Effect of island geological age on the arthropod species richness of Azorean pastures

Abstract

Species richness of six pasture arthropod assemblages (total arthropod species, total herbivore species, sucking and chewing herbivores, total predatory species and spiders) were regressed against several geographical variables (area, distance from the nearest mainland, maximum elevation and geological age of the islands) of three Azorean islands (S. Maria, Terceira and Pico). The species were sampled by the fixed-quadrat size sampling method and the results obtained are consistent with the geological age hypothesis, i.e. the species richness of the six indigenous arthropod assemblages increases with the geological age of the islands, both at local and regional scales. Higher values of indigenous and endemic species richness were consistently found on the older island (S. Maria), and the lowest values on the most recent island (Pico). Moreover, when considering the age of Faial (an older island probably once connected with Pico) as a estimate of the age of Pico, correlations between species richness and island age were improved, thereby strengthening the relationship. The older island (S. Maria) has more specialized herbivores and a greater proportion of herbivores in relation to predatory arthropods. Ecological and biogeographical studies in the Azores should take into account the effects of the time each island has been available for colonization and evolution.

Ranking protected areas in the Azores using standardised sampling of soil epigean arthropods

“…This study of Azorean arthropod biodiversity aimed to accomplish a standardised sampling of the arthropod fauna both at a local and regional scales in indigenous island ecosystems, each protected area being sampled with a constant transect size and a similar number of replicates. As the NFR have different areas and could be considered islands within true islands, this is one way of estimating the number of species when testing the species-area models (Holt 1992;Kohn and Walsh 1994;Borges and Brown 1999). Moreover, if the species-area equilibrium theory model fits the data, a given standard area should have more species on a large island than on a small island (Kohn and Walsh 1994;Rosenzweig 1995).…”

Estimating species richness of arthropods in azorean pastures: the adequacy of suction sampling and pitfall trapping

“…This is a common practice in biodiversity studies and does not compromise scientific accuracy (see Oliver & Beattie, 1996). However, in this study we were able to identify most taxa to species (see Borges, 1997;Borges & Brown, 1999). Identification of juvenile spiders is usually considered impossible (Churchill & Arthur, 1999), but since the Azorean pasture fauna is not particularly rich, most juveniles could be assigned to species.…”

“…We should expect a much higher number of phytophagous species related to predators than obtained and the explanation for this result is explained not by an inefficacy of sampling but by insular disharmony and geological age of the islands (see Borges & Brown, 1999).…”

“…Two replicates of recently sown (3 years old) and old semi-natural pasture (more than 30 years old) were sampled on three Azorean islands (S. Maria, Terceira and Pico). The replicates were standardised in terms of management history and were located distanced such that they could be considered as separate sites for statistical purposes (see Borges, 1997Borges, , 1999Borges & Brown, 1999, 2001 for a detailed description of sites).…”

“…In this paper, we aim to compare quantitatively two of the most widely employed methods, in respect of a wide range of insect taxa and spiders. It is also compared the efficacy of methods in different pasture types, known to have different arthropod guild structure and spider species richness (Borges, 1999;Borges & Brown, 1999).…”