Ecological Feedback Mechanisms Research Articles

Sea urchin Arbacia punctulata feeding preference for algal turf over kelp in a degraded kelp forest ecosystem

Climate change is driving a shift in the distribution of global kelp forests, with the contraction of kelp habitats occurring at warm range edges. Declining kelps often have been replaced by novel algal turf assemblages, which are reinforced by ecological feedback mechanisms and provide fewer ecosystem services. Trophic interactions among marine herbivores, algal turfs, and kelps on algal turf-dominated reefs remain poorly resolved but could have important implications for the stability of algal turf reefs and the potential for kelp forest recovery. Here, we examine herbivory by the Atlantic purple sea urchin, Arbacia punctulata, in a degraded kelp forest ecosystem dominated by algal turf in southern New England, USA. In a localized field survey, we observed lower algal turf cover on reef areas containing A. punctulata (mean ± SE: 62 ± 12% turf cover) as compared to areas with no sea urchins present (92 ± 4% turf cover). Reef areas with and without sea urchins had similarly low cover of the previously dominant kelp, Saccharina latissima (6–8% kelp cover). In laboratory and field experiments, individuals or groups of A. punctulata enclosed with a diet choice of algal turf versus kelp had higher grazing rates on the algal turf. A. punctulata in the laboratory also exhibited greater attraction to algal turf over kelp, physically moving towards this food source. In combination, the results provide evidence that A. punctulata has a feeding preference for algal turf over kelp in southern New England. Future research is warranted to further examine the grazing ecology of A. punctulata, particularly in the context of ongoing kelp forest restoration efforts in this region.

Global sustainable land use and management: Illustrating the linkage between carbon sink and ecological engineering

AbstractEcological engineering has been implemented worldwide to mitigate land use and management stresses. It can remarkably alter the spatiotemporal patterns of carbon sinks and regulate ecosystem functions and processes. However, the linkage between ecological engineering and carbon sink remains unclear. To adequately address this dilemma, we must urgently determine the spatiotemporal patterns and drivers of carbon sinks and illustrate ecological response and feedback mechanisms. We created a Special Issue to answer these questions, establish future research directions, and propose a framework for sustainable land use and management. All these efforts provide a theoretical basis to guide the implementation of ecological projects and contribute to global carbon neutrality.

The levelling-off and recent rapid decline in population density of the highly prolific invasive lionfish on the Saba Bank, Eastern Caribbean

Since its introduction in the Western Atlantic more than 30 years ago, the lionfish (Pterois volitans/miles complex) has spread throughout the Gulf of Mexico, the Caribbean and the Western Tropical Atlantic, with massive and unprecedented ecological impacts. This invasion is among the most studied marine fish invasions but very little is still really known about the population dynamics of the species and the factors ultimately governing its abundance. The species was first documented on the Saba Bank in 2010 and rapidly increased in abundance till the end of 2014. In this note we document its rise and subsequent decline in density and thereby describe the species’ third apparent local population boom-bust event for the Greater Caribbean. We also document gradual increases in the mean size of lionfish of the Eastern Caribbean Saba Bank that coincided with the increase and subsequent decline in abundance. Contrary to the previously documented epizootic disease outbreak associated with the population crash observed in the Gulf of Mexico we were unable to find any signs of the occurrence of epizootic disease. We suggest that the population decline on the Saba Bank might have been due to non-local causes. Boom-bust dynamics are often witnessed in biological invasions and have critical implications for both understanding and managing invasive species. While the underlying cause for the boom-bust event we document remains unknown, our work suggests that in the region, ecological feedback mechanisms are gradually developing that can help level-off deleterious population excesses of this invasive species.

Evidence for density-dependent effects on body composition of a large omnivore in a changing Greater Yellowstone Ecosystem.

Understanding the density-dependent processes that drive population demography in a changing world is critical in ecology, yet measuring performance-density relationships in long-lived mammalian species demands long-term data, limiting scientists' ability to observe such mechanisms. We tested performance-density relationships for an opportunistic omnivore, grizzly bears (Ursus arctos, Linnaeus, 1758) in the Greater Yellowstone Ecosystem, with estimates of body composition (lean body mass and percent body fat) serving as indicators of individual performance over two decades (2000-2020) during which time pronounced environmental changes have occurred. Several high-calorie foods for grizzly bears have mostly declined in recent decades (e.g., whitebark pine [Pinus albicaulis, Engelm, 1863]), while increasing human impacts from recreation, development, and long-term shifts in temperatures and precipitation are altering the ecosystem. We hypothesized that individual lean body mass declines as population density increases (H1), and that this effect would be more pronounced among growing individuals (H2). We also hypothesized that omnivory helps grizzly bears buffer energy intake from changing foods, with body fat levels being independent from population density and environmental changes (H3). Our analyses showed that individual lean body mass was negatively related to population density, particularly among growing-age females, supporting H1 and partially H2. In contrast, population density or sex had little effect on body fat levels and rate of accumulation, indicating that sufficient food resources were available on the landscape to accommodate successful use of shifting food sources, supporting H3. Our results offer important insights into ecological feedback mechanisms driving individual performances within a population undergoing demographic and ecosystem-level changes. However, synergistic effects of continued climate change and increased human impacts could lead to more extreme changes in food availability and affect observed population resilience mechanisms. Our findings underscore the importance of long-term studies in protected areas when investigating complex ecological relationships in an increasingly anthropogenic world.

Fuzzy dynamic system analysis of pollution accumulation in the Anzali wetland using empirical-nonlinear aspects of an economically-socio-environmental interest conflict

Wetlands employ extensive ranges of environmental consideration, pollution control, and financial services in the premise of sustainability. Hence, the study of the pollution of the wetlands is vital. The Anzali wetland-being scoped in this research is located in the Caspian Sea vicinity, the northern part of the Persian plate. Due to proximity to densely populated rural and urban areas, large-scale industries, and agricultural activities, the wetland is exposed to various environmental problems, most of which would be water and soil pollutants. While on the other hand, it provides social, economic, and ecological advantages to local, national, and even worldwide communities in sustainable development. This wetland is in contact with some activities with the main economic benefits investigated in this study and listed in nine sectors. This study's proposed ecological model is a dynamic attitude giving the complex ecological feedback mechanisms to integrate economic aspects. While introducing the wetland restoration level, solving the given model's governing equations specifies the wetland's critical points by providing nonlinear equations between economic and ecological parameters. They were also introduced and applied an empirical fuzzy method solution for the dynamic state analysis of the Anzali wetland. Results show that the Anzali wetland system was irreversible in phosphorus resilience at 0.112% of the wetland entrance. By plotting the wetland's general condition, it was determined that the Anzali wetland is in high levels of contamination and needs urgent care. Finally, the risk of economic activities in the nine sections studied in this study should reach as low as reasonably practicable (ALARP) risk level via more supervision.

Fungal Facilitation in Rangelands: Do Arbuscular Mycorrhizal Fungi Mediate Resilience and Resistance in Sagebrush Steppe?

Arbuscular mycorrhizal fungi (AMF) may exert profound influences on ecosystem resilience and invasion resistance in rangelands. Maintenance of plant community structure through ecological feedback mechanisms such as facilitation of nutrient cycling and uptake by host plants, physical and chemical contributions to soil structural stability, and mediation of plant competition suggest AMF may be important facilitators in stressful arid environments. Plant-AMF interactions could influence succession by increasing native plant community resilience to drought, grazing, and fire and resistance to exotic plant invasion. However, invasive exotic plants may benefit from associations with, as well as alter, native AMF communities. Furthermore, questions remain on the role of AMF in stressful environments, specifically the mycorrhizal dependency of sagebrush (Artemisia spp.) steppe plant species. Here, we review scientific literature relevant to AMF in rangelands, with specific focus on impacts of land management, disturbance, and invasion on AMF communities in sagebrush steppe. We highlight the nature of AMF ecology as it relates to rangelands and discuss the methods used to measure mycorrhizal responsiveness. Our review found compelling evidence that AMF mediation of resilience to disturbance and resistance to invasion varies with plant and fungal community composition, including plant mycorrhizal host status, plant functional guild, and physiological adaptations to disturbance in both plants and fungi. We conclude by outlining a framework to advance knowledge of AMF in rangeland invasion ecology. Understanding the role of AMF in semiarid sagebrush steppe ecosystems will likely require multiple study approaches due to the highly variable nature of plant-AMF interactions, the complex mechanisms of resilience conference, and the unknown thresholds for responses to environmental stressors. This may require shifting away from the plant biomass paradigm of assessing mycorrhizal benefits in order to obtain a more holistic view of plant dependency on AMF, or lack thereof, in sagebrush steppe and other semiarid ecosystems.

Collapse of macrophytic communities in a eutrophicated coastal lagoon.

Collapse of macrophytic communities in a eutrophicated coastal lagoon.

A Negative Feedback Regulation of Replanted Soil Microorganisms on Plant Growth and Soil Properties of Peach

Replant disease is one of the main growth limiting factors, interfering with plant growth and yield of stone fruit trees such as peach trees. The ecological feedback mechanisms by replanted soil microbes regulating peach growth and soil structure are rarely known. In our study, rhizosphere soils collected from 18-year-old peach trees were used to plant new peach seedlings, and all soil microbes (R) and soil microbes with the size of < 100 μm (R<100) and < 40 μm (R<40) were applied into peach rhizosphere. After 90 days of microbial inoculation, compared with no microbe treatment (R0), the treatments such as R, R<40, and R<100 reduced plant growth performance (biomass, leaf number, plant height, and stem diameter) and root morphology (total length, projected area, surface area, diameter, and volume), with treatment R being the most inhibition of all other treatments. Similar response of treatment R was observed on changes in concentrations of chlorophyll a, chlorophyll b, and carotenoid. Interestingly, compared with R0 treatment, R<100 treatment produced a significant increase in glomalin-related soil protein (GRSP), percentage of water-stable aggregates in size of 0.25-0.5 mm, soil polyphenol oxidase activities and soil catalase activities. However, R treatment dramatically decreased the percentage of water-stable aggregates in size of 2-4 mm and soil peroxidase activities. Our results suggested that replanted soil microbes, especially with the size of < 100 μm, played a strong negative role on plant growth and rhizosphere biology of peach.

Ecological feedback mechanisms and variable disturbance regimes: the uncertain future of Mediterranean macroalgal forests

Loss of algal canopies can result in a shift towards a turf-dominated state, where variability in species life-history traits can determine new mechanisms of feedback, and influence the degraded system under variable regimes of disturbance. By focusing on rockpools dominated by Cystoseira brachycarpa, we tested the hypothesis that the alga Dictyopteris polypodioides could take advantage of extreme regimes of disturbance related to storms, and outcompete other turfs through a distinctive combination of life traits. Replacement of the canopy was initially driven by a mix of taxon-specific life-traits and resulting assemblages were susceptible to intense events of disturbance. Subsequently, D. polypodioides dominated removal quadrats, favored by density-dependent abilities to intercept more light and reach larger size than the rest of turf. These new positive feedbacks may contribute to maintain the modified state of the system and influence its ability to withstand extreme abiotic conditions.

Bio-geochemical Circulation of Nitrogen in Lakes and the Role of Microorganisms

In this paper, the nitrogen forms of lacustrine sediments and their roles in biogeochemical cycles were studied. The effects of nitrogen on water-sediments - physical, chemical and biological processes in submerged plant systems, and understanding the physiological and ecological effects and feedback mechanism of submerged macrophytes on eutrophic water bodies can provide a scientific basis for lake endogenous pollution control. The in situ experiments were used to analyze the spatial distribution of ammonia nitrogen concentration, total organic carbon concentration, nitrification activity and the number of ammonia-oxidizing bacteria in Shahe reservoir and the Yangwa depression. Combined with the pollution characteristics and actual characteristics of the two sections, it is found that the concentration of nitrogen and the nitrifying active water at the two gates of Shahe reservoir and Yangwa gate are similar.

Behavioral self-organization underlies the resilience of a coastal ecosystem

Self-organized spatial patterns occur in many terrestrial, aquatic, and marine ecosystems. Theoretical models and observational studies suggest self-organization, the formation of patterns due to ecological interactions, is critical for enhanced ecosystem resilience. However, experimental tests of this cross-ecosystem theory are lacking. In this study, we experimentally test the hypothesis that self-organized pattern formation improves the persistence of mussel beds (Mytilus edulis) on intertidal flats. In natural beds, mussels generate self-organized patterns at two different spatial scales: regularly spaced clusters of mussels at centimeter scale driven by behavioral aggregation and large-scale, regularly spaced bands at meter scale driven by ecological feedback mechanisms. To test for the relative importance of these two spatial scales of self-organization on mussel bed persistence, we conducted field manipulations in which we factorially constructed small-scale and/or large-scale patterns. Our results revealed that both forms of self-organization enhanced the persistence of the constructed mussel beds in comparison to nonorganized beds. Small-scale, behaviorally driven cluster patterns were found to be crucial for persistence, and thus resistance to wave disturbance, whereas large-scale, self-organized patterns facilitated reformation of small-scale patterns if mussels were dislodged. This study provides experimental evidence that self-organization can be paramount to enhancing ecosystem persistence. We conclude that ecosystems with self-organized spatial patterns are likely to benefit greatly from conservation and restoration actions that use the emergent effects of self-organization to increase ecosystem resistance to disturbance.

Population consequences of individual heterogeneity in life histories: overcompensation in response to harvesting of alternative reproductive tactics

Alternative reproductive tactics (ARTs) are examples of individual heterogeneity in which males adopt one of typically two alternative strategies to mate with females: males are either large, armed fighters or small, benign sneakers. ART expression is often conditionally determined, and variation in the expression of conditional ARTs due to genetic and/or environmental influences can greatly affect population composition and trajectory. For example, ecological feedback mechanisms resulting from strong density‐dependent competition over food have been suggested to explain the observation that the harvesting of scramblers (= sneakers) in closed populations of the bulb mite Rhizoglyphus robini did not result in an increase (expected from quantitative genetics theory) but decrease in fighter expression. Here, we exposed closed bulb mite populations to selective fighter or scrambler harvesting for 5–6 generations under abundant food (to halt ecological feedbacks through density‐dependence) to confirm predictions from quantitative genetics theory. However, we found no evolutionary shift in ART expression; rather, we observed an overcompensatory ecological response, whereby the number of fighters increased when we harvested them. Treatment effects on scrambler numbers could not be tested as there were too few in the experimental populations. Further experiments revealed that starved fighters preferentially killed immature males and immature fighters; possibly to reduce male‐male competition as e.g. immature fighters have not yet developed their lethal weaponry. If this is so, then harvesting adult fighters reduced the killing pressure on immature males in our experiment, which resulted in an overcompensatory number of immature fighters that matured as adults. Our results highlight the complexity of how individual heterogeneity in ARTs affects the ecological and evolutionary processes that determine population fluctuations.

The fundamental role of ecological feedback mechanisms for the adaptive management of seagrass ecosystems-a review.

Seagrass meadows are vital ecosystems in coastal zones worldwide, but are also under global threat. One of the major hurdles restricting the success of seagrass conservation and restoration is our limited understanding of ecological feedback mechanisms. In these ecosystems, multiple, self-reinforcing feedbacks can undermine conservation efforts by masking environmental impacts until the decline is precipitous, or alternatively they can inhibit seagrass recovery in spite of restoration efforts. However, no clear framework yet exists for identifying or dealing with feedbacks to improve the management of seagrass ecosystems. Here we review the causes and consequences of multiple feedbacks between seagrass and biotic and/or abiotic processes. We demonstrate how feedbacks have the potential to impose or reinforce regimes of either seagrass dominance or unvegetated substrate, and how the strength and importance of these feedbacks vary across environmental gradients. Although a myriad of feedbacks have now been identified, the co-occurrence and likely interaction among feedbacks has largely been overlooked to date due to difficulties in analysis and detection. Here we take a fundamental step forward by modelling the interactions among two distinct above- and belowground feedbacks to demonstrate that interacting feedbacks are likely to be important for ecosystem resilience. On this basis, we propose a five-step adaptive management plan to address feedback dynamics for effective conservation and restoration strategies. The management plan provides guidance to aid in the identification and prioritisation of likely feedbacks in different seagrass ecosystems.

Impacts of Kentucky bluegrass Invasion (Poa pratensis L.) on Ecological Processes in the Northern Great Plains

On the Ground For every complex problem there is an answer that is clear, simple, and wrong—H. L. Mencken Ecological impacts of Kentucky bluegrass invasion have gone unrecognized by land managers and researchers alike. Current management practices have contributed to increases in Kentucky bluegrass abundance. Invaded areas have altered the ecological processes of net primary productivity, hydrology, nutrient cycling, and species composition. Increased understanding of ecological processes and feedback mechanisms of invaded areas will allow managers to develop appropriate adaptive management strategies.

Human-aided admixture may fuel ecosystem transformation during biological invasions: theoretical and experimental evidence.

Biological invasions can transform our understanding of how the interplay of historical isolation and contemporary (human-aided) dispersal affects the structure of intraspecific diversity in functional traits, and in turn, how changes in functional traits affect other scales of biological organization such as communities and ecosystems. Because biological invasions frequently involve the admixture of previously isolated lineages as a result of human-aided dispersal, studies of invasive populations can reveal how admixture results in novel genotypes and shifts in functional trait variation within populations. Further, because invasive species can be ecosystem engineers within invaded ecosystems, admixture-induced shifts in the functional traits of invaders can affect the composition of native biodiversity and alter the flow of resources through the system. Thus, invasions represent promising yet under-investigated examples of how the effects of short-term evolutionary changes can cascade across biological scales of diversity. Here, we propose a conceptual framework that admixture between divergent source populations during biological invasions can reorganize the genetic variation underlying key functional traits, leading to shifts in the mean and variance of functional traits within invasive populations. Changes in the mean or variance of key traits can initiate new ecological feedback mechanisms that result in a critical transition from a native ecosystem to a novel invasive ecosystem. We illustrate the application of this framework with reference to a well-studied plant model system in invasion biology and show how a combination of quantitative genetic experiments, functional trait studies, whole ecosystem field studies and modeling can be used to explore the dynamics predicted to trigger these critical transitions.

Incentives, social–ecological feedbacks and European fisheries

The European Common Fisheries Policy (CFP) has failed to deliver on social, economic and ecological goals. This failure is in part the result of a number of social–ecological feedback mechanisms. The policy is currently undergoing reform, with unknown practical outcomes. Here, relatively successful fisheries policies outside the European Union are reviewed. Through interviews and workshops with scientists, managers and other stakeholders, complemented with literature reviews, practices that can create incentives for long-term sustainability are investigated. The focus is on how the provision of clear and trusted scientific evidence can stimulate defensible decisions, in turn creating incentives for compliance, leading to positive social–ecological outcomes. Despite differences between Europe and the investigated case studies, the prospects of an increased regionalization within the European CFP provides the best starting point for implementing best practice identified in this study.

Adaptive dynamics of cooperation may prevent the coexistence of defectors and cooperators and even cause extinction.

It has recently been demonstrated that ecological feedback mechanisms can facilitate the emergence and maintenance of cooperation in public goods interactions: the replicator dynamics of defectors and cooperators can result, for example, in the ecological coexistence of cooperators and defectors. Here we show that these results change dramatically if cooperation strategy is not fixed but instead is a continuously varying trait under natural selection. For low values of the factor with which the value of resources is multiplied before they are shared among all participants, evolution will always favour lower cooperation strategies until the population falls below an Allee threshold and goes extinct, thus evolutionary suicide occurs. For higher values of the factor, there exists a unique evolutionarily singular strategy, which is convergence stable. Because the fitness function is linear with respect to the strategy of the mutant, this singular strategy is neutral against mutant invasions. This neutrality disappears if a nonlinear functional response in receiving benefits is assumed. For strictly concave functional responses, singular strategies become uninvadable. Evolutionary branching, which could result in the evolutionary emergence of cooperators and defectors, can occur only with locally convex functional responses, but we illustrate that it can also result in coevolutionary extinction.

Operating Hatcheries within an Ecosystem Context Using the Adaptive Stocking Concept

AbstractAnnual differences in ecological interactions between hatchery origin fish and the taxa that interact with them should be considered when managing hatcheries because of the potential for impacts to target and non‐target taxa (i.e., taxa that are not the target of a management action). A major component of the traditional hatchery paradigm is to release approximately the same number of fish of the same species every year from the same location(s) regardless of ecological conditions. This paradigm occurs in integrated and segregated hatchery programs and generally ignores ecological feedback mechanisms within the environment that can reduce survival of hatchery and wild fish. In addition, it assumes that the carrying capacity of the environment is static and underseeded, which if incorrect can result in replacement of wild fish by hatchery con‐specifics. Furthermore, practitioners of the paradigm may not consider impacts to other species that are not the target of enhancement or assumes impacts to be acceptable. To address these issues, I describe an alternative approach that prescribes stocking in places and times when: (1) ecosystem indicators suggest that risks to non‐target taxa are acceptable, (2) the environment is near or below carrying capacity or density‐dependent impacts are considered acceptable, and (3) ecological feedback mechanisms are in a desirable state. Indicators can also be used to refine fish rearing and stocking practices to enhance ecosystem benefits. According to this concept, fish would not be stocked in places and at times where ecosystem indicators are unfavorable. Although there are many potential ecological, genetic, and economic benefits of context‐specific hatchery releases, the concept should be tested before it is applied broadly. This concept may be untenable in areas with legally‐mandated release locations and numbers, or unnecessary for hatchery programs where all management goals are met.

Mitigation of global climate change – control of greenhouse gas flux by microbes

The role of microbes in ecosystems is generally underappreciated. In any ecosystem microbial biomass represents a large fraction of the macronutrients (C, N, P and S), microbial biochemical activity often dominates transformations of key compounds, and microbial behaviour and physiological activity influence translocation of chemical species. However, perhaps most importantly of all, their rapid growth rates give them a fast feedback response time. Microbes have a greater capacity to participate in ecological feedback mechanisms that contribute to homeostasis than other biological groups. All this means that microbes will be at the forefront of the global response to climate change. They will respond faster and at a larger scale than us. Our generation has the option of managing this global microbial response, either via strategies to adapt to climate change or via introduction of strategies to mitigate climate change.

Diversity and Ecology of Biocontrol Pseudomonas spp. in Agricultural Systems

ABSTRACT Diverse Pseudomonas spp. may act as biological controls of plant pathogens, but the ecology of those natural populations is not well understood. And, while biocontrol potential has been identified in multiple pseudomonad strains, the linkages between genotype and phenotype have yet to be fully delineated. However, intensive studies of one class of biocontrol strains, i.e., those that can produce 2,4-diacetylphloroglucionl (DAPG), have provided new insights into the diversity, distribution, and interactions of biocontrol pseudomonads. Those studies also laid the foundation for future research and development of pseudomonad-based biocontrol strategies. Over the past several years, numerous studies have also revealed that biocontrol pseudomonads are widely distributed in agricultural soils, and that multiple crop and soil factors can affect their abundance and activities. Recent work has shown that a variety of farm management practices that reduce soilborne disease pressure can also alter the rhizosphere abundance of DAPG producers in complex ways. Such studies provide support for the hypothesis of an ecological feedback mechanism whereby a native biocontrol population increase and subsequently reduce root disease severity following infection. It is well established that complex biological interactions can take place among bio-control pseudomonads, plant pathogens, their hosts, and other members of the microbial community. The net result of such interactions likely dilutes biocontrol efficacy at the field scale. Nonetheless, inoculation can be effective, and several successful applications of biocontrol pseudomonads have been developed. Future applications of microbial ecology research will hopefully improve the consistency and efficacy of bio-control mediated by Pseudomonas spp. Current applications and future opportunities for improving pseudomonad-based biological control are discussed.