Abiotic Heterogeneity Research Articles

The assembly of a plant network in alpine vegetation

AbstractQuestionsPositive and negative associations among species influence the structure of plant communities. Yet how these plant associations are assembled at the community level is poorly understood. We propose a new approach that combines spatial ecology, network theory and trait‐based ecology to examine the assembly of plant–plant associations at the community level.LocationGemmipass, Swiss Alps.MethodsWe fully mapped an alpine plant community at the individual plant level, recording both plant coordinates and functional traits for each individual. We identified non‐random species associations using spatial point‐pattern analysis and partialled out the effect of abiotic heterogeneity. We then analysed the plant network structure and used plant traits to predict species associations.ResultsWe identified 36 significant spatial associations between plant species, 34 positive and two negatives. Dominant, stress‐tolerant species such as Dryas octopetala, Linaria alpina and Leontodon montanus were highly connected in the network, whereas rare, water‐ and nutrient‐demanding species such as Saxifraga aizoides, Galium anisophyllon and Thymus praecox were less connected compared to random expectation. The plant network was clustered, meaning that species were overall more connected among each other than expected by chance.ConclusionsPositive associations among species characterized the studied plant community. Besides the primary effect of associations of the “foundation” species D. octopetala with other species, these “subordinate” plants were also associated with each other. Our study reveals the assembly of plant communities as driven by positive associations among stress‐tolerant pioneer species, highlighting their role in supporting the cohesiveness of alpine plant communities.

Green roof and photovoltaic panel integration: Effects on plant and arthropod diversity and electricity production

The combination of green roofs with photovoltaic (PV) panels has been proposed to provide synergistic benefits as the panel is cooled by the presence of the vegetation, and thus produces more electricity, while the solar panel enhances growing conditions for vegetation, and increases abiotic heterogeneity, resulting in higher plant diversity. We tested these hypotheses in a non-irrigated green roof in a Mediterranean climate with replicated plots including green roofs only, green roofs with a PV panel, and a conventional roof surface with a PV panel. We found that presence of a panel resulted in higher heterogeneity in substrate moisture, but there was no effect on plant diversity. Plant species showed enhanced growth in plots with PV, including greater growth of Sedum sediforme and longer flowering time of annual species. On the other hand, arthropod diversity was lower during part of the year, and abundance of some arthropod taxa was lower in green roof plots with PV. The presence of the green roof also did not improve electricity production by the panels. We conclude that in a Mediterranean climate, it would be appropriate to examine the use of irrigation in green roofs with PV panels, including effects on the plant community and on electricity production.

Positive sport–biosphere interactions? — Cross-country skiing delays spring phenology of meadow vegetation

Space requirements by winter sports and accelerating global warming are usually perceived as stressors for mountain meadow plant communities. Cross-country ski track preparation (i.e. grooming), however, might retard effects of climate change and, being limited in space requirements, might increase abiotic heterogeneity. The effect of cross-country ski tracks on meadow vegetation was quantified along a representative ski track that had been operated for 30 years in the Fichtelgebirge, a low mountain range in central Europe. Paired sampling was implemented to assess the effect of skiing operations on snow and soil properties, plant phenology, biomass production and species composition. Additionally, boosted regression tree analyses were used to quantify the relative importance of the cross-country ski track compared to other environmental conditions.The cross-country ski track strongly increased snow density, enhanced soil frost, and retarded snowmelt, thereby delaying flower phenology (by 2.1 days) and the early development stages of plant species on the track. However, biomass, species richness and species composition were unaffected by skiing operations except for one species (Leontodon autumnalis) showing exclusive occurrence on the track while four others showed reduced relative occurrence on the track.While snow and soil properties were influenced by cross-country ski track preparation, natural environmental variability was more influential for species composition and biomass production than the ski track. We therefore conclude that the ski track – without artificial snow – did not negatively affect species composition. By delaying flower phenology, effects of the ski track even counteracted global warming to some degree. Due to their small spatial extent in the landscape, these ski tracks may add to environmental heterogeneity and thus support sustaining diverse species compositions during environmental changes.

Spatial distribution patterns of old-growth forest of dioecious tree Torreya nucifera in rocky Gotjawal terrain of Jeju Island, South Korea

BackgroundSpatial structure of plants in a population reflects complex interactions of ecological and evolutionary processes. For dioecious plants, differences in reproduction cost between sexes and sizes might affect their spatial distribution. Abiotic heterogeneity may also affect adaptation activities, and result in a unique spatial structure of the population. Thus, we examined sex- and size-related spatial distributions of old-growth forest of dioecious tree Torreya nucifera in extremely heterogeneous Gotjawal terrain of Jeju Island, South Korea.MethodsWe generated a database of location, sex, and size (DBH) of T. nucifera trees for each quadrat (160 × 300 m) in each of the three sites previously defined (quadrat A, B, C in Site I, II, and III, respectively). T. nucifera trees were categorized into eight groups based on sex (males vs. females), size (small vs. large trees), and sex by size (small vs. large males, and small vs. large females) for spatial point pattern analysis. Univariate and bivariate spatial analyses were conducted.ResultsUnivariate spatial analysis showed that spatial patterns of T. nucifera trees differed among the three quadrats. In quadrat A, individual trees showed random distribution at all scales regardless of sex and size groups. When assessing univariate patterns for sex by size groups in quadrat B, small males and small females were distributed randomly at all scales whereas large males and large females were clumped. All groups in quadrat C were clustered at short distances but the pattern changed as distance was increased. Bivariate spatial analyses testing the association between sex and size groups showed that spatial segregation occurred only in quadrat C. Males and females were spatially independent at all scales. However, after controlling for size, males and females were spatially separated.ConclusionsDiverse spatial patterns of T. nucifera trees across the three sites within the Torreya Forest imply that adaptive explanations are not sufficient for understanding spatial structure in this old-growth forest. If so, the role of Gotjawal terrain in terms of creating extremely diverse microhabitats and subsequently stochastic processes of survival and mortality of trees, both of which ultimately determine spatial patterns, needs to be further examined.

The Implications of Eco-Evolutionary Processes for the Emergence of Marine Plankton Community Biogeography.

Models of community assembly have been used to illustrate how the many functionally diverse species that compose plankton food webs can coexist. However, the evolutionary processes leading to the emergence of plankton food webs and their interplay with migratory processes and spatial heterogeneity are yet to be explored. We study the eco-evolutionary dynamics of a modeled plankton community structured in both size and space and physiologically constrained by empirical data. We demonstrate that a complex yet ecologically and evolutionarily stable size-structured food web can emerge from an initial set of two monomorphic phytoplankton and zooplankton populations. We also show that the coupling of spatial heterogeneity and migration results in the emergence of specific biogeographic patterns: (i) the emergence of a source-sink structure of the plankton metacommunities, (ii) changes in size diversity dependent on migratory intensity and on the scale at which diversity is considered (local vs. global), and (iii) the emergence of eco-evolutionary provinces (i.e., a spatial unit characterized by some level of abiotic heterogeneity but of homogenous size composition due to horizontal movements) at spatial scales that increase with the strength of the migratory processes.

Modelling native and alien vascular plant species richness: At which scales is geodiversity most relevant?

AbstractAimTo explore the scale dependence of relationships between novel measures of geodiversity and species richness of both native and alien vascular plants.LocationGreat Britain.Time periodData collected 1995–2015.Major taxaVascular plants.MethodsWe calculated the species richness of terrestrial native and alien vascular plants (6,932 species in total) across the island of Great Britain at grain sizes of 1 km2 (n = 219,964) and 100 km2 (n = 2,121) and regional extents of 25–250 km diameter, centred around each 100‐km2 cell. We compiled geodiversity data on landforms, soils, hydrological and geological features using existing national datasets, and used a newly developed geomorphometric method to extract landform coverage data (e.g., hollows, ridges, valleys, peaks). We used these as predictors of species richness alongside climate, commonly used topographic metrics, land‐cover variety and human population. We analysed species richness across scales using boosted regression tree (BRT) modelling and compared models with and without geodiversity data.ResultsGeodiversity significantly improved models over and above the widely used topographic metrics, particularly at smaller extents and the finer grain size, and slightly more so for native species richness. For each increase in extent, the contribution of climatic variables increased and that of geodiversity decreased. Of the geodiversity variables, automatically extracted landform data added the most explanatory power, but hydrology (rivers, lakes) and materials (soil, superficial deposits, geology) were also important.Main conclusionsGeodiversity improves our understanding of, and our ability to model, the relationship between species richness and abiotic heterogeneity at multiple spatial scales by allowing us to get closer to the real‐world physical processes that affect patterns of life. The greatest benefit comes from measuring the constituent parts of geodiversity separately rather than one combined variable (as in most of the few studies to date). Automatically extracted landform data, the use of which is novel in ecology and biogeography, proved particularly valuable in our study.

Predicting aquatic invasion in Adirondack lakes: a spatial analysis of lake and landscape characteristics

AbstractInvasive species continue to pose major challenges for managing coupled human–environmental systems. Predictive tools are essential to maximize invasion monitoring and conservation efforts in regions reliant on abundant freshwater resources to sustain economic welfare, social equity, and ecological services. Past studies have revealed biotic and abiotic heterogeneity, along with human activity, can account for much of the spatial variability of aquatic invaders; however, improvements remain. This study was created to (1) examine the distribution of aquatic invasive species richness (AISR) across 126 lakes in the Adirondack Region of New York; (2) develop and compare global and local models between lake and landscape characteristics and AISR; and (3) use geographically weighted regression (GWR) to evaluate non‐stationarity of local relationships, and assess its use for prioritizing lakes at risk to invasion. The evaluation index, AISR, was calculated by summing the following potential aquatic invaders for each lake: Asian Clam (Corbicula fluminea), Brittle Naiad (Najas minor), Curly‐leaf Pondweed (Potamogeton crispus), Eurasian Watermilfoil (Myriophyllum spicatum), European Frog‐bit (Hydrocharis morsus‐ranae), Fanwort (Cabomba caroliniana), Spiny Waterflea (Bythotrephes longimanus), Variable‐leaf Milfoil (Myriophyllum heterophyllum), Water Chestnut (Trapa natans), Yellow Floating Heart (Nymphoides peltata), and Zebra Mussel (Dreissena polymorpha). The Getis‐Ord Gi* statistic displayed significant spatial hot and cold spots of AISR across Adirondack lakes. Spearman's rank (ρ) correlation coefficient test (rs) revealed urban land cover composition, lake elevation, relative patch richness, and abundance of game fish were the strongest predictors of aquatic invasion. Five multiple regression global Poisson and GWR models were made, with GWR fitting AISR very well (R2 = 76–83%). Local pseudo‐t‐statistics of key explanatory variables were mapped and related to AISR, confirming the importance of GWR for understanding spatial relationships of invasion. The top 20 lakes at risk to future invasion were identified and ranked by summing the five GWR predictive estimates. The results inform that inexpensive and publicly accessible lake and landscape data, typically available from digital repositories within local environmental agencies, can be used to develop predictions of aquatic invasion with remarkable agreement. Ultimately, this transferable modeling approach can improve monitoring and management strategies for slowing the spread of invading species.

Mammal burrowing in discrete landscape patches further increases soil and vegetation heterogeneity in an arid environment

Burrowing mammal disturbances often create heterogeneity within landscapes. Aardvark (Orycteropus afer) are extensive burrowers in sub-Saharan ecosystems and play an important role in structuring communities in arid environments. The burrowing activities of aardvark are often associated with heuweltjies (nutrient-rich mounds differing in soil and vegetation characteristics from surrounding areas) which contribute strongly to landscape heterogeneity. This study determined the impact of aardvark burrowing and heuweltjies on soil and vegetation characteristics. Data were collected at four microsites: 1) at each burrow entrance on a heuweltjie, 2) on the burrowed heuweltjie (i.e. heuweltjie with an aardvark burrow), 3) on the nearest unburrowed heuweltjie, and 4) on the adjacent matrix. Aardvark burrowing and heuweltjies both impacted the soil and vegetation characteristics. Despite having more moderate thermal regimes than other microsites, burrow entrances were largely unvegetated. Although aardvark burrowing did not affect plant species richness on heuweltjies, it decreased vegetation cover. Vegetation composition differed between heuweltjies and the matrix, and this dissimilarity was increased further by aardvark burrowing. As a result, the combined effect of burrowing mammals and heuweltjies increases landscape heterogeneity. This emphasises the important ecosystem engineering role that aardvark have in arid environments, even where considerable abiotic heterogeneity already exists.

Non-random patterns of vegetation clearing and potential biases in studies of habitat area effects

Native vegetation extent is often a proxy for habitat area in studies of human-modified landscapes. However, the loss and retention of native vegetation is rarely random among landscapes. Instead, the extent of native vegetation in landscapes may be correlated with abiotic factors, thereby obscuring or distorting relationships between ecological phenomena and area. We asked: (1) how has the potential for non-random vegetation loss to confound area effects been addressed in the landscape ecology literature? (2) Are consistent patterns of non-random vegetation loss and retention evident from modified regions of two countries? We reviewed 118 papers that related area to an ecological response, to determine whether potential biases associated with non-random vegetation loss and retention were considered. We then analysed ~18,000 100 km2 landscape units in Australia and South Africa to identify how different abiotic factors correlate with the extent of native vegetation retained in those landscapes. Only 21% of the studies we reviewed explicitly or implicitly considered spatial biases in vegetation clearing. Yet, across modified regions of Australia and South Africa, landscape-scale native vegetation extent was consistently and often strongly related to abiotic factors, particularly soil properties and topographic variability. Patterns of vegetation clearing and retention commonly reflect underlying abiotic heterogeneity. These biases, which are infrequently highlighted in studies focussing on area effects, have implications for how we assess the importance of vegetation extent for species and assemblages. Failure to account for correlates of vegetation extent risks erroneous area-based conservation prescriptions in human-modified environments.

Quasi-neutral community assembly: Evidence from niche overlap, phylogenetic, and trait distribution analyses of a subtropical forest in South America

In spite of recent advances, the relative roles of deterministic and stochastic processes in community assembly remains disputed. We tested community assembly hypotheses in a disturbance gradient in a logged mixed conifer-hardwood forest complex in southern Brazil. If abiotic heterogeneity was strong enough (Selection hypothesis), we expected niche clustering and reduced niche overlap between species and between ecological groups, phylogenetic clustering, significant β-diversity departure from a random expectation after controlling for α-diversity variation, and non-random trait distribution due to abiotic filtering and limiting similarity. Null expectations were predicted under the Neutral hypothesis. Under the Quasi-Neutral hypothesis, we expected niche clustering and reduced niche overlap as in the Selection hypothesis, but random phylogenetic distribution, random β-diversity variation, and random trait distribution due to niche-based specialization but weak habitat matching resulting from dispersal limitation and drift. We used a series of null models to provide an integrative evaluation of community assembly including species abundances, environmental preferences, phylogenetic relatedness, and trait distribution. Results supported the Quasi-Neutral hypothesis due to a combination of reduced niche overlap, niche clustering along soil and disturbance gradients, evidence for abiotic filtering of functional traits but absent phylogenetic structure and random β-diversity variation. Support to the Quasi-Neutral hypothesis provides evidence for niche-based species selection along environmental gradients, coupled with poor matches between species distributions and environmental factors due to stochastic processes. It also highlights the importance of an integrative approach to the evaluation of community patterns indicative of assembly processes. Had only a subset of the approaches used been employed and different conclusions would have been reached: niche overlap and trait distribution analyses would have indicated a stronger role for selection, while phylogenetic and abundance analyses would have indicated stochastic community assembly. Future research should include different disturbance regimes along with environmental variation in order to assess the interplay of the different drivers that shape the community assembly process, as well as the potential of the Quasi-Neutral hypothesis as an explanation for the assembly process of complex and species-rich subtropical forests.

Community assembly in harsh environments: the prevalence of ecological drift in the heath vegetation of South America

Metacommunity dynamics is marked by a gradient ranging from pure ecological determinism to pure stochasticity. This gradient encompasses compositional turnover that is governed by ecological drift, selection and dispersal. Here we estimate the influences of selection, dispersal limitation acting in concert with drift, drift acting alone and homogenizing dispersal on the structure of tropical restinga heath vegetation growing under stressful conditions in north‐eastern South America. We hypothesize that if abiotic heterogeneity is strong enough, it could select distinct sets of colonizing species from neighbor ecosystems, with stress sensitive species occupying refuges created by abiotic heterogeneity and stress tolerators dominating the more exposed areas. In this case selection would occur at both biogeographical and local scales. Under its prevalence, we expect selection to have a major signature in the woody plant community structure in a phylogenetic null model. Alternatively, if abiotic heterogeneity is not strong enough to impose significant selection, the environment would be homogeneously stressful for the majority of species, and would be dominated species selected at biogeographical scale only. Under its prevalence, we expect drift to have a major signature in the phylogenetic null model. We used an analytical framework based on phylogenetic and community structure null models to assess the relative importance of ecological processes. We also aimed to characterize the ecosystem features that impose selection and dispersal limitation. We found that 95.1% of turnover in composition is attributable to drift, 2.4% to homogenizing dispersal, 2.1% to selection, and just 0.40% to dispersal limitation, thus confirming our Neutrality hypothesis. As expected, both soil and topographic variables influenced metacommunity structure. However, contrary to our prediction, light availability and vegetation structure were also important. The predominance of coarse spatial patterns correlated to topographic and soil properties suggests that coarse differences in wind exposure and associated vegetation and soil factors represent the main selective forces acting on the studied vegetation. The dominance of drift in the assembly of restinga heath vegetation is likely to result from homogeneously stressful environmental conditions and also from the ongoing colonization process that is taking place in the restinga by immigrants from species‐rich neighboring ecosystems.

Contrasting distribution patterns of invasive and naturalized non‐native species along environmental gradients in a semi‐arid montane ecosystem

AbstractQuestionsMountain systems have high abiotic heterogeneity over local spatial scales, offering natural experiments for examining plant species invasions. We ask whether functional groupings explain non‐native species spread into native vegetation and up elevation gradients. We examine whether non‐native species distribution patterns are related to environmental variables after controlling for elevation and, thus, driven by niche processes.LocationThe Wallowa Mountains, northeast Oregon, USA.MethodsWe surveyed non‐native plant species along three mountain roads and into the native habitat matrix to assess the extent of invasion success along distance from roadside and elevation gradients. We used GLM to predict single species occurrence probabilities, LMM to examine differences in distribution patterns among functional types, and pCCA to examine multivariate responses of the non‐native community to ecological variables.ResultsProbability of occurrence of the eight focal invasive species was not significantly related to distance from the road, but declined with elevation. Non‐native species with annual life history strategies were more restricted to lower elevations than perennial species. Non‐native species considered invasive occurred at lower minimum elevations than naturalized species. Shifts in the species composition of the non‐native plant community were related to changes in soil and climate variables.ConclusionsOur results suggest that invasive species have similar patterns of habitat associations and spread from roadsides to interior vegetation zones, whereas naturalized species partition environmental gradients in this semi‐arid montane ecosystem. Furthermore, annual and invasive species groups occupy lower elevations and perennial and naturalized species groups have invaded further up the mountain roads and into the native vegetation. Thus, functional groupings may explain contrasting distribution patterns of non‐native species and could be used to inform management strategies for non‐native species.

Arctic‐alpine vegetation biomass is driven by fine‐scale abiotic heterogeneity

During recent decades large changes in vegetation biomass have been observed in arctic and alpine areas. While these temporal trends have been clearly linked to changing climatic conditions, the drivers of local spatial variation in biomass are still relatively poorly understood. Thus, we examine the effects of abiotic conditions (topography, soil properties and geomorphological processes) on aboveground vascular plant biomass to understand the determinants of contemporary fine‐scale heterogeneity in this variable. We also compare the results from clip‐harvested biomass samples to three non‐destructive biomass estimates: vegetation cover, height and volume. To investigate the local drivers of biomass we analysed an extensive dataset of 960 1‐m2 cells in arctic–alpine tundra using spatially explicit generalized estimation equations to conduct variation partitioning. The abiotic environment had a clear impact on the distribution of biomass (variance explained 32.89%). Soil properties were most strongly related to aboveground biomass (independent effect in variation partitioning 7.03% and combined effect including joined effects 19.6%). Topography had only little influence after soil and geomorphology were taken into account (independent effect 2.23%, combined effect 18.73%), implying that topography affects biomass only indirectly. Of the non‐destructive biomass estimates, the results for vegetation volume were most similar to those for biomass samples. Thus, we recommend utilizing vegetation volume as a cost‐efficient and robust biomass estimate in arctic‐alpine areas. Our results indicate that the fine‐scale environmental variation has to be taken into account more carefully when modelling vegetation biomass, especially under changing climatic conditions.

Scale‐dependent effects of grazing and topographic heterogeneity on plant species richness in a Dutch salt marsh ecosystem

AbstractQuestionFor over three decades, low‐intensity grazing has been used to maintain or increase plant species richness in European natural areas, but the effects are highly variable. Thus far, good predictors of whether grazing will have positive effects on plant species richness are limited. How does the interplay between low‐intensity grazing and topographic heterogeneity affect plant species richness at different spatial scales?LocationLong‐term grazed and ungrazed salt marshes of the Dutch Wadden Sea island of Schiermonnikoog.MethodsWe selected ten plots of 2200 m2 in grazed and ungrazed areas of our study sites, and recorded and compared plant species richness in 0.1, 1, 10, 100 and 1000 m2 subplots. Topographic heterogeneity was quantified at the plot scale using the standard deviation of the elevation derived from a high‐resolution (5 m × 5 m) digital elevation model. We calculated species–area relationships to analyse our data.ResultsWe found that large‐scale topographic heterogeneity (based on the whole plot of 2200 m2) positively affects plant species richness at all scales (even at the smallest 0.1‐m2 scale), and that grazing has a positive additive effect at the small scales (0.1 and 10 m2). While grazing also had a positive effect on species richness at larger scales (1000 m2), the strength of the effect was dependent on the topographic heterogeneity at that scale. The effectiveness of grazing for increased plant species richness was highest at low topographic heterogeneity, and lowest at intermediate topographic heterogeneity. Effects of intermediate heterogeneity were probably counterbalanced by the effects of grazing.ConclusionsOur results suggest that the variation in elevation is an important predictor of whether low‐intensity grazing has positive effects on plant species richness or not. Grazing appears most beneficial at low topographic heterogeneity, but whether these findings hold for other grazed ecosystems will depend on several factors, most importantly, the relationship between topographic and abiotic heterogeneity. Results of our study are highly relevant for the application of low‐intensity grazing as tool for conservation management in salt marshes and other natural areas.

Biologic interactions determining geographic range size: a one species response to phylogenetic community structure.

Range size variation in closely related species suggests different responses to biotic and abiotic heterogeneity across large geographic regions. Species turnover generates a wide spectrum of species assemblages, resulting in different competition intensities among taxa, creating restrictions as important as environmental constraints. We chose to adopt the widely used phylogenetic relatedness (NRI) measurement to define a metric that depicts competition strength (via phylogenetic similarity), which one focal species confronts in its environment. This new approach (NRIfocal) measures the potential of the community structure effect over performance of a single species. We chose two ecologically similar Peucaea sparrows, which co-occur and have highly dissimilar range size to test whether the population response to competition intensity is different between species. We analyzed the correlation between both Peucaea species population sizes and NRIfocal using data from point counts. Results indicated that the widespread species population size was not associated with NRIfocal, whereas the population of restricted-sized species exhibited a negative relationship with competition intensity. Consequently, a species' sensitivity to competition might be a limiting factor to range expansion, which provides new insights into geographic range analysis and community ecology.

Combined effects of resource heterogeneity and simulated herbivory on plasticity of clonal integration in a rhizomatous perennial herb

Previous lines of investigation assuming potential advantage of clonal integration generally have neglected its plasticity in complex heterogeneous environments. Clonal plants adaptively respond to abiotic heterogeneity (patchy resource distribution) and herbivory-induced heterogeneity (within-clone heterogeneity in ramet performance), but to date little is known about how resource heterogeneity and simulated herbivory jointly affect the overall performance of clones. Partial damage within a clone caused by herbivory might create herbivory-induced heterogeneity in a resource-homogeneous environment, and might also decrease or increase the extent of heterogeneity under resource-heterogeneous conditions. We conducted a greenhouse experiment in which target-ramets of Leymus chinensis segments within homogeneous or heterogeneous nutrient treatments were subject to clipping (0% or 75% shoot removal). In homogeneous environments with high (9:9) nutrient availability, ramet biomass of L.chinensis with intact or severed rhizomes is 0.70 or 0.69g. Conversely, target-ramet biomass with intact rhizomes is obviously lower than that of the severed target-ramets in the homogeneous environments with medium (5:5) and low (1:1) nutrient availability. High resource availability and the presence of herbivory can alleviate negative effects of rhizome connection under homogeneous conditions, by providing copious resource or creating herbivory-induced heterogeneity respectively. Herbivory tolerance of clonal fragments with connected rhizomes was higher than that of fragments with severed rhizomes under heterogeneous conditions. These findings confirmed the unconditional advantage of clonal integration on reproduction under the combined influence of resource heterogeneity and simulated herbivory. Moreover, our results made clear the synergistically interactive effects of resource heterogeneity and simulated herbivory on costs and benefits of clonal integration. This will undoubtedly advance our understanding on the plasticity of clonal integration under complex environmental conditions.

Soil abiotic factors influence interactions between belowground herbivores and plant roots

Root herbivores are important ecosystem drivers and agricultural pests, and, possibly as a consequence, plants protect their roots using a variety of defensive strategies. One aspect that distinguishes belowground from aboveground plant-insect interactions is that roots are constantly exposed to a set of soil-specific abiotic factors. These factors can profoundly influence root resistance, and, consequently, the outcome of the interaction with belowground feeders. In this review, we synthesize the current literature on the impact of soil moisture, nutrients, and texture on root-herbivore interactions. We show that soil abiotic factors influence the interaction by modulating herbivore abundance and behaviour, root growth and resistance, beneficial microorganisms, as well as natural enemies of the herbivores. We suggest that abiotic heterogeneity may explain the high variability that is often encountered in root-herbivore systems. We also propose that under abiotic stress, the relative fitness value of the roots and the potential negative impact of herbivory increases, which may lead to a higher defensive investment and an increased recruitment of beneficial microorganisms by the plant. At the same time, both root-feeding herbivores and natural enemies are likely to decrease in abundance under extreme environmental conditions, leading to a context- and species-specific impact on plant fitness. Only by using tightly controlled experiments that include soil abiotic heterogeneity will it be possible to understand the impact of root feeders on an ecosystem scale and to develop predictive models for pest occurrence and impact.

Daily bursts of biogenic cyanogen bromide (BrCN) control biofilm formation around a marine benthic diatom

The spatial organization of biofilms is strongly regulated by chemical cues released by settling organisms. However, the exact nature of these interactions and the repertoire of chemical cues and signals that micro-organisms produce and exude in response to the presence of competitors remain largely unexplored. Biofilms dominated by microalgae often show remarkable, yet unexplained fine-scale patchy variation in species composition. Because this occurs even in absence of abiotic heterogeneity, antagonistic interactions might play a key role. Here we show that a marine benthic diatom produces chemical cues that cause chloroplast bleaching, a reduced photosynthetic efficiency, growth inhibition and massive cell death in naturally co-occurring competing microalgae. Using headspace solid phase microextraction (HS-SPME)-GC-MS, we demonstrate that this diatom exudes a diverse mixture of volatile iodinated and brominated metabolites including the natural product cyanogen bromide (BrCN), which exhibits pronounced allelopathic activity. Toxin production is light-dependent with a short BrCN burst after sunrise. BrCN acts as a short-term signal, leading to daily "cleaning" events around the algae. We show that allelopathic effects are H(2)O(2) dependent and link BrCN production to haloperoxidase activity. This strategy is a highly effective means of biofilm control and may provide an explanation for the poorly understood role of volatile halocarbons from marine algae, which contribute significantly to the atmospheric halocarbon budget.

Abiotic heterogeneity drives parasite local adaptation in coevolving bacteria and phages

Spatial abiotic heterogeneity can result in divergent selection, hence might increase the magnitude of host-parasite local adaptation (the mean difference in fitness of sympatric vs. allopatric host-parasite combinations). We explicitly tested this hypothesis by measuring local adaptation in experimentally coevolved populations of bacteria and viruses evolved in the same or different nutrient media. Consistent with previous work, we found that mean levels of evolved phage infectivity and bacteria resistance varied with nutrient concentration, with maximal levels at nutrient concentrations that supported the greatest densities of bacteria. Despite this variation in evolved mean infectivity and resistance between treatments, we found that parasite local adaptation was greatly increased when measured between populations evolved in different, compared with the same, media. This pattern is likely to have resulted from different media imposing divergent selection on bacterial hosts, and phages in turn adapting to their local hosts. These results demonstrate that the abiotic environment can play a strong and predictable role in driving patterns of local adaptation.

Seasonal shift of dominance in a submerged rooted macrophyte community of Lake Balaton

Abiotic heterogeneity of the littoral zone of Lake Balaton influences both horizontal and vertical distribution of macrophytes, but biotic differences could shape the nature of a community. Vertical and tem- poral (small timescale) biomass distributions of Potamogeton perfoliatus and Myriophyllum spicatum were analysed in relation to their photosynthetic capacities to understand their coexistence, general presence over the northern shore of the lake seasonal shift of dominance within the community. Our results indicated the adaptation of these macrophytes to the rapidly changing and mostly low irradiance of the Lake Balaton originated from its high turbidity: both P. perfoliatus and M. spicatum had high photosynthetic activity (20 to 50 mg O2.g drw x1 .h x1 ), low dark respiration (around 12-14% of maximal photosynthetic capacity) and high shade tolerance (Ic of plants were 29 i 18 and 26 i 18 mmol.m x2 .s x1 , re- spectively). The majority of photosynthetic parameters had no (or little) seasonal changes. On the other hand, in Lake Balaton P. perfoliatus and M. spicatum differed in vertical distribution of biomass: Myriophyllum concentrated its biomass in the upper, well-lit region of the water more strongly than the Potamogeton. Results suggest that the autogenic shift of dominance from Potamogeton to Myriophyllum in Lake Balaton can't be explained only by seasonal patterns of photophysiological changes, but supported by constitutive differences in plants architecture could led to the described phenomena.