Browsing by Subject "DISSIMILARITY"

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  • Langenheder, Silke; Wang, Jianjun; Karjalainen, Satu Maaria; Laamanen, Tiina M.; Tolonen, Kimmo T.; Vilmi, Annika; Heino, Jani (2017)
    The spatial structure and underlying assembly mechanisms of bacterial communities have been studied widely across aquatic systems, focusing primarily on isolated sites, such as different lakes, ponds and streams. Here, our main aim was to determine the underlying mechanisms for bacterial biofilm assembly within a large, highly connected lake system in Northern Finland using associative methods based on taxonomic and phylogenetic alpha-and beta-diversity and a large number of abiotic and biotic variables. Furthermore, null model approaches were used to quantify the relative importance of different community assembly processes. We found that spatial variation in bacterial communities within the lake was structured by different assembly processes, including stochasticity, species sorting and potentially even dispersal limitation. Species sorting by abiotic environmental conditions explained more of the taxonomic and particularly phylogenetic turnover in community composition compared with that by biotic variables. Finally, we observed clear differences in alpha diversity (species richness and phylogenetic diversity), which were to a stronger extent determined by abiotic compared with biotic factors, but also by dispersal effects. In summary, our study shows that the biodiversity of bacterial biofilm communities within a lake ecosystem is driven by within-habitat gradients in abiotic conditions and by stochastic and deterministic dispersal processes.
  • Ilmarinen, Ville-Juhani; Vainikainen, Mari-Pauliina; Verkasalo, Markku Johannes; Lonnqvist, Jan-Erik (2017)
    Even though homophily (love of the same) is often thought of as a standard feature of friendships, the empirical evidence for attraction based on personality trait similarity is mixed at best. One reason for the inconsistent findings across studies could be variation in the large-scale social environment in which the studies have been conducted. We investigated whether diversity in the everyday social ecologies of 7- to 8-year-old children (N=549) moderates whether friendships are formed on the basis of similar personality traits and similar levels of Cognitive ability. Moderated polynomial regression and response surface analyses showed that classroom size moderated homophily based on Openness to Experience: children similar in Openness were more likely to form friendship ties, but only in larger classrooms. Moreover, we found homophily for Cognitive ability, especially among girls. The results for Openness and Cognitive ability were independent of each other. We discuss the social relevance of trait Openness and the notion that capacity to reciprocate underlies homophily based on Cognitive ability. Copyright (c) 2017 European Association of Personality Psychology
  • Milardi, Marco; Gavioli, Anna; Castaldelli, Giuseppe; Soininen, Janne (2019)
    We investigated the relationships between exotic freshwater fish invasions, environmental factors and ecofunctional diversity (i.e. the combination of ecological traits in communities) in streams. We used data from 335 stream sites, belonging to 105 watersheds and 3 basins in Italy, to test whether the exotic species invasion was dominated by species with generalist traits and whether the environment-ecofunctional trait relationships of exotic and native species would differ from each other. We also tested the hypothesis that ecofunctional uniqueness patterns between exotic and native species would be substantially different. We found that generalist traits were widespread in nearly all areas where exotic species occurred, but not all generalist traits were equally abundant in exotic communities. Only temperature tolerant, low oxygen tolerant and eurytopic traits were typically more dominant in exotic communities than native ones, suggesting that not all generalist traits are equally important in the invasion process and that more complex mechanisms of trait selection could take place. Environment-ecofunctional trait relationships of exotic and native species partly differed both in direction and magnitude, suggesting that invasion dynamics could decouple the linkage between environment and biotic communities, but also that this decoupling might decrease at later invasion stages (i.e. > 30 years after major invasions). Finally, site and trait ecofunctional uniqueness differed between exotic and native species. Exotic species ecofunctional diversity hotspots were located in human-disturbed areas, suggesting that human disturbance might play a strong role in invasion patterns. We advocate for a wider use of ecofunctional approaches in conservation studies in the future, as they could be a key to understand complex ecological processes such as exotic invasions.