Bio205H5: lecture 2
physiological ecology
tolerance
intolerance
Q: How does the ability of an organism to
cope with its abiotic environment influence
its distribution, abundance and interactions
with other species?
stress
intolerance
ecophysiology = physiological responses
of individual organisms to abiotic factors
organism response
stress
low
factor
high
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phenotypic plasticity:
responses to abiotic factors:
• genotypic (selection → adaptation)
• phenotypic (plasticity; reaction norms)
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reaction norms
• reaction norm = range of phenotypes
produced by a genotype under different
environmental conditions (phenotypic
plasticity)
• ideally: look at genetically identical
individuals over range of conditions
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reaction norms:
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comparing reaction norms:
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genetic x environment interaction:
Genotype 2
Genotype 1
e.g. height
phenotype:
phenotype
Genotype 1
Genotype 2
environment
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time scales of responses to abiotic
factors:
environment
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developmental responses:
1. Evolutionary
- over generations (∆ in allele frequencies)
- genotypic (adaptations)
2. Developmental
- within lifespan of organism
- abiotic factors can irreversibly influence
development of an individual
• responses to environmental conditions
during ontogeny (development)
e.g. temperature - dependent sex
determination (TSD)
most lizards, turtles,
crocodiles
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e.g. reproductive maturation in whitefooted mice:
day length:
• affects testicular
development in juveniles
• some breed in year of birth;
some don’t
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-
3. Biochemical / physiological
timescale
measured in units much less than the
lifespan of an individual
• acute responses (e.g. transient
increase in metabolic rate with temp)
• gradual responses (e.g. seasonal
changes in metabolic rate with temp)
acclimation response
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How do organisms cope with abiotic
factors?
•
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results from exposure to new conditions
may be regular or unpredictable changes
seasonal; daily; etc.
reversible
e.g. Arctic fox:
summer phase
winter phase
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1. Avoiders
• in space:
alter microhabitat
alter macrohabitat (migrates)
3 main strategies:
1. avoidance
2. conformity
3. regulation
• in time:
e.g. diapause; torpor
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conformers:
2. Conformers: undergo changes of
internal state similar to external
environment
3. Regulators: maintain internal
environment regardless of external
conditions (homeostasis)
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mixed strategies:
regulators
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temperature relations
• temperature has profound effect on
organisms
• climate broadly defines species
distribution: e.g. trees in N. Am.
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• conduction: movement of heat between
solids in contact
Q: How does heat transfer between
organisms and environment?
• convection: movement of heat between
solids and fluid (gas or liquid)
Heat (energy) transferred by:
1. conduction
2. convection
3. radiation
• radiation: transfer of heat through
electromagnetic waves (infrared)
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heat gain and heat loss
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evaporation
solar radiation
H s = H m ± H cd ± H cv ± H r − H e
radiation
from vegetation
convection
radiation
from animal
s = stored heat
m = metabolic heat
cd = conduction
cv = convection
r = radiation
e = evaporation (1-way transfer)
reflected
solar radiation
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conductance
from ground
radiation
from ground
conductance
to ground
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effects of temperature
psychrophiles
-50°C
thermophiles
100°C
• most organisms: much narrower range!
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extreme temperatures:
• many species have broad geographic
distributions
extreme low temp: freezing of body fluids
- ice crystals damage cells
- osmotic movement of water → ECF
precipitates enzymes
• many live in seasonal environments
• how do they cope with temp extremes
and temp variation?
extreme high temp: denaturation of
enzymes, DNA
- brain damage, middle ear (equilibrium)
no vertebrate can tolerate ≥ 50°C
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temperature affects physiological
processes
• reaction rate:
R2 = R1 ( Q10 )
Q10 =
T2 − T1
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increase in reaction rate for every 10°C
increase in temperature
often ~ 2 - 3
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metabolic rate and temperature
temp effects on plants:
•
• effect on photosynthetic rate
•
metabolic rate → physiological
“performance”
enzymes function best in narrow range of
temp
How to ensure that physiological
performance is optimal over a range
of temperatures?
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adaptations to thermal regime
recall: 3 strategies
1. avoid
• don’t function under temp extremes
poikilotherm = thermal conformer
- body temp ≈ ambient temp
- body temp varies
2. conform
• body temp ≈ ambient; function
maintained
homeotherm = thermal regulator
- body temp ≈ constant (usually >
ambient)
3. regulate
• maintain body at optimal temp
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contrast: variability (constancy) of body
temp
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however.....
ectotherm = body heated externally
- e.g. basking etc.
ectothermic homeotherms = body temp
constant, but dictated by env’t
endotherm = body heated internally
e.g. deep sea fish
contrast: source of body heat
endothermic poikilotherms = body heated
internally, but varies
usually : poikilotherm = ectotherm
homeotherm = endotherm
e.g. naked mole-rat
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Ectotherms: don’t regulate temp internally:
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avoid activity in extreme temps
• dormancy
burrow under frost line, underwater
• freeze tolerance
e.g. wood frogs: can’t dig;
hibernate in leaf litter;
actively control freezing: proteins
nucleate ice crystals
in ECF
1. avoid extreme temperature
• in space: migration
e.g. monarch butterfly
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oxygen consumption
Consider: fish at 5°C; acute change to 25°C
acute response:
increase in metabolic
rate with increasing temp
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Oxygen Consumption
2. conform:
maintain function at “sub-optimal” temps
fish allowed to acclimate to 25°C
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full compensation
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0
10
20
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Temperature °C
0
10
20
30
40
temperature °C
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• molecular/cellular changes can permit
physiological function at varying
temperatures
compensation involves molecular
changes
• expression of isozymes (alternate forms
of enzymes)
• e.g. goldfish: alter expression of heavy
and light myosin chains in muscle at low
temp
• changes in abundance
of mitochondria
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3. regulate:
• ectotherms do not regulate temperature
internally
• manipulate heat exchange with environment
• compensation allows ectotherms to
avoid effects of temp on metabolic rate
- not sluggish in polar regions
- not hyperactive in tropical regions
in ectotherms, metabolic rate can be
independent of ambient temp
(not true of endotherms!)
basking to warm
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burrowing to cool
can maintain optimal temperatures
through behavioural adaptations
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plants are poikilothermic
ectotherms
•
usually do not produce significant
amounts of metabolic heat
•
1.
2.
3.
most terrestrial env’t fluctuate in temp
avoid
conform
regulate
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conform:
• molecular adaptations that permit
photosynthesis at temp extremes
plants can avoid:
• grow in microhabitats that are sheltered
from prevailing conditions
e.g. clover:
arctic saxifrage
produces cyanide in
response to cold
temp
moist slope has trees,
dry slope doesn’t
protects from freezing
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regulate:
• morphology & behaviour regulate heat
exchange with environment
• alter Hr = heat from radiation
• alter Hcv = heat from convection
• alter Hcd = heat from conduction
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• some plants use metabolic heat to warm
flowers
• e.g. skunk cabbage:
large root stores starch
• moved to inflorescence
• burned at high rate;
generates heat
• regulates temp
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next lecture:
• temperature and water relations continued
• introduction to life-histories (Chapter 12)
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