Udell et al. recently published a new way to prioritise and allocate speed restriction zones that will best protect wildlife from boat collisions. Associate Editor, Jonathan Rhodes explains how this research could be applied to a range of conservation efforts around biodiversity and human movements.

Many threats to species of conservation concern arise due to collisions or interactions between species and people or between species and objects made by people. Importantly, interactions depend on the movement patterns of the species and people/objects. Think, for example, about interactions between moving wildlife and poachers, wind farm strikes on moving birds, and moving vehicles that collide with wildlife. These specific types of human-wildlife conflict commonly result in increased mortality rates that require management, often of the movement process itself. Yet, there are two key challenges with managing these types of threats. First, we need to understand how movement processes lead to collisions, or interactions, and where these are most likely to occur. Second, there we need to identify appropriate threat management actions that minimise collisions given the movement processes. This is where encounter theory – a way of modelling encounters between moving objects– comes to the rescue. Encounter theory has been used widely to model interactions between species, but there is no reason why it can’t be used to model interactions between people / objects made by people and wildlife, one or both of which may be moving.

In their recent article, Udell et al. find a solution to this problem and have the novel idea to integrate predictions from encounter theory with decision analysis to prioritise management actions. Essentially, encounter theory predicts the rate of interactions between objects based in information about the distributions/abundances, sizes, and speeds of movement of the objects in an area. They consider the case of fatal collisions between the Florida manatee and watercraft, which is one of the largest sources of human-caused mortalities for this threatened species. Interestingly, they first develop statistical abundance models of both manatees and watercraft in different management zones using real data and then apply encounter theory to model the spatially-explicit risk of collisions in different management zones based on their movement characteristics.

One way to reduce the number of manatee collisions is to set speed restriction zones, but setting up speed restriction zones everywhere would be highly inconvenient and challenging to boaters! A balance is therefore to try to optimise the location of speed restriction zones and Udell et al. tackle this by integrating their model of collision risk with integer linear programming to identify the optimal location of speed restriction zones. They found that the existing speed restriction zone were relatively effective, reducing collision risk by as much as 70% compared to no restrictions. However, importantly, the optimal spatial allocation of speed restriction zones resulted in at least another 10% reduction in risk for the same cost (i.e., a metric of cost that includes the inconvenience to boaters).

Although the authors apply their new approach to manatees and watercraft collisions, there is substantial promise that it could also be used to prioritise other management that tries to minimise encounters.  Potential applications could include prioritising actions to restrict movement of invasive predators or prioritising actions that modify the movement behaviour of threatened species so they avoid interactions with roads or poachers. Clearly, these efforts would require an understanding of the different movement processes involved and the problem would need to be set up slightly differently, but the core spatially-explicit approach that Udell et al. develop is likely to be widely applicable. This could lead to new novel insights into how we better manage both biodiversity and human movements for conservation outcomes.

Read the full article, Integrating encounter theory with decision analysis to evaluate collision risk and determine optimal protection zones for wildlife in Journal of Applied Ecology.