Life history evolution (More in depth version)

Question 1

Define life histories:

Answer 1

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)

Question 2

What are the 3 main aspects of life histories?

Answer 2

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

Question 3

Life histories are ….

Answer 3

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)

Question 4

What is the fast slow continuum also known as?

Answer 4

r & K selection

(Meg if you can still add in pics, could you pls add the one from his slides xx)

Question 5

What is the fast-slow continuum (r/K selection theory)?

Answer 5

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)

Question 6

Give some examples of r-selected species (fast):

Answer 6

Mice, insects, bacteria & weeds

Question 7

What are the key components of an r-selected species?

(5)

Answer 7

• 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

Question 8

What are the characteristics of an r-selected species

(3)

Answer 8

Small body size

Short generation times

High dispersal ability

Question 9

Give some examples of K-selected species (slow):

Answer 9

Elephants, walrus, humans & oak trees

Question 10

What are the key components of a K-selected species?

(5)

Answer 10

• 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

Question 11

What are the characteristics of a K-selected species?

(3)

Answer 11

• Large body size
• Longer generation times
• Strong competitive abilities

Question 12

How does the fast-slow continuum relate to life histories?

Answer 12

Life history theory builds on fast-slow continuum by exploring how organisms balance trade-offs (e.g. reproduction vs survival) to maximise fitness

Question 13

What is an example of a species w mixed traits along the continuum?

Answer 13

Sea turtles - many offspring but long adult lifespans

Question 14

Define reproductive value:

Answer 14

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

Question 15

What is reproductive value dependent on?

(What are the key factors influencing reproductive value)

Answer 15

The fecundity & survival at different ages

Population is growth/decline

Age class contribution

Question 16

When born in a stable population what is the expected offspring?

Answer 16

1

Question 17

Insert reproductive value graph here

Why does the graph look like this?

Answer 17

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

Question 18

What are the key factors that influence reproductive value?

(3)

Answer 18

1 - Fecundity & survival

2 - Population growth or decline

3 - Age class contribution

Question 19

How does fecundity & survival influence reproductive value?

Answer 19

• 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

Question 20

How does population growth/decline influence reproductive value?

Answer 20

• 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

Question 21

How does age class contribution influence reproductive value?

Answer 21

• Diff ages classes (juv, adult, elderly) contribute differently to the pop growth

Young adults at reproductive prime often have highest RV

Question 22

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?

Answer 22

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

Question 23

What are the 3 characteristics of the Darwinian Demon?

Answer 23

• Begins reproducing at birth
• Produces infinite offspring
• Never dies (reproduces indefinitely)

Question 24

What is the “Darwinian demon”?

Answer 24

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

Question 25

What are the constraints on the “Darwinian demon”?

Answer 25

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

Question 26

How does the “Darwinian demon” relate to life histories?

Answer 26

Shows that organisms must allocate limited resources to growth, reproduction & survival - emphasising trade-offs

Question 27

What is the principle of allocation?

Answer 27

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)

Question 28

Need to come back to principle of allocation flow chart

Answer 28

hhhhh

Question 29

How do guppies & whale sharks differ from cod in reproduction?

Answer 29

Guppies & whale sharks give birth to live young, while cod lay millions of eggs