Resource Constraints Water

dehydration

its not that heat that kills, its this → leads to death

humans/mammals can only tolerate 12-14% ___

water and life

essential to organisms, most comprised of 50-90%

humans - 60-70% and jellyfish up to 95%

need to maintain salt concentrations

water is a limiting resource

water budgets

all organisms must regulate internal water concentration based on inputs and outputs, these differ between organisms

aquatic organisms water budget

Wi (internal) = Wd (drinking) - Ws (secretion) ± Wo (osmosis)

salinity in aquatic environments

different organisms are adapted to various amounts of salt (ppt)

freshwater has about 5 ppt, estuaries have about 10-25 ppt (where marine meets fresh), and oceans generally have about 35 ppt

brackish environments and salinity

lakes display range of salinity (1-400 ppt)

are also different ion concentrated, ex sodium or sulfate

diffusion

movement of particles from areas of high to low concentration due to random movement of particles

salt concentrations are equalized in solution

osmosis

a process similar to diffusion but involves the movement of water down a concentration gradient through a semipermeable membrane

ex phospholipid bilayer, permeable only to some molecules such as water

osmolarity

refers to total concentration of solute particles in a solution, describes the solute concentration relative to the volume of the solution

can also refer to an organism in relation to its environment

hypo, hyper or iso

hypoosmotic

low solute and high water (than an environment)

ex marine fish

hypo = h20 = high water

hyperosmotic

high solute and low water (than an environment)

ex freshwater fish

Isoosmotic

same solute and water (than an environment)

ex marine invertebrates

salt-water balance marine organisms

mostly isosmotic, or equal to environment

W(internal) = Wd (drinking) - Ws (secretion) ± Wo (osmosis)

many fish can be hypoosmotic and risk water loss

W(internal) = Wd (drinking) - Ws (secretion) ± Wo (osmosis)

how do marine fish prevent water loss

since many are hypoosmotic …

drink constantly to counteract dehydration, always have their mouths open

low urination rates and volumes, get rid of excess salt through specialized chloride cells in gills

salt-water balance freshwater organisms

mostly hyperosmotic (risk salt loss)

W(internal) = Wd (drinking) - Ws (secretion) ± Wo (osmosis)

how to freshwater organisms prevent salt loss

do not drink, mouth stays closed

excrete excess internal water in dilute urine

replace salts by absorbing sodium chloride in gills and by ingesting food

fish moving between salt and fresh

acclimate to their new environment

or anadromous

ex salmon, smelt, shad, striped bass, sturgeon

anadromous

born in freshwater but spend most of their life in the sea and then return to freshwater to spawn

they are able to cope with changes in salinity/water concentration through shifting secretion cells (take in salt in freshwater and excrete salt in ocean)

ex salmon

catadromous

born in the ocean, spend most of their life in freshwater and return to the ocean to spawn

ex most eels

water budgets for terrestrial systems

Wi = Wd + Wf (food) + Wa (air) - We (evaporation) - Ws (secretion)

plant water budget

Wi = Wr (roots) + Wa (air) - Wt (transpiration) - Ws (secretion)

secretion can be seeds, fruits or nectar

water potential

potential energy or capacity to do work

usually negative, so 0 (high) is pure water and -100 (low) is hot air

water moves from high → low

includes pressure, differs from osmosis

water potential equation

ψ = ψ0 (reference, pure water) + ψg (gravity) + ψs (osmotic pressure) + ψh (water vapour pressure) + ψm (matric pressure, adhesion) + ψp (sum of pressures, ET)

water vapour density

quantity of water vapour that air actually holds

saturation is the maximum quantity at a given temp

air temp and water vapour

warm air can hold more water vapour than cold air and therefore has higher pressure (closer to saturation)

but cold air can hold less water vapour than warm air and so has low pressure (low saturation)

plant water potential

tree canopy will have the lowest, due to ET

the trunk has low to moderate, with matric and osmotic pressures being low

roots have medium to high

and soil has the highest, with highest ψs

(this allows water to move up the tree/plant)

terrestrial plant water acquisition

deep roots are a strategy in plants to acquire deeper water

in drier climates roots tend to be deeper so they can access more groundwater

water acquisition terrestrial animals

Wi = Wd + Wf + Wa - We - Ws

mainly gain water via food and drink, metabolically

or via aerobic respiration

Wf is very efficient

terrestrial water conservation

thicky waxy cuticle/layer can aid in avoiding water loss by covering the epidermis

the drier the climate the more/thicker cuticle (phenotypic plasticity)

ex tree needles, beetles and snail shells

animals storing water

cacti store water in trunks and arms → low surface area to volume ratio to reduce water loss

camels store extra water in their blood stream, they also minimize water loss in excretion (concentrated urine or feces)

behavioural water conservation

kangaroo rats and scorpions use burrows where the microclimate is cooler and lower transpiration

wilting

another water conservation strategy as surface area is reduced (during water stress)

and there is a drop in turgor pressure, transpiration rate also drops as does photosynthesis