Temperature and Water Relations

region biosphere landscape ecosystem community interaction population individual Temperature and water are two significant components of an individual organism’s environment Individuals must regulate their internal temperature and water content – this occurs through individual adaptations (history of past individuals experiencing similar environmental conditions) and acclimation (adjustments made by the organism in response to a change in current conditions)

Macroclimates are divided into many, many microclimates microclimates influenced by factors like exposure, altitude, and aspect organisms live in microclimates temperature and water availability can show broad temporal variation

Most species perform optimally within a fairly narrow range of environmental conditions

Temperature and individual performance narrow optimal temperature range linked to the structure and function of enzymes enzymes optimally bind their substrate within a limited temperature range

most enzymes have stable conformation at low temperatures, but also low reaction rates increasing temperature increases reaction rate, but excessively high temperatures cause proteins to denature (lose their functional shape) enzymes function best at some intermediate temperature range (not too hot, not too cold)

Eastern fence lizards – temperature and metabolizable energy intake (MEI)

Temperature and plant performance Extreme temperatures usually reduce the rate of photosynthesis Like animals, plants usually perform (photosynthesize) optimally within a narrow temperature range Plants can also physiologically adjust their optimal temperature for photosynthesis to accommodate seasonal changes in temperature

Given their often limited range of optimal temperatures and the inevitable variation in temperature in most environments, many organisms have evolved ways to regulate body temperature

Balancing Heat Gain Against Heat Loss H S = H m  H cd  H cv  H r - H e H S = Total heat stored in an organism H m = Gained via metabolism H cd = Gained / lost via conduction H cv = Gained / lost via convection H r = Gained / lost via electromag. radiation H e = Lost via evaporation

Temperature regulation Poikilotherms – don’t regulate internal temperature; temperature varies with environment Ectotherms – rely on external sources of energy to regulate body temperature Endotherms – rely on internally derived metabolic heat energy homeotherms: birds and mammals (maintain relatively constant body temperature, as opposed to certain fish and insects that only heat critical organs)

Temperature regulation in plants Heat storage reduction by desert plants: H S = H cd  H cv  H r - H e -decrease heating by conduction -increase cooling by convection -reduce radiative heating

Temperature regulation in desert plants Arctomecon miriamii

Temperature regulation in arctic and alpine plants Two main options for staying warm: increase heat gain via radiative heating (H r ) darkly pigmented leaves oriented perpendicular to sunlight decrease heat lost through convective cooling (H cv ) compact hemispherical growth form low to ground

Temperature regulation in arctic and alpine plants Two main options for staying warm: increase heat gain via radiative heating (H r ) darkly pigmented leaves oriented perpendicular to sunlight decrease heat lost through convective cooling (H cv ) compact hemispherical growth form low to ground

Alpine cushion plant communities in the Andes

Temperature regulation in ectothermic animals modify behavior to track optimal temperature via radiative heating, convection, conduction (e.g., Eastern fence lizards) pigmentation can aid in radiative heating – may be developmentally plastic trait (e.g., grasshoppers)

Temperature regulation in enothermic animals also use behavioral and anatomical strategies to regulate body temperature BUT, endotherms rely a great deal more on metabolic heat to maintain body temperatures within their optimal range

Thermal Neutral Zone range of environmental temperatures over which an endotherm’s metabolic rate does not change in thermal neutral zone, metabolic rate is at steady resting metabolism – metabolic rate increases dramatically outside this zone the breadth of the thermal neutral zone varies dramatically between different endotherms: narrow in tropical species and much broader in arctic species

Thermal Neutral Zones

Temperature regulation in aquatic endotherms Water temperature much more stable than that of air (takes much greater change in energy content to heat/cool water) Convective and conductive heat loss in water is far more rapid (20-100x) than in air Gills expose a large surface area to this vast heat sink Because of these constraints, few aquatic animals are endothermic

Temperature regulation in aquatic endotherms Aquatic mammals – can be endothermic due to: Air-breathing (no gills) Insulation (blubber/fat or thick fur) Countercurrent heat exchangers (also found in endothermic fish, e.g., tunas and white sharks)

Countercurrent Heat Exchange Vascular arrangements reduce the amount of heat loss to the aquatic environment

Temperature regulation in endothermic insects Bumblebees use metabolic heat to warm their flight muscles Large moths maintain fairly constant metabolic rate and regulate temperature via conductive and convective cooling / heating

Endothermic Plants Some plants generate metabolic heat derived from energy stored as starch Generally used as part of pollination system (e.g., heating up volatile substances to attract insect pollinators Particularly prevalent in the Aroid lilies

Surviving Extreme Temperatures Inactivity: in ectotherms and endotherms - seek shelter during temperature extremes Reducing Metabolic Rate: in endotherms - when energy supply in environment (in form of heat or food or both) is not adequate for supporting normal metabolism Torpor (usually only lasts a short time, i.e., one night) hummingbirds Hibernation (winter) bears Estivation (summer) dwarf lemur

Water relations Most organisms are 50 – 90% water Life originated in salty aquatic environments, and the signature of these origins can still be found in our biochemistry To survive, organisms must maintain the appropriate internal concentrations of water and dissolved substances Water and solute concentrations are regulated through the control of water loss and gain

Water Availability The capacity of water to do work (i.e., flow) is known as water potential The movement of water down concentration gradients ultimately determines the amount of water available to organisms in both terrestrial and aquatic environments

Water Availability – Aquatic organisms in aquatic environments, water moves from areas of higher concentration (fewer solutes) to lower concentration (greater solutes), a process known as osmosis Isosmotic – internal and external concentrations of water and salt are equal hyperosmotic – internal concentration of salt is higher than that in the environment, water concentration lower than that in environment: water moves into organism, salts diffuse out hypoosmotic – internal concentration of salt is lower than that in the environment, water concentration higher than that in environment: water moves out of organism and salts diffuse in

Water Availability – Terrestrial Plants in terrestrial systems, water moves from areas of high water potential (wet soil) to areas of lower water potential (plant vascular tissue, and eventually, air) Ψ plant = Ψ solute + Ψ matric + Ψ pressure – Matric Forces: Water’s tendency to adhere to container walls. – Ψ pressure is the reduction in water potential due to negative pressure created by water evaporating from leaves. As long as Ψ plant < Ψ soil, water flows from the soil to the plant.

Water Regulation – Aquatic animals Sharks: hyperosmotic – water diffuses into the shark’s body through the gills. Sharks excrete urine to compensate for water gain Marine bony fish are hypoosmotic – water diffuses out of the fish through the gills. These fish drink sea water to compensate for water loss, excess salts that are also taken in with sea water are excreted with urine and by specialized cells in the gills. Freshwater fish are hyperosmotic – water diffuses in through the gills, is excreted as large quantities of dilute urine. Salts lost with the urine are replaced by specialized cells in the gills that absorb chloride ions from the water. Salts also taken in with food.

Water Regulation – Terrestrial Animals Animals get their water from: Drinking Food (both directly and through the metabolic breakdown of sugars) Air Animals lose water through: Evaporation Excretions

Water Regulation – Plants plants get their water from: Soil Air plants lose water through: Evaporation (transpiration) Secretions (nectar, seeds, fruit)

Terrestrial Water Conservation Possible ways to conserve water: Thick / waterproof cuticle to keep water in Dense hairs to reduce evaporation and heat gain Limiting activity to times or places where evaporative water loss is reduced Drinking lots of water to compensate for evaporative water loss Storing large quantities of water in your body Increasing the ratio of volume / surface area Periodic dormancy

Poikilohydry Not all terrestrial organisms regulate their internal water content Mosses and other bryophytes are poikilohydric plants: they lack vascular tissues for water transport as well as stomata Internal water content quickly equilibrates with that of the environment

Poikilohydry and Desiccation Tolerance Because they are poikilohydric, many bryophytes only grow in places that never dry out completely Other bryophytes evolved the ability to survive the loss of nearly all (>90%) of their cellular water content: Desiccation tolerance

Tortula ruralis

Craterostigma plantagineum