BIOL 3240 Plant and Animal Ecology Water Relations

BIOL 3240 Plant and Animal Ecology Water Relations © Getty Images/Taxis http: //bellaonthebeach. files. wordpress. com/2009/01/water. jpg 1

Water Availability • The tendency of water to move down concentration gradients, and the magnitude of those gradients, determine whether an organism tends to lose or gain water from its environment. – Microclimate important factor! 2

Water Content of Air • Evaporation accounts for much of water lost by terrestrial organisms. – As water vapor in the air increases, the water concentration gradient from organisms to air is reduced, thus evaporative loss is decreased. – Would you buy a “swamp cooler” to help you keep cool in the cypress swamps of southern U. S. ? 3

Water Content of Air • Relative Humidity: Water Vapor Density Saturation Water Vapor Density (x 100) • Water vapor density is measured as the water vapor per unit volume of air. • Saturation water vapor density is measured as the quantity of water vapor air can potentially hold. – Changes with temperature. 4

Water Content of Air • Total Atmospheric Pressure – Pressure exerted by all gases in the air. • Water Vapor Pressure – Partial pressure due to water vapor. • Saturation Water Vapor Pressure – Pressure exerted by water vapor in air saturated by water. • Vapor Pressure Deficit – Difference between WVP and SWVP at a particular temperature. 5

Evaporative Water Loss 6

Water Movement in Aquatic Environments • Water moves down concentration gradient. – Water is more concentrated in freshwater environments than in the oceans. • Aquatic organisms can be viewed as an aqueous solution bounded by a selectively permeable membrane floating in an another aqueous solution. 7

Water Movement in Aquatic Environments • If two environments differ in water or salt concentrations, substances will tend to move down their concentration gradients. – Diffusion • Osmosis: Diffusion through a semipermeable membrane. 8

Water Movement in Aquatic Environment • Isosmotic: Body fluids and external fluid are at the same concentration. • Hyposmotic: Body fluids are at a higher concentration than the external environment. • Hyperosmotic: Body fluids are at a lower concentration than the external environment. 9

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Water and Salt Balance in Aquatic Environments • Freshwater Fish and Invertebrates – Hyperosmotic organisms that excrete excess internal water via large amounts of dilute urine. • Replace salts by absorbing sodium and chloride at base of gill filaments and by ingesting food. 13

Osmoregulation by Freshwater Organisms 14

Water and Salt Balance in Aquatic Environments • Marine Fish and Invertebrates – Isomotic organisms do not have to expend energy overcoming osmotic gradient. • Sharks, skates, rays - Elevate blood solute concentrations hyperosmotic to seawater. – Slowly gain water osmotically. • Marine bony fish are strongly hypoosmotic, thus need to drink seawater for salt influx. 15

Osmoregulation by Marine Organisms 16

Water Movement Between Soils and Plants • Water moving between soil and plants flows down a water potential gradient. • Water potential (Ψ) is the capacity to perform work. – Dependent on free energy content. – Pure Water ψ = 0. • Ψ in nature generally negative. • Ψsolute measures the reduction in Ψ due to dissolved substances. 17

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Water Movement Between Soils and Plants – Ψplant = Ψsolute + Ψmatrix + Ψpressure – Matrix Forces: Water’s tendency to adhere to container walls. – Ψpressure is the reduction in water potential due to negative pressure created by water evaporating from leaves. – As long as Ψplant < Ψsoil, water flows from the soil to the plant. 19

Water Regulation on Land • Terrestrial organisms face (2) major challenges: – Evaporative loss to environment. – Reduced access to replacement water. 20

Water Regulation on Land - Animals 21

Water Regulation on Land - Animals • Wia= Wd + Wf + Wa - We - Ws • • • Wia= Wd = Wf = Wa = We = Ws = 22

Water Acquisition by Animals • Most terrestrial animals satisfy their water needs via eating and drinking. – Can also be gained via metabolism through oxidation of glucose: • C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O – Metabolic water refers to the water released during cellular respiration. 23

Water Regulation on Land - Plants 24

Water Regulation on Land - Plants • Wip= Wr + Wa - Wt - Ws • • • Wip= Wr = Wa = Wt = Ws = 25

Water Acquisition by Plants • Extent of plant root development often reflects differences in water availability. – Deeper roots often help plants in dry environments extract water from deep within the soil profile. • Park found supportive evidence via studies conducted on common Japanese grasses, Digitaria adscendens and Eleusine indica. 26

Water Conservation by Plants and Animals • Many terrestrial organisms equipped with waterproof outer covering. • Concentrated urine / feces. • Condensing water vapor in breath. • Behavioral modifications to avoid stress times. • Drop leaves in response to drought. • Thick leaves • Few stomata • Periodic dormancy 27

Dissimilar Organisms with Similar Approaches to Desert Life • Camels – Can withstand water loss up to 20%. • Face into sun to reduce exposure. • Thick hair: Increased body temperature lowers heat gradient. • Saguaro Cactus – Trunk / arms act as water storage organs. – Dense network of shallow roots. – Reduces evaporative loss. 28

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Two Arthropods with Opposite Approaches to Desert Life • Scorpions – Slow down, conserve, and stay out of sun. – Long-lived – Low metabolic rates 30

• Cicadas (Diceroprocta apache) – Active on hottest days. – Perch on branch tips (cooler microclimates). – Reduce abdomen temp by feeding on xylem fluid of pinyon pine trees. http: //www. canyouseethesunset. com/uploaded_images/cicada-2. jpg 31 http: //www. learnnowonline. net/nucpan/wp-content/uploads/2007/08/cicada 2. JPG

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