Ecology of Groups Lecture 1

1
Ecology of Groups Lecture 1

• Living in GroupsAndrew Jackson

2
(No Transcript)
3
Living in Groups

• Why live in groups?
• Benefits must outweigh the Costs
• How do animals live in groups?
• Expect that evolution has equipped animals that
  live in groups with appropriate behaviours to
  maximise their fitness

4
What is a group?

• Any set of organisms, belonging to the same
  species, that remain together for a period of
  time interacting with one another to a distinctly
  greater degree than with other conspecifics.
  Wilson 1975.
• When two or more animals live together they
  constitute a group. Lee 1994.

5
Interactions Between Individuals
6
(No Transcript)
7
Groups as Networks

• Social Network Theory
• Nodes
• Connections per node
• Cliques
• Small World Phenomenon

8
Consequences of Grouping

• Benefits
• Anti-predator
• Finding food
• Thermal
• Costs
• Competition for food
• Aggression
• Infection

9
Optimal Group Size
BENEFITS
COSTS
Energetic Gain or Loss (same units)
Group Size
10
Fitness Relationships
Fitness
Group Size
11
Selfish Individuals
Fitness
5
Group Size
12
Redistribution Leads to Super-optimal Groups
18 19 19 20 20 20 21 21 22
18 19 20 20 20 20 21 21 21
17 20 20 20 20 20 21 21 21
12 21 21 21 21 21 21 21 21
4 22 22 22 22 22 22 22 22
0 23 23 23 23 22 22 22 22
20
13
Matlab demo
14
Factors that restore optimal group size
15
Depends on Fitness Curve
Fitness
1
4
5
10
Group Size
16
Who is the Gatekeeper?

• Individuals at optimal size want to bar entry
• All other individuals want to join.

17
Kinship
?
18
Other possible mechanisms

• Fragmentation e.g. by predators
• Sub-groups bud off the main group
• Sub-optimal estimate of fitness. Learning (and
  forgetting) as you navigate the habitat

19
Group Living Summary

• Costs and benefits suggest optimal group size
• But, individuals are selfish and mess this
  process up
• Theory predicts super-optimal sizes
• Some mechanisms can help to some extent

20
Tutorial Task Next Week

• 4 Groups
• Benefits of Grouping
• Costs of Grouping
• Mechanisms and processes of group fission and
  fusion
• Optimal Group sizes in the real world
• Email me or drop your talk in on disk / pen by
  5pm Tuesday 21 October
• a.jackson_at_tcd.ie
• Living in Groups by Krause and Ruxton