More taxonomists describing significantly fewer species per unit effort may indicate that most species have been discovered.

Recent studies show that there are more taxonomists describing species in recent decades than before. However, whether the rate of increase in number of taxonomists is greater than the rate of new species description has been questioned.We found a statistically significant decline in the proportion of species being described per number of taxonomists (i.e., authors of recent species descriptions) during the past century for (i) families of insects that had been stated not to show this trend and (ii) a sample of over 0.5 million marine, terrestrial, and freshwater species. We suggest that this decreased “catch” of species per taxonomic effort, despite scientists’ greater ability to explore and sample habitats, means it is getting harder to discover new species and supports recent studies suggesting that two-thirds of all species have been named. Some scientists consider that describing all remaining species is fruitless when so few have been described, there are insufficient taxonomists, and so many species are or soon will be extinct (Thomas 1997; Benton 2008). Such statements discourage taxonomy if further investment appears futile (Swaisgood and Sheppard 2010; Costello et al. 2013). However, recent analyses indicate that we may already have named one to twothirds of all species (Appeltans et al. 2012; Costello et al. 2012; De Clerck et al. 2013), that there have been high rates of discovery of new species in wellstudied geographic regions (Costello and Wilson 2011; Fontaine et al. 2012), and that there aremore taxonomists describing species than ever before (e.g., Joppa et al. 2011a; Costello et al. 2012; Lohrmann et al. 2012; De Clerck et al. 2013; Tancoigne andDubois 2013). However, whether an observed trend of a decreasing number of species being described per number of taxonomists (i.e., authors of recent species descriptions) is true has been more controversial (Bacher 2012). Does increased taxonomic effort explain the continued high rates of species discovery rather than the ease with which new species may be found? Is the trend of fewer species being discovered per taxonomist true? Here, we review evidence that suggests there have never been so many people describing new species, which can be considered a minimal number of taxonomists. We then provide the first statistical tests of the long-term trends in thenumber of species describedper taxonomist for the past 240 years and calculate the tipping-point year, when a trend for more species per taxonomist switched to one of fewer species per taxonomist.