feeding behavior forage – to look for food – herbivore – carnivore – omnivore
TRANSCRIPT
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Feeding Behavior
• Forage – to look for food– Herbivore – Carnivore– Omnivore
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Feeding Behavior
• Herbivores are prey to carnivores.
• Prey = an animal hunted or seized for food, especially by a carnivorous animal.
• Prey have evolved strategies and defenses to avoid being eaten.
• Carnivores are predators of herbivores
• Predator = an animal that lives by preying on other animals for food by hunting and killing them.
• Predators have evolved strategies that enhance their hunting skills.
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Feeding Behavior
• Evolve = To change over time.• Due to natural selection (survival of the fittest)
predator and prey are slowly changing to become more successful at what they do.
• However, each of the prey’s new adaptations (a trait that makes an animal more successful) for defense is followed by the predator’s new counter-adaptation for hunting.
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Foraging Behavior
• Foragers can make four types of decisions:– where to eat (location of most likely food supply)– when to eat (time of day or night)– what to eat (berries or salmon)– how to eat (individually or in groups)
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Stages in Foraging
• The first stage is a generalized search for appropriate habitat. For example, deer may have learned, or instinctively know, that richer forage is found near streams and rivers.
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Foraging Strategies• The second stage is a
search strategy to find the actual food items. Searching strategies can be divided into two basic types:– sit and wait (carnivores
only)– active searching
(carnivores or herbivores), such as the hunting behavior of coyotes, and the foraging behavior of ungulates (deer-like)
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Foraging Behavior• Once food is discovered animals may find
hoarding is a beneficial component of foraging behavior.
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Foraging Behavior
• The final stage is consumption. – an herbivore consumes the right plant when it is
found– a carnivore must kill its prey before consumption.
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Foraging in Groups
• Problems with foraging in groups:– Uninvited guests. These can be members of the
same or different species. When one animal observes another eating, it is attracted and attempts to share the food.
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Foraging in Groups
• Problems with Foraging in Groups– The animal that finds the food must choose a
balance between defense and consumption. – For the guest, the advantages are numerous
• it eats without searching• avoids the risks involved in capturing and killing prey
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Foraging in Groups
• Benefits of Group Foraging– Cooperative hunting. Animals may cooperate to
trap elusive prey, or in taking down larger prey. – Social bonds derived from kinship or mating may
enhance cooperation. – However, once the prey item is secured,
competition for food among the hunters can be severe and may be regulated by dominance relationships.
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Cost-Benefit Analysis of Feeding Behavior
• Example:– Researcher observes crows eating snails– Researcher divides all of the available snails into
three groups by size: small, medium and large – He observes
• Crows pick up only large snails• Crows fly up 5 m and drop snails. • Snail-shell breaks and crows eat snails.
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Research Questions
1 - Why are only large snails eaten and small and medium snails ignored? Answer in group.
Large snails break more easily than small snails.
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Researcher’s Hypotheses
• How do you test hypothesis 1? Answer in group.
• Results: Large snails break most easily!
Drop different sized snails from various heights and observe if there is any
difference in breakage.
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Research Questions
2 - Why does the crow fly 5m high instead of lower or higher? Answer in group.
Drops less than 5 m do not break snails. Drops greater than 5m do
not increase snail breakage.
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Researcher’s Hypotheses
• How do you test hypothesis 2?
• Results: – As the height of the drop increased up to 5meters
the snails broke more easily. – Above 5 meters there was no improvement in
their breakage.
Drop large snails from heights under 5 meters, at 5 meters, and over 5 meters. Observe how
many break at each height.
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The behavior of the crows is optimal
• Crows do not waste their time (and calories) by foraging for small or medium-sized snails.
• Crows do not waste their time by flying at heights above or below 5 meters.
• Crows reap the highest benefit with the lowest cost.
COSTBENEFIT
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Environmental Factors Affect Feeding Behavior
• Example:– Researcher observes in California:
• Inland garter snakes eat fish and frogs (few slugs available)
• Coastal garter snakes eat banana slugs (slugs are plentiful)
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Research Question
• What controls the feeding behavior of garter snakes? – Is it controlled by genetics? OR – Is it a function of available food?
• Hypothesis: If inland snakes and coastal snakes are
raised in the same environment then they will both readily eat slugs.
(Food availability.)
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Researcher’s Hypothesis
• How do you test this?– Pregnant female snakes
are taken from both environments and kept under identical conditions.
– The baby snakes born in this new environment are offered slugs to eat.
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Observations and Conclusions
• Observations– The offspring of coastal garter snake ate slugs– The offspring of inland garter snake wouldn’t eat
slugs
• Conclusion– The feeding behavior of garter snakes is controlled
by genetics NOT food availability – Therefore the researcher’s hypothesis was
incorrect
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Extension of Garter Snake Experiment
• Experimenter mated the inland snakes with the coastal snakes. (Garter snakes usually bear 10-30 live young*.) – Of the young, some would eat slugs and others
would not. – This reinforced the conclusion that “slug-eating” is
controlled by genetics and shaped by natural selection.
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Conclusions
• Snakes that “liked” slugs were fit on the coast. This trait was naturally selected for in a coastal environment.
• Eating slugs would not make an inland snake more fit. This trait was NOT selected for in an inland environment.
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Game Theory
• Game theory: the payoffs to individuals associated with one behavioral tactic are dependent on the types and frequencies of behaviors exhibited by other animals in the population.
Game Theory Activity
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Evolution of Two Types of Feeding Behavior
• Example: Roseate tern – two different behaviors found in a population (controlled by genetics!)– Fish hunting behavior (bird does NOT have the
stealing behavior)– Fish stealing behavior (bird does NOT have the
hunting behavior)
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Evolution of Two Types of Feeding Behavior
• Is it possible for the stealing birds to evolve without the hunting birds in the population?
• Is it possible for the hunting birds to evolve without the stealing birds in the population?
• Which phenotype evolved first?
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Evolution of Two Types of Feeding Behavior
• Imagine all roseate terms in a population hunt for fish*
• What would happen if a mutation occurred in which a bird didn’t hunt, but instead stole fish from others? Would it survive?
• What would happen if the young of this one mutant bird were all stealers? Would they go hungry?
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Evolution of Two Types of Feeding Behavior
• What would happen if the proportion of stealing birds in the population continued to increase?
• Would the stealing birds go hungry? • What would happen to this behavior in the
population? Increase or decrease?• What happens to the number of hunters if the
population of stealers decreases?
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Populations of Roseate Terns
• Scientists have found about – 35% of roseate terns are stealers – 65% are hunters. – These numbers represent an equilibrium.
• If the % of stealers goes up, the % of hunters goes down.
• Then the % of stealers decrease and the % of hunters increase.
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Conditional Foraging Strategies
• Each animal in a population is able to use more than one method for finding food. The behavior is NOT genetically predetermined
• Each animal alters its behavior depending on the conditions
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Conditional Foraging Strategies
• Example: small sandpiper
• Birds forage for small invertebrates on beach
• Dominant birds monopolize patches of seaweed. They flip it over looking for food. This is the best source of food on the beach.
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Conditional Feeding Strategies
• Subordinate birds are left to probe in the mud and sand for food.
• If they go near the seaweed, the dominant birds chase them away.
• However, if there is a lot of seaweed, all of the birds forage among the seaweed.
• Therefore the birds choose their foraging behavior depending on the condition.
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Feeding Behavior and Skulls