Pattern and Process in the Distributions of Non-diadromous Species – 1: The Galaxias vulgaris Species Complex

Abstract

The non-diadromous Galaxias vulgaris species complex, comprising about 10 genetic lineages, is confined to South and Stewart Islands, primarily to the east of the Southern Alps, though there are a few populations to the northwest of the northern Southern Alps. They fall into two morphotypes, informally called ‘flatheads’ (6 lineages) and ‘roundheads’ (4 lineages). Species richness is low in the north and greatest in the southern sector of the South Island. Greatest diversity in the south, is on an area that is regarded by some as a residual emergent island during the Oligocene marine submergence of much of New Zealand, where 8 of the lineages are found. Distributions of lineages overlap broadly in the south, though sympatry of lineages is only occasional, and where there is sympatry there is minimal evidence for hybridisation. Patterns of distribution tend to connect strongly to existing river catchments, though there are interesting instances where apparently anomalous occurrences relate to know changes in riverine connections associated with changes in earth history and topography.