Lecture 3: Environmental Variation - Temperature and Water

Responses to Environmental Variation

• Tolerance

• Avoidance

Physiological Ecology

• The study of interactions between organisms and the physical environments that influence their survival and persistance

How Does the Physical Environment Influence an Organism’s Ecological Success?

• Availability of energy and resources - impacts growth and reproduction

• Extreme conditions can exceed tolerance limits and impact survival

• Energy supply can influence an organism’s ability to tolerate environmental extremes

Stress

• Environmental change results in decreased rates of physiological processes, lowering the potential for survival, growth, or reproduction

Acclimation

• Adjusting to stress through behaviour or physiology

• Usually short-term and reversable

Adaptation

• Permanent, genetic change in a population over many generations

Temperature Controls Physiological Activity

• High temperatures destroy enzymes function (denature)

• Some species produce different forms of enzymes (isozymes) with different temperature optima that allow acclimation to changing conditions

• At low temperatures, lipid cell membrane can solidify, embedded proteins cannot function, and the cells leak metabolites

• Plants that thrive at low temperatures have higher proportions of unsaturated lipids (with double bonds) in their cell membranes

• Temperature affects water availability, which affects physiological processes

  • The rate at which terrestrial organisms lose water is related to air temperature

Conduction

• Transfer of energy from warmer to cooler molecules

Convection

• Heat energy is carried by moving water or air

• In cold, windy environments, convection is the main heat loss mechanism

Latent heat transfer

• Water absorbs heat as it changes from liquid to gas state

Stomates

• Stomates are guard cells that can control transpiration rates (cooling/sweating of the plant) by opening and closing, also control the leaf temperature

Why is Transpiration Dangerous in Water-Stressed Plants?

• Because the plant is losing moisture faster than its roots can absorb it, and it causes dehydration and leads to the plant wilting

Pubescence

• Hairs on leaf surfaces that reflect solar energy, prevents overheating

• Reduce conductive heat loss (heat transfer from warmer to cooler molecules)

Convective Heat Loss

• If air temperature is lower than leaf temperature, heat can be lost by convection (heat energy carried by moving water/air)

• Convective heat loss is related to speed of air moving across a leaf surface

Boundary Layer

• A zone of turbulent flow due to friction, next to the leaf surface

• Lowers convective heat loss

• A thinner boundary layer means the leaf surfaces are losing more heat,, thicker boundary layers lose less heat

Ectotherms

• Ectotherms regulate body temperature through energy exchange with the external environment

• They have greater tolerance for variation in body temperature than endotherms

• Ex. reptiles, amphibians

Endotherms

• Rely primarily on internal heat generation

• Can maintain internal temperatures near optimum for metabolic functions, extending geographic range

• Birds and mammals

Evaporative Cooling in Animals

• Sweating

• Panting

• Licking the body

Surface Area to Volume Ratio

• Smaller surface area to volume ratio decreases the animal’s ability to gain or lose heat

• Larger surface area allows greater heat exchange, but makes it harder to maintain internal temperature

• As body size increases, surface area to volume ratio decreases

• Small aquatic ectotherms remain the same temperature as water

How Ectotherms Deal With Temperature

• Many terrestrial ectotherms can move around to adjust temperature

• Many insects and reptiles bask in the sun to warm up after a cold night, but this increases predation risk, increasing benefits of camouflage

• Ectotherms in temperate and polar regions must avoid or tolerate freezing

Cryonics

• Preservation of bodies by freezing, in hopes that they can be brought back to life in the future

• In most organisms, freezing results in tissue damage as ice crystals perforate cell membranes and organelles, but in animals that withstand freezing, the freezing water is limited to the space outside the cells

How Endotherms Deal With Temperature

• Endotherms can remain active at subfreezing temperatures

• Endotherms have a high demand for energy (food) to support metabolic heat production

• Metabolic rates are a function of the external temperature and rate of heat loss

• Small endotherms with large surface area to volume ratio have higher metabolic rates and require more energy and higher feeding rates than large endotherms

Feathers, Fur, and Fat

• Insulation limits conductive and convective heat loss

• Fur and feathers provide a layer of still air adjacent to the skin

Heat Stress in Animals

• Some organisms use behavioural changes to control exchange of energy with the environment

Dormancy

• Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little or no metabolic activity occurs

• They survive in cold climates by entering a dormant state called torpor, where body temperature and basal metabolic rates are low, which conserves energy