#1 Thermoregulation

How does body temperature affect animals?

strongly influences physiological processes

What are the physiological processes that body temperature influences? (first 4)

• Rates of many biochemical reactions

• The cellular environment

• An animal’s behavior

• Rates of oxygen consumption

What are the physiological processes that body temperature influences? (last 4)

• Life processes (e.g., growth, development, reproduction)

• An individual’s resistance and reaction to disease

• Performance, survival, and fitness

• Rates of evaporative water loss

Ectotherms

Ectotherms are animals that rely on external environmental sources to regulate their body temperature, primarily through behavior

• Amphibians and reptiles

How do ectotherms control their body temperature?

They regulate temperature behaviorally, such as basking in the sun or retreating into shade or burrows

Why do animals thermoregulate?

To maintain body temperature within an optimal range where physiological performance is maximized and to avoid harmful extremes (hypothermia or hyperthermia)

What happens if body temperature goes beyond thresholds in ectotherms?

It can become lethal if temperatures are too high or too low

Toad vs. Lizard Thermoregulation example→ How does a toad regulate its body temperature?

Behaviorally

• retreating when temperatures reach about 26°C

• emerging when temperatures fall below ~12.5°C

Toad vs. Lizard Thermoregulation example→ When are toads most active?

At relatively low body temperatures, often under cloudy conditions

Toad vs. Lizard Thermoregulation example→ How does a lizard regulate its temperature?

By basking to raise body temperature and retreating during unfavorable conditions like rain

Toad vs. Lizard Thermoregulation example→ What are key differences between toads and lizards?

• Toads prefer lower temperatures and regulate more frequently.

• Lizards operate at higher temperatures and rely more on basking.

• Toad body temperature is usually lower than that of lizards

How do amphibians differ from reptiles in thermoregulation?

• lose water easily

• operate at lower temperatures

• are often nocturnal to reduce water loss

How do reptiles differ from amphibians in thermoregulation?

• skin resistant to water loss

• tolerate sunlight

• can function at higher body temperatures

What are the main sources of heat exchange for animals?

• Solar radiation

• conduction (e.g., contact with warm surfaces)

• environmental positioning

How does body size affect thermoregulation?

Smaller animals heat and cool faster, while larger animals retain heat longer but change temperature more slowly

What factors influence how much solar radiation an animal absorbs?

• Intensity of sunlight (S)

• Surface area (A)

• View factor (vfₛ)

• Absorptivity (a)

How can animals increase heat absorption?

• increasing surface area (flattening body)

• changing orientation to the sun

• darkening their coloration

How does posture affect heat absorption?

• Flattening increases surface area and heat gain.

• Changing orientation relative to the sun alters exposure

Positive orientation

body positioned to maximize sun exposure

Negative orientation

body positioned to minimize sun exposure

How do animals change their heat absorption using color?

By adjusting pigmentation—darker colors absorb more heat, lighter colors reflect it

What cells are responsible for color change?

Melanophores

How do melanophores work?

• Pigment dispersed → darker appearance

• Pigment concentrated → lighter appearance

How does temperature affect performance in ectotherms?

Performance (e.g., sprint speed) increases with body temperature up to an optimal point, then declines if temperature gets too high

How do tegus retain heat?

They can retain environmental heat for long periods

• especially in nesting or breeding conditions

Why do reptiles take time to become active?

They need time to thermoregulate (warm up) before reaching optimal activity levels

Why do smaller animals experience faster temperature changes than larger animals?

Smaller animals have a higher surface area-to-volume ratio, causing them to gain and lose heat more quickly

Why are many amphibians nocturnal?

To reduce evaporative water loss and stay in more humid conditions

How does moving between sun and shade help ectotherms?

It allows them to quickly adjust their body temperature by controlling exposure to solar radiation

Why might a snake coil versus stretch out its body?

Coiling reduces surface area and heat gain, while stretching increases surface area and heat absorption

What happens to an ectotherm’s activity level when environmental temperature reaches an optimal range?

Activity increases because physiological processes and performance are maximized

Why do reptiles retreat when it rains or when sunlight disappears?

Because they rely on external heat sources, and without sunlight they cannot maintain optimal body temperature

How does the environment influence where an animal positions itself?

Animals choose locations (e.g., rocks, soil, shade) based on temperature conditions to regulate heat gain or loss