Opportunistically acquired evidence is unsuitable data to model fox (Vulpes vulpes) distribution in Tasmania

Abstract

Despite the absence of direct observation of live foxes in the Tasmanian environment, a recent study concluded that foxes are now widespread on the island and proposed a habitat-specific model incorporating 9 cases of physical evidence presumed to confirm their unique presence. We briefly review the history of fox incursions into Tasmania and then assess the quality of putative physical evidence against a defined evidentiary standard. Overall, 14 of 17 incidents described since 1998 were associated with between 1 and 4 criteria indicative of unreliable data or were not associated with adequately documented physical evidence. Anonymous and anecdotal information was fully or partially relied upon in 10 of 17 cases and of these 5 were widely acknowledged to be hoaxes. We conclude that opportunistically acquired evidence is a poor substitute for data obtained by properly designed and independent wildlife surveys for confirming unique fox incursions and as the basis of ecological models predicting true habitat-specific fox distribution. Species rarity decreases the reliability of wildlife surveys and population models; thus validation of unique incursions in particular requires appropriate rigor in evidentiary standards and data quality. Precautionary management that may be considered in response to uncertain information, or opportunistically collected specimens of doubtful provenance, does not imply that such information should be treated as scientific data. We suggest that an eradication program is justified as a precautionary measure only after rigorous qualitative analysis reveals data capable of rejecting the null hypothesis that the species of interest is absent. Ó 2014 The Wildlife Society.

Trends in anecdotal fox sightings in Tasmania accounted for by psychological factors

“…The contested quality of the physical evidence remains central to the controversy about the presence of foxes in Tasmania, especially given that no credible empirical data corroborated 13 of 15 claims made by the FEP from 2001 to 2003 pertaining to the existence of an extant fox population (Supporting Information) (Marks et al. ). However, a failure to fully define psychological factors that influence changing public beliefs necessarily reduces the power of our model.…”

“…; Marks et al. ). Because species rarity decreases the reliability of population estimates, a dependence on anecdotal information to qualify species presence can lead to misleading inferences (McKelvey et al.…”

“…The absence of empirically derived survey data confirming the presence of an extant fox population in Tasmania, together with several cases of hoaxing (reviewed by Marks et al. ), suggest that the provenance of these opportunistically acquired postmortem fox specimens was equivocal at best. Anecdotal reports of foxes were heavily relied on in the first year of a program to augment weight‐of‐evidence arguments used to justify the implementation of an eradication‐through‐poisoning program using fluoroacetic acid (1080) baiting (Saunders et al.…”

“…Our first hypothesis was that changes in the extent of media reports concerning foxes are highly dependent on claims made by the FEP from 2001 to 2003 concerning corresponding physical evidence irrespective of its equivocal value (Marks et al. ). We further hypothesized that anecdotal sightings of foxes arise from the misidentification of endemic fauna due to preconceptions and cognitive biases that had been generated by the dissemination of equivocal information via the media.…”

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“…In contrast, an analysis that inferred the 63 spatio-temporal distribution of foxes that could have generated the fox carcass discoveries suggests that 64 the hypothesized widespread population is highly unlikely (Caley et al, 2015). The provenance of the 65 fox carcass data on which this inference was based has been contested (Marks et al, 2014). Therefore, 66 additional, independent inference is needed.…”