BIO 351 Ecology - Water, Heat, and Temperature

Physiological ecology

study of interactions between organisms and their environment and how these interactions influence their survival and persistence

conditions

abiotic factors that are not depleted

resources

abiotic and biotic factors that are depleted or consumed

what are response curves used to illustrate?

response curves are used to illustrate organismal performance in different environmental conditions

what are the two ways that a physical environment influences an organisms ecological success or fitness:

1. availability of energy and resources impacts growth and reproduction

2. extreme conditions can exceed tolerance limits and impact survival

eurytopic vs stenotopic

eurytopic - species that can live in a broad range of environments; eurythermic (temperature), euryhaline (salinity)

stenotopic - species that can live in a narrow range of environments; stenothermic (temperature), stenohaline (salinity)

examples of limiting factors

low temperatures and drought which affect reproduction and survival

4 major components of thermal energy balance of organisms

1. radiant energy - short wave long wave

2. sensible heat - conduction and convection

3. latent heat - from evaporation of water

4. metabolic heat - stored in chemical bonds, released in cellular respiration

temperature vs heat

temperature is a measure of the average random kinetic energy (energy of movement) of the molecules in a substance

the temperature of any object depends on its energy balance

heat is a measure of the total kinetic energy of the molecules in a substance

thermal energy balance

• energy balance for any object: energy in - energy out = 0

• energy gain must = energy loss, or temperature changes

• if energy in > energy out, temperature rises

• if energy out > energy in, temperature falls

radiant energy

energy of the electromagnetic spectrum; shortwave and longwave radiation; depends on surface T^4; no molecules necessary for transmission

sensible heat

transfer via conduction and convection from objects with higher temperature to objects with lower temperature

conduction - molecules by molecule transfer (mostly in solids)

convection - large packages of molecules moving together transfer energy (in liquids and gases)

latent heat

transfer via evaporation or condensation of water from/onto a surface; transfer of heat energy by evaporation or condensation of water vapor from a surface to atmosphere

water vapor has more energy than liquid water; change from liquid to gas involves energy exchange w/ surface

surface loses (evaporation) or gains (condensation) energy

no temperature change in water (but surface does change temp)

metabolic heat and stored energy

thermal kinetic energy and chemical energy

leaf boundary layer

thin zone of calm, unmoving air that clings to the surface of a leaf

the boundary layer lowers convection heat loss

the boundary layer thickness is related to leaf size and surface roughness - small, smooth leaves have thin boundary layers and lose more heat than large or rough leaves

what determines the radiant heat component of energy exchange?

radiant heat - energy emitted by an object depends on its surface temperature, as T^4

shortwave (visible) and longwave (IR)

wavelength is proportional to 1/T

no molecules necessary for transmission of radiant energy

temperature summary

• an organisms temperature depends upon whether the losses of energy to convection and evaporation (latent heat loss due to transpiration) are less than, greater than, or equal to the net gain of radiant energy, plus metabolic energy

• various short term responses and long term adaptations (partially) control these inputs and losses

endothermy

regulation of body temperature by internal heat production (mammals, bees, tuna, birds)

ectothermy

determination of body temperature primarily by external thermal conditions (reptiles, invertebrates, most fish)

poikilotherm

an organism whose body temperature varies according to the temperature of its surroundings (invertebrates, reptiles, amphibians)

• operative temperature range large

• low metabolic rate

• high ability to exchange heat between body an environment (conductivity)

homeotherm

an organism with a fairly constant body temperature (birds, mammals)

• high metabolism and food requirement

• constant (except if hibernating, etc)

• low thermal conductance

• evaporative cooling

• temperature range of internal environment small, but can exploit a wide range of thermal environments

boundary layers

• relatively still layer of air or water surrounding an object

• heat transfers through boundary layer is more through conduction than convection

• size, shape, and surface properties of the object modify the boundary layer

• feathers and fur can increase boundary layer

• larger, more whole objects tend to have large boundary layers; smaller, more ‘broken up’ objects have small boundary layer

do smaller or larger homeotherms have a higher surface:volume ratio?

smaller homeotherms have high surface:volume ratios; they lose heat to their surroundings more rapidly

small homeotherms need high metabolism to keep warm, and need to eat frequently to maintain this high metabolism

costs/benefits of temperature regulation (endotherms vs ectotherms)

endotherms - high cost of oxygen consumption, but benefit of consistent performance

ectotherms - lower oxygen consumption per body mass, but limited performance

surface area law

smaller surface area relative to volume decreases the animal’s ability to gain or lose heat

as body size increases, surface area to volume ratio decreases, and large ectotherms are thus improbably

adaptation

genetic, heritable changes in traits over the course of generations in a population that increase fitness

acclimation or acclimatization or plasticity

non genetic, morphological or physiological changes within an individual in response to environmental conditions

epigenetic effects

changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself that can be passe to offspring

how do the adaptations and acclimation of plants and animals affect the terms of their thermal energy balance?

• radiant energy: behavioral; plants-leaf angle, reflectivity

• latent heat loss: transpiration, sweating, panting

• convective heat exchange: leaf/body size, shape, insulation (fur, feathers), behavior

what are some examples of adaptations of animals to extreme environments?

• extreme cold - countercurrent exchange

countercurrent exchange

• adaptation to maintaining core body temp (by convective heat exchange inside animal)

• blood leaving core for extremity (fin, leg, etc.) is warmer (or cooler) than blood returning

• proximity of blood vessels allows heat exchange

how do animals avoid drought?

• leave the area or become inactive during the dry season

• enter a state of dormancy or diapause

• nocturnal activity

how do animals tolerate drough morphologically or physiologically?

• reduce surface water loss and sweating; stay cool using other mechanisms instead of latent heat loss

• reduce respiratory water loss

• utilize metabolic water

kangaroo rat problems and adaptations

• problems - extreme temps, lack of water, finding food, avoiding predators, finding mates, and raising young

• adaptations - nocturnal (spend day in burrows to reduce heat load and water loss and avoid predators); nearly dry feces, concentrated urine; large, cool nasal passages condense exhaled moisture and retain it internally; never drink water (obtain most of their water from cellular respiration of food)

plant/water relationships

• water potential

• soil-plant-atmosphere continuum

• transpiration and controlling water loss

• whole plant adaptations

water potential

• the difference in energy between pure water at STP and water in a system (such as a cell)

• components of whole system water potential:

  • osmotic (due to solutes; 0 or 0, drives diffusion)

  • pressure (+, 0 or -)(water can be pressing on cell walls in a healthy, turgid cell (+) or pilling in on xylem walls in a transpiring plant)

  • matric and gravitational (more important in soils)

• water moves from greater to lower values of total water potential

is the gradient in water potential between most terrestrial organisms and the atmosphere very high or very low?

very high

soil plant atmosphere continuum

water moves from least negative (largest values) to most negative (smallest values) components of psi, pulled along by gradient in psi

transpiration and control of water loss

• plants transpire much more water than they use metabolically (contented trees in moist soil: 100 to 1000 liters/day!)

• plants control water loss by acclimation as well as adaptation

  • opening or closing stomata

  • direction that leaves are facing

  • anatomical, physiological, and morphological adaptive traits of leaves

plant adaptations to droughts

• deciduousness (lose leaves during drought)

• succulence (store water)

• annuals (grow only during wet periods)

• sclerophytes and xerophytes (plants w/ slower growth and restricted water loss even in good times)

• mesophytes: plants in environments with good water availability most of the time: high water loss and fast growth

energy balance summary

• the energy balance of an organism determines its temperature

• energy balance is determined by:

  • radiant energy exchange (short and long wave)

  • sensible heat flux (mostly convection), modified by boundary layer of the surface - boundary layer is affected by size and shape

  • latent heat exchange (usually, loss), determined by water evaporating from surface

water balance summary

• water potential along the soil plant atmosphere continuum determines occurrence and direction of water movement

• water moves from less negative to more negative water potential

• the components of water potential in plants include osmotic and pressure potential

• the plant controls stomatal conductance and thus water loss

• plants have suites of physiological, morphological and anatomical traits that work together to adapt the to environments with differing water availability