Browsing by Subject "GRADIENTS"

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  • Valanko, Sebastian; Heino, Jani; Westerbom, Mats; Viitasalo, Markku; Norkko, Alf (2015)
    The majority of studies in metacommunity ecology have focused on systems other than marine benthic ecosystems, thereby providing an impetus to broaden the focus of metacommunity research to comprise marine systems. These systems are more open than many other systems and may thus exhibit relatively less discrete patterns in community structure across space. Metacommunity structure of soft-sediment benthic invertebrates was examined using a fine-grained (285 sites) data set collected during one summer across a large spatial extent (1700km(2)). We applied the elements of metacommunity structure (EMS) approach, allowing multiple hypothesis of variation in community structure to be tested. We demonstrated several patterns associated with environmental variation and associated processes that could simultaneously assemble species to occur at the sites. A quasi-Clementsian pattern was observed frequently, suggesting interdependent ecological relationships among species or similar response to an underlying environmental gradient across sites. A quasi-nested clumped species loss pattern was also observed, which suggests nested habitat specialization. Species richness declined with depth (from 0.5 to 44.8m). We argue that sensitive species may survive in shallower water, which are more stable with regard to oxygen conditions and present greater habitat complexity, in contrast to deeper waters, which may experience periodic disturbance due to hypoxia. Future studies should better integrate disturbance in terms of temporal dynamics and dispersal rates in the EMS approach. We highlight that shallow water sites may act as sources of recruitment to deeper water sites that are relatively more prone to periodic disturbances due to hypoxia. However, these shallow sites are not currently monitored and should be better prioritized in future conservation strategies in marine systems.
  • Salgado, Ana L.; Suchan, Tomasz; Pellissier, Loic; Rasmann, Sergio; Ducrest, Anne-Lyse; Alvarez, Nadir (2016)
    Elevation gradients impose large differences in abiotic and biotic conditions over short distances, in turn, likely driving differences in gene expression more than would genetic variation per se, as natural selection and drift are less likely to fix alleles at such a narrow spatial scale. As elevation increases, the pressure exerted on plants by herbivores and on arthropod herbivores by predators decreases, and organisms spanning the elevation gradient are thus expected to show lower levels of defence at high elevation. The alternative hypothesis, based on the optimal defence theory, is that defence allocation should be higher in low-resource habitats such as those at high elevation, due to higher costs associated with tissue replacement. In this study, we analyse variation with elevation in (i) defence compound content in the plant Lotus corniculatus and (ii) gene expression associated with defence against predators in the specific phytophagous moth, Zygaena filipendulae. Both species produce cyanogenic glycosides (CNglcs) such as lotaustralin and linamarin as defence mechanisms, with the moth, in addition, being able to sequester CNglcs from its host plant. Specifically, we tested the assumption that the defence-associated phenotype in plants and the gene expression in the insect herbivore should covary between low-and high-elevation environments. We found that L. corniculatus accumulated more CNglcs at high elevation, a result in agreement with the optimal defence theory. By contrast, we found that the levels of expression in the defence genes of Z. filipendulae larvae were not related to the CNglc content of their host plant. Overall, expression levels were not correlated with elevation either, with the exception of the UGT33A1 gene, which showed a marginally significant trend towards higher expression at high elevation when using a simple statistical framework. These results suggest that the defence phenotype of plants against herbivores, and subsequent herbivore sequestration machineries and de novo production, are based on a complex network of interactions.
  • Fattorini, Simone; Mantoni, Cristina; Di Biase, Letizia; Strona, Giovanni; Pace, Loretta; Biondi, Maurizio (2020)
    The concept of generic diversity expresses the 'diversification' of species into genera in a community. Since niche overlap is assumed to be higher in congeneric species, competition should increase generic diversity. On the other hand, generic diversity might be lower in highly selective environments, where only species with similar adaptations can survive. We used the distribution of tenebrionid beetles in Central Italy to investigate how generic diversity varies with elevation from sea level to 2400 m altitude. Generic diversity of geophilous tenebrionids decreased sharply with elevation, whereas the generic diversity of xylophilous tenebrionids showed similarly high values across the gradient. These results suggest that geophilous species are more sensitive to variation in environmental factors, and that the advantages of close relationships (similar adaptations to harsh conditions) are greater than the possible drawbacks (competition). This is consistent with the fact that geophilous tenebrionids are mostly generalist detritivores, and hence weakly affected by competition for resources. By contrast, xylophilous species are more protected from harsh/selective conditions, but more limited by competition for microhabitats and food. Our results support the environmental filtering hypothesis for the species composition of tenebrionid beetles along an elevational gradient.
  • Tiusanen, Mikko; Huotari, Tea; Hebert, Paul D. N.; Andersson, Tommi; Asmus, Ashley; Bety, Joel; Davis, Emma; Gale, Jennifer; Hardwick, Bess; Hik, David; Körner, Christian; Lanctot, Richard B.; Loonen, Maarten J. J. E.; Partanen, Rauni; Reischke, Karissa; Saalfeld, Sarah T.; Senez-Gagnon, Fanny; Smith, Paul A.; Sulavik, Jan; Syvanpera, Ilkka; Urbanowicz, Christine; Williams, Sian; Woodard, Paul; Zaika, Yulia; Roslin, Tomas (2019)
    Pollination is an ecosystem function of global importance. Yet, who visits the flower of specific plants, how the composition of these visitors varies in space and time and how such variation translates into pollination services are hard to establish. The use of DNA barcodes allows us to address ecological patterns involving thousands of taxa that are difficult to identify. To clarify the regional variation in the visitor community of a widespread flower resource, we compared the composition of the arthropod community visiting species in the genus Dryas (mountain avens, family Rosaceae), throughout Arctic and high-alpine areas. At each of 15 sites, we sampled Dryas visitors with 100 sticky flower mimics and identified specimens to Barcode Index Numbers (BINs) using a partial sequence of the mitochondrial COI gene. As a measure of ecosystem functioning, we quantified variation in the seed set of Dryas. To test for an association between phylogenetic and functional diversity, we characterized the structure of local visitor communities with both taxonomic and phylogenetic descriptors. In total, we detected 1,360 different BINs, dominated by Diptera and Hymenoptera. The richness of visitors at each site appeared to be driven by local temperature and precipitation. Phylogeographic structure seemed reflective of geological history and mirrored trans-Arctic patterns detected in plants. Seed set success varied widely among sites, with little variation attributable to pollinator species richness. This pattern suggests idiosyncratic associations, with function dominated by few and potentially different taxa at each site. Taken together, our findings illustrate the role of post-glacial history in the assembly of flower-visitor communities in the Arctic and offer insights for understanding how diversity translates into ecosystem functioning.
  • Silfver, Tarja; Heiskanen, Lauri; Aurela, Mika; Myller, Kristiina; Karhu, Kristiina; Meyer, Nele; Tuovinen, Juha-Pekka; Oksanen, Elina; Rousi, Matti; Mikola, Juha (2020)
    Climate warming is anticipated to make high latitude ecosystems stronger C sinks through increasing plant production. This effect might, however, be dampened by insect herbivores whose damage to plants at their background, non-outbreak densities may more than double under climate warming. Here, using an open-air warming experiment among Subarctic birch forest field layer vegetation, supplemented with birch plantlets, we show that a 2.3 degrees C air and 1.2 degrees C soil temperature increase can advance the growing season by 1-4 days, enhance soil N availability, leaf chlorophyll concentrations and plant growth up to 400%, 160% and 50% respectively, and lead up to 122% greater ecosystem CO2 uptake potential. However, comparable positive effects are also found when insect herbivory is reduced, and the effect of warming on C sink potential is intensified under reduced herbivory. Our results confirm the expected warming-induced increase in high latitude plant growth and CO2 uptake, but also reveal that herbivorous insects may significantly dampen the strengthening of the CO2 sink under climate warming. Warming is expected to increase C sink capacity in high-latitude ecosystems, but plant-herbivore interactions could moderate or offset this effect. Here, Silfver and colleagues test individual and interactive effects of warming and insect herbivory in a field experiment in Subarctic forest, showing that even low intensity insect herbivory strongly reduces C sink potential.
  • Teittinen, Anette; Wang, Jianjun; Stromgard, Simon; Soininen, Janne (2017)
    Aim: Elevational biodiversity patterns are understudied in high-latitude aquatic systems, even though these systems are important for detecting very early impacts of climatic changes on Earth. The aim of this study was to examine the elevational trends in species richness and local contribution to beta diversity (LCBD) of three biofilm microbial groups in freshwater ponds and to identify the key mechanisms underlying these patterns. Location: One hundred and forty-six ponds in subarctic Finland and Norway distributed across the tree line along an elevational gradient of 10-1,038 m a.s.l., spanning from forested landscape to barren boulder fields. Time period: July-August 2015. Major taxa studied: Diatoms, cyanobacteria and non-cyanobacteria. Methods: Generalized linear models were used to identify the most important pond variables explaining richness and LCBD. Structural equation models were used to explore the direct and indirect effects of multiscale drivers on richness and LCBD. Results: Diatom and cyanobacteria richness showed unimodal elevational patterns, whereas non-cyanobacteria richness decreased with increasing elevation. The LCBD-elevation relationship was U-shaped for all three microbial groups. Diatom and cyanobacteria richness and LCBD were best explained by local pond variables, especially by pH. Non-cyanobacteria richness and LCBD were related to pond variables, elevation as a proxy for climatic conditions, and normalized difference vegetation index as a proxy for terrestrial productivity. Main conclusions: Aquatic autotrophs were primarily controlled by environmental filtering, whereas heterotrophic bacteria were also affected by terrestrial productivity and elevation. All studied aspects of microbial diversity were directly or indirectly linked to elevation; therefore, climatic changes may greatly alter aquatic microbial assemblages.
  • Mikola, Juha Tapio; Silfver, Tarja Hannele; Rousi, Matti (2018)
    Facilitative plant-plant interactions are common in harsh environments such as Arctic and alpine tree lines. In Fennoscandia, mountain birch dominates tree lines, but mixes with Scots pine in less severe areas. Using over 30-yr. old Scots pine common gardens, established at three locations near the present Scots pine tree line, we tested (1) if mountain birch can facilitate Scots pine numbers and (2) if improved soil fertility under mountain birch canopies has a role in facilitation. We counted the number of pines within 1-m and 3-m radii of the tallest mountain birch vs. a random spot in 70-75 planting plots and sampled soil for nutrients at 0.3-, 1- and 3-m distance to the birch in ten plots in each location. Number of Scots pines was 29% higher within a 1-m radius of a mountain birch than of a random spot. This effect did not depend on location, although the locations differed significantly in soil fertility, and no effect was detected within a 3-m radius. Concentrations of water, NH4, NO3 and PO4 decreased significantly with increasing distance to a mountain birch, but only in the least fertile location. Mountain birch can significantly facilitate Scots pine in tree line conditions. However, unlike we expected, improved soil fertility under birch canopies may not have a general role in facilitation.
  • Asmala, Eero; Gustafsson, Camilla; Krause-Jensen, Dorte; Norkko, Alf; Reader, Heather; Staehr, Peter A.; Carstensen, Jacob (2019)
    Coastal ecosystems act as filters of nutrients from land to the open sea. We investigated the role of eelgrass (Zostera marina) metabolism in the coastal filter transforming nitrogen, phosphorus, and organic carbon. Field campaigns following identical methodologies were carried out at two contrasting coastal locations: the mesohaline and nutrient-rich Roskilde Fjord, Denmark, and the mesotrophic brackish Tvärminne archipelago, Finland. Over the 24-h in situ benthic incubations, we measured oxygen concentrations continuously and assessed changes in DOM characteristics and net fluxes of carbon, nitrogen, and phosphorus. Ecosystem metabolism modeled on the basis of the O2 data showed that the systems were either net heterotrophic (Roskilde Fjord; − 1.6 and − 2.4 g O2 m−2 day−1 in eelgrass meadow and bare sand, respectively) or had balanced primary production and respiration (Tvärminne; 0.0 and 0.2 g O2 m−2 day−1). Overall, initial nutrient stoichiometry was a key factor determining benthic–pelagic fluxes of nutrients, which exacerbated the deviations from Redfield ratios of N and P, indicating an efficient use of the limiting nutrient. A net diel uptake of dissolved inorganic N was observed at both locations (− 2.3 μmol l−1 day−1 in Roskilde Fjord and − 0.1 μmol l−1 day−1 in Tvärminne). Despite minor changes in dissolved organic carbon concentrations during the incubations, a marked increase of fluorescent DOM was observed at both locations, suggesting rapid heterotrophic processing of the DOM pool. Our results underline that the biogeochemical role of eelgrass in the coastal filter is not inherent, but strongly dependent on the environmental conditions.
  • Hajializadeh, Parima; Safaie, Mohsen; Naderloo, Reza; Shojaei, Mehdi Ghodrati; Gammal, Johanna; Villnäs, Anna; Norkko, Alf (2020)
    Macrofauna play a key role in the functioning of mangrove ecosystems. Nevertheless, our understanding of the diversity and functional structure of macrofaunal communities across different habitats in the mangrove forests of the Persian Gulf is limited. In this study, we investigated species diversity and biological trait patterns of macrofauna in different mangrove-associated habitats, i.e., encompassing actual mangrove forests, and adjacent Beaches and Creeks, which exhibit different levels of habitat heterogeneity. Samples were collected from the different habitats in five different locations, over four seasons. A total of 122 macrofauna taxa were identified. The diversity of species was higher in summer than in winter. In the Beach habitats, species diversity showed an increasing trend from land toward the mangrove, whereas in Creek habitats diversity decreased from the Creek toward the mangrove. Multivariate community analysis showed differences in the distribution of abundant species and biological traits across all habitats. Deposit-feeding, crawlers, medium-size, and free-living were the dominant trait modalities in all habitats. The similarities within habitats over the four seasons had the same specific pattern of species and biological trait abundance in the Beach and the Creek, increasing from the non-covered habitat into the mangrove trees. Although many species shared similar traits, the abundance-driven differences in trait expression between habitats showed the importance of habitat filtering. The results of this study will be useful in the conservation of mangrove forests and they give a deeper understanding of the ecological patterns and functions of benthic macrofaunal communities in the Persian Gulf.
  • Wang, Qing-Wei; Robson, Thomas Matthew; Pieristè, Marta; Oguro, Michi; Oguchi, Riichi; Murai, Yoshinori; Kurokawa, Hiroko (2020)
    Although sunlight is essential for plant growth and development, the relative importance of each spectral region in shaping functional traits is poorly understood, particularly in dynamic light environments such as forest ecosystems. We examined responses of 25 functional traits from groups of 11 shade-intolerant and 12 understorey shade-tolerant forb species grown outdoors under five filter treatments differing in spectral transmittance: (a) transmitting c. 95% of solar radiation (280-800 nm); (b) attenuating ultraviolet-B (UV-B); (c) attenuating all UV; (d) attenuating all UV and blue light; (e) attenuating all UV, blue and green light. Our results show that UV-B radiation mainly affected the biochemical traits but blue light mainly affected the physiological traits irrespective of functional strategy, whereas green light affected both sets of traits. This would suggest that differentiation among suites of functional trait responses proceeds according to light quality. Biomass accumulation was significantly increased by UV-A radiation (contrasting treatment [b] vs. [c]) among shade-intolerant but decreased by blue light among shade-tolerant species; green and red light affected whole-plant morphological development differently according to functional groups. Shade-tolerant species were more plastic than shade-intolerant species in response to each spectral region that we examined except for UV-B radiation. Synthesis. Our results show that differences in the spectral composition of sunlight can drive functional trait expression irrespective of total irradiance received. The different responses of functional traits between functional groups imply that shade-tolerant and intolerant species have adapted to utilize spectral cues differently in their respective light environments.
  • Olden, Anna; Peura, Maiju; Saine, Sonja; Kotiaho, Janne S.; Halme, Panu (2019)
    Riparian forests have cool and humid microclimates, and one aim of leaving forested buffer strips between clear-cut areas and streams is to conserve these microclimatic conditions. We used an experimental study set up of 35 streamside sites to study the impacts of buffer strip width (15 or 30 m) and selective logging within the buffer strips on summer-time air temperature, relative air humidity and canopy openness 12 years after logging. The buffer strip treatments were compared to unlogged control sites. We found that 15-meter buffer strips with or without selective logging and 30-meter buffer strips with selective logging were insufficient in maintaining temperature, relative humidity and canopy openness at similar levels than they were in control sites. In contrast, 30-meter buffer strips differed only little from control sites, although they did have significantly lower mean air humidity. Microclimatic changes were increased by southern or southwestern aspect of the clear-cut, and by logging on the opposite side of the stream. We also tested how the cover of three indicator mosses (Hylocomium splendens, Pseudobqum cinclidioides and Polytrichum commune) had changed (from pre-logging to 12 years post-logging) in relation to post-logging air temperature, relative air humidity and canopy openness. We found that each of the species responded to at least one of these physical conditions. Air humidity was the most significant variable for explaining changes in the cover of the indicator moss species, suggesting that the changes in this microclimatic component has biological impacts. We conclude that to preserve riparian microclimatic conditions and species dependent on those, buffer strips should exceed 30 m in width, and not be selectively logged. Wider buffer strips are required if the clear-cut is towards south or southwest, or if the two sides of the stream are logged at the same time or during subsequent years.