Distance-based Linear Modelling Research Articles

One-year effects of stand age, pre-fire treatments, and hillslope aspect on recovery of plant diversity and soil properties in a Mediterranean forest burnt by a severe wildfire

Although several management options are adopted to redirect post-fire forest ecosystems towards less vulnerable and more resilient and functional communities, little is known about the interactions among tree stand age, pre-fire forest management, and slope aspects, and their consequences for plant species and soil properties recovery immediately after severe wildfires. To address this knowledge need, this study evaluates the post-fire changes in species richness and diversity (with a specific focus on regeneration mechanisms and life forms) of regenerating plants as well as the main physico-chemical and biological properties of burned soils with the reciprocal relations. Plant cover and diversity, and many soil properties have been monitored in forests of southeast Spain with mature, middle and young stands, presence of pre-fire treatments or not, and north and south hillslopes about one year after the fire. To this aim, the reciprocal relationships among soil properties and plants were evaluated adopting a combination of statistical techniques (PERMANOVA, Non-metric Multi-Dimensional Scaling, Distance-based Linear Modelling, Distance-based Redundancy Analysis, and Spearman correlation analysis). The damage to soil and vegetation was so high that both plants and pre-fire soil properties slowly recovered. Only a few life forms of vegetation (geophytes and herbaceous chamaephytes) were influenced by the stand age. If combined with soil aspect, stand age resulted in significantly lower germinating species in mature stands and lower resprouters in young stands, both on south hillslopes. Plant diversity was high, and the post-fire regeneration did not change the species richness and evenness. The post-fire changes in soil properties were limited, and only slight small differences in pH and betaglucosidase among stands of different age were found. No evident associations between soil properties and plant diversity were revealed by the low correlation coefficient. The low variance in plant cover and diversity, as well as in soil properties, resulted in a low accuracy of the dbRDA model to reproduce its variability among sites with different pre-fire characteristics.

Temporal dynamics of the ichthyoplankton assemblages in the central Aegean Sea during one year and the effects of ecological factors

In this investigation, vertical and horizontal sampling was performed monthly, covering a year, from 16 stations situated in Sığacık Bay. In ichthyoplankton sampling, a standard-type plankton net with a 350-micron mesh size for vertical sampling and a 500-micron mesh size for horizontal sampling was used. This study aimed to investigate temporal changes in the ichthyoplankton assemblages in Sığacık Bay and their relationship with ecological factors. A total of 113 fish taxa belonging to 42 families were identified. The Sparidae, Engraulidae, and Labridae families were found to be the most dominant among the eggs and larvae, with Engraulis encrasicolus, Coris julis, Mullus barbatus, and Gobius niger being the most prevalent species. The highest biodiversity index values were observed in April and May. The cluster analysis revealed the existence of three distinct groups.Based on the SIMPER analysis, S. aurata emerges as the indicator species for months characterised by lower water temperatures, G. niger stands as the indicator species for warm months, and E. encrasicolus represents the indicator species for the hottest months group. Both distance-based linear modelling (DistLM) and distance-based redundancy analysis (dbRDA) highlighted that water temperature, salinity, and chlorophyll-a were the main variables that influenced the temporal variation of the ichthyoplankton assemblage. The results of this study will be of great significance in comprehending the responses of the ichthyoplankton assemblages residing in analogous ecosystems to ecological variables.

Does a high dietary intake of resistant starch affect glycaemic control and alter the gut microbiome in women with gestational diabetes? A randomised control trial protocol

BackgroundGestational Diabetes Mellitus (GDM) is prevalent with lasting health implications for the mother and offspring. Medical nutrition therapy is the foundation of GDM management yet achieving optimal glycaemic control often requires treatment with medications, like insulin. New dietary strategies to improve GDM management and outcomes are required.Gut dysbiosis is a feature of GDM pregnancies, therefore, dietary manipulation of the gut microbiota may offer a new avenue for management. Resistant starch is a fermentable dietary fibre known to alter the gut microbiota and enhance production of short-chain fatty acids. Evidence suggests that short-chain fatty acids improve glycaemia via multiple mechanisms, however, this has not been evaluated in GDM.MethodsAn open-label, parallel-group design study will investigate whether a high dietary resistant starch intake or resistant starch supplement improves glycaemic control and changes the gut microbiome compared with standard dietary advice in women with newly diagnosed GDM. Ninety women will be randomised to one of three groups - standard dietary treatment for GDM (Control), a high resistant starch diet or a high resistant starch diet plus a 16 g resistant starch supplement. Measurements taken at Baseline (24 to 30-weeks’ gestation), Day 10 and Day 56 (approximately 36 weeks’ gestation) will include fasting plasma glucose levels, microbial composition and short-chain fatty acid concentrations in stool, 3-day dietary intake records and bowel symptoms questionnaires. One-week post-natal data collection will include microbial composition and short-chain fatty acid concentrations of maternal and neonatal stools, microbial composition of breastmilk, birthweight, maternal and neonatal outcomes. Mixed model analysis of variance will assess change in glycaemia and permutation-based multivariate analysis of variance will assess changes in microbial composition within and between intervention groups. Distance-based linear modelling will identify correlation between change in stool microbiota, short-chain fatty acids and measures of glycaemia.DiscussionTo improve outcomes for GDM dyads, evaluation of a high dietary intake of resistant starch to improve glycaemia through the gut microbiome needs to be established. This will expand the dietary interventions available to manage GDM without medication.Trial registrationAustralian New Zealand Clinical Trial Registry, ACTRN12620000968976p. Registered 28 September 2020

Macrobenthic community responses to multiple environmental stressors in a subtropical estuary.

We assessed how multi- and univariate models reflect marine environmental health based on macrobenthic community responses to three environmental stressor categories: hydrodynamics, organic enrichment and metal contamination. We then compared the models with the benthic index AMBI (AZTI Marine Biotic Index). Macrobenthic community and physicochemical variables were sampled at 35 sites along Babitonga Bay, a subtropical estuary in Southern Brazil. Distance-based linear modelling identified depth, grain size and organic matter as well as Cu and Zn as key stressors affecting the macrobenthos. Using canonical analysis of principal coordinates (CAP), we developed three multivariate models based on the variability in community composition, creating stress gradients. The metal gradient showed better correlation with the benthic community. Sediment quality indices (Geoaccumulation Index and Contamination Factor) showed a low to moderate contamination status, with higher concentrations for Cr, Ni and Zn at the inner areas of the bay. According to AMBI, Babitonga Bay has a “good” environmental health status, and the AMBI values show stronger correlations with the hydrodynamic and organic enrichment gradients (r = 0.50 and r = 0.47) rather than the metal gradient (r = 0.29). Lumbrineridae polychaetes (not included in the AMBI list) and Scoloplos sp. were negatively related to the metal contamination gradient and were considered sensitive, while Sigambra sp., Magelona papillicornis, the gastropod Heleobia australis and species of the crustacean order Mysida were positively related to the gradient and considered tolerant to higher concentrations of metals in the sediment. Despite the inconsistency in the ecological classification provided by AMBI and its relationship with the metal gradient, our results suggest that the environmental quality was satisfactory for the studied gradients. The metal gradient showed the weakest correlation to AMBI. In such cases, the ecological classification of taxa by the index should be evaluated under the perspective of the action of inorganic genotoxic contaminants represented by metals.

Diet composition of wild Loligo vulgaris paralarvae along the West Iberian Peninsula coast

Trophic interactions in cephalopod paralarvae are difficult to evaluate due to the ingestion of liquified prey contents that are not recognizable by visual methods; however, molecular techniques such as next generation sequencing (NGS) can provide better resolution. In this study, we used NGS techniques to determine the diet of Loligo vulgaris paralarvae collected along the West Iberian Peninsula coast. Trophic analyses were conducted on 31 paralarvae ranging from 1.61-6.01 mm in dorsal mantle length, with an estimated age between 2 and 28 d. The digestive system of each paralarvae was dissected and a 300 bp section of the mitochondrial cytochrome c oxidase subunit I gene was sequenced with the MiSeq platform. After quality selection, 3201878 reads were obtained and 130 amplicon sequencing variants were identified as prey (158457 reads). Crustaceans accounted for 88.09% of the total reads, mainly represented by calanoids (73.22%), euphausiids (5.73%) and decapods (2.75%). Distance-based linear modelling showed that diet patterns depended mainly on spatial variables, accounting for 46.92% of the total variation, with calanoids and euphausiids comprising the dominant prey in the diet of paralarvae from SW Galicia, while siphonophores and myopsids constituted the most important prey on the Northern Galician coast.

Spatial distribution and habitat characterization of marine animal forest assemblages along nine submarine canyons of Eastern Sardinia (central Mediterranean Sea)

Submarine canyons are peculiar habitats of the continental margin due to their hydrodynamic and geomorphological features. Coral assemblages forming marine animal forests (MAFs) are one of the key benthic components dwelling in these habitats, where they enhance the substrate's heterogeneity and provide shelter, feeding and spawning habitats for a wide variety of species. They are also considered Vulnerable Marine Ecosystems (VMEs), since their fragile three-dimensional framework and slow growth rate exposes them to multiple anthropogenic stressors. Understanding the coupling processes between environmental factors and the scale at which coral assemblages develop in these habitats, is an essential step towards their protection. This study aims to identify MAFs along submarine canyons in the central Mediterranean basin (Eastern Sardinia) on the basis of video transects carried out using Remotely Operated Vehicle and test the influence of environmental variables (silt coverage, distance from the coast, water depth and slope of the substrate) in driving the spatial distribution variability. We identified nine MAF assemblages dwelling in both rocky and silted substrate, from 90 to 220 m depth. We found that the most significant variability in densities and diversity of MAF assemblages occurs mostly within canyons rather than among canyons that are distant hundreds of km apart. Distance-based linear modelling (DistLM) identified silt coverage and water depth as the main factors explaining the observed variability. Overall our study provided new insights on MAFs composition and spatial distribution in submarine canyons which are, in turn, strongly influenced by local physical conditions. Such results emphasized the need for sound in situ conservation strategies in order to preserve MAFs and their ecological role.

Phytoplankton in dryland riverine waterholes: environmental drivers, variability and ecosystem-monitoring potential using different levels of taxonomic resolution and dataset reduction

Waterholes that remain in the dry season in intermittent dryland rivers are important biotic refugia, but detailed ecological descriptions of these habitats and their plankton are scarce. We aimed to determine spatial and temporal variation in phytoplankton assemblages in a tropical Australian dryland river system, their main environmental determinants and the potential of the phytoplankton for ecosystem monitoring. We sampled nine sites in three rivers over 2 years using standard methods. Water quality and phytoplankton assemblages varied considerably among sites, rivers and seasons, reflecting lithology, hydrology, bathymetry and local catchment influences. Major environmental drivers included conductivity, pH, temperature and species of N and P. We analysed several derived versions of the original dataset by using density and presence–absence data, eliminating rarer species and grouping species into higher taxa. We found substantial consistency among analyses in environmental drivers, identified using distance-based linear modelling, and in variability among systems, identified using nested permutational multivariate analysis of variance (PERMANOVA). Responsiveness of the algal assemblages to environmental drivers and consistency among analyses, even using subsamples at low taxonomic resolution, suggests potential for ecosystem monitoring and optimising of sample throughput, although variability among systems requires substantial effort to determine the range of reference conditions.

Drivers of zooplankton dynamics in a small tropical lowland river

There is limited information available on the ecology of planktonic invertebrate assemblages of small tropical lowland rivers, despite zooplankton being a vital resource for larval fish. Herein we describe the spatial patterns and temporal dynamics of invertebrate zooplankton at 8 locations over a 25-month period in the lowland section of a short coastal river in the Australian Wet Tropics. Zooplankton were more abundant in slack than flowing waters and assemblages were dominated by Copepoda, but contained many less numerous taxa, including freshwater invertebrates at the more upstream sites. Taxonomic richness, total density and the densities of the most abundant taxa were greatest in the most downstream sites. Seasonal patterns in the density of zooplankton did not differ between the 2 years. Distance-based linear modelling of assemblages identified distance downstream and associated variables, such as salinity, as the most important environmental effects on zooplankton. The zooplankton assemblage in the lower Mulgrave River is strongly influenced by the incised nature of the river, perennial flows, the presence of slack waters, wet season floods and estuarine incursion. Zooplankton dynamics differ from the typical pattern of tropical floodplain systems in that their maximum proliferation occurs during the benign but productive late dry season.

Distribution of Deep-Sea Sponge Aggregations in an Area of Multisectoral Activities and Changing Oceanic Conditions

Discovery and understanding of fragile deep-sea habitats like sponge aggregations, are being outpaced by anthropogenic resource exploitation. Sustainable ocean development in the Faroe-Shetland Channel Nature Conservation Marine Protected Area (FSC NCMPA; northeast Atlantic), which harbours sponge aggregations, now requires adaptive management in the face of encroachment of multisectorial activities in this area (e.g. fishing, oil and gas, shipping) and climate change. We examined sponge morphotype composition, richness, diversity, density and body-size distribution inside and outside the FSC NCMPA, and the role of environmental variability and human impact in these sponge aggregations. Analyses were based on the examination of 465 high resolution images from 13 towed-camera transects. A catalogue for regional sponge morphotypes was also developed and applied for these analyses. Analysis revealed that morphotype composition did not differ between inside and outside the FSC NCMPA but richness, diversity and densities of massive/spherical/papillate and flabellate/caliculate sponges were higher inside than outside the boundary. The sponge aggregations occurred within a narrow zone between 450 and 530 m depth, within relatively warm and saline water masses. Furthermore, multiple size cohorts of sponges were recorded inside the FSC NCMPA, in contrast to the single cohort outside. Distance-based linear modelling showed that demersal fisheries, substratum, salinity and temperature explained a statistically-significant amount of variation (48%, p<0.001) of sponge density across the study area. Findings on density and size cohorts suggest that the FSC NCMPA boundary currently encloses the most vulnerable area, which also demonstrates normal ecosystem functions (e.g. recruitment). However, sponges were constrained to a narrow environmental niche shaped by fisheries and interactions of FSC NCMPA water masses with the slope that in turn likely determine, food supply to the sponge aggregations. Our study illustrated the vulnerability of the FSC NCMPA sponge aggregations to fisheries and changes to water mass properties over time. The morphotype catalogue and suite of indicators (i.e. density and body-size distribution) allow for baseline and future assessments of anthropogenic and climate change impacts on sponge aggregations’ environmental status in the FSC NCMPA, thus guiding management as sectoral encroachment continues in this area.

Seasonal and spatial fatty acid profiling of the calanoid copepods Temora longicornis and Acartia clausi linked to environmental stressors in the North Sea

The Belgian part of the North Sea (BPNS) is subjected to multiple environmental stressors. The impact of these stressors includes the modulation of fatty acid (FA) composition of the zooplankton. This study recorded temporal and spatial patterns of the FA profiles of two dominant calanoid copepods within the BPNS: Temora longicornis (Müller, 1785) and Acartia clausi (Giesbrecht, 1889). By means of distance-based linear modelling and by applying multi model inference to generalized additive models, environmental stressors were linked to patterns of the FA profiles of these species. The FA profiles of A. clausi and T. longicornis showed distinct intraspecific, spatial and temporal differences within the BPNS. Temperature and algal food quality (marked by the ratio of silicate concentration to dissolved inorganic nitrogen concentration, SiO4/DIN) were the most important drivers of seasonal fluctuations in the DHA/EPA ratio of both species. DHA/EPA ratio can be used as marker for stress in copepods in the BPNS in order to have a quick indication of food quality changes at the basis of the food web.

Invertebrate responses to land use in tropical streams: discrimination of impacts enhanced by analysis of discrete areas

We identified influences of land-use disturbances on invertebrate assemblages in streams draining eight areas of the Great Barrier Reef catchment in tropical Australia (~15.7–22°S), a region of high biodiversity. We used distance-based linear modelling (DistLM) to analyse assemblage data (103 taxa), richness and the SIGNAL2 taxon sensitivity index. DistLM of assemblages explained ~40% of variation across all samples and 7–54% of variation in individual areas. DistLM of richness and SIGNAL2 explained respectively 19–81 and 26–95% of variation. Explanatory variables were land use (especially cropping and grazing v. forest), riparian width, instream habitat, climate (drier south) and water quality (conductivity greater in south). Local impacts of activities such as mining were evident in models of individual areas. A detailed comparison of streams with contrasting riparian management demonstrated a 25% loss of richness, but no change in SIGNAL2 score. Accounting for local environmental gradients and using measures appropriate to the type of disturbance improved identification of impacts, and could form a framework for future regional monitoring of stream ecological condition. The impacts identified may be mitigated by remediation such as riparian rehabilitation, although management at catchment scales is required to be effective.

Cafeteria diet and probiotic therapy: cross talk among memory, neuroplasticity, serotonin receptors and gut microbiota in the rat.

The western diet is known to have detrimental effects on cognition and the gut microbiota, but few studies have investigated how these may be related. Here, we examined whether a probiotic could prevent diet-induced memory deficits. Rats were pre-exposed to vehicle, low or high doses of VSL#3 for 2 weeks before half were switched from chow to a cafeteria diet (Caf) for 25 days; VSL#3 treatment continued until death. High-dose VSL#3 prevented the diet-induced memory deficits on the hippocampal-dependent place task, but the probiotic caused deficits on the perirhinal-dependent object task, irrespective of diet or dose. No differences were observed in anxiety-like behaviour on the elevated plus maze. Gut microbial diversity was dramatically decreased by Caf diet and here, VSL#3 was able to increase the abundance of some taxa contained in the probiotic such as Streptococcus and Lactobacillus and also other taxa including Butyrivibrio, which were decreased by the Caf diet. This affected the predicted profile of microbial metabolic pathways related to antioxidant and bile biosynthesis, and fat and carbohydrate metabolism. In the hippocampus, the Caf diet increased the expression of many genes related to neuroplasticity and serotonin receptor (5HT) 1A, which was normalised in Caf-High rats. Distance-based linear modelling showed that these genes were the best predictors of place memory, and related to microbiota principal component (PC) 1. Neuroplasticity genes in the perirhinal cortex were also affected and related to PC1 but object memory performance was correlated with perirhinal 5HT2C expression and microbiota PC3. These results show that probiotics can be beneficial in situations of gut dysbiosis where memory deficits are evident but may be detrimental in healthy subjects.

Ocean acidification impacts bacteria–phytoplankton coupling at low-nutrient conditions

Abstract. The oceans absorb about a quarter of the annually produced anthropogenic atmospheric carbon dioxide (CO2), resulting in a decrease in surface water pH, a process termed ocean acidification (OA). Surprisingly little is known about how OA affects the physiology of heterotrophic bacteria or the coupling of heterotrophic bacteria to phytoplankton when nutrients are limited. Previous experiments were, for the most part, undertaken during productive phases or following nutrient additions designed to stimulate algal blooms. Therefore, we performed an in situ large-volume mesocosm ( ∼ 55 m3) experiment in the Baltic Sea by simulating different fugacities of CO2 (fCO2) extending from present to future conditions. The study was conducted in July–August after the nominal spring bloom, in order to maintain low-nutrient conditions throughout the experiment. This resulted in phytoplankton communities dominated by small-sized functional groups (picophytoplankton). There was no consistent fCO2-induced effect on bacterial protein production (BPP), cell-specific BPP (csBPP) or biovolumes (BVs) of either free-living (FL) or particle-associated (PA) heterotrophic bacteria, when considered as individual components (univariate analyses). Permutational Multivariate Analysis of Variance (PERMANOVA) revealed a significant effect of the fCO2 treatment on entire assemblages of dissolved and particulate nutrients, metabolic parameters and the bacteria–phytoplankton community. However, distance-based linear modelling only identified fCO2 as a factor explaining the variability observed amongst the microbial community composition, but not for explaining variability within the metabolic parameters. This suggests that fCO2 impacts on microbial metabolic parameters occurred indirectly through varying physicochemical parameters and microbial species composition. Cluster analyses examining the co-occurrence of different functional groups of bacteria and phytoplankton further revealed a separation of the four fCO2-treated mesocosms from both control mesocosms, indicating that complex trophic interactions might be altered in a future acidified ocean. Possible consequences for nutrient cycling and carbon export are still largely unknown, in particular in a nutrient-limited ocean.

Ecological succession reveals potential signatures of marine–terrestrial transition in salt marsh fungal communities

Marine-to-terrestrial transition represents one of the most fundamental shifts in microbial life. Understanding the distribution and drivers of soil microbial communities across coastal ecosystems is critical given the roles of microbes in soil biogeochemistry and their multifaceted influence on landscape succession. Here, we studied the fungal community dynamics in a well-established salt marsh chronosequence that spans over a century of ecosystem development. We focussed on providing high-resolution assessments of community composition, diversity and ecophysiological shifts that yielded patterns of ecological succession through soil formation. Notably, despite containing 10- to 100-fold lower fungal internal transcribed spacer abundances, early-successional sites revealed fungal richnesses comparable to those of more mature soils. These newly formed sites also exhibited significant temporal variations in β-diversity that may be attributed to the highly dynamic nature of the system imposed by the tidal regime. The fungal community compositions and ecophysiological assignments changed substantially along the successional gradient, revealing a clear signature of ecological replacement and gradually transforming the environment from a marine into a terrestrial system. Moreover, distance-based linear modelling revealed soil physical structure and organic matter to be the best predictors of the shifts in fungal β-diversity along the chronosequence. Taken together, our study lays the basis for a better understanding of the spatiotemporally determined fungal community dynamics in salt marshes and highlights their ecophysiological traits and adaptation in an evolving ecosystem.

Assessing ecological community health in coastal estuarine systems impacted by multiple stressors

Increasing population pressure, urbanisation of the coastal zone and nutrient and sediment run-off from agriculture and forestry has increased the number of large-scale and chronic impacts affecting coastal and estuarine systems. The need to assess cumulative impacts is a major motivation for the current desire of managers and ecologists to define ecosystem “health” and “stress”. A number of univariate metrics have been proposed to monitor health, including indicator species, indicator ratios and diversity or contaminant metrics. Alternatively, multivariate methods can be used to test for changes in community structure due to stress. In this study we developed multivariate models using statistical ordination techniques to identify key stressors affecting the ‘health’ of estuarine macrofaunal communities. Macrofaunal and associated environmental samples were collected across 75 sites from within Tauranga Harbour, a large estuary located on New Zealand's North Island. The harbour receives discharges from urbanised, industrial, agricultural and horticultural catchments. Distance-based linear modelling identified sediments, nutrients and heavy metals as key ‘stressors’ affecting the ecology of the harbour. Therefore, three multivariate models were developed based on the variability in community composition using canonical analysis of principal coordinates (CAP). The multivariate models were found to be more sensitive to changing environmental health than simple univariate measures (abundance, species richness, evenness and Shannon–Wiener diversity) along an anthropogenic stress gradient. This multivariate approach can be used as a management or monitoring tool where sites are repeatedly sampled over time and tracked to determine whether the communities are moving towards a more healthy or unhealthy state. Ultimately, such statistical models provide a tool to forecast the distribution and abundance of species associated with habitat change and should enable long-term degradative change from multiple disturbances to be assessed.

The effects of exposure in sandy beach surf zones on larval fishes

The influence of wind and wave exposure on larval fish assemblages within a large bay system was investigated. Larval fishes were sampled from two areas with vastly different exposure to waves and wind, namely the windward and leeward sectors of Algoa Bay. In total, 5702 larval fishes were collected using a modified larval seine. Of these, 4391 were collected in the leeward and 1311 in the windward sector of the bay, representing a total of 23 families and 57 species. Dominant fish families included Clinidae, Engraulidae, Kyphosidae, Mugilidae, Soleidae and Sparidae, similar to the situation elsewhere, highlighting continuity in the composition of larval fish assemblages and the utilization of surf zones by a specific group of larval fishes. Nineteen estuary-associated marine species occurred within the surf zones of Algoa Bay and dominated catches (86·7%) in terms of abundance. Postflexion larvae comprised > 80% of the catch, indicating the importance of the seemingly inhospitable surf zone environment for the early life stages of many fish species. The greatest species diversity was observed within the windward sector of the bay. Distance-based linear modelling identified wave period as the environmental variable explaining the largest proportion of the significant variation in the larval fish assemblage. The physical disturbance generated by breaking waves could create a suitable environment for fish larvae, sheltered from predators and with an abundance of food resources.

Biogeographic patterns in scaled chrysophytes from the east coast of North America

Summary1. We assessed the distribution of scaled chrysophytes in fresh waters along 3200 km of the east coast of North America (29° to 48°N) to determine any biogeographic patterns in relation to chemical, physical, climatic and spatial variables.2. Scaled chrysophytes were identified using scanning electron microscopy and counted from 264 waterbodies in nine regions (20 subregions). Eighteen chemical, physical and climate variables were determined for each waterbody. We used Sorensen’s similarity index and analysis of similarity (ANOSIM) to evaluate whether the floras differed between regions, subregions, glaciated and non‐glaciated areas, as well as within sets of waterbodies with similar chemical and physical characteristics but situated in different regions. Distance‐based linear modelling (DISTLM) was used to evaluate the relative importance of the chemical, physical and climate factors in explaining the variability in the assemblages of scaled chrysophytes, and the resulting models were visualised using redundancy analysis (RDA).3. Significant differences in the flora were found between all regions and most subregions, and between glaciated and non‐glaciated areas. Significant differences were also recorded between waterbodies with similar chemical and physical characteristics but situated in different regions. Many species were abundant along specific sections of the latitudinal gradient, but lacking from others. A set of environmental variables explained significant and independent portions of the variation in scaled chrysophytes, with pH and mean minimum July temperature accounting for 20% of the total.4. The distribution of scaled chrysophytes along the east coast of North America is not homogeneous and there are biogeographic patterns, despite apparent dispersal mechanisms (migratory birds and wind events) that might act to reduce differences between regions. Rather, differences exist even between neighbouring subregions containing sites with statistically similar chemical and physical attributes. Environmental variables clearly play a significant role in determining whether species will inhabit a given site. However, species were not always found in waterbodies likely to support growth, implicating inadequate dispersal, poor transportability or both.

Environmental and landscape factors influencing ant and plant diversity in suburban riparian corridors

Urban riparian zones are highly valuable for a range of environmental, social and economic reasons. Despite their ecological complexity, legislative instruments underpinning riparian protection focus predominantly on minimum corridor widths required to fulfill environmental functions. This study sought to identify the dominant environmental variables that influence riparian corridor biodiversity in northern Sydney, Australia. Ant and plant assemblages were sampled from 18 riparian corridors of various widths. Environmental data pertaining to each corridor were collected using field and desktop surveys. Generalised Linear Modelling found perimeter:area ratio and the gradient of the slope perpendicular to the stream to predict significantly ant and plant richness. Plant richness was also influenced by vegetation community type and corridor width. When streamside vegetation communities were considered in isolation, many of the same factors were found to influence species richness. Likewise, Distance-based Linear Modelling identified vegetation community type and landscape connectivity as significant predictors of ant composition both in streamside habitats and those located across the full width of each riparian corridor sampled. While width was the best predictor of plant assemblage composition across the whole riparian corridor, streamside vegetation was influenced more significantly by soil pH. This result arose principally due to a dominance of exotic plants in alkaline soils. Although wider corridors were likely to encompass a greater variety of biotic assemblages, landscape and site scale environmental characteristics appeared to be of greater ecological significance. Environmental managers should therefore consider these factors and target weed invasion when seeking to enhance biodiversity in urban riparian corridors.