Dark extinction: the problem of unknown historical extinctions

Abstract

The extinction of species before they are discovered and named (dark extinction, DE) is widely inferred as a significant part of species loss in the ‘pre-taxonomic’ period (approx. 1500–1800 CE) and, to some extent, in the ‘taxonomic period’ (approx. 1800–present) as well. The discovery of oceanic islands and other pristine habitats by European navigators and the consequent introduction of destructive mammals, such as rats and goats, started a process of anthropogenic extinction. Much ecosystem change happened before systematic scientific recording, so has led to DE. Statistical methods are available to robustly estimate DE in the ‘taxonomic period’. For the ‘pre-taxonomic period’, simple extrapolation can be used. The application of these techniques to world birds, for example, suggests that approximately 56 DEs occurred in the ‘taxonomic period’ (1800–present) and approximately 180 in the ‘pre-taxonomic period’ (1500–1800). Targeting collection activities in extinction hotspots, to make sure organisms are represented in collections before their extinction, is one way of reducing the number of extinct species without a physical record (providing that collection efforts do not themselves contribute to species extinction).

Combined effects of bird extinctions and introductions in oceanic islands: Decreased functional diversity despite increased species richness

“…An incomplete knowledge of original island avifaunas creates uncertainty around these estimates of the magnitude of species compositional change. First, we are likely to underestimate the number of extinct species (Boehm & Cronk, 2021), given that new extinct species are still being described (e.g. Rheindt et al., 2020).…”

The Sixth Mass Extinction: fact, fiction or speculation?

“…For vertebrates, the bones of which may be preserved long after a species went extinct, knowledge of such species is more complete (e.g. Hawaiian birds; , and, with some major assumptions, for instance about constancy of extinction rates, extrapolation back into the past may permit an estimate of the numbers of species that went extinct but that remain unknown (Boehm & Cronk, 2021). According to Tedesco et al (2014), who based their study on vertebrates only, extinction of undescribed species may account for up to 59% of all extinctions, depending on the taxonomic group and region.…”

“…by restoring habitats) is not enough to prevent extinctions. And because it is not feasible to conserve all species we must do our best to collect (and if possible describe) species before they go extinct -"salvage sampling" (Mesibov, 2004)an effort emphasised by Boehm & Cronk (2021) and Engel et al (2021). All this will depend on reviving the venerable but no longer trendy study of natural history and taxonomy -"bionomy" as espoused by Dijkstra (2016), especially in academic institutions in the Global North where it has declined drastically.…”

Combined effects of bird extinctions and introductions in oceanic islands: decreased functional diversity despite increased species richness

“…An incomplete knowledge of original island avifaunas creates uncertainty around these estimates of the magnitude of species compositional change. First, we are likely to underestimate the number of extinct species (Boehm & Cronk, 2021), given that new species keep being described (e.g. Rheindt et al, 2020).…”