Browsing by Subject "community structure"

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  • Halliday, Fletcher W.; Rohr, Jason R.; Laine, Anna-Liisa (2020)
    The dilution effect predicts increasing biodiversity to reduce the risk of infection, but the generality of this effect remains unresolved. Because biodiversity loss generates predictable changes in host community competence, we hypothesised that biodiversity loss might drive the dilution effect. We tested this hypothesis by reanalysing four previously published meta-analyses that came to contradictory conclusions regarding generality of the dilution effect. In the context of biodiversity loss, our analyses revealed a unifying pattern: dilution effects were inconsistently observed for natural biodiversity gradients, but were commonly observed for biodiversity gradients generated by disturbances causing losses of biodiversity. Incorporating biodiversity loss into tests of generality of the dilution effect further indicated that scale-dependency may strengthen the dilution effect only when biodiversity gradients are driven by biodiversity loss. Together, these results help to resolve one of the most contentious issues in disease ecology: the generality of the dilution effect.
  • Hill, Matthew J.; Heino, Jani; White, James C.; Ryves, David B.; Wood, Paul J. (2019)
    Biological Conservation 237: 348-357
    Understanding the spatial patterns and environmental drivers of freshwater diversity and community structure is a key challenge in biogeography and conservation biology. However, previous studies have focussed primarily on taxonomic diversity and have largely ignored the phylogenetic and functional facets resulting in an incomplete understanding of the community assembly. Here, we examine the influence of local environmental, hydrological proximity effects, land-use type and spatial structuring on taxonomic, functional and phylogenetic (using taxonomic relatedness as a proxy) alpha and beta diversity (including the turnover and nestedness-resultant components) of pond macroinvertebrate communities. Ninety-five ponds across urban and non-urban land-uses in Leicestershire, UK were examined. Functional and phylogenetic alpha diversity were negatively correlated with species richness. At the alpha scale, functional diversity and taxonomic richness were primarily determined by local environmental factors while phylogenetic alpha diversity was driven by spatial factors. Compositional variation (beta diversity) of the different facets and components of functional and phylogenetic diversity were largely determined by local environmental variables. Pond surface area, dry phase length and macrophyte cover were consistently important predictors of the different facets and components of alpha and beta diversity. Our results suggest that pond management activities aimed at improving biodiversity should focus on improving and/or restoring local environmental conditions. Quantifying alpha and beta diversity of the different biodiversity facets facilitates a more accurate assessment of patterns in diversity and community structure. Integrating taxonomic, phylogenetic and functional diversity into conservation strategies will increase their efficiency and effectiveness, and maximise biodiversity protection in human-modified landscapes.
  • Koskinen, Janne; Roslin, Tomas; Nyman, Tommi; Abrego, Nerea; Michell, Craig; Vesterinen, Eero J. (2019)
    Fruiting bodies of fungi constitute an important resource for thousands of other taxa. The structure of these diverse assemblages has traditionally been studied with labour-intensive methods involving cultivation and morphology-based species identification, to which molecular information might offer convenient complements. To overcome challenges in DNA extraction and PCR associated with the complex chemical properties of fruiting bodies, we developed a pipeline applicable for extracting amplifiable total DNA from soft fungal samples of any size. Our protocol purifies DNA in two sequential steps: (a) initial salt-isopropanol extraction of all nucleic acids in the sample is followed by (b) an extra clean-up step using solid-phase reversible immobilization (SPRI) magnetic beads. The protocol proved highly efficient, with practically all of our samples-regardless of biomass or other properties-being successfully PCR-amplified using metabarcoding primers and subsequently sequenced. As a proof of concept, we apply our methods to address a topical ecological question: is host specificity a major characteristic of fungus-associated communities, that is, do different fungus species harbour different communities of associated organisms? Based on an analysis of 312 fungal fruiting bodies representing 10 species in five genera from three orders, we show that molecular methods are suitable for studying this rich natural microcosm. Comparing to previous knowledge based on rearing and morphology-based identifications, we find a species-rich assemblage characterized by a low degree of host specialization. Our method opens up new horizons for molecular analyses of fungus-associated interaction webs and communities.
  • Frelat, Romain; Kortsch, Susanne; Kroencke, Ingrid; Neumann, Hermann; Nordstroem, Marie C.; Olivier, Pierre E. N.; Sell, Anne F. (2022)
    Ecological communities are constantly changing as a response to environmental and anthropogenic pressures. Yet, how changes in community composition influence the structure of food webs over time and space remains elusive. Using ecological network analysis, we assessed how food web structure changed across six distinct areas of the North Sea over a sixteen-year time-period. We used multivariate analyses to disentangle and compare spatio-temporal dynamics in community composition (i.e. changes in species abundances) and food web structure (i.e. changes in network properties). Specifically, we assessed how changes in community composition were reflected in food web structure. Our results revealed a strong spatial coupling between community composition and food web structure along a south-north gradient. However, the temporal covariation between community composition and food web structure depended on the spatial scale. We observed a temporal mismatch at regional scale, but a strong coupling at local scale. In particular, we found that community composition can be influenced by hydro-climatic events over large areas, with diverse effects manifesting in local food web structure. Our proposed methodological framework quantified and compared spatio-temporal changes in community composition and food web structure, providing key information to support effective management strategies aimed at conserving the structure and functioning of ecological communities in times of environmental change.
  • Pöysä, Hannu; Elmberg, Johan; Gunnarsson, Gunnar; Holopainen, Sari Taija; Nummi, Petri Johannes; Sjöberg, Kjell (2018)
    The Whooper Swan (Cygnus cygnus) is a good example of successful conservation, with rapidly growing numbers in Fennoscandia in recent decades. To the contrary, Eurasian Wigeon (Mareca penelope) shows a strong negative trend in breeding numbers, which raises conservation concerns. Previous research suggests a causal link between recent population trajectories of the two species. Both preferentially breed on wetlands with abundant horsetail (Equisetum spp.), a plant providing food for Whooper Swan and crucial feeding microhabitat for Eurasian Wigeon broods. We here test predictions based on the hypothesis that grazing on Equisetum by Whooper Swan reduces breeding habitat or breeding habitat quality for Eurasian Wigeon. We use data from 60 lakes in which waterfowl were counted in 1990-1991 and 2016, and Equisetum was mapped in 1990-1991 and 2013-2014. Lakes colonized by Whooper Swan typically had more abundant Equisetum vegetation in the past than lakes not colonized. Lake-specific decrease of Equisetum was not associated with colonization by Whooper Swan. The number of lakes occupied by Eurasian Wigeon decreased, but the decrease was not stronger on lakes colonized by Whooper Swan than on those that were not. Contrary to our prediction, current Eurasian Wigeon abundance was positively associated with Whooper Swan abundance. Moreover, Eurasian Wigeon did not decrease more on lakes from which Equisetum disappeared than on lakes in which there was still Equisetum left. This study does not support the idea that Whooper Swan affects Eurasian Wigeon negatively by grazing on Equisetum.
  • Antao, Laura; Magurran, Anne E.; Dornelas, Maria (2021)
    Species abundance distributions (SADs) describe community structure and are a key component of biodiversity theory and research. Although different distributions have been proposed to represent SADs at different scales, a systematic empirical assessment of how SAD shape varies across wide scale gradients is lacking. Here, we examined 11 empirical large-scale datasets for a wide range of taxa and used maximum likelihood methods to compare the fit of the logseries, lognormal, and multimodal (i.e., with multiple modes of abundance) models to SADs across a scale gradient spanning several orders of magnitude. Overall, there was a higher prevalence of multimodality for larger spatial extents, whereas the logseries was exclusively selected as best fit for smaller areas. For many communities the shape of the SAD at the largest spatial extent (either lognormal or multimodal) was conserved across the scale gradient, despite steep declines in area and taxonomic diversity sampled. Additionally, SAD shape was affected by species richness, but we did not detect a systematic effect of the total number of individuals. Our results reveal clear departures from the predictions of two major macroecological theories of biodiversity for SAD shape. Specifically, neither the Neutral Theory of Biodiversity (NTB) nor the Maximum Entropy Theory of Ecology (METE) are able to accommodate the variability in SAD shape we encountered. This is highlighted by the inadequacy of the logseries distribution at larger scales, contrary to predictions of the NTB, and by departures from METE expectation across scales. Importantly, neither theory accounts for multiple modes in SADs. We suggest our results are underpinned by both inter- and intraspecific spatial aggregation patterns, highlighting the importance of spatial distributions as determinants of biodiversity patterns. Critical developments for macroecological biodiversity theories remain in incorporating the effect of spatial scale, ecological heterogeneity and spatial aggregation patterns in determining SAD shape.
  • Söderström, Panu; Schulman, Harry; Ristimäki, Mika (Finnish Environment Institute, 2015)
    Reports of the Finnish Environment Institute 16/2015
    The study focuses on differences and similarities of land use patterns, regional and urban structures and traffic systems in the Helsinki and Stockholm city regions. The viewpoint of the study is connected to the theory of three urban fabrics (walking city, transit city, car city). The fabrics differ from each other in terms of their physical structure and the travel alternatives they offer. In the GIS analyses, the studied metropolitan regions are divided into urban, peri-urban and rural areas, which are further classified into travel-related zones (pedestrian, transit and caroriented). Statistical data about the amounts and densities of population and workplaces can thus be compared in a rather detailed spatial level between different parts of the metropolitan areas. Finnish city regions have been studied using the travel related zone model quite widely. However it has not been possible to compare Helsinki region to any other city region in Finland, because Helsinki region is the only international level metropolitan area in the country. In this report the zone analyses is extended to a comparison of two Nordic capital regions. The results of the study indicate that Stockholm has managed to channel the growth of the metropolitan area more inwards, densifying the inner areas of the city region. In the Helsinki region the growth has turned from the peri-urban areas to the core areas notably later, but since 2008 the growth of the core areas has been dominant also in Helsinki.
  • Westerbom, Mats; Kraufvelin, Patrik; Erlandsson, Johan; Korpinen, Samuli; Mustonen, Olli; Díaz, Eliecer (2019)
    Abstract Ecological patterns are inherently scale-dependent and driven by the interplay of abiotic gradients and biotic processes. Despite the fundamental importance of such gradients, there are many gaps in our understanding of how abiotic stress gradients interplay with biotic processes and how these collectively affect species distributions. Using a hierarchical design, we sampled two communities separated by depth along wave exposure and salinity gradients to elucidate how these two gradients affect species composition in habitats formed by the foundation species Mytilus trossulus and Fucus vesiculosus. Specifically, we looked at the impacts of regional salinity and temperature, local wave exposure, and site-dependent facilitation effects on the associated community composition. Wave exposure was the best predictor for species assembly structure, which was also affected by Mytilus biomass and by salinity and water temperature. While the tested variables provided robust explanations for community structure and density, they did not provide conclusive explanations for variation in species richness or evenness. Mytilus biomass had a stronger effect on the associated community with increasing wave exposure at the deeper depth, but the patterns were less obvious at the shallower depth. The latter was also the case for Fucus. These findings comply partly with theoretical predictions suggesting stronger facilitation effects in physically harsh environments. Our results indicate that environmental drivers are the main structuring forces that affect species assembly structure, but also foundation species are important. Thus, predicting changes in species distributions and biodiversity requires the simultaneous consideration of environmental gradients, as well as the structure and composition of foundation species and the interplay between these factors. This work advances our understanding of the processes that modulate species distributions in a marginal marine area and broadens the knowledge of how biological and environmental factors interplay and have an influence on hard-bottom community structure in brackish water seas.
  • Ovaskainen, Otso; Rybicki, Joel; Abrego, Nerea (2019)
    A key challenge for community ecology is to understand to what extent observational data can be used to infer the underlying community assembly processes. As different processes can lead to similar or even identical patterns, statistical analyses of non-manipulative observational data never yield undisputable causal inference on the underlying processes. Still, most empirical studies in community ecology are based on observational data, and hence understanding under which circumstances such data can shed light on assembly processes is a central concern for community ecologists. We simulated a spatial agent-based model that generates variation in metacommunity dynamics across multiple axes, including the four classic metacommunity paradigms as special cases. We further simulated a virtual ecologist who analysed snapshot data sampled from the simulations using eighteen output metrics derived from beta-diversity and habitat variation indices, variation partitioning and joint species distribution modelling. Our results indicated two main axes of variation in the output metrics. The first axis of variation described whether the landscape has patchy or continuous variation, and thus was essentially independent of the properties of the species community. The second axis of variation related to the level of predictability of the metacommunity. The most predictable communities were niche-based metacommunities inhabiting static landscapes with marked environmental heterogeneity, such as metacommunities following the species sorting paradigm or the mass effects paradigm. The most unpredictable communities were neutral-based metacommunities inhabiting dynamics landscapes with little spatial heterogeneity, such as metacommunities following the neutral or patch sorting paradigms. The output metrics from joint species distribution modelling yielded generally the highest resolution to disentangle among the simulated scenarios. Yet, the different types of statistical approaches utilized in this study carried complementary information, and thus our results suggest that the most comprehensive evaluation of metacommunity structure can be obtained by combining them.