Vincent Calcagno

High plant diversity is needed to maintain ecosystem services

Biodiversity is rapidly declining worldwide, and there is consensus that this can decrease ecosystem functioning and services. It remains unclear, though, whether few or many of the species in an ecosystem are needed to sustain the provisioning of ecosystem services. It has been hypothesized that most species would promote ecosystem services if many times, places, functions and environmental changes were considered; however, no previous study has considered all of these factors together. Here we show that 84% of the 147 grassland plant species studied in 17 biodiversity experiments promoted ecosystem functioning at least once. Different species promoted ecosystem functioning during different years, at different places, for different functions and under different environmental change scenarios. Furthermore, the species needed to provide one function during multiple years were not the same as those needed to provide multiple functions within one year. Our results indicate that even more species will be needed to maintain ecosystem functioning and services than previously suggested by studies that have either (1) considered only the number of species needed to promote one function under one set of environmental conditions, or (2) separately considered the importance of biodiversity for providing ecosystem functioning across multiple years, places, functions or environmental change scenarios. Therefore, although species may appear functionally redundant when one function is considered under one set of environmental conditions, many species are needed to maintain multiple functions at multiple times and places in a changing world.

Flows of Research Manuscripts Among Scientific Journals Reveal Hidden Submission Patterns

Fathoming Publication Strategies While many studies have tracked numbers of citations after publication, such studies cannot reveal how prepublication dynamics affects subsequent citation history. Calcagno et al. (p. 1065, published online 11 October) surveyed the submission history of more than 80,000 articles published in 16 fields of biology in 2006–2008 and constructed a social network based on manuscript flows among scientific journals. High-impact journals occupied central positions in the network. A majority of manuscripts were published in the first journal to which they were submitted. However, submission history affected the post-publication impact (citation count) of articles, with manuscripts requiring resubmission eventually receiving more citations. A large-scale study of biological manuscript submission history reveals how authors strategically submit their research. The study of science-making is a growing discipline that builds largely on online publication and citation databases, while prepublication processes remain hidden. Here, we report on results from a large-scale survey of the submission process, covering 923 scientific journals from the biological sciences in years 2006 to 2008. Manuscript flows among journals revealed a modular submission network, with high-impact journals preferentially attracting submissions. However, about 75% of published articles were submitted first to the journal that would publish them, and high-impact journals published proportionally more articles that had been resubmitted from another journal. Submission history affected post-publication impact: Resubmissions from other journals received significantly more citations than first-intent submissions, and resubmissions between different journal communities received significantly fewer citations.

Sympatric host races of the European corn borer: adaptation to host plants and hybrid performance

The European corn borer (ECB), Ostrinia nubilalis, is a major pest of maize crops. In Europe, two sympatric host races are found: one feeds on maize (Zea mays) and the other mainly on mugwort (Artemisia vulgaris). The two host races are genetically differentiated, seldom crossing in the laboratory or in the field, and females preferentially lay eggs on their native host species. We conducted two independent experiments, in field and greenhouse conditions, to determine whether the two host races are locally adapted to their host species. The effect of larval density and the performance of hybrids were also investigated. Despite some differences in overall larval feeding performance, both experiments revealed consistent patterns of local adaptation for survival and for larval weight in males. In females the same trend was observed but with weaker statistical support. F1 hybrids did not seem to be disadvantaged compared with the two parental races. Overall, our results showed that both host races are physiologically adapted to their native host. The fitness trade‐off between the two host plants provides a potential driving force for ecological speciation in this species.

Competition–colonization dynamics in experimental bacterial metacommunities

One of the simplest hypotheses used to explain species coexistence is the competition-colonization trade-off, that is, species can stably coexist in a landscape if they show a trade-off between competitive and colonization abilities. Despite extensive theory, the dynamics predicted to result from competition-colonization trade-offs are largely untested. Landscape change, such as habitat destruction, is thought to greatly influence coexistence under competition-colonization dynamics, although there is no formal test of this prediction. Here we present the first illustration of competition-colonization dynamics that fully transposes theory into a controlled experimental metacommunity of two Pseudomonas bacterial strains. The competition-colonization dynamics were achieved by directly manipulating trade-off strength and colonization rates to generate the full range of coexistence conditions and responses to habitat destruction. Our study successfully generates competition-colonization dynamics matching theoretical predictions, and our results further reveal a negative relationship between diversity and productivity when scaling up to entire metacommunities.

Constraints on food chain length arising from regional metacommunity dynamics

Classical ecological theory has proposed several determinants of food chain length, but the role of metacommunity dynamics has not yet been fully considered. By modelling patchy predator–prey metacommunities with extinction–colonization dynamics, we identify two distinct constraints on food chain length. First, finite colonization rates limit predator occupancy to a subset of prey-occupied sites. Second, intrinsic extinction rates accumulate along trophic chains. We show how both processes concur to decrease maximal and average food chain length in metacommunities. This decrease is mitigated if predators track their prey during colonization (habitat selection) and can be reinforced by top-down control of prey vital rates (especially extinction). Moreover, top-down control of colonization and habitat selection can interact to produce a counterintuitive positive relationship between perturbation rate and food chain length. Our results show how novel limits to food chain length emerge in spatially structured communities. We discuss the connections between these constraints and the ones commonly discussed, and suggest ways to test for metacommunity effects in food webs.

Rapid Exploiter-Victim Coevolution: The Race Is Not Always to the Swift

The modeling of coevolutionary races has traditionally been dominated by methods invoking a timescale separation between ecological and evolutionary dynamics, the latter assumed to be much slower than the former. Yet it is becoming increasingly clear that in many cases the two processes occur on similar timescales and that such “rapid” evolution can have profound implications for the dynamics of communities and ecosystems. After briefly reviewing the timescale separations most common in coevolution theory, we use a general model of exploiter‐victim coevolution to confront predictions from slow‐evolution analysis with Monte Carlo simulations. We show how rapid evolution radically alters the dynamics and outcome of coevolutionary arms races. In particular, a fast‐evolving exploiter can enable victim diversification and thereby lose a race it is expected to win. We explain simulation results, using mathematical analysis with relaxed timescale separations. Unusual mutation parameters are not required, since rapid evolution naturally emerges from slow competitive exclusion. Our results point to interesting consequences of exploiter rapid evolution and experimentally testable patterns, while indicating that more attention should be paid to rapid evolution in evolutionary theory.

Divergence in behaviour between the European corn borer, Ostrinia nubilalis, and its sibling species Ostrinia scapulalis: adaptation to human harvesting?

Divergent adaptation to host plant species may be the major mechanism driving speciation and adaptive radiations in phytophagous insects. Host plants can differ intrinsically in a number of attributes, but the role of natural enemies in host plant specialization is often underappreciated. Here, we report behavioural divergence between the European corn borer (ECB, Ostrinia nubilalis) and its sibling species Ostrinia scapulalis, in relation to a major enemy: humans. Harvesting maize imposes selective mortality on Ostrinia larvae: those located above the cut-off line of the stalk face almost certain death. We show that ECB larvae diapause closer to the ground than those of O. scapulalis, which is sympatric but feeds mainly on weeds. The difference in diapause height results from genetically determined differences in geotactic behaviour. ECB larvae descend towards the ground specifically at harvest time, increasing their chances of surviving harvesting by about 50 per cent over O. scapulalis larvae. Natural enemies appear as a major driver of host-plant specialization in this example, stressing the need to consider ‘tri-trophic’ ecological niches to understand insect diversification. Our results also strongly suggest that geotaxis evolved as a singular instance of behavioural resistance in a major agricultural pest.

Keystone Predation and Plant Species Coexistence: The Role of Carnivore Hunting Mode

Plant communities are shaped by bottom‐up processes such as competition for nutrients and top‐down processes such as herbivory. Although much theoretical work has studied how herbivores can mediate plant species coexistence, indirect effects caused by the carnivores that consume herbivores have been largely ignored. These carnivores can have significant indirect effects on plants by altering herbivore density (density‐mediated effects) and behavior (trait‐mediated effects). Carnivores that differ in traits, particularly in their hunting mode, cause different indirect effects on plants and, ultimately, different plant community compositions. We analyze a food‐web model to determine how plant coexistence is affected by herbivore‐consuming carnivores, contrasting those causing only density‐mediated effects with those causing trait‐mediated effects as well. In the latter case, herbivores can adjust their consumption of a refuge plant species. We derive a general graphical model to study the interplay of density‐ and trait‐mediated effects. We show that carnivores eliciting both effects can sustain plant species coexistence, given intermediate intensities of behavioral adjustments. Coexistence is more likely, and more stable, if the refuge plant is competitively dominant. These results extend our understanding of carnivore indirect effects in food webs and show that behavioral effects can have major consequences on plant community structure, stressing the need for theoretical approaches that incorporate dynamical traits.

Diversity spurs diversification in ecological communities

Diversity is a fundamental, yet threatened, property of ecological systems. The idea that diversity can itself favour diversification, in an autocatalytic process, is very appealing but remains controversial. Here, we study a generalized model of ecological communities and investigate how the level of initial diversity influences the possibility of evolutionary diversification. We show that even simple models of intra- and inter-specific ecological interactions can predict a positive effect of diversity on diversification: adaptive radiations may require a threshold number of species before kicking-off. We call this phenomenon DDAR (diversity-dependent adaptive radiations) and identify mathematically two distinct pathways connecting diversity to diversification, involving character displacement and the positive diversity-productivity relationship. Our results may explain observed delays in adaptive radiations at the macroscale and diversification patterns reported in experimental microbial communities, and shed new light on the dynamics of ecological diversity, the diversity-dependence of diversification rates, and the consequences of biodiversity loss.