Simulation model outline – the evolution of lion group territoriality
Anna Mosser
Purpose:
- To define the basic ecological conditions under which group-territoriality is a more
successful strategy than solitary territoriality in a lion-like animal.
Design:
- Individual/agent based (individual female reproductive success)
- Spatial scale: 500 meter grid cell size, 50 km x 50 km total area
- Temporal scale: 2 year time step (seasonality?), 100 years
- Individuals and groups will occupy territories (of some minimum to maximum size,
with limits on shape)
- Individual survival determined by game theory matrix
- Alternative strategies are (solitary vs. group, or 1/group, 2/group, 3/group, 4/group…)
- Frame based model: switching rules for solitary frame  group-territorial frame
- Largely stochastic
Individual
reproductive success
Measured input variables (“ecological conditions”):
- Cost of territorial defense
- Vegetation types and distribution
- Water distribution
- Prey types (size, habitat, migratory?)
- Prey density
- Lion density
- Initial frequency of territorial strategies
Why?
Measured output variables:
Number of females in pride
- Frequency of territorial strategies
- Average reproductive success per female, by strategy type
Relationships between layers:
Landscape:
Vegetation
Ground water
Rainfall
↓
Prey distributions
Kopje locations
Denning sites
Confluences
Lion distribution

+ dispersal
Territory + Average of pair-wise  Individual survival
quality
interactions
Frames:
Solitary territoriality:
- All surviving offspring disperse
- Survival is determined by territory quality and costs of territorial defense
- Cannot catch larger prey (buffalo size)
Group territoriality:
- A proportion of offspring disperse
- Survival is determined by share of territory quality and shared costs of defense
- Able to catch larger prey
- Better defense of young?
Switching rules (unidirectional – solitary to group-territorial):
- Option 1: constant probability of a switch
- Option 2: territory quality determines probability of switch
- In reality, group-territoriality tends to occur when there is an overabundance of
resources in an individual’s territory – when resources have a heterogeneous
distribution. However, with a constant probability of switching, if it’s under the
wrong conditions the group strategy will not persist. In terms of evolution, a
constant probability makes more sense. So, this may be the best option.
Dispersal:
- Birth rate either constant or dependent upon territory quality. Data suggest that birth
rates are fairly constant from year to year and pride to pride, and it is really the cub
survival that varies.
- Cub survival will depend on territory quality, mom’s survival, and stochasticity.
- Dispersal will depend upon open space within a certain distance of natal territory,
territory quality per female or last time-step’s survival probability (if group
territorial), and potentially relative territory quality.
- Cool trade-off here: spreading your type (solitaries) versus building power to hold on
to a good territory (groupies).
Game matrix:
- Variables: R = resources, territory quality
g = your group size
G = opponent’s group size
C = cost of defense
-
Basic equation: (R-g) – c(G/g -1)
Against:
Payoff to:
Solitary
Group (G)
Solitary
R-1
R -1 – C(G-1)
Group (g)
(R –g) – C(1/g-1)
(R – g)- C(G/g -1)