General Water Economy

Importance of Water Body fluids and transport

– water is an essential component of blood Elimination of waste

– nitrogenous waste is toxic - water is used to reduce/dilute the toxicity

– water is essential for movement of egesta Heat loss

– vertebrate heat loss is via evaporation of water.

Water Balance

Water gains– drinking– food– metabolic water

EOHCOOOHC 2226126

Water Balance

Water loss– urine– feces– integumentary water loss– evaporation from respiratory surfaces

Man in the Desert: Energy and water balance

KCAL/hr H2O Loss Resting metabolism

80 155

Walking 200 346 Radiation from sun

150 260

Radiation from ground

300 320

Total 730 1081

Energy and water balance

Man has to lose 730 KCAL of energy every hour to maintain his/her body temperature.

Man requires 1081 gms (1 liter) of water every hour to get rid of the 730 KCAL of energy.

Other animals in the desert

Burros– Capable of losing

20% of their body weight and can then restore it rapidly.

Other animals in the desert

Camels– In the winter, all of their water comes from

their food.– In the summer, they can lose 25% of their

body weight in water and then restore it rapidly. In 10 minutes they can drink 27 gal of water.

Other animals in the desert

Camels cont.– They can replace blood fluid from

intercellular fluid.– They reabsorb water from the urine and

gut.– They utilize urea for protein synthesis.– They are capable of temperature lability

(93° - 103°F).

Other animals in the desert

Camels cont.– They reduce cuticular (integumentary)

water loss via insulation.– What about the hump>

• hump = 50% fat• 1.1lb fat = 1lb H2O

• Hump weighs 110 lbs = 50 lbs H2O, or about 13 gal of water.

Other animals in the desert

Camels cont.• But, to get the water in the hump, they must

increase their metabolic rate, and consequently lose more than 13 galons. There is no net benefit.

Other animals in the desert

Kangaroo rats.– Completely water independent– Exist on metabolic water.– 1g of carbohydrates = 0.6g of water.– Some from food (5% of seed)– They are nocturnal

Other animals in the desert

Kangaroo rats cont.– live in burrow - plug the burrow.

• Near constant temperature environment• are capable of tolerating 15% CO2 , which is

lethal to us.• Re-absorb water from the feces.• Concentrate urine (very long loops of Henle)

No Water in the Environment?

Then do the following:– Avoidance of heat, ie nocturnality– Use of humid environments such as

burrows.– Re-absorb water from the feces.– Consume fleshy foods.– Concentrate urine– Produce metabolic water.

Other animals in the desert

No water cont.– Temperature lability– Development of heat loss devices such as

the ears in jack rabbits.

The Importance of Nocturnality

Being active at night has some significant benefits, but some potential costs as well.

Consider Peromyscus truei, the pinyon mouse of the Southwest.

The mouse weighs about 25g.– What does this mean in terms of surface

area/volume ratio?

Nocturnality in P. truei In the arid Southwest, there is a

significant temperature variation from day to night. Even in the summer, nights can be chilly.

During the winter, nights can be extremely cold.

We expect a small mammal to be active under the most favorable thermal conditions.

Nocturnality in P. truei

However, there are other constraints.– When is the best time to be active relative

to hunger levels, risk of predation, or the chance of encountering potential mates?

Do we expect the patterns of activity for males and females to be the same?

Does reproductive status influence the patterns?

Nocturnality in P. truei

If the animals are non-reproductive, then they should be active when it is energetically efficient. In the winter, this should be shortly after sunset.

Nocturnality in P. truei

Why are the females different?– Females produced a litter in fall, and are

capable of reproducing in the winter if there is a warm spell. It is likely that females are still repaying an energetic debt from the fall reproduction effort, and must forage once more before the night is over.

Nocturnality in P. truei

Notice the same pattern is present in the fall months. The same argument applies.

Nocturnality in P. truei

In the spring, females are reproductive, and the nights are cool, but not as cold. Consequently it is not surprising that females exhibit the same general pattern as before. However, males no longer are constrained by the temperatures, and are active in a different pattern.

Nocturnality in P. truei

In the summer, food is abundant, temperatures are mild, and the living is easy. Patterns in both males and females are relaxed.

Nocturnality in P. truei

A regression of activity level against various environmental parameters shows:– In the fall and winter, activity is positively

related to ambient temperature.– In the fall and winter, the coefficient of

determination is much higher - the mice are more predictable in their use of time.

What else is going on?

During the summer, there is a lot of dispersal (young of the year are moving to new areas).

Males have larger home ranges than females in fall, winter, and spring. Why?

Note: male home ranges are almost always larger than female ranges.

How about use of habitat?

We can look at what portions of the habitat are used by the mice.

The technique used to do this in Canonical Discriminant Functions Analysis.

Habitat use by P. truei

We can compute the scores (projections of old variables on the new axes) for each sex, on a monthly basis. These scores can then be used to compute niche overlaps and niche breadths, as well as illustrate use of the “habitat space”

What does all of this mean?

1) There is a lot going on in the life of a mouse, living in an arid environment.

2) Besides thermal considerations, the must must deal with reproduction and predation.

3) Solving one problem may exacerbate another problem. The mice are constrained, just as we are.

Problems Faced by Birds in Hot Dry Environments Birds are diurnal They have a high metabolic rate and

body temperature, and thus have high heat production and high water loss.

They have air sacs.– Make the bird lighter.– Increase O2 consumption.– Cools internal organs.– But, increases area for water loss.

Problems Faced by Birds in Hot Dry Environments Few birds can make metabolic water in

sufficient quantities. One plus for birds is that they excrete

uric acid rather than urea.

Some Avian Solutions to Water and Temperature

Linnets (house finch)– live near water, drink all the time.

Rock Wren– Live in the desert, but get all their water

from insects.

Some Avian Solutions to Water and Temperature

Abert’s Towhee (Dawson)– Found only near desert streams.– Active only at dawn and dusk.– Temperature lability

Some Avian Solutions to Water and Temperature White Pelicans (Bartholomew&Dawson)

– Nest at salt lake and Salton Sea etc, in the summer.

– Cool off in the water.– Shade the young.– Temperature lability.– Capable of gular fluttering.

Some Avian Solutions to Water and Temperature

Albatross (Howel and Bartholomew)– Eat squid.– Hold webbed feet off the hot sand and flap

them.

Some Avian Solutions to Water and Temperature

Sparrow Hawks (Cade)– temperature lability– evaporative cooling

• panting• sweat from cere• sweat through the cornea of the eye.

Some Avian Solutions to Water and Temperature Woodstork-Ibis (Kahl)

– Urohidrosis Mourning doves

• Can go 1-2 days without water.• Can lose 15% of their body weight and then

drink it all back.• Can fly at 60mph (a very efficient speed) to a

water hole.• Increase water consumption with increase Ta• Increase concentration and filtration of urine in

hot and dry season.

Some Avian Solutions to Water and Temperature Inca Dove (MacMillen)

– Temperature lability– Gular fluttering– Reduce Metabolism at night.

Desert Black Throated Sparrow (Smith and Bartholomew).– Get water from seeds.– Concentrate urine (best of all birds)

Some Avian Solutions to Water and Temperature Tawny Frogmouth and Poorwill

(Lasiewski and Bartholomew)– Increase amplitude and rate of gular

fluttering, can dissipate 100% of metabolic heat.

Sand Grouse (Cade)– Parents fly 15mi to water, fluff feathers

and sit in water, fly back to young who drink 20g of water from the feathers.

Some Avian Solutions to Water and Temperature Quail (Bartholomew, Dawson, and

Hudson)– Temperature lability– Pant– Lose heat through legs.– Torpor at low Ta– Unusually low metabolic and heart rate for

their size– Get water from food.– Need water to reproduce.

Some Avian Solutions to Water and Temperature Zebra Finch

– The Kangaroo Rats of birds.– Metabolic water– Water independent– Breeds only when it rains, whether it is

every 4 weeks, 9 months, or 3 years.