Beetles, Beach Drift, and Island Biogeography
1977; Wiley; Volume: 9; Issue: 1 Linguagem: Inglês
10.2307/2387860
ISSN1744-7429
Autores Tópico(s)Scarabaeidae Beetle Taxonomy and Biogeography
ResumoThirty-one families of beetles were collected in December 1974 in beach drift near Gerroa, New South Wales, Australia. The taxonomic composition of the beetles in the beach drift was neither entirely representative of, nor proportional to, that of the adjacent forest beetle fauna but more closely resembled oceanic island faunas. Comparisons are made with the fauna of the Samoan and Hawaiian Islands. Inferences are made on the usefulness of beach-drift studies as a method that can assist in determining long-distance chance dispersal. LONG-DISTANCE DISPERSAL to islands or between continents has long been a subject of speculation. Various aspects of the subject have been investigated by numerous authors, both from observational and theoretical points of view. However, one aspect, that of utilizing the fauna occurring in beach drift as an indicator of potentially readily dispersible groups, has largely been ignored. The present paper mentions a few aspects of current research, then discusses the seeming usefulness of beach-drift studies. A variety of dispersal mechanisms such as rafting, wind and water transport, and the element of chance have been recognized, being summarized by Carlquist (1965, 1974), Darlington (1938), Vagvolgyi (1976), and Simpson (1952). MacArthur and Wilson (1967) have developed models that relate immigration and extinction, the size of islands. and their distance from a source area. A major problem in considering long-distance dispersal has been the testing of these various assumptions. Variables include: the size and similarity of the source and the island (the target of some authors), the distance over water or other barriers, the chance of hitting the target, the number of propagules. and the length of time. The time element alone, with its implications of past changes in land configurations. changes in oceanic and air currents, and even evolutionary changes in the organisms, makes the testing of any hypotheses extremely difficult. Zimmerman (1948) discussed in detail the origin of the Hawaiian fauna, which seemingly had to have reached the islands by over-water dispersal. Few other oceanic islands have been so well analyzed. Age and proximity to land in earlier geological times have caused debate when similar analyses have been made elsewhere. Recently Wilson and Simberlof (1969) and Simberlof and Wilson (1969, 1970) defaunated a number of small islands in the Florida Keys and studied their reinvasion, showing that they were rapidly repopulated but not necessarily with the same species. Vuilleumier (1970) studied birds in the Andean paramo and found that the MacArthur and Wilson models, relating to island size and distance, had a good predictive value. However, similar studies by Brown (1971) using boreal mammals in the isolated mountains in the North American Great Basin failed to conform to the same models, but Johnson's study (1975) of birds of the same area did fit the models. The volcanic island of Surtsey, formed in 1963 just south of Iceland, allowed scientisits to study the arrival of both flora and fauna. A number of interesting observations were made by Lindroth et al. (1973). Approximately 158 species of terrestrial anthropods reached Surtsey with four becoming established. Lack of any plant cover undoubtedly influenced this initially low success rate. The Surtsey study also showed that aerially transported insects did have some control over landing sites. The results indicated that while long-distance transport to the island may have been by chance. insects could control their landing. Gressitt and Yoshimoto (1964) found a large amount of aerial plankton (mainly insects) in studies made in the South Pacific (see table 1) which primarily showed that many small organisms may be transported long distances by air currents. Many fortuitous observations on windblown grasshoppers, birds, etc., and on rafts of vegetation have also appeared in the literature, but how much these contribute to the development of isolated biotas remains an unanswered question. In December 1974, while my wife and I were staying near Gerroa, New South Wales, Australia, there was an eight-day period of very windy, stormy weather. One coastal strip, named Seven Mile Beach, which was largely undeveloped and had an excellent fringing forest, was visited daily during this period. On the first day we noted tremendous aggregations of insects along the high-tide drift line (figs. 1-4). BIOTROPICA 9(1): 53-57 1977 53 This content downloaded from 207.46.13.160 on Mon, 17 Oct 2016 05:15:55 UTC All use subject to http://about.jstor.org/terms Since we were both interested in Coleoptera we carefully examined the drift and after the second day made an effort to collect representatives of all of the species of beetles (Coleoptera). We also attempted to estimate the relative abundance (very common, common, uncommon, or rare) of each species and noted whether each was alive or dead (table 1). Hymenoptera, Hemiptera, and Diptera were also present in some numbers, but we did not collect these. An average of between 100 and 200 beetles per meter was found along much of the high-tide line (figs. 1-4). During the eight-day period, we estimated that approximately 1,000,000 beetles were present daily in the high-tide beach drift along the 10 kilometers of beach. It was difficult to make a more accurate estimate for several reasons. Perhaps 15 percent of the bettles were quite active, and many rapidly dispersed or dug into the sand. Many others were hidden in mats of seaweed. While we were investigating these, shore birds were giving us considerable collecting competition. In addition to the beach collecting, during the three weeks in the area, we spent much of our time collecting in the nearby forest. A number of families were present in the forest but were not encountered in the drift, for example, Alleculidae, Belidae, Dermestidae, Eucnemidae, Melandryidae, Silphidae, Rhipiceridae, and Trogossitidae. Differences were even more evident if the frequency of occurrence between forest and drift were considered for genera and species. Unfortunately, both time and taxonomic problems prevented an accurate assessment. Explanations for the differences in the taxonomic composition of the beetles in the forest compared to the drift are that TABLE 1. Beetles in beach drift, Gerroa, N.S. W., Australia, December 1974 Living Present Present on In Pacific # of or on Samoa Hawaiian aerial surveys Family spp. Abundancea Deadb (# of spp.) Islands to 1963 Anobiidae 1 R L yes (1) yes yes Anthicidae 1 R L&D yes (1) no no Anthribidae 1 R L yes (14) yes yes Buprestidae 5 UC most D yes (5) no yes Cantharidae 2 C-R L & D no no no Carabidae 5 VC-C L yes (15) yes yes Cerambycidae 7 UC L & D yes (35) yes yes Chrysomelidae 12 C-R L & D yes (17) no yes Cleridae 1 R D yes (3) no no Coccinelidae 4 C-UC L & D yes (5) no yes Cucujidae 1 R L yes (14) yes yes Cupedidae 1 R D no no no Curculionidae 5 C L yes (86) yes no Dytiscidae 2 R L yes (7) yes no Elateridae 3 UC L&D yes (14) yes no Heteroceridae 1 C L no no no Histeridae 1 UC L yes (4) yes no Hydrophylidae 4 R L & D yes (6) yes no Lagriidae 1 C L&D no no no Lucanidae 2 UC L&D yes (6) yes no Lycidae 2 R D yes (2) no no Meloidae 1 R D no no no Melyridae 1 R L yes (2) no no Mordellidae 1 R D yes (8) no no Oedemeridae 2 C-UC L yes (5) no no Passalidae 1 R L&D no no no Ptinidae 1 R L no no no Scarabaeidae 11 C, UC, R L & D yes (7) no yes Staphylinidae 5 VC L yes (24) yes yes Tenebrionidae 3 R L & D yes (22) no yes Throscidae 1 R L yes (1) no no a VC = very common, C common, UC = uncommon, R Rare. b L = living, D = dead.
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