BIO120H1 Lecture Notes - Lecture 2: Volumetric Heat Capacity, Sun Bear, Evaporation
Lecture 2 & 3:Physical challenges of the environment
Animals Geographic ranges usually correspond to biomes (limit to climates or
vegetation), but sometimes it is also affected by other factors:
○ Pronghorns have a broad temperature tolerance range but a narrow
Other organisms ( enemies, friends)
○ Elf owls, gila woodpekers depends on cactus.
○ Tigers can live in any habitat either hot or cold.
Ways to gain or loss heat:
Radiation: emission of electromagnetic energy by a warm surface.
Conduction: transfer of the kinetic energy of heat between substances in contact
with one another.
Convection: transfer of heat by the movement of liquids and gases
Evaporation: efficient cooling from wet surface.
Redistribution: circulatory system redistributes heat among body parts.
Body size and thermal inertia:
Larger organisms tend to lose heat across their surfaces less rapidly than smaller
individuals this is because the surface-to-volume ratio is smaller(V 比SA 大). It is
easier for them to maintain a constant internal environment in the face of
varying external conditions.
○ Bergmann’s Rule: Homeotherms tend to be larger at a higher altitude.
Polar bear lives in the Artic are bigger than Sun bear that live
in the tropics.
○ Allen’s Rule: appendages reduced in cold temperature.
Pika has spherical ear and round body; lives in tundra. Gliding
snake has flat body; lives in tropics
Aquatic animal uses body fats to keep themselves warm.
Blood flowing from the body toward the outside environment continuously
meetings blood returning to the body; arteries and veins should be appressed in
appendages to conserve heat. Ex: Birds leg
Def: a consequence of devoting limited time, energy, or materials to one
structure, function, or behavior at the expense of another.
○ Being long and makes weasels subject to thermal stress but allow
them to be better predatorsthe fitness gains of being a good hunter
balance out the fitness costs of an expansive metabolism.
Extreme Physical Challenges-Kangaroo Rats:
K-rats lives in Sonoran desserts, they can survive without taking any water,
○ Bipedal less heat gain from the ground.
○ Efficient kidney that can produce concentrated urine.
○ Metabolic water water produced by its own fats and seeds.
○ Nocturnal：spend hot days underground
○ Sleep with their foodseeds can recapture water vapor from
Food supply is usually the cause of hibernation and migration.
○ Chipmunk hibernates
○ Pika make hays
Migration vs. Residents
Birds migrate because of the food supply. Therefore birds that doesn’t migrate means that
they have a stable food supply.