Historical comparisons reveal altered competitive interactions in a guild of crustose coralline algae

As the ocean environment changes over time, a paucity of long‐term data sets and historical comparisons limits the exploration of community dynamics over time in natural systems. Here, we used a long‐term experimental data set to present evidence for a reversal of competitive dominance within a group of crustose coralline algae (CCA) from the 1980s to present time in the northeast Pacific Ocean. CCA are cosmopolitan species distributed globally, and dominant space holders in intertidal and subtidal systems. Competition experiments showed a markedly lower competitive ability of the previous competitively dominant species and a decreased response of competitive dynamics to grazer presence. Competitive networks obtained from survey data showed concordance between the 1980s and 2013, yet also revealed reductions in interaction strengths across the assemblage. We discuss the potential role of environmental change, including ocean acidification, in altered ecological dynamics in this system.     

Spatial analysis of ectomycorrhizal fungi reveals that root tip communities are structured by competitive interactions

Microbial ecology has made large advances over the last decade, mostly because of improvements in molecular analysis techniques that have enabled the detection and identification of progressively larger numbers of microbial species. However, determining the ecological patterns and processes taking place in communities of microbes remains a significant challenge. Are communities randomly assembled through dispersal and priority effects, or do species interact with each other leading to positive and negative associations? For mycorrhizal fungi, evidence is accumulating that stochastic and competitive interactions between species may both have a role in shaping community structure. Could the methodological approach, which is often incidence based, impact the outcomes detected? Here, we applied an incidence‐based Terminal Restriction Fragment Length Polymorphism (T‐RFLP) database approach to examine species diversity and ecological interactions within a community of ectomycorrhizal (ECM) fungi. Co‐occurrence analysis revealed that the ECM community colonizing root tips was strongly structured by competitive interactions, or ecological processes generating a similar spatial pattern, rather than neutral processes. Analysis of β‐diversity indicated that community structure was significantly more similar (spatially autocorrelated) at distances equal to or <3.41 m. The eight most frequently encountered species in the root tip community of ECM fungi displayed significant competitive interactions with at least one other species, showing that the incidence‐based approach was capable of detecting this sort of ecological information.     

Are Trade-Offs Among Species’ Ecological Interactions Scale Dependent? A Test Using Pitcher-Plant Inquiline Species

Trade-offs among species' ecological interactions is a pervasive explanation for species coexistence. The traits associated with trade-offs are typically measured to mechanistically explain species coexistence at a single spatial scale. However, species potentially interact at multiple scales and this may be reflected in the traits among coexisting species. I quantified species' ecological traits associated with the trade-offs expected at both local (competitive ability and predator tolerance) and regional (competitive ability and colonization rate) community scales. The most common species (four protozoa and a rotifer) from the middle trophic level of a pitcher plant (Sarracenia purpurea) inquiline community were used to link species traits to previously observed patterns of species diversity and abundance. Traits associated with trade-offs (competitive ability, predator tolerance, and colonization rate) and other ecological traits (size, growth rate, and carrying capacity) were measured for each of the focal species. Traits were correlated with one another with a negative relationship indicative of a trade-off. Protozoan and rotifer species exhibited a negative relationship between competitive ability and predator tolerance, indicative of coexistence at the local community scale. There was no relationship between competitive ability and colonization rate. Size, growth rate, and carrying capacity were correlated with each other and the trade-off traits: Size was related to both competitive ability and predator tolerance, but growth rate and carrying capacity were correlated with predator tolerance. When partial correlations were conducted controlling for size, growth rate and carrying capacity, the trade-offs largely disappeared. These results imply that body size is the trait that provides the basis for ecological interactions and trade-offs. Altogether, this study showed that the examination of species' traits in the context of coexistence at different scales can contribute to our understanding of the mechanisms underlying community structure.     

Local community size mediates ecological drift and competition in metacommunities

The outcome of competitive interactions is likely to be influenced by both competitive dominance (i.e. niche-based dynamics) and ecological drift (i.e. neutral dynamics governed by demographic stochasticity). However, spatial models of competition rarely consider the joint operation of these two processes. We develop a model based on the original competition-colonization trade-off model that incorporates niche and neutral processes and several realistic facets of ecological dynamics: it allows local competition (i.e. competition within a patch) to occur within communities of a finite size, it allows competitors to vary in the degree of competitive asymmetry, and it includes the role of local migration (i.e. propagule pressure). The model highlights the role of community size, i.e. the number of competitors in the local community, in mediating the relative importance of stochastic and deterministic forces. In metacommunities where local communities are small, ecological drift is substantial enough that strong competitors become effectively neutral, creating abrupt changes in the outcome of competition not predicted by the standard competition-colonization trade-off. Importantly, the model illustrates that, even when other aspects of species interactions (e.g. migration ability, competitive ability) are unchanged, local community size can alter the dynamics of metacommunity persistence. Our work demonstrates that activities which reduce the size of local communities, such as habitat destruction and degradation, effectively compound the extinction debt.     

Adaptive genetic diversity of dominant species contributes to species co-existence and community assembly

The synthesis of evolutionary biology and community ecology aims to understand how genetic variation within one species can shape community properties and how the ecological properties of a community can drive the evolution of a species. A rarely explored aspect is whether the interaction of genetic variation and community properties depends on the species'' ecological role. Here we investigated the interactions among environmental factors, species diversity, and the within-species genetic diversity of species with different ecological roles. Using high-throughput DNA sequencing, we genotyped a canopy-dominant tree species, Parashorea chinensis, and an understory-abundant species, Pittosporopsis kerrii, from fifteen plots in Xishuangbanna tropical seasonal rainforest and estimated their adaptive, neutral and total genetic diversity; we also surveyed species diversity and assayed key soil nutrients. Structural equation modelling revealed that soil nitrogen availability created an opposing effect in species diversity and adaptive genetic diversity of the canopy-dominant Pa. chinensis. The increased adaptive genetic diversity of Pa. chinensis led to greater species diversity by promoting co-existence. Increased species diversity reduced the adaptive genetic diversity of the dominant understory species, Pi. kerrii, which was promoted by the adaptive genetic diversity of the canopy-dominant Pa. chinensis. However, such relationships were absent when neutral genetic diversity or total genetic diversity were used in the model. Our results demonstrated the important ecological interaction between adaptive genetic diversity and species diversity, but the pattern of the interaction depends on the identity of the species. Our results highlight the significant ecological role of dominant species in competitive interactions and regulation of community structure.     

Do biotic interactions shape both sides of the humped‐back model of species richness in plant communities?

A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity-diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity.     

Vultures acquire information on carcass location from scavenging eagles

Vultures are recognized as the scroungers of the natural world, owing to their ecological role as obligate scavengers. While it is well known that vultures use intraspecific social information as they forage, the possibility of inter-guild social information transfer and the resulting multi-species social dilemmas has not been explored. Here, we use data on arrival times at carcasses to show that such social information transfer occurs, with raptors acting as producers of information and vultures acting as scroungers of information. We develop a game-theoretic model to show that competitive asymmetry, whereby vultures dominate raptors at carcasses, predicts this evolutionary outcome. We support this theoretical prediction using empirical data from competitive interactions at carcasses. Finally, we use an individual-based model to show that these producer–scrounger dynamics lead to vultures being vulnerable to declines in raptor populations. Our results show that social information transfer can lead to important non-trophic interactions among species and highlight important potential links among social evolution, community ecology and conservation biology. With vulture populations suffering global declines, our study underscores the importance of ecosystem-based management for these endangered keystone species.     

Disentangling the effect of hybrid interactions and of the constant effort hypothesis on ecological community stability

In the last years, a remarkable theoretical effort has been made in order to understand the relation between stability and complexity in ecological communities. Yet, what maintains species diversity in real ecological communities is still an open question. The non‐random structures of ecological interaction networks have been recognized as one key ingredient impacting the maximum number of coexisting species within the ecological community. However most of the earlier theoretical studies have considered communities with only one interaction type (either antagonistic, competitive or mutualistic). Recently, it has been proposed that multiple interaction types might stabilize ecosystems and that, in this hybrid case, increasing complexity increases stability. Here we show that these results depend on ad hoc hypothesis that the authors used in their model and we highlight the need to disentangle the role of multiple interaction types and constant interaction effort allocation on community stability. Indeed, we find that mixing of mutualistic and predator–prey interaction types does not stabilize the community dynamics and we demonstrate that a positive correlation between complexity and stability is observed only if a constant effort allocation is imposed in the ecological interactions. Synthesis In recent years a sparkling research has been devoted to the search of new theoretical mechanisms to explain way ecosystems may persist despite their complexity. Here we show that, contrary to what recently suggested (Mougi et al. 2012), the mismatch between theoretical results and empirical evidences on the stability of ecological community is still there also for communities with both mutualistic and antagonistic interactions, and the ‘complexity‐stability’ paradox is still alive. Indeed, we demonstrate that their results arise as an artifact of the peculiar rescaling of the interaction strengths they imposed. Our study suggests that further theoretical studies and experimental evidences are still needed to better understand the role of interaction strengths in real ecological communities.     

浙江江山公益林物种种间关系及CCA排序

利用浙江省江山市80个公益林固定小班监测数据,基于生态位理论、种间联结、CCA排序方法对研究区内群落优势种种间关系及其与环境的关系进行研究。结果表明:江山市公益林群落中杉木、檵木、紫萁分别在乔木、灌木、草本层中占优势地位;石栎与青冈、隔药柃与山苍子、蕨与海金沙的生态位重叠指数值分别在乔、灌、草本层中最大;而CCA协变量矩阵偏典范对应分析说明物种分布主要受海拔、坡度、坡向(光照强度)以及腐殖质厚度的影响,总体上可以对89.44%的环境因子进行解释。并且还表明,生态位宽度较大的物种其生态位重叠值较大,并在CCA排序图物种集中区分布。反之,生态位重叠较小,在CCA排序图中将偏离物种集中区;除此之外,在CCA排序图上,物种间的距离与其生态位重叠值的大小及种间联结均有密切的关联,若未存在显著的联结性,随物种间的生态位重叠值越高,其在CCA排序上的距离越近,若存在显著联结性,则正相关缩小距离,负相关拉大距离。     

Ecotone formation through ecological niche construction: the role of biodiversity and species interactions

Rapid changes in species composition, also known as ecotones, can result from various causes including rapid changes in environmental conditions, or physiological thresholds. The possibility that ecotones arise from ecological niche construction by ecosystem engineers has received little attention. In this study, we investigate how the diversity of ecosystem engineers, and their interactions, can give rise to ecotones. We build a spatially explicit dynamical model that couples a multispecies community and its abiotic environment. We use numerical simulations and analytical techniques to determine the biotic and abiotic conditions under which ecotone emergence is expected to occur, and the role of biodiversity therein. We show that the diversity of ecosystem engineers can lead to indirect interactions through the modification of their shared environment. These interactions, which can be either competitive or mutualistic, can lead to the emergence of discrete communities in space, separated by sharp ecotones where a high species turnover is observed. Considering biodiversity is thus critical when studying the influence of species–environment interactions on the emergence of ecotones. This is especially true for the wide range of species that have small to moderate effects on their environment. Our work highlights new mechanisms by which biodiversity loss could cause significant changes in spatial community patterns in changing environments.     

Crustose coralline algal species host distinct bacterial assemblages on their surfaces

Crustose coralline algae (CCA) are important components of many marine ecosystems. They aid in reef accretion and stabilization, create habitat for other organisms, contribute to carbon sequestration and are important settlement substrata for a number of marine invertebrates. Despite their ecological importance, little is known about the bacterial communities associated with CCA or whether differences in bacterial assemblages may have ecological implications. This study examined the bacterial communities on four different species of CCA collected in Belize using bacterial tag-encoded FLX amplicon pyrosequencing of the V1–V3 region of the 16S rDNA. CCA were dominated by Alphaproteobacteria, Gammaproteobacteria and Actinomycetes. At the operational taxonomic unit (OTU) level, each CCA species had a unique bacterial community that was significantly different from all other CCA species. Hydrolithon boergesenii and Titanoderma prototypum, CCA species that facilitate larval settlement in multiple corals, had higher abundances of OTUs related to bacteria that inhibit the growth and/or biofilm formation of coral pathogens. Fewer coral larvae settle on the surfaces of Paragoniolithon solubile and Porolithon pachydermum. These CCA species had higher abundances of OTUs related to known coral pathogens and cyanobacteria. Coral larvae may be able to use the observed differences in bacterial community composition on CCA species to assess the suitability of these substrata for settlement and selectively settle on CCA species that contain beneficial bacteria.     

Diversity in a complex ecological network with two interaction types

Most studies on ecological networks consider only a single interaction type (e.g. competitive, predatory or mutualistic), and try to developrules for system stability based exclusively on properties of this interaction type. However, the stability of ecological networks may be more dependent on the way different interaction types are combined in real communities. To address this issue, we start by compiling an ecological network in the Doñana Biological Reserve, southern Spain, with 390 species and 798 mu-tualistic and antagonistic interactions. We characterize network structure by looking at how mutualistic and antagonistic interactions are combined across all plant species. Both the ratio of mutualistic to antagonistic interactions per plant, and the number of basic modules with an antagonistic and a mutualistic interaction are very heterogeneous across plant species, with a few plant species showing very high values for these parameters. To assess the implications of these network patterns on species diversity, we study analytically and by simulation a model of this ecological network. We find that the observed correlation between strong interaction strengths and high mutualistic to antagonistic ratios in a few plant species significantly increases community diversity. Thus, to predict the persistence of biodiversity we need to understand how interaction strength and the architecture of ecological networks with different interaction types are combined.     

Competition and efficiency in closed freshwater algal systems: tests of ecosystem design principles

Seven species of freshwater algae were grown in defined media in monoalgal and mixed cultures, to test whether species interactions and community efficiency were predictable on the basis of ecological theory. Results supported the prediction of competitive interactions, although no differences were detectable in the strength of competition in two and three species mixed cultures, nor was the severity of competitive effects predictable on the basis of relatedness at the level of phyla. On a community level, cultures with two and three species fixed a greater proportion of available carbon than cultures with only one species, implying a more efficient overall use of available resources. Implications for the design of artificial closed ecosystems are discussed.     

Trait positions for elevated invasiveness in adaptive ecological networks

Our ability to predict the outcome of invasion declines rapidly as non-native species progress through intertwined ecological barriers to establish and spread in recipient ecosystems. This is largely due to the lack of systemic knowledge on key processes at play as species establish self-sustaining populations within the invaded range. To address this knowledge gap, we present a mathematical model that captures the eco-evolutionary dynamics of native and non-native species interacting within an ecological network. The model is derived from continuous-trait evolutionary game theory (i.e., Adaptive Dynamics) and its associated concept of invasion fitness which depicts dynamic demographic performance that is both trait mediated and density dependent. Our approach allows us to explore how multiple resident and non-native species coevolve to reshape invasion performance, or more precisely invasiveness, over trait space. The model clarifies the role of specific traits in enabling non-native species to occupy realised opportunistic niches. It also elucidates the direction and speed of both ecological and evolutionary dynamics of residing species (natives or non-natives) in the recipient network under different levels of propagule pressure. The versatility of the model is demonstrated using four examples that correspond to the invasion of (i) a horizontal competitive community; (ii) a bipartite mutualistic network; (iii) a bipartite antagonistic network; and (iv) a multi-trophic food web. We identified a cohesive trait strategy that enables the success and establishment of non-native species to possess high invasiveness. Specifically, we find that a non-native species can achieve high levels of invasiveness by possessing traits that overlap with those of its facilitators (and mutualists), which enhances the benefits accrued from positive interactions, and by possessing traits outside the range of those of antagonists, which mitigates the costs accrued from negative interactions. This ‘central-to-reap, edge-to-elude’ trait strategy therefore describes the strategic trait positions of non-native species to invade an ecological network. This model provides a theoretical platform for exploring invasion strategies in complex adaptive ecological networks.

     

The rotifer communities of acid-stressed lakes of Maine

The structure of the rotifer community in relation to lake pH, trophic status, the type of planktivore assemblage and the crustacean community was assessed in a survey of 23 lakes ranging in pH from 4.4 to 7.3, and in a study of two lakes — one acidic, the other circumneutral — during two summers. In both investigations the number of rotifer species encountered per sample was strongly reduced with pH. Although the reason for this is not clear acid-stress, the ultraoligotrophic nature of the acidic lakes, and competitive interactions with crustacean zooplankters may all have played a role. More importantly the ecological significance of this relationship is not known. The rotifer Keratella taurocephala was a principle species in the most acidic lakes, while several common rotifers were notably absent from these lakes. Although rotifer abundance was correlated with lake pH, the results of this study indicate that rotifer abundance is not a result of lake pH per se, but of lake trophic status and interactions with the crustacean community.     

A process‐based metacommunity framework linking local and regional scale community ecology

The metacommunity concept has the potential to integrate local and regional dynamics within a general community ecology framework. To this end, the concept must move beyond the discrete archetypes that have largely defined it (e.g. neutral vs. species sorting) and better incorporate local scale species interactions and coexistence mechanisms. Here, we present a fundamental reconception of the framework that explicitly links local coexistence theory to the spatial processes inherent to metacommunity theory, allowing for a continuous range of competitive community dynamics. These dynamics emerge from the three underlying processes that shape ecological communities: (1) density‐independent responses to abiotic conditions, (2) density‐dependent biotic interactions and (3) dispersal. Stochasticity is incorporated in the demographic realisation of each of these processes. We formalise this framework using a simulation model that explores a wide range of competitive metacommunity dynamics by varying the strength of the underlying processes. Using this model and framework, we show how existing theories, including the traditional metacommunity archetypes, are linked by this common set of processes. We then use the model to generate new hypotheses about how the three processes combine to interactively shape diversity, functioning and stability within metacommunities.     

Spatial analysis of vector-borne disease: A four-species model

Summary Disease can influence a host population's dynamics directly or indirectly through effects on the host's interactions with competitors and exploiters. We present a stochastic, spatially explicit model for the epidemiological landscape of a vector-borne disease. Two host species, of unequal competitive strength, are attacked by a selective parasite; the parasite serves as a vector for a pathogen. We emphasize the importance of the ecological stencil, i.e. the local area where ecological interactions govern a site's species composition. We demonstrate analytically that varying the size of the ecological stencil critically affects the dynamics of the host densities and the potential equilibrium configuration of the system. We point out how parallel computing can efficiently employ the geometry of the stencil's local transitions to predict large-scale spatio-temporal patterns of the model community.     

Stable isotope analyses reveal dense trophic species packing and clear niche differentiation in a malagasy primate community

Understanding the mechanisms maintaining local species richness is a major topic in tropical ecology. In ecological communities of Madagascar, primates represent a major part of mammalian diversity and, thus, are a suitable taxon to study these mechanisms. Previous research suggested that ecological niche differentiation facilitates the coexistence of lemurs. However, detailed data on all species making up diverse local primate assemblages is rarely available, hampering community‐wide tests of niche differentiation among Malagasy mammals. Here, we took an indirect approach and used stable isotopes as long‐term indicators of individuals' diets to answer the question of whether trophic patterns and food‐related mechanisms stabilize coexistence in a species‐rich lemur community. We analyzed stable carbon and nitrogen isotopes in hair collected from eight syntopic lemurs in Kirindy Forest. We found that lemur species were well separated into trophic niches and ranged over two trophic levels. Furthermore, species were densely packed in isotopic space suggesting that past competitive interactions between species are a major structuring force of this dry forest lemur community. Results of other comparative studies on primates and our findings underline that—in contrast to communities worldwide—the structure and composition of lemur communities follow predictions of ecological niche theory. Patterns of competitive interactions might be more clearly revealed in Malagasy primate communities than elsewhere because lemurs represent a large fraction of ecologically interacting species in these communities. The pronounced trophic niche differentiation among lemurs is most likely due to intense competition in the past as is characteristic for adaptive radiations. Am J Phys Anthropol 153:249–259, 2014. © 2013 Wiley Periodicals, Inc.     

Understanding and predicting effects of modified interactions through a qualitative analysis of community structure

Models of ecological communities are traditionally based on relationships between pairs of species, where the strengths of per capita interactions are fixed and independent of population abundance. A growing body of literature, however; describes interactions whose strength is modified by the density of either a third species or by one of the species involved in a pairwise interaction. These modified interactions have been treated as indirect effects, and the terminology addressing them is diverse and overlapping. In this paper we develop a general analytical framework based on a qualitative analysis of community structure to account for the consequence of modified interactions in complex ecological communities. Modified interactions are found to create both direct and indirect effects between species. The sign of a direct effect can change in some instances depending on the magnitude of a key variable or parameter, which leads to a threshold change in system structure and dynamics. By considering alternative structures of a community, we extend our ability to model perturbations that move the system far from a previous equilibrium. Using specific examples, we reinterpret existing results, develop hypotheses to guide experiments or management interventions, and explore the role of modified interactions and positive feedback in creating and maintaining alternative stable states. Through a qualitative analysis of community structure, system feedback is demonstrated as being key in understanding and predicting the dynamics of complex ecological communities.     

Phylogenetic analysis of community assembly and structure over space and time

Evolutionary ecologists are increasingly combining phylogenetic data with distributional and ecological data to assess how and why communities of species differ from random expectations for evolutionary and ecological relatedness. Of particular interest have been the roles of environmental filtering and competitive interactions, or alternatively neutral effects, in dictating community composition. Our goal is to place current research within a dynamic framework, specifically using recent phylogenetic studies from insular environments to provide an explicit spatial and temporal context. We compare communities over a range of evolutionary, ecological and geographic scales that differ in the extent to which speciation and adaptation contribute to community assembly and structure. This perspective allows insights into the processes that can generate community structure, as well as the evolutionary dynamics of community assembly.