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Behavioral Ecology
Chapter 8
Definition & examplesTheoretical basisAltruismSocialityEusocialitySexual selection
12/8/2010
Behavioral Ecology Defined• Study of social relations between organisms (“Sociobiology”)
• Study of how behavior mediates the relationships between organisms and their environment.
• Examples:– Optimal foraging– Movements associates with temperature and water regulation, or
nutrient/energy acquisition– Dominance interactions– Cooperative behavior– Reproductive interactions– Competition– Predation– Parasitism/disease
22/8/2010
Behavioral Ecology Defined• Study of social relations between organisms (“Sociobiology”)
• Study of how behavior mediates the relationships between organisms and their environment.
• Examples:– Optimal foraging– Movements associates with temperature and water regulation, or
nutrient/energy acquisition– Dominance interactions– Cooperative behavior– Reproductive interactions– Competition– Predation– Parasitism/disease
Today’s lecture
32/8/2010
Evolutionary Basis for Behavior
• Natural selection favors behavior that increases fitness (contribution to future generations).
• Since heritable traits are associated with differences in fitness, behavior must be (to some extent) inherited.
• According to this view, behavior is not simply a “choice,” but has an underlying genetic basis (adaptation).
42/8/2010
Behavioral Theory, continued:
• Sociality is generally associated with cooperative feeding, defense, and/or reproduction.
• Mate choice and competition for mates results in sexual selection (selection for particular traits)
52/8/2010
Like Ecophysiology, Behavioral Ecology draws on Energy Budget & Optimization TheoryTo survive and reproduce, an organism must optimizeits energy use by partitioning its efforts among different tasks .
Fig. 5.34, Molles & Cahill 2008
Exactly how an organism does this varies with conditions
62/8/2010
Key Terms in Behavioral Ecology:
“Fitness” – contribution to the next generation
“Inclusive fitness” – determined by survival and reproduction of individuals and all those sharing genes with those individuals
“Kin selection” – evolutionary force favoring help given to relatives (may increase inclusive fitness)
Behavioral ecology works to demonstrate the adaptive value (fitness benefit) of specific behaviors, recognizing that organisms must allocate energy and resources.
72/8/2010
Early views classified social interactions in simple “binary” terms
Recent views are far more nuanced…
Molles & Cahill 2008 82/8/2010
Reasons for Altruism
1) Manipulation
2) Kin selection
3) Reciprocal altruism
92/8/2010
Altruism through Manipulation
Figs. 8.4 & 8.5 Molles & Cahill 2008
Cowbirds (Molothrus ater) are brood parasites,laying their eggs in the nests of other bird species
Experimental evidence that altruistic species are fooled by cowbirds!
102/8/2010
Altruism through Kin SelectionKin Selection draws on the concept of inclusive fitness.
According to the theory of Kin Selection, it pays to be altruistic if the benefits of altruism outweigh the costs.
Consequently, organisms are most likely to benefit a close relative (sharing some of the same genes).
http://research.uleth.ca/rgs/rep_physiol.cfmhttp://utahcbcp.org/images/uploads/White-tailed-Prairie-Dof-F3.jpg
Warning calls of prairie dogs and ground squirrels provide examples of kin selection
112/8/2010
Reciprocal Altruism
Altruistic behavior may be “adaptive” if there is a high likelihood that it will be reciprocated.
122/8/2010
Sociality & EusocialitySociality involves group living & cooperation• Involves feeding, defense, and restricted reproductive opportunities.• Examples include many birds, wolves,
wild dogs, primates, and lions
Eusociality – highly specialized social behavior • Multigenerational living• Cooperative care of young• Division into sterile (non-reproductive) and reproductive castes• Examples include ants, termites, bees…
What explains social and eusocial behavior?(key: cost/benefit analysis and inclusive fitness) 132/8/2010
Sociality in African Lions
Female lions live in “prides” (groups of several individuals) that cooperate in defense, feeding, and care of young.
This cooperation may enhance inclusive fitness, and can provide other benefits (e.g. experience in raising young).
Fig. 8.6, Molles & Cahill 2008142/8/2010
Male lions form smaller “coalitions” of 2-3 individuals
Kin selection theory suggests males should form smaller groups than females, and this is supported by the data above.
Figs. 8.9 & 8.10, Molles & Cahill 2008 http://www.freefoto.com/images/01/28/01_28_1---Lions_web.jpg152/8/2010
Eusociality• Leafcutter ants live in single,
large colonies
• Divided into “castes” with different functions
Figs. 8.11 & 8.13, Molles & Cahill 2008
Leafcutter ants collect leaves and bring them to underground nests, feeding of the fungi that decompose the leaves. 162/8/2010
Eusociality in “Naked Mole Rats”
172/8/2010
Examples of “castes” in eusocial organisms
Fig. 8.14, Molles & Cahill 2008
In both cases, “kin selection” has been used to explain eusocial behavior.182/8/2010
Sex & Mate Choice
• Most plants and animals display “male” and “female” types. Some organisms (e.g. fungi) have multiple mating types).
• Hermaphroditism – both male and female traits on a single individual.
• Sexual selection – selection for traits by mate choice or by competition for mates (typically applied to male/female examples).
192/8/2010
Sexual Selection
• Darwin observed organisms display “secondary sexual characteristics” (not directly involved in reproduction) and proposed that these conveyed advantages during competition for mates.
• Secondary sexual characteristics can also be a result of “mate choice” (e.g. females choosing “attractive” males or vice versa).
• Sexual selection can result in sexual dimorphism and elaborate mating displays.
202/8/2010
Sexual Dimorphism & Secondary Sexual Characteristics
Elephant Seals (Mirounga sp.)– note prominent male “proboscis”
Male peacock courting a female peahen(Pavo cristatus).
http://en.wikipedia.org/wiki/Elephant_seal http://en.wikipedia.org/wiki/Peacock212/8/2010
Human “peacocking”
http://www.theartofpeacocking.com/minicourse/part1/ 222/8/2010
Experimental studies of sexual selection in guppies
Theory suggests showy males should have a higher fitness.Showy males also have a greater predation risk.
Hypothesis – secondary sex characteristics (showy colors & patterns) represent an optimal balance between fitness and survival.
Fig. 8.16, Molles & Cahill 2008232/8/2010
Endler’s experimental studies of guppies supported the hypothesis that male coloration optimizes fitness with predation risk.
Figs. 8.17 & 8.19, Molles & Cahill 2008 242/8/2010
Endler’s field studies further supported this hypothesis
Figs. 8.18 & 8.20, Molles & Cahill 2008252/8/2010
Non-random mating in plants- is this sexual selection?
Wild radish – Raphanus sativus Pollination experiments demonstrate non-random mating (some pollen more successful than others). Figs. 8.23, Molles & Cahill 2008 262/8/2010
