Environmental correlates of food chain length

Gelatinous filter feeders increase ecosystem efficiency

Gelatinous filter feeders (e.g., salps, doliolids, and pyrosomes) have high filtration rates and can feed at predator:prey size ratios exceeding 10,000:1, yet are seldom included in ecosystem or climate models. We investigated foodweb and trophic dynamics in the presence and absence of salp blooms using traditional productivity and grazing measurements combined with compound-specific isotopic analysis of amino acids estimation of trophic position during Lagrangian framework experiments in the Southern Ocean. Trophic positions of salps ranging 10-132 mm in size were 2.2 ± 0.3 (mean ± std) compared to 2.6 ± 0.4 for smaller (mostly crustacean) mesozooplankton. The mostly herbivorous salp trophic position was maintained despite biomass dominance of ~10-µm-sized primary producers. We show that potential energy flux to >10-cm organisms increases by approximately an order of magnitude when salps are abundant, even without substantial alteration to primary production. Comparison to a wider dataset from other marine regions shows that alterations to herbivore communities are a better predictor of ecosystem transfer efficiency than primary-producer dynamics. These results suggest that diverse consumer communities and intraguild predation complicate climate change predictions (e.g., trophic amplification) based on linear food chains. These compensatory foodweb dynamics should be included in models that forecast marine ecosystem responses to warming and reduced nutrient supply.

Food webs in isolation: The food-web structure of a freshwater reservoir with armoured shores in a former coastal bay area

Many shallow coastal bays have been closed off from the sea to mitigate the risk of flooding, resulting in coastal reservoir lakes with artificial armoured shorelines. Often these enclosed ecosystems show a persistent decline in biodiversity and ecosystem services, which is likely reflected in their food-web structure. We therefore hypothesize that the food webs of coastal reservoir lakes with armoured shorelines (1) consist of relatively few species with a low food-web connectance and short food chains, and (2) are mainly fuelled by autochthonous organic matter produced in the pelagic zone. To investigate these two hypotheses, we used stable-isotope analysis to determine the food-web structure of lake Markermeer (The Netherlands), a large reservoir lake with armoured shorelines in a former coastal bay area. Contrary to expectation, connectance of the food web in lake Markermeer was comparable to other lakes, while food-chain length was in the higher range. However, the trophic links revealed that numerous macroinvertebrates and fish species in this constructed lake exhibited omnivorous feeding behaviour. Furthermore, in line with our second hypothesis, primary consumers heavily relied on pelagically derived organic matter, while benthic primary production exerted only a minor and seasonal influence on higher trophic levels. Stable-isotope values and the C:N ratio of sediment organic matter in the lake also aligned more closely with phytoplankton than with benthic primary producers. Moreover, terrestrial subsidies of organic matter were virtually absent in lake Markermeer. These findings support the notion that isolation of the lake through shore armouring and the lack of littoral habitats in combination with persistent resuspension of sediments have affected the food web. We argue that restoration initiatives should prioritize the establishment of land-water transition zones, thereby enhancing habitat diversity, benthic primary production, and the inflow of external organic matter while preserving pelagic primary production.

Long-term recovery of benthic food webs after stream restoration

The assessment of restoration success often neglects trophic interactions within food webs, focusing instead on biodiversity and community structure. Here, we analysed the long-term recovery of food web structure based on stable isotopes (δ13C and δ15N) of benthic invertebrates and quantified responses of food web metrics to time since restoration. The samples derived from twelve restored sites with different restoration ages, sampled annually from 2012 to 2021, and covering an investigation period of up to 28 years after restoration for the whole catchment. Temporal developments of the restored sites were compared to the development of two near-natural sites. The restoration measures consisted of the cessation of sewage inflow and morphological restoration of the channels. As a clear and consistent result over almost all sites, trophic similarity (proportion of co-existing species occupying similar trophic niches) increased with time since restoration, and reached values of near-natural sites, suggesting an increase in the stability and resilience of the food webs. Surprisingly, resource diversity decreased at most restored sites within 10 years after restoration, probably due to the removal of wastewater-derived resources, and a shift towards leaf litter as the dominant resource following the regrowth of the riparian vegetation. Food chain length showed no consistent pattern over time at the different sites both increasing and decreasing with time since restoration. Overall, restoration had clear effects on the food web structure of stream ecosystems. While some effects such as the increase in trophic similarity were consistent at almost all sites, others such as response of the food chain length were context dependent. The study demonstrates the potential of utilizing food web metrics, particularly trophic similarity, in restoration research to achieve a more holistic understanding of ecosystem recovery.

One Digital Health Intervention for Monitoring Human and Animal Welfare in Smart Cities: Viewpoint and Use Case

Smart cities and digital public health are closely related. Managing digital transformation in urbanization and living spaces is challenging. It is critical to prioritize the emotional and physical health and well-being of humans and their animals in the dynamic and ever-changing environment they share. Human-animal bonds are continuous as they live together or share urban spaces and have a mutual impact on each other's health as well as the surrounding environment. In addition, sensors embedded in the Internet of Things are everywhere in smart cities. They monitor events and provide appropriate responses. In this regard, accident and emergency informatics (A&EI) offers tools to identify and manage overtime hazards and disruptive events. Such manifold focuses fit with One Digital Health (ODH), which aims to transform health ecosystems with digital technology by proposing a comprehensive framework to manage data and support health-oriented policies. We showed and discussed how, by developing the concept of ODH intervention, the ODH framework can support the comprehensive monitoring and analysis of daily life events of humans and animals in technologically integrated environments such as smart homes and smart cities. We developed an ODH intervention use case in which A&EI mechanisms run in the background. The ODH framework structures the related data collection and analysis to enhance the understanding of human, animal, and environment interactions and associated outcomes. The use case looks at the daily journey of Tracy, a healthy woman aged 27 years, and her dog Mego. Using medical Internet of Things, their activities are continuously monitored and analyzed to prevent or manage any kind of health-related abnormality. We reported and commented on an ODH intervention as an example of a real-life ODH implementation. We gave the reader examples of a "how-to" analysis of Tracy and Mego's daily life activities as part of a timely implementation of the ODH framework. For each activity, relationships to the ODH dimensions were scored, and relevant technical fields were evaluated in light of the Findable, Accessible, Interoperable, and Reusable principles. This "how-to" can be used as a template for further analyses. An ODH intervention is based on Findable, Accessible, Interoperable, and Reusable data and real-time processing for global health monitoring, emergency management, and research. The data should be collected and analyzed continuously in a spatial-temporal domain to detect changes in behavior, trends, and emergencies. The information periodically gathered should serve human, animal, and environmental health interventions by providing professionals and caregivers with inputs and "how-to's" to improve health, welfare, and risk prevention at the individual and population levels. Thus, ODH complementarily combined with A&EI is meant to enhance policies and systems and modernize emergency management.

Delineating the food web structure in an Indian estuary during tropical winter employing stable isotope signatures and mixing model

The food and feeding links and sources in an impacted tropical estuary situated along India's western coast, the Ulhas River Estuary (URE) was analyzed employing the stable carbon and nitrogen isotopic signatures (δ¹³C and δ¹⁵N). Three basal carbon sources, such as mangrove leaves, particulate organic matter (phytoplankton), and detritus, were analyzed together with eight consumer groups from various trophic guilds. The δ¹³C varied from - 19.67 to - 24.61‰, whereas δ¹⁵N ranged from 6.31 to 15.39‰ from the primary consumer to the top predator species. The stable isotope mixing model developed for URE revealed a phytoplankton based pelagic food chain and detritus based benthic food chain in URE. The fairly larger value of SEA (Standard Ellipse Area) in the URE suggest a much broader food web structure and high trophic diversity in the ecosystem. Higher influence of detritus on the assimilated diet of majority of consumers and evidences of nitrogen enrichment in the basal sources such as detritus and particulate organic matter by anthropogenic activities in URE point towards nitrogen pollution and subsequent trophic disturbance in this tropical estuarine ecosystem.

Relationship between olive oil consumption and ankle-brachial pressure index in a population at high cardiovascular risk

BACKGROUND AND AIMS

The aim of this study was to ascertain the association between the consumption of different categories of edible olive oils (virgin olive oils and olive oil) and olive pomace oil and ankle-brachial pressure index (ABI) in participants in the PREDIMED-Plus study, a trial of lifestyle modification for weight and cardiovascular event reduction in individuals with overweight/obesity harboring the metabolic syndrome.

METHODS

We performed a cross-sectional analysis of the PREDIMED-Plus trial. Consumption of any category of olive oil and olive pomace oil was assessed through a validated food-frequency questionnaire. Multivariable linear regression models were fitted to assess associations between olive oil consumption and ABI. Additionally, ABI ≤1 was considered as the outcome in logistic models with different categories of olive oil and olive pomace oil as exposure.

RESULTS

Among 4330 participants, the highest quintile of total olive oil consumption (sum of all categories of olive oil and olive pomace oil) was associated with higher mean values of ABI (beta coefficient: 0.014, 95% confidence interval [CI]: 0.002, 0.027) (p for trend = 0.010). Logistic models comparing the consumption of different categories of olive oils, olive pomace oil and ABI ≤1 values revealed an inverse association between virgin olive oils consumption and the likelihood of a low ABI (odds ratio [OR] 0.73, 95% CI [0.56, 0.97]), while consumption of olive pomace oil was positively associated with a low ABI (OR 1.22 95% CI [1.00, 1.48]).

CONCLUSIONS

In a Mediterranean population at high cardiovascular risk, total olive oil consumption was associated with a higher mean ABI. These results suggest that olive oil consumption may be beneficial for peripheral artery disease prevention, but longitudinal studies are needed.

A review on mercury biogeochemistry in mangrove sediments: Hotspots of methylmercury production?

Wetlands are highly productive and biologically diverse environments that provide numerous ecosystem services, but can also be sources of methylmercury (MeHg) production and export. Mangrove wetlands contribute up to 15% of the coastal sediment carbon storage and ~10% of the particulate terrestrial carbon exported to the ocean. Thus, mercury (Hg) methylation in mangrove sediments and subsequent MeHg output to adjacent waters could have a great impact on global Hg cycling. In this review, we provide a comprehensive analysis of the literature on worldwide Hg concentrations in mangrove ecosystems, and the results reveal that a large range of total Hg (THg) and MeHg concentrations is detected in mangrove systems. Then, we discuss the potential roles of organic matter (OM) in controlling the Hg biogeochemistry in mangrove sediments. The intense OM decomposition by anoxic reduction (e.g., sulfate reduction) drastically affects sediment chemistries, such as redox potential, pH, and sulfur speciation, all of which may have a great impact on MeHg production. While the outwelling of carbon from mangroves has been extensively examined, little is known about their roles in exporting MeHg to adjacent waters. Our understanding of Hg biogeochemical processes in mangrove systems is constrained by the limited MeHg data and a lack of in-depth studies on the Hg methylation potential in this ecologically important environment. More efforts are needed to gain better insights into the contributions mangrove wetlands to the global Hg cycle.

El concepto de gremio: del feudalismo a la ecología de comunidades

Se analiza el origen y evolución del término gremio, así como su aplicación en ecología, considerando las múltiples connotaciones que se le ha dado y la confusión que se ha generado por utilizarlo de forma indebida. De igual forma, se discute la importancia de homogenizar los términos y definir de manera clara a los gremios, a fin de tener un leguaje que permita entender los alcances del término sin ambigüedades. El uso del término, así como su persistencia en estudios ecológicos, sugiere que el mismo tiene relevancia considerable dependiendo de la forma y el modo en que es empleado. El uso inadecuado o derivado de este término es arriesgado y peligroso, dado que tiende a reducir el término a una palabra vacía con múltiples significados. Más que nada, esta trivialización constituye una amenaza al uso y significado adecuado del concepto de gremio en ecología.

Periphyton consumption by an invasive snail species is greater in simplified than in complex habitats

Habitat complexity may stabilize consumer–resource interactions and reduce the probability of invasion in aquatic habitats. We tested the hypotheses that (i) higher habitat complexity reduces resource consumption independently of grazer species, but that (ii) invasive grazers have a greater influence on decreasing resources independently of habitat complexity. We performed an experiment using artificial substrates to simulate different complexity levels. We evaluated Melanoides tuberculata (O.F. Müller, 1774) and Aylacostoma chloroticum Hylton Scott, 1954 consumption of specific algal groups and the interaction between habitat complexity and grazer species. Moreover, we evaluated grazer activity on the different substrates during the experiment. The results support only the first hypothesis and indicate lower resource consumption on complex substrates compared with simpler substrates. Additionally, the effect of the grazing of the invasive species on taxon richness was greater in simplified than in complex habitats. The grazing activity on the substrate suggests a relationship between resource exploitation and habitat complexity in which the invasive grazing species visited the simple habitat less frequently. However, the effects of invasive grazers on food resources were higher on the simple substrate. The effects of grazing activity on food resources depend on the interaction between habitat complexity and grazer species. In this way, the introduction of an invasive species may have negative impacts on the structure and function of periphytic communities, mainly in simplified aquatic ecosystems.

Cryptic niche switching in a chemosymbiotic gastropod

Life stages of some animals, including amphibians and insects, are so different that they have historically been seen as different species. 'Metamorphosis' broadly encompasses major changes in organism bodies and, importantly, concomitant shifts in trophic strategies. Many marine animals have a biphasic lifestyle, with small pelagic larvae undergoing one or more metamorphic transformations before settling into a permanent, adult morphology on the benthos. Post-settlement, the hydrothermal vent gastropod Gigantopelta chessoia experiences a further, cryptic metamorphosis at body sizes around 5-7 mm. The terminal adult stage is entirely dependent on chemoautotrophic symbionts; smaller individuals do not house symbionts and presumably depend on grazing. Using high-resolution X-ray microtomography to reconstruct the internal organs in a growth series, we show that this sudden transition in small but sexually mature individuals dramatically reconfigures the organs, but is in no way apparent from external morphology. We introduce the term 'cryptometamorphosis' to identify this novel phenomenon of a major body change and trophic shift, not related to sexual maturity, transforming only the internal anatomy. Understanding energy flow in ecosystems depends on the feeding ecology of species; the present study highlights the possibility for adult animals to make profound shifts in biology that influence energy dynamics.

A mechanistic theory for aquatic food chain length

Multiple hypotheses propose an ostensibly disparate array of drivers of food chain length (FCL), with contradictory support from natural settings. Here we posit that the magnitude of vertical energy flux in food webs underlies several drivers of FCL. We show that rising energy flux fuels top-heavy biomass pyramids, promoting omnivory, thereby reducing FCL. We link this theory to commonly evaluated hypotheses for environmental drivers of FCL (productivity, ecosystem size) and demonstrate that effects of these drivers should be context-dependent. We evaluate support for this theory in lake and marine ecosystems and demonstrate that ecosystem size is the most important driver of FCL in low-productivity ecosystems (positive relationship) while productivity is most important in large and high-productivity ecosystems (negative relationship). This work stands in contrast to classical hypotheses, which predict a positive effect of productivity on FCL, and may help reconcile the contradictory nature of published results for drivers of FCL.

The evolution of ecosystem ascendency in a complex systems based model

General patterns in ecosystem development can shed light on driving forces behind ecosystem formation and recovery and have been of long interest. In recent years, the need for integrative and process oriented approaches to capture ecosystem growth, development and organisation, as well as the scope of information theory as a descriptive tool has been addressed from various sides. However data collection of ecological network flows is difficult and tedious and comprehensive models are lacking. We use a hierarchical version of the Tangled Nature Model of evolutionary ecology to study the relationship between structure, flow and organisation in model ecosystems, their development over evolutionary time scales and their relation to ecosystem stability. Our findings support the validity of ecosystem ascendency as a meaningful measure of ecosystem organisation, which increases over evolutionary time scales and significantly drops during periods of disturbance. The results suggest a general trend towards both higher integrity and increased stability driven by functional and structural ecosystem coadaptation.

Integrated trophic position decreases in more diverse communities of stream food webs

The relationship between biodiversity and ecosystem functioning is an important theme in environmental sciences. We propose a new index for configuration of the biomass pyramid in an ecosystem, named integrated trophic position (iTP). The iTP is defined as a sum of trophic positions (i.e. the average number of steps involved in biomass transfer) of all the animals in a food web integrated by their individual biomass. The observed iTP for stream macroinvertebrates ranged from 2.39 to 2.79 and was negatively correlated with the species density and the Shannon–Wiener diversity index of the local community. The results indicate a lower efficiency of biomass transfer in more diverse communities, which may be explained by the variance in edibility hypothesis and/or the trophic omnivory hypothesis. We found a negative effect of biodiversity on ecosystem functioning.

Radiocesium uptake, trophic transfer, and exposure in three estuarine fish with contrasting feeding habits

This study investigated the effects of different environmental factors on (137)Cs uptake in three subtropical estuarine fish, and the trophic transfer of (137)Cs in the fish from different preys. Our data showed that salinity, potassium, and temperature had appreciable effects on the dissolved uptake of (137)Cs in the fish, but no conclusive relationship was found between the effects of salinity and potassium concentration on the uptake. The dietary assimilation of (137)Cs was 51-55% in the omnivorous fish Siganus fuscescens when fed with macroalgae or bivalve tissues, and was much lower than those in carnivorous fish Sebastiscus marmoratus and Jarbua terapon (70-79%). Dietary pathway dominated the (137)Cs accumulation in the omnivorous and carnivorous fish, both of which exhibited strong potential to biomagnify (137)Cs from their preys. Using the biokinetic model, we demonstrated that salinity and temperature only had minor effects on the overall accumulation of (137)Cs in carnivorous species living in estuarine environment. Modeling calculation suggested that it would take 37-80 days for the fish to reach 95% of steady-state concentration, and lower somatic growth increased the time to reach steady-state in the fish.

Effect of marine protected areas (MPAs) on consumer diet: MPA fish feed higher in the food chain

Marine Protected Areas (MPAs) are often established to mitigate the effects of overfishing and other human disturbances. In Fiji these are locally managed and, where enforced, have significantly higher coral cover, higher fish biomass, and lower seaweed cover than in the adjacent, unprotected reefs (non-MPAs). We investigated how the isotopic signatures of a common, mid-level consumer, Epinephelus merra, differed among three small (0.5- 0.8km²) MPAs versus adjacent, unprotected reefs. Isotopic ratios suggested that the fish in the MPAs fed higher in the food chain than those in the adjacent non-MPAs, despite being slightly smaller in size. Calculations using a brown alga as representative of the basal level of the food chain estimate this difference to be about half a trophic level. Thus, the isotopic ratio of a mid-level consumer can be noticeably altered over scales of only a few hundred meters. This may result from more complete food webs and hence greater prey choice and availability in the MPAs and implies that MPAs affect not only species' abundance and diversity, but also diet composition and trophic biology of member individuals. Our findings suggest E. merra exhibits considerable site fidelity in its feeding biology and thus provides a localized isotopic signal of its reef of residence. If the isotopic signal of this mid-level carnivore is reflective of the composition of the food web beneath it, the signal might provide an easily obtained indication of reef conditions in that area.

Productivity, disturbance and ecosystem size have no influence on food chain length in seasonally connected rivers

The food web is one of the oldest and most central organising concepts in ecology and for decades, food chain length has been hypothesised to be controlled by productivity, disturbance, and/or ecosystem size; each of which may be mediated by the functional trophic role of the top predator. We characterised aquatic food webs using carbon and nitrogen stable isotopes from 66 river and floodplain sites across the wet-dry tropics of northern Australia to determine the relative importance of productivity (indicated by nutrient concentrations), disturbance (indicated by hydrological isolation) and ecosystem size, and how they may be affected by food web architecture. We show that variation in food chain length was unrelated to these classic environmental determinants, and unrelated to the trophic role of the top predator. This finding is a striking exception to the literature and is the first published example of food chain length being unaffected by any of these determinants. We suggest the distinctive seasonal hydrology of northern Australia allows the movement of fish predators, linking isolated food webs and potentially creating a regional food web that overrides local effects of productivity, disturbance and ecosystem size. This finding supports ecological theory suggesting that mobile consumers promote more stable food webs. It also illustrates how food webs, and energy transfer, may function in the absence of the human modifications to landscape hydrological connectivity that are ubiquitous in more populated regions.

Applications of fractals in ecology

Fractal models describe the geometry of a wide variety of natural objects such as coastlines, island chains, coral reefs, satellite ocean-color images and patches of vegetation. Cast in the form of modified diffusion models, they can mimic natural and artificial landscapes having different types of complexity of shape. This article provides a brief introduction to fractals and reports on how they can be used by ecologists to answer a variety of basic questions, about scale, measurement and hierarchy in, ecological systems.

Dimensionality of consumer search space drives trophic interaction strengths

Trophic interactions govern biomass fluxes in ecosystems, and stability in food webs. Knowledge of how trophic interaction strengths are affected by differences among habitats is crucial for understanding variation in ecological systems. Here we show how substantial variation in consumption-rate data, and hence trophic interaction strengths, arises because consumers tend to encounter resources more frequently in three dimensions (3D) (for example, arboreal and pelagic zones) than two dimensions (2D) (for example, terrestrial and benthic zones). By combining new theory with extensive data (376 species, with body masses ranging from 5.24 × 10(-14) kg to 800 kg), we find that consumption rates scale sublinearly with consumer body mass (exponent of approximately 0.85) for 2D interactions, but superlinearly (exponent of approximately 1.06) for 3D interactions. These results contradict the currently widespread assumption of a single exponent (of approximately 0.75) in consumer-resource and food-web research. Further analysis of 2,929 consumer-resource interactions shows that dimensionality of consumer search space is probably a major driver of species coexistence, and the stability and abundance of populations.

Scale and structure in natural food webs

The degree to which widely accepted generalizations about food web structure apply to natural communities was determined through examination of 50 pelagic webs sampled consistently with even taxonomic resolution of all trophic levels. The fraction of species in various trophic categories showed no significant overall trends as the number of species varied from 10 to 74. In contrast, the number of links per species increased fourfold over the range of species number, suggesting that the link-species scaling law, defined on the basis of aggregated webs, does not reflect a real ecological trend.

How many species are there on Earth?

This article surveys current answers to the factual question posed in the title and reviews the kinds of information that are needed to make these answers more precise. Various factors affecting diversity are also reviewed. These include the structure of food webs, the relative abundance of species, the number of species and of individuals in different categories of body size, along with other determinants of the commonness and rarity of organisms.

Food chains in freshwaters

There are three hypothesized controls on food-chain length (FCL): energy supply (or "resource availability"), ecosystem size and disturbance (or "environmental variation"). In this article, the evidence for controls on FCL in freshwater ecosystems is evaluated. First, the various ways FCL can be measured are defined. Food-chain length typically is estimated as (1) connectance-based FCL--an average connectance between basal resources and top consumers, (2) functional FCL--by experimental determination of functionally significant effects of a top predator on lower trophic-level biomass patterns, and (3) realized FCL--an average connectance measure weighted by energy flow between basal consumers and the consumer occupying the maximum trophic position in the food web. Second, all evidence for relationships between the three hypothetical controls and FCL in freshwater ecosystems are evaluated. The review includes studies from streams, lakes, ponds, wetlands, phytotelmata, and experimental containers. Surprisingly, few studies of FCL in freshwaters that test the same suite of controls using the same methods are found. Equally compelling results arise from case studies based on functional, realized, and connectance-based measures of FCL. Third, 10 rules of thumb that could increase similarity of future studies, thereby facilitating synthesis across systems, are suggested. Fourth, it is discussed how FCL influences the concentration of contaminants in large-bodied animals (many of which are consumed by humans) as well as the efficacy of biocontrol applications in agriculture. Finally, there is a discussion of the potential relationships between global climate change, hydrology, and FCL in freshwaters.