Foraging

• Foraging: the search for food, which can include grazing, browsing, hunting, and scavenging.

  • provides energy
  • individuals must search for and capture food
  • know when to move on to another resource
• Optimal Foraging Theory: a behavioral ecology modeling approach that predicts how an animal behaves when searching for food.
• Optimal Diet Model: predicts that animals will select a diet that maximizes energy intake rate.

  • foragers maximize fitness by max. energy
  • food items are encountered one at a time
  • food items can be ranked by profitability
• Handling Time: time to manipulate items before consumption.
• Profitability: energy/ handling time.
• Seagulls at the beach will take clams, fly with them, and then drop them to break them open.
• Optimal Patch Use: predicts how long a forager should exploit a food patch.

  • foragers attempt to max. energy intake
  • all patches are identical
  • travel time is constant
• Optimal Patch Time is Affected by Travel Time:

  • for shorter travel times, the optimal patch time is small.
  • for longer travel times, the optimal patch time is longer.
• Animals can combine sample info. from a patch with prior knowledge about the distribution of patch types in the environment, using Bayesian statistics.
• Antipredator Behavior: Behavior that reduces the likelihood of being preyed upon.

  • animals can do this alone or in a group, actively or passively
• Active Social Defense Example:

  • meerkats come together (mobbing) to protect their colony against a snake. There is a guard to alert them of any dangers.
• Passive Defense Example:

  • Harvest ants aggregating so they are less likely to be eaten by a dragonfly
• Dilution Effect Hypothesis: proposes that associating in groups makes it less likely that any one individual will be preyed upon.
• Selfish Herd Hypothesis: suggests that individuals in a group attempt to reduce predation risk by putting other individuals between themselves and the predator.

  • "Using other animals as a shield between yourself and the predator"
• Other Ways to Avoid Predation:

  • Blend In: camouflage yourself to the environment. Ex. moths
  • Stand Out: aposematic coloration to avoid being eaten. Ex. monarch butterflies.
  • Batesian Mimicry: palatable species mimics a dangerous species to deter predators. Ex. coral snakes
• Stotting in Thomson's Gazelles

  There are many hypotheses for stotting behavior. Stotting is when they jump and show their rear ends.

  • Alarm Signals
  • Social Cohesion
  • Confusion Effect
  • Attack Deterrence
• The primary prediction of the selfish herd hypothesis is that individuals should do which of the following?

  Attempt to move to the center of the group
• Dispersal: a relatively short distance, one-way movement away from a site.
• Competition Hypothesis: If two sites have the same density of individuals but differ in the quantity of food, we can expect higher levels of dispersal behavior in the site with less food.
• Inbreeding Avoidance Hypothesis: one factor driving the evolution of dispersal is a minimization of inbreeding.
• Breeding habitats differ in quality and therefore individuals differ in reproductive success.

  • individuals with low reproductive success may exhibit breeding dispersal
  • individuals with high reproductive success should exhibit site fidelity
• Win Stay Lose Shift: many species exhibit site fidelity after reproductive success and exhibit breeding dispersal after a reproductive failure.
• Migration: relatively long distance and a two-way movement.

  • Evolves when fitness benefit of migration > fitness cost of migration
• In the Serengeti, mammals appear to track biomass and quality of grass during their migration.