Cross-ecosystem bottlenecks alter reciprocal subsidies within meta-ecosystems

Reciprocal subsidies link ecosystems into meta-ecosystems, but energy transfer to organisms that do not cross boundaries may create sinks, reducing reciprocal subsidy transfer. We investigated how the type of subsidy and top predator presence influenced reciprocal flows of energy, by manipulating the addition of terrestrial leaf and terrestrial insect subsidies to experimental freshwater pond mesocosms with and without predatory fish. Over 18 months, fortnightly addition of subsidies (terrestrial beetle larvae) to top-predators was crossed with monthly addition of subsidies (willow leaves) to primary consumers in mesocosms with and without top predators (upland bullies) in a 2 × 2 × 2 factorial design in four replicate blocks. Terrestrial insect subsidies increased reciprocal flows, measured as the emergence of aquatic insects out of mesocosms, but leaf subsidies dampened those effects. However, the presence of fish and snails, consumers with no terrestrial life stage, usurped and retained the energy within in the aquatic ecosystem, creating a cross-ecosystem bottleneck to energy flow. Thus, changes in species composition of donor or recipient food webs within a meta-ecosystems can alter reciprocal subsidies through cross-ecosystem bottlenecks.

Comparison of Bayesian and numerical optimization-based diet estimation on herbivorous zooplankton

Consumer diet estimation with biotracer-based mixing models provides valuable information about trophic interactions and the dynamics of complex ecosystems. Here, we assessed the performance of four Bayesian and three numerical optimization-based diet estimation methods for estimating the diet composition of herbivorous zooplankton using consumer fatty acid (FA) profiles and resource library consisting of the results of homogeneous diet feeding experiments. The method performance was evaluated in terms of absolute errors, central probability interval checks, the success in identifying the primary resource in the diet, and the ability to detect the absence of resources in the diet. Despite occasional large inconsistencies, all the methods were able to identify the primary resource most of the time. The numerical optimization method QFASA using χ²(QFASA-CS) or Kullback--Leibler (QFASA-KL) distance measures had the smallest absolute errors, most frequently found the primary resource, and adequately detected the absence of resources. While the Bayesian methods usually performed well, some of the methods produced ambiguous results and some had much longer computing times than QFASA. Therefore, we recommend using QFASA-CS or QFASA-KL. Our systematic tests showed that FA models can be used to accurately estimate complex dietary mixtures in herbivorous zooplankton. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Effects of fixatives on stable isotopes of fish muscle tissue: implications for trophic studies on preserved specimens

Isotopic ecology has been widely used to understand spatial connectivity and trophic interactions in marine systems. However, its potential for monitoring an ecosystem's health and function has been hampered by the lack of consistent sample storage and long-term studies. Preserved specimens from museum collections are a valuable source of tissue for analyses from ancient and pre-modern times, but isotopic signatures are known to be affected by commonly used fixatives. The aim of the present study was to understand the effects of fixatives on isotopic signatures of bulk tissue (δ¹³ C_m and δ¹⁵ N_m ) and amino acids (δ¹³ C_AA and δ¹⁵ N_AA ) of fish muscle and to provide correction equations for the isotopic shifts. Two specimens of each: blue cod (Parapercis colias), blue warehou (Seriolella brama), and king salmon (Oncorhynchus tschawytscha) were sampled at five locations along their dorsal musculature, at four time periods: (1) fresh, (2) after 1 month preserved in formalin, and after (3) 3 and (4) 12 months fixed in either ethanol or isopropanol. Lipid content was positively correlated with C:N ratio (r² = 0.83) and had a significant effect on δ¹³ C after treatments, but not on δ¹⁵ N. C:N ratio (for δ¹³ C_m ) and percent N (for δ¹⁵ N_m ) from preserved specimens contributed to the most parsimonious mixed models, which explained 79% of the variation due to fixation and preservation for δ¹³ C and 81% for δ¹⁵ N. δ¹³ C_AA were generally not affected by fixatives and preservatives, while most δ¹⁵ N_AA showed different signatures between treatments. δ¹⁵ N_AA variations did not affect the magnitude of differences between amino acids, allowing scientists to retrieve ecological information (e.g., trophic level) independently of time under preservation. Corrections were applied to the raw data of the experiment, highlighting the importance of δ¹³ C_m and δ¹⁵ N_m correction when fish muscle tissues from wet collections are compared to fresh samples. Our results make it possible to retrieve δ¹³ C_m , δ¹⁵ N_m , δ¹³ C_AA , and δ¹⁵ N_AA from museum specimens and can be applied to some of the fundamental questions in ecology, such as trophic baseline shifts and changes in community's food web structure through time.

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'.

Abundance and traits link predator ontogeny to prey communities

Function and abundances shape species interactions and thus ecological communities. While communities are often summarized as the mean function of each species, intraspecific variation in traits and thus function is an important driver of community composition. Ontogeny is a common source of intraspecific variation, but while age-related functional changes can alter species interactions, so too can the effects of those functions on the density of the focal organism. For instance, ontogenetic variation can trigger higher levels of cannibalism, reducing abundances and altering interspecific interactions. I manipulate ontogenetic variation in damselfly larvae to show that intraspecific variation can impact communities through two distinct mechanisms. First, within-species differences affect population sizes, and thus indirectly shape communities (indirect effect). In particular, ontogenetic variation resulted in smaller damselfly populations, likely because of increased cannibalism rates, and thus ontogenetically diverse populations had a smaller total effect on their prey. Second, trait variation can affect communities by creating differences in the strength of per capita species interactions (direct effect). In this case, damselfly populations with greater age variation had smaller per capita effects on prey communities. I conclude that ontogeny of a single species can directly and indirectly shape community composition.

Predators weaken prey intraspecific competition through phenotypic selection

Predators have a key role shaping competitor dynamics in food webs. Perhaps the most obvious way this occurs is when predators reduce competitor densities. However, consumption could also generate phenotypic selection on prey that determines the strength of competition, thus coupling consumptive and trait-based effects of predators. In a mesocosm experiment simulating fish predation on damselflies, we found that selection against high damselfly activity rates - a phenotype mediating predation and competition - weakened the strength of density dependence in damselfly growth rates. A field experiment corroborated this finding and showed that increasing damselfly densities in lakes with high fish densities had limited effects on damselfly growth rates but generated a precipitous growth rate decline where fish densities were lower - a pattern expected because of spatial variation in selection imposed by predation. These results suggest that accounting for both consumption and selection is necessary to determine how predators regulate prey competitive interactions.

[Interactions among soil biota and their applications in synergistic bioremediation of heavy-metal contaminated soils]

Soil is the material basis for human survival. However, in China, soils are wildly polluted by heavy metals, which poses serious health risks to humans. Bioremediation of heavy-metal contaminated soil is widely considered as a sustainable remediation strategy, but low remediation efficiency is still a scientific bottleneck of bioremediation. There are abundant microorganisms, plants and animals living in soils. Among these soil biota, there are complex interactions to form an intricate food web through material circulation and energy transfer. These interactions among soil biota affect the transportation and transformation of pollutants in soil, and consequently influence the bioremediation efficiency. The synergistic remediation by soil biota combines the advantages of diferent organisms to enhance the efficiency of bioremediation. In this paper, the interactions among soil biota and their influence on heavy-metal transportation and transformation, as well as bioremediation efficiency are reviewed. We also propose perspectives for future researches, including targeted regulating the structure of soil food web, improving the bioremediation efficiency of heavy-metal contaminated soil, and building a synergistic remediation technology with multi-organisms based on food web.

Threats from the air: Damselfly predation on diverse prey taxa

To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark-release-recapture (MRR) methods, and with accurate metrics of food consumption by individuals. Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well-defined 12-ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed. We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator-specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non-biting midges or chironomids) of the four damselfly species. The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410-1,800) g, over 2 months. Each individual consumed 29%-66% (95% CL 9.4-123) of its body weight during its relatively short life span (2.1-4.7 days; 95% CL 0.74-7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species. Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%-1.61%) were consumed. Our synthesis of population sizes, per-capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities.

Ecological and Evolutionary Stochasticity Shape Natural Selection

The distribution of biodiversity depends on the combined and interactive effects of ecological and evolutionary processes. The joint contribution of these processes has focused almost exclusively on deterministic effects, even though mechanisms that increase the importance of random ecological processes are expected to also increase the importance of random evolutionary processes. Here we manipulate the sizes of old field fragments to generate correlated sampling effects for a focal population (a gall maker) and its enemy community. Traits and communities were more variable in smaller patches. However, because of the preference of some enemies for some trait values (gall sizes), random variation in population mean trait values exacerbated differences in community composition. The random distribution of traits and interactions created predictable but highly variable patterns of natural selection. Our study highlights how stochastic processes can affect ecological and evolutionary processes structuring the strength and direction of selection locally and at larger scales.

The trophic niche of sculpins Cottus spp. in forage fish assemblages of boreal lakes

We compared the trophic niches of freshwater sculpins Cottus spp. with those of other co-habiting forage fishes in two groups of boreal lakes with distinct habitats and fish communities. Near North Lakes (45° 00' to 47° 30' N) were deeper, stratified and contained lake trout Salvelinus namaycush as the apex piscivore, whereas Far North Lakes (51° 10' to 52° 20' N) were shallower, did not stratify and contained pike Esox lucius and walleye Sander vitreus as the apex piscivores. Trophic niches of sculpins and other forage fishes were compared based on niche metrics calculated from muscle stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope ratios. In Near North Lakes, sculpins were found almost exclusively in deep, offshore waters and their niche positions reflected a greater reliance on pelagic production (lower δ¹³ C) and a higher trophic elevation (higher δ¹⁵ N) compared with most other forage fishes. Furthermore, sculpins in Near North Lakes tended to have larger trophic niches (occupied greater area in δ¹³ C- δ¹⁵ N space), particularly in the food chain (δ¹⁵ N) dimension, than other cohabiting forage fishes. In contrast, sculpins in Far North Lakes were commonly found in the nearshore and had trophic niche positions and sizes that were similar to those of the other cohabiting forage fishes. This study illustrates the flexibility in the realised trophic niches of sculpins in relation to habitat availability and fish community composition in boreal lakes.

Ant-termite interactions: an important but under-explored ecological linkage

Animal interactions play an important role in understanding ecological processes. The nature and intensity of these interactions can shape the impacts of organisms on their environment. Because ants and termites, with their high biomass and range of ecological functions, have considerable effects on their environment, the interaction between them is important for ecosystem processes. Although the manner in which ants and termites interact is becoming increasingly well studied, there has been no synthesis to date of the available literature. Here we review and synthesise all existing literature on ant-termite interactions. We infer that ant predation on termites is the most important, most widespread, and most studied type of interaction. Predatory ant species can regulate termite populations and subsequently slow down the decomposition of wood, litter and soil organic matter. As a consequence they also affect plant growth and distribution, nutrient cycling and nutrient availability. Although some ant species are specialised termite predators, there is probably a high level of opportunistic predation by generalist ant species, and hence their impact on ecosystem processes that termites are known to provide varies at the species level. The most fruitful future research direction will be to evaluate the impact of ant-termite predation on broader ecosystem processes. To do this it will be necessary to quantify the efficacy both of particular ant species and of ant communities as a whole in regulating termite populations in different biomes. We envisage that this work will require a combination of methods, including DNA barcoding of ant gut contents along with field observations and exclusion experiments. Such a combined approach is necessary for assessing how this interaction influences entire ecosystems.

Associated cultivated plants in tomato cropping systems structure arthropod communities and increase the Helicoverpa armigera regulation

Cultivating plant mixtures is expected to provide a higher productivity and a better control of pests and diseases. The structure of the arthropod community is a major driver of the magnitude of natural pest regulations.With the aim of optimizing pest management, a study was carried out to determine the effect of the cropping system type (tomato mono-cropping vs. mixed-cropping) on the diversity and abundance of arthropods from three trophic groups (herbivores, omnivores, predators) and the abundance of Helicoverpa armigera. Therefore, the diversity of cultivated plants and arthropod communities was assessed within tomato fields from 30 farmer's fields randomly selected in South of Benin. Results showed that the arthropod abundance was significantly higher in mixed-cropping systems compared with mono-cropping systems, although the crop type did not alter significantly the arthropod diversity, evenness, and richness. At the level of taxa, the abundances of generalist predators including ants (Pheidole spp., and Paltothyreus tarsatus) and spiders (Araneus spp. and Erigone sp.) were significantly higher in mixed fields than in mono-crop fields. Then, the abundances of omnivore-predator trophic groups have a negative significant effect on the H. armigera abundance. This study allowed better understanding of how plant diversity associated to tomato fields structures arthropod's food webs to finally enhance the ecological management of H. armigera.

Tri-trophic interactions: bridging species, communities and ecosystems

A vast body of research demonstrates that many ecological and evolutionary processes can only be understood from a tri-trophic viewpoint, that is, one that moves beyond the pairwise interactions of neighbouring trophic levels to consider the emergent features of interactions among multiple trophic levels. Despite its unifying potential, tri-trophic research has been fragmented, following two distinct paths. One has focused on the population biology and evolutionary ecology of simple food chains of interacting species. The other has focused on bottom-up and top-down controls over the distribution of biomass across trophic levels and other ecosystem-level variables. Here, we propose pathways to bridge these two long-standing perspectives. We argue that an expanded theory of tri-trophic interactions (TTIs) can unify our understanding of biological processes across scales and levels of organisation, ranging from species evolution and pairwise interactions to community structure and ecosystem function. To do so requires addressing how community structure and ecosystem function arise as emergent properties of component TTIs, and, in turn, how species traits and TTIs are shaped by the ecosystem processes and the abiotic environment in which they are embedded. We conclude that novel insights will come from applying tri-trophic theory systematically across all levels of biological organisation.

Flexibility in a changing arctic food web: Can rough-legged buzzards cope with changing small rodent communities?

Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show how the response of demographic rates of an arctic bird of prey to fluctuations in small rodent abundance changed when small rodent community composition and dynamics changed, possibly under the effect of climate warming. We observed the breeding biology of rough-legged buzzards (Buteo lagopus) at the Erkuta Tundra Monitoring Site in southern Yamal, low arctic Russia, for 19 years (1999-2017). At the same time, data on small rodent abundance were collected and information on buzzard diet was obtained from pellet dissection. The small rodent community experienced a shift from high-amplitude cycles to dampened fluctuations paralleled with a change in species composition toward less lemmings and more voles. Buzzards clearly preferred lemmings as prey. Breeding density of buzzards was positively related to small rodent abundance, but the shift in small rodent community lead to lower numbers relative to small rodent abundance. At the same time, after the change in small rodent community, the average number of fledglings was higher relative to small rodent abundance than earlier. These results suggest that the buzzard population adapted to a certain degree to the changes in the major resource, although at the same time density declined. The documented flexibility in the short-term response of demographic rates to changes in structure and dynamics of key food web components make it difficult to predict how complex food webs will be transformed in a warmer Arctic. The degree of plasticity of functional responses is indeed likely to vary between species and between regions, depending also on the local food web context.

Direct and indirect effects of regional and local climatic factors on trophic interactions in the Arctic tundra

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21 years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

Trait variation across biological scales shapes community structure and ecosystem function

Trait variation underlies our understanding of the patterns and importance of biodiversity, yet we have a poor understanding of how variation at different levels of biological organization structures communities and ecosystems. Here, we use a mesocosm experiment to test for the effects of a larval dragonfly functional trait on community and ecosystem dynamics by creating artificial populations to mirror within- and between-population trait variation observed in our study area. Specifically, we manipulate variation in activity rate, a key functional trait shaping food webs, across three levels of biological organization: within-populations (differences in trait variation in a population), among-populations (differences in population mean trait values), and among-species (species-level differences of co-occurring dragonflies). We show that differences in activity rate alter prey communities, trophic cascades, and multiple ecosystem processes. However, trait variation among populations had much larger effects than differences between co-occurring species or even the presence of a predator, whereas within-population variation had a relatively minor impact. Interestingly, combined with earlier work in the same system, our study suggests that the relative importance of species vs. individual level differences for ecosystem functioning will depend on the spatial scale considered. Ecological processes, including biodiversity-ecosystem-functioning relationships, cannot be understood without accounting for trait variation across biological scales of organization, including at fine scales.

[Assessment of heavy metal bioaccumulation in food web of the coastal waters of Jiangsu Province, China, based on stable isotope values (δ13C and δ15N).]

The coastal waters in Jiangsu Province have always been an important fishery base since ancient time. In recent years, with the development of the industry in coastal cities, heavy metal pollution is becoming serious in Jiangsu Province. However, the bioaccumulation of heavy metals in the coastal food web is still unclear. In this study, we collected samples (including macroalgae, bivalves, cephalopods, gastropods, crustaceans and fish) through fishery resources survey in the coastal waters of Jiangsu in May 2017 and quantified the main ways of the material circulation and energy flows by constructing the food web using stable carbon and nitrogen isotopes. In addition, the bioaccumulation patterns of eight elements (seven heavy metals and 1 metalloid) through the food chains were investigated. The results showed that there were two energy pathways in this offshore ecosystem: the planktonic food-chain and the benthic food-chain, with Scapharca subcrenata and Phalium strigatum as the primary consumers, respectively. The benthic food-chain was the dominant food chain in energy recycling. The mean concentration of heavy metals from high to low in orga-nisms were Zn, Cu, As, Cd, Cr, Pb, Ni and Hg. The highest concentrations of elements were found in bivalves and the lowest ones in fish. The concentration of As in most species, the levels of Cd in bivalves and Oratosquilla oratoria, the Cr in Coilia mystus and the Zn, Cu, Cr in Ostrea denselamellosa exceeded the proposed health advisory levels. Regarding the bioaccumulation, a decrease in the concentration levels of Zn, Cd and Ni were observed along the planktonic food-chain and a significant positive correlation between Hg and trophic position were found across the benthic food-chain. Other elements had no significant change.

Food web structure selects for parasite host range

Complex life cycle parasites, including helminths, use intermediate hosts for development and definitive hosts for reproduction, with interactions between the two host types governed by food web structure. I study how a parasite's intermediate host range is controlled by the diet breadth of definitive host species and the cost of parasite generalism, a putative fitness cost that assumes host range trades off against fitness derived from a host species. In spite of such costs, a benefit to generalism may occur when the definitive host exhibits a large diet breadth, enhancing transmission of generalist parasites via consumption of a broad array of infected intermediate hosts. I develop a simple theoretical model to demonstrate how different host range infection strategies are differentially selected for across a gradient of definitive host diet breadth according to the cost of generalism. I then use a parasitic helminth-host database in conjunction with a food web database to show that diet breadth of definitive hosts promotes generalist infection strategies at the intermediate host level, indicating relatively low costs of parasite generalism among helminths.

Traits of litter-dwelling forest arthropod predators and detritivores covary spatially with traits of their resources

The functional trait approach proposes that relating traits of organisms within a community to variation in abiotic and biotic characteristics of their environment will provide insight on the mechanisms of community assembly. As traits at a given trophic level might act as filters for the selection of traits at another trophic level, we hypothesized that traits of consumers and of their resources covary in space. We evaluated complementary predictions about top‐down (negative) and bottom‐up (positive) trait covariation in a detrital food web. Additionally, we tested whether positive trait covariation was better explained by the Resource Concentration Hypothesis (i.e., most commonly represented trait values attract abundant consumers) or the Resource Specialization Hypothesis (i.e., resource diversity increases niche availability for the consumers). Macroarthopods were collected with pitfall traps over two summers in three forested sites of southern Quebec in 110 plots that varied in tree species composition. Six feeding traits of consumers (detritivores and predators) and six palatability traits of their resources (leaf litter and prey) were matched to assess spatial covariation. Trait matches included consumer biting force/resource toughness, detritivore mandibular gape/leaf thickness, predator/prey body size ratio, etc. Our results demonstrate for the first time a covariation between feeding traits of detritivores and palatability traits of leaf litter (31–34%), and between feeding traits of litter‐dwelling predators and palatability traits of potential prey (38–44%). The observed positive covariation supports both the Resource Concentration Hypothesis and Resource Specialization Hypothesis. Spatial covariation of consumer and resource traits provides a new tool to partially predict the structure of the detrital food web. Nonetheless, top‐down regulation remains difficult to confirm. Further research on top‐down processes will be undoubtedly necessary to refine our capacity to interpret the effect of biotic interactions on co‐distribution.

Spatial insurance in multi-trophic metacommunities

Metacommunity theory suggests that dispersal is a key driver of diversity and ecosystem functioning in changing environments. The capacity of dispersal to mitigate effects of environmental change might vary among trophic groups, potentially resulting in changes in trophic interactions and food web structure. In a mesocosm experiment, we compared the compositional response of bacteria, phyto‐ and zooplankton to a factorial manipulation of acidification and dispersal. We found that the buffering capacity of dispersal varied among trophic groups: dispersal alleviated the negative effect of acidification on phytoplankton diversity mid‐experiment, but had no effect on the diversity of zooplankton and bacteria. Likewise, trophic groups differed in whether dispersal facilitated compositional change. Dispersal accelerated changes in phytoplankton composition under acidification, possibly mediated by changes in trophic interactions, but had no effect on the composition of zooplankton and bacteria. Overall, our results suggest that the potential for spatial insurance can vary among trophic groups.

Microraptor with Ingested Lizard Suggests Non-specialized Digestive Function

Direct indicators of diet and predator-prey relationships are exceedingly rare in the fossil record [1, 2]. However, it is through such traces that we can best understand trophic interactions in ancient ecosystems [3], confirm dietary inferences derived from skeletal morphologies [4], and clarify behavioral and ecological interpretations [5]. Here, we identify a previously unrecognized lizard species in the abdomen of a specimen of Microraptor zhaoianus, a small, volant dromaeosaurid (Paraves) with asymmetrical flight feathers on both its forelimbs and hindlimbs from the Early Cretaceous Jehol Biota [6-8]. The lizard is largely complete and articulated, confirming the current perception of Microraptor as an agile opportunistic predator that, like extant reptiles, including raptorial birds, ingested small prey whole and head first [9]. The lizard can be readily distinguished from previously recognized Early Cretaceous species based on its unusual widely spaced and brachydont dentition. Phylogenetic analysis suggests Indrasaurus wangi gen. et sp. nov. is a basal scleroglossan closely related to the slightly older Liushusaurus [10]. Comparison of ingested remains preserved across Paraves suggests that dromaeosaurids retained the plesiomorphic condition in which ingested prey were fully digested, rather than egested, as has been demonstrated was the case in the probable troodontid Anchiornis [11]. This supports a closer relationship between Aves and Anchiornis [12, 13] and suggests that flight did not precipitate the evolution of pellet egestion in Paraves and that the evolution of the "modern avian" digestive system in paravians was highly homoplastic [14]. A preliminary Jehol food web is reconstructed from current data.

Interaction modifications lead to greater robustness than pairwise non-trophic effects in food webs

Considerable emphasis has been placed recently on the importance of incorporating non-trophic effects into our understanding of ecological networks. Interaction modifications are well-established as generating strong non-trophic impacts by modulating the strength of interspecific interactions. For simplicity and comparison with direct interactions within a network context, the consequences of interaction modifications have often been described as direct pairwise interactions. The consequences of this assumption have not been examined in non-equilibrium settings where unexpected consequences of interaction modifications are most likely. To test the distinct dynamic nature of these "higher-order" effects, we directly compare, using dynamic simulations, the robustness to extinctions under perturbation of systems where interaction modifications are either explicitly modelled or represented by corresponding equivalent pairwise non-trophic interactions. Full, multi-species representations of interaction modifications resulted in a greater robustness to extinctions compared to equivalent pairwise effects. Explanations for this increased stability despite apparent greater dynamic complexity can be found in additional routes for dynamic feedbacks. Furthermore, interaction modifications changed the relative vulnerability of species to extinction from those trophically connected close to the perturbed species towards those receiving a large number of modifications. Future empirical and theoretical research into non-trophic effects should distinguish interaction modifications from direct pairwise effects in order to maximize information about the system dynamics. Interaction modifications have the potential to shift expectations of species vulnerability based exclusively on trophic networks.

[Stable isotopes of zooplankton and their applications in the research of aquatic ecosystems]

Zooplankton plays a mediating role in the food web of aquatic ecosystems, the stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) of which have been widely used to study the utilization of food resources, material cycling pathways, and trophic relationships. The δ¹³C and δ¹⁵N values of zooplankton have been used to predict primary productivity, sources and sinks of pollutants and environmental changes. To better use δ¹³C and δ¹⁵N of zooplankton as ecological and environmental indicators, it is particularly important to understand their temporal and spatial variations and the influencing factors. Based on related literature, we synthesized spatial and temporal variations in δ¹³C and δ¹⁵N of zooplankton in different aquatic ecosystems and taxa groups, and the use of δ¹³C and δ¹⁵N indicators for ecological processes and environmental changes. The δ¹³C and δ¹⁵N of zooplankton are largely affected by its food sources, and its stable isotope compositions are in turn affected by primary productivity and nitrogen sources. We proposed that the combination of δ¹³C and δ¹⁵N in zooplankton with transportation and transformation of emerging pollutants would form a multi-means, multi-disciplinary and multi-scale research direction in the fields of earth science and biology.

Nearshore seascape connectivity enhances seagrass meadow nursery function

Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass-dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young-of the-year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ¹³ C and δ¹⁵ N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N. luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N. luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape-level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.