Trophic Compartments Research Articles

Trading off nature for nature‐based solutions: The bioeconomics of forest management for wildlife, timber, and carbon

AbstractNature‐based solutions are attracting interest for their potential to enlist ecological processes as cost‐effective and safe ways to capture and store carbon in forest ecosystems. Such solutions often need to be implemented in landscapes in which there are longer established values for other ecosystem services including wildlife and timber production. Here we develop an integrative model that illustrates the inherent trade‐offs that will arise among the competing values for landscape space and how to resolve them. The analysis characterizes boreal forest ecosystem dynamics involving interactions among the main trophic compartments of an intact boreal ecosystem, aka “nature.” The model accounts for carbon accumulation via biomass growth of forest trees (timber), carbon loss due to controls from moose herbivory that varies with moose population density (hunting), and soil carbon inputs and release, which together determine the carbon sink strength of the ecosystem. We link the ecological dynamics with an economic analysis by assigning a price to carbon stored within the intact boreal forest ecosystem. We then weigh these carbon impacts against the economic benefits of timber production and hunting across a range of moose population densities. Combined, this carbon‐bioeconomic program calculates the total ecosystem benefit of a modeled boreal forest system, providing a framework for examining how different forest harvest and moose densities influence the achievement of carbon storage targets, under different levels of carbon pricing. The analysis shows that promoting nature‐based solutions merely for carbon storage may result in loss of a key part of “nature” via loss of the trophic structure and key functional controls in the ecosystem.

Long‐term changes in multi‐trophic diversity alter the functioning of river food webs

Abstract Increasing human pressures threaten fish diversity, with potentially severe but unknown consequences for the functioning of riverine food webs. Using a 17‐year dataset from multi‐trophic fish communities, we investigated the long‐term effects of human pressure on the diversity and food web functioning. Combining metabolic scaling and ecological network principles, we calculate the annual energy fluxes through trophic compartments (top‐carnivore, mesocarnivore, detritivore and omnivore). Energy fluxes link trophic compartments, and thus represents food web functions such as carnivory, omnivory, herbivory and detritivory. Species richness across all trophic compartments was positively associated with energy flux. However, species richness decreased over time, as did the energy flux at the whole‐network level, which was reduced by 75%. Human pressure negatively affected both species richness and energy flux. Moreover, the negative impacts of human pressure on energy flux have intensified over time. Our results illustrate how human pressure can reduce diversity and erode the energy flux through food webs, with negative implications for the ecosystem functioning. Read the free Plain Language Summary for this article on the Journal blog.

Animal-vectored nutrient flows across resource gradients influence the nature of local and meta-ecosystem functioning

Organisms move across landscapes mediating nutrient, energy, and biomass exchanges. Meta-ecosystem ecology offers a framework to study how these flows affect ecosystem functions in space and time. However, meta-ecosystem models often represent consumer movement as diffusion along gradients of resources. Crucially, this assumes that consumer movement connects the same trophic compartments among patches of the same ecosystem. Yet, empirical evidence shows that organisms move across different ecosystems and connect diverse trophic compartments in diffusive and non-diffusive ways. Here, we derive a two-patch meta-ecosystem model that accounts for both types of organismal movement, and we investigate their influences on local and meta-ecosystem functions. We apply a novel approach, modelling consumer movement through a dispersers’ pool that captures the fraction of moving organisms and allows us to partition local and regional dynamics. We show that non-diffusive consumer movement increases landscape heterogeneity while diffusive consumer movement enhances source–sink dynamics. Local ecosystem differences driven by consumer movement type are less prevalent at meta-ecosystem extents. Thus, movement type is essential for predicting local ecosystem dynamics. Our results support recent calls to consider explicitly the role of consumers in shaping and maintaining ecosystem functions across spatial extents.

Ecosystem-based assessment of a widespread Mediterranean marine habitat: The Coastal Detrital Bottoms, with a special focus on epibenthic assemblages

IntroductionCoastal detrital bottoms (CDB) are one of the most extensive habitats of the continental shelf worldwide, in the upper levels of the circalittoral zone. Hosting a diverse community structured by sediment grain size, trophic interactions and calcified organisms, CDB exhibit important ecological functions. In the Mediterranean Sea, CDB are constituted by recent elements partly provided by adjacent infralittoral and circalittoral ecosystems. Since the 2010s, the offshore extension of many Marine Protected Areas (MPAs) has resulted in the incorporation of vast areas of CDB, raising the issue of their management. The Marine Strategy Framework Directive (MSFD) has embraced the concept of an ecosystem-based approach involving taking into account the functioning of marine habitats and their related ecosystem services. The purpose of this paper is to propose an ecosystem-based quality index (EBQI) tested on CDB from the north-western Mediterranean Sea, focusing mainly on epibenthic assemblages.MethodsThe first step has been to define a conceptual model of the CDB functioning, including the main trophic compartments and their relative weighting, then to identify appropriate assessment methods and potential descriptors. Twenty-nine sites were sampled along the coast of Provence and French Riviera (Southern France). Study sites were chosen with a view to encompassing a wide range of hydrological conditions and human pressures.ResultsVery well-preserved sites were found in Provence in areas without trawling and terrigenous inputs, while impacted and low-ES sites were located in the vicinity of urbanized areas. The cover of rhodoliths characterizes the seascape and might be an indicator of the good ES of CDB and reduced human pressure. However, the absence of rhodoliths may also be induced by natural phenomena.DiscussionThe EBQI designed for CDB proved representative and useful for a functional assessment based on epibenthic assemblages. However, some descriptors have shown their limitations and should be further explored. We highlight here the priority of establishing an index corresponding to a societal demand (e.g., European Directives, Barcelona convention) as a basis for a broad and large-scale assessment, for practical reasons. We stress the need to better apprehend the role of the macro-infauna and to extend this index over a wider geographical scale.

An integrated conceptual model to characterize the effects of offshore wind farms on ecosystem services

Offshore wind farm development has become a key measure of energy transition in recent years. Coastal territories are particularly favorable to the development of offshore wind farms due to their high energy potential. However, these areas are also hotspots of biodiversity, provide attractive landscapes and are under strong anthropogenic pressures. Preserving and sharing the natural and cultural resources of coastal territories while intensifying renewable marine energies, represents one of the most important challenges for future management of coastal environments. Consequently, systemic models that consider all the effects of offshore wind farms on ecosystems and society are essential. Here, we propose a conceptual model for studying these effects, by mobilizing the concept of ecosystem service in a systemic and integrated assessment approach. To that aim, we reviewed the literature and compiled experts’ knowledge in order to characterize the effects of offshore wind farms on food webs during the construction and operation phases. Then, we analyzed the contribution of trophic compartments on ecosystem functions, ecosystem services and beneficiaries, and how offshore wind farms modify the relationships between these compartments of the marine coastal social-ecological systems. Our approach helps identify the causal chains that generate the most important modifications in this system. This information could then be used to predict impacts of offshore wind farms on ecosystem services, and to suggest management trade-offs. This study reveals the need for further studies relating marine biodiversity to ecosystem services, and developing systemic approaches at different scales. The analysis of the effects of offshore wind farms on ecosystem services is crucial since it is linked to strong ecological, socio-economic and political issues.

Environmental factors controlling structure, litter productivity, and phenology of mangroves in arid region of the Gulf of California

Mangroves are highly productive ecosystems permanently contributing, through their litter productivity, with organic material into the superior trophic compartments. This research took place in three coastal lagoons on the southeast coast of the Gulf of California. The objective is to describe environmental factors controlling structure, phenological, and litter productivity in arid zone mangruves. The study sites were established along a latitudinal arid climate gradient, were evaporation (∼3000 mm year−1) exceeds precipitation (∼300 mm year−1), and a microtidal regime predominates. The study period was from June 2018 to May 2019. Litter productivity was quantified using litter traps, while piezometer were used to monitor surface, interstitial, and groundwater physicochemical properties and the water level. The different mangrove species present in the study area are influenced by high interstitial salinity, due to scarce freshwater inputs, because precipitation runoff is limited to the monsoon (June–August). The flowering phenophase started before the monsoon and peaked during the monsoon season, propagules production was highest in september and peaked from august to october (highest water level). Air and water temperature in warmer months influenced flower and propagules production. Despite the harsh environmental conditions provide a suboptimal scenario for mangroves to grow, resulting in low structural development and low litter productivity (∼4 Mg ha−1 year−1) influenced by temperature, and water properties (i.e. temperature, salinity and ORP), precipitation and flood pattern. An important highlight of this research is the triggered phenological response to temperature (air and water), therefore the importance of long-term monitoring of such processes and variables.

Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and meso- to eutrophic waters. The Marquesas constitute a relevant ecosystem to understand the functioning of low diversity reefs that are also subject to global change. A multi-tracer assessment of organic matter pathways was run to delineate ecosystem functioning, using analysis of fatty acids, bulk and compound specific stable isotope analysis and stable isotopes mixing models. Macroalgae and phytoplankton were the two major food sources fueling this food web with, however, some marked seasonal variations. Specifically, zooplankton relied on phytoplankton-derived organic matter and herbivorous fishes on macroalgae-derived organic matter to a much higher extent in summer than in winter (~ 75% vs. ~ 15%, and ~ 70 to 75% vs. ~ 5 to 15%, respectively) . Despite remarkably high δ15N values for all trophic compartments, likely due to local dynamics in the nitrogen stock, trophic levels of consumers were similar to those of other coral reef ecosystems. These findings shed light on the functioning of low coral cover systems, which are expected to expand worldwide under global change.

The Benthic Trophic Corner Stone Compartment in POPs Transfer from Abiotic Environment to Higher Trophic Levels—Trichoptera and Ephemeroptera Pre-Alert Indicator Role

Persistent organic pollutants (POPs) have been at the forefront of environmental contamination research even before their ban in 2001 at the Stockholm Convention. Their relation to different compartments of the environment (biotic and abiotic) has been thoroughly investigated. This article aims to identify whether the benthos could represent a reliable indicator of environmental contamination with POPs and to highlight its potential transfer role between abiotic and upper trophic compartments—benthos feeders. In this regard, we determined that the Ephemeroptera samples have higher concentrations (p < 0.05) of ΣPCB, ΣHCH, and ΣDDT than sediment samples while Trichoptera samples have higher concentrations (p < 0.05) only in the case of ΣPCB and ΣDDT. This, along with the fact that the frequency of detection for POPs is similar between the sample types (sediments, Trichoptera, and Ephemeroptera), makes the benthos samples valuable indicators of contamination with sediment samples working as complementary information about how recent the contamination is.

Differences in trophic structure and trophic pathways between artificial reef and natural reef ecosystems along the coast of the North yellow Sea, China, based on stable isotope analyses

Artificial reefs have been employed to promote enrichment of degraded habitats communities and support local fisheries. To better evaluate the performance of artificial reefs, simultaneous comparisons with relatively undisturbed natural reefs nearby are essential. With the inclusion of the stable isotope method to characterize and compare ecosystem functioning for two reef systems, both trophic structure and trophic flow at an artificial and at a nearby natural reef are evaluated in the present work. We found that: 1) both macrobenthos and fish can be clustered into five trophic groups for each site, with similar grouping configurations in trophic structures, and 2) energy pathways both from basal resources to macrobenthos and from macrobenthos are similar between the artificial reef and the natural reef, although the pathway magnitudes may be spatially different. To elucidate the trophic pathways from a comprehensive viewpoint, we reconstructed a general model from basal resources up to fishes at each site, where pelagic pathway based on POM and benthic pathway based on either Chlorophyta or a mixture of microphytobenthos, POM and Chlorophyta are identified. We conclude that an artificial reef ecosystem that has been established for years can support a trophic structure and trophic pathways similar to those provided by a natural reef ecosystem. In the future, we call for comparisons of specific trophic compartments and the combination of trophic ecology and community structure, to better understand the development of artificial reef systems.

Structure and function of the southeastern Gulf of California ecosystem during low and high sea surface temperature variability

The southeastern Gulf of California is located where two major ocean systems meet: the California Current at the north and the North Equatorial current at the south, however the ecosystem-level effects that have such confluence remain unknown. In this study, we compared the structure and function of this ecosystem between two periods 1994–1997 and 2006–2007. We based the comparison on food web models built with Ecopath with Ecosim (EwE) modeling software and assumed local sea surface temperature anomalies (1993–2009) as an environmental indicator. We analyzed the ecosystem function using indicators estimated by EwE. We performed structural analysis using topological centrality indices to analyze the role of trophic species in the food web. We found that the structure and function of the ecosystem differed among the two periods, which were characterized by two clearly different levels of variation (low variability in 1994–1997 and high variability in 2006–2007). The total biomass, total system throughput, net production of the system, connectance and Finn’s cycling index decreased from 1994–1997 to 2006–2007. The mean transfer efficiency (MTE) revealed that in the period, the energy flow among trophic levels was more efficient. During 2006/07, there was an increase in the ecosystem’s organization, but at the same time, the ecosystem may have been more vulnerable to external perturbations because its resilience decreased. In relation to the structural role of trophic compartments, there were differences in both periods. We found that most groups change their trophic role under different oceanographic conditions. We discuss that the changes in the ecosystem are related to local variability in sea surface temperature.

First screening of biocides, persistent organic pollutants, pharmaceutical and personal care products in Antarctic phytoplankton from Deception Island by FT-ICR-MS

In recent years, the Antarctic territory has seen a rise in the number of tourists and scientists. This has led to an increase in the anthropogenic footprint in Antarctic ecosystems, namely in terms of emerging contaminants, such as Biocides, Persistent Organic Pollutants (POPs) as well as Pharmaceutical and Personal Care Products (PPCPs). Yet scarce information on the presence of these emerging contaminants is available for trophic compartments, especially the phytoplankton community. Using high resolution Fourier-transform ion cyclotron-resonance mass spectrometry (FT-ICR-MS), an untargeted screening of the metabolome of the phytoplankton community was performed. Seventy different contaminant compounds were found to be present in phytoplankton collected at two sites in Port Foster Bay at Deception Island. These emerging contaminants included 1 polycyclic aromatic hydrocarbon (PAH), 10 biocides (acaricides, fungicides, herbicides, insecticides and nematicides), 11 POPs (flame retardants, paints and dyes, polychlorinated biphenyl (PCB), phthalates and plastic components), 5 PCPs (cosmetic, detergents and dietary compounds), 40 pharmaceutical compounds and 3 illicit drugs. Pharmaceutical compounds were, by far, the largest group of emerging contaminants found in phytoplankton cells (anticonvulsants, antihypertensives and beta-blockers, antibiotics, analgesic and anti-inflammatory drugs). The detection of several of these potentially toxic compounds at the basis of the marine food web has potentially severe impacts for the whole ecosystem trophic structure. Additionally, the present findings also point out that the guidelines proposed by the Antarctic Treaty and Protocol on Environmental Protection to the Antarctic Treaty should be revisited to avoid the proliferation of these and other PPCPs in such sensitive environments.

Screening of Emerging Pollutants (EPs) in Estuarine Water and Phytoremediation Capacity of Tripolium pannonicum under Controlled Conditions

The increasing number of pharmaceuticals in the environment and their difficult biodegradation, can lead to bioaccumulation in different trophic compartments. Their bioaccumulation can have negative consequences, especially in the generation of bacterial resistance by antibiotics, but also in the impairment of plant and animal metabolism. The Tejo estuary in Portugal is the habitat for many plant and animal species, which are also prone to this type of contamination. Therefore, in the present study different classes of emerging pollutants (EPs) were surveyed in water samples in the Tejo estuary, including antibiotics, anticonvulsants, antidepressants, lipid-lowering drugs, anti-inflammatory drugs, beta-blockers and analgesics. According to the results, only four compounds were detected in water samples collected at the three selected salt marshes, including carbamazepine, fluoxetine hydrochloride, venlafaxine hydrochloride and acetaminophen. Having the detected substances as a basis, a subsequent study was performed aiming to investigate the uptake and biodegradation capacity of halophytes, using Tripolium pannonicum as a model plant cultivated under controlled conditions with different concentrations of the found EPs. This experimental approach showed that T. pannonicum was able to uptake and degrade xenobiotics. Moreover, the application of sulfamethazine, as a model antibiotic, showed also that this species can uptake and degrade this compound, although the degradation rate and process proved to be compound-specific. This was also confirmed using crude plant extracts spiked with the different EPs. Thus this species is a potential candidate for the remediation of marine water and sediments contaminated with environmentally-significant EPs.

Shifting levels of ecological network's analysis reveals different system properties.

Network analyses applied to models of complex systems generally contain at least three levels of analyses. Whole-network metrics summarize general organizational features (properties or relationships) of the entire network, while node-level metrics summarize similar organization features but consider individual nodes. The network- and node-level metrics build upon the primary pairwise relationships in the model. As with many analyses, sometimes there are interesting differences at one level that disappear in the summary at another level of analysis. We illustrate this phenomenon with ecosystem network models, where nodes are trophic compartments and pairwise relationships are flows of organic carbon, such as when a predator eats a prey. For this demonstration, we analysed a time-series of 16 models of a lake planktonic food web that describes carbon exchanges within an autumn cyanobacteria bloom and compared the ecological conclusions drawn from the three levels of analysis based on inter-time-step comparisons. A general pattern in our analyses was that the closer the levels are in hierarchy (node versus network, or flow versus node level), the more they tend to align in their conclusions. Our analyses suggest that selecting the appropriate level of analysis, and above all regularly using multiple levels, may be a critical analytical decision. This article is part of the theme issue 'Unifying the essential concepts of biological networks: biological insights and philosophical foundations'.

The same but different: stable isotopes reveal two distinguishable, yet similar, neighbouring food chains in a coral reef

Stable isotope compositions were studied in particulate organic matter (POM), zooplankton and different trophic groups of teleosts to compare food chains based on plankton at two sites (lagoon and outer slope) in a New Caledonian coral reef. For each trophic compartment, δ13C values were always lower in the outer slope than in the lagoon. This result may be explained by potential differences in POM composition between the two environments, suggesting that the two food chains are based on different primary sources of carbon. In contrast, δ15N values did not vary between the lagoon and the outer slope, indicating that these two food chains presented similar length and trophic levels, despite being distinguishable.

Population dynamics of Noctiluca scintillans during a bloom in a semi-enclosed bay in Hong Kong

Noctiluca scintillans, a heterotrophic dinoflagellate responsible for most of the red tides in Hong Kong waters was investigated to determine the influence of biotic and abiotic factors in determining its population dynamics. N. scintillans first occurred in January when temperature was ~17°C, and reached a maximum of 1980cellsL−1 one month later. N. scintillans interacted with trophic compartments from picoplankton to mesozooplankton, but its population development was largely related to the availability of phytoplankton, especially diatoms. Growth rates in microcosms (with mainly biological factors) ranged from −0.38 to 1.11d−1 and were similar to the field in situ growth rates (physical and biological factors). Thus, optimum hydrographical conditions (temperature and water stability), and a rich food supply were necessary for N. scintillans to bloom. Its spatial distribution pattern was a result of biological and physical coupling, but mainly controlled by physical accumulation processes such as winds, tides and currents.

How does a restored oyster reef develop? An assessment based on stable isotopes and community metrics

Oyster reefs host complex food webs, as their three-dimensional biogenic structure provides habitat for a diverse range of invertebrates and fish. Oyster reefs have suffered severe degradation due to anthropogenic activities. Restoration projects aim to mitigate this habitat loss. We compared the development of a restored subtidal oyster reef to that of a natural reef for 29 months by assessing (1) community metrics (e.g., biomass, diversity), (2) the stable isotope composition of food sources and consumers, and (3) biomass-weighted isotopic diversity indices. A clear shift in restored reef community composition occurred 12–15 months after restoration, moving from a community dominated by opportunistic species to a more diverse and evenly distributed community, similar to that of the natural reef. Consumer stable isotope values indicated that the restored reef community was supported by similar food resources and had similar food chain length as the natural reef community by 5-month post-restoration. However, biomass-weighted isotopic diversity indices indicated that the magnitude of the main trophic pathways and characteristics of food web complexity in the restored reef did not recover to natural reef levels until 12–15 months after construction. The functional recovery of the restored reef community was driven by the homogenization of biomass distribution among trophic compartments as oysters and top predators increasingly colonized the reef. Results indicate that oyster reef restoration can support food web functions like those provided by natural reefs. We also demonstrate the importance of combining food web and community structure information in the study of ecological functioning.

Functional and Structural Food Web Comparison of Terminos Lagoon, Mexico in Three Periods (1980, 1998, and 2011)

Terminos Lagoon has a high diversity of species and habitats and is the largest coastal lagoon in the southern Gulf of Mexico. It has been a natural protected area since 1994, but in recent decades, environmental changes have modified its biological communities and habitats. In this study, we construct three trophic models for the periods 1980, 1998, and 2011 using the Ecopath with Ecosim approach to evaluate the status of the ecosystem. Based on model outputs, we compare functional indicators and perform a structural analysis of the food web. We found significant changes in the biomasses of trophic compartments and in other functional indicators. The global productivity of the ecosystem was the main ecosystem indicator that changed over time. The structural analysis included a collection of centrality indices which measure the number, strength, and distance (in terms of number of links) of linkages between each trophic compartment and all other compartments, as indicators of the relative importance of each compartment in overall energy flows. Structure was also assessed by identifying the number and composition of subgroups connected by strong trophic linkages. Certain compartments from lower trophic levels, such as seagrasses, microcrustaceans, meiobenthos, and echinoderms had the higher values of centrality measures in the three periods analyzed. Substructures were relatively stable between periods, confirming that a reduction in productivity was the main ecosystem indicator that changed over time. Some trophic compartments were recurrent in substructures, revealing their key role in the food web structure regardless of changes in productivity. This analysis suggests that those compartments must be prioritized in conservation scenarios because the loss of those species would change the ecosystem structure impacting severely its biological productivity.

Predator-driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry.

Empirical evidence is beginning to show that predators can be important drivers of elemental cycling within ecosystems by propagating indirect effects that determine the distribution of elements among trophic levels as well as determine the chemical content of organic matter that becomes decomposed by microbes. These indirect effects can be propagated by predator consumptive effects on prey, nonconsumptive (risk) effects, or a combination of both. Currently, there is insufficient theory to predict how such predator effects should propagate throughout ecosystems. We present here a theoretical framework for exploring predator effects on ecosystem elemental cycling to encourage further empirical quantification. We use a classic ecosystem trophic compartment model as a basis for our analyses but infuse principles from ecological stoichiometry into the analyses of elemental cycling. Using a combined analytical-numerical approach, we compare how predators affect cycling through consumptive effects in which they control the flux of nutrients up trophic chains; through risk effects in which they change the homeostatic elemental balance of herbivore prey which accordingly changes the element ratio herbivores select from plants; and through a combination of both effects. Our analysis reveals that predators can have quantitatively important effects on elemental cycling, relative to a model formalism that excludes predator effects. Furthermore, the feedbacks due to predator nonconsumptive effects often have the quantitatively strongest impact on whole ecosystem elemental stocks, production and efficiency rates, and recycling fluxes by changing the stoichiometric balance of all trophic levels. Our modeling framework predictably shows how bottom-up control by microbes and top-down control by predators on ecosystems become interdependent when top predator effects permeate ecosystems.

Consequences of warming and resource quality on the stoichiometry and nutrient cycling of a stream shredder.

As a result of climate change, streams are warming and their runoff has been decreasing in most temperate areas. These changes can affect consumers directly by increasing their metabolic rates and modifying their physiology and indirectly by changing the quality of the resources on which organisms depend. In this study, a common stream detritivore (Echinogammarus berilloni Catta) was reared at two temperatures (15 and 20°C) and fed Populus nigra L. leaves that had been conditioned either in an intermittent or permanent reach to evaluate the effects of resource quality and increased temperatures on detritivore performance, stoichiometry and nutrient cycling. The lower quality (i.e., lower protein, soluble carbohydrates and higher C:P and N:P ratios) of leaves conditioned in pools resulted in compensatory feeding and lower nutrient retention capacity by E. berilloni. This effect was especially marked for phosphorus, which was unexpected based on predictions of ecological stoichiometry. When individuals were fed pool-conditioned leaves at warmer temperatures, their growth rates were higher, but consumers exhibited less efficient assimilation and higher mortality. Furthermore, the shifts to lower C:P ratios and higher lipid concentrations in shredder body tissues suggest that structural molecules such as phospholipids are preserved over other energetic C-rich macromolecules such as carbohydrates. These effects on consumer physiology and metabolism were further translated into feces and excreta nutrient ratios. Overall, our results show that the effects of reduced leaf quality on detritivore nutrient retention were more severe at higher temperatures because the shredders were not able to offset their increased metabolism with increased consumption or more efficient digestion when fed pool-conditioned leaves. Consequently, the synergistic effects of impaired food quality and increased temperatures might not only affect the physiology and survival of detritivores but also extend to other trophic compartments through detritivore-mediated nutrient cycling.

Food type and temperature constraints on the fitness of a dominant freshwater shredder

Freshwaters receive a large amount of materials and biologically available energy from their surrounding catchments. In particular, small forested streams are dependent on allochthonous organic matter inputs. However, since the middle 20th century large areas of forests in the Iberian Peninsula have been converted to eucalypt plantations, impairing invertebrate communities and stream energy fluxes. In addition, the dependence of organismal metabolic rates on temperature may influence invertebrate life cycles and development, and ultimately the riparian-stream system. We tested the effects of two food resources (alder and eucalypt) under two different temperatures (9 vs. 14°C) on the life history parameters and elemental composition of Brillia bifida (Chironomidae), a numerically dominant shredder in forested streams of NW Spain. Our results showed: (i) warmer temperature accelerated the development of B. bifida larvae (i.e., three times faster at warm than at cold temperature), (ii) Brillia's growth rate when fed on eucalypt leaves was only 30% of what it was on alder leaves, and (iii) both factors together modified larvae stoichiometry and nutrient fluxes (i.e., through fine particulate organic matter production). The observed elemental imbalances suggest, to some extent, a deviation from the “strict homeostasis” assumption for heterotrophs. Differential effects observed on larval development, growth and elemental composition point out that food type and temperature are influencing B. bifida performance, and this fact may reach other trophic compartments through detritivore-mediated nutrient cycling.