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.
Most animals undergo ontogenetic niche shifts during their life. Yet, standard ecological theory builds on models that ignore this complexity. Here, we study how complex life cycles, where juvenile and adult individuals each feed on different sets of resources, affect community richness. Two different modes of community assembly are considered: gradual adaptive evolution and immigration of new species with randomly selected phenotypes. We find that under gradual evolution complex life cycles can lead to both higher and lower species richness when compared to a model of species with simple life cycles that lack an ontogenetic niche shift. Thus, complex life cycles do not per se increase the scope for gradual adaptive diversification. However, complex life cycles can lead to significantly higher species richness when communities are assembled trough immigration, as immigrants can occupy isolated peaks of the dynamic fitness landscape that are not accessible via gradual evolution.
It is well understood that natural disasters interact to affect the resilience and prosperity of communities and disproportionately affect low income families and communities of color. However, given the lack of a common theoretical framework, it is rare for these interactions to be well understood or quantified. As an example, we consider the interaction of severe weather events (e.g., hurricanes and tornadoes) and epidemics (e.g., COVID-19). Observing events unfolding in southeastern U.S. communities has caused us to conjecture that the interactive effects of catastrophic disturbances and stressors might be much more considerable than previously recognized. For instance, hurricane evacuations increase human aggregation, a key factor that affects the transmission of acute respiratory infections like SARS-CoV-2. Similarly, weather damage to health infrastructure could significantly reduce a community’s ability to provide services to people sick with COVID-19 and other diseases. As globalization and human population and movement continue to increase and weather events due to climate change are becoming more intense and severe, such complex interactions are expected to magnify and significantly impact environmental and human health.
Pest outbreaks, harmful algal blooms, and population collapses are extreme events with critical consequences for ecosystems, highlighting the importance of deciphering the driving ecological mechanisms underlying extreme events. By combining the generalized extreme value (GEV) theory from statistics and the hypothesis of a resource-limited metabolic restriction to population abundance, we evaluated theoretical predictions on the size-scaling and variance of extreme population abundance. Phytoplankton data from the L4 station in the English Channel showed a negative size scaling of the expected value of maxima, whose confidence interval included the predicted metabolic scaling (a = –1). We showed a humped pattern in variance with maxima at intermediate sizes. These results are consistent with the bounded abundance of small-sized populations that are subjected to strong grazing and with the expected decrease in variance towards large sizes. This approach provides unbiased return times, thereby improving the prediction accuracy of the timing of bloom formation, and describes a coherent framework in which to explore extreme population densities in natural communities.
Despite growing interactions between ecology and evolution, there still remain opportunities to further integrate the two disciplines, especially when considering multispecies systems. Here, we discuss two such opportunities. First, we suggest to relax the focus on the distinction between evolutionary and ecological processes. This focus is particularly unhelpful in the study of microbial communities, where the very notion of species is hard to define. Second, we propose that key processes of evolutionary theory such as adaptation should be exported to hierarchical levels higher than populations to make sense of biodiversity dynamics. Together, we argue that broadening our perspective of eco-evolutionary dynamics to be more inclusive of all biodiversity, both phylogenetically and hierarchically, will open up fertile new research directions and help us to address one the major scientific challenges of our time, i.e. to understand and predict changes in biodiversity in the face of rapid environmental change.
Biodiversity may increase ecosystem resilience. However, we have limited understanding if this holds true for ecosystems that respond to gradual environmental change with abrupt shifts to an alternative state. We used a mathematical model of anoxic-oxic regime shifts and explored how trait diversity in three groups of bacteria influences resilience. We found that trait diversity did not always increase resilience: greater diversity in two of the groups increased but in one group decreased resilience of their preferred ecosystem state. We also found that simultaneous trait diversity in multiple groups often led to reduced or erased diversity effects. Overall, our results suggest that higher diversity can increase resilience but can also promote collapse when diversity occurs in a functional group that negatively influences the state it occurs in. We propose this mechanism as a potential management approach to facilitate the recovery of a desired ecosystem state.
Our ability to understand population spread dynamics is complicated by rapid evolution, which renders simple ecological models insufficient. If dispersal ability evolves, more highly-dispersive individuals may arrive at the population edge than less-dispersive individuals (spatial sorting), accelerating spread. If individuals at the low-density population edge benefit (escape competition), high dispersers have a selective advantage (spatial selection). These two processes are often described as forming a positive feedback loop; they reinforce each other, leading to faster spread. Although spatial sorting is close to universal, this form of spatial selection is not: low densities can be detrimental for organisms with Allee effects. Here, we present two conceptual models to explore the feedback loops that form between spatial sorting and spatial selection. We show that the presence of an Allee effect can reverse the positive feedback loop between spatial sorting and spatial selection, creating a negative feedback loop that slows population spread.
An individual’s fitness cost associated with environmental change likely depends on the rate of adaptive phenotypic plasticity, and yet our understanding of plasticity rates in an ecological and evolutionary context remains limited. We provide the first quantitative synthesis of existing plasticity rate data, focusing on acclimation of temperature tolerance in ectothermic animals, where we demonstrate applicability of a recently proposed analytical approach. The analyses reveal considerable variation in plasticity rates of this trait among species, with half-times (how long it takes for the initial deviation from the acclimated phenotype to be reduced by 50% when individuals are shifted to a new environment) ranging from 3.7 to 770.2 h. Furthermore, rates differ among higher taxa, being higher for amphibians and reptiles than for crustaceans and fishes, and with insects being intermediate. We argue that a more comprehensive understanding of phenotypic plasticity will be attained through increased focus on the rate parameter.
Mounting evidence suggests that rapid evolutionary adaptation may rescue some organisms from the impacts of ongoing climate change. However, evolutionary constraints might hinder this process, especially when different aspects of environmental change generate antagonistic selection on genetically correlated traits. Here, we use individual-based simulations to explore how genetic correlations underlying the thermal physiology of ectotherms might influence their responses to the two major concomitant components of climate change---increases in mean temperature and thermal variability. We found that genetic correlations can influence population dynamics under climate change, with declines in population size varying three-fold depending on the type of correlation present. Surprisingly, populations whose thermal performance curves were constrained by genetic correlations often declined less rapidly than unconstrained populations. Our results suggest that accurate forecasts of the impact of climate change on ectotherms will require an understanding of the genetic architecture of the traits under selection.
Forest soil CO2 efflux (FCO2) is a crucial process in global carbon cycling; however, how FCO2 respond to disturbance regimes in different forest biomes is poorly understood. We quantified the effects of disturbance regimes on FCO2 across boreal, temperate, tropical, and Mediterranean forests based on 1240 observations from 380 studies. Globally, FCO2 was increased by 13 to 25% due to climatic perturbations such as elevated CO2 concentration, warming, and increased precipitation. FCO2 was increased by forest conversion to grassland and elevated carbon input by forest management practices but was reduced by decreased carbon input, fire, and acid rain. Disturbance also caused changes in soil temperature and water content, which in turn affected the direction and magnitude of disturbance effects on FCO2. Our results suggest that disturbance effects on FCO2 should be incorporated into earth system models to improve the projection of feedback between the terrestrial C cycle and climate change.
Studies of eco-evolutionary dynamics have integrated evolution with ecological processes at multiple scales (populations, communities, and ecosystems) and with multiple interspecific interactions (antagonistic, mutualistic, and competitive). However, evolution has often been conceptualized as a single process: short-term adaptive genetic change driven by natural selection. Here we argue that other diverse evolutionary processes should also be considered, to explore the full spectrum of feedbacks between ecological and evolutionary processes. Relevant but underappreciated processes include (1) drift and mutation, (2) disruptive selection causing lineage diversification or speciation reversal, (3) evolution driven by relative fitness differences that may decrease population growth, and (4) topics including multilevel selection, sexual selection and conflict, hard and soft selection, and genetic/genomic architectures/signatures. Because natural selection is not the sole mechanism of rapid evolution, it will be important to integrate a variety of concepts in evolutionary biology and ecology to better understand and predict eco-evolutionary dynamics in nature.
Heterogeneity among individuals in fitness components is what selection acts upon. Evolutionary theories predict that selection in constant environments acts against such heterogeneity. But observations reveal substantial non-genetic and also non-environmental variability in phenotypes. Here we examine whether there is a relationship between selection pressure and phenotypic variability by analysing structured population models based on data from a large and diverse set of species. Our findings suggest that non-genetic, non-environmental variation is in general neither truly neutral, selected for, or selected against. We find much variation among species and populations within species, with mean patterns suggesting nearly neutral evolution of life course variability. Populations that show greater diversity of life courses do not show, in general, increased or decreased population growth rates. Our analysis suggests we are only at the beginning in understanding the evolution and maintenance of non-genetic non environmental variation.
Seed limitation can narrow down the number of coexisting plant species and limit plant community productivity. It is also likely to constrain community responses to changing environmental and biotic conditions. In a 10-year full-factorial experiment of seed addition, fertilisation, warming and herbivore exclusion, we tested how seed addition alters community richness and biomass, and how its effects depend on seed origin and environmental and biotic context. We found that seed addition increased richness in all treatments, and increased community biomass depending on nutrient addition and warming. Novel seeded species, originally absent from the communities, increased biomass the most, especially in fertilised plots and in the absence of herbivores, while adding seeds of local species did not affect biomass. Our results show that dispersal limitation can constrain the invasion of novel species and their effects on community biomass, and demonstrate that these relationships are contingent on trophic interactions and environmental conditions.
Climate warming alters the seasonal timing of biological events. This raises concerns that species-specific responses to warming may de-synchronize co-evolved consumer-resource phenologies, resulting in trophic mismatch and altered ecosystem dynamics. Here we explore effects of warming on the temporal coherence of two key phenological events in lakes across Europe: The onset of the phytoplankton spring bloom and the spring/summer maximum of the grazer Daphnia. Simulation of 1,891,744 lake years revealed that, under the current climate, the phenological delay between the two events varies greatly (20-190 days) across lake types and geographic locations. Warming moves both phenological events forward in time and can predictably lengthen or shorten the delay between them by up to 60 days. Our findings expose large extant variation in phenological synchrony of planktonic organisms, provide quantitative predictions of its dependence on physical lake properties and geographic location, and highlight research needs concerning its ecological consequences.
Belowground life is traditionally considered to rely on leaf litter as the main basal resource, whereas the importance of roots remains little understood, especially in the tropics. Here, we analysed the response of 30 soil animal groups to root trenching and litter removal in rainforest and plantations in Sumatra and found that roots are similarly important to soil fauna as litter. Trenching effects were stronger in soil than in litter with animal abundance being overall decreased by 42% in rainforest and by 30% in plantations. Litter removal little affected animals in soil, but decreased the total abundance by 60% both in rainforest and rubber plantations but not in oil palm plantations. Litter and root effects were explained either by the body size or vertical distribution of specific animal groups. Our findings highlight the importance of root-derived resources for soil animals and quantify principle carbon pathways in tropical soil food webs.
An important hypothesis for how plants respond to introduction to new ranges is the evolution of increased competitive ability (EICA). EICA predicts that biogeographical release from natural enemies initiates a tradeoff in which exotic species in non-native ranges become larger and more competitive, but invest less in consumer defenses, relative to populations in native ranges. This tradeoff is exceptionally complex because detecting concomitant biogeographical shifts in competitive ability and consumer defense depend upon which traits are targeted, how competition is measured, the defense chemicals quantified, whether defense chemicals do more than defend, whether “herbivory” is artificial or natural, and where consumers fall on the generalist-specialist spectrum. Previous meta-analyses have successfully identified patterns but have yet to fully disentangle this complexity. We used meta-analysis to reevaluate traditional metrics used to test EICA theory and then expanded on these metrics by partitioning competitive effect and competitive tolerance measures and testing Leaf Specific Mass in detail as a response trait. Unlike previous syntheses, our meta-analyses detected evidence consistent with the classic tradeoff inherent to EICA. Plants from non-native ranges imposed greater competitive effects than plants from native ranges and were less quantitatively defended than plants from native ranges. Our results for defense were not based on complex leaf chemistry, but instead were estimated from tannins, toughness traits, and primarily Leaf Specific Mass. Species specificity occurred but did not influence the general patterns. As for all evidence for EICA-like tradeoffs, we do not know if the biogeographical differences we found were caused by tradeoffs per se, but they are consistent with predictions derived from the overarching hypothesis. Underestimating physical leaf structure may have contributed to two decades of tepid perspectives on the tradeoffs fundamental to EICA.
Ecosystems remain under enormous pressure from multiple anthropogenic stressors. Manipulative experiments evaluating stressor interactions and impacts mostly apply stressors under static conditions without considering how variable stressor intensity (i.e., fluctuations) and synchronicity (i.e., timing of fluctuations) affect biological responses. We ask how variable stressor intensity and synchronicity, and interaction type, can influence how multiple stressors affect seagrass. At the highest intensities, fluctuating stressors applied asynchronously reduced seagrass biomass 36% more than for static stressors, yet no such difference occurred for photosynthetic capacity. Testing three separate hypotheses to predict underlying drivers of differences in biological responses highlighted alternative modes of action dependent on how stressors fluctuated over time. Given that environmental conditions are constantly changing, assessing static stressors may lead to inaccurate predictions of cumulative effects. Translating multiple stressor experiments to the real-world, therefore, requires considering variability in stressor intensity and the synchronicity of fluctuations.
Positive interactions have been hypothesized to influence plant community dynamics and species invasions. However, their prevalence and importance relative to negative interactions remain unclear, but are fundamentally important for both theoretical and applied ecology. We examined pairwise biotic interactions using over 50 years of successional data to assess the prevalence of positive interactions and their effects on each focal species (either native or exotic). We found that positive interactions were widespread and the relative frequency of positive and negative interactions varied with establishment stage and between native and exotic species. Specifically, positive interactions were more frequent during early establishment and less frequent at later stages. Positive interactions involving native species were more frequent and stronger than those between exotic species, reducing the impact of invasional meltdown on succession. Our study highlights the role of positive native interactions in shielding communities from biological invasion and enhancing the potential for long-term resilience.