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Biological invasions are both a pressing environmental challenge and an opportunity to investigate fundamental ecological processes, such as the role of top predators in regulating biodiversity and food-web structure. In whole-ecosystem manipulations of small Caribbean islands on which brown anole lizards ( Anolis sagrei ) were the native top predator, we experimentally staged invasions by competitors (green anoles, Anolis smaragdinus ) and/or new top predators (curly-tailed lizards, Leiocephalus carinatus ). We show that curly-tailed lizards destabilized the coexistence of competing prey species, contrary to the classic idea of keystone predation. Fear-driven avoidance of predators collapsed the spatial and dietary niche structure that otherwise stabilized coexistence, which intensified interspecific competition within predator-free refuges and contributed to the extinction of green-anole populations on two islands. Moreover, whereas adding either green anoles or curly-tailed lizards lengthened food chains on the islands, adding both species reversed this effect—in part because the apex predators were trophic omnivores. Our results underscore the importance of top-down control in ecological communities, but show that its outcomes depend on prey behaviour, spatial structure, and omnivory. Diversity-enhancing effects of top predators cannot be assumed, and non-consumptive effects of predation risk may be a widespread constraint on species coexistence. Whole-ecosystem manipulations of Caribbean islands occupied by brown anoles, involving the addition of competitors (green anoles) and/or top predators (curly-tailed lizards), demonstrate that predator introductions can alter the ecological niches and destabilize the coexistence of competing prey species.

Studies have reported widespread declines in terrestrial insect abundances in recent years 1 – 4 , but trends in other biodiversity metrics are less clear-cut 5 – 7 . Here we examined long-term trends in 923 terrestrial insect assemblages monitored in 106 studies, and found concomitant declines in abundance and species richness. For studies that were resolved to species level (551 sites in 57 studies), we observed a decline in the number of initially abundant species through time, but not in the number of very rare species. At the population level, we found that species that were most abundant at the start of the time series showed the strongest average declines (corrected for regression-to-the-mean effects). Rarer species were, on average, also declining, but these were offset by increases of other species. Our results suggest that the observed decreases in total insect abundance 2 can mostly be explained by widespread declines of formerly abundant species. This counters the common narrative that biodiversity loss is mostly characterized by declines of rare species 8 , 9 . Although our results suggest that fundamental changes are occurring in insect assemblages, it is important to recognize that they represent only trends from those locations for which sufficient long-term data are available. Nevertheless, given the importance of abundant species in ecosystems 10 , their general declines are likely to have broad repercussions for food webs and ecosystem functioning. An analysis of more than 500 sites distributed worldwide finds that declines in the abundance of terrestrial insects are attributable mainly to decreases in species that were formerly abundant, rather than being the result of losses of rare species.

Networks composed of distinct, densely connected subsystems are called modular. In ecology, it has been posited that a modular organization of species interactions would benefit the dynamical stability of communities, even though evidence supporting this hypothesis is mixed. Here we study the effect of modularity on the local stability of ecological dynamical systems, by presenting new results in random matrix theory, which are obtained using a quaternionic parameterization of the cavity method. Results show that modularity can have moderate stabilizing effects for particular parameter choices, while anti-modularity can greatly destabilize ecological networks. Modularity in food webs can be caused by spatial and temporal mismatches in interactions. Here, Jacopo Grilli, Tim Rogers and Stefano Allesina show that modularity, contrary to expectations, does not generally help stabilizing ecological communities.

Although habitat loss is the predominant factor leading to biodiversity loss in the Anthropocene 1 , 2 , exactly how this loss manifests—and at which scales—remains a central debate 3 – 6 . The ‘passive sampling’ hypothesis suggests that species are lost in proportion to their abundance and distribution in the natural habitat 7 , 8 , whereas the ‘ecosystem decay’ hypothesis suggests that ecological processes change in smaller and more-isolated habitats such that more species are lost than would have been expected simply through loss of habitat alone 9 , 10 . Generalizable tests of these hypotheses have been limited by heterogeneous sampling designs and a narrow focus on estimates of species richness that are strongly dependent on scale. Here we analyse 123 studies of assemblage-level abundances of focal taxa taken from multiple habitat fragments of varying size to evaluate the influence of passive sampling and ecosystem decay on biodiversity loss. We found overall support for the ecosystem decay hypothesis. Across all studies, ecosystems and taxa, biodiversity estimates from smaller habitat fragments—when controlled for sampling effort—contain fewer individuals, fewer species and less-even communities than expected from a sample of larger fragments. However, the diversity loss due to ecosystem decay in some studies (for example, those in which habitat loss took place more than 100 years ago) was less than expected from the overall pattern, as a result of compositional turnover by species that were not originally present in the intact habitats. We conclude that the incorporation of non-passive effects of habitat loss on biodiversity change will improve biodiversity scenarios under future land use, and planning for habitat protection and restoration. Analysis of 123 studies of assemblage-level abundances of focal taxa from fragmented habitats finds that increasing fragmentation has a disproportionately large effect on biodiversity loss, supporting the ecosystem decay hypothesis.

Communities that are very rich in species could persist thanks to the stabilizing role of higher-order interactions, in which the presence of a species influences the interaction between other species. High order interactions maintain species diversity How the tremendous biodiversity observed in nature is maintained is a central question in ecology. Simple models of interacting competitors fail to reproduce the stable persistence of very large ecological communities, while neutral models in which species do not interact and diversity is maintained by immigration and speciation yield unrealistically small fluctuations in population abundance. Using competitive network models, Stefano Allesina and colleagues show that higher order interactions, whereby the presence of one species influences the interaction between other species, allow highly diverse communities to persist in closed systems with a fixed number and identity of species and in more realistic open systems, which gain new species through immigration and speciation. Ecologists have long sought a way to explain how the remarkable biodiversity observed in nature is maintained. On the one hand, simple models of interacting competitors cannot produce the stable persistence of very large ecological communities 1 , 2 , 3 , 4 , 5 . On the other hand, neutral models 6 , 7 , 8 , 9 , in which species do not interact and diversity is maintained by immigration and speciation, yield unrealistically small fluctuations in population abundance 10 , and a strong positive correlation between a species’ abundance and its age 11 , contrary to empirical evidence. Models allowing for the robust persistence of large communities of interacting competitors are lacking. Here we show that very diverse communities could persist thanks to the stabilizing role of higher-order interactions 12 , 13 , in which the presence of a species influences the interaction between other species. Although higher-order interactions have been studied for decades 14 , 15 , 16 , their role in shaping ecological communities is still unclear 5 . The inclusion of higher-order interactions in competitive network models stabilizes dynamics, making species coexistence robust to the perturbation of both population abundance and parameter values. We show that higher-order interactions have strong effects in models of closed ecological communities, as well as of open communities in which new species are constantly introduced. In our framework, higher-order interactions are completely defined by pairwise interactions, facilitating empirical parameterization and validation of our models.

Enrichment of nutrients and loss of herbivores are assumed to cause a loss of plant diversity in grassland ecosystems because they increase plant cover, which leads to a decrease of light in the understory 1 – 3 . Empirical tests of the role of competition for light in natural systems are based on indirect evidence, and have been a topic of debate for the last 40 years. Here we show that experimentally restoring light to understory plants in a natural grassland mitigates the loss of plant diversity that is caused by either nutrient enrichment or the absence of mammalian herbivores. The initial effect of light addition on restoring diversity under fertilization was transitory and outweighed by the greater effect of herbivory on light levels, indicating that herbivory is a major factor that controls diversity, partly through light. Our results provide direct experimental evidence, in a natural system, that competition for light is a key mechanism that contributes to the loss of biodiversity after cessation of mammalian herbivory. Our findings also show that the effects of herbivores can outpace the effects of fertilization on competition for light. Management practices that target maintaining grazing by native or domestic herbivores could therefore have applications in protecting biodiversity in grassland ecosystems, because they alleviate competition for light in the understory. Competition for light can cause plant diversity loss in grassland ecosystems when fertilized or herbivores are excluded, and experimentally restoring light can mitigate this biodiversity loss.

Numerous studies have demonstrated that biodiversity drives ecosystem functioning, yet how biodiversity loss alters ecosystems functioning and stability in the long-term lacks experimental evidence. We report temporal effects of species richness on community productivity, stability, species asynchrony, and complementarity, and how the relationships among them change over 17 years in a grassland biodiversity experiment. Productivity declined more rapidly in less diverse communities resulting in temporally strengthening positive effects of richness on productivity, complementarity, and stability. In later years asynchrony played a more important role in increasing community stability as the negative effect of richness on population stability diminished. Only during later years did species complementarity relate to species asynchrony. These results show that species complementarity and asynchrony can take more than a decade to develop strong stabilizing effects on ecosystem functioning in diverse plant communities. Thus, the mechanisms stabilizing ecosystem functioning change with community age. Biodiversity-ecosystem functioning relationships may change over time. Here, Wagg et al. show that richness-productivity and richness stability relationships grow stronger over time in an experimental grassland community, and shed light on the ecological mechanisms.

Land-use intensification is a major driver of biodiversity loss. However, understanding how different components of land use drive biodiversity loss requires the investigation of multiple trophic levels across spatial scales. Using data from 150 agricultural grasslands in central Europe, we assess the influence of multiple components of local- and landscape-level land use on more than 4,000 above- and belowground taxa, spanning 20 trophic groups. Plot-level land-use intensity is strongly and negatively associated with aboveground trophic groups, but positively or not associated with belowground trophic groups. Meanwhile, both above- and belowground trophic groups respond to landscape-level land use, but to different drivers: aboveground diversity of grasslands is promoted by diverse surrounding land-cover, while belowground diversity is positively related to a high permanent forest cover in the surrounding landscape. These results highlight a role of landscape-level land use in shaping belowground communities, and suggest that revised agroecosystem management strategies are needed to conserve whole-ecosystem biodiversity. Land use intensification is a major driver of biodiversity change. Here the authors measure diversity across multiple trophic levels in agricultural grassland landscapes of varying management, finding decoupled responses of above- and belowground taxa to local factors and a strong impact of landscape-level land use.

Rare species are increasingly recognized as crucial, yet vulnerable components of Earth’s ecosystems. This is also true for microbial communities, which are typically composed of a high number of relatively rare species. Recent studies have demonstrated that rare species can have an over-proportional role in biogeochemical cycles and may be a hidden driver of microbiome function. In this review, we provide an ecological overview of the rare microbial biosphere, including causes of rarity and the impacts of rare species on ecosystem functioning. We discuss how rare species can have a preponderant role for local biodiversity and species turnover with rarity potentially bound to phylogenetically conserved features. Rare microbes may therefore be overlooked keystone species regulating the functioning of host-associated, terrestrial and aquatic environments. We conclude this review with recommendations to guide scientists interested in investigating this rapidly emerging research area.

Differences in phenological responses to climate change among species can desynchronise ecological interactions and thereby threaten ecosystem function. To assess these threats, we must quantify the relative impact of climate change on species at different trophic levels. Here, we apply a Climate Sensitivity Profile approach to 10,003 terrestrial and aquatic phenological data sets, spatially matched to temperature and precipitation data, to quantify variation in climate sensitivity. The direction, magnitude and timing of climate sensitivity varied markedly among organisms within taxonomic and trophic groups. Despite this variability, we detected systematic variation in the direction and magnitude of phenological climate sensitivity. Secondary consumers showed consistently lower climate sensitivity than other groups. We used mid-century climate change projections to estimate that the timing of phenological events could change more for primary consumers than for species in other trophic levels (6.2 versus 2.5–2.9 days earlier on average), with substantial taxonomic variation (1.1–14.8 days earlier on average). An ambitious study has used more than 10,000 datasets to examine how the phenological characteristics—such as the timing of reproduction—of various taxa alter in response to climate change, and suggests that differing levels of climate sensitivity could lead to the desynchronization of seasonal events over time. The shifting biological seasons Variations in the phenological responses of different species to climate change have fuelled concerns that key species interactions may desynchronize over time, with consequences for ecosystem functioning. Stephen Thackeray et al . examine the climate sensitivity of 812 terrestrial and aquatic taxa across the United Kingdom, using more than 10,000 phenological data sets spanning 1960 to 2012, together with temperature and precipitation data. There was a systematic difference in the magnitude and direction of phenological climate sensitivity across trophic levels, despite marked heterogeneity among organisms sharing taxonomic affinities and trophic position. In particular, secondary consumers showed lower levels of climate sensitivity than primary producers and consumers. The authors suggest that the differential sensitivity of phenology to climate across trophic levels could result in the desynchronization of seasonal events in the future.