Mira Grönroos

Environmental heterogeneity and β diversity of stream macroinvertebrate communities at intermediate spatial scales

Abstract. Theory predicts that different components of species diversity should increase with environmental heterogeneity. Our main aim was to examine the relationship between &bgr;-diversity and environmental heterogeneity in a system with high habitat heterogeneity and very small spatial distances between sites. This system allowed us to examine the effect of habitat heterogeneity on &bgr;-diversity in the absence of dispersal limitation. We surveyed 100 riffle sites (10 riffles in each of 10 streams) for benthic macroinvertebrates in a boreal drainage basin. Streams differed in average community composition (based on canonical analysis of principal coordinates) and heterogeneity in community composition (based on test of homogeneity of dispersion). These results were robust regardless of the distance measures used in distance-based multivariate analyses. &bgr;-diversity was not significantly correlated with stream habitat heterogeneity, despite the fact that the latter was quantified by a large set of environmental variables deemed important for species occurrence in our study streams. Thus, we suggest that the relationship between &bgr;-diversity and habitat heterogeneity was masked by individual species–environment responses and mass effects. Thus, the &bgr;-diversity–habitat heterogeneity relationship may not always be significant, a result that may have important consequences for understanding the structure of community patterns. Despite the absence of a significant &bgr;-diversity–habitat heterogeneity relationship, community structure was significantly associated with environmental factors (e.g., moss cover, stream width, velocity) across the streams in distance-based redundancy analysis. This finding suggests that different ways to associate &bgr;-diversity, community structure, and environmental conditions may yield different insights into the structure of biotic communities.

Exploring species and site contributions to beta diversity in stream insect assemblages.

It was recently suggested that beta diversity can be partitioned into contributions of single sites to overall beta diversity (LCBD) or into contributions of individual species to overall beta diversity (SCBD). We explored the relationships of LCBD and SCBD to site and species characteristics, respectively, in stream insect assemblages. We found that LCBD was mostly explained by variation in species richness, with a negative relationship being detected. SCBD was strongly related to various species characteristics, such as occupancy, abundance, niche position and niche breadth, but was only weakly related to biological traits of species. In particular, occupancy and its quadratic terms showed a very strong unimodal relationship with SCBD, suggesting that intermediate species in terms of site occupancy contribute most to beta diversity. Our findings of unravelling the contributions of sites or species to overall beta diversity are of high importance to community ecology, conservation and bioassessment using stream insect assemblages, and may bear some overall generalities to be found in other organism groups.

Hierarchical decomposition of trait patterns of macroinvertebrate communities in subarctic streams

Ecological research based on both species and their traits helps us understand the mechanisms structuring ecological communities. Our aim was to dismantle the effects of environmental variables measured at multiple spatial scales on the taxonomic and functional trait composition of benthic macroinvertebrate communities and to clarify the relationship between the environment and communities in high-latitude streams. Traits were combined into unique trait combinations (site-by-traits matrix), called hereafter the overall trait composition of macroinvertebrate communities, and then the matrix was decomposed into progressively smaller parts of individual traits (site-by-individual trait matrix). The effects of variables from different spatial scales on the variation in the overall trait matrix, decomposed trait matrices, and taxonomic data were analyzed using redundancy analysis and partial linear regression modeling. Our analyses indicated that: 1) the taxonomic composition of communities was more closely associated with factors measured at larger spatial scales, and the trait composition of communities was more closely associated with factors measured at smaller spatial scales, even within 1 drainage basin; 2) decomposing overall trait composition to its individual components of single traits revealed important patterns related to the potential causal factors; and 3) the abundances of organisms exhibiting different traits may be linked strongly to different environmental variables operating at different spatial scales. Our findings highlight the benefits of describing both the taxonomic and trait composition of communities when exploring the drivers of community composition. They also have direct applications in monitoring the vulnerability of high-latitude streams to future environmental changes.

Urbanization Reduces Transfer of Diverse Environmental Microbiota Indoors

Expanding urbanization is a major factor behind rapidly declining biodiversity. It has been proposed that in urbanized societies, the rarity of contact with diverse environmental microbiota negatively impacts immune function and ultimately increases the risk for allergies and other immune-mediated disorders. Surprisingly, the basic assumption that urbanization reduces exposure to environmental microbiota and its transfer indoors has rarely been examined. We investigated if the land use type around Finnish homes affects the diversity, richness, and abundance of bacterial communities indoors. Debris deposited on standardized doormats was collected in 30 rural and 26 urban households in and near the city of Lahti, Finland, in August 2015. Debris was weighed, bacterial community composition determined by high throughput sequencing of bacterial 16S ribosomal RNA (rRNA) gene on the Illumina MiSeq platform, and the percentage of four different land use types (i.e., built area, forest, transitional, and open area) within 200 m and 2000 m radiuses from each household was characterized. The quantity of doormat debris was inversely correlated with coverage of built area. The diversity of total bacterial, Proteobacterial, Actinobacterial, Bacteroidetes, and Firmicutes communities decreased as the percentage of built area increased. Their richness followed the same pattern except for Firmicutes for which no association was observed. The relative abundance of Proteobacteria and particularly Gammaproteobacteria increased, whereas that of Actinobacteria decreased with increasing built area. Neither Phylum Firmicutes nor Bacteroidetes varied with coverage of built area. Additionally, the relative abundance of potentially pathogenic bacterial families and genera increased as the percentage of built area increased. Interestingly, having domestic animals (including pets) only altered the association between the richness of Gammaproteobacteria and diversity of Firmicutes with the built area coverage suggesting that animal ownership minimally affects transfer of environmental microbiota indoors from the living environment. These results support the hypothesis that people living in densely built areas are less exposed to diverse environmental microbiota than people living in more sparsely built areas.

The abundance of health-associated bacteria is altered in PAH polluted soils - Implications for health in urban areas

Long-term exposure to polyaromatic hydrocarbons (PAHs) has been connected to chronic human health disorders. It is also well-known that i) PAH contamination alters soil bacterial communities, ii) human microbiome is associated with environmental microbiome, and iii) alteration in the abundance of members in several bacterial phyla is associated with adverse or beneficial human health effects. We hypothesized that soil pollution by PAHs altered soil bacterial communities that had known associations with human health. The rationale behind our study was to increase understanding and potentially facilitate reconsidering factors that lead to health disorders in areas characterized by PAH contamination. Large containers filled with either spruce forest soil, pine forest soil, peat, or glacial sand were left to incubate or contaminated with creosote. Biological degradation of PAHs was monitored using GC-MS, and the bacterial community composition was analyzed using 454 pyrosequencing. Proteobacteria had higher and Actinobacteria and Bacteroidetes had lower relative abundance in creosote contaminated soils than in non-contaminated soils. Earlier studies have demonstrated that an increase in the abundance of Proteobacteria and decreased abundance of the phyla Actinobacteria and Bacteroidetes are particularly associated with adverse health outcomes and immunological disorders. Therefore, we propose that pollution-induced shifts in natural soil bacterial community, like in PAH-polluted areas, can contribute to the prevalence of chronic diseases. We encourage studies that simultaneously address the classic “adverse toxin effect” paradigm and our novel “altered environmental microbiome” hypothesis.

Predicting occupancy and abundance by niche position, niche breadth and body size in stream organisms

The regional occupancy and local abundance of species are thought to be strongly correlated to their body size, niche breadth and niche position. The strength of the relationships among these variables can also differ between different organismal groups. Here, we analyzed data on stream diatoms and insects from a high-latitude drainage basin to investigate these relationships. To generate measures of niche position and niche breadth for each species, we used sets of local environmental and catchment variables separately, applying the outlying mean index analysis. Beta regression and negative binomial generalized linear models were run to predict regional occupancy and mean local abundance, respectively. We found a positive occupancy–abundance relationship in both diatoms and insects, and that niche-based variables were the main predictors of variation in regional occupancy and local abundance. This finding was mainly due to local environmental niche position, whereas the effects of niche breadth on regional occupancy and local abundance were less important. We also found a relationship between body size and local abundance or regional occupancy of diatoms. Our results thus add to current macroecological research by emphasizing the strong importance of niche position rather than niche breadth and body size for regional occupancy and local abundance in rarely studied organisms (e.g., diatoms and insects) and ecosystems (i.e., wilderness streams).

Half-lives of PAHs and temporal microbiota changes in commonly used urban landscaping materials

Background Polycyclic aromatic hydrocarbons (PAHs) accumulate in urban soils, and PAH contamination can change soil microbial community composition. Environmental microbiota is associated with human commensal microbiota, immune system and health. Therefore, studies investigating the degradation of PAHs, and the consequences of soil pollution on microbial communities in urban landscaping materials, are crucial. Methods Four landscaping materials (organic matter 1, 2, 13 and 56%) were contaminated with PAHs commonly found at urban sites (phenanthrene, fluoranthene, pyrene, chrysene and benzo(b)fluoranthene) in PAH concentrations that reflect urban soils in Finland (2.4 µg g -1 soil dry weight). PAHs were analyzed initially and after 2, 4, 8 and 12 weeks by gas chromatography-mass spectrometry. Half-lives of PAHs were determined based on 12-weeks degradation. Bacterial communities were analyzed at 1 and 12 weeks after contamination using Illumina MiSeq 16S rRNA gene metabarcoding. Results Half-lives ranged from 1.5 to 4.4 weeks for PAHs with relatively low molecular weights (phenanthrene, fluoranthene and pyrene) in landscaping materials containing 1–2% organic matter. In contrast, in materials containing 13% and 56% organic matter, the half-lives ranged from 2.5 to 52 weeks. Shorter half-lives of phenanthrene and fluoranthene were thus associated with low organic matter content. The half-life of pyrene was inversely related to the relative abundance of Beta-, Delta- and Gammaproteobacteria, and diversity of Bacteroidetes and Betaprotebacteria. Compounds with higher molecular weights followed compound-specific patterns. Benzo(b)fluoranthene was resistant to degradation and half-life of chrysene was shorter when the relative abundance of Betaproteobacteria was high. Temporal microbiota changes involved increase in the relative abundance of Deltaproteobacteria and decrease in genera Flavobacterium and Rhodanobacter. Exposure to PAHs seems to adjust microbial community composition, particularly within class Beta- and Deltaproteobacteria. Conclusions In this study, PAH degradation depended on the organic matter content and bacterial community composition of landscaping materials. Contamination seems to alter bacterial community composition in landscaping materials depending on material type. This alteration includes changes in bacterial phyla associated with human health and immune system. This may open new possibilities for managing urban environments by careful selection of landscaping materials, to benefit health and wellbeing.

Short‐term direct contact with soil and plant materials leads to an immediate increase in diversity of skin microbiota

Immune‐mediated diseases have increased during the last decades in urban environments. The hygiene hypothesis suggests that increased hygiene level and reduced contacts with natural biodiversity are related to the increase in immune‐mediated diseases. We tested whether short‐time contact with microbiologically diverse nature‐based materials immediately change bacterial diversity on human skin. We tested direct skin contact, as two volunteers rubbed their hands with sixteen soil and plant based materials, and an exposure via fabric packets filled with moss material. Skin swabs were taken before and after both exposures. Next‐generation sequencing showed that exposures increased, at least temporarily, the total diversity of skin microbiota and the diversity of Acidobacteria, Actinobacteria, Bacteroidetes, Proteobacteria and Alpha‐, Beta‐ and Gammaproteobacteria suggesting that contact with nature‐based materials modify skin microbiome and increase skin microbial diversity. Until now, approaches to cure or prevent immune system disorders using microbe‐based treatments have been limited to use of a few microbial species. We propose that nature‐based materials with high natural diversity, such as the materials tested here, might be more effective in modifying human skin microbiome, and eventually, in reducing immune system disorders. Future studies should investigate how long‐term changes in skin microbiota are achieved and if the exposure induces beneficial changes in the immune system markers.

Nature-derived microbiota exposure as a novel immunomodulatory approach

AIM Current attempts to modulate the human microbiota and immune responses are based on probiotics or human-derived bacterial transplants. We investigated microbial modulation by soil and plant-based material. MATERIALS & METHODS We performed a pilot study in which healthy adults were exposed to the varied microbial community of a soil- and plant-based material. RESULTS The method was safe and feasible; exposure was associated with an increase in gut microbial diversity. CONCLUSION If these findings are reproduced in larger studies nature-derived microbial exposure strategies could be further developed for testing their efficacy in the treatment and prevention of immune-mediated diseases.

Different species trait groups of stream diatoms show divergent responses to spatial and environmental factors in a subarctic drainage basin

Understanding the drivers of community structure is an important topic in ecology. We examined whether different species trait groups of stream diatoms (ecological guilds and specialization groups) show divergent responses to spatial and environmental factors in a subarctic drainage basin. We used local- and catchment-scale environmental and spatial variables in redundancy analysis and variation partitioning to examine community structuring. Local and catchment conditions and spatial variables affected diatom community structure with different relative importance. Local-scale environmental variables explained most of the variation in the low-profile and motile guilds, whereas local and spatial variables explained the same amount of the variation in the high-profile guild. The variations in the planktic guild and the specialist species were best explained by spatial variables, and catchment variables explained most variation only in generalist species. Our study showed that diatom communities in subarctic streams are a result of both environmental filtering and spatial processes. Our findings also suggested that dividing whole community into different groups by species traits can increase understanding of metacommunity organization.