Body Size

Question 1

Why is body size one of the most frequently measured traits

Answer 1

• Considered the most informative trait to characterise an organism, as most other traits are strongly correlated with body size
• It is relatively easy to measure for current and extinct organisms
• Most common thing measured

Question 2

What is Bergmann’s rule

Answer 2

In a clade with broad geographic distribution, larger bodied species tend to be found in colder climates, and smaller-bodied species in warmer climates
To do with interspecific competition

Question 3

What is interspecific competition

Answer 3

between different species

Question 4

What is intraspecific competition

Answer 4

Between individuals of the same species

Question 5

Bergmann’s Rule is most often applied to which type of organism

Answer 5

• Most often applied to endotherm
• Larger bodies may be less advantageous for ectotherms in colder climates: needs longer basking times to achieve metabolically optimal temperature

Question 6

What is the suggested reasons behind Bergmann’s rule

Answer 6

• Large species = lower SA:Vol ratios = advantage over smaller relatives in conserving body heat in colder climates
• Larger animals can withstand harsher climatic conditions with larger reserves
• Intraspecific competition favours large body size where diversity and competitive pressure are low at higher latitudes
• Large organisms have greater capacity for dispersal which enables survival in low-productivity cold environments

Question 7

How can Bergmann’s rule be applied to plant height

Answer 7

• Mean max height of species to be greatest at tropics and steadily decline towards the poles
• Species with a wide range of height stategies were present in cold, dry, low productivity systems
• Hence taller plants in the equatorial zones - opposite Bergmann

Question 8

Because Bergmann’s rule is largely a response to the harshness of the climate, how would you expect body size to vary with elevation

Answer 8

• Increases in body size is expected along elevational gradients
• HOWEVER: ambiguous or weak findings across taxa - some conform to BR, others show the opposite trend, or do not change along an elevational gradient

Question 9

What is the ‘deep-water gigantism’ phenomenon

Answer 9

A trend towards increased body size with increasing depth (correlated with increasingly lower temps)
Most clearly seen in crustaceans and been attributed to decreased predation and temperature

Question 10

What is The Island Rule (aka Foster’s rule)

Answer 10

Smaller species tend to increase in size on islands and large species tend to decrease in size
(Steep relationship between ratio of giants to dwarf)

Question 11

What is Secondary insular woodiness

Answer 11

The evolutionary transition from herbaceous towards woody on islands

Question 12

What are the proposed drivers of Secondary insular woodiness

Answer 12

• Competition for sunlight - taller plants with stronger woody stems
• Drought - favours woodiness to safeguard root-to-shoot water transport
• Fire - bark can protect from fatal damage
• Lack of large native herbivores

Question 13

Why are Woody plant species (+ nitrogen fixers) overrepresented on volcanic islands

Answer 13

• Climate conditions and fire are supposed drivers of woodiness
• Fire regimes are supposed to support nitrogen fixers by the mineralisation of nutrients (but there is no nitrogen)
• There is also a loss of herbivatous plants due to ash with sulphur causing damage - leaving only the woody ones to survive
• Woody nitrogen fixers can benefits from these impacts