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Although research on environmental gradients is relatively common, the altitudinal gradient is one of the least explored. The discrepancies between earlier studies attributing highest diversity to lowest altitude and more recent studies where this altitudinal pattern is not maintained justify the pertinence of investigating the way diversity gradually changes with altitude. The studied altitudinal gradient is located inside the volcanic cone, on one of volcanic island Azores, and the investigated altitudes were 450, 600 and 800 meters a.s.l. Malaise traps were used to capture insects and Diptera were selected for this study. Application of the Zipt-Mandelbrot model to rank-abundance curves of Diptera sampled at three different altitudes, as well as analyses of richness, diversity and evenness, led to the conclusion that medium altitude was the stratum with the highest niche diversity, the highest specific diversity and the highest predictability. Non-metric multidimensional scaling allowed an excellent separation of the three altitudes sampled, suggesting that habitat characteristics significantly differ with altitude. The study, undertaken in a volcanic island of the Azores, Atlantic Ocean, will have heuristic interest to the scientific community in general and especially to those researchers studying environmental gradients. The results of this research will underpin further work on the insect biodiversity in the Azores Archipelago.
Content available remote The fossil echinoids of Santa Maria Island, Azores (Northern Atlantic Ocean)
In the relatively young archipelago of the Azores, fossiliferous deposits are restricted to the oldest island (Santa Maria), mainly from late Miocene.early Pliocene deposits, and a few from the Pleistocene. echinoid material collected from these deposits comprises mainly disarticulated skeletal material (primary spines and coronal fragments) and a few complete tests. The taxa present in the Upper Miocene to lower Pliocene beds comprise Eucidaris tribuloides, Echinoneus cf. cyclostomus, Clypeaster altus, Echinocyamus pusillus, Echinocardium sp. 1, Echinocardium sp. 2, Schizobrissus sp. and undetermined spatangoids. The spatangoids and E. cf. cyclostomus, are new records for the Miocene.Pliocene strata of the island. The material collected from Upper Pleistocene outcrops (MISS 5e) included three regular echinoid species, Sphaerechinus granularis, Arbacia lixula and Paracentrotus lividus. The two latter species are recorded for the first time from the Pleistocene deposits of the island. Compared to the older deposits, the Pleistocene record represents a very narrow range of environments and is basically restricted to deposits associated with an ancient rocky shore. Moreover, the conspicuous presence of taxa typical of tropical seas in the Mio-Pliocene sediments contrasts with the Pleistocene and modern echinoid fauna, which is warm temperate in composition.
Novocrania turbinata (POLI, 1795) is documented from the Early Pliocene strata of Santa Maria Island (Azores, Portugal), extending the range of this species to the central Northern Atlantic Ocean. This record increases the meagre brachiopod fauna known from the Pliocene of the Azores, which so far consisted only of Terebratulina retusa (LINNAEUS, 1758). It may also represent an example of a thermophilic species that disappeared locally due to Late Pliocene-Pleistocene climate deterioration.
A holoplanktonic mollusc assemblage from Neogene sediments of the Azorean island Santa Maria is described and analysed to determine the age of the sediments. Sixteen taxa are documented (three heteropods, thirteen pteropods), fourteen of which are new records for the fossil fauna of Santa Maria Island. The composition of the heteropod and pteropod assemblage indicates a Zanclean age, which contrasts with earlier age assignments to the Early, Middle or Late Miocene based on benthic molluscs, but is in good agreement with more recent data based on foraminiferal and geochemical evidence. The pteropod Cavolinia marginata (BRONN, 1862) is re-described based on abundant topotypic material and a neotype is designated. The species Cavolinia vendryesiana (GUPPY, 1873) is considered to be a junior subjective synonym of C. marginata. The temporal range of the pteropod Limacina trochiformis (D.ORBIGNY, 1836) is extended to the Zanclean.
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