Topic 12 Flashcards
Resources are often limited so..
organisms must decide how to allocate time and energy to different activities through lifespan
Allocation decisions
will affect an individuals fitness by influencing growth, reproduction and survival.
Organisms will develop ..
allocation strategies over evolutionary time to adapt to abiotic and biotic conditions in their environment
Trade off
increased allocation of time and energy to some activities results in a decrease allocation to other activities. increase in one thing means decrease in something else
Life history trade off
growth and survival vs reproduction
Reproductive effort
proportion of averrable resources that an individual allocates to reproduction through its lifespan
Reproductive effort =
current and future productive output
Future reproductive output =
survival + fecundity in future
Lifetime reproductive success (LRS)
number of offspring produced throughout the lifespan on an individual
Life history strategy
set of choices and decisions resulting in an individuals allocation to reproductive effort through its lifespan
Life history traits
- Body size / growth
- Age at sexual maturity
- Number of reproductive events
- Number of offspring produced per event
- Offspring size
- Amount of parental care
- Senescence, programmed death
Life history strategies integrates all of these traits in a way that maximizes ;;
fitness that is molded through natural selection by environmental constraints
NO such thing as a perfect life history strategy which…
would result in unlimited production of viable offspring
Body size /growth
general pattern: fecundity increases w body size. larger individuals have more resources to devote to offspring. body size w affect aspects of survival as well
Maturity
general pattern: age maturity increases as adult lifespan or annual survival rate increase
Long lifespan
high annual survival rate. current fecundity should not jeopardize future growth, survival and reproduction. favour growth in 1st few years to increase fecundity. favour reproduction over lifespan
Short lifespan
low annual survival rate. current fecundity at the expense of adult survival (especially if semelparious) don’t favour growth and may die before breeding. favour current reproduction
Birds
low annual survival-breed younger
high annual survival-breed older
Semelparity
reproduce once and die
Iteroparity
reproduce repeatedly throughout life span
Semelparity occurs more..
for organisms living under variable environmental conditions
Semelparity is favoured when
- Adult survival is low (lifespan < 1-2 years)
- Adult survival is high –but long intervals between years with conditions suitable for high offspring survive
Mayflies (fishflies) semelparity
- Adult life stage is short-lived lasting hours to a couple days
- Do not consume food as an adult
- Sole purpose is reproduction
- After copulation the female will go off to lay her eggs and die
Agaves semelparity
inhabit climates w erratic rainfall. plants store nutrients and grow for several years (25 years) reproduce during unusually wet year cause seeds have higher changer on establishment and parents die after flowering
Salmon
fish grow rapidly at sea for years, huge effort to migrate up river to reach spawning grounds and during spawning migration females convert a larger portion of body tissue into eggs and reproduce and die shortly after spawning
Fecundity
general pattern: as more offspring are produced the survival of each offspring decreases
Fewer offspring
allocate more rescuers per offspring
More offspring
allocate less resources per offspring
Allocation to offspring
lots of ways in which parents can devote resources to offspring
Oviparous
eggs provided with yolk hatch externally
Ovoviviparous
eggs provided w yolk hatch internally
Viviparous
nutrition provided directly by mother; live birth
Resource based
different life history strategies are favoured under varying abundances of resources
If resources are abundant
low competition amount individuals, population growth is at its max. Reproduction»_space; growth/survival = r-selected
Abundant resources have large reproduction allocation but ..
invest little in survival
If resources are limited
high competition amount individuals, population growth is low. population at carrying capacity. adaptations will enhance competitive ability. Growth//survival»_space;reproduction = K-selected
Limited resources have large allocation to survival but…
little in reproduction
