Browsing by Author "Triantis, Kostas A."
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- Adapting the IUCN red listing criteria for invertebratesPublication . Cardoso, Pedro; Borges, Paulo A. V.; Triantis, Kostas A.; Ferrández, Miguel A.; Martín, José L.The IUCN Red List is the most useful list of species that are at risk for extinction worldwide, as it relies on a number of objective criteria. Nevertheless, there is a taxonomic bias that excludes species with small body sizes, narrow distribution ranges and low dispersal abilities, which constitute the vast majority of the planet’s biota, particularly local endemics. By evaluating each IUCN criterion separately, we (i) identify the shortcomings for invertebrate applications, (ii) explain how risk categories may be wrongly applied due to inapplicable and/or misleading thresholds, (iii) suggest alternative ways of applying the existing criteria in a more realistic way and (iv) suggest possible new criteria that were not considered in the current evaluation framework but that could allow a more comprehensive and effective assessment of invertebrates. By adapting the criteria to rely more explicitly on the Area of Occupancy and the Extent of Occurrence, their respective trends and by using ecological modelling methods, the criteria’s applicability would be increased. The change in some thresholds or, eventually, the creation of sub-categories would further increase their adequacy. Additionally, co-extinction could be introduced as an explicit part of the classification process. As a case study, we evaluated 48 species of Azorean arthropods and Iberian spiders according to the current criteria. More than one-quarter (27%) of all evaluated species were classified as Critically Endangered, 19% as Endangered, 6% as Vulnerable and 8% as Least Concern. The remaining 40% did not have enough data to reach a classification.
- Are species-area relationships from entire archipelagos congruent with those of their constituent islands?Publication . Santos, Ana C.; Whittaker, Robert J.; Triantis, Kostas A.; Borges, Paulo A. V.; Jones, Owen R.; Quicke, Donald L. J.; Hortal, JoaquínAIM To establish the extent to which archipelagos follow the same species–area relationship as their constituent islands and to explore the factors that may explain departures from the relationship. LOCATION Thirty-eight archipelagos distributed worldwide. METHODS We used ninety-seven published datasets to create island species–area relationships (ISARs) using the Arrhenius logarithmic form of the power model. Observed and predicted species richness of an archipelago and of each of its islands were used to calculate two indices that determined whether the archipelago followed the ISAR. Archipelagic residuals (ArcRes) were calculated as the residual of the prediction provided by the ISAR using the total area of the archipelago, standardized by the total richness observed in the archipelago. We also tested whether any characteristic of the archipelago (geological origin and isolation) and/or taxon accounts for whether an archipelago fits into the ISAR or not. Finally, we explored the relationship between ArcRes and two metrics of nestedness. RESULTS The archipelago was close to the ISAR of its constituent islands in most of the cases analysed. Exceptions arose for archipelagos where (i) the slopes of the ISAR are low, (ii) observed species richness is higher than expected by the ISAR and/or (iii) distance to the mainland is small. The archipelago's geological origin was also important; a higher percentage of oceanic archipelagos fit into their ISAR than continental ones. ArcRes indicated that the ISAR underpredicts archipelagic richness in the least isolated archipelagos. Different types of taxon showed no differences in ArcRes. Nestedness and ArcRes appear to be related, although the form of the relationship varies between metrics. MAIN CONCLUSIONS Archipelagos, as a rule, follow the same ISAR as their constituent islands. Therefore, they can be used as distinct units themselves in large-scale biogeographical and macroecological studies. Departure from the ISAR can be used as a crude indicator of richness-ordered nestedness, responsive to factors such as isolation, environmental heterogeneity, number and age of islands.
- AVOTREX: A Global Dataset of Extinct Birds and Their TraitsPublication . Sayol, Ferran; Wayman, Joseph P.; Dufour, Paul; Martin, Thomas E.; Hume, Julian P.; Jørgensen, Maria Wagner; Martínez‐Rubio, Natàlia; Sanglas, Ariadna; Soares, Filipa C.; Cooke, Rob; Mendenhall, Chase D.; Margolis, Jay R.; Illera, Juan Carlos; Lemoine, Rhys; Benavides, Eva; Lapiedra, Oriol; Triantis, Kostas A.; Pigot, Alex L.; Tobias, Joseph A.; Faurby, Søren; Matthews, Thomas J.Motivation Human activities have been reshaping the natural world for tens of thousands of years, leading to the extinction of hundreds of bird species. Past research has provided evidence of extinction selectivity towards certain groups of species, but trait information is lacking for the majority of clades, especially for prehistoric extinctions identified only through subfossil remains. This incomplete knowledge potentially obscures the structure of natural communities, undermining our ability to infer changes in biodiversity across space and time, including trends in functional and phylogenetic diversity. Biases in currently available trait data also limit our ability to identify drivers and processes of extinction. Here we present AVOTREX, an open-access database of species traits for all birds known to have gone extinct in the last 130,000 years. This database provides detailed morphological information for 610 extinct species, along with a pipeline to build phylogenetic trees that include these extinct species. Main Types of Variables Contained For each extinct bird species, we provide information on the taxonomy, geographic location, and period of extinction. We also present data on island endemicity, flight ability, and body mass, as well as standard measurements of external (matching the AVONET database of extant birds) and skeletal morphology from museum specimens where available. To ensure comprehensive morphological data coverage, we estimate all missing morphological measurements using a data imputation technique based on machine learning. Finally, we provide an R package to graft all extinct species onto a global phylogeny of extant species (BirdTree).
- Comparative phylogeography of endemic Azorean arthropodsPublication . Parmakelis, Aristeidis; Rigal, François; Mourikis, Thanos; Balanika, Katerina; Terzopoulou, Sofia; Rego, Carla; Amorim, Isabel R.; Crespo, Luís C.; Pereira, Fernando E. A.; Triantis, Kostas A.; Whittaker, Robert J.; Borges, Paulo A. V.BACKGROUND: For a remote oceanic archipelago of up to 8 Myr age, the Azores have a comparatively low level of endemism. We present an analysis of phylogeographic patterns of endemic Azorean island arthropods aimed at testing patterns of diversification in relation to the ontogeny of the archipelago, in order to distinguish between alternative models of evolutionary dynamics on islands. We collected individuals of six species (representing Araneae, Hemiptera and Coleoptera) from 16 forest fragments from 7 islands. Using three mtDNA markers, we analysed the distribution of genetic diversity within and between islands, inferred the differentiation time-frames and investigated the inter-island migration routes and colonization patterns. RESULTS: Each species exhibited very low levels of mtDNA divergence, both within and between islands. The two oldest islands were not strongly involved in the diffusion of genetic diversity within the archipelago. The most haplotype-rich islands varied according to species but the younger, central islands contributed the most to haplotype diversity. Colonization events both in concordance with and in contradiction to an inter-island progression rule were inferred, while a non-intuitive pattern of colonization from western to eastern islands was also inferred. CONCLUSIONS: The geological development of the Azores has followed a less tidy progression compared to classic hotspot archipelagos, and this is reflected in our findings. The study species appear to have been differentiating within the Azores for <2 Myr, a fraction of the apparent life span of the archipelago, which may indicate that extinction events linked to active volcanism have played an important role. Assuming that after each extinction event, colonization was initiated from a nearby island hosting derived haplotypes, the apparent age of species diversification in the archipelago would be moved closer to the present after each extinction-recolonization cycle. Exploiting these ideas, we propose a general model for future testing.
- Development of 28 polymorphic microsatellite markers for the endemic Azorean spider Sancus acoreensis (Araneae, Tetragnathidae)Publication . Parmakelis, Aristeidis; Balanika, Katerina; Terzopoulou, Sofia; Rigal, François; Beasley, Rochelle R.; Jones, Kenneth L.; Lance, Stacey L.; Whittaker, Robert J.; Triantis, Kostas A.; Borges, Paulo A. V."We isolated and characterized a total of 28 microsatellite loci from Sancus acoreensis. Loci were screened in 26 individuals originating from seven (Flores, Faial, Pico, São Jorge, Terceira, São Miguel, and Santa Maria) out of the nine islands of the Azores. The number of alleles per locus ranged from 2 to 14, observed heterozygosity ranged from 0.040 to 0.708, and the probability of identity values ranged from 0.02 to 0.97. Sancus acoreensis is a Laurel forest specialist species, endemic to the Azores, and is facing a great extinction risk due to the severe fragmentation of its habitat. The newly developed microsatellite loci will aid in detecting signs of population bottlenecks and pinpoint the island populations that are facing the greatest risk of extinction. […]".
- Dispersal ability determines the scaling properties of species abundance distributions : a case study using arthropods from the AzoresPublication . Borda-de-Água, Luis; Whittaker, Robert J.; Cardoso, Pedro; Rigal, François; Santos, Ana M. C.; Amorim, Isabel R.; Parmakelis, Aristeidis; Triantis, Kostas A.; Pereira, Henrique M.; Borges, Paulo A. V.Species abundance distributions (SAD) are central to the description of diversity and have played a major role in the development of theories of biodiversity and biogeography. However, most work on species abundance distributions has focused on one single spatial scale. Here we used data on arthropods to test predictions obtained with computer simulations on whether dispersal ability influences the rate of change of SADs as a function of sample size. To characterize the change of the shape of the SADs we use the moments of the distributions: the skewness and the raw moments. In agreement with computer simulations, low dispersal ability species generate a hump for intermediate abundance classes earlier than the distributions of high dispersal ability species. Importantly, when plotted as function of sample size, the raw moments of the SADs of arthropods have a power law pattern similar to that observed for the SAD of tropical tree species, thus we conjecture that this might be a general pattern in ecology. The existence of this pattern allows us to extrapolate the moments and thus reconstruct the SAD for larger sample sizes using a procedure borrowed from the field of image analysis based on scaled discrete Tchebichef moments and polynomials.
- Drivers of diversity in Macaronesian spiders and the role of species extinctionsPublication . Cardoso, Pedro; Arnedo, Miquel A.; Triantis, Kostas A.; Borges, Paulo A. V.AIM To identify the biogeographical factors underlying spider species richness in the Macaronesian region and assess the importance of species extinctions in shaping the current diversity. LOCATION The European archipelagos of Macaronesia with an emphasis on the Azores and Canary Islands.
- Drivers of extinction : the case of Azorean beetlesPublication . Terzopoulou, Sofia; Rigal, François; Whittaker, Robert J.; Borges, Paulo A. V.; Triantis, Kostas A.Oceanic islands host a disproportionately high fraction of endangered or recently extinct endemic species. We report on species extinctions among endemic Azorean beetles following 97% habitat loss since AD 1440. We infer extinctions from historical and contemporary records and examine the influence of three predictors: geographical range, habitat specialization and body size. Of 55 endemic beetle species investigated (out of 63), seven can be considered extinct. Single-island endemics (SIEs) were more prone to extinction than multi-island endemics. Within SIEs restricted to native habitat, larger species were more extinction-prone. We thus show a hierarchical path to extinction in Azorean beetles: species with small geographical range face extinction first, with the larger bodied ones being the most threatened. Our study provides a clear warning of the impact of habitat loss on island endemic biotas.
- Extinction debt on oceanic islandsPublication . Triantis, Kostas A.; Borges, Paulo A. V.; Ladle, Richard J.; Hortal, Joaquín; Cardoso, Pedro; Gaspar, Clara; Dinis, Francisco; Pereira, Enésima; Silveira, Lúcia M. A.; Gabriel, Rosalina; Melo, Catarina; Santos, Ana M. C.; Amorim, Isabel R.; Ribeiro, Sérvio P.; Serrano, Artur R. M.; Quartau, José A.; Whittaker, Robert J.Habitat destruction is the leading cause of species extinctions. However, there is typically a time-lag between the reduction in habitat area and the eventual disappearance of the remnant populations. These “surviving but ultimately doomed” species represent an extinction debt. Calculating the magnitude of such future extinction events has been hampered by potentially inaccurate assumptions about the slope of species–area relationships, which are habitat- and taxon-specific. We overcome this challenge by applying a method that uses the historical sequence of deforestation in the Azorean Islands, to calculate realistic and ecologically-adjusted species–area relationships. The results reveal dramatic and hitherto unrecognized levels of extinction debt, as a result of the extensive destruction of the native forest:>95%, in<600 yr. Our estimations suggest that more than half of the extant forest arthropod species, which have evolved in and are dependent on the native forest, might eventually be driven to extinction. Data on species abundances from Graciosa Island, where only a very small patch of secondary native vegetation still exists, as well as the number of species that have not been found in the last 45 yr, despite the extensive sampling effort, offer support to the predictions made. We argue that immediate action to restore and expand native forest habitat is required to avert the loss of numerous endemic species in the near future.
- Functional biogeography of oceanic islands and the scaling of functional diversity in the AzoresPublication . Whittaker, Robert J.; Rigal, François; Borges, Paulo A. V.; Cardoso, Pedro; Terzopoulou, Sofia; Casanoves, Fernando; Pla, Laura; Guilhaumon, François; Ladle, Richard J.; Triantis, Kostas A.Analyses of species-diversity patterns of remote islands have been crucial to the development of biogeographic theory, yet little is known about corresponding patterns in functional traits on islands and how, for example, they may be affected by the introduction of exotic species. We collated trait data for spiders and beetles and used a functional diversity index (FRic) to test for nonrandomness in the contribution of endemic, other native (also combined as indigenous), and exotic species to functional-trait space across the nine islands of the Azores. In general, for both taxa and for each distributional category, functional diversity increases with species richness, which, in turn scales with island area. Null simulations support the hypothesis that each distributional group contributes to functional diversity in proportion to their species richness. Exotic spiders have added novel trait space to a greater degree than have exotic beetles, likely indicating greater impact of the reduction of immigration filters and/or differential historical losses of indigenous species. Analyses of species occurring in native-forest remnants provide limited indications of the operation of habitat filtering of exotics for three islands, but only for beetles. Although the general linear (not saturating) pattern of trait-space increase with richness of exotics suggests an ongoing process of functional enrichment and accommodation, further work is urgently needed to determine how estimates of extinction debt of indigenous species should be adjusted in the light of these findings.
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