Competitor-induced plasticity modifies the interactions and predicted competitive outcomes between annual plants

The competitive effect of one individual on another can have impacts beyond just reductions in performance. Because species plastically respond to their environment, competition can also induce changes in species traits, and in turn, these modified traits can then affect interactions with yet other individuals. In this context, plasticity is often argued to favor species coexistence by increasing the niche differentiation between species, though experimental evidence for this hypothesis that explicitly projects competitive outcomes is largely lacking. Here, we transiently subjected four annual plant species to early-season intraspecific or interspecific competition to explicitly induce plastic responses and then examined the response of these individuals to competitors faced later in life. Competing with nearby individuals early in the growing season tended to amplify the sensitivity of individuals to competition, and particularly so for interspecific competition, but the strength of this effect depended on the identity of the focal species. This increase in interspecific relative to intraspecific competition caused plasticity to decrease the predicted likelihood of pairwise coexistence. By combining recent theory with a new experimental approach, we provide a pathway toward integrating phenotypic plasticity into our quantitative understanding of coexistence.

Balancing limited resources in actin network competition

In cells, multiple actin networks coexist in a dynamic manner. These networks compete for a common pool of actin monomers and actin-binding proteins. Interestingly, all of these networks manage to coexist despite the strong competition for resources. Moreover, the coexistence of networks with various strengths is key to cell adaptation to external changes. However, a comprehensive view of how these networks coexist in this competitive environment, where resources are limited, is still lacking. To address this question, we used a reconstituted system, in closed microwells, consisting of beads propelled by actin polymerization or micropatterns functionalized with lipids capable of initiating polymerization close to a membrane. This system enabled us to build dynamic actin architectures, competing for a limited pool of proteins, over a period of hours. We demonstrated the importance of protein turnover for the coexistence of actin networks, showing that it ensures resource distribution between weak and strong networks. However, when competition becomes too intense, turnover alone is insufficient, leading to a selection process that favors the strongest networks. Consequently, we emphasize the importance of competition strength, which is defined by the turnover rate, the amount of available protein, and the number of competing structures. More generally, this work illustrates how turnover allows biological populations with various competition strengths to coexist despite resource constraints.

Transcriptomics integrated with metabolomics reveal the competitive relationship between co-cultured Trichoderma asperellum HG1 and Bacillus subtilis Tpb55

Microbial co-culture has proven to be an effective way to improve the ability of microorganisms to biocontrol. However, the interactive mechanisms of co-cultural microbes, especially between fungi and bacteria, have rarely been studied. By comparative analysis of morphology, transcriptomics and metabolomics, the interactive mechanisms of a sequential co-culture system of Trichoderma asperellum HG1 and Bacillus subtilis Tpb55 was explored in this study. The results revealed that co- culture has no significant effect on the growth and cell morphology of the two strains, but lead to mycelium wrinkling of HG1. RNA-seq analysis showed that co-culture significantly upregulated the HG1 genes concerning amino acid degradation and metabolism, proteolysis, resisting environmental stress, cell homeostasis, glycolysis, the glyoxylate cycle, and the citric acid (TCA) cycle, while Tpb55 genes related to cell homeostasis, spore formation and membrane fluidization were significantly upregulated, but genes associating to TCA, glycolytic cycles and fatty acid β-oxidation were significantly downregulated. Metabolomic results revealed that some amino acids related to energy metabolism were significantly altered in HG1, whereas palmitic acid, which is related to cell membrane functions, was upregulated in Tpb55. These results indicated that HG1 could interfere with carbon metabolism and cell membrane fluidity, but accelerate spore formation of Tpb55. Biophysical assays further convinced that co-culture could decrease ATP content and inhibit ATPase activity in HG1, and could promote spore formation and reduce the cell membrane fluidity of Tpb55. In addition, co-culture also accelerated the production of intracellular anti-oomycete compound octhilinone. The above results indicate that HG1 and Tpb55 are mainly in a competitive relationship in the co culture system. These findings provide new insights for understanding the interaction mechanism between co cultured microbes.

Stepwise degradation of organic matters driven by microbial interactions in China΄s coastal wetlands: Evidence from carbon isotope analysis

The microbial "unseen majority" as drivers of carbon cycle represent a significant source of uncertain climate change. To comprehend the resilience of life forms on Earth to climate change, it is crucial to incorporate knowledge of intricate microbial interactions and their impact to carbon transformation. Combined with carbon stable isotope analysis and high-throughput sequencing technology, the underlying mechanism of microbial interactions for organic carbon degradation has been elucidated. Niche differentiation enabled archaea to coexist with bacteria mainly in a cooperative manner. Bacteria composed of specialists preferred to degrade lighter carbon, while archaea were capable of utilizing heavier carbon. Microbial resource-dependent interactions drove stepwise degradation of organic matter. Bacterial cooperation directly facilitated the degradation of algae-dominated particulate organic carbon, while competitive feeding of archaea caused by resource scarcity significantly promoted the mineralization of heavier particulate organic carbon and then the release of dissolved inorganic carbon. Meanwhile, archaea functioned as a primary decomposer and collaborated with bacteria in the gradual degradation of dissolved organic carbon. This study emphasized microbial interactions driving carbon cycle and provided new perspectives for incorporating microorganisms into carbon biogeochemical models.

Analyzing tiger interaction and home range shifts using a time-geographic approach

BACKGROUND

Interaction through movement can be used as a marker to understand and model interspecific and intraspecific species dynamics, and the collective behavior of animals sharing the same space. This research leverages the time-geography framework, commonly used in human movement research, to explore the dynamic patterns of interaction between Indochinese tigers (Panthera tigris corbeti) in the western forest complex (WEFCOM) in Thailand.

METHODS

We propose and assess ORTEGA, a time-geographic interaction analysis method, to trace spatio-temporal interactions patterns and home range shifts among tigers. Using unique GPS tracking data of tigers in WEFCOM collected over multiple years, concurrent and delayed interaction patterns of tigers are investigated. The outcomes are compared for intraspecific tiger interaction across different genders, relationships, and life stages. Additionally, the performance of ORTEGA is compared to a commonly used proximity-based approach.

RESULTS

Among the 67 tracked tigers, 42 show concurrent interactions at shared boundaries. Further investigation of five tigers with overlapping home ranges (two adult females, a male, and two young male tigers) suggests that the mother tiger and her two young mostly stay together before their dispersal but interact less post-dispersal. The male tiger increases encounters with the mother tiger while her young shift their home ranges. On another timeline, the neighbor female tiger mostly avoids the mother tiger. Through these home range dynamics and interaction patterns, we identify four types of interaction among these tigers: following, encounter, latency, and avoidance. Compared to the proximity-based approach, ORTEGA demonstrates better detects concurrent mother-young interactions during pre-dispersal, while the proximity-based approach misses many interactions among the dyads. With larger spatial buffers and temporal windows, the proximity-based approach detects more encounters but may overestimate the duration of interaction.

CONCLUSIONS

This research demonstrates the applicability and merits of ORTEGA as a time-geographic based approach to animal movement interaction analysis. We show time geography can develop valuable, data-driven insights about animal behavior and interactions. ORTEGA effectively traces frequent encounters and temporally delayed interactions between animals, without relying on specific spatial and temporal buffers. Future research should integrate contextual and behavioral information to better identify and characterize the nature of species interaction.

Evolution of cooperation in a two-species system with a common resource pool

Understanding the evolution of cooperation is a major question in Evolutionary Biology. Here, we extend a previously proposed mathematical model in Evolutionary Game Theory that investigated how resource use by a single species composed of cooperators and defectors may lead to its maintenance or extinction. We include another species in the model, so as to investigate how different intra and interspecific interactions of cooperative or competitive nature among individuals that share the same essential resource may drive the survival and evolution of the species. Several outcomes emerge from the model, depending on the configuration of the payoff matrix, the individual contribution to the resource pool, the competition intensity between species, and the initial conditions of the system dynamics. Observed results include scenarios in which species thrive due to the action of cooperators, but also scenarios in which both species collapse due to lack of cooperation and, consequently, of resources. In particular, a high initial availability of resources may be the determinant factor to the survival of both species. Interestingly, cooperation may be more favored when individuals have less incentive to cooperate with others, and the survival of their populations may depend crucially on their competitive capacities.

Complex patch geometry promotes species coexistence through a reverse competition-colonization trade-off

Explaining the maintenance of diverse species assemblages is a central goal of ecology and conservation. Recent coexistence mechanisms highlight the role of dispersal as a source of the differences that allow similar species to coexist. Here, we propose a new mechanism for species coexistence that is based on dispersal differences, and on the geometry of the habitat patch. In a finite habitat patch with complex boundaries, species with different dispersal abilities will arrange themselves in stable, concentric patterns of dominance. Species with superior competitive and dispersal abilities will dominate the interior of the patch, with inferior species at the periphery. We demonstrate and explain the mechanism on a simple one-dimensional domain, and then on two-dimensional habitat patches with realistic geometries. Finally, we use metrics from landscape ecology to demonstrate that habitat patches with more complex geometries can more easily support coexistence. The factors that underpin this new coexistence mechanism-different dispersal abilities and habitat patches with complex geometries-are common to many marine and terrestrial ecosystems, and it is therefore possible that the mechanism is a common factor supporting diverse species assemblages.

Eco-evolutionary maintenance of diversity in fluctuating environments

Growing evidence suggests that temporally fluctuating environments are important in maintaining variation both within and between species. To date, however, studies of genetic variation within a population have been largely conducted by evolutionary biologists (particularly population geneticists), while population and community ecologists have concentrated more on diversity at the species level. Despite considerable conceptual overlap, the commonalities and differences of these two alternative paradigms have yet to come under close scrutiny. Here, we review theoretical and empirical studies in population genetics and community ecology focusing on the 'temporal storage effect' and synthesise theories of diversity maintenance across different levels of biological organisation. Drawing on Chesson's coexistence theory, we explain how temporally fluctuating environments promote the maintenance of genetic variation and species diversity. We propose a further synthesis of the two disciplines by comparing models employing traditional frequency-dependent dynamics and those adopting density-dependent dynamics. We then address how temporal fluctuations promote genetic and species diversity simultaneously via rapid evolution and eco-evolutionary dynamics. Comparing and synthesising ecological and evolutionary approaches will accelerate our understanding of diversity maintenance in nature.

Integrating eco-evolutionary dynamics and modern coexistence theory

Community ecology typically assumes that competitive exclusion and species coexistence are unaffected by evolution on the time scale of ecological dynamics. However, recent studies suggest that rapid evolution operating concurrently with competition may enable species coexistence. Such findings necessitate general theory that incorporates the coexistence contributions of eco-evolutionary processes in parallel with purely ecological mechanisms and provides metrics for quantifying the role of evolution in shaping competitive outcomes in both modelling and empirical contexts. To foster the development of such theory, here we extend the interpretation of the two principal metrics of modern coexistence theory-niche and competitive ability differences-to systems where competitors evolve. We define eco-evolutionary versions of these metrics by considering how invading and resident species adapt to conspecific and heterospecific competitors. We show that the eco-evolutionary niche and competitive ability differences are sums of ecological and evolutionary processes, and that they accurately predict the potential for stable coexistence in previous theoretical studies of eco-evolutionary dynamics. Finally, we show how this theory frames recent empirical assessments of rapid evolution effects on species coexistence, and how empirical work and theory on species coexistence and eco-evolutionary dynamics can be further integrated.

Species interactions constrain adaptation and preserve ecological stability in an experimental microbial community

Species loss within a microbial community can increase resource availability and spur adaptive evolution. Environmental shifts that cause species loss or fluctuations in community composition are expected to become more common, so it is important to understand the evolutionary forces that shape the stability and function of the emergent community. Here we study experimental cultures of a simple, ecologically stable community of Saccharomyces cerevisiae and Lactobacillus plantarum, in order to understand how the presence or absence of a species impacts coexistence over evolutionary timescales. We found that evolution in coculture led to drastically altered evolutionary outcomes for L. plantarum, but not S. cerevisiae. Both monoculture- and co-culture-evolved L. plantarum evolved dozens of mutations over 925 generations of evolution, but only L. plantarum that had evolved in isolation from S. cerevisiae lost the capacity to coexist with S. cerevisiae. We find that the evolutionary loss of ecological stability corresponds with fitness differences between monoculture-evolved L. plantarum and S. cerevisiae and genetic changes that repeatedly evolve across the replicate populations of L. plantarum. This work shows how coevolution within a community can prevent destabilising evolution in individual species, thereby preserving ecological diversity and stability, despite rapid adaptation.

Effects of species interactions on the potential for evolution at species' range limits

Species' ranges are limited by both ecological and evolutionary constraints. While there is a growing appreciation that ecological constraints include interactions among species, like competition, we know relatively little about how interactions contribute to evolutionary constraints at species' niche and range limits. Building on concepts from community ecology and evolutionary biology, we review how biotic interactions can influence adaptation at range limits by impeding the demographic conditions that facilitate evolution (which we term a 'demographic pathway to adaptation'), and/or by imposing evolutionary trade-offs with the abiotic environment (a 'trade-offs pathway'). While theory for the former is well-developed, theory for the trade-offs pathway is not, and empirical evidence is scarce for both. Therefore, we develop a model to illustrate how fitness trade-offs along biotic and abiotic gradients could affect the potential for range expansion and niche evolution following ecological release. The model shows that which genotypes are favoured at species' range edges can depend strongly on the biotic context and the nature of fitness trade-offs. Experiments that characterize trade-offs and properly account for biotic context are needed to predict which species will expand their niche or range in response to environmental change. This article is part of the theme issue 'Species' ranges in the face of changing environments (Part II)'.

Fine-scale genetic diversity and putative ecotypes of oxymonad protists coinhabiting the hindgut of Reticulitermes speratus

The hindgut of lower termites is generally coinhabited by multiple morphologically identifiable protist species. However, it is unclear how many protist species truly coexist in this miniaturized environment, and moreover, it is difficult to define the fundamental unit of protist diversity. Species delineation of termite gut protists has therefore been guided without a theory-based concept of species. Here, we focused on the hindgut of the termite Reticulitermes speratus, where 10 or 11 morphologically distinct oxymonad cell types, that is, morphospecies, coexist. We elucidated the phylogenetic structure of all co-occurring oxymonads and addressed whether their diversity can be explained by the "ecotype" hypothesis. Oxymonad-specific 18S rRNA gene amplicon sequencing analyses of whole-gut samples, combined with single-cell 18S rRNA sequencing of the oxymonad morphospecies, identified 210 one-nucleotide-level variants. The phylogenetic analysis of these variants revealed the presence of microdiverse clusters typically within 1% sequence divergence. Each known oxymonad morphospecies comprised one to several monophyletic or paraphyletic microdiverse clusters. Using these sequence data sets, we conducted computational simulation to predict the rates of ecotype formation and periodic selection, and to demarcate putative ecotypes. Our simulations suggested that the oxymonad genetic divergence is constrained primarily by strong selection, in spite of limited population size and possible bottlenecks during intergenerational transmission. A total of 33 oxymonad ecotypes were predicted, and most of the putative ecotypes were consistently detected among different colonies and host individuals. These findings provide a possible theoretical basis for species diversity and underlying mechanisms of coexistence of termite gut protists.

Competition dynamics in long-term propagations of Schizosaccharomyces pombe strain communities

Experimental evolution studies with microorganisms such as bacteria and yeast have been an increasingly important and powerful tool to draw long-term inferences of how microbes interact. However, while several strains of the same species often exist in natural environments, many ecology and evolution studies in microbes are typically performed with isogenic populations of bacteria or yeast. In the present study, we firstly perform a genotypic and phenotypic characterization of two laboratory and eight natural strains of the yeast Schizosaccharomyces pombe. We then propagated, in a rich resource environment, yeast communities of 2, 3, 4, and 5 strains for hundreds of generations and asked which fitness-related phenotypes-maximum growth rate or relative competitive fitness-would better predict the outcome of a focal strain during the propagations. While the strain's growth rates would wrongly predict long-term coexistence, pairwise competitive fitness with a focal strain qualitatively predicted the success or extinction of the focal strain by a simple multigenotype population genetics model, given the initial community composition. Interestingly, we have also measured the competitive fitness of the ancestral and evolved communities by the end of the experiment (≈370 generations) and observed frequent maladaptation to the abiotic environment in communities with more than three members. Overall, our results aid establishing pairwise competitive fitness as good qualitative measurement of long-term community composition but also reveal a complex adaptive scenario when trying to predict the evolutionary outcome of those communities.

The Ecological Importance of Allelopathy

Allelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests that studies of allelopathy have been particularly important for three foci in ecology: species distribution, conditionality of interactions, and maintenance of species diversity. There is evidence that allelopathy influences local distributions of plant species around the world. Allelopathic conditionality appears to arise through coevolution, and this is a mechanism for plant invasions. Finally, allelopathy promotes species coexistence via intransitive competition, modifications of direct interactions, and (co)evolution. Recent advances additionally suggest that coexistence might be favored through biochemical recognition. The preponderance of phenomenological studies notwithstanding, allelopathy has broad ecological consequences.

Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 52 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Evolutionary Dynamics of Treatment-Induced Resistance in Cancer Informs Understanding of Rapid Evolution in Natural Systems

Rapid evolution is ubiquitous in nature. We briefly review some of this quite broadly, particularly in the context of response to anthropogenic disturbances. Nowhere is this more evident, replicated and accessible to study than in cancer. Curiously cancer has been late - relative to fisheries, antibiotic resistance, pest management and evolution in human dominated landscapes - in recognizing the need for evolutionarily informed management strategies. The speed of evolution matters. Here, we employ game-theoretic modeling to compare time to progression with continuous maximum tolerable dose to that of adaptive therapy where treatment is discontinued when the population of cancer cells gets below half of its initial size and re-administered when the cancer cells recover, forming cycles with and without treatment. We show that the success of adaptive therapy relative to continuous maximum tolerable dose therapy is much higher if the population of cancer cells is defined by two cell types (sensitive vs. resistant in a polymorphic population). Additionally, the relative increase in time to progression increases with the speed of evolution. These results hold with and without a cost of resistance in cancer cells. On the other hand, treatment-induced resistance can be modeled as a quantitative trait in a monomorphic population of cancer cells. In that case, when evolution is rapid, there is no advantage to adaptive therapy. Initial responses to therapy are blunted by the cancer cells evolving too quickly. Our study emphasizes how cancer provides a unique system for studying rapid evolutionary changes within tumor ecosystems in response to human interventions; and allows us to contrast and compare this system to other human managed or dominated systems in nature.

Structure and Long-Term Stability of the Microbiome in Diverse Diatom Cultures

Microalgal cultures are often maintained in xenic conditions, i.e., with associated bacteria, and many studies indicate that these communities both are complex and have significant impacts on the physiology of the target photoautotroph. Here, we investigated the structure and stability of microbiomes associated with a diverse sampling of diatoms during long-term maintenance in serial batch culture. We found that, counter to our initial expectation, evenness diversity increased with time since cultivation, driven by a decrease in dominance by the most abundant taxa in each culture. We also found that the site from which and time at which a culture was initially collected had a stronger impact on microbiome structure than the diatom species; however, some bacterial taxa were commonly present in most cultures despite having widely geographically separated collection sites. Our results support the conclusion that stochastic initial conditions (i.e., the local microbial community at the collection site) are important for the long-term structure of these microbiomes, but deterministic forces such as negative frequency dependence and natural selection exerted by the diatom are also at work.

IMPORTANCE Natural microbial communities are extremely complex, with many more species coexisting in the same place than there are different resources to support them. Understanding the forces that allow this high level of diversity has been a central focus of ecological and evolutionary theory for many decades. Here, we used stock cultures of diatoms, which were maintained for years in continuous growth alongside populations of bacteria, as proxies for natural communities. We show that the bacterial communities remained relatively stable for years, and there is evidence that ecological forces worked to stabilize coexistence instead of favoring competition and exclusion. We also show evidence that, despite some important regional differences in bacterial communities, there was a globally present core microbiome potentially selected for in these diatom cultures. Understanding interactions between bacteria and diatoms is important both for basic ecological science and for practical science, such as industrial biofuel production.

Competitive ability of native and alien plants: effects of residence time and invasion status

Competition is commonly thought to underlie the impact of plant invasions. However, competitive effects of aliens and competitive response of natives may also change over time. Indeed, as with time, the novelty of an invader decreases, the accumulated eco-evolutionary experience of resident species may eventually limit invasion success. We aimed to gain insights on whether directional changes in biotic interactions over time or more general differences between natives and aliens, for instance, resulting from an introduction bias, are relevant in determining competitive ability. We conducted a pairwise competition experiment in a target-neighbour design, using 47 Asteraceae species with residence times between 8 years-12,000 years in Germany. We first tested whether there are differences in performance in intraspecific competition amongst invasion status groups, that is casual and established neophytes, archaeophytes or native species. We then evaluated whether competitive response and effects depend on residence time or invasion status. Lastly, we assessed whether competitive effects influence range sizes. We found only limited evidence that native target species tolerate neighbours with longer potential co-existence times better, whereas differences in competitive ability were mostly better explained by invasion status than residence time. Although casual neophytes produced most biomass in intraspecific competition, they had the weakest per-capita competitive effects on natives. Notably, we did not find differences between established neophytes and natives, both of which ranked highest in interspecific competitive ability. This lack of differences might be explained by a biased selection of highly invasive or rare native species in previous studies or because invasion success may result from mechanisms other than interspecific competitive superiority. Accordingly, interspecific per-capita competitive effects did not influence range sizes. Further studies across a broader range of environmental conditions, involving other biotic interactions that indirectly influence plant-plant interactions, may clarify when eco-evolutionary adaptations to new invaders are a relevant mechanism.

Asymmetric Evolvability Leads to Specialization without Trade-Offs

AbstractMany organisms are specialized, and these narrow niches are often explained with trade-offs-the inability for one organism to express maximal performance in two or more environments. However, evidence is lacking that trade-offs are sufficient to explain specialists. Several lines of theoretical inquiry suggest that populations can specialize without explicit trade-offs, as a result of relaxed selection in generalists for their performance in rare environments. Here, I synthesize and extend these approaches, showing that emergent asymmetries in evolvability can push a population toward specialization in the absence of trade-offs and in the presence of substantial ecological costs of specialism. Simulations are used to demonstrate how adaptation to a more common environment interferes with adaptation to a less common but otherwise equal alternative environment and that this interference is greatly exacerbated at low recombination rates. This adaptive process of specialization can effectively trap populations in a suboptimal niche. These modeling results predict that transient differences in evolvability across traits during a single episode of adaptation could have long-term consequences for a population's niche.

When Ecology Fails: How Reproductive Interactions Promote Species Coexistence

That species must differ ecologically is often viewed as a fundamental condition for their stable coexistence in biological communities. Yet, recent work has shown that ecologically equivalent species can coexist when reproductive interactions and sexual selection regulate population growth. Here, we review theoretical models and highlight empirical studies supporting a role for reproductive interactions in maintaining species diversity. We place reproductive interactions research within a burgeoning conceptual framework of coexistence theory, identify four key mechanisms in intra- and interspecific interactions within and between sexes, speculate on novel mechanisms, and suggest future research. Given the preponderance of sexual reproduction in nature, our review suggests that this is a neglected path towards explaining species diversity when traditional ecological explanations have failed.

The evolution of niche overlap and competitive differences

Competition can result in evolutionary changes to coexistence between competitors but there are no theoretical models that predict how the components of coexistence change during this eco-evolutionary process. Here we study the evolution of the coexistence components, niche overlap and competitive differences, in a two-species eco-evolutionary model based on consumer-resource interactions and quantitative genetic inheritance. Species evolve along a one-dimensional trait axis that allows for changes in both niche position and species intrinsic growth rates. There are three main results. First, the breadth of the environment has a strong effect on the dynamics, with broader environments leading to reduced niche overlap and enhanced coexistence. Second, coexistence often involves a reduction in niche overlap while competitive differences stay relatively constant or vice versa; in general changes in competitive differences maintain coexistence only when niche overlap remains constant. Large simultaneous changes in niche overlap and competitive difference often result in one of the species being excluded. Third, provided that the species evolve to a state where they coexist, the final niche overlap and competitive difference values are independent of the system's initial state, although they do depend on the model's parameters. The model suggests that evolution is often a destructive force for coexistence due to evolutionary changes in competitive differences, a finding that expands the paradox of diversity maintenance.

Rapid evolution promotes fluctuation-dependent species coexistence

Recent studies have demonstrated that rapid contemporary evolution can play a significant role in regulating population dynamics on ecological timescales. Here we identify a previously unrecognised mode by which rapid evolution can promote species coexistence via temporal fluctuations and a trade-off between competitive ability and the speed of adaptive evolution. We show that this interaction between rapid evolution and temporal fluctuations not only increases the range of coexistence conditions under a gleaner-opportunist trade-off (i.e. low minimum resource requirement [R^* ] vs. high maximum growth rate) but also yields stable coexistence in the absence of a classical gleaner-opportunist trade-off. Given the propensity for both oscillatory dynamics and different rates of adaptation between species (including rapid evolution and phenotypic plasticity) in the real world, we argue that this expansion of fluctuation-dependent coexistence theory provides an important overlooked solution to the so-called 'paradox of the plankton'.

Optimal control to reach eco-evolutionary stability in metastatic castrate-resistant prostate cancer

In the absence of curative therapies, treatment of metastatic castrate-resistant prostate cancer (mCRPC) using currently available drugs can be improved by integrating evolutionary principles that govern proliferation of resistant subpopulations into current treatment protocols. Here we develop what is coined as an 'evolutionary stable therapy', within the context of the mathematical model that has been used to inform the first adaptive therapy clinical trial of mCRPC. The objective of this therapy is to maintain a stable polymorphic tumor heterogeneity of sensitive and resistant cells to therapy in order to prolong treatment efficacy and progression free survival. Optimal control analysis shows that an increasing dose titration protocol, a very common clinical dosing process, can achieve tumor stabilization for a wide range of potential initial tumor compositions and volumes. Furthermore, larger tumor volumes may counter intuitively be more likely to be stabilized if sensitive cells dominate the tumor composition at time of initial treatment, suggesting a delay of initial treatment could prove beneficial. While it remains uncertain if metastatic disease in humans has the properties that allow it to be truly stabilized, the benefits of a dose titration protocol warrant additional pre-clinical and clinical investigations.

Eco-Evolutionary Feedbacks and the Maintenance of Metacommunity Diversity in a Changing Environment

The presence and strength of resource competition can influence how organisms adaptively respond to environmental change. Selection may thus reflect a balance between two forces, adaptation to an environmental optimum and evolution to avoid strong competition. While this phenomenon has previously been explored in the context of single communities, its implications for eco-evolutionary dynamics at the metacommunity scale are largely unknown. We developed a simulation model for the evolution of a quantitative trait that influences both an organism's carrying capacity and its intra- and interspecific competitive ability. In the model, multiple species inhabit a three-patch landscape, and we investigated the effect of varying the connectivity level among patches, the presence and pace of directional environmental change, and the strength of competition between the species. Our model produced some patterns previously observed in evolving metacommunity models, such as species sorting and community monopolization. However, we found that species sorting was diminished even at low rates of dispersal and was influenced by competition strength, and that monopolization was observed only when environmental change was very rapid. We also detected an eco-evolutionary feedback loop between local phenotypic evolution at one site and competition at another site, which maintains species diversity in some conditions. The existence of a feedback loop maintained by dispersal indicates that eco-evolutionary dynamics in communities operate at a landscape scale.

The evolution of coexistence from competition in experimental co-cultures of Escherichia coli and Saccharomyces cerevisiae

Microbial communities are comprised of many species that coexist on small spatial scales. This is difficult to explain because many interspecies interactions are competitive, and ecological theory predicts that one species will drive the extinction of another species that competes for the same resource. Conversely, evolutionary theory proposes that natural selection can lead to coexistence by driving competing species to use non-overlapping resources. However, evolutionary escape from extinction may be slow compared to the rate of competitive exclusion. Here, we use experimental co-cultures of Escherichia coli and Saccharomyces cerevisiae to study the evolution of coexistence in species that compete for resources. We find that while E. coli usually outcompetes S. cerevisiae in co-culture, a few populations evolved stable coexistence after ~1000 generations of coevolution. We sequenced S. cerevisiae and E. coli populations, identified multi-hit genes, and engineered alleles from these genes into several genetic backgrounds, finding that some mutations modified interactions between E. coli and S. cerevisiae. Together, our data demonstrate that coexistence can evolve, de novo, from intense competition between two species with no history of coevolution.

Rapid evolution destabilizes species interactions in a fluctuating environment

Positive species interactions underlie the functioning of ecosystems. Given their importance, it is crucial to understand the stability of positive interactions over evolutionary timescales, in both constant and fluctuating environments; e.g., environments interrupted with periods of competition. We addressed this question using a two-species microbial system in which we modulated interactions according to the nutrient provided. We evolved in parallel four experimental replicates of species growing in isolation or together in consortia for 200 generations in both a constant and fluctuating environment with daily changes between commensalism and competition. We sequenced full genomes of single clones isolated at different time points during the experiment. We found that the two species coexisted over 200 generations in the constant commensal environment. In contrast, in the fluctuating environment, coexistence broke down when one of the species went extinct in two out of four cases. We showed that extinction was highly deterministic: when we replayed the evolution experiment from an intermediate time point we repeatably reproduced species extinction. We further show that these dynamics were driven by adaptive mutations in a small set of genes. In conclusion, in a fluctuating environment, rapid evolution destabilizes the long-term stability of positive pairwise interactions.

Species coexist more easily if reinforcement is based on habitat preferences than on species recognition

Maladaptive hybridization selects for prezygotic isolation, a process known as reinforcement. Reinforcement reduces gene flow and contributes to the final stage of speciation. Ecologically, however, coexistence of the incipient species is difficult if they initially use identical resources. Habitat segregation offers an alternative to species discrimination as a way to reduce gene flow: production of unfit hybrids is reduced if mate encounters become rare due to differing habitat choice. Using a modelling approach, we show that hybridization avoidance alone can select for habitat specialization, even if neither of the species is intrinsically better at using a specific niche. While habitat segregation and species discrimination both reduce the risk of producing unfit hybrids, these two isolation mechanisms differ from each other with respect to their effects on resource competition. Our model shows that, as a consequence of such differences, reinforcement evolves much more easily if hybridization is avoided based on habitat segregation than if the mechanism involves species recognition (mate choice traits). We also examine the outcomes when both isolation mechanisms evolve jointly. The establishment of one isolation mechanism a priori weakens selection for the other. However, an asymmetry persists here too. The net effect of habitat segregation on species discrimination was typically facilitative, but not vice versa. This asymmetry arises because habitat segregation, by enhancing coexistence, secures time for the subsequent evolution of species discrimination in a mate choice context (still relevant if habitat use is not perfectly segregated). Species discrimination does not have such a stabilizing effect on coexistence. Our results emphasize the importance of habitat segregation in reinforcement and offer a way to interpret findings where closely related taxa show similar performance on different resources or in different habitats. Studies of ecological generalization and specialization should therefore take into account that niche differences can be initiated and/or maintained by hybridization avoidance.

Evolution of diversity explains the impact of pre-adaptation of a focal species on the structure of a natural microbial community

Rapid within-species evolution can alter community structure, yet the mechanisms underpinning this effect remain unknown. Populations that rapidly evolve large amounts of phenotypic diversity are likely to interact with more species and have the largest impact on community structure. However, the evolution of phenotypic diversity is, in turn, influenced by the presence of other species. Here, we investigate how microbial community structure changes as a consequence of rapidly evolved within-species diversity using Pseudomonas fluorescens as a focal species. Evolved P. fluorescens populations showed substantial phenotypic diversification in resource-use (and correlated genomic change) irrespective of whether they were pre-adapted in isolation or in a community context. Manipulating diversity revealed that more diverse P. fluorescens populations had the greatest impact on community structure, by suppressing some bacterial taxa, but facilitating others. These findings suggest that conditions that promote the evolution of high within-population diversity should result in a larger impact on community structure.

Intraspecific Adaptation Load: A Mechanism for Species Coexistence

Evolutionary ecological theory suggests that selection arising from interactions with conspecifics, such as sexual and kin selection, may result in evolution of intraspecific conflicts and evolutionary 'tragedy of the commons'. Here, we propose that such an evolution of conspecific conflicts may affect population dynamics in a way that enhances species coexistence. Empirical evidence and theoretical models suggest that more abundant species is more susceptible to invasion of 'selfish' individuals that increase their own reproductive success at the expense of population growth (intraspecific adaptation load). The density-dependent intraspecific adaptation load gives rise to a self-regulation mechanism at the population level, and stabilizes species coexistence at the community level by negative frequency-dependence.

Unveiling the roles of interspecific competition and local adaptation in phenotypic differentiation of parapatric frogs

Understanding how ecological processes affect phenotypic evolution has been and continues to be an important goal of ecology and evolutionary biology. Interspecific competition for resources can be a selective force driving phenotypic differentiation that reduces competition among sympatric species (character divergence), enabling closely-related species to coexist. However, although patterns of character divergence are well documented in both empirical and theoretical researches, how local adaptation to abiotic environment affects trait evolution in the face of interspecific competition is less known. Here, we investigate how patterns in morphological traits of 2 parapatric frog species, Feirana quadranus and F. taihangnica, vary among allopatric and sympatric regions using range-wide data derived from extensive field surveys. Feirana quadranus was overall larger than F. taihangnica in body size (i.e., snout–vent length [SVL]), and the difference between SVL of both species in sympatry was larger than that in allopatry. From allopatry to sympatry, the 2 species diverged in foot and hand traits, but converged in eye size and interorbital span, even when we controlled for the effects of geographic gradients. Sympatric divergence in SVL, hand and foot traits is likely acting as a case of evolutionary shift caused by interspecific competition. In contrast, sympatric convergence of eye-related traits may derive at least partly from adaptation to local environments. These results imply the relative roles of interspecific competition and local adaptation in shaping phenotypic diversification. Our findings illustrate how traits evolve in parapatric species pair due to sympatric divergent and convergent evolution. It thus provides insights into understanding underlying evolutionary processes of parapatric species, that is, competition and local adaptation.

Performance in a novel environment subject to ghost competition

Background

A central tenet of the evolutionary theory of communities is that competition impacts evolutionary processes such as local adaptation. Species in a community exert a selection pressure on other species and may drive them to extinction. We know, however, very little about the influence of unsuccessful or ghost species on the evolutionary dynamics within the community.

Methods

Here we report the long-term influence of a ghost competitor on the performance of a more successful species using experimental evolution. We transferred the spider mite Tetranychus urticae onto a novel host plant under initial presence or absence of a competing species, the congeneric mite T. ludeni.

Results

The competitor species, T. ludeni, unintentionally went extinct soon after the start of the experiment, but we nevertheless completed the experiment and found that the early competitive pressure of this ghost competitor positively affected the performance (i.e., fecundity) of the surviving species, T. urticae. This effect on T. urticae lasted for at least 25 generations.

Discussion

Our study suggests that early experienced selection pressures can exert a persistent evolutionary signal on species’ performance in novel environments.

The evolution of competitive ability for essential resources

Competition for limiting resources is among the most fundamental ecological interactions and has long been considered a key driver of species coexistence and biodiversity. Species' minimum resource requirements, their R*s, are key traits that link individual physiological demands to the outcome of competition. However, a major question remains unanswered-to what extent are species' competitive traits able to evolve in response to resource limitation? To address this knowledge gap, we performed an evolution experiment in which we exposed Chlamydomonas reinhardtii for approximately 285 generations to seven environments in chemostats that differed in resource supply ratios (including nitrogen, phosphorus and light limitation) and salt stress. We then grew the ancestors and descendants in a common garden and quantified their competitive abilities for essential resources. We investigated constraints on trait evolution by testing whether changes in resource requirements for different resources were correlated. Competitive abilities for phosphorus improved in all populations, while competitive abilities for nitrogen and light increased in some populations and decreased in others. In contrast to the common assumption that there are trade-offs between competitive abilities for different resources, we found that improvements in competitive ability for a resource came at no detectable cost. Instead, improvements in competitive ability for multiple resources were either positively correlated or not significantly correlated. Using resource competition theory, we then demonstrated that rapid adaptation in competitive traits altered the predicted outcomes of competition. These results highlight the need to incorporate contemporary evolutionary change into predictions of competitive community dynamics over environmental gradients. This article is part of the theme issue 'Conceptual challenges in microbial community ecology'.

Diversity and coexistence are influenced by time-dependent species interactions in a predator-prey system

Although numerous studies show that communities are jointly influenced by predation and competitive interactions, few have resolved how temporal variability in these interactions influences community assembly and stability. Here, we addressed this challenge in experimental microbial microcosms by employing empirical dynamic modelling tools to: (1) detect causal interactions between prey species in the absence and presence of a predator; (2) quantify the time-varying strength of these interactions and (3) explore stability in the resulting communities. Our findings show that predators boost the number of causal interactions among community members, and lead to reduced dynamic stability, but higher coexistence among prey species. These results correspond to time-varying changes in species interactions, including emergence of morphological characteristics that appeared to reduce predation, and indirectly facilitate growth of predator-susceptible species. Jointly, our findings suggest that careful consideration of both context and time may be necessary to predict and explain outcomes in multi-trophic systems.

Predator coexistence through emergent fitness equalization

The competitive exclusion principle is one of the oldest ideas in ecology and states that without additional self-limitation two predators cannot coexist on a single prey. The search for mechanisms allowing coexistence despite this has identified niche differentiation between predators as crucial: without this, coexistence requires the predators to have exactly the same R* values, which is considered impossible. However, this reasoning misses a critical point: predators' R* values are not static properties, but affected by defensive traits of their prey, which in turn can adapt in response to changes in predator densities. Here I show that this feedback between defense and predator dynamics enables stable predator coexistence without ecological niche differentiation. Instead, the mechanism driving coexistence is that prey adaptation causes defense to converge to the value where both predators have equal R* values ("fitness equalization"). This result is highly general, independent of specific model details, and applies to both rapid defense evolution and inducible defenses. It demonstrates the importance of considering long-standing ecological questions from an eco-evolutionary viewpoint, and showcases how the effects of adaptation can cascade through communities, driving diversity on higher trophic levels. These insights offer an important new perspective on coexistence theory.

Evolution in the Anthropocene: Informing Governance and Policy

The Anthropocene biosphere constitutes an unprecedented phase in the evolution of life on Earth with one species, humans, exerting extensive control. The increasing intensity of anthropogenic forces in the twenty-first century has widespread implications for attempts to govern both human-dominated ecosystems and the last remaining wild ecosystems. Here, we review how evolutionary biology can inform governance and policies in the Anthropocene, focusing on five governance challenges that span biodiversity, environmental management, food and other biomass production, and human health. The five challenges are: ( a) evolutionary feedbacks, ( b) maintaining resilience, ( c) alleviating constraints, ( d) coevolutionary disruption, and ( e) biotechnology. Strategies for governing these dynamics will themselves have to be coevolutionary, as eco-evolutionary and social dynamics change in response to each other.

Can Isogroup Selection of Highly Zoophagous Lines of a Zoophytophagous Bug Improve Biocontrol of Spider Mites in Apple Orchards?

Zoophytophagous predators provide benefits in agroecosystems when feeding on pests, but they can also cause crop damage. Optimizing the use of zoophytophagous predators as biocontrol agents would require improving pest control and/or limiting damage. Populations of a zoophytophagous species can be composed of a mix of individuals diverging in their level of diet specialization. Consequently, depending on their level of zoophagy, individuals would vary widely in the benefits and risks they provide to pest management. We tested the hypothesis that manipulating the composition of the population of a zoophytophagous insect, the mullein bug, Campylomma verbasci (Hemiptera: Miridae), towards an increased zoophagy would increase their net benefit in an apple orchard. We compared the inherent benefits and risks of two different isogroup lines of mullein bug that genetically differed in their level of zoophagy. In spring, when damage occurs, both strains infrequently punctured apple fruit, which rarely lead to damage and therefore represented a low risk. During summer, only the highly-zoophagous line impacted the spider mite population, while the lowly-zoophagous line did not differ from the control treatments. We concluded that manipulating the composition of the zoophytophagous predator population provided extra net benefits that improved pest control.

Aspects of Invasiveness of Ludwigia and Nelumbo in Shallow Temperate Fluvial Lakes

The relationship between invasive plant functional traits and their invasiveness is still the subject of scientific investigation, and the backgrounds of transition from non-native to invasive species in ecosystems are therefore poorly understood. Furthermore, our current knowledge on species invasiveness is heavily biased toward terrestrial species; we know much less about the influence of allochthonous plant traits on their invasiveness in aquatic ecosystems. In this paper, we present the results of a study on physiological and ecological traits of two introduced and three native macrophyte species in the Mantua lakes system (northern Italy). We compared their photophysiology, pigment content, leaf reflectance, and phenology in order to assess how the invasive Nelumbo nucifera and Ludwigia hexapetala perform compared to native species, Nuphar lutea, Nymphaea alba, and Trapa natans. We found L. hexapetala to have higher photosynthetic efficiency and to tolerate higher light intensities than N. nucifera and the native species especially at extreme weather conditions (prolonged exposure to high light and higher temperatures). Chlorophyll a and b, and carotenoids content of both allochthonous species were substantially higher than those of native plants, suggesting adaptive response to the ecosystem of Mantua lakes system. Higher variability of recorded data in invasive species was also observed. These observations suggest advanced photosynthetic efficiency of the invasive species, especially L. hexapetala, resulting in faster growth rates and higher productivity. This was supported by the evaluation of seasonal dynamics mapped from satellite remote sensing data. This study provides empirical evidence for the relationship between specific plant physiological traits and invasiveness of aquatic plant species, highlighting the importance of trait studies in predicting ecosystem-level impacts of invasive plant species.

Earlier phenology of a nonnative plant increases impacts on native competitors

Adaptation to climate is expected to increase the performance of invasive species and their community-level impacts. However, while the fitness gains from adaptation should, in general, promote invader competitive ability, empirical demonstrations of this prediction are scarce. Furthermore, climate adaptation, in the form of altered timing of life cycle transitions, should affect the phenological overlap between nonnative and native competitors, with potentially large, but poorly tested, impacts on native species persistence. We evaluated these predictions by growing native California grassland plants in competition with nonnative Lactuca serriola, a species that flowers earlier in parts of its nonnative range that are drier than its putative European source region. In common garden experiments in southern California with L. serriola populations differing in phenology, plants originating from arid climates bolted up to 48 d earlier than plants from more mesic climates, and selection favored early flowering, supporting an adaptive basis for the phenology cline. The per capita competitive effects of L. serriola from early flowering populations on five early flowering native species were greater than the effects of L. serriola from later flowering populations. Consequently, the ability of the native species to increase when rare in competition with L. serriola, as inferred from field-parameterized competition models, declined with earlier L. serriola phenology. Indeed, changes to L. serriola phenology affected whether or not one native species was predicted to persist in competition with L. serriola Our results suggest that evolution in response to new climatic conditions can have important consequences for species interactions, and enhance the impacts of biological invasions on natural communities.

Effects of rapid evolution on species coexistence

Increasing evidence for rapid evolution suggests that the maintenance of species diversity in ecological communities may be influenced by more than purely ecological processes. Classic theory shows that interspecific competition may select for traits that increase niche differentiation, weakening competition and thus promoting species coexistence. While empirical work has demonstrated trait evolution in response to competition, if and how evolution affects the dynamics of the competing species-the key step for completing the required eco-evolutionary feedback-has been difficult to resolve. Here, we show that evolution in response to interspecific competition feeds back to change the course of competitive population dynamics of aquatic plant species over 10-15 generations in the field. By manipulating selection imposed by heterospecific competitors in experimental ponds, we demonstrate that (i) interspecific competition drives rapid genotypic change, and (ii) this evolutionary change in one competitor, while not changing the coexistence outcome, causes the population trajectories of the two competing species to converge. In contrast to the common expectation that interspecific competition should drive the evolution of niche differentiation, our results suggest that genotypic evolution resulted in phenotypic changes that altered population dynamics by affecting the competitive hierarchy. This result is consistent with theory suggesting that competition for essential resources can limit opportunities for the evolution of niche differentiation. Our finding that rapid evolution regulates the dynamics of competing species suggests that ecosystems may rely on continuous feedbacks between ecology and evolution to maintain species diversity.

An ecological and evolutionary perspective on species coexistence under global change

Whether assemblages of insect species locally coexist or are only being slowly lost from communities remains an enduring question. Addressing this question is especially critical in the wake of global change, which is expected to reshuffle biological communities and create novel interspecific interactions. In reviewing studies of putative insect species coexistence, we find that few have demonstrated necessary criteria to conclude that species coexist. We also find that few integrate ecological and evolutionary perspectives towards understanding coexistence. Yet, both micro-evolutionary and macroevolutionary processes can play a critical role in shaping species coexistence mechanisms, especially in response to global change. We suggest that understanding how global change may affect the makeup of communities can be best achieved by developing a research program focused on the joint contribution of ecological and evolutionary processes.

Evolutionarily stable communities: a framework for understanding the role of trait evolution in the maintenance of diversity

Biological diversity depends on the interplay between evolutionary diversification and ecological mechanisms allowing species to coexist. Current research increasingly integrates ecology and evolution over a range of timescales, but our common conceptual framework for understanding species coexistence requires better incorporation of evolutionary processes. Here, we focus on the idea of evolutionarily stable communities (ESCs), which are theoretical endpoints of evolution in a community context. We use ESCs as a unifying framework to highlight some important but under-appreciated theoretical results, and we review empirical research relevant to these theoretical predictions. We explain how, in addition to generating diversity, evolution can also limit diversity by reducing the effectiveness of coexistence mechanisms. The coevolving traits of competing species may either diverge or converge, depending on whether the number of species in the community is low (undersaturated) or high (oversaturated) relative to the ESC. Competition in oversaturated communities can lead to extinction or neutrally coexisting, ecologically equivalent species. It is critical to consider trait evolution when investigating fundamental ecological questions like the strength of different coexistence mechanisms, the feasibility of ecologically equivalent species, and the interpretation of different patterns of trait dispersion.

Do soil biota influence the outcome of novel interactions between plant competitors?

1. Species are shifting their ranges, for example to higher elevations, in response to climate change. Different plant species and soil microbiota will likely shift their ranges at different rates, giving rise to novel communities of plants and soil organisms. However, the ecological consequences of such novel plant-soil interactions are poorly understood. We experimentally simulated scenarios for novel interactions arising between high- and low elevation plants and soil biota following asynchronous climate change range shifts, asking to what extent the ability of plants to coexist depends on the origin of the soil biota. 2. In a greenhouse experiment, we grew pairs of low- (Poa trivialis and Plantago lanceolata) and high- (Poa alpina and Plantago alpina) elevation plant species alone and against a density gradient of con- or heterospecific neighbours. Plants grew on sterilized field soil that was inoculated with a soil community sampled from either low- or high elevation in the western Swiss Alps. We used the experiment to parameterize competition models, from which we predicted the population-level outcomes of competition in the presence of the different soil biota. 3. In the absence of neighbours, three of the four species produced more biomass with the low elevation soil biota. As a result of generally similar responses across plant species, soil biota tended not to affect plant interaction outcomes, with the low elevation species generally predicted to competitively exclude high elevation species irrespective of the soil biota origin. However, the low elevation grass Poa trivialis was only able to invade communities of Poa alpina in the presence of a low elevation soil biota. This suggests that, at least in some cases, the outcome of novel competitive interactions between plants following climate change will depend on whether shifts in the distribution of plant and soil organisms are asynchronous. 4. Synthesis. Our results indicate that the changing soil communities that plants encounter during range expansion can influence plant performance. However, this is only likely to alter expectations for the ability of plants to coexist following climate change if plant species respond differently to the change in the soil community.

Coexistence via coevolution driven by reduced allelochemical effects and increased tolerance to competition between invasive and native plants

Coevolution can promote long-term coexistence of two competing species if selection acts to reduce the fitness inequality between competitors and/or strengthen negative frequency dependence within each population. However, clear coevolution between plant competitors has been rarely documented. Plant invasions offer opportunities to capture the process of coevolution. Here we investigated how the developing relationship between an invasive forb, Alliaria petiolata, and a native competitor, Pilea pumila, may affect their long-term coexistence, by testing the competitive effects of populations of varying lengths of co-occurrence on each other across a chronosequence of invasion history. Alliaria petiolata and P. pumila tended to develop greater tolerance to competition over invasion history. Their coexistence was promoted more by increases in stabilizing relative to equalizing processes. These changes likely stem in part from reductions in allelopathic traits in the invader and evolution of tolerance in the native. These results suggested that some native species can evolve tolerance against the competitive effects of strong invaders, which likely promoted their persistence in invaded communities. However, the potential for coevolutionary rescue of competing populations is likely to vary across native species, and evolutionary processes should not be expected to compensate for the ecological consequences of exotic invasions.