Life history evolution (More in depth version) Flashcards
Define life histories:
Life histories are the unique patterns of growth, reproduction & survival that an organism undergoes in its lifetime
LHs are influenced by various factors (genetics, environment & natural selection)
What are the 3 main aspects of life histories?
Growth –> how an organism grows & develops from birth to adulthood
Reproduction –> when & how an organism reproduces, incl no & size of offspring
Survival –> how an organism copes w challenges & threats in its environment & how long it lives
Life histories are ….
Diverse
2 diff species of birds can have entirely different strategies e.g. blue tit lives to 2-3 y/o & lay clutch sizes of 10-12 –> hummingbirds, 10 y/o, lay 1-2 eggs
(More of a context card)
What is the fast slow continuum also known as?
r & K selection
(Meg if you can still add in pics, could you pls add the one from his slides xx)
What is the fast-slow continuum (r/K selection theory)?
Ecological concept that explains how species optimise their life history strategies, based on environmental conditions
Species are categorised into a spectrum of reproductive strategies from: Fast (r) to Slow (K)
Give some examples of r-selected species (fast):
Mice, insects, bacteria & weeds
What are the key components of an r-selected species?
(5)
- Thrive in unstable or unpredictable environments
- Prioritise rapid reproduction & high reproductive output over individual survival
- Tend to produce many offspring w low parental investment
- Offspring mature quickly w short lifespans
- Population below carrying capacity
What are the characteristics of an r-selected species
(3)
Small body size
Short generation times
High dispersal ability
Give some examples of K-selected species (slow):
Elephants, walrus, humans & oak trees
What are the key components of a K-selected species?
(5)
- Thrive in stable or predictable environments (where competition for resources is intense)
- Prioritise quality over quantity - investing heavily in fewer offspring to ensure survival
- Often have long lifespans & offspring mature slowly
- Populations closer to environment’s carrying capacity
What are the characteristics of a K-selected species?
(3)
- Large body size
- Longer generation times
- Strong competitive abilities
How does the fast-slow continuum relate to life histories?
Life history theory builds on fast-slow continuum by exploring how organisms balance trade-offs (e.g. reproduction vs survival) to maximise fitness
What is an example of a species w mixed traits along the continuum?
Sea turtles - many offspring but long adult lifespans
Define reproductive value:
The expected number of future offspring an individual expects to have over rest of life
It measures the contribution an individual (based on its age or life stage) makes to the growth or maintenance of the population
What is reproductive value dependent on?
(What are the key factors influencing reproductive value)
The fecundity & survival at different ages
Population is growth/decline
Age class contribution
When born in a stable population what is the expected offspring?
1
Insert reproductive value graph here
Why does the graph look like this?
RV - increases at first, bc v young individuals may not survive long enough to breed –> RV declines after age at maturity bc survival is less than 1
It is better to reproduce early in a growing pop bc then offspring can start reproducing too
What are the key factors that influence reproductive value?
(3)
1 - Fecundity & survival
2 - Population growth or decline
3 - Age class contribution
How does fecundity & survival influence reproductive value?
- RV depends on how likely an individual is to survive to future ages & reproductive potential (fecundity) at those ages
- e.g. longer individuals have lower RV bc they may not survive to maturity –> adults typically have higher RVs
How does population growth/decline influence reproductive value?
- RV depends on whether the pop is: growing, stable or declining
- In a growing/stable pop - offspring produced earlier in life contribute more to pop growth than those produced later
- Bc earlier offspring have more time to reproduce themselves
How does age class contribution influence reproductive value?
- Diff ages classes (juv, adult, elderly) contribute differently to the pop growth
Young adults at reproductive prime often have highest RV
Reproductive schedules
Consider two genotypes, that reproduce clonally only twice in their life:
a has one offspring in one year, and another in the next
b has none in first year and two in second
WHY does a have higher fitness than B?
Bc fitness in this context is a measure of reproductive success relative to others –> a reproduces earlier, this means:
- It contributes to population growth sooner (grandchildren b4 b has had children)
- Minimises risk of zero reproductive success due to mortality in the 2nd year
What are the 3 characteristics of the Darwinian Demon?
- Begins reproducing at birth
- Produces infinite offspring
- Never dies (reproduces indefinitely)
What is the “Darwinian demon”?
A hypothetical “perfect” organism that faces no trade-offs or limitations impose by natural selection
It does not exist due to constraints - bacteria is probs the closest we come to this
What are the constraints on the “Darwinian demon”?
1 - Energy limitations –> energy is finite & must be balanced between growth, reproduction & survival
2 - Environmental constraints –> Resources such as food, water & space are limited (also predation & disease are risks) - principle of allocation?
3 - Biological trade offs –> traits beneficial for one function but may affect another negatively (e.g. early reproduction, reduced lifespan)
4 - Evolutionary limitations –> evolution shapes organisms incremetally to be “good enough” for their environment, not perfect
How does the “Darwinian demon” relate to life histories?
Shows that organisms must allocate limited resources to growth, reproduction & survival - emphasising trade-offs
What is the principle of allocation?
It starts that organisms have a finite amount of energy & resources , which they must allocate among growth, reproduction & survival
Bc resources are limited, inc investment in one area often red. resources available for other areas = trade-offs (these trade off shape life histories)
Need to come back to principle of allocation flow chart
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How do guppies & whale sharks differ from cod in reproduction?
Guppies & whale sharks give birth to live young, while cod lay millions of eggs
