Transcript BIOL 4120: Principles of Ecology Lecture 8: Life History

BIOL 4120: Principles of Ecology
Lecture 7: Life Histories and
Evolutionary Fitness
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Http://faculty.tnstate.edu/dhui/biol4120
Life History
Life history is species lifetime pattern of
growth, development and reproduction.
Measure of organism’s 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.
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?
Reproduction effort may vary with
latitude

Duck and blackbird
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
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:
1.Chicks in larger broods would be survive poorly
2.At temperate and arctic latitudes, birds have longer
days to gather food during summer when they
reproduce young.
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.
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
7.1 Trade-offs in the allocation of
resources provide a basis for
understanding life histories
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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?
Important stage of life history:
Maturity, Age of first reproduction; Parity, number of
episodes of reproduction; Fecundity, number of offspring
produced per reproductive episode; Longevity, age to live.
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.
Environmental conditions influence the
evolution of life history traits
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Idea was conceived by Robert
MacArthur and Edward O. Wilson: “rvs. K-selected strategists”
Derivation of the terminology comes
from population models (see future
lecture):
• “r” is population growth rate; rselected 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
Examples of r- and K-selected organisms

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r-selected organisms—short-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.
7.3 Life histories balance trade-offs
between current and future reproduction
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Age at first reproduction
Trade-off between fecundity and
survival
Trade-off between growth and
fecundity
Important stage of life history:
Maturity, Age of first reproduction; Parity, number of
episodes of reproduction; Fecundity, number of offspring
produced per reproductive episode; Longevity, age to live.
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.
Recap
Acclimation and Developmental response
Life history
Life histories vary along a slow-fast continuum
Grime’s 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
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.
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.
Trade-off between fecundity and survival
Relationship of adult’s fitness and fecundit
F = S + S0 B
S=SNSR
F = S N SR + S 0 B
SR = F/SN – (S0/SN) B
F: adult’s 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
Survival rate and
fecundity
Different adult fitness
High F, high survival of
reproductive risk
Large slope: high S0 and low Sn
(high offspring survive and low adult
survive)
The trade-off between growth and fecundity
Indeterminate growth: fish, reptiles, amphibians
Different investments on growth and reproduction
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;
<300 g, do not reproduce.
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.
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.
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Timing production: When – early or late
How many offspring: cost of the fecundity and its own
survival.
Agaves and Lobelia telekii are
semelparous plants
Other semelparous examples
Sockeye 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.
periodical cicadas
Parental investment depends on the
number and size of offspring
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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 ?
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Family care (Grandmothers, Grandfathers, Aunts, Uncles, Brothers and Sisters)
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
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
Desert annuals
Extreme
with
released
eggs of
some fish
such as cod
(millions of
eggs) etc
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.
It’s a fact of life. Caused by natural wear
and tear. Environments also influence,
but mostly, it is under genetic control.
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.
7.6 Life histories respond to variations in
the environment
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Storage of food and buildup of
reserves
Dormancy
Stimuli for change
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.
Dormancy
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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
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
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 (>13
hours); northern, flower in summer (>16 hrs)
• Water fleas: Michgan, enter diapause in mid-Sept (<=12
hrs); Alaska, diapause in mid-August (<=20 hrs)
7.7 Individual life histories are sensitive to
environmental influences
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
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.
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.
Central place foraging
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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?

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.
Optimal foraging
model can be used to
predict behavior
Using a controlled
experiment, Alex
Kacelnik of Oxford
University, tested
how food load
change with travel
times
Changed food
availability and
distance
Risk-sensitive foraging
Foraging is potential dangerous: risk factor
James Gilliam and Douglas Fraser’s fish experiment
The End
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 MillerRushing (Boston University) 2003-2006,
43 common species
Penology network:
http://www.usanpn.org/
Henry David Thoreau
(1817-1862)
Mean annual
T increased
by 2.4 oC
from 1852 to
2006
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
8.1 Sexual or Asexual Reproduction
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Asexual reproduction (produce offspring without involving
of egg and sperm)
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•
•
•
•
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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
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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
8.2 Types of sexual reproduction
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Dioecious
• Sexes are separate
individuals
• Greatest diversity of
offspring
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Hermaphroditic
• Perfect
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Male and females
organs in same
flower
Can result in
significant
inbreeding
• Monoecious
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Floral structure
Plants
Separate male and
female flowers
Reduces but does
not eliminate
inbreeding
8.3 Mating Systems describe pairing of
males and females
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Different mating strategies have different advantages
and disadvantages
• Monogamy (one to one, form of a lasting pair bond between one
male and one female)
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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)
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Greatest number of offspring
Large amount of competition
Female only responsible for offspring in terms of resources
• Poorer survival chance for offspring
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
The End
No only clutch
size, the
incubation time
also varies
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
37.8~38oC, RH 85-90%
Another interesting thing is that it takes the same amount of time to
hatch in nature and incubators (for current setting)