Ecology as a discipline can be subdivided into:

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Ecology as a discipline can be subdivided
into 1) Physiological Ecology - the adaptations
of individual organisms 2) Behavioural Ecology
- the behaviour(s) of individuals in an
ecological setting 3) Population Ecology - the
dynamics of groups of individuals living in
potentially reproductive groups 4) Community
Ecology - the dynamics of the groups of species
living together in a habitat 5) Ecosystem Ecology
- the processes that occur within a community
as an integrated unit 6) Landscape Ecology - a
new area that considers larger scale processes
among related ecosystems
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Well consider each of these approaches to
ecology basically in that order through the
semester. Physiological Ecology By example,
consider the adaptations necessary for
success 1) in a fresh water fish (a rainbow
trout)
Where did fish evolve? Under what physical
conditions? Are these the same conditions as
those where rainbow trout are found today?
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2) a desert lizard species (a Chihuahuan
whiptail)
What is the desert like (daytime and nighttime
temperature, water regime)? What adaptations
are necessary (activity time, place to spend hot
days, physiological adaptations to water limits)?
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We can consider physiological ecology to be the
study of adaptations to the physical conditions
of the environment. A species has tolerance to
some range of each abiotic factor, i.e.
temperature, water availability, salinity,
nutrient avail- ability. Here is a generalized
curve of distribution
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• In the range labeled as OPTIMAL ENVIRONMENT
• survival, growth, and reproduction can occur
• more individuals are found
• BUT
• In sub-optimal environments (zones of stress)
• individuals may survive, but growth rate will be
  lower
• reproduction is impossible or unlikely
• fewer individuals are found

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The concept of a tolerance limit is embodied in
Leibigs law of the minimum. It states Under
stable conditions, the essential constituent most
closely approaching the minimum for survival
(and/or reproduction) tends to limit the
occurrence of a species. An alternative
statement, stolen from a WWII movie A chain is
only as strong as its weakest link. (Hayakawa
via Cavett) When conditions are varying, this
law doesnt work very well. What was limiting
at one time may be abundant only a short time
later. The law of the minimum neglects the
possibility that there is too much of something
salt, calcium, temperature, water
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That led to the Shelford law of tolerance. In a
paraphrase A species will be found only
where its needs are met and its tolerances
are not exceeded.
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Temperature is one of the abiotic factors for
which tolerance limits are frequently
apparent. In the Rocky Mountains the distribution
of tree species is evidence of species specific
differences in tolerance...
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Another example (indicative of climate change
during the 20th century the change in the
position of treeline along the eastern shore of
Hudson Bay. The water of the Bay is colder than
latitude would lead you to expect, since water
enters Hudson Bay from the high arctic to the
west, then circulates through the Bay to exit on
the east. Tree line has moved 12km closer to the
water on the eastern margin, indicating a general
warming trend through the century
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One last example southern flying squirrels
(Glaucomys volans). They are small, nocturnal,
and fly by gliding. They are particularly
vulnerable to thermal stress. As they approach
their northern limit (45?N), animals huddle
together in their nest during colder months.
Otherwise the expenditure of energy to keep warm
would be too great. A key number is expenditure
of 2.5x basal metabolic rate. That also
parallels the range limit for a number of birds.
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The previous examples have dealt with low
temperature What about high temperature? Some
animals have physiological tolerance to a wide
temperature range, even during the course of a
single day The antelope ground squirrel of the
Mohave and Sonoran deserts forages during the
day, but must frequently withdraw to its burrow,
where it lies on the cool, moist soil and
dumps heat, before going back to foraging. The
squirrel is a homeotherm, but look at the core
body temperature variation it tolerates...
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In the deserts of the American southwest, 70 out
of 70 studied vertebrates use burrows. Most are
nocturnal, avoiding the heat of the day. Many
have physiological adaptations to accompany the
behavioural pattern.
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So that you dont think only of temperature
tolerance, heres the distribution of prairie
plants that characteristically grow on badger
mounds, separated along a soil moisture
gradient
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Water abundance and availability is another
common physical factor for which tolerance
determines distribution On prairie slopes (e.g.
eskers in Iowa and Nebraska) swales are more
mesic, and upper slopes more xeric.
Different grasses are found in different portions
of the slope.
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• Adaptations to the problem of water loss are
  necessary to
• live on land
• amphibians mostly remain in moist environments
• some animals have evolved relatively impermeable
  skin -
• keratinized skin of reptiles
• chitinous exoskeleton of invertebrates like
  insects
• behavioural adaptations like a fossorial
  strategy
• countercurrent exchange - warm air breathed in
  evaporates
• water from passages, cooling them. The cool
  passages then
• condense water from air being exhaled.
• desert animals have long digestive tracts that
  absorb as
• much water as possible before feces are
  excreted.
• how nitrogenous waste is excreted in urine...

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Urea and ammonia are relatively more toxic, and
must be excreted in dilute solution, costing
water. Uric acid is less toxic and can be
excreted in concentrated form.
Nitrogenous waste excretion
Organism Habitat Waste form Birds
Terrestrial uric acid Snakes lizards
Terrestrial uric acid Gastropods
Terrestrial uric acid Mammals
Terrestrial urea Amphibians Aquatic
ammonia Teleost fishes Aquatic ammonia
urea
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• Where does the water come from to support the
  needs of
• desert animals?
• drinking dew
• reduction of water excretion
• use of metabolic water
• Oxidative metabolism has water as a waste
  product.
• C6H12O6 6O2 ? 6CO2 6H2O
• For each gram of glucose metabolized, .6g of
  water is
• produced, for starch, 0.56g, and for fat an
  average of 1.02g
• Kangaroo rats can subsist on metabolic water and
  the small
• free water content in dry seeds when the
  relative humidity
• is gt10.

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So, we have most of the answers to understand how
the whiptail lizard survives desert
conditions. 1. use of metabolic water 2.
excretion of a concentrated urine of uric
acid 3. adaptation in the time of activity 4.
tolerance of variation in body temperature 5.
drinking dew 6. keratinized skin 7. long
digestive tract to resorb water . What about
the freshwater fish? Necessary adaptations are
related to salinity...
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• Life evolved in the sea. Cells and tissues in
  living organisms
• generally have salt concentrations similar to sea
  water.
• However, their environments may have radically
  different
• salt concentrations.
• Organisms have two approaches to deal with this
  problem
• they can be euryhaline - tolerate variation in
  salt
• concentration internally they are
  osmoconformers.
• they can be stenohaline - require a narrow range
  of salt
• concentration internally they regulate salt
  concentration in
• response to environmental variation, they are
• osmoregulators.

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Even in the marine system, at least near the
coastlines where fresh water enters the oceans,
salt concentration can vary widely. Some exposed
organisms are osmo- conformers, e.g. starfish and
oysters. Others are osmo- regulators, e.g.
crabs. In fresh water, osmoregulation is
necessary. Animals in fresh water are hypertonic
compared to their environment. Osmosis tends to
move water into their tissues. They have to get
rid of excess water. They excrete dilute
urine (teleost fishes urinate 1/3 of their body
weight per day). In the process, they lose
critical salts. The gills actively transport
those salts from the water into the fishs body.
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So, there is the answer to how the trout has
adapted to a freshwater environment 1. They
are osmoregulators. 2. They achieve regulation
by excreting a copious, dilute urine. 3.
They collect salts needed in their tissues by
active transport of needed ions.
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There are many ways achieve a goal. Marine water
is generally more saline than marine fish. Set
seawater at 100 of osmotic potential, and
compare it to the osmotic potential of fish and
sharks Seawater marine salmon shark Na
45 20 28 K 10
2 4 other 45 18
27 urea _0_ _0_ 41 ?
100 40 100 The shark brings its
osmotic potential equal to seawater with urea.
There is no net movement of water for the shark.
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For the marine salmon, osmotic potential is a
problem. With lower osmotic potential than
seawater, they tend to lose water, but need to
replace it. They drink seawater to replace it,
but the salt that comes with it must be excreted.
Excretion occurs across gills and kidneys at high
metabolic cost. So, the marine fish isnt better
off, it just has different problems.
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• What about plants?
• Youve already seen grasses and other prairie
  plants
• distributed along a water gradient.
• Where water is scarce, there are three approaches
  to permit
• plant survival and growth
• deep roots Adropogon gerardii, big bluestem,
  growing
• on the Ojibway prairie, can have roots 12
  deep, prairie
• roses can have roots gt20 deep.
• Prairie plants also tend to have very thick
  cuticles to
• minimize evaporative loss from leaf surfaces.

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Heres a basic comparison, not just for prairie
plants, but for differences on a larger scale
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How do roots pull water from the soil into the
plant? Answer osmotic pressure The osmotic
potential of the root tissues is higher (its
actually a large negative number), and water
moves from the soil into the roots. Because the
cell membranes are semi-permeable, water can
enter, but may solutes (larger ions) cannot
diffuse out. Root cells may also spend energy to
actively transport the samller ions that can get
through the membrane. The osmotic potential of
the roots of some desert plants can reach -60
atmospheres (at significant metabolic cost).
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Plants conduct water from roots to above ground
tissues and leaves through the xylem. How? The
water (osmotic) potential of the leaves must
exceed that of the roots. The difference must be
sufficient to work against both gravity and the
resistance of the xylem elements. That potential
is generated by transpiration. Dry air has a
water potential of -1,332 atmospheres. Add
humidity and that pressure drops, but is still
much more than enough to dry water up from roots
into leaves to replace water lost to
transpiration. The theory underlying this is
called the tension-cohesion theory. Heres the
diagram from your text
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• Reduced (or no) leaf surfaces - cactus in the
  New World
• Euphorbiaceae in the Old World can survive and
  grow
• using green stems, but no leaves

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• different photosynthetic systems - the most
  common type
• of photosynthesis is Calvin-Benson (or C3)
  cycle. The
• forward reaction binding CO2 requires a high
  concentration
• of CO2 to proceed.
• Alternate photosynthetic pathways, C4 and CAM,
  have
• much higher binding affinities for CO2 and, as
  a result, can
• proceed even with leaf stomates closed, so that
  evaporative
• water loss is greatly reduced.
• Here are what Calvin-Benson and C4 pathways
  (the binding
• steps) look like

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The binding process
Calvin-Benson or C3
C4 photosynthesis
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The third pathway is called Crassulacean acid
metabolism. A number of desert plants use it. In
CAM photosynthesis CO2 is assimilated at night
when water loss is minimized. The carbon is
stored in the form of malate, a 4-carbon
molecule. The rest of photosynthesis occurs
during the day with stomates closed. Both CAM
and C4 require higher light levels, and
are limited to open environments. Forest
species are all C3. Corn (Zea mays) is an
example of a C4 plant the Kentucky bluegrass on
the lawn outside is a C3.
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There is also an important anatomical difference
between these pathways. It has significant effect
on herbivores...
C3
C4 or Krantz anatomy
Note the difference in the spongy mesophyll and
bundle sheath!
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A short digression on biological adaptation to
nutrient availability the nutrient recovery
hypothesis Lemmings (like other microtine
rodents) undergo dramatic cycles in population
number with a cyclic period of about 4 years. For
lemmings, the cycling may well be related to the
nutritional quality of the plants they eat. There
is a strong correlation to phosphorus content of
the plants...
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Lemming number
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What is the take-home lesson from these various
examples of physiological adaptation? The
distributions of species indicate regions they
can reach and that have suitable conditions for
sustenance/growth/ reproduction. What limits
those distributions is the existence of some
limiting factor, whether insufficiently present
or overabundant. To achieve the distribution we
observe, species have evolved adaptations that
permit survival under conditions that are not
optimal. Today we have looked at adaptations in
the physiology of organisms. We will later
consider other types of adaptations.