Inferring wildlife poaching in southeast Asia with multispecies dynamic occupancy models

Determining the range dynamics of co-occurring species is crucial to assess the extinction risk of species threatened by poaching. Multi-species site-occupancy models allow the examination of distribution patterns of species while accounting for imperfect detection. These models can be extended to describe species interactions explicitly, by considering the extinction and colonisation probabilities of a species conditional on the presence or absence of the others. Here, we develop a hidden Markov modelling formulation of dynamic two-species site-occupancy models that provides a flexible framework to decompose complex species interaction patterns. We apply our model to a case study on wildlife poaching in the Eastern plains of Cambodia. We used 4 years of survey on locations of snares and wildlife, provided by the SMART partnership to study the distribution dynamics between poachers and six ungulate species regarded as main prey of tigers. Our results showed that a substantial proportion of sites occupied by ungulate species went extinct over the years of the study while the proportion of sites colonised by poachers increased. We also showed that spatio-temporal heterogeneity in the patrolling effort explains a great deal of the variation in the detection of poachers and ungulates. To ensure that our estimates were unbiased, we also performed a simulation study considering the presence/absence of species co-occurring across fictive study sites. Our approach provides practitioners with a robust tool to assess conservation status and extinction risk of wildlife populations. It can assist managers in better evaluating, learning and adapting the patrolling strategies of rangers.