Biotic Similarity Research Articles

Global biogeographic regions for ants have complex relationships with those for plants and tetrapods

On a global scale, biodiversity is geographically structured into regions of biotic similarity. Delineating these regions has been mostly targeted for tetrapods and plants, but those for hyperdiverse groups such as insects are relatively unknown. Insects may have higher biogeographic congruence with plants than tetrapods due to their tight ecological and evolutionary links with the former, but it remains untested. Here, we develop a global regionalization for a major and widespread insect group, ants, based on the most comprehensive distributional and phylogenetic information to date, and examine its similarity to regionalizations for tetrapods and vascular plants. Our ant regionalization supports the newly proposed Madagascan and Sino-Japanese realms based on tetrapod delineations, and it recovers clusters observed in plants but not in tetrapods, such as the Holarctic and Indo-Pacific realms. Quantitative comparison suggests strong associations among different groups—plants showed a higher congruence with ants than with tetrapods. These results underscore the wide congruence of diverse distribution patterns across the tree of life and the similarities shared by insects and plants that are not captured by tetrapod groups. Our analysis highlights the importance of developing global biogeographic maps for insect groups to obtain a more comprehensive geographic picture of life on Earth.

U-Pb Dating of the Kolchugino Group Basement (Kuznetsk Coal Basin, Siberia): Was the Change in Early–Middle Permian Floras Simultaneous at Different Latitudes in Angaraland?

The Kuznetsk Basin (Kuzbass) is one of the largest coal basins in Siberia and a reference area for the ancient Angaraland continent. The proximity of the Kuzbass and Siberian Platform caused their biotic similarities in the Late Palaeozoic. However, due to biota endemism, the Kuzbass Upper Palaeozoic does not correlate directly with the International Chronostratigraphic Chart (ICC). This paper discusses radioisotopic (CA-ID-TIMS) dating of zircons from a volcanic tuff located in the Starokuznetsk Formation (Fm). This level matches the interval of the Balakhonka/Kolchugino (B/K) floral change in Kuzbass, i.e., the gradual replacement of cordaitoid-dominated wet forests (Balakhonka flora) with more arid fern–pteridosperm–cordaitoid assemblages (Kolchugino flora). New age (276.9 ± 0.4 Ma) directly correlates the Starokuznetsk Fm with the Upper Kungurian of the ICC. We compared the Kuzbass data with data of the Western Verkhoyanie, where Middle Permian ammonoids (Sverdrupites assemblage) occur in strata recording the B/K floral change. The available (ICC) and new datings indicate the lag between the B/K floral change in low (Kuzbass) and high (Verkhoyanie) latitudes of Angaraland. The B/K floral change in the Kuzbass began in the early Late Kungurian and was completed by the end of this age. In contrast, the B/K floral change in Verkhoyanie began at the end of the Late Kungurian and was completed in the Late Wordian. The delay in the floral changes at different latitudes of Angaraland suggests that existing interregional correlations need further improvement.

Effects of repeated sediment bypassing on stream ecosystems in a Japanese mountainous river

Sediment bypassing connects the upstream and downstream regions of dam impoundments through tunnels and is expected to partly restore natural processes (flood pulse and sediment regime) in dam‐altered river ecosystems. However, few reports examined the effects of restoration on stream biota. We examined the effectiveness of repeated sediment bypassing (12 times) over a period of 5 years in a Japanese dammed river using a before‐after‐reference‐impact design. We compared the abiotic parameters (water quality and substrate environment), biotic assemblages (algae, macroinvertebrates, and fish), and similarities between the dam downstream and undammed reference reaches. The reference sites exhibited high temporal variability in abiotic environments and species composition over the 5‐year period. Most abiotic and biotic parameters downstream of the dam improved and approached those of the changing reference states. However, these indices returned to pretrial conditions after the last trial. Biotic similarities between the downstream and reference reaches gradually increased throughout successive sediment‐bypassing trials for macroinvertebrates and algae; however, these similarities diminished after the last trial. Conversely, the abundance‐based composition of fish assemblages in the restored reach consistently diverged from that of the reference conditions throughout the study period. Our results show that the success and failure of restoration by sediment bypassing may be affected by the amount of bedload in the flushing flows and other regional processes such as migratory connectivity. Sediment bypassing can partially re‐establish natural processes and is a useful tool for improving sediment‐associated environments and biota.

Advances in understanding and predicting the spread of invading insect populations.

Understanding and predicting the spread of invading insects is a critical challenge in management programs that aim to minimize ecological and economic harm to native ecosystems. Although efforts to quantify spread rates have been well studied over the past several decades, opportunities to improve our ability to estimate rates of spread, and identify the factors, such as habitat suitability and climate, that influence spread, remain. We review emerging sources of data that can be used to delineate distributional boundaries through time and thus serve as a basis for quantifying spread rates. We then address advances in modeling methods that facilitate our understanding of factors that drive invasive insect spread. We conclude by highlighting some remaining challenges in understanding and predicting invasive insect spread, such as the role of climate change and biotic similarity between the native and introduced ranges, particularly as it applies to decision-making in management programs.

Environmental resistance predicts the spread of alien species.

The unabating rise in the number of species introduced outside of their native range makes predicting the spread of alien species an urgent challenge. Most predictions use models of the ecological niche of a species to identify suitable areas for invasion, but these predictions may have limited accuracy. Here, using the global alien avifauna, we demonstrate an alternative approach for predicting alien spread based on the environmental resistance of the landscape. This approach does not require any information on the ecological niche of the invading species and, instead, uses gradients of biotic similarity among native communities in the invaded region to predict the most likely routes of spread. We show that environmental resistance predicts patterns of spread better than a null model of random dispersal or a model based on climate matching to the native range of each species. Applying this approach to simulate future spread reveals major regional differences in projected invasion risk, shaped by proximity to existing invasion hotspots as well as gradients in environmental resistance. Our results show how environmental resistance may provide a general and complementary approach for predicting invasion risk that can be rapidly deployed even when information on the niche or the identity of potential invaders is unknown.

Under the karst: detecting hidden subterranean assemblages using eDNA metabarcoding in the caves of Christmas Island, Australia

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 DNA (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.

Dispersion fields reveal the compositional structure of South American vertebrate assemblages

The causes of continental patterns in species richness continue to spur heated discussion. Hypotheses based on ambient energy have dominated the debate, but are increasingly being challenged by hypotheses that model richness as the overlap of species ranges, ultimately controlled by continental range dynamics of individual species. At the heart of this controversy lies the question of whether species richness of individual grid cells is controlled by local factors, or reflects larger-scale spatial patterns in the turnover of species’ ranges. Here, we develop a new approach based on assemblage dispersion fields, formed by overlaying the geographic ranges of all species co-occurring in a grid cell. We created dispersion fields for all tetrapods of South America, and characterized the orientation and shape of dispersion fields as a vector field. The resulting maps demonstrate the existence of macro-structures in the turnover of biotic similarity at continental scale that are congruent among vertebrate classes. These structures underline the importance of continental-scale processes for species richness in individual assemblages.

Evaluating Devonian bioregionalization: quantifying biogeographic areas

AbstractThe work of Arthur J. Boucot (vale, 1924–2017) is foundational to Devonian biogeography. Cited more than 1000 times and mentioned in excess of 105,000 times, his classification of the Old World, Eastern Americas, and Malvinokaffric realms has become the framework for Devonian biogeographic and faunal studies. This study is the first to test and quantify the biotic area classification using the distributional data of trilobite, brachiopod, and fish taxa across the Lower, Middle, and Late Devonian. The biotic similarity analysis of 676 genera (ca. 30,000 occurrences) of late Silurian (Ludlow–Pridoli) and Devonian taxa represents the largest quantification of distributional data undertaken in Devonian biogeography. The temporal area approach (TAAp), applied here for the first time, failed to recover in the area phenogram many of the realms and regions used by Devonian biogeographers, excepting the Malvinokaffric realm, across the entirety of the Devonian. The Old World and Western Gondwana realms are found to be artificial and in need of revision. Without natural areas, bioregionalizations (area classifications) become unstable and unusable, resulting in authors creating further artificial regions and provinces. This study offers a better solution, namely, to identify artificial areas in existing area classifications using TAAp and biotic similarity analysis and revise them. Area classifications are modeled on taxonomic process (Wilson and Brown 1953; Starrett 1958) and the movement toward revision is necessary to break the cycle of reinvention of realms and regions within bioregionalization.

Temporal area approach for distributional data in biogeography.

A structural approach to temporality in distributional data for use in palaeobiogeography is described herein. Pre-established areas in the distributional data matrix are split temporally, allowing a single geographical space to have multiple iterations [e.g. Area A (Lower Devonian), Area A (Middle Devonian)]. The resulting temporal matrix will allow the representation and capture of any differing relationships through time. Designed primarily for Parsimony Analysis of Endemicity (PAE) and biotic similarity analyses, this approach simply structures distributional data within a temporal partition, meaning that numerical methods can be used to assess relationships between areas to find a branching diagram. Created through the application of the temporal matrix to a given analysis, Temporal Area Approach (TAAp) is a structural approach that facilitates exploration of the data rather than being a hypothesis-driven model following analysis. Understanding the behaviour of non-phylogenetic palaeobiogeographical data and reducing the prevalence of temporal artefacts will lead to more robust area classifications.

It takes one to know one: Similarity to resident alien species increases establishment success of new invaders

AbstractAimDarwin's naturalization hypothesis states that dissimilarity to native species may benefit alien species establishment due to empty niches and reduced competition. We here add a new dimension to large‐scale tests of community invasibility, investigating the role that previously established alien species play in facilitating or hindering new invasions in plant communities.LocationPermanent grasslands across France (including mainland and Corsica), as a receding ecosystem of great conservation importance.MethodsFocusing on 121 alien plant species occurring in 7,215 vegetation plots, we quantified biotic similarity between new invaders and resident alien species (i.e., alien species with longer residence times) based on phylogenetic and trait distances. Additionally, we calculated distances to native species for each alien species and plot. Using multispecies distribution models, we analysed the influence of these biotic similarity measures and additional covariates on establishment success (presence/absence) of new invaders.ResultsWe found that biotic similarity to resident alien species consistently increased establishment success of more recently introduced species. Phylogenetic relatedness to previous invaders had an equally strong positive effect as relatedness to native species. Conversely, trait similarity to natives hindered alien establishment as predicted by Darwin's naturalization hypothesis. These results highlight that various mechanisms may act simultaneously to determine alien establishment success.Main conclusionsOur results suggest that, with greater similarity among alien species, invasion success increases. Such a pattern may arise either due to actual facilitation among invaders or as a result of weaker competitive interactions among invaders than between native and alien species, leading to an indirect facilitative effect. Alternatively, recent environmental changes (e.g., eutrophication, climate change) may have added new environmental filters. Determining how initial invasions might pave the road for subsequent invasions is crucial for effective multispecies management decisions and contributes a new aspect to our understanding of community assembly.

Over the top: do thermal barriers along elevation gradients limit biotic similarity?

Organismal dispersal through mountain passes should be more constrained by temperature‐related differences between lowland and highland sites in montane environments. This may lead to higher rates of diversification through isolation of existing lineages toward the tropics. This mechanism, proposed by Janzen, could influence broad‐scale patterns of biodiversity across mountainous regions and more broadly across latitudinal gradients. We constructed two complementary analyses to test this hypothesis. First, we measured topographically‐derived thermal gradients using recently‐developed climatic data across the Americas, reviewing the main expectations from Janzen's climatic model. Then, we evaluated whether thermal barriers predict assemblage similarity for amphibians and mammals along elevational gradients across most of their latitudinal extent in the Americas. Thermal barriers between low and high elevation areas, initially proposed to be unique to tropical environments, are comparably strong in some temperate regions, particularly along the western slopes of North American dividing ranges. Biotic similarity for both mammals and amphibians decreases between sites that are separated by elevation‐related thermal barriers. That is, the stronger the thermal barrier separating pairs of sites across the latitudinal gradient, the lower the similarity of their species assemblages. Thermal barriers explain 10–35% of the variation in latitudinal gradients of biotic similarity, effects that were stronger in comparisons of sites at high elevations. Mammals' stronger dispersal capacities and homeothermy may explain weaker effects of thermal barriers on gradients of assemblage similarity than among amphibians. Understanding how temperature gradients have shaped gradients of montane biological diversity in the past will improve understanding of how changing environments may affect them in the future.

Effects of fragmentation and landscape variation on tree diversity in post-logging regrowth forests of the Southern Philippines

The conservation value of forest fragments remains controversial. An extensive inventory of rainforest trees in post-logging regrowth forest in the southern Philippines provided a rare opportunity to compare stem density, species richness, diversity and biotic similarity between two types of post-logging forests: broken-canopy forest fragments and adjacent tracts of closed-canopy ‘contiguous’ forest. Tree density was much lower in the fragments, but rarefied species richness was higher. ‘Hill’ numbers, computed as the exponential of Shannon’s diversity index and the inverse of Simpson’s diversity index, indicated that fragments have higher numbers of typical and dominant species compared to contiguous forest. Beta diversity (based on species incidence) and the exponential of Shannon’s diversity index was higher in fragmented forest, indicating higher spatial species turnover than in contiguous forest samples. Lower mean values of the Chao-Jaccard index in fragmented forest compared to contiguous forest also indicated a lower probability of shared species across fragments. The high species richness of contiguous forest showed that an earlier single logging event had not caused biodiversity to be degraded leaving mostly generalist species. Fragmentation and further low-level utilisation by local farmers has also not caused acute degradation. Post-logging regrowth forest fragments present a window of opportunity for conservation that may disappear in a few years as edge effects become more apparent. For the conservation of trees in forests in south-east Asia generally, our findings also suggest that while conservation of remaining primary forest may be preferable, the conservation value of post-logging regrowth forests can also be high.

Patterns of Distribution of the Helminth Parasites of Freshwater Fishes of Mexico

In order to draw patterns in helminth parasite composition and species richness in Mexican freshwater fishes we analyse a presence-absence matrix representing every species of adult helminth parasites of freshwater fishes from 23 Mexican hydrological basins. We examine the distributional patterns of the helminth parasites with regard to the main hydrological basins of the country, and in doing so we identify areas of high diversity and point out the biotic similarities and differences among drainage basins. Our dataset allows us to evaluate the relationships among drainage basins in terms of helminth diversity. This paper shows that the helminth fauna of freshwater fishes of Mexico can characterise hydrological basins the same way as fish families do, and that the basins of south-eastern Mexico are home to a rich, predominantly Neotropical, helminth fauna whereas the basins of the Mexican Highland Plateau and the Nearctic area of Mexico harbour a less diverse Nearctic fauna, following the same pattern of distribution of their fish host families. The composition of the helminth fauna of each particular basin depends on the structure of the fish community rather than on the limnological characteristics and geographical position of the basin itself. This work shows distance decay of similarity and a clear linkage between host and parasite distributions.

Depth transect of an Upper Triassic (Rhaetian) reef from Gosau, Austria: Microfacies and community ecology

In the Late Triassic (~235–201.3Ma) scleractinian corals and hypercalcified sponges built large, diverse reef ecosystems, the most famous of which are the Dachstein reefs. This study presents a depth transect along an Upper Triassic (lower Rhaetian) Dachstein reef from the Gosausee margin of the Dachsteingebirge (Gosau, Austria). The Gosausee microbial-sponge-coral reef is a complete barrier reef with an almost continuous fore reef to lagoon transect preserved (a very rare occurrence for the Triassic), and thus provides a window into depth zonation of Dachstein-type reef facies and biotic succession. The Gosausee reef facies exhibit strong depth control and five classic reef facies or zones are identified: the fore reef, reef front, reef crest, back reef, and lagoon facies. Thin, rare microbial fabrics and a high abundance of fine-grained, mud-rich skeletal wackestones (transported reef debris) characterize the deepest fore reef. As the reef shallows, muddy sediments decrease in abundance and are replaced by microbial fabrics, corals, and cements. Abundant sponges, microbial crusts, and thick, marine cements typify the reef crest, whereas microbialite-coated phaceloid corals are dominant in the back reef facies. Heavily cemented oncoids or microbial-sponge bindstones are characteristic of the lagoon. Based on their compositional and biotic similarities, the Gosausee reef was likely part of the same barrier reef systems as the source reef for the Gosaukamm reef breccia (one of the classic Norian–Rhaetian Dachstein reefs). The reef zones of the Gosausee margin can be used to interpret the depth or reef zone of less well preserved reef fragments, can inform models of community ecology and niche utilization in the Late Triassic, and highlight the need for additional research into the environmental factors that controlled biotic distribution in Upper Triassic reefs.

Tendency towards homogenization in fish assemblages in the cascade reservoir system of the Tietê river basin, Brazil

Measurements of biotic homogenization are important for ascertaining the nature and extent of human impacts on biodiversity, especially in relation to habitat alteration, species introductions and water quality degradation. All of these impacts are typical of impounded systems. Our objectives in this study were to investigate the increasing biotic homogenization and the impacts of introduced species in the Tietê cascade reservoir system (State of São Paulo, Brazil). Biotic homogenization is the replacement of local biota by non-indigeonous species, leading to a gradual increase in biotic similarity over time. In this study, the decades analyzed (1980–89, 1990–99 and 2000–2009), revealed the progressive loss of the native species in the system. We used Jaccard's coefficient to measure the changes in biotic homogeneity across decades. In the first comparison (2000s vs. 1980s), the predominant process observed was differentiation, meaning that the biotic assemblages, in the sequence of five reservoirs studied, became more dissimilar. These changes were related to the extirpation of common species from reservoirs. In the second comparison period (2000s vs. 1990s), we observed a tendency towards biotic homogenization, meaning that the number of species in common among reservoirs was increasing. This shift was related to the loss of unique native species and the progressive environmental maturation of each reservoir. The process of homogenization may continue as the reservoirs age and as introduced fish species are dispersed and native species are displaced. For example, we observed the replacement of Geophagus brasiliensis (native) by Geophagus surinamensis (non-native) in the downstream reservoirs, likely due to the introduction of non-native predators (Cichlidae spp.).

Jurassic hot spring deposits of the Deseado Massif (Patagonia, Argentina): Characteristics and controls on regional distribution

The Deseado Massif, Santa Cruz Province, Argentinean Patagonia, hosts numerous Middle to Late Jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs (sinters and travertines, respectively), hydrothermal breccias, quartz veins, and widespread hydrothermal silicification. They indicate pauses in explosive volcanic activity, marking the final stages in the evolution of an extensive Jurassic (ca. 178–151 Ma) volcanic complex set in a diffuse extensional back-arc setting heralding the opening of the Atlantic Ocean. Published paleo-hot spring sites for the Deseado Massif, plus additional sites identified during our recent field studies, reveal a total of 23 locations, five of which were studied in detail to determine their geologic and facies associations. They show structural, lithologic, textural and biotic similarities with Miocene to Recent hot spring systems from the Taupo and Coromandel volcanic zones, New Zealand, as well as with modern examples from Yellowstone National Park, U.S.A. These comparisons aid in the definition of facies assemblages for Deseado Massif deposits – proximal, middle apron and distal siliceous sinter and travertine terraces and mounds, with preservation of many types of stromatolitic fabrics – that likely were controlled by formation temperature, pH, hydrodynamics and fluid compositions. Locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and/or fluvial sediments, silicic to intermediate lava domes, and hydrothermal mineralization, all of which are related to local and regional structural lineaments. Moreover, the numerous geothermal and significant epithermal (those with published minable resources) deposits of the Deseado Massif geological province mostly occur in four regional NNW and WNW hydrothermal–structural belts (Northwestern, Northern, Central, and Southern), defined here by alignment of five or more hot spring deposits and confirmed as structurally controlled by aeromagnetic data. The Northern and Northwestern belts, in particular, concentrate most of the geothermal and epithermal occurrences. Hence, Jurassic hydrothermal fluid flow was strongly influenced by the most dominant and long-active geological boundaries in the region, the outer limits of the Deseado Massif ‘horst’ itself.

Palaeobiogeography and palaeogeographical implications of Permian marine bivalve faunas in Northeast Asia (Kolyma–Omolon and Verkhoyansk–Okhotsk regions, northeastern Russia)

The paper considers the biogeography and palaeogeographic implications of the Permian marine bivalve faunas of Northeast Asia, with a focus on the dynamic relationships between biotic similarities and palaeogeographic distance through an interval of ca. 50 million years. A stage-by-stage time series analysis of the biotic similarities between two previously recognized biochores in Northeast Asia, the Kolyma–Omolon and Verkhoyan–Okhotsk provinces, has been carried out using both the Jaccard and Dice similarity indices based on the spatio-temporal distributions of 355 Permian marine bivalve species in Northeast Asia. The outcome of this analysis, combined with other empirical data and previously published tectonic, sedimentological and palaeontological information, suggests that (1) the bivalve faunas from these two provinces were distinctive from one another as two separate biochores throughout all but the earliest (Asselian) Permian stages and (2) the biotic similarities between the Verkhoyan–Okhotsk and Kolyma–Omolon provinces remained consistently low since Sakmarian, all falling well below the minimum threshold of the Jaccard index of 0.42 required for distinguishing marine biotic provinces. We interpret these below-threshold Jaccard biotic similarities as an indication of significant palaeogeographic separation between the Verkhoyan-Okhotsk and Kolyma–Omolon provinces, which is in turn considered to indicate rifting and sea-floor spreading of the Omolon microcontinent and associated terranes and island arcs away from the North Asian craton, at least from the Sakmarian to the beginning of the Late Permian. Palaeo-distance separation appears to be the primary and most significant biogeographic determinant in accounting for the differences in the spatial distribution of most Permian bivalve species in Northeast Asia. Several other variables also appear to have played a significant role, including regional climate conditions, ocean currents and merged island chains as geographic barriers. In particular, the relatively high biotic similarity between the Verkhoyan–Okhotsk and Kolyma–Omolon provinces during the Late Wuchiapingian and Changhsingian may have been related to the shallowing of the deep-water basins (Oimyakon, Ayan-Yuryakh, Balygychan and Sugoi basins) that had previously separated the two provinces and the flooding (submergence) of the Okhotsk–Taigonos volcanic arc system, thus allowing the invasion of lower latitude warm-water Palaeotethyan and even Gondwanan species into Northeast Asia.

Microbial Biogeography of Six Salt Lakes in Inner Mongolia, China, and a Salt Lake in Argentina

We used cultivation-independent methods to investigate the prokaryotic biogeography of the water column in six salt lakes in Inner Mongolia, China, and a salt lake in Argentina. These lakes had different salt compositions and pH values and were at variable geographic distances, on both local and intercontinental scales, which allowed us to explore the microbial community composition within the context of both contemporary environmental conditions and geographic distance. Fourteen 16S rRNA gene clone libraries were constructed, and over 200 16S rRNA gene sequences were obtained. These sequences were used to construct biotic similarity matrices, which were used in combination with environmental similarity matrices and a distance matrix in the Mantel test to discover which factors significantly influenced biotic similarity. We showed that archaeal biogeography was influenced by contemporary environmental factors alone (Na+, CO3(2-), and HCO3(-) ion concentrations; pH; and temperature). Bacterial biogeography was influenced both by contemporary environmental factors (Na+, Mg2+, and HCO3(-) ion concentrations and pH) and by geographic distance.

Environmental and spatial influences on benthic community composition in wooded headwater streams in Zoar Valley, New York, USA

This study determined the relative influences of environmental variation versus spatial autocorrelation on benthic macroinvertebrate community composition of temperate headwater streams. We enumerated fauna in riffle zones of 23 separate (i.e., not tributaries to each other) but closely grouped from first- to third-order woodland streams surrounding Zoar Valley Canyon, western New York State, USA, during spring, summer, and fall of 2006. Watershed geomorphology (stream order, catchment area, and forest cover) and semi-quantitative habitat characteristics, the latter of which were incorporated into a Qualitative Habitat Evaluation Index (QHEI), were also recorded for each stream. Non-metric Multidimensional Scaling (NMDS) ordination was used to establish patterns of biotic similarity among these streams. Matrices of biological and environmental Euclidean distances were constructed for all between-stream pairings. Additionally, a between-stream spatial matrix was constructed based on global position system coordinates of sampling sites. Non-significant partial Mantel coefficients indicated that biological distances were uncorrelated with spatial distances both among all 23 study streams and among 12 first-order streams only. In contrast, biological distances were positively correlated with environmental distances (rM = 0.375 and 0.289 for all streams and for first-order streams only, respectively; P values 0.05), indicating that the measured environmental characteristics were not spatially structured. Each of the geomorphological and habitat variables was statistically associated with NMDS community composition axes (stepwise multiple regression, one-factor MANOVA). These results suggest that environmental filters and niche-based species sorting may operate here between separate streams, and that study sites appear to be effectively insular in their biota despite close physical proximity.

Do humans homogenize or differentiate biotas? It depends

Do humans homogenize or differentiate biotas? It depends