bio lec 6
what is the need for age srtuctures pop growth models
the previous models assumed that all women have the same birth and death rate however this is not true the birth and death rate is also linked with age and as the age of indivudual increases the fecundity decreases.
what is the diff bw this model and the ones we did before
this takes into accoiund age and so the pop growth model is based on a specific age class not a generalised time step like the previous ones
why are life history strategies important
they are important as they are different in different species and this determines the survivorship and fecundity rates in diff species. the general like history strategy is that individuals grow and at this time of resource accumilation they are not reproducing, at birth the survivorship is maximum 1 as all indivuduals are just newly alive then dec over time . as individuals reproduce they have to sacrifice with tradeoffs
why do age class models ignore males
only females reproduce and the males have many sperms and so they are not a limiting factor and cannot correctly determine pop growth. this can work as assuming men : female is 1:1 and so find pop by females and multiply by 2
what are age classes determined by
total life span of an individual such as for humans who usually live up to 80 years each age gap or age class could be 5 years each
what is lx and what are the graphs of lx
lx is the survivorship rate if it was plotted againt x it would usually give curved line but log lx against x for the survivorship type 2 curve gives a straigt line with neg gradient. survivorship type 3 is when there is alot of early death and type 1 is when there are fewer deaths at first. they all reach the same point at the end
bx or mx
it is the fecundity rate which is how many offspring an indivual is able to produce, unlike lx these are not prob so can be greater than one
what is R0
the net reproductive rate = the average number of offsprings that an individual will produce in her lifespan
R0= sum of (lx*bx)
similarities between lamda ans R0
both are density independant and both are constants
they both can be seen wahter pop grows is same or dec by being greater than 1 less than one or equal to one
what is the generation time
the age at which an individual produces the av munber of offsprong
T = sum of (x lx bx)/R0
what is semelparity and what is interoparity
semelparity are when indivuduals only produce once in their lifetime but when they do they procduce a high quantity of seeds with large fruits due to alot of resource accumulation usually in plants. iteroparity is when an individual reproduces many times in his lifetime. indivudals who live more than two growth seasons are called perrinials this is usual for iteroparous individuals but not for semelparous
what favours for semelparity
large number of offsprings so more chances of survival with predator satiation and synchrony which is when many semelparous plants reproduce togehter anf this also causes preadator satiation, reducaes intraspecific cometition and inc seed dispersal and chaces of seeds surviving
what is vx
reproductive value