View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquatic Commons November 1994 NOTICIAS DE GALAPAGOS 15 NOTES ON THE STATUS OF TERRESTRIAL ARTHROPODS IN GALÁPNCOS By: Léon Baert (Translation assisted by Heidi Snell and K. Thalia East) Despite far outnumbering the terrestrial vertebrates na. Such information is also of interest to the Galápa- in species diversity and population numbers, com- gos National Park Service (GNPS) and to CDRS for paratively little is known about the terrestrial developing and implementing management policies invertebrates of the Galápagos Archipelago. Most and for studies offaunal changes occuring due to the publications about Galápagos fauna deal with the sys- ever increasing human population within the islands. tematics, phylogeny, physiology, ecology, ethology Linsley and Usinger (1966) compiled the first and preservation of native vertebrates for which the insect species list for Galápagos, enumerating some islands are famous. Much work has also been con- 618 species, treated in about 190 publications. The ducted on introduced birds and mammals. In contrast, list was derived fromresults of collecting campaigns terrestrial arthropods have been given little attention. of 21 multidisciplinary expeditions ever since Charles ln 1982, Friedman Köster, then director of the Darwins visitin 1835. In alater supplement, Linsley Charles Darwin Research Station (CDRS), asked in (191 I ) added another 265 species, treated in 1 1 8 pub- an annual report , 'How many species of introduced lications. These additions were principally the result insects and invading invertebrates are there in the of collecting efforts of the Galápagos International islands?'. At that time even the number of native Scientific Program of the Californian Academy of invertebrates in Galápagos was unknown. This real- Sciences in 1963-64 and the collecting campaign of ization prompted some important changes. Three Leleup (1965) in 1964-65. long-term studies on the systematics and evolution- With this initial list, the first task of the Belgian, ary ecology ofterrestrial arthropods in the archipelago Canadian andAustrian research groups was to com- were initiated. In 1982, K. Desender, J.P. Maelfait pile summaries of known data on terrestrial and I, from the Royal Belgian Institute of Natural invertebrates in Galápagos. A data base was con- Sciences in Brussels, began a study of Arachnids, structed, containing the following types of Carabid beetles and Isopods. In 1985, Stewart Peck information: and several of his colleagues from Carleton Univer- 1) Literature citations for all invertebrate species of sity, Canada, started a study of several arthropod the archipelago. groups, especially beetles. Also in 1985, Heinrich 2) Distribution information of each species within and Irene Schatz of the University of Innsbruck, and between islands as well as on the continent. Austria, commenced a study of Oribatoid mites and 3) Whethereach species is introduced, native or "erì- Tenebrionid beetles. All three projects continue to demic". this day and while the groups work independently, 4) Ecological data for each species, such as habitat they have coordinated their projects to complement preference, seasonality, elevational zonation, dis- one another. persal power, diet and host specificity. Before any serious ecological work on a arthro- All major islands and volcanoes have been at least pod group could be conducted in Galápagos it was roughly sampled by the scientists. Due to improved necessary to have an understanding of the diversity arthropod capturing techniques such as pitfall, mal- and population numbers of all species inhabiting the aise, flying interception and bait traps the teams were islands. This required extensive taxonomic research able to almost double the arthropod species list dur- to identify and describe the existing invertebrate fau- ing the 1980s (see Table 1). Even now a collection t6 NOTICIAS DE GALAPAGOS No.54 Table 1. Growing number of species for the most important terrestrial arthropod groups. t966 1980 l99t Insecta 618 883 t592 Scorpions 2 0 2 Pedipalpi 0 0 7 Solifugae 0 0 1 Pseudoscorpiones 0 0 16 Opiliones 0 0 I Araneae 70 81 152 Acari 38 0 192 Amphipoda 0 0 4 Isopoda 0 0 l1 Chilopoda 10 0 13 Diplopoda 2 0 9 Symphyla 0 0 1 made on any island or volcano can add a new species ing small and large scale allopatry,parapaty, allopa- to the list. Table 2 provides a detailed example of try with secondary contact of sister species, and how the total number of spider (Araneae) species allo-parapatry. The same is true for spiders (e.g. recorded in Galápagos has increased after each col- Maelfait &Baert,1986) and may be intrinsic to small lecting trip. arthropods. Due to the efforts of the teams, we have a fairly Another important group of invertebrates in good idea of the composition of some of the arthro- Galápagos is the cave dwelling Cryptozoa. Other pod groups in the archipelago and have been able to than some fossil remnants of a probably endemic rat, conduct ecological analyses of the data. For exam- the only animals found in caves are invertebrate rep- ple, we have been able to compare spider communities resentatives of Crustacea, Arachnida, Chilopoda, among the different vegetation zones of Santa Cruz Diplopoda and Insecta. Leleup (1965) pioneered a Island (Baert et al., 1991) and of the five volcanoes study of cave animals in Galápagos which is now on Isabela Island (Baert et aI., 7990). We have con- being followed up by S. Peck and his team (see Her- cludedthat species compositionof spiders is correlated nandez Pacheco et aI.,I992). Cryptozoic arthropo ds primarily with the altitudinal gradient and thus the are of special interest in studying the principals and vegetation zones. On Isabela spider communities are historical processess of animal geography. They are also influenced by the age of the volcanos as well as often considered archaic or relictual and as having an by the presence or absence of human settlements and exceedingly slow dispersal potential. Some Crypto- agriculture. zoans have adapted to an extreme and can be K. Desender has been investigating distribution morphologically characteized by reduced or absent patterns of Carabid beetles (Desender et aI.,l992a). eyes, a reduction of body pigmentation, often a thin- He has shown that the Carabid beetles have a wide ning of body cuticle, flightlessness in normally winged variety of distribution and speciation patterns includ- groups and an increased physiological sensitivity to November 1994 NOTICIAS DE GALAPAGOS t7 Table 2. Growing number of spider species. Year Number of Total Number Collectin&Expedition Species Added of Species 1877 6 6 1 889 5 11 1902 t7 38 Hopkins-Stanford 1 898- 1 899 1924 5 43 Williams 1923 t930 6 49 Norwe gian Zo olo gical 19 25 r970 2I 70 Cal. Acad. Sci. and Leleup ('64-'65) t982 11 81 Various publications 1982 29 110 Baert and Maelfait 1985 2 172 H.and L Schatz (1991) 1985 Ja 115 Peck et al. 1986 7 t22 Baert, Maelfait and Desender (1989) 1988 4 126 Baert, Desender and Maelfait (1991) 1989 8 134 Peck et al. (1991) t99t 11 t45 Baert, Desender and Maelfait (1991) t99l 4 r49 Peck and Heraty a r992 J t52 Abedrabbo dehydration. Peck (1990) lists 56 species ofeyeless long-legged Scytodes longipes, and all the beautiful and reduced-eyed arthropods, of which 4O are native jumping spiders around Puerto Ayora, Santa Cruz, or endemic and 16 have become well established since such as Hasarius adansonii, Menemerus bivittatus their probably inadvertent introduction by man. and Plexippus paykulli (Fig. 1). Theridion rufipes, which lives both indoors and out and is often found INTRODUCED ARTHROPODS under the plank beds of tourist boats, tends to be carried from island to island. Latrodectus geometricus which V/hile a large proportion of arthropod species in I have only found under wooden seats at the Canal de Galápagos certainly colonized the islands naturally, Itabaca (Santa Cruz Island) and in the town of Puerto itis obvious that anumberhave been introduced since Baquerizo Moreno (San Cristóbal lsland) is another the islands were discovered and inhabited by humans. example of an introduced man-dependent spider. Kramer (1984) stated that the problem of introduced The true number of introduced species is difficult invertebrates, many of which may be man-dependent to assess because few extensive studies of arthropod immigrants, had not yet been and needed to be tack- groups in Galápagos have been published. However, led. Part of the problem was that it is often difficult it is known that 13 out of 18 cockroach species (Peck to know whether a non-endemic species was intro- and Roth, 1992),7 out of 8 Diplopod species (Shear duced by man or immigrated naturally. No doubts and Peck, 1981) and 10 out of 13 Chilopod species exist in the case of man-dependent immigrants, ex- (Shear and Peck, 1992) have been introduced to the amples of which are the spiders Heteropodavenatoria, islands by man. which inhabits almost every house in Galápagos, the Introduced species can negatively affect existing 18 NOTICIAS DE GALAPAGOS No.54 rapid spread of the introduced fire ant Wasmannia zuropunctata (Lubin, 1 984; 1 985). W. auropunctata was probably introduced to in- habited islands of Galápagos during the 1930s. In I97 5 , it was discovered on an uninhabited island at a camping area used by scientists. W. auropunctata is a tiny ant which lives in small colonies containing several queens and has a high level of swarming ac- tivity by which it disperses easily over large areas. The ants are highly aggressive and do not tolerate other invertebrates in their immediate vicinity. Areas infested by them undergo the loss of many endemic and native invertebrate species. This is especially true in the transition zoîe on Santa Cruz where they are most abundant.