Winter WanderingForaging efficiency is how much energy Foraging efficiency is how much energy

a deer GAINS from the food it eats a deer GAINS from the food it eats compared to how much energy a deer compared to how much energy a deer

SPENDS to get the food.SPENDS to get the food.Foraging efficiency = Foraging efficiency = GAINED GAINED SPENT SPENT

Foraging Efficiency values bigger than 1 mean that a deer is spending less than

it gains. Foraging Efficiency values less than 1 mean a deer is spending

more than it gains, and probably losing weight as

a result.

Foraging Efficiency values bigger than 1 mean that a deer is spending less than

it gains. Foraging Efficiency values less than 1 mean a deer is spending

more than it gains, and probably losing weight as

a result.

Help Daisy decide where to go:It’s winter, and food is hard to

come by. What’s more, it’s snowy!Daisy needs to decide if she

should stay in her home patch of forest, or if she should cross the snowy meadow

to a new patch of forest with fresh shrubs to eat.

Here are the numbers:

+ Energy Gains +

If Daisy stays in the first patch of forest, where she’s eaten most of the food, she can eat enough food to gain 2.0 Jewels/minute for the next day (24 hours).

If she gets to the new patch of forest, she can eat enough food to gain 3.0 J/min for the next day.

+ Energy Gains +

If Daisy stays in the first patch of forest, where she’s eaten most of the food, she can eat enough food to gain 2.0 Jewels/minute for the next day (24 hours).

If she gets to the new patch of forest, she can eat enough food to gain 3.0 J/min for the next day.

+ Energy spent +

If Daisy stays in her patch of forest, she burns 3.5 J/min, and this is the same as in the new patch of forest.

But to get to the new patch of forest, she needs to cross 300 meters of knee-deep snow.

This costs her 4 times as much energy as usual per minute, and it takes her 30 min to cross the meadow.

+ Energy spent +

If Daisy stays in her patch of forest, she burns 3.5 J/min, and this is the same as in the new patch of forest.

But to get to the new patch of forest, she needs to cross 300 meters of knee-deep snow.

This costs her 4 times as much energy as usual per minute, and it takes her 30 min to cross the meadow.

What should Daisy do?

Go back and carefully read he information, then use the concept of FORAGING EFFICIENCY (gain/spent), calculated for the next 24 hours,

to help Daisy decide what to do.

Here are the steps:

1) Calculate energy GAINS for the old versus new forest patches:Old forest GAIN = 2.0 J/min x 60 min/hour x 24 hour/day = 2,880 J

New forest GAIN= 2.7 J/min x 60 min/hour x 23.5 hour/day*= 3,807 J

* did you see this tricky part? 30 minutes were spent walking to the new patch of forest , so no energy was gained during this time eating.

Here are the steps:

2) Calculate energy SPENT for the old versus new forest patches:Old forest SPENT = 3.5 J/min x 60 min/hour x 24 hour/day = 5,040 J

New forest SPENT= 3.5 J/min x 60 min/hour x 23.5 hour/day + (3.5J/min x 4) x 30 min = 4,935 + 420 = 5, 355 J

Here are the steps:

3) Calculate foraging efficiency (FE) for the old versus new forest patches:

Old forest FE = 2,880 J / 5,040 J = 0.57

New forest FE = 3,807 J / 5, 335 J = 0.71

Answer: Daisy should move to the new forest patch. Her foraging efficiency is

higher... she gets 71% (.71) of her spent energy back from her food this way, better

than 57% if she stayed.Did you notice?Did you notice?

No matter what she does, Daisy is No matter what she does, Daisy is LOSING energy each day in the LOSING energy each day in the

winter. Deer lose weight all winter winter. Deer lose weight all winter long, making up the energy they long, making up the energy they

need each day by burning fat stored need each day by burning fat stored on on their bodies. Deer also lower on on their bodies. Deer also lower their daily metabolic rate, so that their daily metabolic rate, so that they burn less energy than during they burn less energy than during

the summer.the summer.