On using iNaturalist data to estimate trends

Abstract

A discussion is presented of the use of citizen science data to study trends in population  abundance and on numbers of species. The discussion is framed around two widely accepted models of indices of biological signal per unit of effort. When the trend is number of species per unit of effort, the model is the Michaelis-Menten equation, that has an asymptote. When the trend is in abundance per unit effort, the model is the simple linear “catch/effort” model of fisheries. It is found that diversity per unit of effort has an artifactual tendency to negative trends, while abundance per unit effort is less likely to be influenced by artifacts of the metrics. The results strongly suggest that, at least for trends in species numbers, the use of citizen science data is unadvisable when the sampling effort is increasing.