Global trends in the description of aquatic and semiaquatic Heteroptera species, 1758-2004

Abstract

Species description trends for the 4782 species of aquatic and semiaquatic Heteroptera (Gerromorpha, Nepomorpha, and Leptopodomorpha) named during the 246 year interval from 1758 through 2004 are analyzed in regard to number of species descriptions per year and cumulative number of species. These data are graphed both on a world basis, and for seven major zoogeographic regions (Palearctic, Nearctic, Neotropical, Afrotropical, Oriental, Australian and Pacific). This analysis reveals that our taxonomic knowledge of aquatic and semiaquatic Heteroptera, as measured by species descriptions, has accumulated at a progressively faster rate over time when assessed on a world basis, albeit in an episodic and uneven fashion, with peaks of high activity interspersed with periods of relatively low output. When examined at the level of individual zoogeographic regions, the accumulation of taxonomic descriptions is seen to be pronouncedly episodic, and contingent upon the productivity of particular regional experts during the courses of their careers, with just ten authors accounting for over 40 percent of all currently accepted species descriptions. Species accumulation curves, based on published descriptions, indicate that description of extant aquatic and semiaquatic Heteroptera species is nearly complete for the Palearctic and Nearctic regions, and well advanced for the Neotropical region. The Oriental and Australian (including New Guinea) regions show continuing sharp upward trends, indicating that these regions are still far from completely documented. The flattening of the description accumulation curves in the Afrotropical and Pacific regions is interpreted to be an artifact produced by a relative paucity of recent taxonomic work in these regions, and thus not truly indicative of well documented biotas in these areas. Rates of species description in aquatic and semiaquatic Heteroptera were highest immediately after World War II, a level of productivity that has been approached once again in recent decades. If the current average rate of 51 species descriptions per year can be maintained, the estimated 1100 species of aquatic Heteroptera remaining undescribed on a global basis will be formally named within the next 25 years, basically completing the taxonomic documentation of this group.