MS130 - Biology
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Pete Markiewicz
Week 07
Web links week 07 - Ecology as a science
A parable of Easter Island
http://www.netaxs.com/~trance/rapanui.html
ECOLOGY VERSUS ENVIRONMENTALISM
Definition of ecological SCIENCE - study of living communities
Definition of Enivronmentalism - a political, moral, ethical belief system that we should/should not
interact with living communities in certain ways, based on ecological principles.
ECOLOGICAL PRINCIPLES OUTSIDE OF NATURE
Living Worlds (versus lame ones): The Ecology of Game Design
A good discussion of why games which echo real ecology and biology are
better than those that don't - also, how to apply ideas taken from biology and
ecology to game design.
http://www.gamasutra.com/features/20070508/carter_01.shtml
POPULATION BIOLOGY
Ecology arises from the study of interaction of populations of living
things with their physical (non-living) environment, and each other
The laws of population biology"
http://www.ecology.info/laws-population-ecology.htm
- Populations - groups of reproducing organisms of the same species.
Growth is modeled by birthrate versus death rate.
rate of change = (birth rate per
individual - death rate per individual)
The mathematical model based on this idea is that the population size
for one generation depends on the size of the previous generation, and it is
a multiple. This is expressed mathematically by the following equation:
http://www.arcytech.org/java/population/facts_math.html
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difference equation |
 |
|
| t |
represents the time period (which could be
minutes, weeks, years, etc. depending on the species being
considered), |
| pt |
represents the population size at time t. The
units of time could be hours, days, years, etc., |
| pt+1 |
represents the population size at the next time
period. Again, it could be the next hour, next day, next year,
etc., and |
| r |
referred to as the Malthusian factor, is the
multiple that determines the growth rate. |
MALTHUSIAN GROWTH MODEL OF POPULATIONS
Logistic Curve (shows cumulative growth or resources consumed over time)
- as resources become limiting, growth slows and stops. Growth is slow at early
stages, fast in the middle stage, slow at the end of resource depletion. Growth
may also be slowed by other factors (see carrying capacity description below). Formalized in math by Pierre Francois Verhulst in 1846
http://en.wikipedia.org/wiki/Logistic_curve
Hubbert Curve (derivative of logistic curve, shows amount of growth or
resources consumed at each timepoint) - shows that there is a "peak" or
resource utilization midway through the growth cycle. Afterwards, growth falls,
even though nearly half the resources are still available. Often used in "peak
resource" discussions.
http://en.wikipedia.org/wiki/Hubbert_curve
Malthusian Curve - developed by the Englishman Thomas R.
Malthus who did the early work in 1798 on the problem. His theories were
adapted by Darwin in his theory of natural selection.
http://www.szooek.slu.se/~EcoForest/Block1/naw/popgrow.htm
- Populations grow exponentially
- Resources grow slowly or not at all (arithematically)
- Population soon rises to to consume all available resources, and
may even (temporarily) "overshoot" resources.
- Population competes for declining resources (leads to Darwin's
theory of "natural selection")
- "Die off" - a portion of the population dies until resources
again exceed the survivor's needs
- Example for bacterial growth in a closed container with finite food
http://www.tulane.edu/~dmsander/WWW/109/Techniques.html
CARRYING CAPACITY AND POPULATION CYCLES
Carrying capacity is the maximum population size that a given habitat can
support. We’ll denote that as K. If the population is far below K,
it would tend to grow rapidly, but as it approaches K, the growth would
slow down. If the population size would exceed its upper limit K, the
growth would actually be negative
| rate of change |
 |
| full difference equation |
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- Forces determining carrying capacity (K)
- Finite food, water, air resources limit growth
- Waste products limit reproduction (environmental degradation)
- Competition between organisms for resources - one may deny
the other food, shelter
- Predators, parasites begin "culling" population (the enlarged
population becomes a new "resource" for them)
LAWS FOR POPULATION CHANGE
Derived from Malthus, carrying capacity concepts. Populations of living
things often enter cyclic population levels, with "boom" and "bust" eras, which
correspond to a set of linked Malthusian cycles. Species grow until their
"overshoot" carrying capacity and then decline.
- Lotka-Volterra law - A more complex version of the "difference
equations" above with two species (predator and prey). In a population with limited resources,
predators and prey numbers ultimately oscillate around a mean of the
carrying capacity in a negative feedback loop.
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Theoretical |
Experimental data |
- Additional population biology "laws"
- Leibg's law - In the set of predators and resources, one
of them is the limiting factor preventing unlimited population
growth
Example - iron in oceans limits plantkon growth, nitrogen in soil
limits growth of land plants
- Fenchel's, Calder's Generation/Time laws - for
plant-eaters, increasing body size increases time needed to
reproduce and decreases the rate of growth
- Ginzberg's law - Population growth in any one generation
is determined by the health of the previous generation - makes
growth "inertial" and capable of overshooting/undershooting carrying
capacity.
COMMUNITIES
Recurring assemblages of plants and animals,
having a consistent composition
http://www.globalchange.umich.edu/globalchange1/current/lectures/ecol_com/ecol_com.html
- A huge number of interlinked growth/decline cycles as shown
above
- Overall system is more stable than the individual cycles
- Origin - exploitation of resources, limits created by physical environment
- Co-evolution of predator and prey - one species treats another as a resource (all animals)
- Parasitism - special case of predator/prey
- Mutualism/symbiosis - two species come to depend on each other (e.g. insects, flowering plants)
- Competition - species compete for same resources (e.g. sunlight by trees)
- Example - headland stream community
http://www.globalchange.umich.edu/globalchange1/current/lectures/ecol_com/streamweb.gif
- Evolutionary "niche"
- A particular stable mix of resources, shelter within a community
- Formed by physical environment and other species present
- Complex communities have large numbers of niches
- A particular evolutionary strategy "creates" organisms ideally
adapted to exploit a given ecological niche.
BIOMES
- The resources of the physical environment (rainfall, temperature,
light) determine possible evolutionary niches
- A dominant ("keystone") species (e.g. grass) may alter the physical
environment to change existing niches, or open up new ones, eliminate others
by their presence.
- Interaction of resources and dominant species in a finite number of distinct physical
environments and environment-altering species
- Biomes - the finite number of possible environments
- Organisms occupy biome niches in similar ways, even if the
"players" (species) are different
- Earth's major "classic" biomes
- Rainforest - high rainfall, soil poor in nutrients, limited sesasons
- Temperate forestland - good soil, extreme seasons
- Alpine - reduced atmospheric pressure, UV light, low humidity, high
winds
- Tundra - soil below 1-2 feet permanently frozen all year, short, wet
summer
- Taiga - soil not frozen, cold, extreme winter conditions
- Prairie/grasslands - fertile soil but low rainfall/humidity
- Savannah - fertile soil with moderate rainfall (allows some trees to
grow)
- Desert - very limited rainfall
- Rivers - moving, highly oxygenated water
- Freshwater lakes - still, low-oxygen water
- Coral reefs - shallow water in deeper ocean, lots of shelter
- Coastal wetlands - shallow marine or fresh/marine water, tides, high
nutrient level from river deposition of sediment
- Oceanic - very low nutrient levels, high oxygen, no solid surface
- Hadal (deep ocean) - nutrients high, low oxygen, no light, water
temperature hovers near
freezing point, extremely high pressure
- Polar - extremely cold, high UV, dark 6 months of the year, waters
nutrient-rich
- Oceanic upwellings - cold water rises to surface, deposits nutrients
in warm, sunny water
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| Polar |
Taiga |
Grassland |
Oceanic |
- Newly described biomes
- Hydrothermal vents - no light, non-solar energy source in sulfides
released by vents
- Deep rock - microscopic pores with water connect through solid rock,
low nutrients, often high temperature, occasional nutrients areas (e.g.
oil deposits). Up to 2 miles below surface
- Clouds - ultra-low nutrient, high humidity, light, strong winds,
no solid surface, unstable
 |
 |
| Hydrothermal vent in the deep ocean on earth. The "black smoker"
releases superhot, sulfur-laden water into the environment,
providing a source of energy for chemoauthtrophic bacteria. |
Picture of Alvin submarine exploring a massive geothermal vent
structure several miles beneath the ocean surface. Click image for
more detail |
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| Enceladus, a moon of Saturn, showing cracks near the south pole
in which geysers of water under pressure have been detected. The
second image shows water vapor rising from a geyser. Click images
for more information. |
A model for water geyser production on Enceladus. The
pressurized liquid H2O pockets create a potential biome for
chemoautotrophic bacteria similar to geothermal vent biomes. Click
image for more information. |
ECOSYSTEMS
Definition - all organisms (in communities) plus the physical, non-living environment.
- Often display stable composition of living species over long periods of
time
- Energy and resource utilization is often constant
- Vary greatly in complexity
- The "players" (species) may change over evolutionary time, but the
overall ecosystem may remain with the same community structure, physical
environment.
HOW ECOSYSTEMS CHANGE OVER TIME
- Ecological succession example - burned or cleared field back to "old forest"
- Forest burns down completely, bare ground covered with ash
- Small weeds
- Larger weeds and shrubs
- Small trees
- Larger trees, shut out light to smaller trees and shrubs
- Low-light plants cover forest floor
- Organisms constantly compete, even in stable "climax" communities
- Competition leads to evolution
- Evolution constantly re-defines the "rules" of your community
(e.g. your prey gets smarter)
- Relationships with all organisms in in the community will change over time
- You must evolve constantly to maintain your position ("run in place")
- The result? Constant evolution, but relative stability of
ecological "players", and chance of extinction is constant over
evolutionary time
ENERGY AND MATTER FLOWS IN ECOSYSTEMS
Energy flows
- All living things in an ecosystem must process energy to survive
- Useful energy - the amount of energy converted into biomass (10%
or less of incident energy)
- Solar energy
- Used by most surface life
- Sunlight activates photosynthesis in plants ("autotrophs").
The energy of sunlight is used to construct the plant tissue from
inorganic compounds (CHON, minerals)
- Animals ("heterotrophs") eat their stored energy
- Decomposers draw the remaining energy from the bodies of
dead plants and animals, turn them into low-energy inorganic matter
(e.g. CHON)
- Plants, animals and decomposers all release stored energy
via respiration (see Week 02)
- Decomposed matter (much of it turned into gas) is re-used
by plants
- Chemo-synthetic energy (operates without the sun)
- Used by deep ocean vent and "deep rock" communities
http://www.biosbcc.net/ocean/marinesci/04benthon/dsvents.htm
- Some bacteria use chemical energy to construct their
tissue from inorganic CHON and minerals (plant-like)
- Animals store the bacteria in their bodies for food (vent
worms, vent clams)
- Animals eat the animals storing bacteria in their bodies
(plant-like)
- Decomposers convert animal bodies back to CHON
Matter flows
- Element cycles - movement of elements and compounds (carbon, water, phosphorus, nitrogen) through the ecosystem
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Model of geothermal vent showing temperature gradients,
matter flows and
location of microbes feeding off the chemical energy released.
Click image for more detail.
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Part of the oceanic iron cycle. Iron is normally a limiting factor
in ocean ecosystems - it is in short supply relative to the other
minerals used by photosynthetic plants. Part of the ocean's iron
budget comes from dust swept off the continents by dust storms. Dust
storms sweep iron-rich particles (mineral aerosols) from the
continents into the atmosphere. They fall into, or are rained into,
the oceans, where iron dissolves into a form that is used, along
with other nutrients such as nitrate (N) and phosphate (P), by
phytoplankton and bacteria to live and grow. Small marine animals
(zooplankton) eat phytoplankton and bacteria. When they excrete
fecal pellets or die, organic matter is transferred to the depths.
Credit: Jack Cook, Woods Hole Oceanographic Institution &
Astrobiology magazine
http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1915&mode=thread&order=0&thold=0
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FOOD WEBS, CHAINS, PYRAMIDS
Describes interconnections among species via matter AND energy flow -
complete description of ecosystem
(from:
http://www.geog.ouc.bc.ca/conted/onlinecourses/geog_210/210_2_5.html )
Ecological or "trophic" Pyramids - progressive loss of energy as it moves from
primary to secondary energy consumers
- Ecosystems spontaneously organize into pyramids
- 10-fold loss of energy at each level
- Energy loss translates to 1/10 biomass at each successively
higher level
- Reduced biomass translates to 1/10 the number of individuals
at each successively higher level
- Example of "trophic levels" in food chain for grassland
GO TO WEEK 08
