The Geographical and Ecological Distribution of Arboreal Psocoptera

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Annu. Rev. Entomol. 1985.30:175-196. Downloaded from arjournals.annualreviews.org by Mr. Bas van Berkum on 10/10/07. For personal use only. Annual Reviews www.annualreviews.org/aronline 188 THORNTON between 2440 and 3200 m. Mesopsocus montanus, found in the Erica zone (3320-3660 m), occurs at similar heights on Kilimanjaro. The effect of altitude on psocid distribution can perhaps best be examined by studying the fauna of a single tree species that has a sufficiently wide altitudinal range. On mango in Jamaica an increase in diversity of 3.3 species per 300 m increase in altitude from 150 to 1220 m was found (100). Over this range more high-altitude stenotopes were added as species were replaced by close relatives at successively higher, less disturbed habitats. About 95% of the high altitude stenotopes were endemic, in contrast to 50% of those from regions below about 600 m. Such confinement of endemics to native highland vegetation is common on many tropical islands. As in the Hagenia zone of Mount Kenya, psocids were extremely sparse in Jamaica from 1200 to 2300 m; at these altitudinal ranges, humidities are extremely high and bryophytes and hymenophyllous ferns replace the lichens of the lower sclerophyll forest. A marked reduction in psocid numbers and diversity is also characteristic of mountain tops with wet conditions and epiphytic mosses in many parts of the Pacific. On mango in Trinidad the psocid fauna was more diverse, but the same general trends were apparent over the range of altitudes studied (0 to 610 m) (19). In Yorkshire, England, the fauna of larch was studied from near sea level to 400 m (16). In contrast to the Caribbean studies, no change in species numbers or species replacement was found, but density increased markedly with altitude. Mesopsocus unipunctatus was found to occur at both low and high elevations (above 260 m), whereas its close relative M. immunis, believed to be at the northern end of its range, was confined to lower altitudes. Greater winter loss of egg batches and greater sensitivity to low temperatures in regard to oviposition were suggested as possible critical factors in deternfining the absence of M. immunis from the higher forests (23). Elipsocus mclachlani, a facultative lichen feeder, was found only above 200 m, but the six other common species were eurytopic. On Kauai Island, Hawaiian Islands, I collected some 34 species from Acacia koa from 500 to 1200 m on the Kokee massif over a period of a few days. Of these, seven could be considered eurytopic (occurring from 650 to 1200 m) six were only taken from 800 to 950 m, nine from 800 to 1200 m (four most common at 1200 m), and nine only on the Kokee plateau at about 1200 m. Eight of the high altitude stenotopes were endemics, including all five species of the endemic genus Palistreptus found in this transect. TREES AS HABITATS There is evidence that the psocid faunal spectrum on trees varies considerably according to the type and species of tree, even in the same locality. Tree "preferences" In Europe, a broad division between associations on coniferous and broad-leaved trees is generally accepted. Although similar in
Annu. Rev. Entomol. 1985.30:175-196. Downloaded from arjournals.annualreviews.org by Mr. Bas van Berkum on 10/10/07. For personal use only. Annual Reviews www.annualreviews.org/aronline DISTRIBUTION OF ARBOREAL PSOCOPTERA 189 psocid diversity, these types of tree generally differ in species spectrum, and "conifer species" and "broad-leaved species" of psocids can be identified. In North America there is evidence (40) that natural species groups Caecilius occur predominantly on particular vegetation types, such as grasses, sedges, palms, conifers, and broad-leaved trees. In Brazil, a "preference" for the dead fronds arid leaf bases of palms has been noted for some predominantly litter-frequenting epipsocids (60), and three closely related species of Lachesilla appear to be extremely closely associated with Syagrus palms (59, 61). Various other species are probably palmicolous in other parts of the world and, in Caecilius, may be more closely related to those frequenting grasses and sedges than to those frequenting other trees (40). In a 16-ha area near Sydney, Australia, Smithers (76) found that the different vegetation types supported different associations of psocopterans. Of the 43 species present, three were found predominantly on Casuarina spp., three on bracken, two on Maclura pomifera. One was restricted to a sandstone shrub layer, and five to a small patch of depauperate rain forest. Within the general categories of coniferous and broad-leaved trees, "preferences" for particular tree species have been noted (22, 30, 33, 58, 67, 91). For example, of three closly related Elipsocus species at Malham, Yorkshire, E. mclachlani predominated on larch, E. westwoodi on hawthorn, and E. hyalinus on sallow and spruce. In Jamaica, weekly samples taken from Juniperus and Podocarpus at 1200 m over a period of 10 months revealed that seven of the eight most common psocids predominated on one or the other tree species. A striking preference for juniper was seen in Peripsocus juniperi (3787 individuals, to 43 on Podocarpus) while the reverse preference was clear in Caecilius pallidobrunneus (72:2714) and H emipsocus roseus (4:1197). These trees offer very different substrates; for example, the needles of Podocarpus are broad and flattened, in contrast to those of juniper. Turner (91) suggested food requirements, differential protection from rain, and the structural features of the needles, which on Podocarpus may favor normally leaf-inhabiting species such as H. roseus, as factors that may affect the observed preferences. New (58) showed that the natural movement of Betula and Populus leaves in southern England inhibits settling by foliicolous psocid species such as Caeciliusflavidus. Such species lay eggs on leaves, which become widely scattered in autumn, and overwinter in leaf litter where the spring generation is passed. The adults then fly up to the trees. Settlement at this time is thus a crucial completion of the life cycle. Surface texture of leaves, which varies between tree species, was also shown to affect their suitability as oviposition sites for three psocids, and the distribution and size of leaf hairs apparently affect the availability of food to young psocid nymphs. The amount and kind of food carried on leaves of different trees differs: some trees develop distinctive crops of microepiphytes as the season progresses.
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The Geographical and Ecological Distribution of Arboreal Psocoptera

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