L19 - Life histories

Question 1

Why is age distribution important in understanding populations?

Answer 1

It reveals the population’s make-up and is sensitive to biotic and abiotic ecological influences

Question 2

What do life tables describe, and what can be extracted from them?

Answer 2

Life tables describe population age structure and provide parameters like survivorship and age-specific mortality.

Question 3

How is survivorship calculated?

Answer 3

Survivorship = number surviving this year / total number born

Question 4

How is age-specific mortality calculated?

Answer 4

Age-specific mortality = number dying / number surviving

Question 5

What can mortality data reveal about a population?

Answer 5

It can indicate factors like predation that affect population dynamics

Question 6

What characterizes Type I survivorship curves?

Answer 6

Organisms with relatively few offspring that invest significant time and effort in them.

Question 7

What characterizes Type III survivorship curves?

Answer 7

Organisms with many offspring but minimal time or effort invested in their care

Question 8

How do environmental factors influence survivorship curves?

Answer 8

Factors like predation or herbivory can alter the shape of survivorship curves.

Question 9

What does an organism’s life history describe?

Answer 9

The timing of key activities such as age at maturity, inter-birth intervals, generation time, and litter size

Question 10

What is the simple population growth model for seasonal breeders?

Answer 10

Nt +1 = R0Nt, where R0 is the net reproductive rate

Question 11

How does the continuous breeders’ growth model differ?

Answer 11

It uses 𝑑𝑁/𝑑𝑡=𝑟𝑁
, which generates exponential growth: Nt = N0ert

Question 12

Why are simple growth models limited?

Answer 12

They assume unlimited resources and are only applicable in special cases, like new species in empty niches.

Question 13

What does the logistic growth model account for?

Answer 13

Resource limitations, resulting in population stabilization near the carrying capacity:

dN/dt=rN(1−N/K)

Question 14

What does the time-lag variation of the logistic model address?

Answer 14

Delayed density-dependent effects, such as disease or predation, modeled as
dN/dt=rN(1−(N
t−τ/K)).

Question 15

What are r-selected species, and what is their growth strategy?

Answer 15

Species with high per capita growth rates, focusing on rapid reproduction

Question 16

What are K-selected species, and what is their growth strategy?

Answer 16

Species with stable populations close to carrying capacity, emphasizing long-term survival

Question 17

Why is age estimation important for savannah elephants?

Answer 17

It helps understand population dynamics, including reproductive and survival rates

Question 18

How is age estimated in elephants using shoulder height?

Answer 18

Shoulder height is used with Von Bertalanffy growth functions, accurate up to 15 years for females and 36 years for males.

Question 19

What does the Von Bertalanffy growth function represent?

Answer 19

Height at age
𝑖: ℎ𝑖 = ℎ𝑏 + (𝐻∞ − ℎ𝑏) (1−𝑒^−𝑘𝑡)
where
𝐻∞ is maximum adult height.

Question 20

How does Darwin’s theory relate to population growth models?

Answer 20

Darwin’s theory requires animals to reproduce rapidly, yet populations remain constant due to limiting factors, modeled mathematically.

Question 21

What are the two opposing life history strategies described by growth models?

Answer 21

• r-selection: High growth rates, opportunistic strategies.
• K-selection: Stable populations, competitive strategies near carrying capacity.