Knowledge shortfalls' interactions shadow our perception of species' exposure to human threats

Only a small fraction of the species on Earth is known (Linnean shortfall), while geographic ranges of already described species are poorly documented (Wallacean shortfall). While the effect of both shortfalls in conservation assessments has been analyzed and discussed individually, it is still unclear how these knowledge shortfalls interplay affect our perception of species' exposure to human-driven changes. To asses this, by simulating virtual species in a geographically-fragmented ecoregion, we raised hypothetical scenarios of taxonomical and/or geographical knowledge accumulation through time. We described how such accumulation affects our perception of species' exposure to climate and land-use changes. We found that filling both Wallacean and Linnean shortfalls separately, could generate contrasting perceptions on the potential response of species to a given threat. Moreover, the filling of both gaps together would increase or decrease our risk perception depending, exclusively, on the trend of taxonomic changes. These findings highlight a clear but poorly considered interplay between Linnean and Wallacean shortfalls. Trends on basic knowledge accumulation for a given taxon, especially its taxonomic stability, will determine the degree and direction of our biases in estimating its exposure to human threats. Robust assessments of taxonomic effort and geographic ignorance are essential in conservation assessments. There is also a pressing need to bridge the gap between taxonomic and biogeographic efforts, taking into account the interplay between geographic and taxonomic knowledge deficits, to achieve accurate conservation assessments and resource allocations.