DiBetti & Janson (2001). Social foraging and the finder’s share in capuchin monkeys, Cebus apella.
Capuchins? • Capuchins show remarkable organization/spatial structure when foraging • Why so good? Increases foraging success • Also: like to be in front of foraging group: first to encounter food • Dominant capuchins most likely to be in front-will be very close to animals in front, can aggressively displace them from food resources
Capuchins form troops in wild. • Spatial positions taken by different individuals during foraging may affect foraging tactics • Is an “order” to how they move through the forest.
Two kinds of foraging models • Solitary foraging • Social foraging
Kleptoparasitism • Social foraging models for individuals who exploit food made available by others • Kleptoparasitism: Stealing food from others in your group • Information sharing: • assume all individuals in group look for food • When food is found, all other animals in group join the discoverer to share food • Producer-scrounger models: • game theoretifcal, negative frequency dependent models: two very different tactics • Animals can be producers: individuals that actively search/find food sources that may be shared with group members
Scrounging • Animals can be scroungers: individuals that parasitically exploit food made available by producers • Frequency of scrounging is dependent on payoffs: • when scroungers are rare they receive larger payoff than producers; • when scroungers are common, producers do better • If two are competitively equal: same payoff • BUT: in dominance-structured groups- dominant animals can monopolize larger share than subordinates
Finder’s share • Sharable resource: more items than the finder can consume before the arrival of joiners • Finder’s advantage: When resource is sharable, number of items obtained by finder before arrival of others: a • Finder’s share: proportion of items obtained by finder in a particular patch: • Finders share = a/F
Kleptoparasitism vs. Finder’s Share:Two models make different predictions • In producer-scrounger model: finder’s share affects frequency of use of scrounger tactic (frequency of scrounger is small when finder’s share Is large) • In information sharing model: finder’s share determines costs imposed on social foragers when compared to solitary foragers: cost is small when finder’s share is large • What factors affect? • Number of food items in clump • Time elapsed until scroungers arrive • How does kleptoparasitism tie in with other dominant variables for foraging: dominance rank, tolerance, age, and sex of discoverer.
What purpose of study: • how is probability of discovering new food sources affected by spatial position occupied when foraging and what other factors affect probability of discovering new food sources? • what affects tendencies of animals to parasitize food discoveries by others? • what factors affect finder’s share and total amount consumed by finder from newly discovered source?
Method: • Wildlife park: Iguazu National Park in Argentina • 24-26 tufted capuchins; well established group • Omnivorous primates • Wide range; tend to visit new sites in range each day, not repeat visits • Examined foraging from fixed platforms arranged by researchers
Behavioral Measures • 5 min time samples of focal animal in group • Identity • Nearest neighbor • Spatial position within the group • Outmost front • Middle front • Central • Middle rear • Outermost rear • Finding platform: time of arrival; time of first call to tell others; number of fruit taken/left, distance of next neighbor, time of arrival of first scrounger
Results:Factors that affect probability of finding and joining • Alpha male/female tended to occupy anterior central positions • Two adult non-natal males and an adult female found on periphery of group, especially in front; were least tolerated, most picked on • Adult females were in all positions • Juveniles: increased amount of time in periphery as grew older • Dominant individuals tended to occupy front positions
Results:Factors that affect probability of finding and joining • Front animals more likely to find food platform, but this may be more a function of rank than location • Animals most likely to discover platforms did not get most food from platform • Alphas monopolized feeding on platforms discovered by nontolerated and juveniles • When take alpha male out of equation, more platforms discovered = more food obtained
Results:Factors affecting finders’ share/amount consumed by finder • amount of food in discovery platform • varied with time elapsed until others joined • varied with relative feeding rate of finder • greater number of bananas, smaller the finder’s share • finder’s share increased with increased time of arrival of others • finder’s share increased with relative feeding rate before arrival of others • no affect of sex, age, dominance rank • in general: • finders should avoid other group members unless food sources contain so few items that can be consumed before arrival of others • most critical factor: time of arrival of the others
Spatial position and rate of finding new food: • Animals that preferentially forage in front periphery of group more like to find new food sources • Alpha male/female strategically located to displace finders from new food sources • Advantage: consume before alphas get there • Advantage to front center foragers: take newly discovered food from finders • Dominant scroungers occupy central positions; finders occupy the periphery
Finder’s share: Three factors: • number of food items in patch: mostly environmental factors; finder can manipulate by size/handling time of resources • time elapsed until joiners arrive: avoid being noticed by others and foraging far away (although increases predation chance) • feeding rate of finder: subordinate animals more nervous, eat less in same amount of time
Total consumption by finder: • try to increase total amount of food found, not just finder’s share • dominance rank may also play (small) role here • dominance not affect finder’s share (is alone share), but affects total consumption because subordinate cannot rejoin feeding station once dumped off
Food distribution and kleptoparasitism: • most studies: high ranking animals join food discovered by low ranking individuals • finder-joiner relationship established at relatively clumped resources where dominant individuals can control access • in some species (sparrows?)- food finding and joining not related to dominance and may change with flock composition and food type
Conclusions: • social rank affected spatial positions occupied by the monkeys during foraging activities • this affected probability of animals discovering new sources • out front animals more likely to discover; central (and dominant) animals more like to steal! • not really support either model! • Dominance did not affect finder’s share • Did affect total consumption!
Blundell, G.N., Ben-David, M., & Bowyer, R. T. (2002). Sociality in river otters: cooperative foraging or reproductive strategies
Two reasons why animals form social groups? • Avoidance of predators • Successful acquisition of food • Note: ecological and behavioral constraints may affect genders differently
Otters! • What is a mustelid? • Aquatic carnivore • Otters (river and ocean) • Seals, sea lions, etc.
To what two types of prey do river otters have access? How does this affect their sociality? • Both solitary and group animals • Show scent marking and social cooperation • Two major types of prey • Schooling pelagic fishes (seasonal): HIGH energy density • Intertidal demersal organisms- tide pool crustaceans: LOW energy density • Cooperation improves foraging success for schooling fish • Solitary behavior better for tide pool crustaceans
Gender Differences? • Males: • Larger • Stronger • superior swimming ability • Females: • more parenting • smaller size • smaller home range • Males should eat more pelagic fish • Male to male competition for female may inhibit sociality at certain seasons • Note: short, 1 month mating season in Alaska, etc.
Hypotheses of this study • more social otters should have diets higher in better quality pelagic fishes • sociality should enhance foraging success • sociality should change seasonally • increased foraging success as result of cooperative foraging should be negatively correlated with home range or territory size • sociality should enhance defensive success resulting in larger home ranges (that are shared)
the method • Subjects: otters in Prince William sound • Apparatus: radiotelemetry to track • Procedures • Caught 11 otters • Weighed, examined diet and morphometrics • Radio collared and followed • observed
Data analysis were conducted? • Group size: Examined who they hung out with • Sociability: Who with and how many • Diet • Home range • Morphometrics
Results: Group Size • Changed for males, but not females • Changes in male group size corresponded to availability of pelagic fish • Groups up to 9 during May-Sept • Groups of 4 or so after September • differed by age class for males as well • juveniles in smaller groups or alone
Results: Sociality • Males more social than females • Only 24.4% males solitary • 47.4 % females solitary • Negative correlation between home range size and sociality
Results: Diet • Herring, adult lsalmon, sand lance, juvenile salmon • Three groups: • Intertidal and Demersal fish • Pelagic fish • Firewater fish • Males and females ate significantly different food during spring/early summer • MORE pronounced in late summer/early fall • More males ate pelagic fish • Also differed by social factors • More social = more pelagic fish and by season
Morphometrics • Males larger • Only males formed groups and engaged in cooperative foraging • helped get more pelagic fish and by season
Factors that may have accounted for the “sexual partitioning • Swimming differences between males and females • Females joined male groups to get pelagic fish • Females had to take care of offspring
Why form groups? • Multiple predators increased the size of the catch of fish? • So why form groups? • Cooperation! • Safety • Did predation risk play a role in sociality? • Difficult to assess (who are their predators?) • Predation pressure is pretty low- mostly infanticide
Why form groups? • Having young reduced social interactions for females • This may be protective • stayed in den • Kept young safe at home • Evidence for this: • Females with young have smaller home range • Group size declines for males during mating season! • Why did the otters form groups? • Helps them eat better! • Keeps them a little safer • But they eat better!
Inhibition of optimal behavior by social transmission in the guppy depends on shoaling Bates, L. & Chappell, J
Social Transmission • Social transmission. • Really is social learning or modeling • Important for group foraging • Animal B learns “aspects of behavioral similarity” from conspecific A • May transmit foraging strategies • adaptive vs. maladaptive? • Adaptive if transmitting good info • Maladaptive if transmitting bad/wrong info
Purpose of this study? • Determine IF learn suboptimal routine • Test fish both in groups and alone • Determine if fish continue to choose energetically costly route when • Was beneficial because of antipredation benefit • Remaining with the shoal outweighed cost incurred in taking longer route • Which would they choose and did it depend on the model group?
Method • Subjects: 35 adult female guppies • 12 founders • 8 experimental group • 8 control group • 7 retained as spares • Apparatus • 4 identical tanks • Divided in half lengthwise • Two holes: one at each end • PVC pipe: trap door • Blue end vs red end • Long route to feeder • Short route to feeder • reinforcers = Freeze dried bloodworms
Procedures • Modeling Conditions • Experimental group observed route choices of founder group • Trained founder fish to swim long route • Control fish had comparable experience with tank, but no observation • IV = test condition • Individual • With a shoal • DV: preferred route (long or short)
Three hypotheses: • Fish should prefer shorter route: conserve energy • If observed behavior is purely outcome of suboptimal socially transmitted learning • fish should take long route in both individual and shoal condition • If following socially transmitted longer route is outcome of trade off between benefits of shoaling and energetic costs of taking longer route, • fish should take long route when in shoal, short route when alone
Control group: took short route Experimental group: Short route when isolated Long route when in shoal avail.
Results • What route did the control group prefer? • Control group preferred shortest route in both shoal and individual situation • Route preferred by shoal group: • In shoal condition: long route • In alone condition: short route • What hypotheses were supported? • A blend of the first two • Third hypothesis- is a trade off
Allomemesis, Modeling and Fish! • Probability of an individual adopting a particular behavior or state is an increasing function of the number of individuals that already are exhibiting that behavior • Sounds like social psych to me! • In general, socially transmitted info has higher probability of being reinforced • Thus, more likely to maintain the socially learned behavior than go out on limb and act alone!
Conclusions • may be reasons for shoaling • Shoaling = Predatory trade off; • better off in a group • otherwise take shortest route! • solitary fish DID NOT use the same strategy as the group? • Suggests social learning in the guppy • but that social learning may not be “good learning” • Can learn to use info situationally! • Don’t continue to use “bad” info