Author response of: Camera trap monitoring of unmarked animals: a map of the relationships between population size estimators. Round#1

Estimating population size over a given area, i.e., estimating population density, has historically been done using capture-recapture methods for marked animals or distance sampling.However, over the last decades, the rise of camera trap data has led to the development of numerous methods estimating population density from photographs of unmarked animals recorded by camera traps.While many of these methods have different data requirements and could appear unrelated, Calenge (2026) describes how the various methods connect mathematically to each other under the assumption that animals move according to the ideal gas model (Hutchinson & Waser 2007, 2009).He focuses on methods that use the field of view of the camera rather than an effective sampling area of the traps (Gilbert et al. 2021).There was a previous indication in the literature that some of the former methods might be connected (Palencia et al. 2021) but no comprehensive map of the relationships between the diverse estimators, even under this simple movement model.In addition to providing such a map, the paper carefully dissects why the estimators are linked, which might have otherwise remained hidden to many practitioners.The standardized notation and pedagogical approach employed by Calenge (2026) will no doubt help to understand better these links.Which links may hold or not under more general assumptions or different movement models is a natural follow-up question.As the author sketches in the discussion, it is also a challenging one.