Global change drivers alter multiple components of community composition, with cascading impacts on ecosystem stability. However, few studies have examined the complex interplay between global change drivers, synchrony, and diversity, especially over long-term successional dynamics. We analyzed a 22-year time series of grassland community data from Cedar Creek, USA, to examine the joint effects of pulse soil disturbance and press nitrogen addition on community synchrony, diversity, and stability during transient and post-transient periods of succession. Using multiple regression and structural equation modeling, we found that global change drivers decreased both synchrony and stability, thereby decoupling classic theoretical relationships, such as the portfolio effect. While the effect of soil disturbance weakened through time, nitrogen addition induced unexpected dynamics with maintained long-term impacts on composition, synchrony, and stability. Our findings underscore the need for long-term data and a comprehensive approach when managing ecosystems under ongoing global environmental changes.

With many species interacting in nature, determining which describe community dynamics is nontrivial. By applying a new Bayesian-sparse modelling approach to an extensive field survey, we assessed the importance of interactions from con- and hetero-specific plants, pollinators, and insect herbivores on plant performance. We compared the inclusion of the interaction effects as aggregate "generic" terms versus specific terms. We found that a continuum of positive to negative interactions, containing mostly generic but a few strong specific interactions, was sufficient to describe variation in plant performance. While interactions with herbivores and conspecifics varied from weakly negative to weakly positive, heterospecific plants mainly promoted competition and pollinators facilitated plants. The consistency of these empirical findings over three years suggests that a broad resolution, including the generic effects of guilds and a few specific groups rather than all pairwise and high-order interactions, can accurately describe species variation in plant performance across natural communities.

For decades community ecology has examined empirical relationships between ecosystem productivity and diversity. Despite this long history, tests of hypothesized mechanisms, namely the interplay between environmental filtering, biotic interactions, and dispersal, are lacking, largely due to their intractability using traditional approaches. Across a productivity gradient in a serpentine grassland in California, USA, we coupled occupancy data for four annual plants with persistence measures of paired transplants under natural conditions and reduced biotic interactions with neighbors. We found a positive relationship between productivity and biodiversity (i.e., the proportion of our four focal species found in a location) despite strong competition limiting species persistence in productive environments. Additionally, across species and for the community, we found a strong mismatch between occupancy and persistence, largely due to dispersal excess. Our results suggest that biodiversity-productivity relationships can be largely driven by dispersal and its interactive effects with local biotic and abiotic conditions.

Disturbance and environmental change may cause communities to converge on a steady state, diverge towards multiple alternative states, or remain in long-term transience. Yet, empirical investigations of successional trajectories are rare, especially in systems experiencing multiple concurrent anthropogenic drivers of change. We examined succession in old field grassland communities subjected to disturbance and nitrogen fertilization using data from a long-term (22-year) experiment. Regardless of initial disturbance, after a decade communities converged on steady states largely determined by resource availability, where species turnover declined as communities approached dynamic equilibria. Species favored by the disturbance were those that eventually came to dominate the highly fertilized plots. Furthermore, disturbance made successional pathways more direct under low nutrients, revealing an important interaction effect between nutrients and disturbance as drivers of community change. Our results underscore the dynamical nature of grassland and old field succession, demonstrating how community properties such as beta-diversity change through transient and equilibrium states.

Disturbance and environmental change may cause communities to converge to a steady state, diverge towards multiple alternative states, or remain in long-term transience. Yet, empirical tests of these successional trajectories are rare, especially in systems experiencing multiple concurrent anthropogenic drivers of change. We compared competing models of succession in grassland communities subjected to disturbance and nitrogen fertilization using data from a long-term (22-year) experiment. Regardless of disturbance, after a decade communities settled on equilibrium states largely determined by resource availability, with species turnover declining as communities approached dynamic equilibria. Species favored by the disturbance were those that eventually came to dominate the highly fertilized plots. Furthermore, disturbance made successional pathways more direct, revealing an important interaction effect between nutrients and disturbance as drivers of community change. Our results underscore the dynamical nature of grassland succession, demonstrating how community properties such as beta-diversity change through transient and equilibrium states.

Global change is altering patterns of community assembly, with net outcomes dependent on species’ responses to the environment, both directly and mediated through biotic interactions. Here, we assess alpine plant community responses in a 15-year factorial nitrogen addition, warming and snow manipulation experiment. We used a dynamic competition model to estimate the density-dependent and independent processes underlying changes in species-group abundances over time. Density-dependent shifts in competitive interactions drove long-term changes in abundance of species-groups under global change. Density-independent processes were important when counteracting environmental drivers limited the growth response of the dominant species. Furthermore, competitive interactions shifted with environmental change, primarily with nitrogen, and drove non-linear abundance responses across environmental gradients. Our results highlight that global change can either reshuffle species hierarchies or further favor already dominant species; predicting which outcome will occur requires incorporating both density-dependent and independent mechanisms and how they interact across multiple global change factors.

Restoration success is often measured by comparing target species abundance between restored and reference populations. Abundance may poorly predict long-term success, however, because seed addition may initially inflate restored population abundances, and reference population abundances may fluctuate with environmental variation. A demographic approach, informed by modern coexistence theory, may allow for more accurate diagnosis of restoration trajectories. We modeled population dynamics of an endangered plant (Lasthenia conjugens) in restored vernal pools and compared them to reference populations over 18 years (2000-2017). Model estimates of L. conjugens growth rates were better predictors of long-term trends than observed abundances. Although populations fluctuated in reference pools, annual rainfall variability acted as a stabilizing factor for L. conjugens. In restored pools however, invasive grasses and associated litter accumulation overrode the benefits of environmental variability. Our approach improves assessment of restoration outcomes and indicates when management actions, such as grass removal, will improve future trajectories.

Biological invasions have long fascinated ecologists as they fundamentally alter ecological communities, often in surprising ways. The demography of interacting native and exotic populations are core drivers of invasion impact. Demographic models estimate the strength of species interactions but have several shortcomings, often ignoring positive interactions and focusing only on competition, disregarding individual-level variance in demographic parameters, and focusing on one exotic species at a time. In this study, we investigate the fitness outcomes of eleven native and exotic species from a diverse annual plant community in Western Australia. We use a Bayesian demographic modelling approach that integrates demographic variation. Positive effects of exotic species played an integral role in the invaded community, but demographic variation caused many species interaction outcomes to vary from positive to negative, regardless of abiotic conditions. Our approach reveals variation that could be responsible for the diverse and unexpected impacts of exotic species on recipient communities.

Biological invasions have long fascinated ecologists as they fundamentally alter ecological communities, often in surprising ways. The demography of interacting native and exotic populations are core drivers of invasions. Demographic models estimate the strength of species interactions but have several shortcomings, including disregarding facilitation and focusing only on competition, disregarding individual-level variance in demographic parameters, and focusing on one exotic species at a time. In this study, we investigate the fitness outcomes of eleven native and exotic species from a diverse annual plant community in Western Australia. We use a Bayesian demographic modelling approach that integrates demographic stochasticity and facilitation. Facilitation mediated by exotic species played an integral role in the invaded community, but demographic stochasticity caused many species interactions to vary from facilitative to competitive, regardless of abiotic conditions. Our approach reveals variation that could be responsible for the diverse and unexpected impacts of exotic species on recipient communities.