Colin Fontaine

Stability of Ecological Communities and the Architecture of Mutualistic and Trophic Networks

Building a Network The relation between the architecture of ecological networks and community stability is important to understand the assembly of complex communities. By combining a model approach and a meta-analysis of a large collection of ecological networks, Thébault and Fontaine (p. 853; see the Perspective by Bascompte) found that network architecture and stability fundamentally differed between trophic networks that involved herbivory and mutualistic networks that involved pollination. These findings have implications for the understanding of community structure, evolution, and response to perturbation. Ecological network architecture differs between models of trophic (herbivore) and mutualistic (pollination) communities. Research on the relationship between the architecture of ecological networks and community stability has mainly focused on one type of interaction at a time, making difficult any comparison between different network types. We used a theoretical approach to show that the network architecture favoring stability fundamentally differs between trophic and mutualistic networks. A highly connected and nested architecture promotes community stability in mutualistic networks, whereas the stability of trophic networks is enhanced in compartmented and weakly connected architectures. These theoretical predictions are supported by a meta-analysis on the architecture of a large series of real pollination (mutualistic) and herbivory (trophic) networks. We conclude that strong variations in the stability of architectural patterns constrain ecological networks toward different architectures, depending on the type of interaction.

Ecophylogenetics: advances and perspectives

Ecophylogenetics can be viewed as an emerging fusion of ecology, biogeography and macroevolution. This new and fast‐growing field is promoting the incorporation of evolution and historical contingencies into the ecological research agenda through the widespread use of phylogenetic data. Including phylogeny into ecological thinking represents an opportunity for biologists from different fields to collaborate and has provided promising avenues of research in both theoretical and empirical ecology, towards a better understanding of the assembly of communities, the functioning of ecosystems and their responses to environmental changes. The time is ripe to assess critically the extent to which the integration of phylogeny into these different fields of ecology has delivered on its promise. Here we review how phylogenetic information has been used to identify better the key components of species interactions with their biotic and abiotic environments, to determine the relationships between diversity and ecosystem functioning and ultimately to establish good management practices to protect overall biodiversity in the face of global change. We evaluate the relevance of information provided by phylogenies to ecologists, highlighting current potential weaknesses and needs for future developments. We suggest that despite the strong progress that has been made, a consistent unified framework is still missing to link local ecological dynamics to macroevolution. This is a necessary step in order to interpret observed phylogenetic patterns in a wider ecological context. Beyond the fundamental question of how evolutionary history contributes to shape communities, ecophylogenetics will help ecology to become a better integrative and predictive science.

The ecological and evolutionary implications of merging different types of networks.

Interactions among species drive the ecological and evolutionary processes in ecological communities. These interactions are effectively key components of biodiversity. Studies that use a network approach to study the structure and dynamics of communities of interacting species have revealed many patterns and associated processes. Historically these studies were restricted to trophic interactions, although network approaches are now used to study a wide range of interactions, including for example the reproductive mutualisms. However, each interaction type remains studied largely in isolation from others. Merging the various interaction types within a single integrative framework is necessary if we want to further our understanding of the ecological and evolutionary dynamics of communities. Dividing the networks up is a methodological convenience as in the field the networks occur together in space and time and will be linked by shared species. Herein, we outline a conceptual framework for studying networks composed of more than one type of interaction, highlighting key questions and research areas that would benefit from their study.

New Species in the Old World: Europe as a Frontier in Biodiversity Exploration, a Test Bed for 21st Century Taxonomy

The number of described species on the planet is about 1.9 million, with ca. 17,000 new species described annually, mostly from the tropics. However, taxonomy is usually described as a science in crisis, lacking manpower and funding, a politically acknowledged problem known as the Taxonomic Impediment. Using data from the Fauna Europaea database and the Zoological Record, we show that contrary to general belief, developed and heavily-studied parts of the world are important reservoirs of unknown species. In Europe, new species of multicellular terrestrial and freshwater animals are being discovered and named at an unprecedented rate: since the 1950s, more than 770 new species are on average described each year from Europe, which add to the 125,000 terrestrial and freshwater multicellular species already known in this region. There is no sign of having reached a plateau that would allow for the assessment of the magnitude of European biodiversity. More remarkably, over 60% of these new species are described by non-professional taxonomists. Amateurs are recognized as an essential part of the workforce in ecology and astronomy, but the magnitude of non-professional taxonomist contributions to alpha-taxonomy has not been fully realized until now. Our results stress the importance of developing a system that better supports and guides this formidable workforce, as we seek to overcome the Taxonomic Impediment and speed up the process of describing the planetary biodiversity before it is too late.

The Whereabouts of Flower Visitors: Contrasting Land-Use Preferences Revealed by a Country-Wide Survey Based on Citizen Science

Background In the past decade, accumulating evidence of pollinator decline has raised concerns regarding the functioning of terrestrial ecosystems and the sustainability of crop production. Although land-use changes have been advanced as the major causes, the affinities of most wild pollinators with the main land-use types remain unknown. Filling this gap in our knowledge is a prerequisite to improving conservation and management programmes. Methodology/Principal Findings We estimated the affinity of flower visitors with urban, agricultural and natural land-uses using data from a country-wide scale monitoring scheme based on citizen science (Spipoll). We tested whether the affinities differed among insect orders and according to insect frequency (frequent or infrequent). Our results indicate that the affinities with the three land-use types differed among insect orders. Apart from Hymenopterans, which appeared tolerant to the different land-uses, all flower visitors presented a negative affinity with urban areas and a positive affinity with agricultural and natural areas. Additionally, infrequent taxa displayed a lower affinity with urban areas and a higher affinity with natural areas than did frequent taxa. Within frequent taxa, Hymenoptera and Coleoptera included specialists of the three land-use types whereas Diptera and Lepidoptera contained specialists of all but urban areas. Conclusions/Significance Our approach allowed the first standardised evaluation of the affinity of flower visitors with the main land-use types across a broad taxonomical range and a wide geographic scope. Our results suggest that the most detrimental land-use change for flower visitor communities is urbanisation. Moreover, our findings highlight the fact that agricultural areas have the potential to host highly diverse pollinator communities. We suggest that policy makers should, therefore, focus on the implementation of pollinator-friendly practices in agricultural lands. This may be a win-win strategy, as both biodiversity and crop production may benefit from healthier communities of flower visitors in these areas.

Large-scale trade-off between agricultural intensification and crop pollination services

Unprecedented growth in human populations has required the intensification of agriculture to enhance crop productivity, but this was achieved at a major cost to biodiversity. There is abundant local-scale evidence that both pollinator diversity and pollination services decrease with increasing agricultural intensification. This raises concerns regarding food security, as two-thirds of the worlds major food crops are pollinator-dependent. Whether such local findings scale up and affect crop production over larger scales is still being debated. Here, we analyzed a country-wide dataset of the 54 major crops in France produced over the past two decades and found that benefits of agricultural intensification decrease with increasing pollinator dependence, to the extent that intensification failed to increase the yield of pollinator-dependent crops and decreased the stability of their yield over time. This indicates that benefits from agricultural intensification may be offset by reductions in pollination serv...

POPULATION SYNCHRONY INDUCED BY RESOURCE FLUCTUATIONS AND DISPERSAL IN AN AQUATIC MICROCOSM

Two of the principal explanations for regional population synchrony, large-scale environmental variability and dispersal, have received considerable theoretical attention. Although time series analysis has helped to validate the relative importance of these two explanations, very little of this theory has been confirmed by experiment. Here, we demonstrate the dual synchronizing effect of dispersal and temporal environmental variation. We used an experimental model system based on the rotifer Brachionus calyciflorus and its algal prey Chlorella vulgaris. We constructed temporal prey fluctuations with two periodic components that matched the generation time and life span of the rotifer. By varying the amplitude of these two periods we created prey variability with “white” (both periods had equal power) and “red” (the longest period had greatest power) spectra. In the absence of dispersal only the red fluctuations induced synchrony in the population dynamics of the rotifer. Dispersal had a strong and rapid synchronizing effect. The combination of red (but not white) fluctuations and dispersal resulted in the highest levels of synchrony. These results confirm the predictions of recent theory, but they also suggest that the temporal structure of environmental variability determines its capacity to synchronize population dynamics over large spatial scales.

Artificial light at night as a new threat to pollination

Pollinators are declining worldwide and this has raised concerns for a parallel decline in the essential pollination service they provide to both crops and wild plants. Anthropogenic drivers linked to this decline include habitat changes, intensive agriculture, pesticides, invasive alien species, spread of pathogens and climate change. Recently, the rapid global increase in artificial light at night has been proposed to be a new threat to terrestrial ecosystems; the consequences of this increase for ecosystem function are mostly unknown. Here we show that artificial light at night disrupts nocturnal pollination networks and has negative consequences for plant reproductive success. In artificially illuminated plant–pollinator communities, nocturnal visits to plants were reduced by 62% compared to dark areas. Notably, this resulted in an overall 13% reduction in fruit set of a focal plant even though the plant also received numerous visits by diurnal pollinators. Furthermore, by merging diurnal and nocturnal pollination sub-networks, we show that the structure of these combined networks tends to facilitate the spread of the negative consequences of disrupted nocturnal pollination to daytime pollinator communities. Our findings demonstrate that artificial light at night is a threat to pollination and that the negative effects of artificial light at night on nocturnal pollination are predicted to propagate to the diurnal community, thereby aggravating the decline of the diurnal community. We provide perspectives on the functioning of plant–pollinator communities, showing that nocturnal pollinators are not redundant to diurnal communities and increasing our understanding of the human-induced decline in pollinators and their ecosystem service.

Evolutionary History and Ecological Processes Shape a Local Multilevel Antagonistic Network

Uncovering the processes that shape the architecture of interaction networks is a major challenge in ecology. Studies have consistently revealed that more closely related taxa tend to show greater overlap in interaction partners, fuelling the idea that interactions are phylogenetically conserved. However, local ecological processes such as exploitative or apparent competition (indirect interactions) might instead cause a decrease in overlap in interacting partners. Because of the taxonomic and geographic coarseness of existing studies, the structuring effect of such processes has been overlooked. Here, we assess the relative importance of phylogeny and ecological processes in a local, highly resolved, four-level antagonistic network. Across all network levels we consistently find that phylogenetic relatedness among resource species is correlated with consumer overlap but that phylogenetic relatedness among consumer species is not or negatively correlated with resource overlap. This pervasive pattern indicates that the antagonistic network has been shaped by both phylogeny on resource range and by exploitative competition limiting resource overlap among closely related consumer species. Intriguingly, the strength of phylogenetic signal varies in a consistent way across the network levels. We discuss the generality of our findings and their implications in a changing world.

Sustaining ecosystem functions in a changing world: a call for an integrated approach

With ever-increasing human pressure on ecosystems, it is critically important to predict how ecosystem functions will respond to such human-induced perturbations. We define perturbations as either changes to abiotic environment (e.g. eutrophication, climate change) that indirectly affects biota, or direct changes to biota (e.g. species introductions). While two lines of research in ecology, biodiversity-ecosystem function (BDEF) and ecological resilience (ER) research, have addressed this issue, both fields of research have nontrivial shortcomings in their abilities to address a wide range of realistic scenarios. We outline how an integrated research framework may foster a deeper understanding of the functional consequences of perturbations via simultaneous application of (i) process-based mechanistic predictions using trait-based approaches and (ii) detection of empirical patterns of functional changes along real perturbation gradients. In this context, the complexities of ecological interactions and evolutionary perspectives should be integrated into future research. Synthesis and applications. Management of human-impacted ecosystems can be guided most directly by understanding the response of ecosystem functions to controllable perturbations. In particular, we need to characterize the form of a wide range of perturbation-function relationships and to draw connections between those patterns and the underlying ecological processes. We anticipate that the integrated perspectives will also be helpful for managers to derive practical implications for management from academic literature. Management of human-impacted ecosystems can be guided most directly by understanding the response of ecosystem functions to controllable perturbations. In particular, we need to characterize the form of a wide range of perturbation-function relationships and to draw connections between those patterns and the underlying ecological processes. We anticipate that the integrated perspectives will also be helpful for managers to derive practical implications for management from academic literature.