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Foraging and prey selection

Optimal Foraging theory: Individuals will maximize benefit:cost Model predictions only as good as the parameters put into them 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 Eat in closest tree, regardless of species Eat any leaf in that tree Eat entire leaf Low costs:many calories Behavior 2 Search out a few trees of a rare species Eat only young leaves Often eat only leaf petiole 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 trap jaw ants: 52 m/s cheetah : 31 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.

New Caledonian Crow Chimpanzees

Kenward, Weir, Rutz, Kacelnik (Oxford) Nature

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.

Shifts in body size: large ants lost worker head width (mm) % of horned lizard diet Argentine ant Argentine ant frequency worker head width (mm)

Proportion initial weight Hatchling horned lizards can not subsist on a diet of Argentine ants.

Proportion initial weight Hatchling horned lizards can not subsist on a diet of Argentine ants.

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):

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. H3: They help to preserve food longer Sherman PW, Billing J Source: BioScience 49: