Why are so many species based on a single specimen?

• A considerable number of insect species, including Trichoptera, are described from a single specimen, also knownas a 'unique' or a 'singleton'. We ask the question of whether this reflects failure to consider variation and relatedspecies, lack of collecting effort, or true rarity. In an attempt to answer this question we examine the availableliterature and data on the Trichoptera of Tasmania and New Caledonia. We note a low level of taxonomicsynonymy among species in these faunas. Moreover, a significant proportion of species from Tasmania that werebased originally on singletons have been re-collected subsequently, but this is not true for New Caledonia. Thepossible significance of these figures is considered following examination of data on diversity and abundance ofHydroptilidae collected by regular, standardised light trapping over almost two years at a northern Australiantropical stream. We conclude that quite a large proportion of the Trichoptera species based on singletons are rare,valid species, but for others the appearance of rarity may be a consequence of inadequate collecting, particularbehavioural attributes of the species, including seasonality, and failure to consider fully the structural diversity ofrelated species. Lastly, we discuss briefly the consequences of rarity, apparent or real, on conservationmanagement.

Subject headings

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Keyword

Diversity of life

Livets mångfald

Publication and Content Type

ref (subject category)

art (subject category)