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Unprecedented rates of species extinctions have prompted extensive research into the consequences of biodiversity losses on ecosystem functioning. While aquatic species are most threatened, research with freshwater and marine model systems has lagged behind progress made in terrestrial environments. This editorial to a special feature summarizes the main outcomes of a conference aimed at setting the stage for exploring the potential of aquatic systems to assess the role of biodiversity in ecosystem functioning. This series of papers proposes fresh approaches to the study of biodiversity effects on ecosystem functioning, outlines a new way of analyzing experimental data, presents a model that considers scale as an important factor determining outcomes, explores the effects of multiple stressors on species richness and ecosystem processes, and develops a food-web perspective that relates ecosystem properties to biodiversity. An insightful synthesis of lessons learned from aquatic systems is premature at present, but the papers clearly demonstrate the role that marine and freshwater systems can play in resolving open questions. The implications go well beyond the biodiversity in, and functioning of, ecosystems shaped by free-flowing or standing water. [ABSTRACT FROM AUTHOR]

Comments on the elements of ecology and evolution. Ecological stoichiometry as the study of the balance of energy and multiple chemical elements in ecological interactions; Expansion of the concept of ecological stoichiometry to other organism and other ecosystems; Applications and horizons for stoichiometric theory.

In this paper, we address the question whether and through which mechanisms herbivores can induce spatial patterning in savanna vegetation, and how the role of herbivory as a determinant of vegetation patterning changes with herbivore density and the pre-existing pattern of vegetation. We thereto developed a spatially explicit simulation model, including growth of grasses and trees, vertical zonation of browseable biomass, and spatially explicit foraging by grazers and browsers. We show that herbivores can induce vegetation patterning when two key assumptions are fulfilled. First, herbivores have to increase the attractiveness of a site while foraging so that they will revisit this site, e.g. through an increased availability or quality of forage. Second, foraging should be spatially explicit, e.g. when foraging at a site influences vegetation at larger spatial scales or when vegetation at larger spatial scales influences the selection and utilisation of a site. The interaction between these two assumptions proved to be crucial for herbivores to produce spatial vegetation patterns, but then only at low to intermediate herbivore densities. High herbivore densities result in homogenisation of vegetation. Furthermore, our model shows that the pre-existing spatial pattern in vegetation influences the process of vegetation patterning through herbivory. However, this influence decreases when the heterogeneity and dominant scale of the initial vegetation decreases. Hence, the level of adherence of the herbivores to forage in pre-existing patches increases when these pre-existing patches increase in size and when the level of vegetation heterogeneity increases. The findings presented in this paper, and critical experimentation of their ecological validity, will increase our understanding of vegetation patterning in savanna ecosystems, and the role of plant–herbivore interactions therein. [ABSTRACT FROM AUTHOR]

In an influential paper, Harte et al. highlighted the scaling or ‘self-similar’ character of the power law species–area relationship (SAR), and used this feature to derive a species abundance distribution (SAD) and an endemics–area relationship. Here I show that their analysis was incorrect and leads to unrealistic results. I develop a different approach and obtain different results, both for SAD and for endemism. In particular, I show that the power law SAR is naturally associated with the power law statistical distribution, which is the only self-similar distribution and closely matches empirical SADs. The results in this paper shed light on some of the main issues that have been discussed with regard to SARs: their relationship with the lognormal and with the neutral theory, the relative importance of sampling effects vs other mechanisms, and the deviations from a power law. The equations that I develop are simple and easy to apply to field studies. [ABSTRACT FROM AUTHOR]

Research on ecological communities, and plant–pollinator mutualistic networks in particular, has increasingly benefited from the theory and tools of complexity science. Nevertheless, up to now there have been few attempts to investigate the interplay between the structure of real pollination networks and their dynamics. This study is one of the first contributions to explore this issue. Biological invasions, of major concern for conservation, are also poorly understood from the perspective of complex ecological networks. In this paper we assess the role that established alien species play within a host community by analyzing the temporal changes in structural network properties driven by the removal of non-native plants. Three topological measures have been used to represent the most relevant structural properties for the stability of ecological networks: degree distribution, nestedness, and modularity. Therefore, we investigate for a detailed pollination network, 1) how its dynamics, represented as changes in species abundances, affect the evolution of its structure, 2) how topology relates to dynamics focusing on long-term species persistence; and 3) how both structure and dynamics are affected by the removal of alien plant species. Network dynamics were simulated by means of a stochastic metacommunity model. Our results showed that established alien plants are important for the persistence of the pollination network and for the maintenance of its structure. Removal of alien plants decreased the likelihood of species persistence. On the other hand, both the full network and the subset native network tended to lose their structure through time. Nevertheless, the structure of the full network was better preserved than the structure of the network without alien plants. Temporal topological shifts were evident in terms of degree distribution, nestedness, and modularity. However the effects of removing alien plants were more pronounced for degree distribution and modularity of the network. Therefore, elimination of alien plants affected the evolution of the architecture of the interaction web, which was closely related to the higher species loss found in the network where alien plants were removed. [ABSTRACT FROM AUTHOR]

Although the contribution of community members to functional diversity is a key question of conservation ecology, its measurement and interpretation are rather problematic. In this paper, we suggest a novel method for decomposing functional diversity. To do this we consider functional units (i.e. species or a group of species with identical traits) as the functional building blocks of communities. Then we propose the use of a recently developed measure of functional diversity (called modified functional attribute diversity or MFAD) and suggest additive decomposition of MFAD into functional values contributed by the functional units. We point out that functional values are related to changes in MFAD if the functional unit is removed from the community. This property of decomposition allows the quantification of the contribution of community members to functional diversity. By studying artificial and actual communities we compare the performance of our new method with other recently developed contribution measures, which are based on dendrograms and ordinations. Both theoretical considerations and analyses of artificial and actual data sets suggest that the proposed method of calculating functional values expresses more explicitly the contribution of community members to functional diversity and hereby can be used as a simple, yet efficient method for searching for functional keystones in ecological communities or for quantifying the contribution of community members to functional diversity. [ABSTRACT FROM AUTHOR]

In this paper, we tested whether the spatial distribution of a given species in more or less fragmented and disturbed landscapes depends on the species habitat specialization. We studied 891 spatial replicates from the French Breeding Bird Survey (FBBS) monitored at least two years during 2001–2005, and two independent landscape databases measuring respectively landscape fragmentation and recent landscape disturbance on each FBBS replicate. We used a continuous habitat specialization index for the 105 most common bird species monitored by the FBBS. We further modelled the spatial variation in abundance of each species according to fragmentation and disturbance across FBBS replicates, accounting for habitat differences and spatial trends. We then tested whether more or less specialized species responded to landscape fragmentation and disturbance. We found that the more specialist a species, the more negative its spatial response to landscape fragmentation and disturbance. Although there was a very high variation around these tendencies indicating that there are many other drivers of species distribution, our results suggest that measuring specialization may be helpful in predicting which species are likely to thrive in human degraded landscapes. We also emphasize the need to consider both positive and negative species responses when assessing consequences of habitat change in communities. [ABSTRACT FROM AUTHOR]

The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the density-area relationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics of density-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids' dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity. [ABSTRACT FROM AUTHOR]

Species distributions often show an aggregated pattern, which can be due to a number of endo- and exogenous factors. While autologistic models have been used for modelling such data with statistical rigour, little emphasis has been put on disentangling potential causes of aggregation. In this paper we ask whether it is possible to infer sources of aggregation in species distributions from a single set of occurrence data by comparing the performance of various autologistic models. We create simulated data sets, which show similar occupancy patterns, but differ in the process that causes the aggregation. We model the distribution of these data with various autologistic models, and show how the relative performance of the models is sensitive to the factor causing aggregation in the data. This information can be used when modelling real species data, where causes of aggregation are typically unknown. To illustrate, we use our approach to assess the potential causes of aggregation in data of seven bird species with contrasting statistical patterns. Our findings have important implications for conservation, as understanding the mechanisms that drive population fluctuations in space and time is critical for the development of effective management actions for long-term conservation. [ABSTRACT FROM AUTHOR]

The effects of productivity on the parameters of the species–area curve were investigated in this paper using two data sets on terrestrial plant communities: (1) one including 48 plots in 12 experimental sites on ploughed, formerly cultivated fields in the Siena region, Italy, and (2) one including 40 plots in hay meadows in the Bremen region, Germany. In both regions, species presence of vascular plants was recorded in nested plots ranging in size from 0.004 to 256 m2 and 0.001 to 1000 m2, respectively. Productivity was estimated as dry standing biomass. In the Siena data set, species richness showed a humped-back relation to biomass in the plot sizes up to 1 m2. For the larger plot sizes, no significant correlations were found. In the Bremen data set, positive relation between species number and biomass was observed at the smallest spatial scale (0.001 m2), whereas the relation disappeared or tended to be negative for the larger plot sizes. In general, the slopes z of the log species–log area curves (SAC) were negatively related to biomass in both data sets, while the intercept c increased with biomass in the Siena data set and was unrelated to biomass in the Bremen data set. The relationship between c and z was negative in the Siena data set and positive in the Bremen data set. The above results differed somewhat depending on which plot sizes were considered for the calculation of the SAC. Literature data confirmed that there are no clear patterns in the inter-correlations between productivity, small scale and large scale species richness. Sites differing in productivity and in the slopes and intercepts of SAC may thus give rise to different species richness–productivity relationships. There can be one possible relation between species richness and biomass at one spatial scale (e.g. humped-back) and another type of relation, even opposite, at another spatial scale. This suggests that the properties of species–area curves do not respond in a uniform way to the changes in productivity, but depend on the type of habitat or plant community and its particular properties. The parameter of the SAC can then hardly be used as scale-independent parameter to investigate the effects of ecological factors, such as productivity, on species richness. The lack of clear patterns in the relations between small scale and large scale species richness implies that the predictions of the species-pool hypothesis may fail when applied to plot sizes as dealt with in this study. [ABSTRACT FROM AUTHOR]

The species–time relationship (STR) describes how the species richness of a community increases with the time span over which the community is observed. This pattern has numerous implications for both theory and conservation in much the same way as the species–area relationship (SAR). However, the STR has received much less attention and to date only a handful of papers have been published on the pattern. Here we gather together 984 community time-series, representing 15 study areas and nine taxonomic groups, and evaluate their STRs in order to assess the generality of the STR, its consistency across ecosystems and taxonomic groups, its functional form, and its relationship to local species richness. In general, STRs were surprisingly similar across major taxonomic groups and ecosystem types. STRs tended to be well fit by both power and logarithmic functions, and power function exponents typically ranged between 0.2 and 0.4. Communities with high richness tended to have lower STR exponents, suggesting that factors increasing richness may simultaneously decrease turnover in ecological systems. Our results suggest that the STR is as fundamental an ecological pattern as the SAR, and raise questions about the general processes underlying this pattern. They also highlight the dynamic nature of most species assemblages, and the need to incorporate time scale in both basic and applied research on species richness patterns. [ABSTRACT FROM AUTHOR]

In this paper we investigate ecological flow networks via graph theory in search of the real sequential chains through which energy passes from producers to consumers in complex food webs. We obtain such fundamental pathways by identifying strongly connected components (SCCs), subsystems that groups species that take part in cycling, and performing topological sorting on the acyclic graphs that are obtained. Topological sorting identifies preferential directions for energy to flow from sources to sinks, while recycling remains confined within each SCC. Resolving food web networks for SCC highlights the possibility that compartments can be found in ecosystems, but this does not seem a general rule. The four aquatic food webs described in detail show a rather clear subdivision between benthic and pelagic subcommunities, a result that is discussed in the light of other studies. Should further research confirm these results, new insight into the way ecosystems use energy will be provided, with implications on cycling, reciprocal dependency of variables and indirect effects. [ABSTRACT FROM AUTHOR]

Human activities have differentially altered biogeochemical cycling at local, regional and global scales. We propose that a stoichiometric approach, examining the fluxes of multiple elements and the ratio between them, may be a useful tool for better understanding human effects on ecosystem processes and services. The different scale of impacts of the elements carbon, nitrogen and phosphorus and the different nature of their biogeochemical cycles, imply a large variation of their stoichiometric ratios in space and time and thus divergent impacts on biota.In this paper, we examine the effects of anthropogenic perturbations on nutrient ratios in ecosystems in two examples and one case study. Altered stoichiometry in agricultural systems (example 1) can affect not only crop yield and quality but also the interactions between plants and their pollinators, pests and pathogens. Human activities have also altered stoichiometry in coastal ecosystems (example 2). Increased N loading has especially lead to increased N:P and reduced Si:N ratios, with detrimental effects on ecosystem services derived from coastal pelagic food webs, such as fish yield and water quality. The terrestrial–aquatic linkage in stoichiometric alterations is illustrated with a case study, the Mississippi River watershed, where anthropogenic activities have caused stoichiometric changes that have propagated through the watershed into the northern Gulf of Mexico.Coupled with altered stoichiometric nutrient inputs are the inherent differences in variation and sensitivity of different ecosystems to anthropogenic disturbance. Furthermore, the connections among the components of a watershed may result in downstream cascades of disrupted functioning. Applying a multiple element perspective to understanding and addressing societal needs is a new direction for both ecological stoichiometry and sustainability. [ABSTRACT FROM AUTHOR]

The two main fire response traits found in the Mediterranean basin are the resprouting capacity (R) and the propagule-persistence capacity (P). Previous studies suggested that these two traits might be correlated. In this paper we first test whether R and P have evolved independently. Then, we ask if the correlation occurs because (a) one trait is not the target of selection but it is genetically linked to the other trait which is the one under selection pressure (indirect selection), or (b) because different evolutionary responses to the same selective pressure are acting in parallel on populations at different genetic starting points (parallel selection). Finally, we test to what extent resprouting is associated with some vegetative and reproductive traits.To answer these questions we used a traits database for the eastern Iberian Peninsula and we assembled the phylogenetic tree on the basis of published information. The results indicate that the two traits are negatively associated and support the parallel selection scenario in which changes in R precedes changes in P. The phylogenetic–informed associations of resprouting with other traits (plant height, age at maturity) support the existence of allocation tradeoffs.The results are consistent with the biogeographical history of the Mediterranean basin flora where most of lineages already resprouted to persist after a disturbance during the Tertiary, thus making it improbable that an additional costly persistence strategy would evolve under the Quaternary climatic conditions. [ABSTRACT FROM AUTHOR]

Predation refugia can facilitate the coexistence of predators and prey within an ecosystem by weakening trophic links between the two. The marginal macrophytes of shallow lakes are used facultatively by zooplankton to escape fish predation, leading to the stabilisation of lentic food webs. Little is known about such a role for the marginal macrophytes of lotic systems. In this paper, we examine whether the marginal macrophytes of chalk streams help buffer the interaction between the freshwater shrimp,Gammarus pulexand a benthic fish predator,Cottus gobio, both characteristically abundant in such systems.Quantitative surveys were taken ofGammarusand bullheads in winter and summer in a southern English chalk stream. These indicated thatGammarusseasonally switched their habitat preference, from marginal macrophytes in summer, to midchannel habitats in winter. Bullheads exhibited an opposite trend, preferring midchannel habitats in summer and all habitats, particularly marginal macrophytes, in winter. LargeGammarusand precopula pairs were found almost exclusively in the margins in summer. This spatial separation betweenGammarusand bullheads in summer, though not in winter, was reflected in bullhead diets, as determined by gut analysis.In field manipulation experiments, bullhead presence was the strongest factor explaining the between-habitat distribution ofGammarusin both summer and winter, indicating that the habitat shift ofGammaruswas driven by the distribution of fish. Other abundant invertebrate taxa, includingAsellus, mayflies and chironomids, exhibited little avoidance of habitat patches of high bullhead density.We conclude that marginal macrophytes in chalk streams can potentially facilitate the coexistence of high densities of bothGammarusand bullheads by spatially separating predator and prey in summer. They may further allow large populations ofGammarusto persist in the presence of high bullhead density at stretch-wide spatial scales, by reducing the predation by bullheads of large breeding and newly born individuals ofGammarusin summer. [ABSTRACT FROM AUTHOR]

Studies of microbial communities from aquatic ecosystems provide important insights into relations between various aspects of ecosystem functioning and changes in biodiversity. Aquatic microbial systems provide a valuable counterpoint to studies of terrestrial systems, because patterns reflect consequences of interactions occurring over many generations of community development, and are unlikely to represent artifacts of the initial conditions established in experimental communities. In this paper we re-analyse our previously published data to separate the contributions of temporal and spatial variation to overall variation in ecosystem functioning. A new analysis based on re-sampling confirms a negative relationship between richness and the variability of one ecosystem process, carbon dioxide flux. The negative relationship reflects high variation among communities of low species richness, rather than high temporal variation within communities of low richness. We also review the various transformations and summary statistics proposed as alternate measures of variability in ecosystem functioning, to point out that different measures are often appropriate for different kinds of data. Finally, we conclude that arguments about the cosmopolitan distribution of microbes do not preclude the existence of important relations between microbial species richness and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Literature on plant leaf litter decomposition is substantial, but only in recent years have potential interactions among leaves of different species during decomposition been examined. We review emerging research on patterns of mass loss, changes in nutrient concentration, and decomposer abundance and activity when leaves of different species are decaying in mixtures. Approximately 30 papers have been published that directly examine decomposition in leaf mixtures as well as in all component species decaying alone. From these litter-mix experiments, it is clear that decomposition patterns are not always predictable from single-species dynamics. (Characteristics of decomposition in litter-mixes that deviate from responses predicted from decomposition of single-species litters alone are designated "non-additive"; "additive" responses in mixes are predictable from component species decaying alone.) Non-additive patterns of mass loss were observed in 67% of tested mixtures; mass loss is often (though not always) increased when litters of different species are mixed. Observed mass loss in some mixtures is as much as 65% more extensive than expected from decomposition of single-species litter, but more often mass loss in mixtures exceeds expected decay by 20% or less. Nutrient transfer among leaves of different species is striking, with 76% of the mixtures showing non-additive dynamics of nutrient concentrations. Non-additive patterns in the abundance and activity of decomposers were observed in 55% and 65% of leaf mixes, respectively. We discuss some methodological details that likely contribute to conflicting results among mixed-litter studies to date. Enough information is available to begin formulating mechanistic hypotheses to explain patterns in litter-mix experiments. Emerging patterns in the mixed-litter decomposition literature have implications for relationships between biodiversity and ecosystem function (in this case, the function being decomposition), and for potential mechanisms through which invasive plant species could alter carbon and nutrient dynamics in ecosystems. [ABSTRACT FROM AUTHOR]

The concept of the ecological community is examined from the perspective of its criteria and domain. The multiple definitions and uses of this concept indicate a variety of scales and approaches. In this paper, a core definition of the minimal criteria and domain is proposed. Using those criteria, a model of the ecological community is developed based on a focal individual and its interactions with other individuals. In order to increase the scale of the domain of this approach, additional criteria are required. This model is used to explore characteristics of the minimum domain and larger scales of the community concept. The structure that emerges emphasizes context dependency and the potential for indeterminacy for most types of interactions. A prominent historical argument, the nature of boundaries between communities, has no relevance in this model. [ABSTRACT FROM AUTHOR]

Disturbance is one of the mechanisms which counteract competitive exclusion of populations in resource-limited communities, thereby facilitating coexistence and maintaining community species diversity. The intermediate disturbance hypothesis predicts maximum diversity at intermediate disturbance intensities and frequencies. This paper reports results of an experimental test of this hypothesis using a coastal benthic community of rhizopods (Protozoa: Rhizopoda), and experimental sediment resuspension as a simulated natural disturbance. We carried out two experiments of 5 d duration which focussed on the effects of resuspension intensity and frequency, respectively, on the abundance, species richness and on the Shannon-Weaver diversity index of rhizopod communities in surface sediments of natural sediment cores from the coastal southern Baltic. Care was taken to adjust the experimental treatments to the natural disturbance regime in this area. Twenty-four and 28 rhizopod species were present during the intensity and frequency experiment, respectively. Small bacterivorous rhizopods of the Vannellidae, Cochliopodidae, Paramoebidae and Rhizopoda incertae sedis dominated the communities during both experiments. Rhizopod abundance, species richness and diversity increased towards the end of the intensity experiment, but they did not show effects of disturbance intensity. Similarly, no effects of disturbance frequency were found during the frequency experiment. Our results indicate that coexistence and community diversity maintenance in benthic rhizopod communities, and probably in benthic heterotrophic protistan communities in general, may rely on different mechanisms than intermediate disturbance, such as trophic niche separation and high rates of dispersal and colonisation. [ABSTRACT FROM AUTHOR]

Proposes a non-linear trade-off between biomass allocation to resprouting and seeding. Range pertaining to fire in woody ecosystems; Description of the cultural history of the site; Changes in human activity.

The relationship between biodiversity and ecosystem functioning has emerged as a major scientific issue today. As experiments progress, there is a growing need for adequate theories and models to provide robust interpretations and generalisations of experimental results, and to formulate new hypotheses. This paper provides an overview of recent theoretical advances that have been made on the two major questions in this area: (1) How does biodiversity affect the magnitude of ecosystem processes (short-term effects of biodiversity)? (2) How does biodiversity contribute to the stability and maintenance of ecosystem processes in the face of perturbations (long-term effects of biodiversity)? Positive short-term effects of species diversity on ecosystem processes, such as primary productivity and nutrient retention, have been explained by two major types of mechanisms: (1) functional niche complementarity (the complementarity effect), and (2) selection of extreme trait values (the selection effect). In both cases, biodiversity provides a range of phenotypic trait variation. In the complementarity effect, trait variation then forms the basis for a permanent association of species that enhances collective performance. In the selection effect, trait variation comes into play only as an initial condition, and a selective process then promotes dominance by species with extreme trait values. Major differences between within-site effects of biodiversity and across-site productivity–diversity patterns have also been clarified. The local effects of diversity on ecosystem processes are expected to be masked by the effects of varying environmental parameters in across-site comparisons. A major reappraisal of the paradigm that has dominated during the last decades seems necessary if we are to account for long-term effects of biodiversity on ecosystem functioning. The classical deterministic, equilibrium approaches to stability do not explain the reduced temporal variability of aggregate ecosystem properties that has been observed in more diverse systems. On the other hand, stochastic, nonequilibrium approaches do show two types of biodiversity effects on ecosystem productivity in a fluctuating environment: (1) a buffering effect, i.e., a reduction in the temporal variance; and (2) a performance-enhancing effect, i.e., an increase in the temporal mean. The basic mechanisms involved in these long-term insurance effects are very similar to those that operate in short-term biodiversity effects: temporal niche complementarity, and selection of extreme trait values. The ability of species diversity to provide an insurance against environmental fluctuations and a reservoir of variation allowing adaptation to changing conditions may be critical in a long-term perspective. These recent theoretical developments in the area of biodiversity and ecosystem functioning suggest that linking community and ecosystem ecology is a fruitful avenue, which paves the way for a new ecological synthesis. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in understanding the ecological importance of ecosystem engineers. In this paper we argue that parasites, through the phenotypic alterations they induce intheir hosts, are likely to be involved in engineering processes for at least two reasons. First, when ecosystem engineers are themselves infected, phenotypic alterations induced by parasites can interfere with host traits involved in the engineering processes. Secondly, parasites themselves can be ecosystem engineers since the phenotypic alterations of hosts directly modify the habitat of all the species inhabiting free-living organisms. This new research area at the interface between ecology and parasitology should improve our understanding of the ecological consequences of phenotypic alterations induced by parasites in ecosystems. [ABSTRACT FROM AUTHOR]

Predictions occupy a central position in environmental management. To make predictions, models are constructed and analyzed. In this framework the quantitative approach based on large simulation models dominates. It has been shown in various ecological contexts that relevantaspects of the systemis behavior may depend on the structure of the interactions. In this paper a strategy to reconstruct the structure of a freshwater ecosystem is presented. It uses statistical patterns and field observations combined with a qualitative algorithm, that of the loop analysis. This procedure leads to unambiguous conclusions about system structure, although alternatives are possible. The models obtained are then qualitatively investigated and results discussed about management opportunities. [ABSTRACT FROM AUTHOR]

The pollen content of the organic layers of nine soil profiles in the Forest of Abernethy, Inverness-shire was examined. From a discussion of the process of raw humus formation, it would appear that Mor is a broadly stratified deposit in which favourable conditions exist for the preservation of pollen, although a number of factors which may lead to the deterioration of pollen, or disturbance of stratification are also considered. Pollen diagrams from Mor profiles were interpreted with the aid of surface sample data from Abernethy presented in an earlier paper, 14C-dating of soil material, and documentary evidence. It is concluded that substantial areas of Calluna-dominated heathland have existed in Abernethy since at least AD 400, and that prior to heathland formation, some parts of Abernethy may have contained vegetation consistent with the presence of Mull rather than Mot. [ABSTRACT FROM AUTHOR]

Disagreement exists between the results of theoretical and empirical exploration into the effect of increasing community complexity on the stability of multispecies ecosystems. A recent return to interest in this area suggests previous results should be re-assessed, from both experimental studies and models, to understand where this discrepancy arises from. Here we propose various simple extensions to a standard multispecies community model that each increase the complexity of the system in a different way. We find that increasing the number of species in a community leads to a decrease in community persistence after the system is perturbed, and go on to show that increasing the dynamical diversity of the community members leads to an increase in stability through a reduction in extinction events, relative to the less complex form of the model. Our results suggest that different forms of complexity lead to different outcomes in the stability properties of the community. While aspects of this work agree with previous empirical findings that more complex communities are more robust to perturbation, we stress that the type of complexity included and the measure of stability used in community models must be properly defined, to allow objective comparisons to be made with previous and future work. [ABSTRACT FROM AUTHOR]

Examines the interactions in a microcosm-assembled cladoceran community. Comparison of the population parameters; Reduction in the maximal population density; Assessment of the biotic communities and ecosystems.

Pollen deposition in each of five categories of vegetation in the Forest of Abernethy was examined by collecting surface samples. Qualitative differences in the composition of pollen spectra from category to category were revealed enabling simple distinctions between vegetation categories to be made. Comparison between categories was then placed on a semi-quantitative basis by compiling modal percentage frequencies for each main pollen type recorded in each category, and this data was used to construct surface pollen assemblages characteristic of each vegetation category. The application of these surface pollen assemblages to the paleoecological problems of Scots Pine forest will be considered in detail in a subsequent paper. [ABSTRACT FROM AUTHOR]

A method is described by which the rate of degradation of different kinds of cellulose fibers was determined in aquatic environments. The fiber samples were enclosed in small bags of nylon fabric with a fine mesh and weight losses of bags placed in water or sediments were measured over periods of several months. Newly processed pulp fibers were rapidly degraded in aerobic, nutrient-rich water whereas previously dried pulp and fibers derived from cotton were degraded more slowly. Lignin-containing mechanical pulp was hardly degraded at all. Cellulose decomposition was slow in unpolluted sea water and in the heavily polluted, anaerobic water outside a paper mill but relatively rapid both in the anaerobic water and the sediment of a nutrient-rich lake. The applications and limitations of the bag method in studies of decomposition processes in aquatic ecosystems are discussed. [ABSTRACT FROM AUTHOR]

This paper reports current research concerning Oribatid populations occurring in three ecosystems (an oak forest, a meadow and a poplar plantation). The main criterion used in the faunistic analysis is the relative density; this is expressed as a percentage and conventionally represented by ten classes (Fig. 1). The specific components of each habitat are compared at first wholly (Fig. 2) and then on the more rational basis or the Oribatid mites group peculiar to each milieu or in common with all the habitats (Tab. 1). The study of the relative density sums indicates the interspecifics quantitative connections, but also the similarities and the divergences between the three habitats (Tab. 2, Fig. 3). In the same way, the relationships between the three communities are established on the basis of the species list; those results show not only the connecting species but also the discriminating species (Fig. 4). The conclusions obtained are validated by considering various concepts such as the diversity, the constraint index and the specificity. [ABSTRACT FROM AUTHOR]

Focuses on evidences that plant species richness increases ecosystem productivity. Reduction of the resistance and resilience of plant biomass production to drought; Causative role of plant species diversity; Factors that covaried with plant species richness.

According to the Millennium Ecosystem Assessment, common indicators are needed to monitor the loss of biodiversity and the implications for the sustainable provision of ecosystem services. However, a variety of indicators are already being used resulting in many, mostly incompatible, monitoring systems. In order to synthesise the different indicator approaches and to detect gaps in the development of common indicator systems, we examined 531 indicators that have been reported in 617 peer-reviewed journal articles between 1997 and 2007. Special emphasis was placed on comparing indicators of biodiversity and ecosystem services across ecosystems (forests, grass- and shrublands, wetlands, rivers, lakes, soils and agro-ecosystems) and spatial scales (from patch to global scale). The application of biological indicators was found most often focused on regional and finer spatial scales with few indicators applied across ecosystem types. Abiotic indicators, such as physico-chemical parameters and measures of area and fragmentation, are most frequently used at broader (regional to continental) scales. Despite its multiple dimensions, biodiversity is usually equated with species richness only. The functional, structural and genetic components of biodiversity are poorly addressed despite their potential value across habitats and scales. Ecosystem service indicators are mostly used to estimate regulating and supporting services but generally differ between ecosystem types as they reflect ecosystem-specific services. Despite great effort to develop indicator systems over the past decade, there is still a considerable gap in the widespread use of indicators for many of the multiple components of biodiversity and ecosystem services, and a need to develop common monitoring schemes within and across habitats. Filling these gaps is a prerequisite for linking biodiversity dynamics with ecosystem service delivery and to achieving the goals of global and sub-global initiatives to halt the loss of biodiversity. [ABSTRACT FROM AUTHOR]

Link arrangement in food webs is determined by the species’ feeding habits. This work investigates whether food web topology is organized in a gradient of trophic positions from producers to consumers. To this end, we analyzed 26 food webs for which the consumption rate of each species was specified. We computed the trophic positions and the link densities of all species in the food webs. Link density measures how much each species contributes to the distribution of energy in the system. It is expressed as the number of links species establish with other nodes, weighted by their magnitude. We computed these two metrics using various formulations developed in the ecological network analysis framework. Results show a positive correlation between trophic position and link density across all the systems, regardless the specific formulas used to measure the two quantities. We performed the same analysis on the corresponding binary matrices (i.e. removing information about rates). In addition, we investigated the relation between trophic position and link density in: a) simulated binary webs with same connectance as the original ones; b) weighted webs with constant topology but randomized link strengths and c) weighted webs with constant connectance where both topology and link strengths are randomized. The correlation between the two indices attenuates, vanishes or becomes negative in the case of binary food webs and simulated data (weighted and unweighted). According to our analysis, link density in food webs decreases with trophic position so that it is greatly reduced toward the top of the trophic hierarchy. This outcome, that seems to challenge previous conclusions based on null models, strongly depends on link quantification. Including interaction strengths may improve substantially our understanding of food web organization, and possibly contradict results based on the analysis of binary webs. [ABSTRACT FROM AUTHOR]

Accelerating rates of species extinction have generated much recent interest in understanding how biodiversity affects the functioning of ecosystems. Experiments to date have shown communities composed of fewer species generally capture a smaller fraction of available resources, and achieve lower standing stock biomass than more diverse communities. However, it is uncertain how changes in biodiversity and the resulting alterations in biomass affect the rates of important ecological processes like primary production, which regulates fluxes of CO2 and O2 between the biotic and abiotic components of the environment. Here we show that species richness influences not only the standing stock biomass of primary producers, but also rates of gross primary production measured by changes in O2 concentrations in aquatic systems. We manipulated the richness of five widespread species of algae in laboratory microcosms and then quantified how richness impacts algal biomass, rates of gross primary production (GPP), and the ratio of production to respiration. Algal biomass increased by a factor of 1.82 for each level of species richness, and GPP by a factor of 1.20, for each additional species. Production to respiration ratios increased about 10% for each additional species, indicating that systems with more species were increasingly autotrophic – that is, they produced more O2 than they consumed, and accumulated CO2 faster than they released it. These trends were driven by two highly productive species that became co-dominant in species rich polycultures at the expense of other taxa. Our experiment suggests that changes in biodiversity may influence not only the rates at which O2 and CO2 are produced and released in ecosystems, but also the total amount of carbon that is sequestered and stored as biomass. [ABSTRACT FROM AUTHOR]

Over evolutionary time, the number of species in a community reflects the balance between the rate of speciation and the rate of extinction. Over shorter time-scales local species richness is also affected by how often species move into and out of the local community. These processes are at the heart of Hubbell's ‘unified neutral theory of biodiversity’ ( Hubbell 2001 ). Hubbell's spatially implicit, dispersal-limited neutral model is the most widely used of the many implementations of neutral theory and it provides an estimate of the rate of speciation in a metacommunity (if metacommunity size is known) and the rate at which species migrate into the local community from the wider metacommunity. Recently, this neutral model has been used to compare rates of speciation and migration in the species-rich fynbos of South Africa and in neotropical forests. Here we use new analytical methods for estimating the neutral model's parameters to infer speciation and dispersal rates for three sites in species-rich sclerophyll shrublands (equivalent to fynbos) in Western Australia (WA). Our estimates suggest that WA shrublands are intermediate between fynbos and tropical rainforest in terms of speciation and dispersal. Although a weak test, the model predicts species abundance distributions and species accumulation curves similar to those observed at the three sites. The neutral model's predictions also remain plausible when confronted with independent data describing: (1) known edaphic relationships between sites, (2) estimates of metacommunity species richness and (3) rates of speciation among resprouters and nonsprouters. Two of the site pairs, however, show species turnovers significantly different from those predicted by the spatially implicit form of the neutral model that we use. This suggests that non-neutral processes, in this case probably edaphic specialisation, are important in the WA shrubland metacommunity. The neutral model predicts similar rates of speciation in resprouter and sprouter taxa, a finding supported by recent molecular phylogenies. Finally, when converted into temporally scaled speciation rates and species longevities, the estimates produced by the neutral model seem implausible. The apparent departure from neutrality in the turnover of species between some sites and the implausible temporal dynamics may be due to the particular model chosen and does not reduce the significance of our other results, which confirm that local dispersal limitation, coupled with broader scale edaphic fidelity, combine to structure this biodiverse metacommunity. [ABSTRACT FROM AUTHOR]

The loss of a predator from an ecological community can cause large changes in community structure and ecosystem processes, or have very little consequence for the remaining species and ecosystem. Understanding when and why the loss of a predator causes large changes in community structure and ecosystem processes is critical for understanding the functional consequences of biodiversity loss. We used experimental microbial communities to investigate how the removal of a large generalist predator affected the extinction frequency, population abundance and total biomass of its prey. We removed this predator in the presence or absence of an alternative, more specialist, predator in order to determine whether the specialist predator affected the outcome of the initial species removal. Removal of the large generalist predator altered some species’ populations but many were unaffected and no secondary extinctions were observed. The specialist predator, though rare, altered the response of the prey community to the removal of the large generalist predator. In the absence of the specialist predator, the effects of the removal were only measurable at the level of individual species. However, when the specialist predator was present, the removal of the large generalist predator affected the total biomass of prey species. The results demonstrate that the effect of species loss from high trophic levels may be very context-dependent, as rare species can have disproportionately large effects in food webs. [ABSTRACT FROM AUTHOR]

We used an individual-based spatially-explicit model to assess the role of facilitation and plant strategies in shaping the ‘community biomass–species richness’ relationship. Facilitation had few impacts on community's richness under both the most benign (high community biomass) and the most severe (low community biomass) environments where its intensity was weak. From medium to high environmental severity, facilitation increased community richness, because all plant strategies were facilitated. In contrast, from low to medium environmental severity facilitation decreased community richness, because only the most competitive species were facilitated, which induced a decrease in the richness of the stress-tolerant species overwhelming the increase in richness of the competitive species. Above all, our simulations show how ‘strategy-dependent’ interactions among species combine to shape the humped-back biomass–species richness relationship. It also demonstrates that facilitative effects might have long-term negative effects on species richness, which result is not included in current facilitation models. [ABSTRACT FROM AUTHOR]

Current predictions regarding the ecological consequences of climate change on animal populations are generally autecological and species-specific, and/or non-mechanistic extrapolations of recent short-term patterns. To better understand and predict the effects of climate change on the distribution of species and the abundance of populations we offer a novel, broad theoretical framework. Climate-induced changes in trophic structure may actually be more predictable than effects on individual species. The logic is that there are general differences in climatic sensitivity among trophic levels – specifically, that as one moves up trophic levels, there is an increase in the temperature sensitivity of vital rates. More precisely, we provide: (1) a formal mathematical definition of distribution limits that is both operational and conceptual, introducing the concept DL50, defined as the geographic and climatic isoline representing an equilibrium occupancy of half of the suitable habitats; (2) a matrix of the possible changes in trophic structure from climate change and the general theoretical consequences; and (3) a new idea that predicts broad effects of climatic warming on trophic systems. Our intention is to help meet the challenge of developing and testing general theoretical models that can predict which species will be winners and losers in ecological time, which evolutionary traits will be favoured or selected against, and what will be consequences for ecosystem structure and function. [ABSTRACT FROM AUTHOR]

When does community assembly lead to a predictable species composition and when does this process depend on chance events, such as the timing of species arrivals? We studied the combined effects of enrichment and predation on the occurrence of priority effects, i.e. dependency on the timing of arrival, using a model of a small food web consisting of a predator, two competing prey and interference through allelopathy. Our analysis shows the conditions under which priority effects can occur. In the system we studied, the interfering species has to be the weaker resource exploiter of the two consumers, or it has to be more susceptible to predation. When it is the weaker resource exploiter, a minimum level of nutrient input is required for interference to be strong enough to cause a priority effect. When the interfering species is more susceptible to predation, a priority effect actually requires predation, which in itself also requires a minimum level of nutrient inflow. However, the priority effect disappears when predation pressure rises above a threshold value, also when the two competitors are equally preferred by the predator. This is so because predation reduces population densities and thereby the strength of interference. Our analyses make clear how the effects of resources and predation can combine to result in the absence or presence of priority effects during community assembly. [ABSTRACT FROM AUTHOR]

The metabolic theory of ecology (MTE) is an intriguing but controversial theory that tries to explain ecological patterns at all scales on the basis of first principles. Temperature plays a pivotal role in this theory. According to MTE, the Arrhenius relationship that describes the effect of temperature on biochemical reactions extends to a ‘universal temperature dependence’ that encompasses all kinds of processes and scales up to the cellular, the organismal, and the community level. In this study we test the prediction that community growth rate is temperature dependent in an Arrhenius-like way. First, we performed a literature review of the scanty data on the temperature dependence of the rates of metabolism, photosynthesis and growth of communities. In contrast to the predictions of MTE, the community activation energies did not cluster around 0.32 eV, the activation energy of photosynthesis and primary production or around 0.65 eV, the activation energy of metabolism. However, in none of the published studies the conditions were sufficiently controlled to allow firm conclusions. We therefore also performed replicated and controlled experiments using natural assemblages of marine plankton. As predicted by MTE, the maximal growth rates of community biomass increased linearly in an Arrhenius plot, with a slope close to 0.32 eV. However, a diversity of other models for the temperature dependence of community growth rates fit our data equally well. Hence, our results are at best a weak confirmation of MTE. [ABSTRACT FROM AUTHOR]

The role of competition in structuring communities of herbivorous insects is still debated. Despite this, few studies have simultaneously investigated the strength of various forms of competition and their effect on community composition. In this study, we examine the extent to which different types of competition will affect the presence and abundance of individual leaf miner species in local communities on oak trees Quercus robur. We first use a laboratory experiment to quantify the strength of intra- and interspecific competition. We then conduct a large-scale field experiment to determine whether competition occurring in one year extends to the next. Finally, we use observational field data to examine the extent to which mechanisms of competition uncovered in the two experiments actually reflect into patterns of co-occurrence in nature. In our experiment, we found direct competition at the leaf-level to be stronger among conspecific than among heterospecific individuals. Indirect competition among conspecifics lowered the survival and weight of larvae of T. ekebladella, both at the branch and the tree-level. In contrast, indirect competition among heterospecifics was only detected in one out of three species pairs examined. In the field experiment, the presence of a given moth species in one year affected the relative abundance of leaf miner species in the next year. Nevertheless, patterns of competition observed in these experiments did not translate into repulsion among free-ranging leaf miners: conspecific larvae of four leaf-mining species were aggregated on the same trees, shoots and leaves. In contrast, heterospecific larvae were only aggregated at the tree-level. We propose that despite the fact that leaf miners do compete and that such effects extend through time, the incidence and strength of competition is relatively small at realistic densities. Hence, competition will likely be of minor importance in shaping the distribution of leaf miners in a natural setting. [ABSTRACT FROM AUTHOR]

Orchid mycorrhiza probably affects about 25 000 plant species and thus roughly one tenth of all higher plants. Histologically, this symbiosis resembles other kinds of endomycorrhiza, the fungal hyphae growing within living plant cells. Considerable evidence, however, suggests that it is not a two-way exchange relationship and thus not potentially mutualistic, such as the wide-spread endomycorrhiza between plants and Glomalean fungi, known as arbuscular mycorrhiza. During the achlorophyllous seedling stage orchids are obligately dependent on the fungi; some species remain so through life, while others establish photosynthesis but to varying degrees remain facultatively dependent of /responsive to fungal infection as adults. None of the fungi involved are so far known to depend on the symbiosis with orchids. Transfer of organic carbon compounds from hyphae to the orchid has been demonstrated repeatedly, but it is not clear to what extent this takes place during a biotrophic phase while the intracellular hyphae remain intact, or during the subsequent extensive degradation of the hyphal coils. The advantage of viewing orchid mycorrhiza basically as a unilateral mycophagous relationship, in spite of hypothetical beneficial spin-offs to the mycobiont, is that it provides a conceptual framework similar to that of other parasitic or fungivore relationships; mechanisms known in such relationships could be searched for in future studies of the orchid–fungus symbiosis. These could include mechanisms for recognition, attraction and selection of fungi, physiological regulation of internal hyphal growth, breakdown, and material transfer, nutritional consequences of the plant's preference(s) and trophic changes, fungal avoidance mechanisms, and consequences at population and ecosystem levels. A whole range of possible life strategies becomes apparent that could support divergent evolution and lead to the proliferation of species that has indeed occurred in the orchid family. We outline some of the possible physiological mechanisms and ecological implications of this approach. [ABSTRACT FROM AUTHOR]

Ecological coupling by material exchanges or dispersal between spatially distinct communities has important impacts on ecological processes, such as diversity–stability relationships, ecosystem function, and food web dynamics. One important mode of coupling between ecosystems occurs via organisms with complex life histories, which often switch between distinct ecosystems during their life cycle, and so can be channels of material exchanges between these ecosystems. Some organisms with complex life histories (e.g. frogs, dragonflies) can be abundant and effective predators during one or more life stages, and so provide conduits for strong direct and indirect interactions across ecosystem boundaries, linking the dynamics of discrete and often quite dissimilar community types. We present simple models and a case study (tailored to pond ecosystems), to explore how interactions within larval habitats can indirectly impact ecological interactions in adult habitats. Using our case study as a springboard, we propose that cohorts of predators emerging from natal habitats (e.g. ponds) cast ‘predation shadows’ on the surrounding adult (e.g. terrestrial) landscape. Trophic interactions within ponds, and the distribution of ponds on the landscape, can thus affect the spatial pattern in the strength of these predation shadows, creating strong spatial patterning in terrestrial trophic cascades. Our findings emphasize the importance of organisms with complex life histories as generators of strong links across ecosystem boundaries, and as potential sources of spatial variation in the strength and indirect impacts of interspecific interactions. [ABSTRACT FROM AUTHOR]

The effect of biodiversity on ecosystem functioning has proven variable both within and among manipulative studies. Species richness is the most commonly used measure of biodiversity in such studies, but the range of species’ functional traits (functional diversity), not the number of species per se, likely underpins a key mechanistic link between species richness and ecosystem functioning. However, the majority of experiments that have examined the effect of functional diversity have manipulated functional group richness, an approach recognised to suffer numerous limitations. Continuous measures of functional diversity avoid many of these limitations, but the relationship between continuous functional diversity and the magnitude of ecosystem processes has been largely untested. Using one vs two-species mixtures of rock pool macroalgae as a model, we conducted a field experiment to determine the effect of a continuous measure of functional diversity (functional attribute diversity, FAD, the degree of functional differentiation based on four functional traits) on the magnitude of net primary productivity and overyielding, based upon two alternative null-models. The total magnitude of productivity was largely determined by the identity of species present, not FAD. However, FAD proved to be a good predictor of overyielding (variation in productivity after the dominant effects of species identity had been accounted for). Furthermore, despite differences in the mean magnitude of the effect of combining species, the positive relationship between FAD and overyielding was consistent according to both additive and substitutive null-models. Our findings imply that whilst knowledge of species’ independent contributions remains indispensable in the prediction of biotic effects on ecosystem functioning within a trophic level, continuous measures of functional diversity should be used as a supplementary tool to predict the magnitude of overyielding, thereby refining predictions. [ABSTRACT FROM AUTHOR]

Nestedness analysis has become increasingly popular in the study of biogeographic patterns of species occurrence. Nested patterns are those in which the species composition of small assemblages is a nested subset of larger assemblages. For species interaction networks such as plant–pollinator webs, nestedness analysis has also proven a valuable tool for revealing ecological and evolutionary constraints. Despite this popularity, there has been substantial controversy in the literature over the best methods to define and quantify nestedness, and how to test for patterns of nestedness against an appropriate statistical null hypothesis. Here we review this rapidly developing literature and provide suggestions and guidelines for proper analyses. We focus on the logic and the performance of different metrics and the proper choice of null models for statistical inference. We observe that traditional ‘gap-counting’ metrics are biased towards species loss among columns (occupied sites) and that many metrics are not invariant to basic matrix properties. The study of nestedness should be combined with an appropriate gradient analysis to infer possible causes of the observed presence–absence sequence. In our view, statistical inference should be based on a null model in which row and columns sums are fixed. Under this model, only a relatively small number of published empirical matrices are significantly nested. We call for a critical reassessment of previous studies that have used biased metrics and unconstrained null models for statistical inference. [ABSTRACT FROM AUTHOR]

Most studies investigating the relationship between plant diversity and ecosystem functioning lasted only a few years. These studies generally showed a positive relationship between diversity and productivity that strengthened with time. This pattern suggests the experimental communities have not yet reached maturity, which raises the question whether a positive relationship between diversity and productivity will remain if communities approach equilibrium conditions. Here, we analyze eight years of data from a plant diversity experiment without legumes. A positive relationship between plant diversity and productivity arose in the second year and increased until the fifth year. This relationship persisted throughout the remainder of the experiment, but the slope of the relationship remained constant at approximately 50 g/m2/log2[richness]. The positive relationship between diversity and productivity was caused by strong complementarity effects, which initially increased but remained constant after the fourth year of the experiment. Our results show a positive relationship between diversity and productivity is a long-term phenomenon, driven by complementary interactions. [ABSTRACT FROM AUTHOR]

Parasites are ubiquitous in ecological communities but it is only recently that they have been routinely included in food web studies. Using recently published data and the tool of network analysis, we elucidate features associated with the pattern of parasitism in ecological communities. First we show here that parasitism is non-random in food webs. Second we demonstrate that parasite diversity, the number of parasite species harboured by a host species, is related to the network position of a host species. Specifically, a host species with high parasite diversity tends to have a wide diet range, occupy a network position close to many prey species, or occupy a network position that can better accumulate resources from species at lower trophic levels. Lastly our results also suggest that a host species with higher vulnerability to predators, being at a network position close to many predatory species, or being involved in many different food chains, tends to be important in parasite transmission. [ABSTRACT FROM AUTHOR]

Liebig's law of the minimum, which states that only one element limits the growth of organisms at any given time, is widely used in ecology. This principle is routinely applied to organisms, populations and communities, but can it really be applied indistinguishably across these different scales? Here we show, by prediction of a resource ratio conceptual model and with an experimental test carried out in microcosms with bacteria that, unlike single species, communities are likely to adjust their stoichiometry to that of their resources. This adjustment results from competitive exclusion and coexistence mechanisms, and is sensitive to the overall diversity of species in the community. It guaranties co-limitation, i.e. simultaneous limitation by multiple resources, at the community scale and optimal use of resources and maximization of community biomass for wide ranges of resource ratios. These results question the applicability of the Liebig's law of the minimum at the community level, and the relevance of ecosystem models relying on this principle. [ABSTRACT FROM AUTHOR]

Applying ideas of statistical mechanics in ecology have recently received quite some attention. The entropy maximization (EM) formalism looks particularly attractive, as it provides a simple algorithm to infer detailed system variables from a limited number of constraints. However, we point out that a blind application of this formalism can easily lead to wrong conclusions. To illustrate this, we reanalyze an ecological data set that has been used to claim the good performance of EM in predicting species abundances from trait measurements. We show that these results are entirely due to the restrictive constraints, and do not provide any support for the applicability of EM in ecology. By comparing with a simple example from physics, we indicate which characteristic mechanism of EM, and of statistical mechanics in general, is missing for the ecological example. This analysis introduces a series of methods to evaluate future attempts to apply EM in ecology. [ABSTRACT FROM AUTHOR]

Recently, there has been a vigorous interest in community ecology about the structure of mutualistic networks and its importance for species persistence and coevolution. However, the mechanisms shaping mutualistic networks have been rarely explored. Here we extend for the first time the neutral theory of biodiversity to a multi trophic system. We focus on nestedness, a distinctive pattern of mutualistic community assembly showing two characteristics, namely, asymmetrical specialization (specialists interacting with generalists) and a generalist core (generalists interacting with generalists). We investigate the importance of relative species abundance (RSA) for the nested assembly of plant–animal mutualistic networks. Our results show that neutral mutualistic communities give rise to networks considerably more nested than real communities. RSA explains 60–70% of nested patterns in two real communities studied here, while 30–40% of nestedness is still unexplained. The nested pattern in real communities is better explained when we introduce interaction-specific species traits such as forbidden links and intensity of dependence (relative importance of fruits for the diet of a frugivore) in our analysis. The fact that neutral mutualistic communities exhibit a perfectly nested structure and do not show a random or compartmentalized structure, underlines the importance of RSA in the assembly of mutualistic networks. [ABSTRACT FROM AUTHOR]