Ecosystem engineering in space and time

The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than 10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism – engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences.     

Ecosystem engineering as an energy transfer process: a simple agent-based model

Ecosystem engineers are defined as organisms who modulate the availability of resources for themselves and other organisms by physically changing the environment. Ecosystem engineering is a well-recognised ecological interaction, but there is a limited number of general models due to the recent development of the field. Agent-based models are often used to study how organisms respond to changing environments and are suitable for modelling ecosystem engineering. To our knowledge, agent-based methodology has not yet been used to model ecosystem engineering. In this paper, we develop a simple agent-based population dynamics model of ecosystem engineering as an energy transfer process. We apply energy budget approach to conceptually explain how ecosystem engineers transfer energy to the environment and define various types of energy transfers relative to their effects on the engineers and other organisms. We simulate environments with various levels of resource abundance and compare the results of the model without ecosystem engineering agents to the model with ecosystem engineering agents. We find that in environments with higher levels of resources, the presence of ecosystem engineers increases the average carrying capacity and the strength of population fluctuations, while in environments with lower levels of resources, ecosystem engineering mitigates fluctuations, increases average carrying capacity and makes environments more resilient. Finally, we discuss about the further application of agent-based modelling for the theoretical and experimental development of the ecosystem engineering concept.     

Interactions between seagrasses and burrowing ghost shrimps and their influence on infaunal assemblages

The current study examined the direct interactions between intertidal seagrasses (Zosteraceae) and burrowing ghost shrimps (Callianassidae) and their influence on associated infaunal assemblages. Reciprocal transplant experiments conducted in two temperate regions revealed different interactions between both types of organism. In the U.S.A., seagrass prospered in all treatments, irrespective of the presence of ghost shrimp, whilst ghost shrimp declined in plots containing seagrass. In New Zealand, neither transplanted ghost shrimp nor seagrass became established in experimental plots, at the same time, neither type of organism appeared to be affected by the experimental addition of transplants. The differences in interactions between seagrass and ghost shrimp appeared to be related to seasonal differences in the timing of the transplant experiments and the pairing of particular ghost shrimp and seagrass species in each region. Infaunal assemblages showed distinct differences between seagrass and ghost shrimp treatments and reflected the dominant type of organism present. In treatments where transplanted seagrass or ghost shrimp became established, assemblage composition shifted in accordance with the type of transplanted organism. Differences in assemblage composition were characterised by higher relative abundances of discriminating taxa in treatments dominated by seagrass. The overall patterns of infaunal assemblage composition were correlated with a number of variables including the number of shoots, above-, below-ground seagrass biomass, % fines/sand, % total organic carbon, and sediment chlorophyll a. Findings from this study highlight the functional importance of intertidal seagrasses and burrowing ghost shrimps and reveal some of the ecological repercussions associated with changes in the distribution of these sympatric ecosystem engineers.     

生态系统质量及其状态演变的生态学理论和评估方法之探索

生态文明建设和生态环境治理是国家治理的基本任务之一,我国已经明确提出了提升生态系统质量和稳定性的目标。然而,生态系统质量的科学概念及其状态演变的评估理论和方法却是一直困扰学术界且尚未形成广泛共识的难题。本文在梳理生态系统质量的科学概念及其状态演变研究进展基础上,借鉴物质生产的产品质量、质量管理和质量评价概念,论述了生态系统质量概念及生态学理论基础,从生态系统的自然属性-社会属性-经济属性及其相互关系,生态系统组分-结构-过程-功能-服务-功效的级联关系,系统要素-系统-环境互馈关系,以及生态系统的状态波动-数量变化-质量改变的逻辑关系等视角,讨论了生态系统质量及演变的科学内涵,进而从自然资源环境系统、典型生态系统、区域宏观生态系统、生态工程效应/功效等方面,提出了多应用目标的生态系统质量变化评估的视角和方法。     

Using ecosystem engineers to restore ecological systems

Ecosystem engineers affect other organisms by creating, modifying, maintaining or destroying habitats. Despite widespread recognition of these often important effects, the ecosystem engineering concept has yet to be widely used in ecological applications. Here, we present a conceptual framework that shows how consideration of ecosystem engineers can be used to assess the likelihood of restoration of a system to a desired state, the type of changes necessary for successful restoration and how restoration efforts can be most effectively partitioned between direct human intervention and natural ecosystem engineers.     

Autochthonous or allochthonous resources determine the characteristic population dynamics of ecosystem engineers and their impacts

Ecosystem engineering, or the modification of physical environments by organisms, can influence trophic interactions and thus food web dynamics. Although existing theory exclusively considers engineers using autochthonous resources, many empirical studies show that they often depend on allochthonous resources. By developing a simple mathematical model involving an ecosystem engineer that modifies the physical environment through its activities, its resource, and physical environment modified by the engineer, we compare the effects of autochthonous and allochthonous resources on the dynamics and stability of community with ecosystem engineers. To represent a variety of real situations, we consider engineers that alter either resource productivity, engineer feeding rate on the resource, or engineer mortality, and incorporate time-lagged responses of the physical environment. Our model shows that the effects of ecosystem engineering on community dynamics depend greatly on resource types. When the engineer consumes autochthonous resources, the community can exhibit oscillatory dynamics if the engineered environment affects engineer’s feeding rate or mortality. These cyclic behaviors are, however, stabilized by a slowly responding physical environment. When allochthonous resources are supplied as donor-controlled, on the other hand, the engineer population is unlikely to oscillate but instead can undergo unbounded growth if the engineered environment affects resource productivity or engineer mortality. This finding suggests that ecosystem engineers utilizing allochthonous resources may be more likely to reach high abundance and cause strong impacts on ecosystems. Our results highlight that community-based, compounding effects of trophic and physical biotic interactions of ecosystem engineers depend crucially on whether the engineers utilize autochthonous or allochthonous resources.     

Water quality assessment in shrimp culture using an analytical hierarchical process

Water quality assessment is an important activity for controlling harmful crisis in aquaculture systems. The objective of our study was to develop a new Water Quality Index focused on monitoring of shrimp farms; detecting poor water quality and preventing negative effects in the ecosystem. Usually, several water quality parameters are monitored and measured in a shrimp farm during a farming period. Those parameters are classified according to their negative effects in the ecosystem and their respective allowed limits are also defined. The proposed Water Quality Index assigns a priority level to each water parameter through a new analytical hierarchical process (AHP), which allows an accurate assessment of the water quality. Our proposed index was applied to assess the water quality condition in extensive shrimp farms in Mexico. A comparison between our approach and those proposed in the literature shows its good performance when real environments are assessed.     

Ecosystem engineering affects ecosystem functioning in high-Andean landscapes

Ecosystem engineers are organisms that change the distribution of materials and energy in the abiotic environment, usually creating and maintaining new habitat patches in the landscape. Such changes in habitat conditions have been widely documented to affect the distributions and performances of other species but up to now no studies have addressed how such effects can impact the biotically driven physicochemical processes associated with these landscapes, or ecosystem functions. Based on the widely accepted positive relationship between species diversity and ecosystem functions, we propose that the effects of ecosystem engineers on other species could have an impact on ecosystem functions via two mutually inclusive mechanisms: (1) by adding new species into landscapes, hence increasing species diversity; and (2) by improving the performances of species already present in the landscape. To test these hypotheses, we focused on the effects of a high-Andean ecosystem engineer, the cushion plant Azorella monantha, by comparing the accumulation of plant biomass and nitrogen fixed in plant tissues as species richness increases in landscapes with and without the engineer species. Our results show that both ecosystem functions increased with species richness in both landscape types, but landscapes including A. monantha cushions reached higher outcomes of plant biomass and nitrogen fixed in plant tissues than landscapes without cushions. Moreover, our results indicate that such positive effects on ecosystem functions could be mediated by the two mechanisms proposed above. Then, given the conspicuousness of ecosystem engineering in nature and its strong influence on species diversity, and given the well-known relationship between species diversity and ecosystem function, we suggest that the application of the conceptual framework proposed herein to other ecosystems would help to advance our understanding of the forces driving ecosystem functioning. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Functional groups of ecosystem engineers: a proposed classification with comments on current issues

Ecologists have long known that certain organisms fundamentally modify, create, or define habitats by altering the habitat's physical properties. In the past 15 years, these processes have been formally defined as "ecosystem engineering", reflecting a growing consensus that environmental structuring by organisms represents a fundamental class of ecological interactions occurring in most, if not all, ecosystems. Yet, the precise definition and scope of ecosystem engineering remains debated, as one should expect given the complexity, enormity, and variability of ecological systems. Here I briefly comment on a few specific current points of contention in the ecosystem engineering concept. I then suggest that ecosystem engineering can be profitably subdivided into four narrower functional categories reflecting four broad mechanisms by which ecosystem engineering occurs: structural engineers, bioturbators, chemical engineers, and light engineers. Finally, I suggest some conceptual model frameworks that could apply broadly within these functional groups.     

Ecosystem engineering and biodiversity in coastal sediments: posing hypotheses

Coastal sediments in sheltered temperate locations are strongly modified by ecosystem engineering species such as marsh plants, seagrass, and algae as well as by epibenthic and endobenthic invertebrates. These ecosystem engineers are shaping the coastal sea and landscape, control particulate and dissolved material fluxes between the land and sea, and between the benthos and the passing water or air. Above all, habitat engineering exerts facilitating and inhibiting effects on biodiversity. Despite a strongly growing interest in the functional role of ecosystem engineering over the recent years, compared to food web analyses, the conceptual understanding of engineering-mediated species interactions is still in its infancy. In the present paper, we provide a concise overview on current insights and propose two hypotheses on the general mechanisms by which ecosystem engineering may affect biodiversity in coastal sediments. We hypothesise that autogenic and allogenic ecosystem engineers have inverse effects on epibenthic and endobenthic biodiversity in coastal sediments. The primarily autogenic structures of the epibenthos achieve high diversity at the expense of endobenthos, whilst allogenic sediment reworking by infauna may facilitate other infauna and inhibits epibenthos. On a larger scale, these antagonistic processes generate patchiness and habitat diversity. Due to such interaction, anthropogenic influences can strongly modify the engineering community by removing autogenic ecosystem engineers through coastal engineering or bottom trawling. Another source of anthropogenic influences comes from introducing invasive engineers, from which the impact is often hard to predict. We hypothesise that the local biodiversity effects of invasive ecosystem engineers will depend on the engineering strength of the invasive species, with engineering strength defined as the number of habitats it can invade and the extent of modification. At a larger scale of an entire shore, biodiversity need not be decreased by invasive engineers and may even increase. On a global scale, invasive engineers may cause shore biota to converge, especially visually due to the presence of epibenthic structures.     

An examination of the spatial and temporal generality of the influence of ecosystem engineers on the composition of associated assemblages

The present study evaluated the generality of ecosystem engineering processes by examining the influence of sympatric burrowing shrimps (Callianassidae) and intertidal seagrasses (Zosteraceae) on benthic assemblage composition in two temperate regions, south-eastern New Zealand and north-western U.S.A. In each region, intertidal macrofauna assemblage composition was determined at sites of different burrowing shrimp/seagrass density and where both species co-occured, in three different size estuaries/tidal inlets, on two occasions. Results from both regions showed that the presence of shrimps and seagrasses consistently influenced the composition of the associated infaunal assemblages at all sites, in both summer and winter. Macrofauna assemblages at shrimp sites were significantly different to those at seagrass-only and mixed sites, whereas the composition of the latter sites was similar. The differences observed between sites were best explained by sediment variables. In New Zealand, % fines and seagrass debris showed the highest correlation to differences in assemblage composition, and in the U.S.A. % fines, % carbon and sediment turnover (by shrimp) appeared to be the most important environmental parameters measured. Four to six taxa exhibited the greatest discriminating significance (including corophiid amphipods, spionid polychaetes and oligochaetes) for dissimilarities in assemblage composition observed at the different sites, with generally lower abundances at shrimp than at seagrass sites. The present study highlights the functional importance of seagrasses and bioturbating shrimps as ecosystem engineers in soft-sediment environments, and reveals the generality of their influence on associated macro-invertebrate assemblages. The findings also allow for further development of a heuristic model for ecosystem engineering by shrimp and seagrass which indicate that numerical models that aim to explore the relationship between ecosystem engineer populations and habitat modification should be expanded to capture the interaction of co-occurring engineers and be both spatially and temporally explicit.     

Ecosystem engineering effects on species diversity across ecosystems: a meta‐analysis

Ecosystem engineering is increasingly recognized as a relevant ecological driver of diversity and community composition. Although engineering impacts on the biota can vary from negative to positive, and from trivial to enormous, patterns and causes of variation in the magnitude of engineering effects across ecosystems and engineer types remain largely unknown. To elucidate the above patterns, we conducted a meta‐analysis of 122 studies which explored effects of animal ecosystem engineers on species richness of other organisms in the community. The analysis revealed that the overall effect of ecosystem engineers on diversity is positive and corresponds to a 25% increase in species richness, indicating that ecosystem engineering is a facilitative process globally. Engineering effects were stronger in the tropics than at higher latitudes, likely because new or modified habitats provided by engineers in the tropics may help minimize competition and predation pressures on resident species. Within aquatic environments, engineering impacts were stronger in marine ecosystems (rocky shores) than in streams. In terrestrial ecosystems, engineers displayed stronger positive effects in arid environments (e.g. deserts). Ecosystem engineers that create new habitats or microhabitats had stronger effects than those that modify habitats or cause bioturbation. Invertebrate engineers and those with lower engineering persistence (<1 year) affected species richness more than vertebrate engineers which persisted for >1 year. Invertebrate species richness was particularly responsive to engineering impacts. This study is the first attempt to build an integrative framework of engineering effects on species diversity; it highlights the importance of considering latitude, habitat, engineering functional group, taxon and persistence of their effects in future theoretical and empirical studies.     

Structure and function of hemocyanin from thalassinid shrimp

Summary The subunit structure, association equilibria, and oxygen binding of the hemocyanins of three thalassinid shrimp have been investigated. The organismsCallianassa californiensis, Callianassa gigas andUpogebia pugettensis are found in similar but distinct habitats in a limited region. All of the hemocyanins exhibit a common pattern of subunit structure, but differ in details of the response of that structure to variations in ionic environment. All three are heterogeneous in polypeptide chain composition, but have quite different distributions of components. The oxygen binding of the twoCallianassa hemocyanins is virtually identical under conditions approximating physiological; that ofUpogebia, which shows lower tolerance to anoxia, is significantly different. These similarities and differences are discussed in terms of the physiological requirements of the species.     

SPI-ing on the seafloor: characterising benthic systems with traditional and in situ observations

This work aimed to show that the sea bed of two environmentally-different regions of the North Sea varies both spatially and temporally with respect to their biological communities and bioturbation characteristics. The two contrasting sites studied were north of the Dogger Bank (ND) (85 m) and the Oyster Grounds (OG) (45 m). The physical environment varied between and within sites, mainly influenced by sediment chlorophyll a content and water temperature. Our data revealed that the depth of the apparent Redox Potential Discontinuity (aRPD) layer at OG varied between 2.2 cm in February and 6.5 cm in October; evidence of bioturbation activity (e.g., feeding voids) was observed within the sediment profile. In contrast, at the ND site the aRPD values ranged from 1.7 cm in February to 2.5 cm in May and feeding voids and infaunal burrows were restricted to sediment depths far shallower than those observed at OG. Communities at ND were dominated by a number of surficial-sediment dwelling polychaete species (e.g., Notomastus latericeus, capitellids) while those of OG were dominated by the brittlestar Amphiura filiformis, together with significant numbers of deeper-dwelling taxa such as the ghost shrimp Callianassa subterranea and the bivalve mollusc Corbula gibba. Our data imply that regions of the North Sea which experience dissimilar environmental conditions not only possess different infaunal communities but also contrasting seasonal fluctuations and bioturbation capacities. The ecological implications of these findings, including inferences for carbon and nutrient cycling, are discussed in relation to the wider North Sea ecosystem.     

Patch dynamics in a landscape modified by ecosystem engineers

Ecosystem engineers, organisms that modify the environment, have the potential to dramatically alter ecosystem structure and function at large spatial scales. The degree to which ecosystem engineering produces large-scale effects is, in part, dependent on the dynamics of the patches that engineers create. Here we develop a set of models that links the population dynamics of ecosystem engineers to the dynamics of the patches that they create. We show that the relative abundance of different patch types in an engineered landscape is dependent upon the production of successful colonists from engineered patches and the rate at which critical resources are depleted by engineers and then renewed. We also consider the effects of immigration from either outside the system or from engineers that are present in non-engineered patches, and the effects of engineers that can recolonize patches before they are fully recovered on the steady state distribution of different patch types. We use data collected on the population dynamics of a model engineer, the beaver, to estimate the per-patch production rate of new colonists, the decay rate of engineered patches, and the recovery rate of abandoned patches. We use these estimated parameters as a baseline to determine the effects of varying parameters on the distribution of different patch types. We suggest a number of hypotheses that derive from model predictions and that could serve as tests of the model.     

The emergence of ecological engineering as a discipline

Pioneering efforts in ecological engineering (a precedent setting engineering and applied science discipline in which the self-engineering capabilities of ecosystems are managed for the benefit of the environment and humankind) research and practice have proven to be tremendous strides toward establishing a new engineering discipline with a science base in ecology. Case studies, demonstrations and applications pertaining to restoration, rehabilitation, conservation, sustainability, reconstruction, remediation and reclamation of ecosystems using ecological engineering techniques are numerous. This has brought the field to the current level where many scientists and engineers adequately support the concept of, and need for, ecological engineering, and generally agree that ecological engineering has been sufficiently defined. There is also general agreement that full emergence as an engineering discipline remains a difficult task. Certain general characteristics of existing engineering disciplines can guide the emergence of ecological engineering and thus are a vital context covered in this paper. From the context of engineering practice, three concepts are evident including: (1) establishment of formal foundations for ecological engineering research and development; (2) development of core ecological engineering sciences and curricula; and (3) certification in ecological design. These elements are important components of a formal approach to develop ecological engineering as a principled, quantitative, recognized, practical, novel, and formal engineering discipline that coalesces past and future research and practice into cohesive underpinnings.     

Sedimentary context controls the influence of ecosystem engineering by bioturbators on microbial processes in river sediments

By modifying the physical environment, ecosystem engineers can have inordinately large effects on surrounding communities and ecosystem functioning. However, the significance of engineering in ecosystems greatly depends on the physical characteristics of the engineered habitats. Mechanisms underlying such context‐dependent impact of engineers remain poorly understood even though they are crucial to establish general predictions concerning the contribution of engineers to ecosystem structure and function. The present study aimed to decrypt such mechanisms by determining how the environmental context modulates the effects of ecosystem engineers (bioturbators) on microorganisms in river sediments. To test the effects of environmental context on the role of bioturbators in sediments, we used mesocosms and recreated two sedimentary contexts in the laboratory by adding a layer of either fine or coarse sand at the top of a gravel‐sand matrix. For each sediment context, we examined how the sediment reworking activity of a bioturbating tubificid worm (Tubifex tubifex) generated changes in the physical (sediment structure and permeability) and abiotic environments (hydraulic discharge, water chemistry) of microorganisms. Microbial characteristics (abundances, activities) and leaf litter decomposition – a major microbially‐mediated ecological process – were measured to evaluate the impact of bioturbation on biotic compartment. Our results showed that the permeability, the availability of oxygen and the activities of microorganisms were reduced in sediments covered with fine sand, in comparison with sediments covered with coarse sand. Tubifex tubifex significantly increased permeability (by about six‐fold), restored aerobic conditions and ultimately stimulated microbial communities (resulting in a 30% increase in leaf litter breakdown rate) in sediments covered with fine sand. In contrast T. tubifex had low effects in sediments topped by coarse sand, where O₂ was already available for hyporheic microorganisms. Our study supports the idea that context dependency mainly modulates the effects of engineering by controlling the ability of engineers to create changes on abiotic (O₂ in the present study) factors that are limiting for surrounding communities.     

Ecotone formation through ecological niche construction: the role of biodiversity and species interactions

Rapid changes in species composition, also known as ecotones, can result from various causes including rapid changes in environmental conditions, or physiological thresholds. The possibility that ecotones arise from ecological niche construction by ecosystem engineers has received little attention. In this study, we investigate how the diversity of ecosystem engineers, and their interactions, can give rise to ecotones. We build a spatially explicit dynamical model that couples a multispecies community and its abiotic environment. We use numerical simulations and analytical techniques to determine the biotic and abiotic conditions under which ecotone emergence is expected to occur, and the role of biodiversity therein. We show that the diversity of ecosystem engineers can lead to indirect interactions through the modification of their shared environment. These interactions, which can be either competitive or mutualistic, can lead to the emergence of discrete communities in space, separated by sharp ecotones where a high species turnover is observed. Considering biodiversity is thus critical when studying the influence of species–environment interactions on the emergence of ecotones. This is especially true for the wide range of species that have small to moderate effects on their environment. Our work highlights new mechanisms by which biodiversity loss could cause significant changes in spatial community patterns in changing environments.     

Biomechanical warfare in ecology; negative interactions between species by habitat modification

Since the introduction of the term ecosystem engineering by Jones et al. many studies have focused on positive, facilitative interactions caused by ecosystem engineering. Much less emphasis has been placed on the role of ecosystem engineering in causing negative interactions between species. Here, we report on negative interactions between two well known ecosystem engineers occurring at the interface of salt marsh and intertidal flat (i.e. common cordgrass Spartina anglica and lugworms Arenicola marina ), via modification of their joint habitat. A field survey indicated that, although both species share a common habitat, they rarely co-occur on small spatial scales (<1 m). Experiments in the field and in mesocosms reveal that establishment of small Spartina plants is inhibited in Arenicola -dominated patches because of low sediment stability induced by the lugworms. In turn, Arenicola establishment in Spartina -dominated patches is limited by high silt content, compactness and dense rooting of the sediment caused by Spartina presence. Our results show that negative interactions by modification of the environment can result in rapid mutual exclusion, particularly if adverse effects of habitat modification are strong and if both species exhibit positive feedbacks. This illustrates the potential for negative interactions via the environment to affect community composition.     

Considerations in Developing a Functional Approach to the Governance of Large Marine Ecosystems

Interest in the management of the environment and its resources on an ecosystem basis has been increasing, in both terrestrial and marine contexts. In recent years, the concept of the large marine ecosystem has become a point of focus at the national and international levels as a possible unit for management of ocean and coastal areas. An ecosystem approach, however, challenges the manner in which marine resources and the environment that sustains them have been managed in the past. Governance is a key element in ecosystem management and encompasses the formal and informal arrangements, institutions, and mores that determine how resources and the environment are utilized. This study explores some of the problems, concepts, and principles involved in efforts to provide needed governance arrangements if large marine ecosystem-based management is to be implemented and made effective.