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Foraging and prey selection
Optimal Foraging theory:
Individuals will maximize benefit:cost
Costs
Time/energy spent
locating food
Time/energy spent
handling food
Benefits
Calories gained
How can we reduce costs?
Minimize time spent looking for and handling food.
Develop search image for common prey
How can we reduce costs?
Minimize time spent looking for and handling food.
Reduce handling time
Catania and Remple, 2005 Nature
New York Times
Underground Gourmet: Mole Sets a
Speed Record
February 8, 2005
In the world of competitive eating, it's
time to crown a new champion.
Researchers at Vanderbilt University have found that the
star-nosed mole can eat 10 mouthful-size chunks of
earthworm, one at a time, in 2.3 seconds, or 0.23 second a
chunk. It is the fastest eating ever measured in any
mammal.
July 4th, 2004 World Hotdog
Eating Championships
Takeru Kobayashi pounded 53
hotdogs in just 12 minutes to set
a new world record! That's more
than one dog every 15 seconds!
Behavior 1
Behavior 2
Eat in closest tree,
regardless of species
Search out a few trees of
a rare species
Eat any leaf in that tree
Eat only young leaves
Eat entire leaf
Often eat only leaf petiole
Low costs:many calories High costs:few calories
Based only on maximizing
calories, which behavior
should howler monkeys
perform?
Why don’t howlers forage “optimally”?
Because we failed to consider some of the costs of
each behavior:
Most tree species have high levels of alkaloid
poisons and indigestible tannins
In rare tree species, individual trees vary in their
level of alkaloids and tannins
Young leaves have more water and higher nutritive
value than old leaves
Leaf petiole has lower alkaloids than leaf blade
Costs of predation on foraging behavior:
Leaf-cutter ants and parasitoid fly
Ants cut & collect leaves
to feed to fungus, which
they eat.
Costs of predation on foraging behavior:
Leaf-cutter ants and parasitoid fly
Variation in worker size leads to variation in energy
gained:used efficiency
Most efficient sizes most frequent foragers, but only at
night!
Risk of parasitoid fly (Phoridae) during day
changes costs for large workers.
Possible control
strategy for introduced
red imported fire ants.
How can we reduce costs?
Minimize time spent looking for and handling food.
Excel at capturing prey
angler fish jaw protrusion: 10 m/s
mantis shrimp: 23 m/s
How can we reduce costs?
Minimize time spent looking for and handling food.
Excel at capturing prey
cheetah : 31 m/s
trap jaw ants: 52 m/s
not a fair comparison, but diving
peregrine falcons reach 77 m/s
How can we maximize benefits?
Increase caloric intake relative to expenditure.
How can we maximize benefits?
Increase caloric intake relative to expenditure.
How can we maximize benefits?
Strategies can change with age / size.
Chimpanzees
New Caledonian Crow
Kenward, Weir, Rutz, Kacelnik (Oxford). 2005 Nature
http://www.nature.com/nature/journal/v433/n7022/extref/433121a-s4.mov
Two common foraging strategies:
“sit and wait” (ambush predator - uses primarily
visual cues, movement)
advantages - expend little energy, not seen by
predators
disadvantages - how often does food come along?
“active predators” (hunters - use visual and olfactory
cues)
Lizard families fall
into two
categories:
Blue = sit and wait
Orange = active
Our favorite lizard again…
Phrynosoma coronatum
Declining throughout its range.
A “sit and wait” ant specialist.
% of horned lizard diet
Argentine
ant
6
4
2
0
0
0.5
1.0
1.5
2.0
worker head width (mm)
2.5
50
40
Argentine
ant
30
20
10
0
0.2
0.6
1.0
1.4
worker head width (mm)
Shifts in body size: large ants lost
1.8
kg meat/lion/day
9
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
hunting group size
Caraco and Wolf
Packer
Why do humans use spices?
H1: They provide extra calories
But very little amounts are used
H2: They provide rare nutrients
Nutritional analyses say no
H3: They help to preserve food longer
Prediction 1: spices show antimicrobial properties
See also: Srinivasan K. Food Research International 38 (1): 77-86. 2005
H3: They help to preserve food longer
Prediction 2: spice use should be proportional
not to availability, but to risk of food spoilage
Spices are more commonly used in hot
climates where spoilage is more common.
Sherman PW , Billing J Source: BioScience 49: 453-463 1999