General Water Economy

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General Water Economy
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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.

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Water Balance

• Water gains
• drinking
• food
• metabolic water

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Water Balance

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

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Man in the Desert Energy and water balance
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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.

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Other animals in the desert

• Burros
• Capable of losing 20 of their body weight and
  can then restore it rapidly.

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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.

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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 -
  103F).

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Other animals in the desert

• Camels cont.
• They reduce cuticular (integumentary) water loss
  via insulation.
• What about the humpgt
• hump 50 fat
• 1.1lb fat 1lb H2O
• Hump weighs 110 lbs 50 lbs H2O, or about 13 gal
  of water.

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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.

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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

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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)

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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.

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Other animals in the desert

• No water cont.
• Temperature lability
• Development of heat loss devices such as the ears
  in jack rabbits.

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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?

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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.

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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?

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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.

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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.

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Nocturnality in P. truei

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

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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.

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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.

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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.

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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?

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

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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

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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.

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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.

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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.

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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.

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Some Avian Solutions to Water and Temperature

• Aberts Towhee (Dawson)
• Found only near desert streams.
• Active only at dawn and dusk.
• Temperature lability

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Some Avian Solutions to Water and Temperature

• White Pelicans (BartholomewDawson)
• 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.

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Some Avian Solutions to Water and Temperature

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

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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.

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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.

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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)

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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.

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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.

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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.