Topic 5 - Animals & Environmental Variability (BIOL 2300)

physiological ecology

how an individual responds to its abiotic envr.

• emphasis: response of animals to fluctuations in temp. (determines all the biochemical interactions in animal & plant bodies)

what does fitness depend on

individiua’s ability to cope with environmental change

what must be done to maximize fitness

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

3 categories of responses to environmental change

1. developmental (years)

2. acclimatory (days - weeks)

3. regulatory (seconds - minutes)

developmental (years) - individual responses

• individual alters its development to produce a phenotype most suitable to a persistent slow change in environmental conditions

• typically irreversible

acclimatory (acclimation) (days -weeks)- individual responses

• changes in response to seasonal variations 

• e.g. thickening of fur for winter

• e.g. frost hardening in plants

acclimatory - definition

habituation of an organism’s physiological response to environmental conditions

acclimation

applied to laboratory

acclimatization

applied to nature

regulatory (seconds - minutes) - individual responses

• immediate rapid changes in behavior or rates of physiological processes

• e.g. shivering in animals

• e.g. open/close stomata in plants 

compare & contrast 3 categories of responses to envr. change

1. developmental (years): not reversible, individual alters its development to produce a phenotype most suitable to a persistent slow change in environmental conditions

2. acclimatory (days - weeks): reversible, changes in response to seasonal variations, shifts in the ranges of the regulatory responses, e.g. thickening of fur for winter

3. regulatory (seconds - minutes): reversible, rapid changes in behavior or rates of physiological processes

• e.g. shivering in animals

• e.g. open/close stomata in plants

conformers - variation in regulatory responses

allow internal conditions to change withe external changes

(any kind of internal conditions, not just temp.)

regulators -variation in regulatory responses

maintain constant internal conditions under external changes

homeostasis

maintenance of relatively constant internal conditions under external changes

• always involves a negative feedback system

1. sensor: way to sense internal conditions and compares to set point

2. response: way to alter the internal conditions to set point

thermoregulation

maintaining internal temperature within a range

endothermy

generate heat by metabolism

• birds, mammals ~36-41*C

• high energy costs but active in wide temp. range

ectothermy

gain heat from external sources

• invertebrates, fishes, amphibians, reptiles

• low energy costs but only active in narrow temp. range

poikilotherm

body temp. varies with envr.

• typically ectotherms but some endotherms vary body temps

• e.g. bats, hummingbirds

homeotherm

body temp. does not vary with envr. (relatively constant)

• typically endotherms but some ectotherms maintain relatively constant body temps.

• e.g. fish, inverts living under stable temps.

limitations of ectotherms

• must behaviorally generate heat

• generate heat when active: every aspect of ecology and behavior is influenced by the need to regulate body temp.

• e.g. digestion in fish is strongly influenced by water temp. (move to warmer weather to increased digestion, increase growth)

limitations of endotherms

ability to maintain constant body temp. is limited under low temps.

• short-term: by physiological capacity to generate heat

• long-term: by ability to gather food (or energy) to satisfy requirements for metabolic heat productions → animals usually starve to death before they die of direct causes of cold temps. 

• reduce energetic costs through adaptations that alter the loss/gain of heat from the envr. in a number of ways

energy conservation endotherms (3)

1. lower regulated temp. of a portion of their body (circulatory adaptation)

2. lower regulated body temp. (set point) over periods

3. larger body size

lower regulated temp. of a portion of their body (circulatory adaptation) - energy conservation endotherms

e.g. Birds - regulate blood flow to skin

• counter-current heat exchange (circulatory adaptation)

• seen in feet, tails & flippers (and some mammals)

• heat loss is minimized by reducing temperature gradient between leg and envr.

lower regulated body temp. (set point) over periods - energy conservation endotherms

e.g. hummingbirds, bats

• torpor = temporary (daily) reduction in metabolic activity and body temp.

• hibernation= extend reduction… (e.g. over the winter)

• inactive at low temps: body temp. is regulated around a different (lower) temp

• 50% less energy consumed

• heat loss is minimized by reducing the temp. gradient between body & envr. → otherwise would starve to death overnight

• *key adaptation for small birds and small mammals

larger body size - energy conservation endotherms

• body size is one of the most important animal characteristics: body size dictates morphology, ecology, physiology of an organism

• important is due to allometric relationships

• basal metabolic rate (BMR) = metabolic rate of endotherm at rest

• metabolic rate ~ body mass ¾ smaller animals have higher BMR per gram than larger animals

allometric relationships

relative increase in a physical or physiological property in relation to body size

energy conservation - endotherms

• key reason for higher BMR per gram of smaller animals is the surface area to volume ratio

• larger the volume, greater toral amount of heat required to keep war. → but less heat is lost through the outer surface of the organism

• small animals: high SA relative to low volume → lose lots of heat through SA

• large: low SA relative to high volume →lose less heat through low SA

___________ animals must reach a critical size: heat _______ > > heat _____

endothermic, generation, loss

as body size _______, volume _____ faster than SA

as body size changes, ____/____ changes

as SA/V changes, heat ______ to _______ changes

increases, increases

SA/V

loss, environment