Temperature and Water
Relations
biosphere
region
landscape
ecosystem
community
interaction
population
individual
Temperature and water are two
significant components of an
individual organism’s
environment
Individuals must regulate their
internal temperature and water
content – this occurs through
individual adaptations (history of
past individuals experiencing
similar environmental
conditions) and acclimation
(adjustments made by the
organism in response to a
change in current conditions)
Macroclimates are divided into many,
many microclimates
• microclimates
influenced by factors
like exposure, altitude,
and aspect
• organisms live in
microclimates
• temperature and
water availability can
show broad temporal
variation
Most species perform optimally within
a fairly narrow range of environmental
conditions
Temperature and individual
performance
• narrow optimal temperature range linked
to the structure and function of enzymes
• enzymes optimally bind their substrate
within a limited temperature range
• most enzymes have stable conformation at
low temperatures, but also low reaction rates
• increasing temperature increases reaction
rate, but excessively high temperatures cause
proteins to denature (lose their functional
shape)
• enzymes function best at some intermediate
temperature range (not too hot, not too cold)
Eastern fence lizards – temperature
and metabolizable energy intake (MEI)
Temperature and plant performance
• Extreme temperatures usually reduce the rate of
photosynthesis
• Like animals, plants usually perform
(photosynthesize) optimally within a narrow
temperature range
• Plants can also physiologically adjust their optimal
temperature for photosynthesis to accommodate
seasonal changes in temperature
Given their often limited range of
optimal temperatures and the
inevitable variation in temperature in
most environments, many organisms
have evolved ways to regulate body
temperature
Balancing Heat Gain Against Heat
Loss
•
HS = Hm  Hcd  Hcv  Hr - He
•
•
•
•
•
•
HS = Total heat stored in an organism
Hm = Gained via metabolism
Hcd = Gained / lost via conduction
Hcv = Gained / lost via convection
Hr = Gained / lost via electromag. radiation
He = Lost via evaporation
Temperature regulation
• Poikilotherms – don’t regulate internal
temperature; temperature varies with
environment
• Ectotherms – rely on external sources of
energy to regulate body temperature
• Endotherms – rely on internally derived
metabolic heat energy
• homeotherms: birds and mammals (maintain
relatively constant body temperature, as
opposed to certain fish and insects that only
heat critical organs)
Temperature regulation in plants
•
Heat storage reduction by desert plants:
HS = Hcd  Hcv  Hr - He
- decrease heating by conduction
- increase cooling by convection
- reduce radiative heating
Temperature regulation in desert plants
Arctomecon miriamii
Temperature regulation in arctic and
alpine plants
• Two main options for staying warm:
• increase heat gain via radiative heating (Hr)
• darkly pigmented leaves oriented perpendicular to sunlight
• decrease heat lost through convective cooling (Hcv)
• compact hemispherical growth form low to ground
Temperature regulation in arctic and
alpine plants
• Two main options for staying warm:
• increase heat gain via radiative heating (Hr)
• darkly pigmented leaves oriented perpendicular to sunlight
• decrease heat lost through convective cooling (Hcv)
• compact hemispherical growth form low to ground
Alpine cushion plant communities in the Andes
Temperature regulation in ectothermic
animals
• modify behavior to track optimal temperature via
radiative heating, convection, conduction (e.g.,
Eastern fence lizards)
• pigmentation can aid in radiative heating – may be
developmentally plastic trait (e.g., grasshoppers)
Temperature regulation in enothermic
animals
• also use behavioral and anatomical strategies to
regulate body temperature
• BUT, endotherms rely a great deal more on
metabolic heat to maintain body temperatures
within their optimal range
Thermal Neutral Zone
• range of environmental temperatures over which
an endotherm’s metabolic rate does not change
• in thermal neutral zone, metabolic rate is at steady
resting metabolism – metabolic rate increases
dramatically outside this zone
• the breadth of the thermal neutral zone varies
dramatically between different endotherms:
narrow in tropical species and much broader in
arctic species
Thermal Neutral Zones
Temperature regulation in aquatic
endotherms
• Water temperature much more stable than that of air
(takes much greater change in energy content to
heat/cool water)
• Convective and conductive heat loss in water is far
more rapid (20-100x) than in air
• Gills expose a large surface area to this vast heat sink
• Because of these constraints, few aquatic animals are
endothermic
Temperature regulation in aquatic
endotherms
Aquatic mammals – can be endothermic due to:
• Air-breathing (no gills)
• Insulation (blubber/fat or thick fur)
• Countercurrent heat exchangers (also found in
endothermic fish, e.g., tunas and white sharks)
Countercurrent Heat Exchange
• Vascular arrangements reduce the amount of heat loss to the
aquatic environment
Temperature regulation in endothermic
insects
• Bumblebees use metabolic heat to warm their flight muscles
• Large moths maintain fairly constant metabolic rate and regulate
temperature via conductive and convective cooling / heating
Endothermic Plants
• Some plants generate metabolic heat derived from energy stored
as starch
• Generally used as part of pollination system (e.g., heating up
volatile substances to attract insect pollinators
• Particularly prevalent in the Aroid lilies
Surviving Extreme Temperatures
• Inactivity: in ectotherms and endotherms - seek shelter during
temperature extremes
• Reducing Metabolic Rate: in endotherms - when energy supply in
environment (in form of heat or food or both) is not adequate for
supporting normal metabolism
• Torpor (usually only lasts a short time, i.e., one night)
• hummingbirds
• Hibernation (winter)
• bears
• Estivation (summer)
• dwarf lemur
Water relations
• Most organisms are 50 – 90% water
• Life originated in salty aquatic environments, and the signature of
these origins can still be found in our biochemistry
• To survive, organisms must maintain the appropriate internal
concentrations of water and dissolved substances
• Water and solute concentrations are regulated through the
control of water loss and gain
Water Availability
• The capacity of water to do work (i.e., flow) is known as water
potential
• The movement of water down concentration gradients ultimately
determines the amount of water available to organisms in both
terrestrial and aquatic environments
Water Availability – Aquatic organisms
• in aquatic environments, water moves from areas of higher
concentration (fewer solutes) to lower concentration (greater
solutes), a process known as osmosis
• Isosmotic – internal and external concentrations of water and salt
are equal
• hyperosmotic – internal concentration of salt is higher than that in
the environment, water concentration lower than that in
environment: water moves into organism, salts diffuse out
• hypoosmotic – internal concentration of salt is lower than that in the
environment, water concentration higher than that in environment:
water moves out of organism and salts diffuse in
Water Availability – Terrestrial Plants
• in terrestrial systems, water moves from areas of high water
potential (wet soil) to areas of lower water potential (plant
vascular tissue, and eventually, air)
Ψplant = Ψsolute + Ψmatric + Ψpressure
– Matric 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.
Water Regulation – Aquatic animals
• Sharks: hyperosmotic – water diffuses into the shark’s body
through the gills. Sharks excrete urine to compensate for water
gain
• Marine bony fish are hypoosmotic – water diffuses out of the fish
through the gills. These fish drink sea water to compensate for
water loss, excess salts that are also taken in with sea water are
excreted with urine and by specialized cells in the gills.
• Freshwater fish are hyperosmotic – water diffuses in through the
gills, is excreted as large quantities of dilute urine. Salts lost with
the urine are replaced by specialized cells in the gills that absorb
chloride ions from the water. Salts also taken in with food.
Water Regulation – Terrestrial Animals
• Animals get their water from:
• Drinking
• Food (both directly and through the metabolic breakdown of sugars)
• Air
• Animals lose water through:
• Evaporation
• Excretions
Water Regulation – Plants
• plants get their water from:
• Soil
• Air
• plants lose water through:
• Evaporation (transpiration)
• Secretions (nectar, seeds, fruit)
Terrestrial Water Conservation
• Possible ways to conserve water:
• Thick / waterproof cuticle to keep water in
• Dense hairs to reduce evaporation and heat gain
• Limiting activity to times or places where evaporative water loss is
reduced
• Drinking lots of water to compensate for evaporative water loss
• Storing large quantities of water in your body
• Increasing the ratio of volume / surface area
• Periodic dormancy
Poikilohydry
Not all terrestrial organisms regulate their internal water
content
Mosses and other bryophytes are poikilohydric plants: they
lack vascular tissues for water transport as well as stomata
Internal water content quickly equilibrates with that of the
environment
Poikilohydry and Desiccation Tolerance
Because they are poikilohydric, many bryophytes
only grow in places that never dry out completely
Other bryophytes evolved the ability to survive the
loss of nearly all (>90%) of their cellular water
content: Desiccation tolerance
Tortula ruralis
Craterostigma plantagineum