Animal behaviour L20-25

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Animal behaviour L20-25
2015-12-05 23:06:23
Animal behaviour biology

University of Manitoba animal behaviour BIOL3360 Lectures from 20-25
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  1. L20 Magnetic compass
    • Potential cues for orientation
    • - Polarity
    • - Intensity (strongest at poles)
    • - Inclination of lines of force (most animals that use magnetic cues use this one)
  2. Use of magnetic cues
    • Polarity: used by small number of species e.g. salamanders, salmon fry, mole rats, bats
    • Intensity: not known for any species
    • Inclination of lines of force: implicated as critical aspect of magnetic stimulation in most studies of magnetic orientation
  3. Magnetic orientation
    • Initially discovered in birds - European robins, homing pigeons
    • Controversial topic during 1950s and 1960s - results of empirical studies apparently contradictory
  4. Common methodology - Helmholtz coil
    • Can experimentally alter magnetic field
    • - Reverse polarity
    • - Alter inclination of field
  5. Experimental findings of Helmholtz coil with pigeons
    • Never any effect of polarity
    • Effects of inclination varied among experiments

    Via meta-analysis, Keeton identified cloud cover as the factor determining whether inclination change affected orientation
  6. Keeton meta-analysis found:
    • Inclination compass only critical for navigation on overcast days
    • When sun available, European robins and homing pigeons use sun compass
    • - Ignore information from altered inclination compass
    • Redundancy of systems provides backup
  7. How do birds sense magnetic cues?
    • Earth's magnetic field weak (ca. 50μT)
    • difficult to resolve in biological systems
    • 2 traditional candidate mechanisms
    • - Lateral line system (limited to fish and amphibians)
    • - Ferromagnetic particles (e.g. magnetite)
    • -> Have been found in association with nerve endings in upper beak of birds
    • -> Ablation of those nerves doesn't affect compass orientation
    • An alternative mechanism must underlie avian magnetic compass orientation
  8. Sensing magnetic cues: Insight into that mechanism comes from effect of light on orientation ability
    • in newts, fruit flies, and birds, experiments have consistently demonstrated the orientation responses to magnetic cues are dependent upon wavelength of light
    • Under short wavelength (blue-green)/high energy light, orientation fine
    • Under long wavelength (yellow-red)/low energy light, unable to orient

    Compass requires light energy
  9. Sensing magnetic cues
    Further insight from other results:
    • Wiltschko et al. 2002. Lateralization of magnetic compass orientation in a migratory bird
    • Bird's ability to orient is eye dependent
    • - If left eye covered, orientation unaffected
    • - If right eye covered, unable to orient

    Except for garden warblers. They use both eyes.

    How does high energy light striking the right eye allow magnetic orientation?
  10. Thorsten Ritz - UC Irvine
    • biophysicist with background in quantum physics of bacterial photosynthesis
    • became interested in light-dependence of avian orientation and collaborated with Wiltschko
  11. Sensing magnetic cues
    Explained by Thorsten Ritz:
    • Pigment molecules called "cryptochromes" located in avian retina
    • Light energy excites electrons, influencing electron spin states of "radical pairs" 
    • ---> Closely opposed groups of atoms, each with an odd number of electrons
    • Radical pairs exist in either a single or triplet conversion state (depending on electron spin)

    • Ratio of states is affected by magnetic fields, changing predictably with angle of animal relative to inclination of field
    • Found that orientation disrupted by low freq. RF energy (0.1-10 MHz)
    • RF of such wavelengths known to affect transition states of radical pairs, but not operation of magnetite receptors

    • Bird's magnetic compass is in effect a "chemical compass"
    • Mechanism of transduction from ratio of radical-pair transition states to neural stimulation as yet unknown
  12. Sensing magnetic cues
    Explained by Thorsten Ritz
    Sequential study
    Suggests parallel arrangement of cryptochrome membranes in receptor may allow radical-pairs to form and influence membrane permeability and thus produce angle-dependent firing rates

    • Cryptochrome-based receptors give rise to axons that ultimately project to centers where visual and gravitational input integrated
    • Suggests birds may perceive field as a "shadow" in the visual domain, with intensity contingent on angle of orientation
    • While left and right eye would "see" mirror images, eye-dependence results suggest that central mechanisms filter information producing right-eye dependence.
  13. "A visual pathway links brain structures active during magnetic compass orientation in migratory birds" Heyers et al. 2007
    Builds upon earlier finding that cryptochromes and area of forebrain (the "N cluster") show increased activity in the context of compass orientation.
  14. Heyers et al. 2007
    • Worked with migratory garden warblers
    • - Used neuronal tracing to identify how cryptochromes and "N cluster" interact
    • Identified a functional neural connection between retinal neurons and "N cluster" via the visual thalamus
    • Magnetic information transduced by the cryptochromes is part of the ascending visual processing system
    • Suggests birds "see" compass information provided by earth's magnetic field
  15. True navigation
    Ability to maintain reference to a goal without the use of landmarks

    • Requires compass and map
    • Map may be -
    • Magnetic:
    • - Birds become lost in areas of geomagnetic anomalies on sunny days
    • - Whale strandings common in areas of such anomalies

    • Olfactory
    • implicated in navigation by some fish

    • Auditory
    • e.g. Homing pigeons - Atmospheric progation modeling indicates homing pigeons use loft-specific infrasonic 'map' cues
  16. True Navigation #2
    • Commonly expressed in animals that migrate
    • - Periodic movements between one area & climate and another area & climate

    Methods employed in study of migration have improved dramatically over the years
  17. Studying migration
    • Marked individuals - bands
    • Radiotelemetry
    • Satellite telemetry
    • Geolocators
  18. Geolocators
    • Light electronic devices that periodically record ambient light intensity over time to determine location
    • - day length (dawn-dusk) determines latitude
    • - mid time between dawn and dusk gives longitude
    • Far less costly than satellite telemetry if archival
  19. Geolocator - purple martins
    • Purple martins did not migrate faster or arrive earlier at breeding sites in an early spring
    • Possible fitness costs if they missed peak food for young
  20. Natural chemical tags
    • Chemical composition of organism varies among geographical locations
    • quantification of that variation allows identification of origin

    • e.g. Wassenaar ad Hobson. Natal origins of migratory monarch butterflies at wintering colonies in Mexico: New isotopic evidence
    • - They migrate up 3500km
  21. Wassenaar & Hobson 1998
    Monarch butterfly migration (use thermals)
    • Examined hydrogen isotope composition of monarchs from wintering grounds in Mexico
    • - Concentrations of deuterium in rain water varies predictably across continent (More deuterium in coastal than inland regions)
    • Found each overwintering group consisted of individuals from across the monarch's breeding range
    • Good news for monarch breeding populations given deforestation in Mexico

    • Merlin, Gegear and Reppert
    • Antennal circadian coordinates sun compass orientation in migratory
    • - We show that the antennae are necessary for proper time-compensated sun compass orientation
  22. Other inverts migrate as well
    • Spiny lobsters migrate to deeper waters as winter approaches
    • Form single-file lines
    • Rely on magnetic cues to orient migration (Lohmann 1984)

    NOT swift current direction or swell
  23. Piscine migration
    • European eels have 2.5 year journey to Sargasso sea (as larvae)
    • Larvae return to freshwater and mature
  24. L21. Piscine homing
    • Salmon hatch in freshwater rivers or lakes
    • Descend from natal streams into the ocean
    • Spend 1-5 years (depending on species) at sea before attaining breeding condition
    • At maturity leave feeding grounds and return to same river in which they hatched to spawn
    • Rely on different cues for orientation at different stages of their journey.
  25. Salmon homing
    Returning to shoreline: magnetism, sun compass, moon compass, polarized light 

    • Returning to home stream: Olfactory cues
    • Determined experimentally 
    • - Blinding doesn't impede return to home stream
    • - Olfactory impairment (zinc sulfate or nose plugs) significantly reduces homing
  26. Salmon homing - Arthur Hasler 1975
    • Reared groups of young salmon in water of three possible types:
    • -Containing morpholine
    • -Containing phenethyl alcohol (PEA)
    • -Control water (no chemical added)

    • Fish marked as to group of origin and released into lake equidistant from streams containing test chemicals
    • - Along 200 km of shoreline, 19 streams with one containing morpholine and one with PEA
    • - Trapped fish entering all 19 streams
    • - Over 90% of the fish caught in the morpholine and PEA treated streams had been reared in water containing those chemicals as smolts
    • Morpholine and PEA fish never caught in opposite chemical-treated stream
    • Young fish imprint to their odour of their home stream
    • Stream odour derives from mixtures of chemicals from rocks, soil, and plants plus those of mucus, feces and pheromones in the stream in nature
  27. Salmon homing - further studies
    From telemetry work
    • Individual fish orient directly to the shoreline
    • At shoreline, individuals "cruise" the shore
    • Individuals sample the chemical effluent of each stream until they arrive at the one matching the chemical bouquet of their home stream
    • Engage in both positive rheotaxis and positive chemotaxis at home stream (if odour lost, fish will float downstream until odour re-acquired
  28. Reptilian migration
    • 1800 km to lay eggs on shore of Ascension island 
    • -Use chemical cues
    • - Mostly magnetic cues- Geomagnetic map used in sea-turtle navigation (Lohmann et al. 2004)
    • (Steeper or shallower inclination depending on latitude)
  29. Mammalian migration - reindeer
    • Return to traditional calving grounds
    • In calving grounds, predators are easier seen
    • On coast/calving grounds, wind from coast, keeps flies away
  30. Mammalian migration - gray whale
    • 10,000 km migration from above arctic circle to calving grounds off Baja
    • (Warmer for calves to survive because they don't have enough blubber) greater survivorship of young
  31. Avian migration
    • Arctic tern nest within 10 degrees of north pole, but overwinter in the Antarctic 
    • Annually circumnavigate globe (travel ca. 44,000 km/yr)
    • They follow maximized daylight
  32. Egevang et al. 2010
    • Tracking of Arctic terns reveals longest animal migration
    • - 82,000 km/yr
  33. Why do animals migrate? (function)
    • 1. Remain within limits of survival: may be unable to withstand climate
    • 2. Reproductive benefits: certain areas impart greater success
    • 3. Energetic payoffs: cost of living in harsh environment exceeds cost of migration
    • (All relate to abiotic environment, but biotic environment important as well)
    • 4. Reduced competition: move to areas of reduced population density or to areas with more resources. Explains return to temperate zone to breed.
    • 5. Reduced predation (possibly): move to areas with fewer predators
    • 6. Reduced parasitism (flawed. only theoretically, not observed) 
    • - Prevent close adaptation of parasite to host

    Reasons not mutually exclusive
  34. Evolution of migration - hypotheses
    • 1. Glacial retreat hypothesis
    • 2. Radiation hypothesis
    • 3. Resource distribution hypothesis
    • 4. Continental drift hypothesis
  35. 1. Glacial retreat hypothesis
    • Wisconsinan glaciation - ca. 80 - 10kybp
    • Temperate animals forced south
    • Glacial retreat - animals return to ancestral breeding grounds
    • Some current routes follow path of glaciers
    • Why not stay south?
  36. 2. Radiation hypothesis
    • Vast majority of species evolved in tropics
    • Expanded range to temperate regions:
    • - Reduced competition
    • - Exploitation of resources
    • Return to warmer ancestral area for winter
  37. 3. Resource distribution hypothesis
    • Makes no assumption about area of origin
    • Migrate to exploit ephemeral or moving resources
    • e.g. monarchs moving to exploit milkweed (They sequester the toxin)
  38. 4. Continental Drift Hypothesis
    • Earth about 4.5 billion years old
    • Pangea - supercontinent (225 mybp drifted apart)
    • Migration evolved as spp. followed drift
    • Continents in present position 65 mybp
    • - Many migrants evolved after continental drift
    • - Can explain only some spp. migration
    • e.g. Green sea turtles
  39. Orientation mechanisms place animals in suitable habitat
    • - a place to live
    • Also allow orientation relative to other elements of the environment

    • --> Food to eat - foraging
    • --> Predators to avoid - antipredator behaviour
  40. FORAGING - definition
    Methods employed in locating and consuming food

    • All living things require energy 
    • Animals obtain energy by finding and consuming food
  41. L.22 Animal foraging behaviour
    Principal foraging strategies
    • 1. Filter feeding
    • 2. Herbivory
    • 3. Carnivory

    - Not mutually exclusive, but convenient in terms of behaviour
  42. Filter feeding - bivalve molluscs
    • Filter food particles from water by moving water through gills
    • Not just in invertebrates
    • - Adult paddlefish
    • - Baleen whales
    • - Flamingos
    • - Mallards, shoverlers
  43. Behavioural decisions for filter feeders?
    • Animals decide:
    • When to filter 
    • Where to filter (orient to areas of abundant prey)
  44. Herbivory
    • Consumption of material produced by plants
    • May involve simple behavioural decisions:
    • e.g. simplest form of herbivory - grazing
    • - When to graze
    • - Where to graze
    • - Discern edible from inedible items (what)
    • May also involve complex behaviours
  45. Honey bee foraging on alfalfa
    • Honey bees normally avoid pollen foraging from alfalfa 
    • - Alfalfa has spring-loaded anther that strikes bee
    • If we force honey bees to forage from alfalfa:
    • - Bees adopt two strategies

    • 1. Recognized and visit only "tripped" flowers (only spring once)
    • 2. Chew through side of flowers, avoiding anther
  46. Animal agriculture definition 
    e.g. Black-tailed prairie dogs
    Fostering growth of another species for consumptive purposes

    • e.g. Black-tailed prairie dogs
    • Pull non-preferred grasses from areas around burrows
    • Culling ensures proliferation of preferred plant species
    • May have evolved to preclude growth of tall-growing grasses that act as visual obstruction
  47. Animal agriculture definition 
    e.g. Mountain gorilla
    • Fostering growth of another species for consumptive purposes
    • Rip down large plants or parts of small trees
    • Results in surge of growth of young, succulent vegetation
    • Individuals return to areas they modify to feed on new growth (but also potential display function to other competing males)
  48. Animal agriculture - Leaf cutter ants
    • Cut fresh leaves and return those to the nest
    • Don't feed directly upon the leaves
    • Actively prepare leaves to be used as substrate to grow fungus
    • Inoculate leaf material with hyphae and grow fungus to eat
    • This fungus only grows in these colonies
  49. Animal agriculture - aphid tending
    • Move aphids from plant to plant, milking them for "honeydew"
    • Ants provide protection and foraging opportunities for aphids
    • Ant/aphid mutualism
  50. Domestication
    Where members of one species assume control of the feeding, breeding, and general care of members of another species

    e.g. Aphid tending
  51. Carnivory
    • Consumption of animals
    • May involve simple behavioural decisions
    • e.g. simplest forms of carnivory - like grazing: gleaners/scavengers
    • - When to eat
    • - Where to eat
    • - Discern edible from inedible items

    e.g. scavengers

    *Not saying that other behaviours are simple for scavengers (e.g. communication)

    May also involve complex behaiours
  52. Carnivory - Predation
    • Pursuit
    • Ambush
    • Trap use
    • Tool use
  53. Pursuit
    • Involve active chasing of prey
    • e.g. Cheetah
    • Stalks to within a few hundred meters of prospective prey
    • Charges prey at speed up to 115 kph
    • Averages nearer 60 kph
    • Bursts of speed typically sufficient to capture prey
  54. Ambush
    • Waiting motionless until prey draws close enough to strike
    • e.g. cats, frogs, and toads, snakes, spiders

    • Key to success is avoiding detection 
    • - Use of cover
    • - Crypsis
    • - Aggressive mimicry
  55. Examples of animals using cover while ambushing
    • Moray eels (hide underneath rocks and corals)
    • California trapdoor spider:
    • Crounches behind moveable cover of underground burrow
    • When prey detected above ground, spider pops out and grabs it
  56. Crypsis
    Blending with background via evolutionary modification of colouration, markings, morphology, and behaviour

    e.g. Spotted coats of leopards and jaguars
  57. Ambush using crypsis
    • Insectivorous mantid with body parts and colours resembling flowers of orchid on which it rests
    • Walks unevenly, mimicking petals blowing in wind
  58. Aggressive mimicry
    Where a species mimics the appearance or behaviour of a harmless or beneficial species for the purpose of agression
  59. Ambush using aggressive mimicry
    • e.g. False cleaner wrasse ("blenny") mimics appearance and behaviour of actual cleaning wrasses
    • Cleaner wrasses remove external parasites, fungi, and bacteria from others
    • Blennys take a bite out of "unsuspecting" hosts

    • e.g. Angler fish
    • - Have modified spine of dorsal fin on tip of snout
    • Tip fleshy or endowed with tuft of fibres resembling prey item
    • Animated and thus attracts smaller fish

    • Body otherwise cryptic
    • Lure brings potential prey close enough to ambush

    • e.g. Firefly "femme fatales" Lloyd 1975
    • Females attract males with flashes of light
    • Signals and counter signals are species specific
    • Female Photuris versicolor "femme fatale"
    • - Mimics signals of several different Photinus spp.
    • - Attract Photinus males
    • - Eat Photinus  males gaining energy and defensive chemicals (lucibufagins)
  60. L. 23 Traps - spiders
    • Spiders spin silken web with proteinaceous glue --> captures prey
    • Often incorporates thickened cross-like structure
    • Stabilimentum 

    • Tension and stabilize web
    • Attract prey (by reflecting UV light)
    • Warn vertebrates not to collide with web
  61. Craig and Bernard 1990 - stabilimentum
    • Caught more insects with stabilimentum
    • Experiment of using half webs with either stabilimentum not present, present on other half, and present on the interested half
  62. Blackledge 1998 - stabilimentum
    • Compared damage to decorated versus undecorated
    • 45% less damage to decorated webs
    • - Stabilimentum attracts prey
    • - Stabilimentum warns off vertebrates

    BUT stabilimentum also imposes a cost
  63. Herberstein 2000 - Stabilimentum
    Attracts predators
  64. Traps - antlions and worm lions
    worm lions dig holes in sand near an object. Obstacle encourages ants to walk along edge of hole, and sides of hole begin to collasping, bring the ant towards the worm lion
  65. Traps - humpback whales Earle 1979
    • Corral krill and small fish using air bubbles
    • Swim through middle with open mouth consuming prey
  66. Traps - dolphins
    • Beat silt with tails to create rings
    • Fish try to jump out of "mud" ring and get eaten by waiting dolphins
  67. Tool use - Tools
    • Inanimate objects that are not of internal manufacture, that are used to alter the position or form of some other object in the environment
    • - Originally thought to be limited to humans
    • Many non-humans examples of tool use in the context of foraging
  68. Examples of tool use
    • Egyptian vulture using stones to open ostrich eggs
    • Sea otters using rocks as anvils to open sea urchins
    • Archer fish - use water to shoot at prey
    • Dolphin using sponges to probe bottom for flouders and protect from stony fish
  69. Examples of modified tool use
    • Woodpecker finch - shortening cactus spines
    • Chimpanzee - modify sticks
    • Winnow ants 0 use leaf pieces to sop up hemolymph of inverts a bring to colony
  70. 5 uses of sticks
    • 1. Pounder: destroy nest (I think)
    • 2. Enlarger: (makes stringless bee nests opening bigger)
    • 3. Dip stick: to get honey
    • 4. Probe: termite/ant hills
    • 5. Poker/spear: hunt bush babies
  71. Other examples of tool use
    • Kacelnik's crow: New Caledonian crows: companion curled wire to get access
    • Cheke's Eurasian jays: Selectively chooses heaviest rubber to raise water level to access food
    • Green heron fishing baits: Uses bread to attract fish
    • Elephants use leaf fonds to swat bugs
    • e.g. Chimp knocking a drone out of the air
    • Gorilla uses walking stick and land probe
  72. Evolution of tool use in foraging
    • 1. Species entering foraging niche with extensive competition
    • 2. Lack specialized equipment for dealing with prey
    • e.g. Sea otters - only marine otters. Recently invaded marine environment
    • e.g. Human and ancestors - only primates to exploit mammals as prey (other than chimps)
  73. Foraging
    • Methods employed in locating and consuming food
    • Have dealt with foraging strategies

    Foraging as a process
  74. Foraging as a process
    • 1. Prey detection (locating food)
    • 2. Which prey to attack? (What to eat)
    • 3. Where to forage? (where to eat)
    • 4. Anti-predator behaviour (avoiding being eaten)
  75. Prey detection
    • Frogs and toads: visual cues
    • Bats: auditory cues
  76. Prey detection in sharks
    • Olfaction:
    • - Detect blood from up to 4km away
    • - Detect minute concentrations (1 drop/100L)

    • Hearing:
    • - Respond to sounds from up to 1 km away ( to low freq. sound)

    • Vision
    • - Detect prey at close range (15 m)
    • - More rods than cones (low light sensitivity)
    • - Tapetum lucidum: reflects light, focuses light onto retina
  77. Motion detection in sharks
    • Lateral line system
    • Neuromasts respond to mechanical disturbances
  78. Electric field detection in sharks
    • All animals generate electric fields: action potentials, muscle contractions, potential difference across membranes
    • Injury - cut/scratch (2x signal released)
    • Detect via Ampullae of Lorenzini
  79. Examples of other "alien" senses
    • Mosquitoes detect heat and CO2
    • Pit vipers and boas use thermal signatures
  80. 2. What to eat?
    • Variety of potential food items?
    • Some prey/food are:
    • Easier to find
    • Easier to handle/process
    • Easier to digest
    • Have higher nutritive value

    Greatest payoff from maximizing benefit and minimizing costs
  81. Optimal foraging
    • Predicts animals will select forage items that maximizes the net difference between costs and benefits
    • Animals that forage optimally enjoy selective advantage
    • --> Foraging has been a favorite topic of those studying optimality
  82. Why foraging and optimality?
    • 1. Foraging as a process involves a series of decisions
    • - Which prey item to choose
    • - How long to stay in one area

    • 2. Consequences of alternative decisions can easily be quantified
    • Costs and benefits can be translated into energy units (calories):
    • - Time to find and handle food
    • - Caloric value of item
    • - Cost of digestion
  83. To forage optimally, animals must distinguish between profitable and unprofitable prey/items
    Unprofitable food requires more energy to process than it provides

    Do animals make such distinctions?

  84. L. 24 Optimal foraging in Northwestern Crows - Reto Zach
    • Crows forage on whelks
    • Fly with whelk in beak
    • Drop whelk to ground
    • - If it breaks, whelk eaten
    • - If not, repeats drop or chooses another whelk
  85. Optimal foraging in Northwestern Crows Reto Zach
    • Examined size choice
    • Size of shell fragments
    • Predominantly large shell fragments
    • But smaller fragments swept away?

    Conducted experiment
  86. Crow choices of whelk size - Zach expt. 1 (1978)
    • Crows preferred large and rejected small whelks
    • But why are small whelks rejected?
  87. Are smaller whelks inedible? Zach expt. 1978
    • Offered crows de-shelled whelks - presented equal number of whelks in all three size classes
    • Crows ate equal numbers of different size whelks - Large not selectively taken due to calories
    • --> On per morsel basis, absolute number of calories trades off with handling time (small whelks eaten faster than large whelks)
    • Small not toxic nor unpalatable

    Why selectively forage based on size?
  88. Why selectively forage based on size?
    Zach's hypothesis
    • Whelk size influences the ease with which whelks break open when they're dropped from the air
    • --> Easier opening decreases handling time and overall energetic cost

    Tested hypothesis by dropping whelks of various sizes from different heights
  89. Whelk dropping: Zach expt. 3 (1979)
    • Large whelks more likely to break from any height with fewer drops (optimum ca 5.23 m)
    • For all 3 sizes, there's a maximized return height
  90. Net profit of whelks - Zach 1979
    • Based on:
    • Energy cost (drop height & # drops)
    • Energy gain (calories/whelk)

    • Net energy profit:
    • - Large = 1.49 kcal/whelk
    • - Medium = -0.30 kcal/whelk
    • - Small = -1.23 kcal/whelk

    Crows in field dropped large whelks from an average of 5.23 m above ground

    Crows forage optimally
  91. Other example of animal foraging optimally
    Blue whales optimize foraging efficiently by balancing oxygen use and energy gain as a function of prey density
  92. Profitability
    = net energy gain/handling time
  93. Factors influencing forage item choice
    • Caloric content of item
    • Energetic cost of obtaining and digesting item
    • Handling and processing time, but, other factors are critical as well
  94. Profitability cont'd
    • Animals are confronted with multiple potential forage items
  95. Should animals eat some of each or focus on only the most profitable item?
    • It depends!
    • Abundance of most profitable item
    • Other nutrient requirements
  96. Profitability - abundance
    • When most profitable item detected, it should be consumed
    • But
    • - If most profitable item relatively rare, it takes a long time to find
    • Therefore animal increases overall energy intake by accepting any item that provides an energy gain
  97. Profitability - Abundance
    e.g. Krebs, Erichsen, Webber, and Charnov

    With Great tits
    • "Food conveyor" study - control abundance of different types of prey
    • Used mealworm chunks of 2 different sizes
    • When few mealworms of either size:Birds are without preference
    • When abundance of large increased: birds took large only, even when # of small increased
    • *Preference for large items not based on proportion in the population
  98. Profitability - Nutrients
    • Choice of item cannot be based solely on energetic payoff
    • Physiological processes require a variety of nutrients including essential vitamins and minerals
    • --> Animals must trade-off energetic gain to obtain a balanced diet
  99. Optimal diet and example
    May involve compromise of energy budget to obtain balance of nutrients

    • e.g. Belovsky(1978) - Moose foraging
    • - Browse on leaves and buds on deciduous trees (High energy): deficient in sodium
    • - 80% foraging in time on aquatic plants: rich in sodium but fewer calories
    • *Being in water likely details (avoids) pests
  100. Factors influencing forage item choice (ignoring competitors and predators for now)
    • Caloric content of item
    • Energetic cost of obtaining and digesting item
    • Handling and processing time
    • Abundance of most profitable item
    • Nutrient content of item
  101. Foraging as a process
    • 1. Prey detection - Locating food
    • 2. Which prey to attack - what to eat
    • 3. Where to forage?
    • 4. Anti-predator behaviour
  102. Where to forage?
    • Animals forage in discrete patches
    • Food distribution usually clumped: animals will search in the most profitable patches
    • Abundance of food items and the number of individuals competing for them influence profitability
  103. Fretwell and Lucas 1970
    • Proposed model to explain distribution of birds throughout their habitat
    • --> Ideal free distribution

    • Animals distribute themselves among habitat patches in proportion to resource availability in those patches
    • --> Resource matching rule
  104. Ideal free distribution - Fretwell and Lucas cont'd
    • Habitat patch 1 (food enters 10 units/min) and Habitat patch 2 (20 units/min)
    • Predict twice as many individuals to occupy patch 2 as opposed to patch 1
  105. IFD Resource matching - 
    Empirical test: Milinski 1979
    • Findings support the resource matching rule
    • When the sides of the tanks were switched, the fish adjusted their density accordingly
  106. To determine which foraging site is most profitable, foragers must sample sites periodically
    e.g. Smith and Sweatman with Oak titmouse
    • Established birds in aviary
    • Allowed birds to forage among food patches with different densities of mealworms
    • Birds came to prefer patches with the greatest density
    • Birds continue to sample less profitable patches
    • Though birds are still testing habitat (private info)
  107. Individuals use public information to locate suitable forage materials
    2 hypotheses
    Local enhancement hypothesis (Thorpe 1956; Loman and Tamm 1980): individuals increase their foraging efficiency by observing foraging activities of conspecifics at a foraging patch, and recruiting to such patches

    Information centre hypothesis (Ward & Zahavi 1973): information regarding food resources acquired at a colony or roost may enhance the foraging success of individual group members
  108. L.25 Where to forage?
    • Animals choose patches with the highest profitability
    • - Affected by average abundance of food items within patch (& number of individuals)
    • - Also affected by degree of variability in food supply within patch
    • --> animal may be faced with choice between a patch that reliably supplies a modest amount of food and one that cycles between large and little amounts
    • Variability = risk
  109. Risk-sensitive foragers (not predator related)
    • Animals that "consider" variability in food abundance in deciding where to forage
    • Risk sensitivity depends on state of satiation and need of forager
    • - Satiated animal at no risk of starvation likely to prefer predictable (stable) food source
    • - Hungry animals selected to endure risk associated with variability in source, since moderate amount may not suffice anyway
  110. Risk-sensitive foraging example with utility functions
    • e.g. Caraco, Martindale, and Whittam 1980 with yellow eyed juncos
    • Presented birds with choice of two seed stray
    • - fixed amount (5 seeds)
    • - variable amount (0 or 10 seeds)

    • Examined  value (utility) of each item of food taken for:
    • - Hungry birds
    • - Satiated

    • Satiated birds should be risk averse
    • Hungry birds should be risk prone (greater utility with more seeds)

    • They found:
    • Satiated juncos preferred the fixed amount trays
    • - had positive energy budget
    • - were risk averse

    • Hungry juncos preferred trays with variable payoff
    • - were risk prone
  111. Risk-sensitive foraging:
    Also demonstrated for:
    • Shrews (Barnard and Brown 1985)
    • Bumble bees (Carter and Dill 1990)

    Willingness to endure risk reduces probability of starvation

    Underlying energy budget exerts a profound influence on foraging in a social situation (Giraldeau and Caraco book on social foraging theory)
  112. Producer-scrounger Game
    A game theoretical Model incorporating two potential foraging strategies

    Producers: locate food for themselves, producing information about food that can be used by others

    Scroungers: rely on information from others to make foraging decisions

    Two strategies experience differential variance in return on foraging (Individuals can switch between strategies)

    • Producers: high variance (potentially high payoff) 
    • Predict adoption by risk-tolerant inds.

    • Scroungers: low variance (but predictable payoff)
    • Predict adoption by risk-averse inds.
  113. Producers-Scrounger Game supported?
    Theoretical predictions borne out by empirical data for multiple species

    e.g. Scaly breasted Munia (bird) Wu & Giraldeau
  114. Where to forage?
    • As an animal forages within a patch, food becomes more difficult to obtain
    • Food becomes depleted
    • Prey take evasive action
    • e.g. Plants produce chemicals against herbivory

    • Ultimately favours moving to new patch
    • Bell curve graph of food intake over patch time (Drickamer and Vessey 1992)
  115. Optimal foraging theory allows prediction of how long animal should stay in a patch
    Two factors are critical in deciding when to leave patch

    • 1. Capture rate at present location relative to other available patches in environment
    • 2. Cost of journey to another patch
    • - Predation risk
    • - Energy used in travel
  116. Marginal Value Theorem
    Charnov 1976
    • Optimality model
    • Maximizing long term rate of return for resources that are patchily distributed
    • Predicts when animal should give up present patch and move to another
    • Two domains of prediction
    • 1. Patch quality
    • 2. Travel time between patches
  117. Marginal Value Theorem - Charnov
    1. Patch quality and example
    • Giving up times inversely related to average patch quality in environment 
    • e.g. Krebs et al. with Chickadees 
    • Move to a new patch when return in current patch drops to average for environment (marginal value)
  118. Evidence for patch quality effect
    Krebs et al. 1974 with chickadees

    • Established birds in aviary where mealworms placed in wooden dowels
    • Could manipulate both average patch quality and travel time between patches

    Had wonky df and used one-tailed test (sneaky)

    • Patch quality results
    • Giving up times
    • - Time between last capture and leaving patch
    • - Inversely related to average capture rate for the environment
    • --> Stay longer without finding food if average patch value is low
    • --> Stay less time if average patch value is high
  119. Marginal Value Theorem - Charnov
    2. Travel time
    Individual should remain in current patch longer as distance between patches increases

    • With little distance between patches:
    • --> little predation risk in moving
    • --> little energetic cost in moving

    • With greater distance between patches:
    • --> Risks and costs increase
    • --> Offset potential gain of moving
  120. Central Place Foragers
    Gather food in cheek pouches and return it to their nest (chipmunks)
  121. Evidence for travel time effect - Giraldeau and Kramer
    • Central Place Foragers - chipmunks
    • Provided chipmunks with trays containing sunflower seeds - trays with seeds serve as patches of food
    • Manipulated travel time by varying distance of trays from nest

    • As distance between patches and nest increases
    • --> Time spent foraging in each patch increases

    • Travel time substitutable for:
    • --> risk of predation
    • --> effort required to forage
  122. Foraging effort = travel time
    Cowie 1977
    Established birds in aviary like Krebs, but mealworms in sawdust filled cups

    Manipulated effort by placing lids on cups

    Increased effort increased foraging time within a given patch
  123. It appears that the birds are basing their foraging behaviour on past investment

    Why base behaviour on past investment?
    To do so places organism at risk of committing the Concorde Fallacy
  124. Concorde Fallcy
    Continued investment based upon past outlay with no possibility of offsetting future payoff
  125. Are great tits committing the Concorde fallacy?
    • not necessarily
    • Greater effort required to forage in patches with hard to open lids decreases average profitability of patches in environment
    • --> decreases future payoff associated with giving up
    • In other cases, past investment may be correlated with future payoff, and behaviour based upon that

    Travel time effect upheld Cowie 1977
  126. Marginal value theorem not restricted to optimality and foraging
    • Any time a resource depletes as a function of use
    • And costs are associated with traveling between patches of that resource
    • Can use marginal value theorem to solve for optimal patch time
    • Useful in studies of:
    • - Mating behaviour
    • - Social behaviour
    • - Parasitoid host use

    e.g. Walmart placement takes advantage of human "foraging"
  127. Optimal host use in Parasitoid wasps - Hubbard and Cook (1978)
    • Venturia canescens oviposit on flour moth larvae (Ephestia cautella)
    • Presented wasps with patches that varied in host density
    • Monitored oviposition over 1 week period
    • Encounter rate (with unparasitized host) at end of week did not differ among patches of different densities
    • Patches depleted to same marginal value

    • Uncovered mechanism of patch departure in Venturia that provides optimal exploitation
    • - Host larvae produce cuticular chemical that causes Venturia habituates to the chemical and leaves the patch
    • --> But with successful oviposition, effects of habituation are temporarily reversed
    • --> As oviposition rate drops, habituation prevails and Venturia leaves patch
  128. Aspects of optimality exist in resource extraction systems
    • Overall expression of optimality is subject to constraints
    • 1. Competition: 
    • Allospecifics (ones w/ same resource demands) and conspecifics
    • 2. Predators:
    • Eat without being eaten
    • Foraging represents trade-off between energy payoff, nutritional balance, and safety