Life History Flashcards
What is life maturity?
juvenile development, age of sexual maturity, first reproduction, number of offspring and level of parental investment, senescence and death
demographic variance?
variability in population growth rate
generation time?
average time between two successive generations (close to average age at birth) - humans = 22-33 years
species w/ longer generation times experience less demographic stochasticity (random fluctuations in birth, reproduction and death rates)
What does studying life history have major ramifications for?
- conservation
- biological invasions
- population management
- speciation & extinction
Human life history diversity
- human life histories vary in many ways
- different traits are positively and negatively correlated with each other
why have tetrapods evolved such diverse life history?
resources (time, energy) are limited
resources needed for: survival, growth, reproduction
investing resources in one aspect of life history (survival, growth, reproduction) requires sacrifices in another aspect of life history
r/K selection - MacArthur & Wilson 1967
Ecological theory of life history evolution
What are r and K strategists?
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 - 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
Fast-Slow continuum
Slow - fast
Low mortality - high mortality
low fecundity - high fecundity
slow maturation - rapid maturation
prioritise future reproduction - prioritise current reproduction
covariation between a suite of life history traits
Does a fast-slow continuum exist in tetrapods?
yes, but there are important clade-specific patterns
lots of variation in life history at the species level cannot be described as fast-slow variation
What determines where a species is placed on a fast-slow dimension is largely unknown
- age-specific mortality (Charnov, 1993)
- environmental variability (Rose & Charlesworth, 1980)
Amniotic egg
- features
features:
- amnion; allantois; chorion; yolk sac; yolk (nutrients); albumen; shell; amniotic cavity w/ amniotic fluid; embryo
Benefit of unique membrane and yolks in amniotic eggs
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 quickly - and spend greater proportion of total lifespan reproducing - compared to amphibians
impacts of amniote egg on size of offspring and extra investment parents provide their offspring in yolk may explain why amniotes exhibit higher levels of lifetime reproductive investment and relative offspring size than amphibians
Amphibian egg features
- yolk sac; embryo/tadpole; jelly
Amniotic egg as enabling a new strategy
allocate more resources to producing fewer high-quality offspring
Endothermy
- enables more metabolic power and potential for production
- is energetically costly to maintain
- enables extensive incubation of embryos
- limits the minimum size of animals
- facilitates adaptation to a wide range of environments
