Definition: conspecifics (i.e., same species) living in groups !and meeting two criteria:!!1. they must exchange information!!2. they must have social attraction (i.e., seek each !!other out rather than simply preferring the same !!environment) (excludes parenting and mating)!!Social Behavior!First: General discussion of benefits/costs ! !of living in groups, using !! !examples from marine animals!!Then: Case studies of two marine !animals: eusocial shrimp (inverts)!!and cetaceans (mammals)!Why be Social?!1. Predator Defense: living in groups decreases chance of predation for members of the groups! !!(Treherne and Foster, 1980)!a. ‘Many-eyes’ theory: Larger groups !more effective at detecting approaching !predators. Ex: ocean skaters !approached by an artificial predator.!1. Predator defense!2. Enhanced foraging!3. Reduced costs!b. Dilution of risk: If predators can only eat a certain amount of food !(e.g., one individual), then the rest of the group can escape.!Chances of being eaten in a successful attack decreases as a! factor of 1/N: !!Probability of being eaten = α * 1/N,!!where α is the probability that predator succeeds.!Example: Crouton ‘prey’!fed to gulls!(Fels et al. 1995)!Croutons thrown to gulls !in groups of 1-5!Predator defense!N=total number in the group!Overall Risk Model for Predation:!Predator defense!c. Predator confusion: If predators find it more difficult to single out !individual prey from a group, then prey have increased survival.!Ex: Four marine predators: squid, !cuttlefish, pike, carp.!Presented with 1, 6, or 20 prey!(Neill and Cullen 1974)!Predator defense!Efficiency of capturing prey!if predator makes contact !with group!2. Enhanced Foraging: living in groups increases the effectiveness with which food can be found. !a. Information exchange: Members of the group exchange information on food location. Ex: seabird colony acts as information center for following successful foragers. !b. Increases range of potential prey: Allows capture of prey too ! big, too agile, or too dangerous for a single individual (hunting in ! herds)!1. Predator defense!2. Enhanced foraging!3. Reduced costs!Ex: Common dolphins herding fish !with bubbles.!3. Reduced Energetic Costs: living in groups is less !expensive than living alone.!a. Keeping warm: animals conserve heat by huddling; reduces fraction!of their surface area exposed. !Ex: Emperor penguin huddling !insures egg viability.!1. Predator defense!2. Enhanced foraging!3. Reduced costs!3. Reduced Energetic Costs: living in groups is less !expensive than living alone.!b. Traveling cheaply: animal groups !use less energy to fly or swim!Ex1: Seabirds flying in formation; !Ex2: Antarctic krill living in aggregates!Ex3: Fish schooling !1. Predator defense!2. Enhanced foraging!3. Reduced costs!a. Less food : !1. Competition for same food !2. Kleptoparasitism by group ! members!3. Shadow interference: downstream ! filter feeders get less food!!!! !4. Prey alarm: Ex: Wading birds ! scare predators from surface!(Selman and Goss-Custard 1988)!Redshank!10 !seconds!100 !seconds!Why be non-Social? Costs of group living!b. Increased parasite burden: ! Positive relationship between group size and parasite load for birds, fish;! Enhances parasite reproduction ! Ex: Stickleback in Quebec salt marsh!(Poulin 1999)!Number of copepod!parasites!Size of stickleback group!Case Studies: Eusocial shrimp Synalpheus!!Definition of eusocial: Specialized social behavior in !which some members of the group are permanently sterile !but cooperate in raising relatives!§ Shrimp live inside sponges, Western Atlantic, Belize!§ Colonies size: <10 to >300 animals!§ Live in the internal canals of the !sponge!§ Feed on host tissue!§ Predators are polychaete worms!§ Large claw used for threat !displays and for physical attacks!Social structure: !§ One mature female lays eggs, several males, !many female workers !§ No planktonic dispersal stage; juveniles stay in !the sponge where born!!Altruism: Why would individuals give up the ability to reproduce for themselves?!Duffy J E , Macdonald K S Proc. R. Soc. B 2010;277:575-584 crawling larvae E = eusociality index!contribution to work!contribution to reproduction!E!Synalpheus species in Belize sponges!E = eusociality index!Habitat Saturation?!“…cooperative groups enjoy an advantage in challenging habitats…”!Case Studies: Social behavior in cetaceans !§ Odontoceti (toothed whales) more social than Mysteceti !(baleen whales)!§ Dolphins, Killer whales, and Sperm whales have most !developed social groups !§ Social groups are called ‘pods’: the largest cohesive group !of individuals that travel together for at least 50% of the !time !§ Size range: 4 to 40 whales!If resource distribution varies, will social structure differ?!!§ Stable family groups!§ Closely related individuals!§ Offspring stay with group!Social structure of Dolphins is Variable: !Ex: Dusky Dolphins!Argentina populations exhibit ‘fission/fusion’ behavior!!Hunt in small groups!!Feed cooperatively in large groups!!Social groups split and converge!!New Zealand populations!!Form large groups of several hundred!Case Studies: Social behavior in cetaceans !§ Mysteceti (baleen whales) are less social!§ Most associations are between mother and calves!§ Other associations don’t involve fixed groups !(i.e., the composition of the groups is not stable)!§ Males have multiple mates!§ Females can have multiple mates, depending on species !(Gray whales)!Why be Social?!§ To escape predators!§ To be a better predator!§ To conserve energy and resources!In Order to:!§ Maximize food acquisition !§ Maximize reproduction!Symbiosis!Physical association between two unrelated organisms!• Commensalism: relationship to advantage of one,!does not affect the other!• Inquilinism: commensalism in which one organism!lives in burrow or nest of another!• Mutualism: relationship to the advantage of both!• Parasitism: relationship to the advantage of one,!detrimental to the other!Special case of commensalism!Algal-Animal!Categorize based on!organisms participating!• Restricted to shallow waters (photic zone)!• Most common in tropics; not known in polar regions!Cellular symbiosis: !Entire algal cell is enclosed within