists attribute
these extinctions to human activities?
Is this consistent with a human induced mass extinction?
Populations can grow, shrink or remain stable:
This determined by four variables:
Population change = (births + immigration) – (deaths + emigration)
The capacity for population growth under ideal conditions is
termed a species “biotic potential”
Typically, large species have a low biotic potential while smaller
species have a high biotic potential.
Environmental resistance is the combination of all factors that
act to limit the growth of a population.
Hence, biotic potential and environmental resistance
determine the carrying capacity (K).
What is the carrying capacity?
The maximum population of a species a habitat can maintain
indefinitely without degradation.
A key question in sustainability science is what is the human
carrying capacity?
Different species have different reproductive strategies:
Species with high biotic potential often have many small off-
spring and provide them little parental care.
Recruitment (survival to breeding age) tends to be low with this
strategy.
Species with this strategy tend to be opportunists and under go
rapid population growth when conditions are good.
When conditions are less favorable their populations may crash.
Mice resulting from 4 nights trapping during a
mouse plague in Victoria, Australia, 1917
Locust Plague 11th Apr 2010 QLD
Australia (the golf tournament
went ahead)
An alternative strategy is to have a few off-spring with fairly long
life spans.
This is the strategy adopted by competitor species.
• Tend to produce later in life
• Off-spring well developed when born
• Mature slowly
• Well cared for until reproductive age (1 or both parents,
possibly a whole herd)
“J-curve crash” (often observed for
Stable logistic growth (often observed
opportunistic species)
for competitor species)
Lets look at real data for sheep in Tasmania
“Dieback”
However, when the population exceeds the carrying capacity
irreversible population crashes may occur.
1944 reindeer (29) introduced to St. Matthew Island .
Population increased to 6,000 by the summer of 1963 and
underwent a crash/die-off the following winter to less than 50
animals (only 1 male known to have survived by 1966)
When environmental resistance factors are density dependent
the population generally remains within a certain range.
• When population increases environmental resistance
increases and growth slows.
• When population decreases resistance lessens and growth
increases.
Some environmental resistance factors are density independent.
• Population has no impact on environmental resistance
(mortality, fertility)
Often abiotic factors:
• Fires
• Sudden deep freeze
• El Nino
A central question in population management is:
“how many of a particular species can be removed without
destroying the stock?”
We shall build up a simple population growth model to explore
this idea.
Consider a population of a single organism which produces a
single off-spring each reproductive cycle.
Cycle 3
This is called exponential
Population
population growth.
Cycle 2
Notice there is no limit to the
population.
Cycle 1
After a few cycles the population
increases very rapidly
Time
Is this how real populations grow?
Population
1000
800
600
400
200
0
0
2
4
6
8
10
Reproductive cycle
Simple exponential models neglect a several key points
• Not all the population participates in each cycle of
reproduction
• There is a maximum sustainable population determined
by the resources available.
12
Population
10
Sexual maturity
8
6
Age limit
4
2
0
-200
300
Age
800
At anyone time only a fraction of the population is reproducing
Eventually some members of the population die (or leave through
migration).
We should develop models that take these factors into account.
1.2
Carrying capacity (K)
Population
1
Slow growth
0.8
0.6
Rapid Growth
Slope of curve is equal
to rate of population
growth.
0.4
Slow growth
0.2
0
-6
-4
-2
0
2
4
6
8
10
Time
One common improved model is called the “logistic growth”
while being a long way from perfect it is a substantial
improvement on the simple exponential model.
0.25
Maximum sustainable yield
(MSY)
Growth rate
0.2
0.15
Maximum growth
0.1
Slow growth
0.05
Slow growth
0
0
0.2
0.4
0.6
Population
0.8
1
1.2
How can we find an indicator that lets us know how close we are
to the maximum sustainable yield?
If we know the carrying capacity (K) we can approximate the
maximum sustainable yield by K/2.
In reality it is unlikely we will know this.
However what is found is that a plot of “yield” versus
“harvesting effort” displays the same relationship as the MSY
curve.
• Use harvesting effort and yield as indicators of how
close we are to MSY.
Growth rate
0.25
0.2
0.15
Sustainable use of the resource
0.1
0.05
MSY
0
0.25
0
0.2
0.4
0.6
0.8
1
Population
Yield
0.2
0.15
0.1
0.05
0
0
0.2
0.4
0.6
0.8
1
1.2
Harvesting effort
If we find that we increase our harvesting effort and there is no
increase or a decrease in yield then we are exceeding the MSY
1.2
In the “classical” form we have been discussing MSY excludes
the effects of:
• Competition between species
• Symbiotic or commensal relationships between species
• Trophic (feeding) relationships
• Changes to carrying capacity due to Human influences
• Changes to carrying capacity due to “extreme” natural
phenomena
There have been some spectacular failures of the MSY concept
to successfully predict unsustainable resource use.
e.g. the collapse of the Peruvian anchovy fishery in 1972.
Anchovies are a traditional indicator of El Niño
• Fisherman would notice decreased yield in El Niño years
Pre-1972 the Peruvian anchovy fishery was the World’s largest.
The productivity of this fishery was largely the result of the
upwelling of nutrients from deep in the ocean.
At its peak the Peruvian anchovy fishery was responsible for
~22% of the World’s total fish catch.
Even in 1971, immediately prior to its collapse, ~15% of the total
global catch came from these waters.
What went wrong?
The MSY of the fishery was estimated to be ~10 million tonnes by
plotting yield against fishing effort (“million tonne trips”)
MSY
0.25
Yield
0.2
0.15
0.1
0.05
0
0
0.2
0.4
0.6
0.8
1
1.2
Harvesting effort
Although the anchovy were heavily exploited in the 1950’s and
1960’s this was within the estimated MSY.
However, this modeling failed to take into account several key
factors:
1. Anchovy and sardine have a relationship in that a
drop in the population of one species leads to a
growth spurt in the population of the other.
As a result the Peruvian fishery has transformed from one
dominated by anchovy to one dominated by sardine
2. The upwelling in the Pacific is disrupted due to the El Niño
event every 2 to 10 years.
In 1972 there was an El Niño event, this results in a growth in the
population of Horse Mackerel that feed on anchovy. Heavy
fishing (within estimated MSY) was allowed to continue.
Ultimately the fishery collapsed.
What were the social consequences?
Resulted in the loss of ~10% of global resource:
• Fishing fleet cut from 1500 to 800 boats.
• Fish processing plants reduced from 100 to 50
• Number of people employed reduced from 25000 to
12000.
“Here lies the concept MSY
It advocated yields to high,
And didn’t spell out how to slice the pie,
We bury it with the best of wishes,
Especially on behalf of fishes”
Larkin, 1977
However, MSY is far from “buried” and continues to be used
extensively in fisheries management.
In 1992 the UN identified at least six SI’s that relied on MSY as a
result of the discussions at the Rio Earth Summit.
1. Ratio of MSY to actual abundance
2. Deviation of stock from MSY
3. Ratio of current fishing effort to effort at MSY
4. Ratio of spawning biomass to MSY
Etc…..
In 2006 as part of F0.1 objective the European Union stated:
“The European Commission considers implementing fish stocks
management systems based on the maximum sustainable yield
will contribute to reverse the decline in fish stocks”
Similarly, criticism of management models based on MSY
continues.
“the supposed catch-effort relationship underlying the concept of
MSY is apparently illusory. The level at which these stocks are
“sustainable” is unknown and is unlikely to be unknown for many
years, if ever” (Aikman 1997)
Why does MSY continue to be used almost unquestionably
despite concerns being raised by scientists for several decades?
• Its simplicity has resulted in its use by non-scientists for
purposes it was never intended.
• MSY has become institutionalized, once this occurs it is
very difficult to introduce new (better) concepts.
We had previously defined a biome as:
“a grouping of ecosystems of a similar type”
Major terrestrial biomes include:
• Desert
• Grasslands
• Forests
• Mountains
The reason why regions are of one biome and not another is a
largely a result of climate.
What factors impact climate?
• Location with respect to bodies of water
• Altitude
• Latitude
Hikers rule of thumb of :
“for every 1,000 foot rise in altitude there is a 4°F drop in
temperature”
Is found to be surprisingly accurate.
Deserts can be defined as:
“regions where evaporation exceeds precipitation”
Characterized by:
• scattered, low precipitation rates
• little vegetation, thus, heat rapidly lost from ground.
• slow rates of nutrient cycling
• low species diversity
Consequently, deserts are fragile ecosystems.
Grasslands tend to occur in the interior of continents:
Characterized by:
• more rainfall than deserts but less than forested areas
• often affected by drought and fires
• resistant to grazing herbivores
As Grasslands are ideal as sites for growing crops and grazing
life stock which they are under increase threat by human
activities as demand for food increases.
Forests are lands dominated by trees:
• biodiversity is greater here than in grasslands or deserts
• many types including:
• tropical rain forests
• deciduous forests
• Evergreen coniferous forests (taigas or boreal
forest)
• Coastal coniferous forests
Mountains occupy about 25% of the Earth’s surface.
•They play major roles in modifying the Earth’s climate
(reflection from snow and ice)
• Storing water
• Contain majority of Earth’s forests
The 2005 Millennium ecosystem assessment ~62% of the World’s
major terrestrial ecosystems are being degraded or used
unsustainably.