BIOL 4120: Principles of Ecology Lecture 7: Life Histories and Evolutionary Fitness

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BIOL 4120 Principles of Ecology Lecture 7 Life
Histories and Evolutionary Fitness

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu
• Http//faculty.tnstate.edu/dhui/biol4120

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Life History

• Life history is species lifetime pattern of
  growth, development and reproduction.
• Measure of organisms reproductive success is
  fitness Those individuals who leave the largest
  number of mature offspring are the most fit the
  environments.
• Trade-off between growth and reproduction mode
  of reproduction, age at rep., allocation to rep.
  number and size of eggs, young or seeds, parental
  care.

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Reproduction efforts vary with latitude

• Why same species of birds, for example, songbirds
  in tropics, lay fewer eggs at a time than their
  counterparts that breed at high latitudes?

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Reproduction effort may vary with latitude

• Birds in temperate regions have a larger clutch
  size than tropical birds
• Food supply, with longer day length in springtime
  to forage for food to support larger broods
• large climate variation, decreases popul. below
  carrying capacity, need more young
• Greater mortality in winter results in more food
  for survivors next spring

Duck and blackbird
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• David Lack, Oxford University
• 1947
• Birds would increase fitness by increasing clutch
  size, unless reduced survival of offspring in
  large broods offset this advantage
• Hypotheses
• Chicks in larger broods would be survive poorly
• At temperate and arctic latitudes, birds have
  longer days to gather food during summer when
  they reproduce young.

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Experiments that adding eggs decrease survival of
offspring
Hogstedit, Science 1980 European magpie Average
clutch is 7 (maximum the pair can handle), add
more or reduce could reduce the fitness.
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Life History and Evolutionary Fitness

• 7.1 Trade-offs in the allocation of resources
  provide a basis for understanding life histories
• 7.2 Life histories vary along a slow-fast
  continuum
• 7.3 Life histories balance trade-offs between
  current and future reproduction
• 7.4 Semelparous organisms breed once and then die
• 7.5 Senescence is a decline in physiological
  function with increasing age
• 7.6 Life histories respond to variations in the
  environment
• 7.7 Individual life histories are sensitive to
  environmental influences
• 7.8 Animals forage in a manner that maximizes
  their fitness

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7.1 Trade-offs in the allocation of resources
provide a basis for understanding life histories

• There are many trade-offs involved in
  reproduction effort decision
• Allocation of resources Given time and resources
  are limited, how can the organisms best use them
  to achieve its maximum possible fitness?

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Important stage of life historyMaturity, Age of
first reproduction Parity, number of episodes of
reproduction Fecundity, number of offspring
produced per reproductive episode Longevity, age
to live.
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7.2 Life histories vary along a slow-fast
continuum
Life history traits of different species vary
consistently with respect to environments
variation in one life history traits is often
correlated to others. Variations can be arranged
along a single continuum of values.
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Environmental conditions influence the evolution
of life history traits

• Idea was conceived by Robert MacArthur and Edward
  O. Wilson r- vs. K-selected strategists
• Derivation of the terminology comes from
  population models (see future lecture)
• r is population growth rate r-selected species
  have traits that increase r
• K is population carrying capacity K-selected
  species have traits that increase carrying
  capacity and competitive ability when populations
  fill environment

Spotted and redback salamanders
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Examples of r- and K-selected organisms

• r-selected organismsshort-lived, e.g.,
  dandelion, with rapid population growth rate,
  small body size, early maturity, larger number of
  offspring, minimal parental care (animals).
  Inhabit unstable conditions, disturbed areas.
• K-selected organisms competitive species,
  long-lived, e.g., oak tree with long life,
  production of few, large seeds that can grow
  readily in shaded environments, but lack of mean
  of wide dispersal, poor colonizers of new or
  empty habitats.

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7.3 Life histories balance trade-offs between
current and future reproduction

• Age at first reproduction
• Trade-off between fecundity and survival
• Trade-off between growth and fecundity

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Important stage of life historyMaturity, Age of
first reproduction Parity, number of episodes of
reproduction Fecundity, number of offspring
produced per reproductive episode Longevity, age
to live.
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Age at first reproduction
Long-lived organisms typically begin to reproduce
at an older age than short-lived
ones. Albatrosses (sea bird) high annual
survival rate (94), start at 10 yrs. Small
songbirds 50 survival rate, start at 1
yr. Natural selection favors the age of maturity
that results in the greatest number of offspring
over the lifetime of the individual.
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Recap

• Acclimation and Developmental response
• Life history
• Life histories vary along a slow-fast continuum
• Grimes plants Competitors, Ruderal, and
  Stress Tolerators
• r- and k-selected strategists
• Life histories balance trade-offs between current
  and future reproduction
• Age at first production

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Age at first reproduction
Long-lived organisms typically begin to reproduce
at an older age than short-lived
ones. Albatrosses (sea bird) high annual
survival rate (94), start at 10 yrs. Small
songbirds 50 survival rate, start at 1
yr. Natural selection favors the age of maturity
that results in the greatest number of offspring
over the lifetime of the individual.
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Trade-off between fecundity and survival
Trade-off Experimental study to demonstrate that
chicks with more competing siblings grow more
slowly and fewer survive to reach
adulthood. European kestrels Dijkstra et al.
1990.
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Trade-off between fecundity and survival
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Relationship of adults fitness and fecundity
F S S0 B SSNSR F SNSR S0 B SR
F/SN (S0/SN) B F adults fitness S survival
probability SR adult survival related to
reproduction SN not directly related to
reproduction S0 survival to one year of
age offspring B of offspring produced
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Survival rate and fecundity Different adult
fitness High F, high survival of reproductive
risk
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Large slope high S0 and low Sn (high offspring
survive and low adult survive)
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The trade-off between growth and fecundity
Indeterminate growth fish, reptiles,
amphibians Different investments on growth and
reproduction
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• Animals
• Ectothermic (cold-blooded) animals
• Production of offspring in fish increases with
  size, which increases with age
• Gizzard shad 2-yr, 59,000 eggs
• 3-yr, 379,000 eggs
• Endothermic (warm-blooded)
• similar patterns exist for some animals
• European red squirrel body weight and
  reproduction success lt300 g, do not reproduce.

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Mortality rate influences life history Experiment
of David Reznick et al. , UC Riverside, on guppy
Poecilia reticulata Streams in Trinidad
waterfalls created two environments below
waterfalls, predators fish species (pike cichild
and killifish) above waterfalls, relatively
predator-free.
Predators transplant experiment confirmed that
after a few generations of adding predators, they
showed same life histories.
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7.4 Semelparous organisms breed once and then die

• Semelparity
• One reproductive effort with all resources, then
  die
• Most insects and other invertebrates, some fish
  (salmon) and many plants (bamboo, ragweed)
• Some are small, short lived, grown in disturbed
  habitats
• Environmental effect can be disastrous
• Iteroparity
• Produce fewer young at one time and repeat
  reproduction throughout their lifetime
• Multiple cycles of reproduction means the
  organism must balance growth, maintenance,
  escaping predators, defending territory, etc
  against reproduction
• Most vertebrates, perennial herbaceous plants,
  shrubs, and trees.
• Timing production When early or late
• How many offspring cost of the fecundity and its
  own survival.

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Agaves and Lobelia telekii are semelparous plants
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Other semelparous examplesSockeye salmon swim as
far as 6,000 km from Pacific Ocean feeding
grounds to spawning streams, lay thousands of
eggs, then die from the exertion.
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periodical cicadas
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Parental investment depends on the number and
size of offspring

• Given certain resource allocated to rep., one can
  produce many small young or few large ones. The
  number of offspring affects parental investment.
• Produce large number of offspring, less or no
  parental care (fish-eggs, plants-seeds)
• Produce helpless offspring (produce young, spend
  less energy in incubation, but require
  considerable parental care)
• Altricial
• Mice
• Longer period suckling
• Robin
• Other bird feeds
• Produce more mature offspring (longer gestation,
  born in advantaged stage of development)
• Precocial
• Chicken, cow, deer, turkey
• Humans ?
• Family care (Grandmothers, Grandfathers, Aunts,
  Uncles, Brothers and Sisters)

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African elephants produce one offspring at a
time, once every few years over a long lifetime,
and protect each offspring intensively (much like
humans)

• Few Number
• More resources per individual
• More chance of accidental loss

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By contrast, many plants and some insects,
reproduce once (annually), producing vast numbers
of seeds/eggs that are poorly protected, if at
all
Large Number Less resources per individual More
chances of success Extreme with released eggs of
some fish such as cod (millions of eggs) etc
Desert annuals
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7.5 Senescence is a decline in physiological
function with increasing age

• Senescence A gradual increase in mortality and a
  decline in fecundity as physiological function
  deteriorates over time.
• Its a fact of life. Caused by natural wear and
  tear. Environments also influence, but mostly, it
  is under genetic control.

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The strength of selection varies with extrinsic
mortality rates
The strength of selection for changes in
mortality and fecundity at a particular age is
related to the proportion of individuals in the
population alive at that age, which depends
largely on rates of mortality caused by extrinsic
factors earlier in life.
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7.6 Life histories respond to variations in the
environment

• Storage of food and buildup of reserves
• Dormancy
• Stimuli for change

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Storage for food and buildup of reserves
Plants and animals can store food and build
reserves during the good environments. For
example, Desert Cacti to store water plants
store nutrients Arctic animals accumulate fat
during mild weather in winter winter active
mammals (squirrels) and birds (acorn woodpeckers)
cache food supplies.
Chaparral plants store food reserves in
fire-resistant root crowns.
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Dormancy

• Dormancy physiologically inactive state.
• Tropical and subtropical trees shed leaves during
  drought
• Temperate and Arctic trees shed leaves in fall
• Hibernate
• Mammals squirrels, bears?
• Diapause some insects entering resting state

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Recap

• Life histories balance trade-offs between current
  and future reproduction
• Age at first production
• Survival and fecundity
• Growth and fecundity
• Parity and parental investment
• Senescence
• Life histories respond to variations in the
  environment
• Storage of resources
• Dormancy
• Stimuli for change

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Stimuli for change

• Many events in life history of an organism are
  timed to match predictable change in
  environments.
• Proximate factors day length etc, no direct
  effect on fitness
• Ultimate factors such as food supplies
• Photoperiod length of daytime
• Different populations of a single species may
  differ greatly in their responses to photoperiod.
• Side oats gama grass southern, flower in winter
  (gt13 hours) northern, flower in summer (gt16 hrs)
• Water fleas Michgan, enter diapause in mid-Sept
  (lt12 hrs) Alaska, diapause in mid-August (lt20
  hrs)

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7.7 Individual life histories are sensitive to
environmental influences
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Relationship between age and size at
metamorphosis between frogs raised with high and
low food suplies.
Travis 1984.
Marbled salamanders and spotted
salamanders Gape-limited predation
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The probability of survive from fire increases
with increasing stem diameter. When fires are
frequent, there is a strong selection of the
rapid growth of stem at the expense of developing
root systems.
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7.8 Animals forage in a manner that maximizes
their fitness
Foraging involves many different decisions to
make, such as where to forage, how long to feed
in a certain patch of habitat, which type of food
to eat etc. Food supplies vary spatially,
temporally, and with respect to the quality of
food items Foraging is dangerous as it expose
the individual to predation. Optimal foraging
try to explain these behavioral responses in
terms of the likely costs and benefits of each
possible alternative behavior.
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Central place foraging

• When birds feed offspring in a nest, the chicks
  are tied to a single location, while the parents
  are free to search for food at some distance from
  the nest. This situation is referred to as
  Central Place Foraging.
• Trade-offs
• Increase foraging distance, increase food
  availability, also increase the time, energy and
  risk costs of foraging
• Is there some best distance from the nest at
  which a parent bird should forage, and how much
  food should the parent bring to its brood with
  each trip? How much time should the parent
  gathering food before it returns to its nest?

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• European starlings
• Forage on lawns or pasture for leatherjackets
  capture time increases with number of prey
  already caught, maximum 8 can carries
• Foraging trip including both the time spent at
  the foraging area and traveling time between
  foraging area and nest
• Rate at which a parent can delivers food to its
  offspring is the number of prey caught divided
  by the time of foraging trips
• How to maximum the rate?
• an individual can spend an intermediate amount
  of time at the foraging area during each trip and
  bring back something less than the maximum
  possible food load.

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Optimal foraging model can be used to predict
behavior
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Using a controlled experiment, Alex Kacelnik of
Oxford University, tested how food load change
with travel times Changed food availability and
distance
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Risk-sensitive foraging Foraging is potential
dangerous risk factor James Gilliam and Douglas
Frasers fish experiment
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The End
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Global warming and flowering time
Started flowering observation study in Concord,
Massachusetts 1852-1858 500 plant species,
weekly Alfred Hosmer 1878, 1888-1902, 700 plant
species Pennie Logemann 1863-1993, 250
species Richard Primack and Arbaham
Miller-Rushing (Boston University) 2003-2006, 43
common species Penology network
http//www.usanpn.org/
Henry David Thoreau (1817-1862)
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Mean annual T increased by 2.4 oC from 1852 to
2006
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Flowering time of some species did not change, on
average, flowering time today is 7 days earlier
than 150 years ago Blueberry is 3-4 weeks earlier
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8.1 Sexual or Asexual Reproduction

• Asexual reproduction (produce offspring without
  involving of egg and sperm)
• New individuals are the same as the parent
• Many plants (underground stem) such as
  strawberry
• some animals (hydra, some aphids,
  parthenogenesis)
• If fitness is high, matches organism to
  environment
• If fitness is low, possible extinction (less
  variation)
• Stress can result in use of sexual cycle to give
  new gene combinations (hydra, aphid)
• Sexual Reproduction
• More common form.
• Can produce new gene combinations able to cope
  with a changing environment.
• Greater energy commitment
• Specific organelles
• Production of gametes, courtship activities, and
  mating are energetically expensive.
• Feeding offspring
• The expense of reproduction is not shared equally
  by both sexes

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8.2 Types of sexual reproduction

• Dioecious
• Sexes are separate individuals
• Greatest diversity of offspring
• Hermaphroditic
• Perfect
• Male and females organs in same flower
• Can result in significant inbreeding
• Monoecious
• Separate male and female flowers
• Reduces but does not eliminate inbreeding

Floral structure
Plants
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8.3 Mating Systems describe pairing of males and
females

• Different mating strategies have different
  advantages and disadvantages
• Monogamy (one to one, form of a lasting pair bond
  between one male and one female)
• Most prevalent among birds, rare among mammals
• Seasonal or permanent
• Allows sharing of cost of raising offspring
• Increases survival chances of offspring
• Cheating does occur and has specific advantages
  to fitness
• Polygamy (one to two or more, a pair bond exists
  between individual and each mate)
• More than one mate of one sex for a single
  individual of the other sex (polygyny and
  polyandry)
• Free individual to compete for resources and
  protect territory
• Better food etc for mates
• Some protection of offspring from competition
• Promiscuity (one to one or many and no pair bound
  formed)
• Greatest number of offspring
• Large amount of competition
• Female only responsible for offspring in terms of
  resources
• Poorer survival chance for offspring

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8.4 Sexual Selection

• For Monogamy, Polygamy and Promiscuity
• All involve the selection of a mate and therefore
  sexual selection
• Selection for secondary sexual characteristics
• Peacock versus Peahen
• Large tail feathers, more mating
• Smaller tail feathers, less mating
• Deer
• Characters that aid competition such as horns
• Humans
• Faster sports car such as a Ferrari

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The End
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No only clutch size, the incubation time also
varies
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Set nest boxes at two places
Illinois
Panama
Monitor and collect newly laid eggs over one
breeding season
Eggs are marked by date and weighted
Hatched in incubators at 37.838oC, RH 85-90
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Another interesting thing is that it takes the
same amount of time to hatch in nature and
incubators (for current setting)