The Comparative Method

Question 1

Describe John Crook’s 1964 initial observations

Answer 1

• Southern masked weavers and Village weavers founded polygamous societies that nested in colonies
• Red-headed weaver existed in monogamous, highly dispersed territories with cryptic nests

Question 2

Describe John Crook’s 1954 subsequent observations with regards to mating system

Answer 2

• more likely to be monogamous if the food source was found in insects
• more likely to be polygamous if the source was seeds
• 22:1 monogamous to polygamous societies feeding on insects
• 2:26 feeding on seeds

Question 3

Describe John Crook’s 1954 subsequent observations with regards to social system

Answer 3

• insects led to more solitary social systems
  -seeds led to more grouped and colonial ones (21:2) solitary to grouped/colonial with insects as a food source; 0:33 for seeds)

Question 4

Describe John Crook’s 1964 conclusions

Answer 4

• if a bird species ate insects, it was more likely to be monogamous and solitary
• if it fed on seeds, it was more likely to be polygamous and grouped or colonial

Question 5

Describe John Crook’s 1964 explanation for his conclusions

Answer 5

• since insects are a sparse but evenly distributed food source, breeding was more efficient in separate places with solitary monogamous pairs
• since seeds were rare temporally but hugely abundant, group foraging, and a colonial social system was more efficient
• colonial lifestyle was more likely to induce male competition, and therefore sexual polygamy would be introduced into the system

Question 6

Describe the faults with John Crook’s 1964 experimental method

Answer 6

• lack of an a priori alternative or competing hypothesis
• no ecological quantification of his variables by testing his data alongside another

Question 7

Describe primate classification

Answer 7

• in terms of their sexual dimorphism
• calculated as male weight divided by female weight

Question 8

What is the sexual dimorphism ratio of the Indri

Answer 8

1.0

Question 9

What is the sexual dimorphism ratio of the Macaques

Answer 9

1.5

Question 10

What is the sexual dimorphism ratio of the Papio Baboon

Answer 10

2.0

Question 11

Describe Clutton-Brock and Harvey’s 1977 experiment

Answer 11

• two alternative hypotheses to explain the variation in sexual dimorphism observed between primate species
  i) caused by niche differentiation in order to reduce competition
  ii) selected for sexually
• quantify ecological variables against the sex ratio in a breeding group, measured as the number of females per male

Question 12

What was the problem with Clutton-Brock and Harvey’s 1977 experiment?

Answer 12

statistical analytical assumption of species independence

Question 13

Describe Grassland Weaver populations

Answer 13

87.5% of the organisms are found in the Euplectes genus

Question 14

Describe non-independent species

Answer 14

• closely related species would exhibit commonly descended traits and features and corresponding lifestyles
• enhanced similarity relative to independently evolved organisms

Question 15

Why can’t non-independent datapoints be used in statistical analysis

Answer 15

• pseudoreplication
• significance boundaries more easy to reach, fallibly

Question 16

What is pseudoreplication

Answer 16

experiments in which replicate number, and therefore sample size is inflated

Question 17

Describe the comparative method

Answer 17

• takes independent contrasts between sister taxa
• uses this difference between species as the datapoint
• accounts for the lack of independence among sister taxa by comparing between them
• beneficial in its removal of unknown variation

Question 18

What does the comparative method necessitate?

Answer 18

• artificial reconstruction of ancestors in order for accurate comparison
• a perfect pylogeny is beneficial

Question 19

Comparative method NB

Answer 19

Calculation of the independent contrast must be performed in the same direction across the study, to make sure opposite results are not obtained.

Question 20

Describe the reproductive behaviours of parasitic fig wasps

Answer 20

• highly specific: each fig species has its own partner wasp
• pollen-laden female wasp enters an unripened fig
• pollinates the flowers
• lays her eggs
• is trapped and dies.
• flowers upon which her larvae have been deposited form galls
• flowers which have not produce seeds
• galls produce both male and female wasps
• after a month of development, the wingless males fertilise the females and ultimately never leave the fig
• the females leave the galls, sometimes collecting pollen from the mature male flowers within the fig and exiting via a tunnel
• begin search for new fruits in which to lay their own eggs

Question 21

Describe male parasitic fig wasp morphology

Answer 21

• tiny antenna and eyes
• tradeoff
• more energy is inputted into their cleft chin mating organ

Question 22

Describe what happens if parasitic female fig wasps enter a fig without having first collected pollen

Answer 22

• fig will not grow seeds
• may be aborted by the tree
• any offspring lain in the fig will die when it drops

Question 23

Describe comparative analysis of conflict of pollinating and non-pollinating wasps

Answer 23

• characteristics are grouped phylogenetically
• pollinators do not fight
• non-pollinators fight to varying degrees
• violence is high when female density development in the fig is low

Question 24

Explain the utilisation of game theory in comparative analysis of conflict in pollinating and non-pollinating wasps

Answer 24

• female resource is limited
• greater benefit to fighting, rather than fleeing for alternative female acquisition

Question 25

Describe some species of non-pollinating wasps

Answer 25

- males are winged and highly armoured - adapted to fighting behaviours - frequently undergo morbidity through decapitation in combat

Question 26

Describe the advantages of the comparative method

Answer 26

- illustrates broad and general trends and relationships across species - amenability of their hypotheses

Answer 27

the experimental studies still provide advantages in terms of their ability to detail individual behaviour, and their testability over their observationality.