life history evolution Flashcards
what is meant by life history
refers to the major dramatic events of any organisms life such as development, age of sexual matrity, first reproduction, number of offspring and level of parental investment
why is studying life history important in studying demography of species
has a major influence on how populations of animals work (demography)
= Species with longer generation times experience less demographic stochasticity (random fluctuations in birth, reproduction and death rates)
= this has applications in conservation as understanding life history demography means you can see if there are any unusal patterns = for example spp who have short generation times but are not declining dont need conservation but if you see a species with long generation times decline it is something to worry about
what can understanding life history be applied to
conservation
biological invasions
population management
speciation and extinction
how can understanding life histories be applied to biological invasions
the start/edge of the invasion front has less competion from individuals of the same species meaning individual reproduce alot faster and more contirbution ot the next invasion generation
= by understanding life histories of the invading species such as reproduction timings etc we can offer solutions to tackle the invasion and how to target organisms with certain life histories for contorl e.g. cane toad in NE Australia
give an example showing how tetrapod life histories are so diverse
amphibian clutch sizes vary dramatically from species to species = differences in reproduction
Tree frog = 1-3 eggs vs mountain bull frog =10-20,000 eggs in a clutch
what are the three components of fitness
survival
growth
reproduction
how do the three components of fitness help explain why tetrapods have evolved such diverse life history
Resources (time and energy) are limited so investing resources in one aspect of life history such as growth means that they have to sacrifice another aspect of life history such as reproduction = trade offs which differ between species e.g.
= trade off between growth (age at maturity) and reproduction (clutch size) - as age of maturity increases clutch size decreases - charnov 1993
what is meant by a Darwinian demon
an organism which exists as a consequence of a thought experiment which conists of a species with infinite fitness e.g. starts reproduing as soon as born, unlimited resoyrces
= this spp would take over but does not exist as all resources are limited
what is the difference between the ecological theory of life history evolution involving r and k select species
K strategists have traits that allow them to compete in environments close to carrying capacity.
e.g. long lifespan, infrequent reproduction, small clutches, late maturity, parental care.
r strategists have opposite traits that allow populations to grow quickly in environments where fitness is not density-dependent.
e.g. short lifespan, frequent reproduction, large clutches, early maturity, no parental care.
how can we simplify the diversity of life history stratergies (r/k select spp)
using a fast-slow continuum which allows covariation between a suite of life history traits such as high mortality and slow maturation which are seperated when explaining it in terms of r/k select
give some examples of features which are considered slow or fast life history strategies
slow= low mortality, low fecundity, slow maturation and prioritse future repro
fast = high mortality, high fecundity, rapid maturation, prioritse current repro
does a fast-slow continuum exist in tetrapods
yes but there are important clade-specific patterns
= there is lots of variation in life history at the species level which cant be described as fast-slow variation
= look at powerpoint as lots of research supporting and not supporitng this
what are the major shifts in life histories which have allowed new life history stratergies to be explored
viviparity in repriles
evolution of endothermy
evolution of flight
the amniotic egg
how has the emergence of the amniotic egg changed life histories
Amniotic eggs contain unique membranes which allow them to be much larger and maintain higher rates of respiration than those of amphibians, which are limited by the rate of diffusion of oxygen through the egg (Seymour and Bradford 1995; Thompson and Russell 1998). Because offspring can spend longer in the egg, amniotes supply their eggs with substantial yolks that allow offspring to develop to a greater degree before hatching (Romer 1957). These adaptations allow amniotes to emerge at a higher stage of development than amphibian offspring do (Romer 1957) and may help amniotes reach reproductive maturity more quickly—and spend a greater proportion of their total lifespan reproducing—compared to amphibians. These impacts of the amniote egg on the size of the offspring and the extra investment parents provide their offspring in yolk may also explain why amniotes exhibit higher levels of lifetime reproductive investment and relative offspring size than amphibians
what new strategy was enabled as a result of the amniotic egg
allowed the allocation of more resources to producing fewer high quality offspring
