Biosecurity coalitions in small heterogenous networks

Preventing disease outbreaks can have widespread benefits that are dependent on the actions of many farmers but can be undermined by the inaction of others. Consequently, understanding conditions where or how well farmers will work together is important to designing policies in preventing outbreaks. We use a coalition game theoretic approach, where farmers who have two decisions, whether to cooperate in a coalition and how much effort they put into preventing outbreaks. Additionally, each farmer considers three costs; a cost from an outbreak on their farm, a cost from an outbreak on a “neighbouring” farm (e.g. within range of movement restrictions), and the costs of outbreak prevention. For two heterogeneous farms, two similar farms are likely to cooperate, whereas farms with significantly different costs are unlikely to cooperate. For three identical farms, we consider two networks: all farms are “neighbours” (triangle network) or two farms are “neighbours” to be a third middle farm (line network). For triangle networks, full cooperation requires small on-farm costs, whereas for line networks, full cooperation can happen in situations where on-farm costs are larger than those from neighbouring farms. This all suggests that location and structure is important to whether farmers cooperate.