Human activities have increased the intensity and frequency of natural stressors and created novel stressors, altering host-pathogen interactions, and changing the risk of emerging infectious diseases. Despite the ubiquity of such anthropogenic impacts, predicting the directionality of outcomes has proven challenging. Here, we conduct a review and meta-analysis to determine the primary mechanisms through which stressors affect host-pathogen interactions and to evaluate the impacts stress has on host fitness (survival and fecundity) and pathogen infectivity (prevalence and intensity). We assessed 891 effect sizes from 71 host species (representing seven taxonomic groups) and 78 parasite taxa from 98 studies. We found that infected and uninfected hosts had similar sensitivity to stressors and that responses varied according to stressor type. Specifically, limited resources compromised host fecundity and decreased pathogen intensity, while abiotic environmental stressors (e.g., temperature and salinity) decreased host survivorship and increased pathogen intensity, and pollution increased mortality but decreased pathogen prevalence. We then used our meta-analysis results to develop Susceptible-Infected theoretical models to illustrate scenarios where infection rates are expected to increase or decrease in response to resource limitation or environmental stress gradients. Our results carry implications for conservation and disease emergence and reveal areas for future work.

Anthropogenic activities expose many ecosystems to multiple novel disturbances simultaneously. Despite this, how biodiversity responds to simultaneous disturbances remains unclear, with conflicting empirical results on their interactive effects. Here, we experimentally test how one disturbance (an invasive species) affects the diversity of a community over multiple levels of another disturbance regime (pulse mortality). Specifically, we invade stably coexisting bacterial communities under four different pulse frequencies, and compare their final resident diversity to uninvaded communities under the same pulse mortality regimes. Our experiment shows that the disturbances synergistically interact, such that the invader significantly reduces resident diversity at high pulse frequency, but not at low. This work therefore highlights the need to study simultaneous disturbance effects over multiple disturbance regimes as well as to carefully document unmanipulated disturbances, and may help explain the conflicting results seen in previous multiple-disturbance work.

A document by Julian Lilkendey. Click on the document to view its contents.

Animal migration impacts organismal health and disease transmission: migrants are simultaneously exposed to parasites and able to reduce infection at the population and individual levels. However, these dynamics are difficult to study; empirical studies reveal disparate results while existing theory makes assumptions that simplify natural complexity. Here, we systematically review empirical studies of migration and infection across taxa, highlighting key gaps in our understanding. Next, we develop a unified evolutionary framework incorporating different mechanisms of parasite-migration interactions while accounting for ecological complexity that goes beyond previous theory. Our framework generates diverse migration-infection patterns paralleling those seen in empirical systems, including partial and differential migration. Finally, we generate predictions about which mechanisms dominate which empirical systems to guide future studies. Our framework provides an overarching understanding of selective pressures shaping migration patterns in the context of animal health and disease, which is critical for predicting how environmental change may threaten migration.

Biodiversity is diminishing at alarming rates due to multiple anthropogenic drivers. To mitigate these drivers, their impacts must be quantified accurately and comparably across drivers. To enable that, we present a generally applicable framework introducing fundamental principles of ecological impact quantification, including the quantification of interactions between multiple drivers. The framework contrasts biodiversity variables in impacted against those in unimpacted or other reference situations, while accounting for their temporal dynamics through modelling. Properly accounting for temporal dynamics reduces biases in impact quantification and comparison. The framework addresses key questions around ecological impacts in global change science, namely, how to compare impacts under temporal dynamics across stressors, how to account for stressor interactions in such comparisons, and how to compare the success of management actions over time.

Metabolomics provides an unprecedented window on diverse plant secondary metabolites that represent a potentially critical niche dimension in tropical forests underlying co-existence. Here, we used untargeted metabolomics to evaluate the chemical composition of 358 tree species and its relationship to phylogeny and variation in light environment, soil nutrients, and insect-herbivore leaf damage in a tropical rain forest plot. We found that tree species that co-occur locally are less chemically similar than random, and that local chemical dispersion and metabolite diversity reduce herbivory, especially that of specialist insect herbivores. Our results suggest that plant secondary metabolites have the potential to mediate plant-herbivore interactions in a manner consistent with diversity maintenance at the community scale.

Vector-borne diseases cause significant financial and human loss, with billions of dollars spent on control. Arthropod vectors experience a complex suite of environmental factors that affect fitness, population growth, and species interactions across multiple spatial and temporal scales. Temperature and water availability are two of the most important abiotic variables influencing their distributions and abundances. While extensive research on temperature exists, the influence of humidity on vector and pathogen parameters affecting disease dynamics are less understood. Humidity is often underemphasized, and when considered, is often treated as independent of temperature even though desiccation likely contributes to declines in trait performance at warmer temperatures. This Perspectives explores how humidity shapes the thermal performance of mosquito-borne pathogen transmission. We summarize what is known about its effects and propose a conceptual model for how temperature and humidity interact to shape the range of temperatures across which mosquitoes persist and achieve high transmission potential. We discuss how failing to account for these interactions hinders efforts to forecast transmission dynamics and respond to epidemics of mosquito-borne infections. We outline future research areas that will ground the effects of humidity on the thermal biology of pathogen transmission in a theoretical and empirical framework to improve spatial and temporal prediction of vector-borne pathogen transmission.

Ecosystems function in a series of feedback loops that can change or maintain vegetation structure. Vegetation structure influences the ecological niche space available for animals to partition, shaping many aspects of behavior and reproduction. In turn, animals perform ecological functions that shape vegetation structure. However, most studies concerning 3D vegetation structure consider only one of these relationships. Here, we review these separate lines of research and integrate them into a single concept that describes a feedback mechanism. We also show how remote sensing and animal tracking technologies are now available at the global scale to describe feedback loops and their consequences for ecosystem functioning. An improved understanding of how animals interact with vegetation structure in feedback loops is needed to conserve ecosystems that face major disruptions in response to climate and land use change.

Species invasions are predicted to increase in frequency with global change, but quantitative predictions of how environmental filters and species traits influence the success and consequences of invasions for local communities are lacking. Here we investigate how invaders alter the structure, diversity and stability regime of simple communities across gradients of habitat productivity, temperature, and community size structure. We examine all three-species trophic modules (apparent and exploitative competition, trophic chain and intraguild predation) with empirically derived temperature and body mass scaling of vital rates. We show that the success of an invasion and its effects on community stability and diversity are predictably determined by the effects of environmental factors on each species and the relative strengths of trophic interactions between resident and invading species. We predict that successful invaders include smaller competitors and comparatively small predators, suggesting that species invasions may facilitate the downsizing of food webs under global change.

Plant community productivity generally increases with biodiversity, but the strength of this relationship exhibits strong empirical variation. In meta-food-web simulations, we addressed if the spatial overlap in plants' resource access and movement of animals can explain such variability. We found that spatial overlap of plant resource access is a prerequisite for positive diversity-productivity relationships, but causes exploitative competition that can lead to competitive exclusion. Movement of herbivores causes apparent competition among plants, resulting in negative relationships. However, movement of larger top predators integrates sub-food-webs composed of smaller species, offsetting the negative effects of exploitative and apparent competition and leading to strongly positive diversity-productivity relationships. Overall, our results show that spatial overlap of plant resource access and animal movement can greatly alter the strength and sign of such relationships. In particular, the scaling of animal movement effects opens new perspectives for linking landscape processes without effects on biodiversity to productivity patterns.

Microbial life in an ecosystem with low energy supply has been considered to employ two energy utilization strategies. The first is energy conservation at an individual level, while the second is energy use optimization in response to the availability of energy resources. Here, using an oxidation-reduction (redox) reaction network model where microbial metabolic pathways are established through multiple species-level competition and cooperation within a redox reaction network, we hypothesize that microbial ecosystems can move forward to increase energy use efficiency, namely an energy efficiency strategy at the community level. This strategy is supported by microbial functional diversity that enables species to interact with others in various ways of metabolic handoffs. Moreover, the high energy use efficiency is attributable to the mutualistic division of labor that increases the complexity of metabolic pathways, which actively drives material cycling to exploit more energy.

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.

Tropical rainforests around the world are rapidly converted into cash crop agricultural systems. The associated massive losses of plant and animal species lead to changes in arthropod food webs and the energy fluxes therein. These changes are poorly understood, in particular in the extremely biodiverse canopies of tropical ecosystems. Using canopy fogging followed by stable isotope and energy flux analyses, we show that land-use conversion from rainforest to rubber and oil palm plantations not only causes a drastic reduction in energy fluxes of up to 75%, but also shifts fluxes among trophic groups. While rainforest featured high levels of both herbivory and algae-microbivory, and a balanced ratio of herbivory to predation, relative fluxes were shifted towards predation in rubber and towards herbivory in oil palm plantations, indicating profound shifts in ecosystem functioning. Our results highlight that the ongoing loss of animal biodiversity and biomass in tropical canopies degrades animal-driven functions and restructures canopy food webs.

Non-native plants are typically released from specialist enemies in new ranges, but continue to be attacked by generalists, but whether they shift relative allocation to constitutive or induced defenses is unknown. We compared herbivory on co-occurring native and non-native species and also constitutive and induced defenses. Non-natives suffered less damage than natives and constitutive defenses of non-natives was lower than that of native congeners, whereas induced defense was the opposite. The strength of constitutive defenses for a species was correlated with the intensity of herbivory experienced, for non-natives, whereas induced defenses showed the reverse. The defenses of natives were not related to herbivory pressure. Finally, the strength of induced defenses correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. These results expand our understanding of fundamental tradeoffs in constitutive and induced defenses and provide novel insight into how herbivory pressure affects defense allocation.

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.

Urbanisation is increasing worldwide, with major impacts on biodiversity, species interactions and ecosystem functioning. Pollination is an ecosystem function vital for terrestrial ecosystems and food security, however, the processes underlying the patterns of pollinator diversity and the ecosystem services they provide in cities have seldom been quantified. Here, we present a comprehensive meta-analysis, using 133 studies, on the effects of urbanisation on pollinator diversity and pollination. Our results confirm the widespread negative effects of urbanisation on pollinator diversity, particularly of Lepidoptera. Additionally, pollinator responses were found to be trait-specific, with below ground nesting, solitary, and spring flyers more severely affected from urbanisation. Meanwhile, cities promote a greater diversity of non-native pollinators, which may exacerbate conservation risks to native ones. Surprisingly, despite the negative effects of urbanisation on pollinator diversity, pollination services in cities are enhanced and mediated by the high flower visitation rates of abundant generalists and managed pollinators. We highlight that the richness of local flowering plants could mitigate the negative effects of urbanisation on pollinator diversity. Overall, the results demonstrate the varying magnitudes of multiple moderators on urban pollinators and pollination service provision and could help guide conservation actions for biodiversity and ecosystem function for a sustainable future.

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.