Transcript Notes

BIOL 3240 Plant and Animal Ecology
Water Relations
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Water Availability
• The tendency of water to move down
concentration gradients, and the magnitude of
those gradients, determine whether an
organism tends to lose or gain water from its
environment.
– Microclimate important factor!
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Water Content of Air
• Evaporation accounts for much of water lost
by terrestrial organisms.
– As water vapor in the air increases, the water
concentration gradient from organisms to air is
reduced, thus evaporative loss is decreased.
– Would you buy a “swamp cooler” to help you
keep cool in the cypress swamps of southern U.S.?
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Water Content of Air
• Relative Humidity:
Water Vapor Density
Saturation Water Vapor Density
(x 100)
• Water vapor density is measured as the water
vapor per unit volume of air.
• Saturation water vapor density is measured as
the quantity of water vapor air can potentially
hold.
– Changes with temperature.
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Water Content of Air
• Total Atmospheric Pressure
– Pressure exerted by all gases in the air.
• Water Vapor Pressure
– Partial pressure due to water vapor.
• Saturation Water Vapor Pressure
– Pressure exerted by water vapor in air saturated
by water.
• Vapor Pressure Deficit
– Difference between WVP and SWVP at a
particular temperature.
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Evaporative Water Loss
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Water Movement in Aquatic
Environments
• Water moves down concentration gradient.
– Water is more concentrated in freshwater
environments than in the oceans.
• Aquatic organisms can be viewed as an
aqueous solution bounded by a selectively
permeable membrane floating in an another
aqueous solution.
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Water Movement in Aquatic
Environments
• If two environments differ in water or salt
concentrations, substances will tend to move
down their concentration gradients.
– Diffusion
• Osmosis: Diffusion through a semipermeable
membrane.
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Water Movement in Aquatic
Environment
• Isosmotic: Body fluids and external fluid are at
the same concentration.
• Hyposmotic: Body fluids are at a higher
concentration than the external environment.
• Hyperosmotic: Body fluids are at a lower
concentration than the external environment.
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Water and Salt Balance in Aquatic
Environments
• Freshwater Fish and Invertebrates
– Hyperosmotic organisms that excrete excess
internal water via large amounts of dilute urine.
• Replace salts by absorbing sodium and chloride at base
of gill filaments and by ingesting food.
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Osmoregulation by Freshwater
Organisms
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Water and Salt Balance in Aquatic
Environments
• Marine Fish and Invertebrates
– Isomotic organisms do not have to expend energy
overcoming osmotic gradient.
• Sharks, skates, rays - Elevate blood solute concentrations
hyperosmotic to seawater.
– Slowly gain water osmotically.
• Marine bony fish are strongly hypoosmotic, thus need to
drink seawater for salt influx.
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Osmoregulation by Marine Organisms
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Water Movement Between Soils and
Plants
• Water moving between soil and plants flows
down a water potential gradient.
• Water potential (Ψ) is the capacity to perform
work.
– Dependent on free energy content.
– Pure Water ψ = 0.
• Ψ in nature generally negative.
• Ψsolute measures the reduction in Ψ due to dissolved
substances.
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Water Movement Between Soils and
Plants
– Ψplant = Ψsolute + Ψmatrix + Ψpressure
– Matrix Forces: Water’s tendency to adhere to
container walls.
– Ψpressure is the reduction in water potential due to
negative pressure created by water evaporating
from leaves.
– As long as Ψplant < Ψsoil, water flows from the soil
to the plant.
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Water Regulation on Land
• Terrestrial organisms face (2) major
challenges:
– Evaporative loss to environment.
– Reduced access to replacement water.
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Water Regulation on Land - Animals
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Water Regulation on Land - Animals
• Wia= Wd + Wf + Wa - We - Ws
•
•
•
•
•
•
Wia=
Wd =
Wf =
Wa =
We =
Ws =
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Water Acquisition by Animals
• Most terrestrial animals satisfy their water
needs via eating and drinking.
– Can also be gained via metabolism through
oxidation of glucose:
• C6H12O6 + 6O2  6CO2 + 6H2O
– Metabolic water refers to the water released during cellular
respiration.
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Water Regulation on Land - Plants
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Water Regulation on Land - Plants
• Wip= Wr + Wa - Wt - Ws
•
•
•
•
•
Wip=
Wr =
Wa =
Wt =
Ws =
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Water Acquisition by Plants
• Extent of plant root development often
reflects differences in water availability.
– Deeper roots often help plants in dry
environments extract water from deep within the
soil profile.
• Park found supportive evidence via studies conducted
on common Japanese grasses, Digitaria adscendens
and Eleusine indica.
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Water Conservation by Plants and
Animals
• Many terrestrial organisms equipped with
waterproof outer covering.
• Concentrated urine / feces.
• Condensing water vapor in breath.
• Behavioral modifications to avoid stress times.
• Drop leaves in response to drought.
• Thick leaves
• Few stomata
• Periodic dormancy
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Dissimilar Organisms with Similar
Approaches to Desert Life
• Camels
– Can withstand water loss up to 20%.
• Face into sun to reduce exposure.
• Thick hair: Increased body temperature lowers heat
gradient.
• Saguaro Cactus
– Trunk / arms act as water storage organs.
– Dense network of shallow roots.
– Reduces evaporative loss.
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Two Arthropods with Opposite
Approaches to Desert Life
• Scorpions
– Slow down, conserve, and stay out of sun.
– Long-lived
– Low metabolic rates
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• Cicadas (Diceroprocta apache)
– Active on hottest days.
– Perch on branch tips (cooler microclimates).
– Reduce abdomen temp by feeding on xylem fluid of
pinyon pine trees.
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