Browsing by Subject "community assembly"

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  • Norberg, Anna; Abrego Antia, Nerea; Blanchet, F. Guillaume; Adler, Frederick R.; Anderson, Barbara J.; Anttila, Jani; Araújo, Miguel B.; Dallas, Tad Anthony; Dunson, David; Elith, Jane; Foster, Scott; Fox, Richard; Franklin, Janet; Godsoe, William; Guisan, Antoine; O'Hara, Bob; Hill, Nicole A.; Holt, Robert D.; Hui, Francis K.C; Husby, Magne; Kålås, John Atle; Lehikoinen, Aleksi; Luoto, Miska; Mod, Heidi K.; Newell, Graeme; Renner, Ian; Roslin, Tomas Valter; Soininen, Janne; Thuiller, Wilfried; Vanhatalo, Jarno Petteri; Warton, David; White, Matt; Zimmermann, Niklaus E.; Gravel, Dominique; Ovaskainen, Otso Tapio (2019)
    A large array of species distribution model (SDM) approaches has been developed for explaining and predicting the occurrences of individual species or species assemblages. Given the wealth of existing models, it is unclear which models perform best for interpolation or extrapolation of existing data sets, particularly when one is concerned with species assemblages. We compared the predictive performance of 33 variants of 15 widely applied and recently emerged SDMs in the context of multispecies data, including both joint SDMs that model multiple species together, and stacked SDMs that model each species individually combining the predictions afterward. We offer a comprehensive evaluation of these SDM approaches by examining their performance in predicting withheld empirical validation data of different sizes representing five different taxonomic groups, and for prediction tasks related to both interpolation and extrapolation. We measure predictive performance by 12 measures of accuracy, discrimination power, calibration, and precision of predictions, for the biological levels of species occurrence, species richness, and community composition. Our results show large variation among the models in their predictive performance, especially for communities comprising many species that are rare. The results do not reveal any major trade-offs among measures of model performance; the same models performed generally well in terms of accuracy, discrimination, and calibration, and for the biological levels of individual species, species richness, and community composition. In contrast, the models that gave the most precise predictions were not well calibrated, suggesting that poorly performing models can make overconfident predictions. However, none of the models performed well for all prediction tasks. As a general strategy, we therefore propose that researchers fit a small set of models showing complementary performance, and then apply a cross-validation procedure involving separate data to establish which of these models performs best for the goal of the study.
  • Abrego, Nerea; Roslin, Tomas; Huotari, Tea; Ji, Yinqiu; Schmidt, Niels Martin; Wang, Jiaxin; Yu, Douglas W.; Ovaskainen, Otso (2021)
    Species interactions are known to structure ecological communities. Still, the influence of climate change on biodiversity has primarily been evaluated by correlating individual species distributions with local climatic descriptors, then extrapolating into future climate scenarios. We ask whether predictions on arctic arthropod response to climate change can be improved by accounting for species interactions. For this, we use a 14-year-long, weekly time series from Greenland, resolved to the species level by mitogenome mapping. During the study period, temperature increased by 2 degrees C and arthropod species richness halved. We show that with abiotic variables alone, we are essentially unable to predict species responses, but with species interactions included, the predictive power of the models improves considerably. Cascading trophic effects thereby emerge as important in structuring biodiversity response to climate change. Given the need to scale up from species-level to community-level projections of biodiversity change, these results represent a major step forward for predictive ecology.
  • Kyrö, Kukka; Kankaanpaeae, Tuomas; Vesterinen, Eero J.; Lehvävirta, Susanna; Kotze, David Johannes (2022)
    Vegetated roofs are human-manufactured ecosystems and potentially promising conservation tools for various taxa and habitats. Focussing on arthropods, we conducted a 3 year study on newly constructed vegetated roofs with shallow substrates (up to 10 cm) and vegetation established with pre-grown mats, plug plants and seeds to describe pioneer arthropod communities on roofs and to compare them with ground level communities. We vacuum sampled arthropods from the roofs and nearby ground level sites with low, open vegetation, i.e., potential source habitats. We showed that the roofs and ground sites resembled each other for ordinal species richness but differed in community composition: with time the roofs started to resemble each other rather than their closest ground level habitats. Species richness increased with time on roofs and at ground level, but the roofs had consistently less species than the ground sites and only a few species were unique to the roofs. Also, the proportion of predators increased on roofs, while not at ground level. We conclude that vegetated roofs established with similar substrates and vegetation, filter arthropods in a way that produces novel communities that are different from those at ground level but similar to one another. The role of these insular communities in species networks and ecosystem function remains to be investigated.
  • 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.
  • Siqueira, Tadeu; Saito, Victor S.; Bini, Luis M.; Melo, Adriano S.; Petsch, Danielle K.; Landeiro, Victor L.; Tolonen, Kimmo T.; Jyrkänkallio-Mikkola, Jenny; Soininen, Janne; Heino, Jani (2020)
    Ecological drift can override the effects of deterministic niche selection on small populations and drive the assembly of some ecological communities. We tested this hypothesis with a unique data set sampled identically in 200 streams in two regions (tropical Brazil and boreal Finland) that differ in macroinvertebrate community size by fivefold. Null models allowed us to estimate the magnitude to which beta-diversity deviates from the expectation under a random assembly process while taking differences in richness and relative abundance into account, i.e., beta-deviation. We found that both abundance- and incidence-based beta-diversity was negatively related to community size only in Brazil. Also, beta-diversity of small tropical communities was closer to stochastic expectations compared with beta-diversity of large communities. We suggest that ecological drift may drive variation in some small communities by changing the expected outcome of niche selection, increasing the chances of species with low abundance and narrow distribution to occur in some communities. Habitat destruction, overexploitation, pollution, and reductions in connectivity have been reducing the size of biological communities. These environmental pressures might make smaller communities more vulnerable to novel conditions and render community dynamics more unpredictable. Incorporation of community size into ecological models should provide conceptual and applied insights into a better understanding of the processes driving biodiversity.
  • Leboucher, Thibault; Budnick, William R.; Passy, Sophia; Boutry, Sebastien; Jannoneau, Aurelien; Soininen, Janne; Vyverman, Wim; Tison-Rosebery, Juliette (2019)
    Aim To quantify the relative contributions of local community assembly processes versus gamma-diversity to beta-diversity, and to assess how spatial scale and anthropogenic disturbance (i.e. nutrient enrichment) interact to dictate which driver dominates. Location France and the United States. Time period 1993-2011. Major taxa studied Freshwater stream diatoms. Methods beta-diversity along a nutrient enrichment gradient was examined across multiple spatial scales. beta-diversity was estimated using multi-site Sorensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus gamma-diversity to beta-diversity across spatial scales, with a null model. Finally, we estimated the response of beta-diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests. Results beta-diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. beta-diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of beta-diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom beta-diversity and pure environmental distances under these conditions, highlighting the role of species sorting in local assembly processes. Conversely, in heavily enriched sites, only spatial distances were significantly correlated with beta-diversity, which indicated a substantial role of dispersal processes. Main conclusions Nutrient concentration mediated the expected increase in beta-diversity with spatial scales. Across spatial scales, beta-diversity was more influenced by local assembly processes rather than by gamma-diversity. Nutrient enrichment was associated with an overall decline in diatom beta-diversity and a shift in assembly processes from species sorting to dispersal, notably due to the elimination of some specialists and their subsequent replacement by generalists.
  • Hogle, Shane L.; Hepolehto, Iina; Ruokolainen, Lasse; Cairns, Johannes; Hiltunen, Teppo (2022)
    A popular idea in ecology is that trait variation among individuals from the same species may promote the coexistence of competing species. However, theoretical and empirical tests of this idea have yielded inconsistent findings. We manipulated intraspecific trait diversity in a ciliate competing with a nematode for bacterial prey in experimental microcosms. We found that intraspecific trait variation inverted the original competitive hierarchy to favour the consumer with variable traits, ultimately resulting in competitive exclusion. This competitive outcome was driven by foraging traits (size, speed and directionality) that increased the ciliate's fitness ratio and niche overlap with the nematode. The interplay between consumer trait variation and competition resulted in non-additive cascading effects-mediated through prey defence traits-on prey community assembly. Our results suggest that predicting consumer competitive population dynamics and the assembly of prey communities will require understanding the complexities of trait variation within consumer species.
  • Rigal, Francois; Cardoso, Pedro; Lobo, Jorge M.; Triantis, Kostas A.; Whittaker, Robert J.; Amorim, Isabel R.; Borges, Paulo A. V. (2018)
    Aim: Land-use change typically goes hand in hand with the introduction of exotic-species, which mingle with indigenous species to form novel assemblages. Here, we compare the functional structure of indigenous and exotic elements of ground-dwelling arthropod assemblages across four land-uses of varying management intensity. Location: Terceira Island (Azores, North Atlantic). Methods: We used pitfall traps to sample arthropods in 36 sites across the four land-uses and collated traits related to dispersal ability, body size and resource use. For both indigenous and exotic species, we examined the impact of land-uses on trait diversity and tested for the existence of non-random assembly processes using null models. We analysed differences in trait composition among land-uses for both indigenous and exotic species with multivariate analyses. We used point-biserial correlations to identity traits significantly correlated with specific land-uses for each element. Results: We recorded 86 indigenous and 116 exotic arthropod species. Under high-intensity land-use, both indigenous and exotic elements showed significant trait clustering. Trait composition strongly shifted across land-uses, with indigenous and exotic species being functionally dissimilar in all land-uses. Large-bodied herbivores dominated exotic elements in low-intensity land-uses, while small-bodied spiders dominated exotic elements in high-intensity land-uses. In contrast, with increasing land-use intensity, indigenous species changed from functionally diverse to being dominated by piercing and cutting herbivores. Main conclusions: Our study revealed two main findings: first, in high-intensity - land-uses, trait clustering characterized both indigenous and exotic elements; second, exotic species differed in their functional profile from indigenous species in all land-use types. Overall, our results provide new insights into the functional role of exotic species in a land-use context, suggesting that, in agricultural landscape, exotic species may contribute positively to the maintenance of some ecosystem functions.
  • Opedal, Oystein H. (2018)
    Premise of research. Phenotypic traits that consistently mediate species' responses to environmental variation (functional traits) provide a promising approach toward generalizing ecological and evolutionary patterns and thereby gaining insights into the processes generating them. In the plant functional ecology literature, most trait-based studies have focused on traits mediating either resource competition or responses to variation in the abiotic environment, while traits mediating reproductive interactions have often been neglected. Methodology. Here, I discuss the value of herkogamy, the spatial separation of male and female functions in flowers, as a functional trait in plant reproductive biology and review the evidence relevant to the hypothesis that taxa exhibiting greater herkogamy have historically experienced more reliable pollination and more outcrossed mating systems. Pivotal results. A large body of work in the field of plant reproductive biology has identified a set of nearly ubiquitous correlations between average herkogamy and features of plant mating systems, notably, autofertility (seed set in the absence of pollinators) and outcrossing rate. Herkogamy often varies extensively among populations and species, and the adaptive interpretation is that herkogamy exhibits local adaptation to the reliability of the pollination environment. Conclusions. These results underline the value of herkogamy as a functional trait representing variation in mating histories. Many important insights are likely to emerge from studies leveraging herkogamy as an easily measured proxy of plant mating systems, as already demonstrated in comparative studies and studies of reproductive interactions. Greater consideration of herkogamy and other reproductive-function traits in studies of species coexistence may provide a more complete understanding of community assembly processes.
  • Ge, Yihao; Liu, Zhenyuan; García-Girón, Jorge; Chen, Xiao; Yan, Yunzhi; Li, Zhengfei; Xie, Zhicai (Elsevier BV, 2022)
    Ecological Indicators
    Under a global change scenario, human-induced impacts alter multiple facets of river biodiversity (i.e., taxonomic, functional and phylogenetic). Hence, focusing on changes in community assembly and different diversity dimensions along anthropogenic impact gradients is of paramount importance for ecological research. Here, we classified stream sites into near-pristine (NP), moderately impacted (MI) and highly impacted (HI) categories based on a comprehensive anthropogenic impact score for the Hanjiang River Basin (China), and tested for differences in patterns of functional (FD) and phylogenetic diversity (PD). Our study suggests that NP sites showed higher FD and PD than impacted streams (MI and HI), with their communities being phylogenetically overdispersed and mostly shaped by random processes. Anthropogenically impacted sites mostly harbored closely related and functionally similar species, although the degree of clustering varied between NP, MI and HI streams, thereby confirming predictions that human activities contribute to the loss of evolutionary history and functional space in running waters. Importantly, we identified the influence of underlying deterministic mechanisms on the homogenization of both functional and phylogenetic facets of diversity. Similarly, NP sites exhibited the greatest proportion of evolutionarily distinct lineages, suggesting that anthropogenic impacts also threaten phylogenetically unique clades. Overall, this study contributed to a better understanding of multiple diversity patterns in aquatic insect communities by generating new empirical evidence of human-induced degradation of subtropical stream ecosystems in China.
  • Sarremejane, Romain; Truchy, Amélie; McKie, Brendan G.; Mykrä, Heikki; Johnson, Richard K.; Huusko, Ari; Sponseller, Ryan A.; Muotka, Timo (John Wiley & Sons, 2021)
    Journal of Animal Ecology 90 (4), 886-898
    1. Community responses to and recovery from disturbances depend on local (e.g. presence of refuges) and regional (connectivity to recolonization sources) factors. Droughts are becoming more frequent in boreal regions, and are likely to constitute a severe disturbance for boreal stream communities where organisms largely lack adaptations to such hydrological extremes. 2. We conducted an experiment in 24 semi-natural stream flumes to assess the effects of local and regional factors on the responses of benthic invertebrate communities to a short-term drought. We manipulated flow (drought vs. constant-flow), spatial arrangement of leaf litter patches (aggregated vs. evenly distributed) and colonization from regional species pool (enhanced vs. ambient connectivity) to test the combined effects of disturbance, resource arrangement and connectivity on the structural and functional responses of benthic invertebrate communities. 3. We found that a drought as short as 1 week reduced invertebrate taxonomic richness and abundance, mainly through stochastic extinctions. Such changes in richness were not reflected in functional diversity. This suggests that communities were characterized by a high degree of functional redundancy, which allowed maintenance of functional diversity despite species losses. Feeding groups responded differently to drought, with organic matter decomposers responding more than scrapers and predators. 4. Three weeks were insufficient for complete invertebrate community recovery from drought. However, recovery was greater in channels subjected to enhanced connectivity, which increased taxonomic diversity and abundance of certain taxa. Spatial configuration of resources explained the least variation in our response variables, having a significant effect only on invertebrate abundance and evenness (both sampling occasions) and taxonomic richness (end of recovery period). 5. Even a short drought, if occurring late in the season, may not allow communities to recover before the onset of winter, thus having a potentially long-lasting effect on stream communities. For boreal headwaters, extreme dewatering poses a novel disturbance regime that may trigger substantial and potentially irreversible changes. An improved understanding of such changes is needed to underpin adaptive management strategies in these increasingly fragmented and disturbed ecosystems.
  • Ge, Yihao; Meng, Xingliang; Heino, Jani; García‐Girón, Jorge; Liu, Yang; Li, Zhengfei; Xie, Zhicai (Ecological Society of America, 2021)
    Ecosphere 12 (7), e03675
    Deterministic and stochastic processes are two major factors shaping community dynamics, but their relative importance remains unknown for many aquatic systems, including those in the high-elevation Qinghai–Tibet Plateau. Here, we explored the causes of multidimensional beta diversity patterns (i.e., taxonomic, functional, and phylogenetic) of a macroinvertebrate metacommunity in this large aquatic system by using multiple approaches (i.e., null models, phylogenetic signal testing, and ordination-based approaches). To obtain insights into community assembly mechanisms, we also analyzed beta diversity in two deconstructed sub-metacommunities (e.g., different tributaries and the main lake body). We found that most functional traits showed significant phylogenetic signals, indicating that the functional traits were profoundly influenced by evolutionary history. The null models showed randomness of functional and phylogenetic beta diversities for the whole basin and its tributaries, confirming the importance of stochasticity over deterministic processes in controlling community structure. However, both phylogenetic and functional community structures were clustered in the Qinghai Lake, probably reflecting the importance of environmental filtering. Ordination-based approaches also revealed that both environmental factors and spatial processes accounted for variation in taxonomic, functional, and phylogenetic beta diversity. More specifically, environmental filtering was more important than spatial processes for the functional dimension, but the opposite was true for the taxonomic and phylogenetic dimensions. The paleogeographic history of the Qinghai Lake basin may have contributed substantially to the prevalence of stochastic processes. Overall, this study provides a better understanding of ecological patterns and assembly mechanisms of macroinvertebrate communities across this poorly known high-elevation aquatic system that is highly sensitive to climate warming.