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1

Physiological Ecology

how an individual responds to its abiotic environment – Emphasis: responses of animals to fluctuations in temperature

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• Organisms live in constantly changing environments – Many temporal scales:

daily, seasonally, annually
• Variation may be predictable or unpredictable

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Fitness depends on

an individual’s ability to cope with environmental change

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To maximize fitness

an individual’s response to these changes must be shorter than the period of change

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Individual Responses
• Responses to environmental change fall into 3 categories:

1. developmental
2. acclimatory
3. regulatory

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Developmental (years)

irreversible
• Individual alters its development to produce a phenotype most suitable to a persistent
slow change in environmental conditions
E.g. Wing length in European freshwater Water Striders (genus Gerris) –
inhabiting temporary ponds
• Eggs hatch (spring)
• Adult lifespan is short (reproduce & die during one summer)

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Acclimatory

(days – weeks) - reversible • changes in response to seasonal variations
e.g. thickening of fur for winter
e.g. frost hardening in plants
= habituation of an organism’s physiological response to environmental conditions
• Acclimation – applied to laboratory
• Acclimitization – applied to nature
– Tolerances are not fixed but are preconditioned by the recent experience with environmental conditions

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Regulatory

(seconds–minutes)-reversible
• Rapid changes in behaviour or rates of physiological processes

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• animals vary in their responses to environmental change

1. conformers
2. regulators

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(1) Conformers

allow internal conditions to follow external changes

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(2) Regulators

maintain constant internal conditions

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homeostasis

ability to maintain constant internal conditions in a varying environment
• Always involves a negative feedback system

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negative feedback system

1. mechanism that senses the internal condition 2. means of comparing the actual with the desired
internal condition
3. apparatus that alters the internal condition in
preferred direction

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Temperature Regulation
• Another way to categorize animals:

• Poikilothermy (Conforming)
• Homeothermy (Regulating)

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Poikilothermy (Conforming)

cannot maintain constant body temperature
– Most amphibians, fish and insects
– Only active in a narrow range of temperatures

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• Homeothermy (Regulating)

maintain constant body temperature
– most birds and mammals ~ 36 – 410C (temp. at which biochemical processes
within cells are efficient)
– Highly active under varying temperatures

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• There are many ways in which organisms can regulate body temperature within a certain range...

-ectotherms
-endotherms

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• Ectotherms

regulate body temperature by gaining heat from external sources (Poikilotherm)
– Adv. - energy expenditure can be low
– Disadv. – growth, reproduction and survival is limited by temperature fluctuations
• Active only in a narrow range of temps

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• Endotherms

- regulate body temperature by the production of heat
(metabolism)
– Adv. – growth, reproduction & survival is not as affected by temperature
fluctuations
• Constant performance of biochemical reactions at a range of environmental
temperatures
• Active at a wide range of temperatures
– Disadv. - energy expenditure must be is high to maintain metabolic heat production

20

Limitations of Ectotherms

• Ectothermsmustbehaviourallygenerateheat
• Ectothermsgenerateheatwhenactive
– Every aspect of ecology and behaviour is influenced by the need to regulate body temperature
e.g. digestion in fish is strongly influenced by water temperature

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Limitations of Endotherms

• Endotherm’sabilitytomaintainconstantbodytemperatureis limited under low temperatures
– Short-term – by physiological capacity to generate heat
– Long-term – by ability to gather food (or energy) to satisfy requirements for
metabolic heat production
• animals usually starve to death before they die of direct causes of cold
temperatures
• Reduceenergeticcostsbyalteringtheloss/gainofheatfrom
environment in a number of ways...

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Energy Conservation - Endotherms

1. Lower the regulated temperature of a portion of their body
2. Lower the regulated temperature at certain times of the day
3. Become larger!

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1. Lower the regulated temperature of a portion of their body

E.g. Birds – legs & feet
– Counter-current heat exchange
– heat loss is minimized by reducing the temperature gradient between leg and
environme nt

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2. Lower the regulated temperature at certain times of the day

-torpor
-hibernation
Eg. Hummingbirds
Inactive at low temps:
• body temperature is regulated around a lower temp
• reduces heat loss to environment
• Otherwise would starve to death!

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torpor

temporary reduction in metabolic activity and lowered body temperature

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Hibernation

extended reduction... (e.g. over the winter)

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3. Become larger!

body size is one of the most important animal characteristics
– body size dictates the morphology, ecology, physiology and evolution of an organism
– the importance of body size in energy conservation lies in the surface area to volume ratio...

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Allometry:

Surface Area to Volume Ratio

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Allometric Relationship

= a relative increase in a physical or physiological property of an organism in
relation to its body size
As body size ^, V v faster than SA
As body size changes, SA/V ratio changes
As SA/V ratio changes, Heat loss to environment changes

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Consequences of Allometry

• Body heat is produced through metabolic processes (endotherms)
• The larger the V, the greater the total amount of heat required to keep warm ... but less heat is lost through the outer surface of the organism
• Consequence:
•Small Organisms:
• High SA/V
• Require less heat but hard to keep warm! •Large Organisms
• Low SA/V
• Require more heat but it is retained easier