Temperature Relations
Reading: Molles & Cahill 2008 – Chapter 5
Ecophysiology (Physiological Ecology):
• considers physiological responses of
individual organisms to environmental
conditions.
• Today we will consider individual
responses to temperature.
– Note that this topic is often related to water
(our next topic.)
Temperature responses have both
genetic and environmental components
• Acclimation – physiological adjustment to
environmental conditions over an
individual’s life.
• Adaptation – evolutionary adjustment (via
genetic traits) to environmental conditions
over the long term.
Key terms:
Long-term
response
Adaptation - evolutionary response - Genetically fixed
Acclimation –physiological adjustment
Controlled by organism
Behavioral responses (“strategies”)
Short term
response
These terms differ according to the time frame and mechanism of response.
Key terms (continued)
• Macroclimate – what affects biome distributions, and
what we measure with weather stations (affected by
altitude, season, etc.)
• Microclimate – what individual organisms experience
(affected by slope, aspect, albedo, height off the ground,
proximity to water, behavior, etc.)
Macroclimate and microclimate are inter-related
(e.g. microclimate is partly determined by
macroclimate)
Temperature and moisture are two factors that vary
dramatically with macro/microclimate
Examples of factors influencing
microclimate
•
•
•
•
Slope and aspect
Proximity to neighbors (“nurse plants”)
Albedo (reflectivity)
Proximity to water (thermal mass)
Slope (steepness) & aspect (direction of slope) affect temperature and moisture
Fig. 5.2, Molles & Cahill 2008
Proximity to neighbors – e.g. “Nurse plant effect” –affects microclimate
The presence of a “nurse plant” often enables germination and survival of younger
plants, particularly in hot climates.
Molles 2008
Albedo (reflectivity) affects microclimate
White vs. black sands
Snow vs. soil background
Fig. 5.4, Molles & Cahill 2008
Proximity to water affects microclimate
Large water bodies with their high thermal mass (heat capacity) tend to buffer
temperatures
Fig. 5.7, Molles & Cahill, 2008
…Note the thermal stability of water, compared to air
Molles 2008
Thermal tolerance
Some organisms must exist within a narrow temperature range
in order to function – this temperature range defines their “thermal tolerance”)
Understanding tolerance limits and how they affect fitness and distributions
of organisms have been central topics in physiological ecology.
Temperature response curves
of bacteria
Psychrophilic bacteria
from Antarctica
Thermophilic bacteria
from hot springs
Adaptation or acclimation? How can we tell?
Figs. 5.14 & 5.15, Molles & Cahill, 2008
Temperature response curves
in plants
Plants from contrasting biomes
Transplant experiments
… but is this a genetic adaptation
or phyiological acclimation?
… reveal physiological
acclimation
Figs. 5.12 & 5.13, Molles & Cahill 2008
Evidence for acclimation in fish
Further evidence for physiological acclimation at a biochemical level
Fig. 5.10, Molles & Cahill 2008
“Energy Balance”
• A quantitative analysis of an organism’s
response to microclimate.
• Derived from the First Law of
Thermodynamics (conservation of energy)
• Provides a formal, mathematical way to
understand temperature responses.
One version of the energy balance equation
Where:
(Molles 2008)
Hs = heat storage by organism
Hm = heat gained by metabolism
Hcd = heat gained or lost via conduction
Hcv = heat gained or lost via convection
Hr = heat transferred through radiation/re-radiation (radiative transfer)
He = heat lost via evaporation (vaporization)
Organisms control their energy balance through adaptation, acclimation,
and behavioral responses
Terminology related to temperature:
• Endotherms – metabolic control over body
temperature. (e.g. homeotherms must
maintain constant body temperature – e.g.
mammals) – formerly called “warmblooded”
• Ectotherms – body temperature controlled
by environment (poikilotherms – e.g. most
reptiles & plants) – formerly called “coldblooded”
Terminology related to temperature:
• Endotherms – metabolic control over body
temperature. (e.g. homeotherms must
maintain constant body temperature – e.g.
mammals) – formerly called “warmblooded”
• Ectotherms – body temperature controlled
by environment (poikilotherms – e.g. most
reptiles & plants) – formerly called “coldblooded”
Endotherms vary metabolic rate
to maintain a constant temperature
Note how the
“thermal neutral zone”
defines the optimal
temperature for an
endotherm
Fig. 5.25, Molles & Cahill 2008
“Thermal neutral zones” for arctic and tropical mammals
Fig. 5.26, Molles & Cahill 2008
Manduca sexta (moth) – an example of an endotherm
Fig. 5.30, Molles & Cahill 2008
Plants are normally ectotherms, but some plants can be endotherms!
(use metabolically generated heat to warm the plant body)
Figs. 5.31 & 5.32 - Molles & Cahill, 2008
Terminology related to temperature:
• Endotherms – metabolic control over body
temperature. (e.g. homeotherms must
maintain constant body temperature – e.g.
mammals) – formerly called “warmblooded”
• Ectotherms – body temperature controlled
by environment (poikilotherms – e.g. most
reptiles & plants) – formerly called “coldblooded”
Lizards are a good example of ectotherms
– use external energy to regulate body temperature.
Lizards exhibit behavioral responses to
maintain an optimal temperature
Fig. 5.21, Molles & Cahill 2008
Molles 2008
Evidence of genetic constraints on optimal temperature in lizards
Fig. 5.11, Molles & Cahill 2008
Like lizards, many plants use behavior to
adjust their energy balance
Darwin, C. (1880) The Power of Movement in Plants
http://en.wikipedia.org/wiki/Nyctinasty
Some plant organs (leaves and flowers) can alter their temperature through
“heliotropism” (solar tracking - following or avoiding the sun).
These arctic flowers act as solar-tracking parabolic reflectors, directing the heat to
the ovaries and hastening seed production.
Papaver radicatum - Arctic poppy
Dryas integrifolia
(Images from Wikipedia)
Plants adjust their temperature by a variety of responses
(adaptation, acclimation, and behavior)
Fig. 5.16, Molles & Cahill 2008
Fig. 5.19, Molles & Cahill 2008
What do organisms do when temperatures
exceed their range of thermal tolerance?
Get dressed!
Escape!
Die!
Certain mammals hibernate to avoid temperature or moisture extremes
Molles 2008
Limits to thermal tolerance:
extinction of local snail populations in Switzerland with warming
Molles 2008