Detecting target species: with how many samples?

Abstract

The detection of target species is of paramount importance in ecological studies, with implications for environmental management and natural resource conservation planning. This is usually done by sampling the area: the species is detected if the presence of at least one individual is detected in the samples. Green & Young (Green & Young 1993 Sampling to detectrare species. Ecol. Appl . 3 , 351–356. ( doi:10.2307/1941837 ) introduce two models to determine the minimum number of samples n to ensure that the probability of failing to detect the species from them, if the species is actually present in the area, does not exceed a fixed threshold: based on the Poisson and the Negative Binomial distributions. We generalize them to two scenarios, one considering the area size N to be finite, and the other allowing detectability errors, with probability δ . The results in Green & Young are recovered by taking N → ∞ and δ = 0. Not taking into consideration the finite size of the area, if known, leads to an overestimation of n , which is vital to avoid if sampling is expensive or difficult, while assuming that there are no detectability errors, if they really exist, produces an undesirable bias. Our approximation manages to skirt both problems, for the Poisson and the Negative Binomial.

Catch me if you can: current status and topical issues on the use of eDNA-based targeted detection of rare and endangered animal species

“…However, this is a process that can be laborious, time-consuming, and deficient in taxonomic discrimination capacity, in particular for organisms low on distinctive morphological features, such as the case of some invertebrate fauna. In addition, when the targets are rare species, i.e., species with small populations sizes, or elusive species, the detection probabilities are typically low in any ecosystem and a greater sampling effort is needed to maximize the chances of species detection, which is not always feasible (Delgado, 2022;Goldberg et al, 2011;Jerde et al, 2011;Ma et al, 2022;Sgarbi et al, 2020). Although the term "rare species" is commonly associated with indigenous endangered species, non-indigenous species can be considered rare species as well, namely early in the invasion process when their population sizes are still small (Ficetola et al, 2008;Goldberg et al, 2011;Jerde et al, 2011).…”