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45 results for “island assemblages”
Determinants of Reef Fish Assemblages on Tropical Oceanic Islands
<p><strong>ABSTRACT</strong></p> <p>Diversity patterns are determined by biogeographic, energetic, and anthropogenic factors, yet few studies have combined them into a large-scale framework in order to decouple and compare their relative effects on fish faunas. Using an empirical dataset derived from 1527 underwater visual censuses (UVC) at 18 oceanic islands (five different marine provinces), we determined the relative influence of such factors on reef fish species richness, functional dispersion, density and biomass estimated from each UVC unit. Species richness presented low variation but was high at large island sites. High functional dispersion, density, and biomass were found at islands with large local species pool and distance from nearest reef. Primary productivity positively affected fish richness, density and biomass confirming that more productive areas support larger populations, and higher biomass and richness on oceanic islands. Islands densely populated by humans had lower fish species richness and biomass reflecting anthropogenic effects. Species richness, functional dispersion, and biomass were positively related to distance from the mainland. Overall, species richness and fish density were mainly influenced by biogeographical and energetic factors, whereas functional dispersion and biomass were strongly influenced by anthropogenic factors. Our results extend previous hypotheses for different assemblage metrics estimated from empirical data and confirm the negative impact of humans on fish assemblages, highlighting the need for conservation of oceanic islands.</p> <p><strong><em>Keywords:</em></strong> species richness, functional dispersion, density, fish biomass, biogeographic factors, energetic factors, anthropogenic factors, marine provinces<em>.</em></p>
Figure 1 in Life in the extreme environment: Structure and species richness of bird assemblages on Yuzhny Island of Novaya Zemlya, Russia
Figure 1. Study region on Yuzhny Island of Novaya Zemlya. (A) Map of Novaya Zemlya. The yellow circle indicates the study region of Yuzhny Island. (B) Detailed map of the study region with the location of counting routes. The shaded area represents the study area (1). The dashed red lines indicate the counting routes (2). The dashed black line indicates the helicopter route (3).
Figure 4 in Life in the extreme environment: Structure and species richness of bird assemblages on Yuzhny Island of Novaya Zemlya, Russia
Figure 4. Relative bird species abundance (log10 scale) over habitat patches on Yuzhny Island of Novaya Zemlya. Numbers of (01) – (10) are the codes of the habitat types. Differences between assemblages were all significant (Kruskal-Wallis test: p = 0.003). Images show habitat types; numbers indicate their codes (see Table 2 for detail). (Photos: V. M. Spitsyn).
Figure 3 in Life in the extreme environment: Structure and species richness of bird assemblages on Yuzhny Island of Novaya Zemlya, Russia
Figure 3. Species diversity of bird assemblages on Yuzhny Island of Novaya Zemlya. (A) Bi-plot of detrended correspondence analysis (DCA) with supplementary variables, showing the ordination of species and environmental variables. Circles indicate bird species abundance (categorical estimations by using a logarithmic scale, see Table 3), abundances decrease with increasing distance from each point in a unimodal fashion (ter Braak and Smilauer, 2002). Data represent independent samples from various habitats (n = 10). Total variation is 2.44, supplementary variables account for 66.1% (adjusted explained variation is 23.8%). Eigenvalues (lambda) are 0.675, 0.162, 0.069, and 0.025 for first (horizontal), second (vertical), third and fourth axes, respectively. The first two axes explain 34.4% of the variation. The pseudo-canonical correlations of bird abundance and environmental variables for axes 1 and 2 are 0.77 and 0.91, respectively. For an explanation of environmental variables, see Table 4. For abbreviations of species names see Fig. 4. (B) Bi-plot of the same analysis revealing the ordination of species richness over a range of habitats and environmental variables. Circles indicate bird assemblages in primary types of habitats (size of each circle corresponds to the number of bird species). The red numbers near the circles indicate species richness. The black numbers near the circles (01–10) indicate the codes of habitat types (see Fig. 4 and Table 2 for detail).
An assemblage-level comparison of genetic diversity and population genetic structure between island and mainland ant populations
<p>Island biotas provide unparalleled opportunities to examine evolutionary processes. Founder effects and bottlenecks, for example, typically decrease genetic diversity in island populations, while selection for reduced dispersal can increase population structure. Given that support for these generalities mostly comes from single-species analyses, assemblage-level comparisons are needed to clarify how (i) colonization affects the gene pools of interacting insular organisms, and (ii) patterns of genetic differentiation vary within assemblages of organisms. Here, we use genome-wide sequence data from ultraconserved elements (UCEs) to compare genetic diversity and population structure of mainland and island populations of nine ant species in coastal southern California with respect to genetic diversity and population structure. As expected, island populations (from Santa Cruz Island) had lower than expected heterozygosity and Watterson's theta compared to mainland populations (from the Lompoc Valley). Island populations, however, exhibited smaller genetic distances among samples, indicating less population subdivision and a higher capacity for dispersal compared to mainland populations. Within the focal assemblage, pairwise F<sub>st</sub> values revealed pronounced interspecific variation in mainland-island differentiation, which increases with gyne body size. Our results reveal differences in genetic diversity and population genetic structure across an assemblage of interacting species, and illuminate general patterns of insularization in ants. Compared to single-species studies, our analysis of nine species pairs from the same island-mainland system offers a powerful approach to studying fundamental evolutionary processes.</p>
Figure 1 in Spider assemblages and dynamics on a seasonal island in the Pripyat River, Belarus
Figure 1. Location of the study area – Belarus, the Turov Meadows at the Pripyat River (●).
Figure 1 in Fish larvae assemblages of Gökçeada Island, North Aegean Sea: effect of weekly sampling interval on their incidences
Figure 1. Map of the sampling location on Gökçeada Island, North Aegean Sea.
Figure 2 in Fish larvae assemblages of Gökçeada Island, North Aegean Sea: effect of weekly sampling interval on their incidences
Figure 2. Temporal variations of sea surface temperature and salinity at the sampling location.
Figure 3 in Fish larvae assemblages of Gökçeada Island, North Aegean Sea: effect of weekly sampling interval on their incidences
Figure 3. Temporal variations of Shannon_H biodiversity indices and dominance.
The role of island physiography and oceanographic factors in shaping species richness and turnover of nesting seabird assemblages on islands across the southeastern Pacific
<p>For seabirds, food supplies and nest sites are largely driven by oceanographic gradients and island habitats, respectively. Research into seabirds' ecological roles in insular ecosystems is crucial to understanding processes that structure seabird nesting assemblages. We examined the influence of island physiography and oceanographic factors on the spatial variation in α and β-diversity of nesting seabird assemblages.<br> <br> <strong>Location</strong><br> Southeastern Pacific Ocean.<br> <br> <strong>Taxon</strong><br> Birds<br> <br> <strong>Methods</strong><br> We compiled data from 53 seabirds breeding on 41 coastal and oceanic islands using different sources: our field records, online databases, environmental reports, and literature. We used generalized linear models (GLM) to describe the effect of island physiography (area, elevation, and isolation) and oceanographic factors (surface temperature, salinity, and primary productivity) on seabird species richness (α-diversity). We applied multivariate GLM to test the effects of physiographic and oceanographic predictors on species composition (β-diversity). We used Jaccard dissimilarities on species occurrences per island to calculate β-diversity partitioned into turnover and nestedness. Polynomial models allowed us to model these metrics against geographical and environmental gradients and so analyze patterns in seabird β-diversity across spatial scales.<br> <br> <strong>Results </strong><br> Species richness was highest in Galápagos, Pitcairn, and Rapa Nui. Changes in seabird α-diversity across islands were determined by island area and distance to South America but not by oceanographic variables. Physiographic and oceanographic factors were significant in determining β-diversity. Changes in β-diversity were mostly due to species replacement (β-turnover) across three major island Systems (Galápagos Archipelago, Chilean coastal islands, and oceanic islands of the southeastern Pacific). The contribution of β-nestedness was restricted to small scales (within archipelagos).<br> <br> <strong>Main conclusions</strong><br> Physiographic and oceanographic factors explain species diversity of seabird assemblages on islands of the southeastern Pacific. Oceanographic variables did not affect species richness but significantly influenced species composition. Change in species composition reflects gradients across three marine biogeographical realms: Temperate South, Eastern Indo-Pacific, and Tropical Eastern Pacific. The low degree of species nestedness may reflect multiple evolutionary origins.</p>
An assemblage-level comparison of genetic diversity and population genetic structure between island and mainland ant populations
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Data from: Non-random patterns of invasion and extinction reduce phylogenetic diversity in island bird assemblages
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The role of island physiography and oceanographic factors in shaping species richness and turnover of nesting seabird assemblages on islands across the southeastern Pacific
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Under the karst: detecting hidden subterranean assemblages using eDNA metabarcoding in the caves of Christmas Island, Australia
<p>Subterranean ecosystems are understudied and challenging to conventionally survey given the inaccessibility of underground voids and networks. In this study, we conducted a eukaryotic environmental (eDNA) metabarcoding survey across the karst landscape of Christmas Island, (Indian Ocean, Australia) to evaluate the utility of this non-invasive technique to detect subterranean aquatic 'stygofauna' assemblages. Three metabarcoding assays targeting the mitochondrial 16S rRNA and nuclear 18S genes were applied to 159 water and sediment samples collected from 23 caves and springs across the island. Taken together, our assays detected a wide diversity of chordates, cnidarians, porifera, arthropods, molluscs, annelids and bryozoans from 71 families across 60 orders. We report a high level of variation between cave and spring subterranean community compositions which are significantly influenced by varying levels of salinity. Additionally, we show that dissolved oxygen and longitudinal gradients significantly affect biotic assemblages within cave communities. Lastly, we combined eDNA-derived community composition and environmental (water quality) data to predict potential underground interconnectivity across Christmas Island. We identified three cave and spring groups that showed a high degree of biotic and abiotic similarity indicating likely local connectivity. This study demonstrates the applicability of eDNA metabarcoding to detect subterranean eukaryotic communities and explore underground interconnectivity.</p>
The fate of páramo plant assemblages in the sky islands of the northern Andes - Appendix S1. Vegetation and occurrence data used in this study
<p><strong>Aims:</strong> Assessing climate change impacts on biodiversity is a main scientific challenge, especially in the tropics, therefore, we predicted the future of plant species and communities on the unique páramo sky islands. We implemented the <i>Spatially Explicit Species Assemblage Modelling</i> framework, by i) calculating species' maximum dispersal distance, ii) modelling species distributions at present up to 2100, iii) assembling models into communities. Finally, we assessed the vulnerability of sky islands based on richness and composition changes.</p> <p><strong>Location: </strong>Ecuadorian super-páramo (>4200 m)</p> <p><strong>Methods:</strong> Using species trait data, the maximum dispersal distance of 435 species was calculated. Species distribution models (SDM) were fitted to obtain current and future distribution predictions based on dispersal and bioclimatic factors. The final assemblages for present and 2100 were achieved by stacking all probabilistic SDMs and applying the probability ranking rule. The vulnerability of each sky island was evaluated by quantifying richness and composition changes.</p> <p><strong>Results: </strong>Maximum dispersal distances ranged between 0.008-6027 m/year, and across all scenarios, 70% of models showed a net loss in species distribution while 9% of all species were predicted to undergo extinction by 2100. Local richness was estimated to decrease by 56.63% on average, and composition changes in each sky island suggested a mean loss of 64.74% of their original species pool against a 12.97% gain. Finally, 5% of the sky island floras reconverted from high-elevation to low-elevation species. These numbers were usually more important for high-elevation species and the mountains Pichincha, Ilinizas and Antisana.</p> <p><strong>Conclusions:</strong> Our study is methodologically pioneer and provides novel insight on the future of páramo biodiversity. Significant losses in species distribution and changes in community richness and composition suggest drastic impacts and call for further study considering additional factors, such as land-use. Finally, we recommend focusing monitoring and conservation strategies on the northern sky islands in priority.</p>
Data from: Rat eradication and the resistance and resilience of passerine bird assemblages in the Falkland Islands
Norway rats (Rattus norvegicus) were introduced to the Falkland Islands and are detrimental to native passerines. Rat eradication programs are being used to help protect the avifauna. The present study assesses the effectiveness of eradication programs while using this conservation practice as a natural experiment to explore the ecological resistance, resilience, and homeostasis of bird communities. We conducted bird surveys on 230 islands: 85 in the presence of rats, 108 that were historically free of rats, and 37 from which rats had been eradicated. Bird detection data were used to build occupancy models for each species and estimate species-area relationships. Count data were used to estimate relative abundance and community structure. Islands with invasive rats had reduced species richness of passerines and a different community structure than islands on which rats were historically absent. Although the species richness of native passerines was remarkably similar on eradicated and historically rat-free islands, community structure on eradicated islands was more similar to that of rat-infested islands than to historically rat-free islands. The results suggest that in the Falkland Islands, species richness of passerines is not resistant to invasive rats, but seems to be resilient following their removal. In contrast, community structure seems to be neither resistant nor resilient. From a conservation perspective, rat eradication programs in the Falkland Islands appear to be effective at restoring native species richness, but they are not necessarily beneficial for species of conservation concern. For species that do not recolonize, translocations following eradications may be necessary.
Data from: Evidence for stratigraphy in molluscan death assemblages preserved in seagrass beds: St. Croix, U.S. Virgin Islands
Death assemblages that occupy the upper tens of centimeters of sediment in shallow-marine settings are often subject to extensive mixing, thereby limiting their usefulness in assessing environmentally mediated compositional changes through time in the local biota. Here, we provide evidence that dense, Thalassia-rich seagrass beds preserve a stratigraphic record of biotic variation because their dense root–rhizome mats inhibit mixing. We sampled benthic mollusk assemblages at seven localities in Thalassia-rich beds around St. Croix, USVI, collecting three separate sediment intervals of ~13 cm each to a total depth of ~40 cm below the sediment–water interface, and found evidence that sedimentary intervals preserved compositional stratigraphy. Further, some localities displayed systematic, directional changes down-core. An examination of interval-to-interval changes in composition revealed that compositional variation was unique from locality to locality rather than reflecting coordinated, island-wide transitions. In general, however, relative abundances of epifaunal gastropods and small lucinid bivalves tended to decrease with depth below the sediment–water interface. Quantitative comparisons of life-to-death assemblages from each successive sedimentary interval demonstrated that the shallowest death assemblages were typically more similar to the life assemblages than were deeper assemblages, suggesting that deeper intervals provide records of earlier community states.
Data from: Bird assemblages on Amazonian river islands: patterns of species diversity and composition
The principles of island biogeography are rarely used to investigate the animal assemblages of Amazonian river islands. Here, we apply this approach to compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and at 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages are characterized by lower species richness and a higher abundance of a few dominant species. Additionally, species composition of the islands was significantly distinct from the mainland, including the nearby floodplain habitats. Number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbour an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial environments could be disproportionally threatened by river channel disturbances such as climate change events, and hydroelectric building.
Data from: A hierarchical model of whole assemblage island biogeography
Island systems have long played a central role in the development of ecology and evolutionary biology. However, while many empirical studies suggest species differ in vital biogeographic rates, such as dispersal abilities, quantitative methods have had difficulty incorporating such differences into analyses of whole-assemblages. In particular, differences in dispersal abilities among species can cause variation in the spatial clustering and localization of species distributions. Here, we develop a single, hierarchical Bayes, assemblage-wide model of 252 bird species distributions on the islands of Northern Melanesia and use it to investigate a) whether dispersal limitation structures bird assemblages across the archipelago, b) whether species differ in dispersal ability, and c) test the hypothesis that wing aspect ratio, a trait linked to flight efficiency, predicts differences inferred by the model. Consistent with island biogeographic theory, we found that individual species were more likely to occur on islands with greater area, and on islands near to other islands where the species also occurred. However, species showed wide variation in the importance and spatial scale of these clustering effects. The importance of clustering in distributions was greater for species with low wing aspect ratios, and the spatial scale of clustering was also smaller for low aspect ratio species. These findings suggest that the spatial configuration of islands interacts with species dispersal ability to affect contemporary distributions, and that these species differences are detectable in occurrence patterns. More generally, our study demonstrates a quantitative, hierarchical approach that can be used to model the influence of dispersal heterogeneity in diverse assemblages and test hypotheses for how traits drive dispersal differences, providing a framework for deconstructing ecological assemblages and their drivers.
Data from: Edge-mediated compositional and functional decay of tree assemblages in Amazonian forest islands after 26 years of isolation
1.Islands formed upstream of mega hydroelectric dams are excellent experimental landscapes to assess the impacts of habitat fragmentation on biodiversity. We examined the effects of plot-, patch- and landscape-scale variables on the patterns of floristic diversity across 34 forest islands that had experienced 26 years of isolation since the creation of the 4,437 km2 Balbina Hydroelectric Reservoir of central Brazilian Amazonia. In addition, three undisturbed continuous forest sites in neighbouring mainland areas were also sampled across a comparable elevational gradient. 2.We identified all live trees ≥10 cm DBH at species level within a total of 87 quarter-hectare forest plots and conducted a comprehensive compilation of functional attributes of each tree species. We then examined species-area relationships (SARs) and the additional effects of patch and landscape scale metrics on patterns of tree assemblage heterogeneity, both in terms of taxonomic and functional diversity. 3.Despite a clearly positive SAR, edge-mediated forest disturbance was the single most important driver of species composition and abundance within islands. Our results suggest that non-random floristic transitions within island plots followed a predictable pattern, with different life-history traits either penalizing or rewarding local persistence of different functional groups. Distance to edges mediated the probability of tree mortality induced by windfalls and episodic surface fires, clearly resulting in faster species turnover and unidirectional changes in guild structure within small islands where light-wooded fast-growing pioneers largely replaced heavy-wooded species of the old-growth flora. 3.Synthesis ─ Following a simultaneous 26-year post-isolation history, we disentangle the effects of habitat loss and insularization on tree assemblages within a large set of Amazonian 'true' forest islands, of variable sizes, sharing a uniform open-water matrix. Area effects are expressed via a response to edge effects, with trees in smaller islands being more vulnerable to edge-related surface fires and windthrows. Additionally, forest edge effects can be a powerful driver of non-random floristic transitions across islands within the Balbina archipelago via a process of rapid pioneer proliferation, drastically affecting both the taxonomic and functional composition of insular tree communities. Finally, our results indicate that detrimental effects of forest fragmentation induced by hydroelectric dams are considerably stronger than those of forest patches embedded within a terrestrial vegetation matrix.
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