Biotic integrity of the arthropod communities in the natural forests of Azores

Abstract

The loss of biotic integrity in ecosystems due to human pressure has been receiving much attention from the scientific community. The primary aim of this study is to understand how the increasing human pressure on natural forests in the Azorean archipelago (North Atlantic) is affecting their epigean arthropod communities and which biological parameters it affects most. An expert team did fieldwork covering most of the natural forests (mainly inside nature reserves) of the archipelago using standardized pitfall trapping. To build a multimetric index we tested a number of taxonomic and ecological parameters that can potentially be influenced by disturbance. Sixteen of these were found to be significantly influenced by disturbance in forests. We retained seven metrics due to both, desirable scalability properties and relatively low correlation between them. These included the percentages of endemic and predator species richness and also predator abundance, which are inversely related to disturbance; and the percentages of native and saprophagous species richness and introduced and herbivore abundance, which are positively related to disturbance. All seven metrics were combined in an Index of Biotic Integrity (IBI) value. We then proceeded to understand which potential disturbance factors are influencing the biotic integrity of communities and how such influence is felt. Five disturbance factors were found to influence the IBI, although in different ways: the size and fragmentation of reserves, the distance of sites to the reserve borders, the invasion by alien plants and the density of human paths at the sites. Given that only percentages of taxonomical or ecological characteristics were chosen as metrics, we tested and found the scalability of the IBI to be possible, allowing the comparison of sites with different collecting effort or even the comparison of reserves with different areas and numbers of collecting sites in each. Finally, we propose a novel graphical representation for multimetric indices like the IBI, one which allows retaining much of the information that is usually lost in multimetric indices.

Selection of priority areas for arthropod conservation in the Azores archipelago

“…Previous studies in some of these small patches indicate that they have a poor native fauna with a high occurrence of introduced species (Borges et al unpublished data), so these fragments were not considered in this study. Native forest fragments vary in area (Table 1), isolation from the nearest fragments, geological age of soil (lava) substrate, altitude, plant species composition and structure (see Gaspar et al 2008 for more details), and also in their biotic integrity (as defined by Cardoso et al 2007). Terceira island alone contains almost half of the total area of native forest cover of the archipelago ( Table 1).…”

“…This may help to decide which optimal solution to choose and thus reduce the risk of a set of priority areas being considered ineffective after it has been implemented for conservation action. The biotic integrity index (IBI) developed by Cardoso et al (2007) was calculated for each forest fragment studied. This index was created based on the epigean arthropods of the Azorean native forests by determining biotic parameters that could be highly influenced by disturbance.…”

A spatial scale assessment of habitat effects on arthropod communities of an oceanic island

“…The fragments, varying in size from 4 to 1000 ha, are often disturbed by the invasion of introduced species (Silva and Smith, 2004;Borges et al, 2006). This disturbance is also reflected in the varying values of biotic integrity that arthropod communities across natural forest fragments present (Cardoso et al, 2007).…”

Assessing the completeness of bryophytes inventories: an oceanic island as a case study (Terceira, Azorean archipelago)

“…The observed spatial bias indicates that the zone of major interest for bryologists has traditionally been the central part of the island where the most luxuriant laurel forests are believed to remain from the Tertiary. In contrast, we show that the best regions to recent discoveries of new species are concentrated toward the westernmost extensive forests of Juniperus brevifolia and Laurus azorica inside the Caldeira de Santa Bárbara, an area which has also been recognised as a genuine bryologist's paradise (Frahm 2004) and is considered to be one of the most undisturbed native forests of the Azores (Cardoso et al 2007). It is obvious that bryologists preferably collected in native forest environments (4,974 database-records, about 60% of all gathered information), and that this tendency will continue in the future.…”