7.12. (10/7) Life Histories Flashcards
How many offspring does an organism produce that live to reproduce?
on average, one
What are life histories?
Attributes of the schedule of an individual’s life
What are the different ways an organism produces one offspring that lives to reproduce?
- salmon go far to lay thousands of eggs, then dies
- elephant has one baby every several years (lots of energy to protect and care)
- loggerhead sea turtle buries dozens of eggs and leaves them to fend for themselves
- female mayfly lays 50-10k eggs as an adult for one day, then dies
what is age at maturity?
age of first reproduction
what is parity?
number of reproductive events
what is fecundity?
number of offspring produced per reproductive episode
What are life history traits?
- fecundity
- parity
- age of maturity
- size of offspring
- life span and aging
How does natural selection affect life histories?
- reproductive success depends on life history traits which influence evolutionary fitness
- they vary with respect to environmental factors/ habitats
what is the principle of allocation?
organisms have finite amounts of energy that they have to choose how to use because it affects each area differently
* reductions and trade-offs
* weigh potential costs of varied production
How does resource allocation affect fitness?
- increased seed production may lead to more offspring
- seed size is reduced in order to make more which could affect their survival as seedlings
- more energy is used to produced seeds rather than making roots for an adult tree which affects survival
- so much energy spent now can affect future seed production
Who has the largest seed? smallest?
- double coconut: few seeds of ~50 pounds
- spotted coralroot orchid: billions of seeds of ~0.000002 g
what kind of relationship exists between seed size and seed number?
there is a negative relationship between seed size and seed quantity where the smaller number of seeds produced yields a bigger size and the smaller the seed the more are made
When is it advantageous to produce a large number of small seeds?
areas with high disturbance
When is it advantageous to produce a small number of large seeds?
in stable environments with lots of plant biomass and competition because each is more capable of surviving environmental hazards
What causes variations in maturity age?
When the chances of an organism surviving to adulthood is low they use a lot of energy to reproduce at a younger age, but if they do survive, they wait until they have enough energy to reproduce (they also invest less resources for reproduction)
What is the trend for species that have high mortality/short lives?
they have a higher fecundity
what are semelparous organisms?
organisms that only reproduce once and die
* big bang
What are iteroparous organisms?
reproduce multiple times in their life
How are life histories classified?
they are based of population characteristics of fecundity, survival, relative offspring size, and age of reproductive maturity
what is mx?
fecundity
what is Ix?
survival
By who and when were r and K selection defined
By MacArthur and Wilson in the 1960s
what are r selection species?
Favors high potential population growth rate in species that colonize new or disturbed habitats
what are K selection species?
Favors those that are good at attaining resources and maintain their populations at carrying capacity
What is distinct about the r and K selection definition?
This definition exists at the ends of a continuum and relates population dynamics to their environment
what are characteristics of a r selection species?
- high population increases
- bad competitor
- rapid development of life stages
- early reproduction with one event (semelparity)
- small body size with many small offspring
what are characteristics of a K selection species?
- competitive
- low population increases
- slow development
- late reproduction many times (iteroparity)
- large body size
What are two species that represent r and K selection well?
mice as an r selection species and elephants as K (for mammals)
What is the Grime’s Scheme?
states that intensity of disturbance and stress are the two important variables that affect the life history characteristics of plants
What does intensity of disturbance mean?
how intense and limiting the periodic process of biomass removal was for plants
what does intensity of stress mean?
how much external pressure and constraint limits rate of growth
* examples include nutrient poor, extreme weather
what are the three kinds of habitats according to Grime’s Scheme?
- low disturbance-low stress
- low disturbance-high stress
- high disturbance-low stress
(form a triangle)
Who are the competitors?
- they are at the top of the grime’s scheme triangle with low disturbance and low stress
- lots of plants grow here so they compete for available resources
Who are the stress tolerators?
- they are on the left side of grime’s scheme triangle with low disturbance and high stress
- high background stress like deserts
who are the ruderals?
- they are on the right side of grime’s scheme triangle with high disturbance and low stress
- they are good at occupying habitats that are disturbed (lawns)
what are the characteristics of stress tolerators?
- limited resources
- allocate/conserve resources to defense, maintenance, adaption
- grow slowly
- vegetative/asexual reproduction
- variable life form
- leathery, needles leaf form
- evergreen leaves
- late reproductive maturity
- slow potential growth rate
- long longevity
- low proportion of energy used to make seeds
- vegetative reproduction is often important
what are the characteristics of ruderals?
- colonize disturbed habitats
- rapid growth
- invest a lot of resources/energy to reproduction
- mature quickly
- produce many seeds (easily dispersed)
- r strategists
- herb life form
- variable leaf form
- herbaceous life form
- variable leaf form
- deciduous leaves
- early reproductive maturity
- rapid potential growth rate
- short longevity
- high energy invested in seed production
- vegetative reproduction is rarely important
what are the characteristics of competitors?
- grow rapidly large
- allocate energy toward early growth
- good at obtaining resources
- long lifespan
- variable life form
- variable leaf form
- variable life form/leaf form
- deciduous leaves
- late reproductive maturity
- fast or slow potential growth rate
- moderate to long longevity
- low energy for seeds
- vegetative reproduction is sometimes important
what is phenology?
timing of biological events that are playing out over a year
- when a particular species leaf out, set flower, set seed
who is Aldo Leopold? What was discovered because of him?
- In the 1930s and 40s, he kept a notebook about the timing of flowering and spring bird events
- advancement of spring events
Why does changing phenology matter?
if all species started their activities earlier there would be no problem, but since only some species are shifting, it disrupts important ecological interactions for dependent species
