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Unformatted text preview: Sociality and Group Living Sociality Why be Social? Why Individuals are social when two individuals acting together Individuals each do better than they could acting alone each Not all species are social (Nor are all solitary species entirely solitary) Sociality may or may not imply cooperation Some social behaviors are simple to understand
Biparental care Predator deterrence Some are more complicated Reproductive restraint Dominance Hierarchy Dominance Exist when individuals cooperate in social situations Some individuals accept subordinate status to others Some Dominant members have higher reproductive success than Dominant subordinates subordinates Benefits of Social Living Improved detection of predators; many eyes Division of labor Improved repulsion of predators Dilution Effect - prey group together in large numbers to overwhelm the feeding capacity of the predator Musk Ox in Defensive Posture Costs of Social Living Increased competition for food, mates, and other limiting Increased resources resources Increased vulnerability to disease and parasitism Risk of exploitation by other group members = Cheating Selfish Herd
• Musk oxen Musk • Sawflies Shared resources 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 hunting group size kg meat/lion/day Caraco and Wolf Packer Shared resources Fieldfare The larger the colony, the higher probability that some offspring will die of starvation. Cooperation and Altruistic Behavior Nonbreeding helpers are found in mammals, birds, and Nonbreeding insects insects Remember side-blotched lizard example Altruists apparently sacrifice their reproductive success to Altruists help others help How are genes for altruism perpetuated? Reciprocal altruism, kin selection, improved status Theory of Kin Selection Theory Proposed by William Hamilton Genes associated with caring for relatives may be Genes favored by selection favored Altruists pass on genes indirectly by helping relatives Altruists who have copies of those genes to survive and reproduce reproduce Kin Selection Kin
Hamilton’s Rule B = benefit C = cost r = degree of relatedness ~ degree Probability of sharing genes by common descent Probability Altruist have a net benefit when: Br > C Calculating r Calculating Each gene comes in pairs Since half your genes come from each parent, r = Since 0.5 to each parent 0.5 Relatedness of half sibs
p = 0.5 genes in self are in parent 50% chance parent also passed same gene to sib Rhalf sibs = 0.5 X 0.5 = 0.25 0.5 For Altruism to Evolve via Kin Selection For
Parent A Parent B Half sibs: Half
B(0.25) > C B(0.25) B must be 4 times > C × Full Sibs
B(0.5) > C B must be 2 times > C
Sibling 1 OR /2 (0.5) probability
1 /2 (0.5) probability
1 Sibling 2 **Lionesses communally nurse cubs of sisters and cousins **Ground squirrels warn sisters, daughters, aunts and other sibs of predators Eusociality Dominance Hierarchy Division of Labor Example: Social Insects Workers in colonies of social insects are sterile These colonies are extended families Workers pass on their genes indirectly by helping relatives Workers reproduce reproduce Australian Honeypot Worker Army Ant Soldier Termites Termites Workers and soldiers are sterile A single queen and one or more kings are the parents of the single entire colony entire Honeybees Honeybees Workers are sterile females A single queen is the mother of all members of the single colony colony At certain times of the year, the colony produces At drones--fertile males that leave the colony and mate drones--fertile Naked Mole-Rats Only mammals known to have a Only sterile worker caste sterile Single queen reproduces with one to Single three males three DNA evidence shows clan members DNA are all closely related (r = 0.81) are A few dispersing individuals may few limit inbreeding limit ...
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This note was uploaded on 02/12/2011 for the course BSC 2008 taught by Professor Blohm during the Spring '08 term at University of Florida.
- Spring '08