Social Behavior
Types of Social Behavior
Cooperation –an interaction between A and B that gives both increases in direct fitness
Postponed cooperation – A will eventually gain access to a resource controlled by B because of its prior help
(By helping the dominant female now, the subordinate has a high chance of inheriting the nest later.)
Reciprocity– B directly pays A back for its prior aid
Maladaptive Altruism – A sacrifices its lifetime inclusive fitness in order to help B
Adaptive Altruism – Initial direct fitness gained by B from help from A leads to indirect fitness gained later by A
Options for year-old males that are unable to find mates
• Primary helpers– bring fish to their mothers and siblings and
attack predatory nest enemies like snakes
• Secondary helpers- help unrelated nesting pairs and go on to
breed next year
• Delayers– wait around, don’t use up valuable energy to help
rear anyone else’s offspring, breed next year
Discussion
-Some helpers inherit natal territories and reproduce the next season (does this enhance the helpers’ direct or indirect fitness?)
-Some helpers don’t reproduce but help their parents. And these parents rear more offspring than those without helpers. (does this enhance the helpers’ direct or indirect fitness?)
Discussion questions
1. What factors have likely been responsible for the evolution of bird species with helpers?
- lack of suitable nest site
- strength in numbers
- low adult mortality
2. How can you test the hypothesis that young birds remain on their natal territories because they can’t find suitable nesting habitat?
- If there is shortness of nesting site, then if I lower/decrease the population, maybe the birds will disperse/leave and mate on their own.
How is altruism different for vertebrates compared to invertebrates like bees, ants, wasps?
– Vertebrates engage in Facultative Altruism.
– Eusocial insects like honeybees engage in Obligate Altruism.
facultative Altruism is a temporary loss of direct fitness (with potential for indirect fitness gain followed by personal reproduction)
Obligate Altruism is the permanent loss of direct fitness (with potential for indirect fitness gain)
Why is cooperative breeding in birds linked to monogamy?
- Higher relatedness gives higher indirect fitness
- The closer cooperative birds they are relatedness than independent birds, the more likely they are to help in the nest
