Memoirs of the Museum of Vicloria 56(2):435-439 ( 1997) 28 February 1997 https://doi.org/10.24199/j.mmv.1997.56.35 DIVERSITY IN CENTRAL AUSTRALIAN LAND SNAILS (GASTROPODA: PULMONA TA) BRONWEN SCOTT Department of Zoology, James Cook University of North Queensland. Townsville, Qld 4811, Auslralia Abstract Scott, B., I 997. Diversity in central Australian land snails (Gastropoda: Pulmonata). Ml'moin of //1e Museum of Victoria 56(2): 435-439. land snail diversity in central Australia is due 10 camaenids (70 of 83 spp.). Much of the_ any � .ca1;1aen1d species have restricted distributional ranges so that. although land snail d1vers1ty_ In Central Australia is relatively high, local diversity is generally low. The faunaof the KnchauffRange in the Central Ranges is an exception to this general rule as the Finke Gorge National Park contains at least 25 species of snails, 30% of the central Australian fauna. Similar areas in the Central Ranges. such as the George Gill Range and eastern MacDonnell Ranges have a significantlylower diversity of land snails. It is postulated that high levels of diversity and endemicity in central Australian camaenids are the product of vicariance events related to Tertiary and Quaternary changes in climate. Introduction Origins and diversification of the Central Over 80 species ofland snails fromeight families Australian land snail fauna have been recorded from central Australia It has been suggested that many families rep­ (Solem, I 989, 1991, 1993; Scott, in prep.). The resented in central Australia were Tertiarv land snail fauna is dominated by the families invaders from Asia and that the apparen·t Camaenidae and Pupillidae s./., both of which reduction in diversity from north to south and are widespread across mainland Australia. from east to west is a result of dispersal from Other familiesare represented in this area by no tropical centres of origin (Solem, 1959, 1992, more than two species each. It has been 1993). The most diverse of those families, the suggested that the relatively small number of Camaenidae. is postulated to have entered Aus­ families in the central Australian fauna (com­ tralia in several waves (Solem, 19 59, I 992, I 99 3; pared with the greater complement in coastal Bishop, 1981 ), the products of the earliest wave areas) is the result of dispersal from coastal having the most extensive distribution and those centres of origin to the interior, combined with of the most recent restricted to the eastern rain­ the effect of filtering due to fluctuating climatic forests (Solem, 1959). This interpretation is conditions (Solem, 1993). Problems arise, how­ based on the assumption ofmonophyly ofAmer­ ever, with dispersal hypotheses as explanations ican and Australasian camaenids but this of the origin and distribution of organisms as assumption is probably incorrect (Scott, 1996). they are ad hoc narratives used to describe It is possible that the Australasian component of specific cases and, as such, are generally untest­ this familyis closely related to the Asian Brady­ able. baenidae (Scott, 1996) and is of Gondwanan Hypotheses concerning vicariance biogeogra­ origin (Scott, in press). phy provide alternative interpretations of distri­ Central Australian camaenids show a high butions. In that model of historical biogeogra­ degree of regional endemisrn but two genera in phy, it is assumed that taxa and the areas they the subfamily Sinumeloninae, Sinume/on and occupy have evolved together (Nelson and Plat­ Pleuroxia, have ranges that extend beyond the nick, 1981 ). Reconstruction of a phylogeny Centre. Species of these genera occur in the allows the reconstruction of the history of a Centre and in southern and parts ofwestern Aus­ region. Biogeographic hypotheses erected using tralia (Solem, 1992, 1993). This has been data fromone group of organisms can be tested interpreted as the result of primary differen­ with those from another. Land snails are excel­ tiation of ancestral taxa in the Centre, followed lent subjects for such biogeographic studies as by southerly and westerly migrations to give rise they are 'vicariant conformers' (Springer, 1981: to local radiations (Solem. I 992, 1993). Present 230), responding rapidly to environmental dis­ distributions may, however, also be explained as ruptions (Gould, 1969). the result of tectonic or climate-induced vicar- 435 436 B. SCOTT iance events which caused populations of ances- further away from Alice Springs may have been tral taxa to become isolated and thus to give rise less thoroughly explored. to modern taxa. Preliminary studies on the phy- Camaenid species comprise 66% of the land togeny and cladistic biogeography of the Sinu- snail fauna of the Central Ranges and demon- meloninae indicate that fauna of southern and strate a high level of endemism compared with western coastal areas was separated from that of species in other families (Table 2). The non- central Australia early in the evolutionary his- camaenid species of that fauna are largely wide- tory of the group (Scott, in prep.). Within the spread, shared with other parts of Central Aus- central Australian region, some montane areas, tralia and, in several cases, also with coastal such as the Central Ranges, may have become areas. isolated from adjacent areas not long after the The pattern of diversity demonstrated by Centre-SW split. Vicariance events causing dis- camaenids in the Central Ranges can be seen in ruptions of these magnitudes may have been other areas such as the Kimberlev and adjacent associated with cyclical climate change in the ranges (Solem. 1979, 1981a, l'981b, 1984b, Caenozoic, when periods of relative dryness 1985, 1988a, 1989). Many of these endemic associated with global cooling alternated with species have narrow ranges which are usually warm and humid pluvial stages. Alternation of allopatric to congeners (Solem, 1988b). This arid grasslands and extensive water bodies in the appears to be a common pattern among land plains and valleys may have presented signifi- snails (Solem, 1 984c) and it is rare for two short- cant barriers to formerly widespread snail taxa. range Central Ranges endemics to occur sympa- Which of the two extremes may have played the trically, although they are frequently found with more significant role cannot be determined, but other more widely-distributed species. Geo- they may have acted synergistically. graphic ranges do not appear to be restricted by Congeners of the central Australian bulimulid competition as they are never parapatric and, as Bothriembryon spencen (Tate, 1 894) are found narrow-range endemics do not come into con- in southern and western parts of the continent. tact with each other, there can be no evidence of as well as the south-eastern coast of Tasmania repressive interactions. (Smith, 1992). There is generally little spatial Pleuroxia adcockiana (Bednall, 1894) is the overlap between the Camaenidae and Bulimuli- sole representative of the genus in the Central dae as camaenids do not occur in Tasmania or Ranges and the edges of its distribution coincide the extreme south-west of the mainland and with those of the Central Ranges biogeographi- Bothriembryon is not found in the north or east. cal area. The four species of Sinumelon in this However, although the distributions of area are moderate-range endemics and divide Bothriembryon and the two camaenid genera, the Central Ranges into four units: far western Sinumelon and Pleuwxia, do not correspond MacDonnell Ranges. Krichauff and James entirely, broad geographical congruence Ranges (S. exposition Iredale. 1937). near west- between the three genera is such that future ern MacDonnell Range and Alice Springs (S. phylogenetic and biogeographic analysis of one bednalli Ponsonby, 1904), eastern MacDonnell genus will provide a hypothesis available for Range (S. dulciensis Solem, 1993) and George testing with the other two genera. Gill Range (S. gillemis Solem. 1993) (Solem, 1993). The genera Patterns of diversity in the Central Ranges Gramdomelon and Semotrachia show very land snail fauna high degrees of endemism. Three of five species of Gramdomelon are found in the Almost half of the Central Australian species of Central Ranges and two of those are known only land snail have been recorded from the Central from single localities, at opposite ends of Finke Ranges (MacDonnell, Krichauff and George Gorge (Solem, 1993; Scott, in prep.). Semotra- Gill Ranges) (Smith, 1992; Solem, 1993; Scott, chia is an extremely diverse genus, with 18 of its in prep.), which cover 12% of the area of this 28 species known only from the Central Ranges region, while Finke Gorge, in the Krichauff (Solem, 1992; Scott, in prep.). Many (16) of Range, alone contains almost a third of the cen- these species are narrow-range endemics, con- tral Australian land snail species (Table 1). The fined to single gorges in the eastern and western snail fauna of the Central Ranges is well-known MacDonnell Ranges, or from rock walls in the as collecting sites are readily accessible, but Krichauff, James and George Gill Ranges. direct comparison between the Central Ranges Combination of patterns of distribution from and adjacent areas may present problems as sites these species suggests that although the Central DIVERSITY IN CENTRAL AUSTRALIAN LAND SNAILS 437 Table 1. Land snail diversity in Central Ranges (data compiled from Solem, 1989, 1991, 1993; a b Scott, in prep.) ( total number of species recorded from the Central Ranges = 39; total number of species recorded from central Australia