Predators and parasitoids occupy the matrix habitat and cause mortality during dispersal. The ‘fritillaries’ are the actual players, which occur as a metapopulation and share the individual aim of maximizing lifetime reproductive success
Equipment: As the game is preferably played outdoors, the players will need sturdy boots, good clothes, and a pen or pencil. You will also need colored cardboard cards (in as many colours as there are patches, and as many cards per colour as there are territories in a patch – see below)
Players and assistants: preferably a minimum of 20 individuals, with one “patch controller” per patch, 1-3 predators and/or parasitoids, and 12-20 Fritillaries.
The setup: To outline the network of habitat patches that offers the game arena, several patches are drawn in the sand (e.g. 5-7 patches work well for 20-30 players, but the optimum number of patches will depend on the distance between them). To illustrate the relation between habitat area and local population size, local carrying capacity (K) is set proportional to patch size. K is symbolized by territories (sectors, see figure), and patches vary in size from large (ca 10 territories) to small (2-3 territories). To mimic intraspecific competition, players can only enter vacant territories. There are more territories than players (with some empty territories in each patch), and at least one completely empty (=uncolonized) patch at the start of the game. The initial distribution of players in patches should have an even sex ratio. The players get to choose their patch themselves (to allow for different strategies)
Simplified start setup. Two patches shown, one with K=8, one with K=4. Both patches have two empty territories and an equal sex ratio. The smaller patch contains individuals of a rarer genotype (red) than the larger patch (blue); these individuals will therefore have more chances for outbreeding. On the other hand, starting out in a large patch offers more opportunities for immediate mating (inbreeding) events without dispersal (3x). These conflicting considerations allow the players to adopt several alternative strategies.
Dynamics: There are males and females in the game, and the objective is to maximize lifetime reproductive success. Each person starts with a card reflecting his/her genotype. This genotype is shown by the colour of the card. In the beginning there is complete inbreeding, so in every patch the fritillaries have cards of the same colour. The maximum number of lifetime reproductive events (matings) is agreed upon by the start of the game. [make it about ten to start with]
A male and a female can mate when both in the same patch. Any gender can start courtship. If a mating partner declines the invitation, no mating occurs! If he/she agrees, both partners show their cards to the patch controller. Depending whether the colours match, they are given a certain amount of credits (more for outbreeding less for inbreeding).
Scores for mating: To illustrate the negative impact of inbreeding (inbreeding depression), a player scores less for mating with an individual of his/her own genotype than with an unrelated individual.
Inbreeding (two cards of the same genotype) = 1 point
Outcrossing (two cards of different genotype) = 2 points.
At reproduction, the patch controller scribbles these scores on the papers of the mating couple. And – when a player has mated the maximum number of times agreed upon, he/she stops playing. The game continues until all players are ‘dead’ (attacked by a predator) or have reached the maximum number of mating events
Local extinctions: To illustrate the relation between local population size and the expected local population persistence, local extinction risk is set proportional to population size (or patch size). After a time proportional to local population size (“as many minutes as there are territories”), the patch controller forces everybody out of the patch. The players in that patch have to disperse to a new patch. After local extinction, there is a refractory time of 1 min before anybody can enter the patch (patch controller keeps hand raised)
Dispersal and mortality: To achieve outbreeding, and/or in response to local extinction, fritillaries have to migrate. There are two types of harmful agents in the matrix (and they cannot enter the patches!): predators and parasitoids. Predators will kill the player by touching them. Anybody touched by a predator is out of the game. Parasitoids will naturally parasitize the offspring – hence, anybody touched by a parasitoid looses his/her latest clutch. (The parasitoid achieves this by crossing out the latest mating score on the card). NB: although the player looses a brood, this repdroductory event is subtracted from the total number of matings allowed for this player.
Objective: The winner of the game is the one who acquires the highest lifetime reproductive success. Different strategies might work out (taking a high risk but dying with still a lot of unrealised fecundity left, or making a lot of low-credit inbreeding matings, etc).
Predators and parasitoids get scored by the number of prey killed / parasitized.
Once the game has been played a few times (some 30 min at a time), the students can suggest further rules for the next few rounds. This offers a nice opportunity for the students to apply what they have learnt during the course, and to identify further key processes of (meta)population dynamics.