Life History Patterns

Flashcard maker : Joan Grant
an organism life history
encompass traits and behaviours that help individuals achieve fitness
life history
lifetime pattern of growth development and reproduction and survival involve adaptations to the physiology, morphology and behavior
the study of life histories is a search for patters
and for explanations for those patterns
life history traits
represents an allocation of limited time and resources to achieve maximum reproductive success

parental investment
life expectancy

the number of offspring produced by an organism per reproductive episode
the number of reproductive episodes an organism experiences
parental investment
the time and energy given to an offspring by its parents
longevity (life expectancy)
the lifespan of an organism
some questions of interest
why do clutch size vary
why does age at maturity vary
why does gestation length vary
why do fecundity vary from one egg every other year to as many as eight in one clutch
patterns of reproduction and sexual selection
Are important because reproduction is the major vocation of al living things
goals of life history theory
to answer why all this variation and to construct models which predict what sorts of traits will be favored in what sorts of environments. for highest fitness one will start early, reproduce every year and produce large numbers
Problem with this theory
assumption of limited time and resources and the need to allocate these to particular traits
trade offs
Key Life history traits
size at birth
age at maturity
size at maturity
longevity length of life
optimization approach
most often used assume that observed combinations of life history traits are those with the highest fitness. but there are other approaches such as bet hedging spreading the risk – conservative, diversified, aaptive coin flipping
reproductive value
fitness : the genetic contribution by an individuals descendants to future generations
natural selection favours those individuals that make the greatest proportionate contribution to the future of the population to which they belong. all life history component will affect this contribution through their effect on fecundity and survival.
one measure of fitness is the reproductive value
slow to fast continuum
life history traits often vary consistently with life form, habitat or envvironmental conditions. variation in one life history trait is often correlated with variation in other life history traits.

slow: long time to sexual. maturity low numbers of offspring
high parental investment : elephants

fast: short time to sexual maturity
short life spans high number of offsprings
little parental investment : fruitflies, weeds

patterns of reproduction
asexual and sexual
asexual\” fomation of new individuals without fertilization

sexual: involving the production of haploid gametes, egg and sperm that combine to form a diploid cell or zygote

Sexual reproduction
may involve separate male and female individuals


monoecious or hermaphrodite where individual organisms possess both male and female organs.
bisexual flowers: termed perfect and asynchronous timing of the maturation of pollen and ovules often reduces the chance of self fertilization. lillies

monoecious: separate male and female flowers on the same plant imperfect hemlock trees this can be an advantage in colonization. a single self fertilized hermaphroditic plant can colonize new habitat reproduce and establish a new population (weeds)

hermaphroditsm in animals
simultaneous hermaphrodism in earthworms. potential to produce twiced a many offspring. male organ of one individual mated withthe female organ of another and vice versa

sequential hermaphrodism: environmental stimulates sex change or change in sex ration marine fish

trade offs
natural selection favors indivuduals that produce the maximum number of reproducing offspring in a lifetime. parents have to make a trade off in the allocation of their resource into growth, maintenace, protection and reproduction.
trade off definition
negative relationships between two life history characteristics in which increases inone are associated with decreases in the other as a results of such compromises
reproductive effort
time and energy allocated to reproduction over a period of time
principle of allocation
the observation that when resources are devoted to one body strructure, physilogical function or behavior they cannot be alloted to another. an optimized life history resolves conlicts between competing demands of survival and reproduction to achieve maximum fitness
key trade offs
current reproduction vs survival
reproduction vs condition/growth
number vs quality of offspring
current reproduction vs future reproduction
offspring number vs parental care
as the offspring number increases the amount of parental care decreases and this reduces the chances of offspring survival.
depends on environmental conditions. such as the number of daylight house that parents have to find resources for their offspring

Having more offspring can stimulate parents to hunt harder for food to feed their offspring. this additional effort can affect the parents fitness

the cost of reproduction
individuals have a limited amount of resource/energy to be allocated to growth, maintenance, reproduction, survival. reproduction involves both benefits and costs to individual fitness. by increasing current allocation to reproduction you likely decrease survival and or rate of growth and hence decrease the potential for future reproduction
the behavioral, physiological and energetic activities involved in reproduction
extract a cost to future reproductive success on the parent in the form of reduces survival fecundity and growth
tradeoffs of trinidadian guppies
low stream guppies have short life expectancies because high predation. in higher elevation have long life expectancies
natural selection will favor the age at maturity that
reuslts in the greatest number of offspring produced over the liftetime of an indicidual. environmentl factors that result in reduced adult survival select for earlier maturation and the reduced juvenile survival relative to that of adults select for delaye maturation
mating systems
the patterns of mating between males and females in a population

monogamy: formation of lasting pair bond between one female andone male. exist where cooperation is needed to raise young successfully. birds. but may cheat to increase their fitness

promiscuity : males and females mate with one or many of the opposite sex and form no pair bond.

polygamy: acquisition by an individual of two or more mates. one male several females polygyny
one female several males polyandry – sandpipers

sexual selection
adaptations that increase mating success of individuals.
sexual reproduction
requires the acquisition of mates which involves both mating systems and sexual selection
two basic types of mating systems
monogamy polygamy
but there may be a wide range of situation in between involving the strengths of pair bonds
sexual selection encompasses
intra sexual selection usually male male
inter sexual selection
mate choice
modes of sexual selection
competition among males appearance and behavior social dominance

resource based selection: choice based on resources such as territory or access to food which will improve her fitness

genes only selection: by selecting the male with exaggerated traits the female will also be acquiring genes for highest fitness

sexual conflict
sexual cannibalism
intersexual conflicts
gene based mode of sexual selection
handicap hypothesis
if a male can carry a handicap and survive it is a proof of a superior genotypes. genes with higher viability despite exposure to predators (peacocks)

high survival rate of offspring
high growth of offspring
low parasitic infection on bright males
lead to increased fitness

female choice
lek species
females control the situation. animals aggregate into groups on communal courtship ground that hold no resource males defend these territories and express visual and vocal displays. females visit the leks select a male mate and move on

dominant males risk monopolising all the mating

male mate choice
less prevalent
female rank or status
female age
sexual swelling
males do not choose females as mates for good genes
parental investment
parents have only a limited amount of energy from which they have to allocate a certain amount to their own maintenance and survival. to make its maximum contribution to future generations an organism must balance the profits of immediate reproductive investment of time and energy against the costs to future prospects
invest a maximum amount of energy into a single reproductive effort in a life time annual plants, salmon
allocate less energy to each reproduction and repeat reproductive efforts through a lifetime most vertebrates
a problem for iteroparous organisms is
timing reproduction.
early means less growth, earlier maturity and reduced survivorship and potential for future reproduction
later allows increased growth maturity and survivorship but decrease of fecundity after each bout of reproduction. the organism has therefore to make a trade off between present progeny and future offspring this trade off relate tot he reproductive values of individuals in a population
reproductive effort- parental care
caring for young is a major reproductive expenditure -providing food, shelter and protection from predator brooding grooming and an related activity that increase the fitness of the offspring.
based on the degree of development at hatching or at birth two types of young are produces
precocial: young are able to move about at or shortly after birth long infancy and grow slow

altricial : animals are born helpless naked or nearly so and often blind grow rapidly and mature early

parental energy budgets
how organisms allocate energy to growth and reproduction is central to their reproductive strategy.
if an organism directs more energy to reproduction it has less energy to allocate to growth and maintenance. such an individual may grow more slowly to the next age or fail to reproduce or to survive
organism may optimise the allocation of their investment through
clutch size( adjustment or manipulation)
, brood reduction, ( adjustment by failure to feed one of the siblings younger or older, siblicide in the masked boody (battle between the offspring)
asynchronous hatching
parental investmesnt depends on age and size
for many species clutch size/ weight and fecundity are related to age and size of the parent
the true measure of an organisms reproductive success is
fitness. evolution is the product of differential reproduction of individuals and the process of natural selection.
reproductive sucess
the number of offspring that survive to reproduce
designing an organism to maximize its fitness
reproduce as soon as possible after birth, reproduce continuously producing large numbers of large offsprings that it would nurture and protect not possible because organism have limited amount of resources available for growth/
organisms face trade offs
characteristics related to reproduction. modes of reproduction timing number and size of egg, young or seeds parental care. these trades off are imposed by constraints of physiology energetics and prevailing physical and biotic environment
reproduction maybe sexual or asexual
sexual: two diploid individuals produce haploid gamete that combine to form a diploid cell or zygote thathas a full complement of chromosomes. because the number of gene recombinations is enormous, recomibination is an immediate and major source of genetic variation

asexual: produce offspring without the involvement of egg and sperm. it takes many forms but in all cases the new individuals are genetically the same as parent
hydras budding. a bud pinches off as new individual

ovum develops without fertilization insects
organisms that rely heavily on asexual reproduction
occasionally revert to sexual reproduction and this in induced by environmental change. when its warm hydras turn to sexual to produce eggs that lie in the winter and fromwhich young hydras mature and reproduce asexually.
tradeoff in sexual or asexual reproduction
asexual produces genetically identical offspring that are well adapted to their local environment because al the individuals are capable of reproducing there is a potential for high population growth
loss of genetic variability responds more uniformly to a change in environmental and can lead to extinction.

sexual: genetically unique offsprings produces a broader range of potential responses to the environment.
each offsprings contributes only one half as much to the evolutionary fitness of either parent.
involves specialized reproductive organs that aside from reproduction have no direct relationship to survival. production of gametes, courtship activities, mating are energetically expensive.
expense of reproduction is not shared equally by both sexes, eggs much larger than sperm

no parental duty individual can devote more time and energy for competition for mates and resources food or quality
the nature and evolution of male female relationships
are influenced by environmental conditions, availability and distribution of resources and the ability of individuals to controll access to resources

if a female doesnt gain anything by beingmonogamous in a poor territory shell go to a better territory and be polygamous to increase her fitness

reproductive effort may vary with latitude
clutch size (birds) or litter size (mammals) is higher in high latitude than low, because of adaptations to food supply, different allocation of energy to egg production
lack clutch size
natural selection will favor not the largest clutch size but a compromise clutch size which by balancing the number produced against their subsequent survival leads to the maximum number of offspring surviving to maturity. but did not consider fitness of individual offspring long term survival and did not consider cost of reproduction
r selection and K selection
r stands for intrinsic rate of natural increase
k carrying capacity
organisms living in unpredicted environment allocate greater energy to reproduction and they expand rapidly when conditions are favourable. r selected
short lived, small body size, large number of offsprings, earlier maturity, possibly semelparity
k selection
organisms that occupy a more predictable environment and are more subject to density related mortality tend to allocate less energy to reproduction they are said tobe K selected. because selection favour efficient use of the environment
larger body size
slower development
larger and fewer offsprings
phenotypic plasticity
ability of an organism to express itself in different ways in different envionments
habitat selection
reproductive success depends heavily on choice of habitat
settling on less than optimal habitat can result in reproductive failure. habitat selection is important in organism life history pattern.
structure, diversity of vegetation cover food.
quality may be modified by the avialability of nestling sites escape cover,
individuals across a species exhibit regional plasiticity in selection of habitats. plans are better in certain habitat types and dispersal aids

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