1 - Energy, Reproduction and Death

Question 1

What is life history in biology

Answer 1

Life history refers to an organism’s age-specific schedule of reproduction and mortality

It captures how organisms allocate resources to growth, reproduction, and survival over their lifetime

Question 2

What does “survival” mean in life history terms

Answer 2

Survival is the proportion of a cohort still alive at each age

It begins at 1 (all individuals alive) and only ever goes down to 0

Question 3

What is mortality

Answer 3

Mortality is the rate of death. Unlike survival, it can go up or down at different life stages

Question 4

What is fertility in this contex

Answer 4

Fertility is the rate at which individuals produce offspring, which can increase or decrease with age

Question 5

What kinds of traits are considered life history traits

Answer 5

Traits like reproductive rate, lifespan, age at first reproduction, gestation time, weaning age, and rate of ageing

Question 6

What is the “fast-slow continuum” in life history strategies

Answer 6

Fast-living species: Short lifespan, early maturity, high reproduction (e.g. mice)

Slow-living species: Long lifespan, delayed reproduction, fewer offspring (e.g. elephants)

Some species don’t fit this model perfectly

Question 7

Can similar-sized or related species have different life histories

Answer 7

Yes. Even closely related or similar-sized species can show different life history strategies due to ecological pressures and evolutionary history

Question 8

What’s the fundamental problem in life history theory

Answer 8

The theory predicts that high fitness = high reproduction + long life, but in reality, organisms face trade-offs that prevent both from being maximised

Question 9

What are the main trade-offs in life history (4)

Answer 9

Reproduction vs. survival

Offspring size vs. number

Immunity vs. reproduction

Early vs. late maturity

Question 10

What is the Y-model of resource allocation

Answer 10

A model showing that resources used for one function (e.g. reproduction) cannot be used for another (e.g. survival), explaining trade-offs

Question 11

Do all individuals face the same trade-offs

Answer 11

No. Some individuals acquire more resources than others, so in nature, positive correlations between traits (e.g. survival and reproduction) can be seen

Question 12

What is Lack’s Optimal Clutch Size Theory

Answer 12

Proposed by David Lack (1947), it suggests that natural selection favours the clutch size that maximises the number of surviving offspring, not necessarily the largest clutch

Question 13

What evidence supports Lack’s optimal clutch theory

Answer 13

Experimental evidence: Great tits (Parus major) show optimal clutch sizes under manipulated conditions

Observational data: Eurasian lynx show litter sizes that balance survival and cost

Question 14

What is semelparity

Answer 14

A reproductive strategy where an organism reproduces once in its lifetime, then dies

Examples: Pacific salmon, octopus, some annual plants

Question 15

What is iteroparity

Answer 15

A reproductive strategy where an organism reproduces multiple times throughout its life

Examples: Humans, birds, most mammals

Question 16

When is semelparity favoured

Answer 16

When adult survival is low, so one big reproductive event maximises fitness

Question 17

When is iteroparity favoured

Answer 17

When adult survival is high, allowing for multiple reproductive events over time

Question 18

Why does natural selection often favour early reproduction

Answer 18

It increases fitness by reducing generation time and increasing total reproductive output

Question 19

How does reproductive timing differ in R- vs. K-selected species

Answer 19

R-selected species (unstable environments): early reproduction, many offspring, low investment

K-selected species (stable environments): delayed reproduction, fewer offspring, high investment

Question 20

Are there exceptions to these general patterns in reproductive timing

Answer 20

Yes – e.g. small semelparous marsupials like the brown antechinus:

Males die after mating
Young are altricial (helpless)
Females care once, then most die before breeding again

Question 21

What is a precocial species

Answer 21

Offspring are born relatively developed, needing little parental care

Examples: Ducks, deer, many reptiles

Question 22

What is an altricial species

Answer 22

Offspring are born helpless, requiring lots of parental care

Examples: Songbirds, rodents, primates.

Question 23

Can closely related species differ in altricial/precocial strategies

Answer 23

Yes – e.g. rabbits (altricial) vs. hares (precocial)

Question 24

What are the trade-offs of being precocial or altricial

Answer 24

Precocial: More energy invested during pregnancy, less after birth

Altricial: Less pre-birth investment, more post-birth care

Question 25

In which species is menopause observed

Answer 25

Rare in mammals – seen in humans, orcas, and a few others

Question 26

Why is menopause an evolutionary puzzle

Answer 26

Natural selection usually favours lifetime reproduction, but menopause stops reproduction while the individual continues living

Question 27

What is the Mother Hypothesis

Answer 27

Menopause avoids reproductive risks at older ages, ensuring survival of existing children

Question 28

Grandmother hypothesis

Answer 28

Post-reproductive females increase fitness by helping raise grandchildren, though they are less related (r = 0.25 vs. 0.5 for children)

Question 29

What is the Reproductive Conflict Hypothesis

Answer 29

Menopause reduces reproductive competition between older and younger females, especially between mothers and daughters

Question 30

Are these menopause hypotheses mutually exclusive

Answer 30

No – there is empirical support for all three, and menopause likely evolved through a combination of relatedness, social structure, and conflict reduction

Question 31

What’s a wild example of extreme post-reproductive strategy

Answer 31

The menopausal aphid, where older individuals sacrifice themselves to protect the colony and enhance survival of their descendants

Question 32

What are the benefits of altricial young

Answer 32

Lower resource investment in eggs or foetuses Potential for larger adult brain size due to postnatal brain development

Question 33

What are the costs of altricial young

Answer 33

Require extensive parental care after birth or hatching Prolonged dependence limits mobility and exposes offspring to risk

Question 34

What are the benefits of precocial young

Answer 34

High level of independence soon after birth or hatching Offspring may survive with little or no parental care

Question 35

What are the costs of precocial young

Answer 35

Eggs or foetuses demand more resources from the mother before birth Less opportunity for postnatal brain development, limiting brain size