Homogeneous Environmental Conditions Research Articles

Volatile diversity in wild populations of rosemary (Rosmarinus officinalis L.) from the Tyrrhenian Sea vicinity cultivated under homogeneous environmental conditions

Rosemary (Rosmarinus officinalis L.) is an evergreen plant, a member of the Lamiaceae family. It is distributed throughout the Mediterranean, where it is used primarily as a spice herb for culinary purposes. In the present study 18 wild populations of rosemary distributed throughout the Tyrrenian Sea and its vicinity were tested for chemical profile. The populations were initially cultivated for 2 years under homogenous environmental conditions to minimize the potential effect of geographic surroundings on volatile composition (phenotype) that masked the true genotypic differences. A total of 58 compounds, representing 95.5–98.7% of the volatiles were detected. Volatile compounds were grouped into 27 oxygenated monoterpenes, 18 sesquiterpenes hydrocarbons, 10 monoterpene hydrocarbons, 1 oxygenated sesquiterpene, and 2 miscellaneous compounds. Sesquiterpenes and oxygenated terpenes were the main constituents in the rosemary oil. PCA and UPGMA dendrogram identified three chemotypes designated ‘chemotype A’ dominated by 1,8-cineole and β-pinene; ‘chemotype B’ dominated by α-pinene and verbenone and ‘chemotype C’, dominated by camphor and myrcene. The variability of volatiles in the 18 populations was moderately correlated (0.48≤r≤0.75) to geographic coordinates (latitude and longitude), suggesting that once environmental effects are removed genetics and origin are the key factors in chemotype variation in rosemary.

Selected pomegranate germplasm from Afghanistan: morphological variability and relationship among collected accessions

During the period 2008-09 and in the frame of PHDP 58 Afghan and 18 foreign pomegranate accessions have been collected and grown under homogeneous environmental and cultivation practice conditions in ex situ collections. Standardized procedures were adopted to describe mature trees, leaves, flowers and fruits for a total of 30 phenotypic traits. Within the National Collection of Pomegranate of Afghanistan, coefficients of variability ranged from 8.8 to 31.7% for fruit diameter and weight of non edible part, respectively. Principal component analysis revealed the absence of correlated variables among different organs. The whole set of accessions resulted discriminated on the basis of the studied morphological parameters and all the accessions were grouped into 3 sub-sets by hierarchical cluster analysis. Local accessions resulted distributed in the 3 clusters, nevertheless the largest one held all the foreign varieties while the second one included all the accessions collected under the putative name of ‘Bedana’. The adopted morphological studies allowed to identify one true-to-type ‘Bedana’ accession, considered the best Afghan variety for fresh consume due to its very soft seed, and to solve the cases of homonymy. Analogously, various accessions originally collected from different regions of Afghanistan under the name of ‘Kandahari’ were identified and renamed.

Field heritability of a plant adaptation to fire in heterogeneous landscapes.

The strong association observed between fire regimes and variation in plant adaptations to fire suggests a rapid response to fire as an agent of selection. It also suggests that fire-related traits are heritable, a precondition for evolutionary change. One example is serotiny, the accumulation of seeds in unopened fruits or cones until the next fire, an important strategy for plant population persistence in fire-prone ecosystems. Here, we evaluate the potential of this trait to respond to natural selection in its natural setting. For this, we use a SNP marker approach to estimate genetic variance and heritability of serotiny directly in the field for two Mediterranean pine species. Study populations were large and heterogeneous in climatic conditions and fire regime. We first estimated the realized relatedness among trees from genotypes, and then partitioned the phenotypic variance in serotiny using Bayesian animal models that incorporated environmental predictors. As expected, field heritability was smaller (around 0.10 for both species) than previous estimates under common garden conditions (0.20). An estimate on a subset of stands with more homogeneous environmental conditions was not different from that in the complete set of stands, suggesting that our models correctly captured the environmental variation at the spatial scale of the study. Our results highlight the importance of measuring quantitative genetic parameters in natural populations, where environmental heterogeneity is a critical aspect. The heritability of serotiny, although not high, combined with high phenotypic variance within populations, confirms the potential of this fire-related trait for evolutionary change in the wild.

Biodiversity and environmental context predict dung beetle‐mediated seed dispersal in a tropical forest field experiment

Biodiversity–ecosystem functioning (BEF) literature is dominated by investigations conducted in temperate grassland ecosystems under homogenous environmental conditions. Consequently, studies concerned with the functional importance of higher trophic levels, or with the role of environmental conditions in shaping BEF relationships, are comparatively uncommon. To address this, we assessed dung beetle diversity‐functioning relationships in situ, in a field experiment in the Brazilian Amazon. Dung beetles perform a number of ecological functions in habitats across the globe; in tropical forests they play a key role in the secondary dispersal of seeds. We therefore experimentally tested how the functional diversity of dung beetle communities affects seed dispersal and how BEF relationships varied with environmental context, by replicating the experiments under contrasting soil conditions. Relationships between dung beetle diversity and function were examined using diversity indices calculated using continuous morphological traits of the individuals involved in experiments, and functioning was measured as the dispersion of artificial seeds throughout the soil profile and the probability of burial. Ninety experimental plots were established across three distinct primary forest sites. We collected, identified, and measured almost 2000 beetles, and sieved around 11 Mg of soil to quantify the dispersion of 1800 seed mimics. There was a significant effect of dung beetle functional diversity on both seed dispersion and seed burial, although this depended on environmental context, with the strength or direction of responses differing across the contrasting soils. Regardless of soil type, functional richness, but not species richness, predicted seed dispersion. We therefore advocate the use of functional diversity indices over taxonomic approaches in dung beetle‐focused BEF investigations. Furthermore, we highlight the difficulties in generalizing BEF relationships, even considering a single function within the same ecosystem.

Separating the role of biotic interactions and climate in determining adaptive response of plants to climate change

Altered rainfall regimes will greatly affect the response of plant species to climate change. However, little is known about how direct effects of changing precipitation on plant performance may depend on other abiotic factors and biotic interactions. We used reciprocal transplants between climatically very different sites with simultaneous manipulation of soil, plant population origin, and neighbor conditions to evaluate local adaptation and possible adaptive response of four Eastern Mediterranean annual plant species to climate change. The effect of site on plant performance was negligible, but soil origin had a strong effect on fecundity, most likely due to differential water retaining ability. Competition by neighbors strongly reduced fitness. We separated the effects of the abiotic and biotic soil properties on plant performance by repeating the field experiment in a greenhouse under homogenous environmental conditions and including a soil biota manipulation treatment. As in the field, plant performance differed among soil origins and neighbor treatments. Moreover, we found plant species-specific responses to soil biota that may be best explained by the differential sensitivity to negative and positive soil biota effects. Overall, under the conditions of our experiment with two contrasting sites, biotic interactions had a strong effect on plant fitness that interacted with and eventually overrode climate. Because climate and biotic interactions covary, reciprocal transplants and climate gradient studies should consider soil biotic interactions and abiotic conditions when evaluating climate change effects on plant performance.

Irreversible collective migration of cyanobacteria in eutrophic conditions.

In response to natural or anthropocentric pollutions coupled to global climate changes, microorganisms from aquatic environments can suddenly accumulate on water surface. These dense suspensions, known as blooms, are harmful to ecosystems and signicantly degrade the quality of water resources. In order to determine the physico-chemical parameters involved in their formation and quantitatively predict their appearance, we successfully reproduced irreversible cyanobacterial blooms in vitro. By combining chemical, biochemical and hydrodynamic evidences, we identify a mechanism, unrelated to the presence of internal gas vesicles, allowing the sudden collective upward migration in test tubes of several cyanobacterial strains (Microcystis aeruginosa PCC 7005, Microcystis aeruginosa PCC 7806 and Synechocystis sp. PCC 6803). The final state consists in a foamy layer of biomass at the air-liquid interface, in which micro-organisms remain alive for weeks, the medium lying below being almost completely depleted of cyanobacteria. These "laboratory blooms" start with the aggregation of cells at high ionic force in cyanobacterial strains that produce anionic extracellular polymeric substances (EPS). Under appropriate conditions of nutrients and light intensity, the high photosynthetic activity within cell clusters leads the dissolved oxygen (DO) to supersaturate and to nucleate into bubbles. Trapped within the EPS, these bubbles grow until their buoyancy pulls the biomass towards the free surface. By investigating a wide range of spatially homogeneous environmental conditions (illumination, salinity, cell and nutrient concentration) we identify species-dependent thresholds and timescales for bloom formation. We conclude on the relevance of such results for cyanobacterial bloom formation in the environment and we propose an ecient method for biomass harvesting in bioreactors.

Trait dimensionality explains widespread variation in local adaptation.

All species are locked in a continual struggle to adapt to local ecological conditions. In cases where species fail to locally adapt, they face reduced population growth rates, or even local extinction. Traditional explanations for limited local adaptation focus on maladaptive gene flow or homogeneous environmental conditions. These classical explanations have, however, failed to explain variation in the magnitude of local adaptation observed across taxa. Here we show that variable levels of local adaptation are better explained by trait dimensionality. First, we develop and analyse mathematical models that predict levels of local adaptation will increase with the number of traits experiencing spatially variable selection. Next, we test this prediction by estimating the relationship between dimensionality and local adaptation using data from 35 published reciprocal transplant studies. This analysis reveals a strong correlation between dimensionality and degree of local adaptation, and thus provides empirical support for the predictions of our model.

Environmental heterogeneity leads to higher plasticity in dry‐edge populations of a semi‐arid Chilean shrub: insights into climate change responses

Summary Interannual variability in climatic conditions should be taken into account in climate change studies in semi‐arid ecosystems. It may determine differentiation in phenotypic plasticity among populations, with populations experiencing higher environmental heterogeneity showing higher levels of plasticity. The ability of populations to evolve key functional traits and plasticity may determine the survival of plant populations under the drier and more variable climate expected for semi‐arid ecosystems. Working with populations of the semi‐arid Chilean shrub Senna candolleana along its entire distribution range, we assessed inter‐ and intra‐population variation in functional traits as well as in their plasticity in response to water availability. We measured morphological and physiological traits related to drought resistance in both field conditions and in a greenhouse experiment, where drought response was evaluated under two water availability treatments. All populations responded plastically, but higher precipitation heterogeneity in dry‐edge populations seemed to have selected for more plastic genotypes compared to populations growing at mesic sites and with more homogeneous environmental conditions. Synthesis. Our results suggest adaptive plasticity since higher levels of phenotypic plasticity were positively associated with plant performance. However, we did not find evidence for genetic variation for plasticity within populations. To the extent that phenotypic plasticity may play a key role in future persistence, populations at mesic sites may be more vulnerable to climate change due to their lower plasticity and their current limitations to evolve novel norms of reaction. Conversely, although Senna candolleana populations at the dry edge are exposed to higher levels of stress, they may be less susceptible to climate change in view of their greater plasticity. We highlight the need to consider population differentiation in both mean traits and their plasticity to model realistic scenarios of species distribution under climate change.

Dispersal among local communities does not reduce historical contingencies during metacommunity assembly

Ample evidence suggests that ecological communities can exhibit historical contingencies. However, few studies have explored whether differences in assembly history can generate alternative local community states in metacommunities in which local communities are linked by dispersal. In a protist microcosm experiment, we examined the influence of species colonization history on metacommunity assembly under homogeneous environmental conditions, by manipulating both the sequence of species colonization into local communities and the rate of dispersal among local communities. Whereas the role of dispersal in structuring local communities decreased over time and became non‐significant towards the end of the experiment, species colonization history significantly influenced local communities throughout the experiment. Local communities, regardless of the rate of dispersal among them, exhibited two alternative states characterized by the dominance of different species. The alternative community states, however, emerged in the absence of priority effects that were often associated with alternative community states found in other assembly studies. Rather, they were driven by variation in species interaction strength among local communities with different assembly histories. These results suggest that dispersal among local communities may not necessarily reduce the role of species colonization history in shaping metacommunity assembly, and that differences in species colonization history need to be explicitly considered as an important factor in causing heterogeneous community states in metacommunities.

The importance of micrometeorological variations for photosynthesis and transpiration in a boreal coniferous forest

Abstract. Plant canopies affect the canopy micrometeorology, and thereby alter canopy exchange processes. For the simulation of these exchange processes on a regional or global scale, large-scale vegetation models often assume homogeneous environmental conditions within the canopy. In this study, we address the importance of vertical variations in light, temperature, CO2 concentration and humidity within the canopy for fluxes of photosynthesis and transpiration of a boreal coniferous forest in central Sweden. A leaf-level photosynthesis-stomatal conductance model was used for aggregating these processes to canopy level while applying the within-canopy distributions of these driving variables. The simulation model showed good agreement with eddy covariance-derived gross primary production (GPP) estimates on daily and annual timescales, and showed a reasonable agreement between transpiration and observed H2O fluxes, where discrepancies are largely attributable to a lack of forest floor evaporation in the model. Simulations in which vertical heterogeneity was artificially suppressed revealed that the vertical distribution of light is the driver of vertical heterogeneity. Despite large differences between above-canopy and within-canopy humidity, and despite large gradients in CO2 concentration during early morning hours after nights with stable conditions, neither humidity nor CO2 played an important role for vertical heterogeneity of photosynthesis and transpiration.

Gap analysis comparing protected areas with potential natural vegetation in Tuscany (Italy) and a GIS procedure to bridge the gaps

The aim was to compare the protected area (PA) network in Tuscany, Italy, with the areas referenced to different types of potential natural vegetation (PNV), to determine whether they are adequately represented for plant and habitat conservation purposes. For PNV, an existing but slightly updated and modified Italian Vegetation Series (VS) map was used. Each VS type corresponds to vegetation complexes that live under homogeneous environmental conditions and can each be considered an ecological land unit at the working scale employed here. Using GIS techniques, the geographic layers of PAs and VS were processed with spatial intersection to extract and quantify the VS contained within the boundaries of PAs. As a minimum conservation goal, we used the widely accepted 10% target threshold. It was found that, even though Tuscan PAs covered almost 20% of the total land surface, 94% of VS types resulted to be included in PAs with a percentage of at least 10% of their total area. The survey shows that the VS with the higher degree of inclusion in PAs are distributed in the Mediterranean Tuscany (coast and Tuscan Archipelago) and in some inner areas such as Apuan region, northern Apennines, Amiata Mt. and Farma-Merse Valley. Two VS types must be considered under-protected (i.e. contained in an existing PA network with percentages < 10%). We propose a simple GIS procedure based on certain priority assumptions: (a) existing PAs should be enlarged rather than new ones created and (b) their naturalness taken into account. This procedure produces a suitability map useful for identifying the best areas in which a local administration might look for solutions to bridge the gaps.

Assessing fish assemblages similarity above and below a dam in a neotropical reservoir with partial blockage.

Damming rivers disrupts the water flow and changes the ichthyofauna organisation. We investigated an impoundment with permanent connection and homogeneous environmental conditions between the zones above and below the dam. Temperature was comparatively higher during wet season irrespective of zone, and both zones had higher dissolved oxygen, conductivity and transparency in the dry season. A total of 1687 individuals comprising 27 species were collected in the downriver zone, while the reservoir had 879 individuals and 23 species. Each zone had different fish assemblage composition and structure, but assemblages were not explained by the examined environmental variables (r2 = 0.08; p = 0.307). Migratory species such as Pimelodus maculatus, Pimelodus fur, Leporinus copelandii and Prochilodus lineatus were the most affected, and probably are prevented to perform upriver migrations. On the other hand, lentic adapted species such as G. brasiliensis, Hoplias malabaricus and Hoplosternum littorale successfully colonised the reservoir. Therefore we conclude that the presence of the lateral hydrological connectivity alone does not guarantee the ecological connectivity since fish assemblage similarity differed between the two zones. Fish passage facilities should be monitored and managed to evaluate and improve their functionality.

GENETIC ALGORITHM BASED SIMULATION–OPTIMIZATION FOR FIGHTING WILDFIRES

Wildfire is one of the most significant disturbances responsible for reshaping the terrain and changing the ecosystem of a particular region. Its detrimental effects on environment as well as human lives and properties, and growing trend in terms of frequency and intensity of wildfires over the last decade have necessitated the development of efficient forest fire management techniques. During the last three decades, Forest Fire Decision Support Systems (FFDSS) have been developed to help in the decision-making processes during forest fires by providing necessary information on fire detection, their status and behavior, and other aspects of forest fires. However, most of these decision support systems lack the capability of developing intelligent fire suppression strategies based upon current status and predicted behavior of forest fire. This paper presents an approach for development of efficient fireline building strategies via intelligent resource allocation. A Genetic Algorithm based approach has been proposed in this paper for resource allocation and optimum fireline building that minimizes the total damage due to wildland fires. The approach is based on a simulation–optimization technique in which the Genetic Algorithm uses advanced forest fire propagation models based upon Huygens principles for evaluation of cost index of its solutions. Both homogeneous and heterogeneous environmental conditions have been considered. Uncertainties in weather conditions as well as imperfect knowledge about exact vegetation and topographical conditions make exact prediction of wildfires very difficult. The paper incorporates Monte-Carlo simulations to develop robust strategies in uncertain conditions. Extensive simulations demonstrate the effectiveness of the proposed approach in efficient resource allocation for fighting complex wildfires in uncertain and dynamic conditions.

Unveiling the taphonomy of elusive natural tank deposits: A study case in the Pleistocene of northeastern Brazil

Fossiliferous natural tanks are a singular type of sedimentary deposit restricted to northeastern Brazil, which usually preserves a diversified late Pleistocene vertebrate fauna. Their fossil assemblages are taxonomically well known, but their taphonomy is poorly understood. This work presents a detailed taphonomic analysis of a tank deposit from Jirau site (Ceará State, Northeastern Brazil) to improve understanding of the processes that influenced fossil deposition and preservation in natural tanks and to shed light on paleoecological and paleoenvironmental aspects related to the late Pleistocene vertebrate fauna from Northeastern Brazil. Tank deposits from different localities were also compared to figure out potential taphonomic patterns among them. Additionally, comparisons with other Brazilian Pleistocene deposits and other debris-flow deposits bearing vertebrates were undertaken.The study revealed the predominance of the megamammal Eremotherium laurillardi in the deposit, which we attributed to its abundance in late Pleistocene biocoenosis as well as bone resistance. Scarcity of non-mammalian vertebrates is likely related to their paucity in late Pleistocene biocoenosis. Time-averaging was evidenced by the co-occurrence of different weathering, petrographic and color patterns, and may have affected the ontogenetic profile of the accumulation relative to the original biocoenosis. Analyses of weathering stages, tooth and trample marks, indicate wide exposition of the thanatocoenosis before burial. Abrasion and petrographic patterns allow reworking in the assemblage to be inferred. Permineralization and substitution are the fossilization processes observed. Taphonomy indicates that floods deposited clasts and bioclasts in the tank under an arid or semiarid climate in a debris-flow regime.Comparison with other tank deposits revealed several similar taphonomic features and differences related to sedimentology and stratigraphy. Taphonomic similarities suggest rather homogeneous environmental conditions in the northeastern Brazil during the late Pleistocene, as previously suggested by taxonomic studies. Comparison with other Brazilian Pleistocene deposits shows that tanks have more temporal fidelity than caves, coastal and some fluvial deposits. The Jirau vertebrate accumulation was produced by the reworking and transport of skeletal elements accumulated in a nearby thanatocoenosis and is similar to other better known debris-flow hosted vertebrate accumulations.

Resource‐based determinants of range sizes of forest vascular plants in Germany

AbstractAimTo examining whether niche breadth, niche position and a compound measure of the two variables help to explain the range sizes of forest vascular plants.LocationsDeciduous forests in two regions of Germany, the Weser–Elbe region and Bavarian Alps.MethodsWe compiled range size data for vascular plant species (30 in the Weser–Elbe region, 35 in the Bavarian Alps) on regional, national and continental scales by determining the area of occupancy (number of occupied grid cells) in both regions, Germany and Eurasia. Estimates of realized niche breadth and niche position (ecological optimum) for soil pH and light were based on measurements in 46 sites for all species. Frequency distributions of pH values on regional and national scales served to calculate the ‘available niche breadth’, i.e. niche breadth values corrected for the different availabilities of pH values in the region and country.ResultsRegional range size in the Weser–Elbe region increased with increasing niche breadth for both soil pH and light and with decreasing pH niche position. pH niche breadth was positively correlated to national range size in the Weser–Elbe region and to Eurasian range size in the Bavarian Alps. In the latter region, all other relationships with range size were (partly marginally) non‐significant. Available niche breadth was generally more closely related to the regional and national distribution of species in both regions than either niche breadth or position alone.Main conclusionsNiche breadth and position performed well as predictors of range size only for soil pH and in the Weser–Elbe region, which shows more homogeneous environmental conditions than the Bavarian Alps. If the frequencies of different ranges of pH values can be quantified, the calculation of available niche breadth for soil pH appears to be a promising approach for assessing the possible effects of niche variables on the range sizes of species.

Oligarchies in Amazonian tree communities: a ten‐year review

This paper revisits various hypotheses about oligarchic patterns in Amazonian tree communities put forward by Pitman et al. (2001). Together, these hypotheses predict that most lowland sites in the Amazon are located within large patches of relatively homogeneous edaphic and other environmental conditions, where an oligarchy of common, frequent tree species accounts for a majority of trees. To assess the degree to which these hypotheses have been corroborated or refuted over the last ten years, we reviewed &gt; 200 studies published since 2001. We found overwhelming support for the hypo thesis that large‐scale oligarchies of common and frequent species are a common feature of Amazonian tree communities. At least 22 studies have documented oligarchies in Amazonian woody plant communities to date, and no studies have looked for oligarchies as defined by Pitman et al. (2001) and failed to find them. We argue that six publications that offer critiques of the oligarchy hypothesis do not constitute valid tests. The other hypotheses in Pitman et al. (2001)– one regarding the specific oligarchic taxa that dominate forests near the eastern base of the Andes and one that attempts to explain why oligarchic species exist – are less well supported by the literature, in large part because they have not been subjected to many tests. We discuss links between these hypotheses and other well‐known patterns and hypotheses in ecology (the abundance–occupancy relationship, the Janzen–Connell hypothesis, the niche‐environment hypothesis, and the niche breadth hypothesis), and provide additional detail to facilitate rigorous tests in the future. The paper concludes by presenting remote sensing evidence that large patches of relatively homogeneous environmental conditions account for most of the upland forest landscape across Amazonian Peru.

Changes in distribution of Greenland halibut in a varying environment

AbstractMorgan, M. J., Garabana, D., Rideout, R. M., Román, E., Pérez-Rodriguez, A. and Saborido-Rey, F. 2013. Changes in distribution of Greenland halibut in a varying environment. – ICES Journal of Marine Science, 70: 352–361. Fish are expected to respond to changing oceanographic temperature by altering their distribution. Off the coast of Newfoundland, Canada, there have been major changes in oceanographic temperature over the last several decades, with both record cold and record warm years being observed. Greenland halibut is an important flatfish species in the area, and is distributed in deep waters over a very wide geographic range. Thus, it might be buffered from temperature change in the overall area by reduced temperature variation at depth, and the diverse temperature conditions over its wide range. We examined intrapopulation variation in temperature and depth distribution, and the biological changes in relation to changes in available temperature. On the Flemish Cap, variation in available temperature was limited, and changes in depth were related to changing age composition and the differential depth distribution with age/size. In other areas there was a larger decline in available temperature, and associated with this, Greenland halibut moved to deeper waters and occupied warmer temperatures than they had previously. Concurrently, growth declined and condition increased. This study shows that shifts in distribution may not result in maintenance of homogeneous environmental conditions, and that resulting biological changes will be difficult to predict.

Sampling precision and variability of tree species abundance ranks in a semideciduous Atlantic forest fragment

Among other objectives, forest inventories are aimed to identify ecological communities and to correlate community composition with environmental variables. The identification of different communities would require several forest inventories, each covering small sampling areas with relatively homogeneous environmental conditions. The multiple plot sampling method, traditionally used in local inventories of tropical forests, cannot assure such homogeneity, since even small sampling areas would show environmental heterogeneity influencing vegetation. In this paper we assessed the consequences of this heterogeneity for sampling by quantifying the variability of species abundance ranks for species sampled with 10 or more individuals in a set of plots covering a small sampling area. The species reference abundance ranks were obtained from a sample of 100 plots of 10 m × 10 m each randomly set in a sampling area of 6.5 ha in a tropical forest fragment (Southeastern Brazil). For each species we used resamplings (30 trials) to obtain the species abundance ranks in sub-samples, considering different sampling intensities (n = 25, 50 and 75 plots), and compared these ranks with the species reference rank (n = 100 plots). Then, we compared the species ranks in sub-samples of 50 plots (10.000 trials) with the reference rank and assessed the frequency and extent of rank displacements. Species rank was highly variable across resampling trials for the sampling intensities of n = 25 and n = 50, but decreased considerable with a sampling intensity of n = 75 plots. The mean rank variability and especially the maximum displacement raised significantly from the seventh most abundant species on, and some species occupied quite discrepant abundance ranks in up to 10% of the 10.000 resampling trials. This high internal variability of forest samples may impair the search for floristic patterns as scale lessens, say, to the meso-scale (1–100 km2). We discussed some possible ways to increase internal homogeneity of tropical forest samples with the multiple plot sampling method. Among these, objective entitation, based on an ancient phytosociological procedure, is suggested as the most appropriate for use on the hilly relieves of the Atlantic forest biome.

Analysis of the community structure of abyssal kinetoplastids revealed similar communities at larger spatial scales

Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000-3000 km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales.

Could our fisheries be more productive? Indirect negative effects of bottom trawl fisheries on fish condition

Summary1. The nets used in bottom trawl fisheries cause mortality of benthic invertebrates and this can decrease the long‐term availability of prey to exploited fish species by reducing the abundance of benthic invertebrates. This may have consequences for the sustainability of fisheries.2. We assessed the impact of bottom trawling on the food availability of fish by comparing the condition of fish (as weight‐at‐length) in an area that had a steep commercial bottom‐trawling gradient in the Irish Sea but otherwise homogeneous environmental conditions.3. We found that the condition of the important commercial flatfish plaice Pleuronectes platessa was negatively related to trawling frequency, and this could be explained by a reduced production of the infaunal invertebrates they feed on. Density‐dependent changes in competition over food could not explain this difference. No effect of trawling on the condition of the flatfish dab Limanda limanda was detected. Whiting Merlangius merlangus feeds primarily on fish, and therefore, no effect of bottom trawling on its condition was expected or detected.4. This study therefore indicates that bottom trawl fisheries may have a negative effect on the condition of some of their target species, but not others, by reducing the abundance of their benthic prey.5. Synthesis and application. Bottom trawls may indirectly affect the population size and growth rate of the target fish species and result in lower fishing yields. Such reductions in the yield and sustainability of fisheries are highly undesirable. The effects of bottom trawls may be mitigated by the modification of fishing gears or by minimizing the area of the seabed fished by bottom trawls.