envs lecture 11 Flashcards
what are life history traits
traits that affect survival and reproduction across various stages of life
what is variation in life history tied to
variation in history
what do life history trait do
evolve
what are life history strategies
the series of events that take place across the life of a given organism
what is the first life history variable that comes to mind when we think about variables tied to fitness
lifespan
if an organism lives long what does it have the potential to do
reproduce a lot
do all species have same lifespan
nope; species vary greatly
what two things can evolve by natural selection
fecundity and lifespans
what kind of tradeoffs are involved
self-maintenance (survival) and growth & reproduction
is fecundity the same among living things
no, it varies
who reproduces more slowly, long-lived organisms or short-lived organisms
long-lived organisms reproduce more slowly
what is fecundity
number of offspring
what did some biologists used to think
some species produced huge numbers of eggs to compensate for high mortality to ensure the survival of the species
what do we need to know in order to understand how fecundity and lifespan
age at which reproduction begins and ends, fecundity at each age, avg survival to each possible age
what did biologists used to think was the reason why species produced huge numbers of eggs
to compensate for high mortality to ensure survival of species
what else did biologists think in terms of why animals died of old age
to make room for the new generation
what are both of these statements
group selectionist statements
why is group selection wrong
future presistence or extinction of a species cannot affect the course of natural selection acting among individuals
what is group selection
a proposed mechanism of evolution in which natural selection acts at the level of the group, instead of at the level of the individual or gene
what is a component of fitness that operates on diff life history traits
natural selection
what does natural selection perate w/
diff intensity during various parts of life cycle, bC of tradeoffs among life history functions: self maintenance (survival), growth, and reproduction
what needs to be allocated to diff life cycle events
energy and nutrients
why does selection operate w/ diff intensity during various parts of life cycle
b/c of tradeoffs among life history functions –> self-maintenance (survival), growth, and reproduction
what can the fitness benefits of one function may be
a fitness cost for another
how does fitness vary
varies among life stages and times
is variance in fitness more pronounced in some stages or the same throughout
more pronounced in some stages; must be partitioned between life stages, or between times functionally significant for reproductive success
what is strongly correlated w/ measures of fitness
body size
describe how body size is correlated w/ measures of fitness
mores strongly correlated at some life history stages than others
what else has positive correlation (but not as steep a slope)
fertility of males and offspring survivorship
what is the cost of reproduction
trade-off between reproduction and all other functions
what does brown anole experiment demonstrate
high cost of reproduction on growth and survival of these lizards
what did individuals w/ ovaries removed have
much higher survival than controls
what does allocation to reproduction do
reduced both females’ growth and survival
semelparous life history
simple case where individuals produce once than die (pacific salmon)
iteroparous life history
individuals reproduce more than once in their lives
what do we need to do for iteroparous life history
need to add up reproduction over all ages to calculate lifetime reproductive success
is it harder to determine fitness for iteroparous or semelparous organisms
iteroparous
how do we determine fitness for iteroparous organisms
a life table to predict average expected lifetime reproductive success
in species w/ separate sexes, describe life tables of males and females
different life tables
what is lifetime reproductive success related to
intrinsic rate of increase (r)
what happens if R is much diff from 1
then age at when children are born needs to be taken into account
what do we use life tables for
to determine fitness and predict avg expected lifetime reproductive success (R)
what is lifetime reproductive success (R) a sum of
all the products of probability of survival and the average fecundity across all ages in a given population of organisms
what is expected lifetime reproductive success (R) related to
intrinsic rate of increase (r)
describe R and r in a population with stable size
R=1, r = 0
what is R=1
accurate measure of fitness; if R not 1 then a correction is needed
what does natural selection favor
early reproduction
what happens if we have 2 asexual lizards with R=2
1st lives 2years, produces 2 offspring and dies. 2nd matures after one year, produces two offspring then dies (reproduces at an earlier age). after 2 years first lizard has 2 descendants and second lizard has 4. genes of second lizard are spreading more quickly in population –> natural selection favors early reproduction
why doesn’t natural selection act to prolong survival beyond the last age of reproduction
increasing survival and fecundity at earlier age has larger effect on fitness than increasing it at a later age.
senescence
organisms aging
does nat selection act to prolong survival beyond age of last reproduction
nope, unless there is post-reproductive parental care
what 2 major factors explain idea that increasing survival and fecundity at earlier ages has a larger effect on fitness than at later ages
mutation accumulation and antagonistic pleiotropy
what two factors affect senescence and lifespan
mutation accumulation and antagonistic pleiotropy
who identified mutation accumulation
peter medwar
what is mutation accumulation
mutations that compromise important biological functions will reduce fitness less the later in life they exert these effects
describe selection against these mutations
weaker
what happens as a result of selection against these mutations being weaker
persist at higher frequencies than if they affected younger reproductive individuals
what does mutation accumulation cause
greater genetic variance in reproductive success for older rather than younger age classes of individuals
who came up w/ antagonistic plieotropy
george williams
what is pleiotropy
when a single gene can have multiple phenotypic effects
what is antagonistic pleiotropy
because of allocation tradeoffs, alleles that increase reproduction early in life are likely to have pleiotropic effects on reproduction and survival later in life
why do alleles that increase reproduction early in life have pleiotropic effects on reproduction and survival later in life
because allocation of resources to reproduction comes at a cost, so alleles that increase the allocation to reproduction early in life will reduce function later in life
what does the greater the fitness impact on early reproduction cause
advantage of reproducing when young to outweigh the pleiotropic disadvantages when older
describe the relationship b/w early reproduction and longevity & later reproduction
negative relationship
what happens to reproduction with age
dwindles
what happens to production early in life
reduce allocation to maintenance later in life
what two things play a role in senescence
mutation accumulation and antagonistic pleiotropy
what happens if mutation accumulation is an important factor in senescence
genetic variance for reproductive success increase w/ age
describe the tradeoff in allocation
population that has been selected for older reproduction cannot allocate as much to reproduction at an early age
what are values of survival and fecundity in populations affected by
population growht rates
what “should” happen as mutations that increase R (lifetime reproductive success) spread thru a population
“should” cause a high rate of population growth
but what actually happens as populations grow large
pop growth limited by resources, predation, or disease
what do these factors cause population growth to be
density-dependent
what does density dependent mean
growth rate r is constrained by population size
what does reduction in population size cause
causes population size to reach a stable equilibrium called carrying capacity (K)
what are values of survival and fecundity affected by
population growth rates
what happens when populations of these flies are near or at carrying capacity
nat selection favors alelles that affect characteristics that increase K (carrying capacity)
what happens as population density approaches equilibrium
a more competitive genotype may sustain positive population growth, this more competitive genotype is likely to achieve a higher EQ density (K)
what does the densities of these two populations increasing over 70 generations imply
implies adaptation to high densities and improved conversion of food into flies
what would happen w/o evolutionary change
potential rate of increase of this species is so great that w.o evolutionary change, population would reach carrying capacity in less than 10 weeks and would remain constant in size
what does this imply
nat selection can act on the evolution of rates of increase in population density
what happens when populations are at or near carrying capacity
nat selection favors alleles that affect characters that can increase carrying capacity (K)
example of nat selection favoring alleles that affect characters that can increase carrying capacity
alleles that increase an individual’s ability to compete w/ others for limited resources
what two types of populations do we see
K-selected populations and r-selected populations
what are K-selected populations
those that are adapted to crowded conditions, lower r (growth rates), and large bodied offspring
what are r-selected populations
species where populations w/ higher r (growth rates) have higher fitness, high fecundity at young ages
describe K-selected species
well-adapted to crowded conditions near carrying capacity, stable environment, low fecundity, long life expectancy, large bodied, parental care
example of K selected species
rhino
what kind of trade-offs do k-selected species have
pleiotropic trade-offs that decrease population’s max growth rate when far below carrying capacity
what are r-selected species
well-adapted to rapid growth; unstable environment, high fecundity at young ages, short generation time, small bodied, dispersed offspring
trade-offs for r-selected species
may be poor competitors
what animals don’t fit this r or K model
long-lived, large, lots of eggs, no parental care
what specific animals don’t fit this r-K model
swordfish; common life-history strategy for fish
what plants don’t fit this model
cabbage palm, bamboo
why don’t some plants fit this model
cuz some are semelparous –> reproduce once, after many years, then die
what are species w/ high rates of adult survival more likely to have
delayed onset of reproduction
describe the guppies
guppies from high predation environment reproduce earlier in life than LP.
what happens if we move guppies from HP area to LP environment
evolve characteristics typical of LP populations
what are LP fish adapted to
high density
what does this workd emonstrate
life history differences b/w guppies from HP and LP environments are genetic
what happens when reared in a controlled env.
populations founded w/ guppies from LP env. are less sensitive to effects of density than those from HP env.; LP fish adapted to high density
what do coho salmon do
pre and post-breeding put all of their resources and E into a single big bang reproductive event
what happens to coho salmon
their physiological and physical condition deteriorates as their E goes into reproductive activities; they die as semblances of their former selves
why do they put all their E into reproduction
bc unlikely to mate more than once
when is semelparous/big bang reproduction favored
if probability of survival increases w/ body mass, and if there is an exponential relationship b/w body mass and reproductive output
describe annual reproductive effort
semelparous
what is prennial reproductive ffort
iteroparous
what is reproductive effort measured by
proportion of biomass allocated to flowers
where is reproductive effort lower
iteroparous organisms
why is reproductive effort lower in iteroparous species
b/c they put less effort into each individual reproductive effort
where is reproductive effort greater
annual/semelparous species
major advantage of iteroparity
increases the chances of successful reproduction in fluctuating environments, when reproduction or survival of offspring vary across reproductive seasons
where do we see trade-offs in
clutch size (number of eggs laid in single nesting)
what happens w/ clutch sive
parental survival is reduced by having to care for increased clutch sizes
when is overall fitness optimized
intermediate sized clutch
what is another factor that varies across species
seed size
what is size/mass of seeds correlated w/
microhabitat (in which seedlings grow)
what are larger seeds adapted for
species whose seedlings grow slowly due to dim light
what are smaller seeds adapted to light gaps
germinate quickly
how do we understand evolution of life history traits like reproductive rates and longevity
in terms of age-specific components of fitness
when do diff selective forces act
at diff times in an organism’s life cycle
how do organisms allocate resources for diff functions
allocate resources among diff functions at diff times
what can selection favor depending on env. and life history
long life and low fecundity, long life and high fecundity, short life and high fecundity
when is selection usually weakerr
advanced ages
how does senescence occur
thru mutational accumulation and antagonistic pleiotropy
