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Comparative Study
, 13 (4), e0195492
eCollection

A Comparative Analysis of Terrestrial Arthropod Assemblages From a Relict Forest Unveils Historical Extinctions and Colonization Differences Between Two Oceanic Islands

Affiliations
Comparative Study

A Comparative Analysis of Terrestrial Arthropod Assemblages From a Relict Forest Unveils Historical Extinctions and Colonization Differences Between Two Oceanic Islands

Mário Boieiro et al. PLoS One.

Abstract

During the last few centuries oceanic island biodiversity has been drastically modified by human-mediated activities. These changes have led to the increased homogenization of island biota and to a high number of extinctions lending support to the recognition of oceanic islands as major threatspots worldwide. Here, we investigate the impact of habitat changes on the spider and ground beetle assemblages of the native forests of Madeira (Madeira archipelago) and Terceira (Azores archipelago) and evaluate its effects on the relative contribution of rare endemics and introduced species to island biodiversity patterns. We found that the native laurel forest of Madeira supported higher species richness of spiders and ground beetles compared with Terceira, including a much larger proportion of indigenous species, particularly endemics. In Terceira, introduced species are well-represented in both terrestrial arthropod taxa and seem to thrive in native forests as shown by the analysis of species abundance distributions (SAD) and occupancy frequency distributions (OFD). Low abundance range-restricted species in Terceira are mostly introduced species dispersing from neighbouring man-made habitats while in Madeira a large number of true rare endemic species can still be found in the native laurel forest. Further, our comparative analysis shows striking differences in species richness and composition that are due to the geographical and geological particularities of the two islands, but also seem to reflect the differences in the severity of human-mediated impacts between them. The high proportion of introduced species, the virtual absence of rare native species and the finding that the SADs and OFDs of introduced species match the pattern of native species in Terceira suggest the role of man as an important driver of species diversity in oceanic islands and add evidence for an extensive and severe human-induced species loss in the native forests of Terceira.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Species abundance distributions (SADs) for spiders and ground beetles from the native forests of Terceira and Madeira islands.
The best fit models (logseries in red triangles and PLN in blue squares) are plotted together with the empirical data. The number of native species is presented in green while the number of introduced species is shown in white. (A) SAD of Terceira ground beetles. (B) SAD of Madeira ground beetles. (C) SAD of Terceira spiders. (D) SAD of Madeira spiders.
Fig 2
Fig 2. Occupancy-frequency distributions (OFDs) for spiders and ground beetles from the native forests of Terceira and Madeira islands.
Overall species richness per occupancy class is shown in grey and the contribution of introduced species is highlighted in green. The mean and standard deviation of regional occupancy is shown together with the overall species richness (S) and the number of sampling units (n). (A) OFD of Terceira ground beetles. (B) OFD of Madeira ground beetles. (C) OFD of Terceira spiders. (D) OFD of Madeira spiders.
Fig 3
Fig 3. Evaluation of potential rare spider and ground beetle species from the native forests of Terceira and Madeira.
Potential rare species (i.e. low-abundance and range-restricted) were classified as tourists (red), microhabitat pseudo-rare species (green) and truly rare species (blue). The number of evaluated species (n) from each island and study group is also shown.

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Publication types

Grant support

The Fundação para a Ciência e a Tecnologia (https://www.fct.pt/) provided financial support through grants to MB (SFRH/BPD/86215/2012) and to CR (SFRH/BPD/91357/2012), and projects (PDCT/BIA-BDE/59202/2004, PTDC/BIA-BEC/99138/2008, PTDC/BIA-BEC/100182/2008) and UID/BIA/00329/2013. Direcção Regional dos Recursos Florestais dos Açores funded field work in Terceira (17.01-080203). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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