A biogeographical analysis of the freshwater plants of Australasia

Abstract

Patterns in the distribution of Australasian species of freshwater aquatic plants were sought, to determine whether vicariance, distance dispersal, local speciation, or a mixture of these could best explain the distribution. The distribution was recorded from 10 regions of Australasia that include sizeable areas of wetland: Papua New Guinea, Cape York Peninsula, south-east Queensland, eastern New South Wales, Victoria, Tasmania, New Zealand, northern Northern Territory, the Kimberley, and south-west Western Australia. Matrices of 553 species by 10 regions, 139 genera by 10 regions, and 56 families by 10 regions were analysed using hierarchical fusion, nearest neighbour and ordination techniques. The results indicate that there are two distinct elements in the aquatic flora, tropical and temperate. The diffuse boundary between these two climatic zones could be interpreted as a barrier in the sense used in definitions of vicariance. There is little effective spread between tropical and temperate areas but, within each of these climatic zones, the species are mobile and many spread reasonably readily between regions, provided suitable habitats and dispersal opportunities are available. Where geographic barriers to distance dispersal have been great then these may become as important as the climatic barrier. This is demonstrated, at least in part, by the differences between some of the generic and species dendrograms. Local speciation (not shown by our PATN analyses because of the endemic species being ignored in them) has been important where some primarily aquatic genera have proliferated when conditions have been suitable. Local speciation has occurred in cosmopolitan aquatic genera that have presumably arrived in regions via long distance dispersal. The significance of bird migration and dispersal patterns are discussed. The aquatic flora of the monsoon tropics has evolved mainly from long distance dispersal but with significant local speciation in some genera such as Nymphoides, Utricularia, Nymphaea and Vallisneria. The pattern of distribution was compared with those recorded from other ecologically defined groups such as the Australian arid and alpine floras.

An investigation of long-distance dispersal based on species native to both Tasmania and New Zealand

“…2) has been noted previously, and has been attributed to various mechanisms such as dispersal by water birds (e.g. Jacobs and Wilson 1996). The high incidence of disjunct species in coastal environments, both aquatic and non-aquatic (Fig.…”

Complex environmental gradients predict distributions of river-dependent plants in eastern Australia

“…The Australasian biogeographic region contains some 439 species of freshwater macrophytes, about half of which are regional endemics (Chambers et al 2008). Jacobs and Wilson (1996) suggested that spatial patterns in the freshwater flora of Australia, New Zealand and Papua New Guinea reflect an interplay of vicariance, related to climatic differences between the tropical north and the temperate south, and long-distance dispersal, especially through transport by waterfowl. At the sub-continental scale of the Australian state of New South Wales (NSW), Growns (2009) found that longitude was the strongest predictor of the similarity of aquatic macrophyte assemblages among geographical grid cells, with lesser roles for catchment area, average annual rainfall, and maximum and minimum temperatures.…”

The flora and vegetation of the seasonal and perennial wetlands of the southern Carnarvon Basin, Western Australia

“…Our study area overlaps the northern edge of their south west Western Australian region but the affinities of the freshwater plants (defined in Jacobs and Wilson's study as plants that grow in or near water) in our study are largely with the arid zone Oessop, 1985) and not with New Zealand. Jacobs and Wilson's (1996) work does indicate the lack of knowledge of the seasonal and permanent wetlands in the arid temperate zone (south of the Tropic) is not restricted to southern Carnarvon Basin but is true across Australia. With an increase in knowledge of the wetland systems of arid areas of both the temperate and tropical zones the very strong division between the tropical and temperate regions reported by them can be expected to break down.…”