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Gregory H. Adler - One of the best experts on this subject based on the ideXlab platform.
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Dispersal and speciation of skinks among Archipelagos in the tropical Pacific Ocean
Evolutionary Ecology, 1995Co-Authors: Gregory H. Adler, Christopher C. Austin, Robert DudleyAbstract:We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific Archipelagos. The entire tropical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found within more than one Archipelago) and endemic (found within only one Archipelago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 Archipelagos in the study area. Nine geographic variables reflecting Archipelago size, isolation and elevation were estimated for each Archipelago. Principal components analysis was used to reduce the nine variables to three uncorrelated composite variables that were interpreted as representing Archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an Archipelago were related to the composite geographic variables using multiple linear regression analysis. Archipelago size and isolation were important predictors of both skink diversity and endemism. Results were then compared to diversity and endemism of birds within the study area. Skinks showed an Archipelago-wide level of endemism similar to that of birds. On an Archipelago by Archipelago basis, however, large differences between birds and skinks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Marquesas were nearly completely endemic, while no endemic skinks occurred in these two Archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rates of colonization and speciation. Differences may also be due partly to morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as separate species. The discovery of such cryptic species, however, is unlikely to increase the endemic skink fauna of Hawaii and other distant Archipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ecological interactions.
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Dispersal and speciation of skinks in the tropical Pacific Ocean among Archipelagos
1995Co-Authors: Gregory H. Adler, Christopher C. Austin, Robert DudleyAbstract:Summary We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific Archipelagos. The entire tropical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found within more than one Archipelago) and endemic (found within only one Archipelago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 Archipelagos in the study area. Nine geographic variables reflecting Archipelago size, isolation and elevation were estimated for each Archipelago. Principal components analysis was used to reduce the nine variables to three uncorrelated composite variables that were interpreted as representing Archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an Archipelago were related to the composite geographic variables using multiple linear regression analysis. Archipelago size and isolation were important predictors of both skink diversity and endemism. Results were then compared to diversity and endemism of birds within the study area. Skinks showed an Archipelago-wide level of endemism similar to that of birds. On an Archipelago by Archipelago basis, however, large differences between birds and skinks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Marquesas were nearly completely endemic, while no endemic skinks occurred in these two Archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rates of colonization and speciation. Differences may also be due partly to morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as separate species. The discovery of such cryptic species, however, is unlikely to increase the endemic skink fauna of Hawaii and other distant Archipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ecological interactions.
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Endemism in birds of tropical Pacific islands
Evolutionary Ecology, 1992Co-Authors: Gregory H. AdlerAbstract:I analysed avifaunal data from 30 Archipelagos and isolated islands in the tropical Pacific Ocean to examine the effects of geography on endemism. I divided the total bird species list (pelagic and migrant species excluded) for each island group into continental (also found outside of the study area), Pacific (found only within the study area but within more than one Archipelago), and endemic (found only within a single Archipelago) species and estimated ten variables related to the geography of each Archipelago. I used multiple linear regression analysis to relate numbers and proportions of species in each category to the geographical variables. Total land area of an Archipelago was the most improtant variable in explaining variation in the number of species in each category, with elevation and isolation also being important. The relationships between the proportions of species in each category and the geographical variables underscore the importance of isolation and the number of large islands in promoting endemism, presumably by allowing both inter- and intra-archipelagal speciation to proceed.
K.a. Triantis - One of the best experts on this subject based on the ideXlab platform.
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A global model of island species–area relationships
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Thomas Matthews, F. Rigal, K.a. Triantis, Robert WhittakerAbstract:The increase in species richness with island area (ISAR) is a well-established global pattern, commonly described by the power model, the parameters of which are hypothesized to vary with system isolation and to be indicative of ecological process regimes. We tested a structural equation model of ISAR parameter variation as a function of taxon, isolation, and Archipelago configuration, using a globally distributed dataset of 151 ISARs encompassing a range of taxa and Archipelago types. The resulting models revealed a negative relationship between ISAR intercept and slope as a function of Archipelago species richness, in turn shaped by taxon differences and by the amount and disposition of Archipelago area. These results suggest that local-scale (intra-Archipelago) processes have a substantial role in determining ISAR form, obscuring the diversity patterns predicted by island theory as a function of Archipelago isolation. These findings have implications for the use and interpretation of ISARs as a tool within biogeography, ecology, and conservation.
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Archipelagos and meta-Archipelagos
Frontiers of Biogeography, 2018Co-Authors: Robert J Whittaker, F. Rigal, Jm Fernández-palacios, Thomas J. Matthews, K.a. TriantisAbstract:Author(s): Whittaker, Robert J.; Fernandez-Palacios, Jose M.; Matthews, Thomas J.; Rigal, Francois; Triantis, Kostas A. | Abstract: The term meta-Archipelago has been in use in cultural studies for some time, to refer to certain complex island areas in which the boundaries between conventionally recognised Archipelagos are indistinct, although the concept also carries additional connotations. Use of the term in biogeography appears more recent and without effort to prescribe its meaning. We outline, from a biogeographical perspective, distinctions between meta-Archipelagos and Archipelagos and those islands not occurring within either collective grouping, highlighting that network analysis tools provide metrics for formal analytical purposes.
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modeling directional spatio temporal processes in island biogeography
Ecology and Evolution, 2015Co-Authors: P. Cardoso, F. Rigal, K.a. Triantis, Jose Carvalho, P.a.v. BorgesAbstract:A key challenge in island biogeography is to quantity the role of dispersal in shaping biodiversity patterns among the islands of a given Archipelago. Here, we propose such a framework. Dispersal within oceanic Archipelagos may be conceptualized as a spatio-temporal process dependent on: (1) the spatial distribution of islands, because the probability of successful dispersal is inversely related to the spatial distance between islands and (2) the chronological sequence of island formation that determines the directional asymmetry of dispersal (hypothesized to be predominantly from older to younger islands). From these premises, directional network models may be constructed, representing putative connections among islands. These models may be translated to eigenfunctions in order to be incorporated into statistical analysis. The framework was tested with 12 datasets from the Hawaii, Azores, and Canaries. The explanatory power of directional network models for explaining species composition patterns, assessed by the Jaccard dissimilarity index, was compared with simpler time-isolation models. The amount of variation explained by the network models ranged from 5.5% (for Coleoptera in Hawaii) to 60.2% (for Pteridophytes in Canary Islands). In relation to the four studied taxa, the variation explained by network models was higher for Pteridophytes in the three Archipelagos. By the contrary, small fractions of explained variation were observed for Coleoptera (5.5%) and Araneae (8.6%) in Hawaii. Time-isolation models were, in general, not statistical significant and explained less variation than the equivalent directional network models for all the datasets. Directional network models provide a way for evaluating the spatio-temporal signature of species dispersal. The method allows building scenarios against which hypotheses about dispersal within Archipelagos may be tested. The new framework may help to uncover the pathways via which species have colonized the islands of a given Archipelago and to understand the origins of insular biodiversity.
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Modeling directional spatio-temporal processes in island biogeography
Ecology and Evolution, 2015Co-Authors: J.c. Carvalho, P. Cardoso, F. Rigal, K.a. Triantis, P.a.v. BorgesAbstract:A key challenge in island biogeography is to quantity the role of dispersal in shaping biodiversity patterns among the islands of a given Archipelago. Here, we propose such a framework. Dispersal within oceanic Archipelagos may be conceptualized as a spatio-temporal process dependent on: (1) the spatial distribution of islands, because the probability of successful dispersal is inversely related to the spatial distance between islands and (2) the chronological sequence of island formation that determines the directional asymmetry of dispersal (hypothesized to be predominantly from older to younger islands). From these premises, directional network models may be constructed, representing putative connections among islands. These models may be translated to eigenfunctions in order to be incorporated into statistical analysis. The framework was tested with 12 datasets from the Hawaii, Azores, and Canaries. The explanatory power of directional network models for explaining species composition patterns, assessed by the Jaccard dissimilarity index, was compared with simpler time-isolation models. The amount of variation explained by the network models ranged from 5.5% (for Coleoptera in Hawaii) to 60.2% (for Pteridophytes in Canary Islands). In relation to the four studied taxa, the variation explained by network models was higher for Pteridophytes in the three Archipelagos. By the contrary, small fractions of explained variation were observed for Coleoptera (5.5%) and Araneae (8.6%) in Hawaii. Time-isolation models were, in general, not statistical significant and explained less variation than the equivalent directional network models for all the datasets. Directional network models provide a way for evaluating the spatio-temporal signature of species dispersal. The method allows building scenarios against which hypotheses about dispersal within Archipelagos may be tested. The new framework may help to uncover the pathways via which species have colonized the islands of a given Archipelago and to understand the origins of insular biodiversity. © 2015 The Authors.
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accounting for data heterogeneity in patterns of biodiversity an application of linear mixed effect models to the oceanic island biogeography of spore producing plants
Ecography, 2013Co-Authors: Jairo Patino, K.a. Triantis, Francois Guilhaumon, Robert J Whittaker, Robbert S Gradstein, Lars Hedenas, Juana Maria Gonzalezmancebo, Alain VanderpoortenAbstract:The general dynamic model of oceanic island biogeography describes the evolution of species diversity properties, including species richness (SR), through time. We investigate the hypothesis that SR in organisms with high dispersal capacities is better predicted by island area and elevation (as a surrogate of habitat diversity) than by time elapsed since island emergence and geographic isolation. Linear mixed effect models (LMMs) subjected to information theoretic model selection were employed to describe moss and liverwort SR patterns from 67 oceanic islands across 12 Archipelagos. Random effects, which are used to modulate model parameters to take differences among Archipelagos into account, included only a random intercept in the best-fit model for liverworts and in one of the two best-fit models for mosses. In this case, the other coefficients are constant across Archipelagos, and we interpret the intercept as a measure of the intrinsic carrying capacity of islands within each Archipelago, independently of their size, age, elevation and geographic isolation. The contribution of area and elevation to the models was substantially higher than that of time, with the least contribution made by measures of geographic isolation. This reinforces the idea that oceanic barriers are not a major impediment for migration in bryophytes and, together with the almost complete absence of in situ insular diversification, explains the comparatively limited importance of time in the models. We hence suggest that time per se has little independent role in explaining bryophyte SR and principally features as a variable accounting for the changing area and topographic complexity during the life-cycle of oceanic islands. Simple area models reflecting habitat availability and diversity might hence prevail over more complex temporal models reflecting in-situ speciation and dispersal (time, geographic connectivity) in explaining patterns of biodiversity for exceptionally mobile organisms.
Robert Dudley - One of the best experts on this subject based on the ideXlab platform.
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Dispersal and speciation of skinks among Archipelagos in the tropical Pacific Ocean
Evolutionary Ecology, 1995Co-Authors: Gregory H. Adler, Christopher C. Austin, Robert DudleyAbstract:We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific Archipelagos. The entire tropical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found within more than one Archipelago) and endemic (found within only one Archipelago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 Archipelagos in the study area. Nine geographic variables reflecting Archipelago size, isolation and elevation were estimated for each Archipelago. Principal components analysis was used to reduce the nine variables to three uncorrelated composite variables that were interpreted as representing Archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an Archipelago were related to the composite geographic variables using multiple linear regression analysis. Archipelago size and isolation were important predictors of both skink diversity and endemism. Results were then compared to diversity and endemism of birds within the study area. Skinks showed an Archipelago-wide level of endemism similar to that of birds. On an Archipelago by Archipelago basis, however, large differences between birds and skinks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Marquesas were nearly completely endemic, while no endemic skinks occurred in these two Archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rates of colonization and speciation. Differences may also be due partly to morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as separate species. The discovery of such cryptic species, however, is unlikely to increase the endemic skink fauna of Hawaii and other distant Archipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ecological interactions.
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Dispersal and speciation of skinks in the tropical Pacific Ocean among Archipelagos
1995Co-Authors: Gregory H. Adler, Christopher C. Austin, Robert DudleyAbstract:Summary We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific Archipelagos. The entire tropical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found within more than one Archipelago) and endemic (found within only one Archipelago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 Archipelagos in the study area. Nine geographic variables reflecting Archipelago size, isolation and elevation were estimated for each Archipelago. Principal components analysis was used to reduce the nine variables to three uncorrelated composite variables that were interpreted as representing Archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an Archipelago were related to the composite geographic variables using multiple linear regression analysis. Archipelago size and isolation were important predictors of both skink diversity and endemism. Results were then compared to diversity and endemism of birds within the study area. Skinks showed an Archipelago-wide level of endemism similar to that of birds. On an Archipelago by Archipelago basis, however, large differences between birds and skinks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Marquesas were nearly completely endemic, while no endemic skinks occurred in these two Archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rates of colonization and speciation. Differences may also be due partly to morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as separate species. The discovery of such cryptic species, however, is unlikely to increase the endemic skink fauna of Hawaii and other distant Archipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ecological interactions.
Kimmo K. Kahma - One of the best experts on this subject based on the ideXlab platform.
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The wave spectrum in Archipelagos
Ocean Science, 2019Co-Authors: Jan-victor Björkqvist, Heidi Pettersson, Kimmo K. KahmaAbstract:Abstract. Sea surface waves are important for marine safety and coastal engineering, but mapping the wave properties at complex shorelines, such as coastal Archipelagos, is challenging. The wave spectrum, E(f) , contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in Archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish Archipelago. The shape of the wave spectrum showed a systematic transition from a single-peaked spectrum to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the Archipelago was H 1 / 3 = 0.881 H s , but the ratio varied with the spectral width ( Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax∕Hs , was only 1.58. A wider Archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges caused by the instability of the peak frequency for an Archipelago spectrum are presented, and the mean frequency, weighted with E(f)4 , is proposed as a compromise between stability and bias with respect to the peak frequency. The possibility of using the frequency and width parameters of this study as a starting point for a new analytical parameterisation of an Archipelago type spectrum is discussed.
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The wave spectrum in Archipelagos
2019Co-Authors: Jan-victor Björkqvist, Heidi Pettersson, Kimmo K. KahmaAbstract:Abstract. Sea surface waves are important for marine safety and coastal constructions, but mapping the wave properties at complex shorelines, such as coastal Archipelagos, is challenging. The wave spectrum, E(f), contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in Archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish Archipelago. The shape of the wave spectrum showed a systematic transition from a single peaked spectrum, to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the Archipelago was H1/3 = 0.881 Hs, but the ratio varied with the spectral width (Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax/Hs, was only 1.58. A wider Archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges regarding the instability of the peak frequency and the difficulties in finding a good characteristic frequency for an Archipelago spectrum is discussed. The mean frequency, weighted with E(f)4, is proposed as a compromise between stability, and bias with respect to the peak frequency.
Robert Whittaker - One of the best experts on this subject based on the ideXlab platform.
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A global model of island species–area relationships
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Thomas Matthews, F. Rigal, K.a. Triantis, Robert WhittakerAbstract:The increase in species richness with island area (ISAR) is a well-established global pattern, commonly described by the power model, the parameters of which are hypothesized to vary with system isolation and to be indicative of ecological process regimes. We tested a structural equation model of ISAR parameter variation as a function of taxon, isolation, and Archipelago configuration, using a globally distributed dataset of 151 ISARs encompassing a range of taxa and Archipelago types. The resulting models revealed a negative relationship between ISAR intercept and slope as a function of Archipelago species richness, in turn shaped by taxon differences and by the amount and disposition of Archipelago area. These results suggest that local-scale (intra-Archipelago) processes have a substantial role in determining ISAR form, obscuring the diversity patterns predicted by island theory as a function of Archipelago isolation. These findings have implications for the use and interpretation of ISARs as a tool within biogeography, ecology, and conservation.
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Beyond the Last Glacial Maximum: Island endemism is best explained by long-lasting Archipelago configurations
Global Ecology and Biogeography, 2019Co-Authors: Sietze Norder, F. Florens, Konstantinos Proios, Robert Whittaker, María Alonso, Paulo Borges, Michael Borregaard, Robert Cowie, António De Frias Martins, Miguel IbáñezAbstract:Aim: To quantify the influence of past Archipelago configuration on present-day insular biodiversity patterns, and to compare the role of long-lasting Archipelago configurations over the Pleistocene to configurations of short duration such as at the Last Glacial Maximum (LGM) and the present-day. Location: 53 volcanic oceanic islands from 12 Archipelagos worldwide—Azores, Canary Islands, Cook Islands, Galápagos, Gulf of Guinea, Hawaii, Madeira, Mascarenes, Pitcairn, Revillagigedo, Samoan Islands and Tristan da Cunha. Time period: The last 800 kyr, representing the nine most recent glacial–interglacial cycles. Major taxa studied: Land snails and angiosperms. Methods: Species richness data for land snails and angiosperms were compiled from existing literature and species checklists. We reconstructed Archipelago configurations at the following sea levels: the present-day high interglacial sea level, the intermediate sea levels that are representative of the Pleistocene and the low sea levels of the LGM. We fitted two alternative linear mixed models for each Archipelago configuration using the number of single-island endemic, multiple-island endemic and (non-endemic) native species as a response. Model performance was assessed based on the goodness-of-fit of the full model, the variance explained by Archipelago configuration and model parsimony. Results: Single-island endemic richness in both taxonomic groups was best explained by intermediate palaeo-configuration (positively by area change, and negatively by palaeo-connectedness), whereas non-endemic native species richness was poorly explained by palaeo-configuration. Single-island endemic richness was better explained by intermediate Archipelago configurations than by the Archipelago configurations of the LGM or present-day. Main conclusions: Archipelago configurations at intermediate sea levels—which are representative of the Pleistocene—have left a stronger imprint on single-island endemic richness patterns on volcanic oceanic islands than extreme Archipelago configurations that persisted for only a few thousand years (such as the LGM). In understanding ecological and evolutionary dynamics of insular biota it is essential to consider longer-lasting environmental conditions, rather than extreme situations alone.
