Data from: Toward reliable population density estimates of partially marked populations using spatially explicit mark-resight methods

(1) Camera traps are used increasingly to estimate population density for elusive and difficult to observe species. A standard practice for mammalian surveys is to place cameras on roads, trails, and paths to maximize detections and/or increase efficiency in the field. However, for many species it is unclear whether track‐based camera surveys provide reliable estimates of population density. (2) Understanding how the spatial arrangement of camera traps affects population density estimates is of key interest to contemporary conservationists and managers given the rapid increase in camera‐based wildlife surveys. (3) We evaluated the effect of camera‐trap placement, using several survey designs, on density estimates of a widespread mesopredator, the red fox Vulpes vulpes, over a two‐year period in a semi‐arid conservation reserve in south‐eastern Australia. Further, we used the certainty in the identity and whereabouts of individuals (via GPS collars) to assess how resighting rates of marked foxes affect density estimates using maximum likelihood spatially explicit mark–resight methods. (4) Fox detection rates were much higher at cameras placed on tracks compared with off‐track cameras, yet in the majority of sessions, camera placement had relatively little effect on point estimates of density. However, for each survey design, the precision of density estimates varied considerably across sessions, influenced heavily by the absolute number of marked foxes detected, the number of times marked foxes was resighted, and the number of detection events of unmarked foxes. (5) Our research demonstrates that the precision of population density estimates using spatially explicit mark–resight models is sensitive to resighting rates of identifiable individuals. Nonetheless, camera surveys based either on‐ or off‐track can provide reliable estimates of population density using spatially explicit mark–resight models. This underscores the importance of incorporating information on the spatial behavior of the subject species when planning camera‐trap surveys.

(1) 相机陷阱（Camera traps）正日益被用于估算行踪诡秘、难以直接观测的物种种群密度。针对哺乳动物的常规调查做法是将相机布设于道路、步道与小径之上，以最大化探测成功率并提升野外作业效率。然而，目前尚不明确基于兽径的相机调查能否获得可靠的种群密度估算结果。
(2) 随着基于相机的野生动物调查规模快速扩张，明晰相机陷阱的空间布局如何影响种群密度估算结果，已成为当代保护学者与管理者的核心关切。
(3) 本研究以澳大利亚东南部半干旱保护保护区内的广布中型捕食者——赤狐（Vulpes vulpes）为研究对象，在为期两年的周期内采用多种调查设计方案，评估了相机陷阱布设对其种群密度估算的影响。此外，研究借助GPS项圈获取个体身份与空间位置的确定性信息，采用最大似然空间显式标记-重捕（mark–resight）方法，评估了标记赤狐的重捕率对种群密度估算的作用效果。
(4) 相较于步道外布设的相机，布置在兽径上的相机对狐狸的探测率显著更高；但在多数调查周期中，相机布设对种群密度的点估计值影响相对有限。不过，针对每种调查设计，密度估算的精度在不同周期间差异显著，且主要受以下因素强烈影响：被探测到的标记赤狐绝对数量、标记赤狐的重捕次数，以及未标记狐狸的探测事件总数。
(5) 本研究证实，采用空间显式标记-重捕模型得到的种群密度估算精度，对可识别个体的重捕率极为敏感。尽管如此，无论是基于兽径还是步道外布设的相机调查，通过空间显式标记-重捕模型均可获得可靠的种群密度估算结果。这凸显了在规划相机陷阱调查时，纳入目标物种空间行为信息的重要性。