General Ecology

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General Ecology

• Life History Strategies

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We are interested in a few basic questions.

• When should you reproduce?
• How often should you reproduce?
• With whom should you reproduce?
• How much energy should you invest in reproduction
  / offspring?

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To answer these questions we need to understand
our ultimate objective.

• Maximize inclusive fitness.

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If evolution / natural selection works, we expect

• Organisms should behave reproductively in a way
  that maximizes inclusive fitness.
• Do organisms so this?

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We can make a basic observation

• Parental care and fecundity are inversely
  related.
• Organisms that invest a lot of energy in their
  offspring, generally have fewer offspring. Think
  of elephants.
• Organisms that invest very little energy in their
  offspring, generally have very many offspring.
  Think of flies or rabbits.

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What are the consequences of the investment
strategy?

• Offspring that receive little parental investment
  generally have a poor probability of survival.
• Offspring that receive a great deal of parental
  investment, generally have a high probability of
  survival.
• Again, think of bunnies and elephants.

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Which is better?

• This depends on the availability of resources (as
  well as other factors).
• In general, if you supply organisms with more
  resources, they invest more in their offspring,
  and offspring survival increases. Similarly, if
  you reduce the availability of resources, they
  invest less in their offspring and offspring
  survival decreases.

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Compare Peromyscus truei and Dipodomys
panamintinus.

• The pinyon mouse lives on average about 6 mo. It
  produces litters of about 5 or 6. The young are
  weaned within a few weeks, and leave the nest in
  about 4 weeks.
• Panamint K-rats live about 8 years, they produce
  2 offspring, sometimes they delay reproduction,
  and the offspring dont leave the nest for months.

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Are there other differences?

• K-rats have remarkable hearing and easily detect
  snakes and owls. They are saltatorial, and if
  confronted by a predator, accelerate rapidly.
• Pinyon mice have no special predator avoidance
  techniques.
• What are the implications?

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WITH WHOM SHOULD YOU REPRODUCE?

• How do birds select mates?
• How do lizards select mates?
• How do fish select mates?
• How do deer select mates?
• Notice, in each case, females evaluate some
  quality in the male. Mate choice is for the most
  part, practiced by the female. Why?

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When should you reproduce?

• Does it make a difference?
• Does reproduction early in life influence
  reproduction later in life?
• In terms of inclusive fitness, is it better to
  delay reproduction, or as the saying goes, vote
  early and vote often?
• Consider green wood-hoopoes in Africa.

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When to reproduce

• If individuals engaging prematurely in sexual
  competition lose out to larger, more experienced
  competitors in addition to suffering a reduction
  in their liklihood of future reproductive
  success, then sexual bimaturism will be
  selected David Barash.

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How aggressive should a male be?

• Male aggression is not just a matter of
  testosterone.
• Is there a cost and or benefit to aggression?

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When should parents terminate parental investment?

• First, what is parent offspring conflict?
• Is a cost/benefit analysis possible?

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Are humans different?

• Do we fit the patterns?
• Do we exhibit ornamentation?
• Does the ornamentation advertise quality?
• Permanent breasts?
• Pubic and facial hair?
• Male pattern baldness?
• Does size matter?
• Who selects whom?

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What happens when the environment is
unpredictable?

• Do environmental fluctuations influence juvenile
  survival or parental survival?
• If the fluctuations reduce juvenile survival
  probabilities, what should the parent do?
• If the fluctuation reduce parental survival, what
  should the parents do?

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What kind of mating system should be used?

• Monogamy?
• Polygyny?
• Polyandry?
• Promiscuity?

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Which System is Best?

• How do we decide?
• What is best for females?
• What is best for males?

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Monogamy

• 1 male and 1 female.
• Pair bonds may be permanent or serial.
• What environmental conditions favor monogamy?
• Think about distribution of resources.
• How about energy required to rear young?
• Would you expect altricial or precocial young?
• How common is monogamy in primates?

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Monogamy

• Selection must favor an equalization of
  reproductive effort. Monogamy is the derived
  condition.
• Note most birds are monogamous. Why?

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Polygamy

• There are 2 forms of polygamy
• Polygyny
• 1 male and several females.
• Polyandry
• 1 female and several males.
• Is polygyny a good system for males?
• Is polygyny a good system for females?

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Conditions for Polygamy

• Local or seasonal superabundance of food.
• Risk of heavy predation.
• Precocial young.
• Sexual bimaturism.
• Nested territories due to niche division between
  sexes.

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Superabundance of food

• If food is superabundant, female can rear young
  by herself and male is free to pursue other
  copulations.
• If male has high quality territory, it may be
  advantageous to female to join the harem of this
  male, rather than pair bond with a single male
  with a low quality territory. This is the
  polygyny threshold.

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Risk of heavy predation

• Heavy predation of territorial animals favors
  monogamy, assuming parents can ward off predators.

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Precocial young

• If female can guide young to best feeding areas,
  safe from predation, male is free to pursue other
  mates.

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Sexual bimaturation extended longevity

• If courting sex is long-lived, it can delay
  reproduction to gain dominance.
• Dominance can provide courting male with access
  to enough females fo compensate for delayed
  maturation.

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Nested territories

• Males and females have different niches, but male
  niche/territory includes several female feeding
  territories.
• If female is capable of caring for young, male is
  free to pursue other females.

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Polygyny

• What kind of males are found in polygynous
  systems?
• Are these high quality males?
• What constitutes high quality?
• Do females select high quality?
• What are the costs and benefits of polygyny for
  females?

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Polygyny

• Fundamentally, organisms are polygamous. To be
  otherwise requires something special.
• Males and females rarely have equal reproductive
  success, reproductive effort, or variance of
  reproductive success.

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Group size

• In some sense, maintenance of a harem is the
  ultimate in group sociality.
• Think about non-reproductive groups.
• What influences group size?
• What is necessary (in terms of behavior) to
  maintain groups?
• Are you better off alone, or in a group?