Life History Patterns

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Life History Patterns

• Chpt. 20, pp 427-454, 5th edition
• Chpt. 13, pp 214-239, 6th edition

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Most organisms major task in life is to
reproduce. By transmitting genetic characters to
the next generation, individuals maximize their
number of descendants. All life-history
patterns, activities, or traits are directed
towards transmitting genetic characters
(reproducing).
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Maximizing Fitness Affects

• Methods of acquiring/selecting a mate.
• Mode of reproduction.
• Number of young and frequency.
• Is the underlying reason for
• Bright colors fragrances of flowers.
• Songs of birds.
• Antlers of deer.
• Lights of fireflies.

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Costs of L/H Patterns

• Behaviors, activities, and morphologies are
  metabolically expensive to individuals.
• Parents must decide how to allocate energy to
  growth, defense, and reproduction.

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Patterns of Reproduction

• Reproduction falls into two categories..
• Asexual formation of a new individual
  genetically identical to the parent. E.g.
  paramecium divide into two plants like
  strawberry may spread by runners, Daphnia thru
  parthenogenesis.
• Sexual involves production of haploid gametes,
  egg sperm that combines to form a diploid cell
  or zygote.
• allows recombination of genes to mix gene
  pool.
• mixing supplies the genetic variability needed
  to meet changing selective pressures.

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Mating Systems
Mating systems are means by which organisms
obtain a mate. It includes of mates a
male or female acquire. manner of
acquisition. pair bonds. patterns of
parental care. The nature and evolution of
male-female relationships is influenced by
availability and distribution of resources.
ability of individuals to control access to
resources or mates.
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The nature and evolution of male-female
relationships is influenced by availability
and distribution of resources. ability of
individuals to control access to resources or
mates. For Example If a male does not care
for young or protect them, it makes no sense for
the female to remain with the male. In a
Homogenous environment (or nearly) the of young
raised will be similar everywhere gtgtgt
monogamy. If Habitat is diverse, female would
be better off to share habitat with other females
under the control of a territorial male gtgtgtgt
polygamy.
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• MONOGAMY formation of a pair bond between one
  male and one female.
• - prevalent among birds
• - rare among mammals (except some carnivores,
  e.g. foxes, beaver).
• Monogamy generally occurs in species that need
  cooperation by the parents to rear young
  successfully.
• gt 90 of all birds are seasonally monogamous.

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Young birds are helpless need warmth
food protection (provided by the
female). Male can best increase his fitness by
staying with female and caring for the existing
young, not going off to breed again. Note
about 100 species of birds cheat on their mates
(for e.g. mallards).
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• POLYGAMY acquiring 2 or more mates, none of
  which is mated to another individual.
• The greater the distribution of critical
  resources (food, habitat) the greater the
  opportunity for a successful individual to
  control the resources and available mates.
• Types of Polygamy
• Polygyny male controls 2 or more females (e.g.
  W.T. Deer).
• Polyandry individual female controls 2 or more
  males (e.g. shorebirds).
• Promiscuity males and females copulate with 1
  or many of the opposite sex and form no pair
  bonds.

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• SEXUAL SELECTION
• Males are not picky, females usually are.
• Intrasexual competition intense male rivalry
  for female attention.
• For species that battle for dominance (w.t.
  deer), the winner is usually thought to be
  fittest.
• Females should try to increase her fitness by
  breeding with the fittest male

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Sexual Selection Natural Selection

• The way in which sexual selection and natural
  selection are linked is hypothesized to be
• Novel male genetic character (e.g. bright
  plumage).
• Female selection for that character in mate
  selection.
• Offspring have both the genetic character (males
  with bright plumage) and females have a selection
  for that character.
• This results in positive feedback which is
  runaway in both these male and female traits.

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Handicap Hypothesis

• The handicap hypothesis consists of 3
  characteristics..
• Male handicap (e.g. bright plumage leads to
  higher predation).
• Female mating preference for the handicap.
• A general viability trait.
• Viability trait the handicap should reduce
  survival of the male, if it still survives it
  must be better than the rest at surviving.
• Therefore, offspring should also have this trait
  good mate choice because offspring should have
  higher viability!

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Sexual Selection
J. Maynard Smith (1991) classified processes of
selection as 2 types I. Intrasexual selection
usually male-to-male (occasionally
female-to-female) competition for the
opportunity to mate. II. Intersexual
selection mostly female choice of mate.
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Sexual Selection

• BUT, How do females make their final choice?
• Three Female Choice Models
• Resource-based selection.
• Genes-only Selection
• Lek Behavior

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• Three Female Choice Models
• Resource-based selection.
• (a) females choose male and accept the
  territory /resources that come with him.
• (b) females choose the territory and accept the
  male that comes with it.
• Examples
• 1. Fantail darter males w/ fleshy-egg-like
  knobs on dorsal spines to mimic eggs (Egg
  mimicry, females prefer males with eggs).
• 2. Songbirds males w/ very complex songs had
  best territories, females responded to complex
  songs.

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Three Female Choice Models 2. Genes-Only
selection. Female selects a mate based on his
fitness May select mate from among winners
of combatants (bighorn sheep, elk, seals).
May select on the intensity of the courtship
display or some morphological feature that
reflects genetic superiority. Examples In
Long-tailed Windowbirds the males with longer
tails were selected for by females. Researchers
did manipulations cutting and gluing on tails.
Females preferred the artificially long tails.
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Three Female Choice Models 3. Lek Behavior
Leks are arenas where lek species aggregate
on common courtship grounds. Males defend small
territories with no resources and advertise their
presence by colorful vocal and visual
displays. Females choose their male to mate
with, then move on. This is an uncommon
female choice, but it is taxonomically-
widespread in the animal world (found in frogs,
insects, birds, and mammals).
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Hypotheses to explain Leks..

• Female Choice females prefer leks because it is
  the safest place to mate and males aggregate,
  providing a better choice.
• Hotspot Model Males cluster in areas where
  encounters with females will be high, e.g. sage
  grouse near female wintering areas.
• Hotshot Model in smaller leks the males set up
  a hierarchy, dominant male controls mating (only
  1 mates).

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Reproductive Effort

• Natural selection favors the individuals that
  produce the highest number of surviving offspring
  in a lifetime.
• Parents allocate a certain amount of resources
  and time to fecundity.
• Reproductive effort is the nature and amount of
  allocations to reproduction over a period of time.

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Reproductive Effort

• Caring for young is a major reproductive
  expenditure.
• E.g. Providing food shelter and protection from
  predators brooding, grooming, and any activity
  that increases fitness of the offspring.
• Amount of care is influenced by the maturity of
  the young at birth.
• 2 Major MaturityTypes of Young Produced
• Precocial able to move about at or shortly
  after birth.
• Altrical born helpless, naked, or nearly
  blind.

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Parental Care Examples

• MAMMALS humans are altrical - helpless and
  blind as young.
• dolphins are precocial, can swim etc. at
  birth.
• Degree of Parental Care
• Varies from no care (many eggs), e.g. some fish
  like cod
• To Humans, 1 young usually, 18 years of care.
• Most insects have little parental care (except
  social insects like ants).

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Parental Investment

• Reproduction is costly in terms of energy
  expended and the effect on survival.
• Organisms have a limited amount of energy. They
  can
• - mature early and have lower fecundity.
• - mature later and have higher fecundity.
• Think of parental investment as a budget. An
  animal has so much it can spend on reproduction.
  It can either be spent on one expensive item or
  many less expensive items.

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How an animal allocates its reproductive energy
can be described by two terms Semelparous are
organisms that have one major reproductive output
per lifetime. e.g. salmon, mayflies, most annual
plants. Iteroparous are organisms that have
fewer young at one time, but repeat
reproduction. e.g. largemouth bass, dolphins,
deer, rabbits, red oak
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QUESTION Since it is easier to make one more
sperm, egg, or seed than to survive an additional
year, then why are any organisms iteroparous?
ANSWER Iteroparity (or perrenial) is favored
when young mortality is high and adult mortality
is low and population growth is
slow. Semelparity (or annual) is favored when
the population growth rate is high, juvenile
survival is high, and adult survival and
likelihood of reproducing a 2nd time is low.
Within a species, a large investment in one year
may mean reduced output the next year.
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Organisms must partition energy between growth
and reproduction. Early maturity leads to
reduced growth Late maturity leads to higher
growth Often increased size means higher
fecundity.

• Reproduction is Energetically Expensive.
• Many N.A. fish may lose up to 25 of mass and gt
  25 of total body energy in spawning.
• Birds expend _at_ 4X basal metabolism rate in
  feeding their young.
• Lactating mammals use up to 2.5 5 X basal
  metabolic rate.

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Clutch Size

• Only so much energy is available for
  reproduction.
• After some point dividing the energy into higher
  numbers of young is pointless as the fitness on
  the individual young gets too low.
• Two basic Choices of Parental Investment
• 1. Many small young
• 2. Or a concentrated investment in a few larger
  ones.

OR
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Parents Can Adjust Brood or Clutch Size

• Experiments were conducted to increase or
  decrease clutch size in birds. It was expected
  that increased clutches would have lower
  survival.
• What happened?
• artificially increased clutches had smaller
  individuals that had fewer young and S.
• Artificially reduced clutches had S.

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Latitudinal Effects at more northerly latitudes
birds had higher clutch sizes.
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Other Unusual L-H Traits

• Hermaphrodism What about when males and females
  are the same individuals?
• Hermaphrodism is especially common in plants.
• Most are not self-conpatable.
• Even worms mate with other worms, not usually
  themselves.
• Usually (e.g. Jack0in-the-pulpit) are not a
  female 2 years in a row due to higher energy
  demands.
• Some fish species are hermaphroditic are males
  as young fish and switch to females when older
  and larger (e.g. sea basses).

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Age Size

• For many species size fecundity is related to
  size and age of the parent.
• especially in plants and poikilotherms
• Examples
• Virginia Pine
• - in open stands produce seed in 5 8 years.
• - in dense stands may delay seed for 50 years.
• White Oak
• - dont produce seed until age 50.
• - at 16 DBH produce 700 acorns.
• - at 24 DBH produce gt 2000 acorns

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• Examples
• Gizzard shad
• - If they mature at age 2 F 59,000 eggs.
• - If they delay to age-3 F 379,000 eggs.
• Note 15 spawn at age-2, 80 spawn at age-3.

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Body Size Influences Fecundity in Homeotherms,
too!
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Gender Allocation

• We expect a 5050 ratio between sexes.
• If one sex is less expensive to rear, the sex
  ratio will be skewed (eventually) toward the
  least expensive sex.
• If it becomes skewed towards females, then
  anything that leads a bearer to produce more sons
  than daughters will be selected for.
• (The opposite for males to mate gt for female
  offspring).

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r-selection and K-selection
Remember the Logistic model. N r N (K -
N) N r-selected small, high
reproduction rates and short lives. K
selected low reproductive rates and long lives.
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r-selection and K-selection
From MacArthur Wilson (1967) - Island
Biogeography Theory R-selected Empty islands
should be colonized by a variety of immigrants,
most successful will be ones with best dispersal
and best ability for rapid population growth in
unfavorable habitats. (M is density-independent).
K-selected As populations increased,
conditions get crowded and natural selection
favors most competitive individuals, those able
to continue population growth at high sustained
densities near carrying capacity (M is
density-related).
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R-strategists are typically short-lived, with
high reproductive rates at low N, early and
single reproduction, small body size, high
offspring with low survival, low degree of
parental care. K-strategists are competitive
species with stable populations of long-lived
individuals. BET HEDGING Among K-strategists,
random fluctuations in the environment that
reduces fitness may cause K-strategists to forego
reproduction in one year.obviously r-strategists
may not be able to do this.
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When Should You Mature? In a variable
environment with high adult mortality and low
juvenile mortality, selection should favor early
mortality. Under the same conditions if adult
mortality is low and juvenile mortality if high
you should mature late. This selection can be
observed in sunfish populations that receive
heavy fishing pressure for larger fish which are
stunted with early reproducing fish vs. a
well-managed lake where bass keep young sunfish
numbers low and reproduction is dominated by
larger, later-maturing individuals.
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Habitat Selection

• Most animals appear to select habitat based upon
  large scales first..
• . Does it have water?
• .. Does it have cover plants, etc.
• 2. Secondarily they look on a smaller, finer
  scale, e.g. Then, does it have song perches,
  drumming logs, etc.