Foraging Risk and Variation shortened - Diet and Foraging...

Diet and Foraging Behavior
Part 2: When economics goes bad
Optimal foraging theory – how the previous lecture
was framed; it’s basically an economics approach
It assumes that maximizing something (like E/T) is
what’s important.
- variation in that “something” is not important
- variation among individuals is not important
Size of prey Energy / Time
Optimal Foraging :
birds always try to
maximize; everything else
is “error”
Size of prey
Energy / Time
Might variation be
important, too?

Importance of Variation
The basic idea : when a bird is easily able to
attain the maximum, it will behave differently
than when variation in food is great and it can
rarely attain that maximum.
But how might this work ?
A hypothetical example :
•
Assume a bird needs 10 units of food per day to survive
•
It has 2 choices on where to forage
1. It will always get 9.5 units/day; no variation
2. It will get an average of 9.0 units/day; much variation
What’s more important, the average or the variation?

Do birds really respond to variation?
Juncos need 2 seeds/minute Tom
Caraco
Junco
2
2
2
2
2
2
2
2
2
2
0
4
0
0
0
0
0
4
4
4
4
4
Average = 2 seeds/min
No variation
Average = 2 seeds/min
High variation
Juncos always
chose this side.
“Risk Averse”

Change the average, not the variation
1
1
1
1
1
1
1
1
1
1
0
2
0
0
0
0
0
2
2
2
2
2
Average = 1 seed/min
No variation
Average = 1 seeds/min
High variation
Juncos always
chose this side.