Predicting the sign of trophic effects: individual-based simulation versus loop analysis

Food web research needs to be predictive in order to support decisions system-based conservation. In order to increase predictability and applicability, complexity needs to be managed in such a way that we are able to provide simple and clear results. One question emerging frequently is whether certain perturbations (environmental effects or human impact) have positive or negative effects on natural ecosystems or their particular components. Yet, most of food web studies do not consider the sign of effects. Here, we study 6 versions of the Kelian River (Borneo) food web, representing six study sites along the river. For each network, we study the signs of the effects of a perturbed trophic group i on each other j groups. We compare the outcome of the relatively complicated dynamical simulation model and the relatively simple loop analysis model. We compare these results for the 6 sites and also the 14 trophic groups. Finally, we see if sign-agreement and sign-determinacy depend on certain structural features (node centrality, interaction strength). We found major differences between different modelling scenarios, with herbivore-detritivore fish behaving in the most consistent, while algae and particulate organic matter behaving in the least consistent way. We also found higher agreement between the signs of predictions for trophic groups at higher trophic levels in sites 1–3 and at lower trophic levels in site 4–6. This means that the behaviour of predators in the more natural sections of the river and that of producers at the more human-impacted sections are more consistently predicted. This suggests to be more careful with the less consistently predictable trophic groups in conservation management.

Analysis of complex trophic networks reveals the signature of land-use intensification on soil communities in agroecosystems

Increasing evidence suggests that agricultural intensification is a threat to many groups of soil biota, but how the impacts of land-use intensity on soil organisms translate into changes in comprehensive soil interaction networks remains unclear. Here for the first time, we use environmental DNA to examine total soil multi-trophic diversity and food web structure for temperate agroecosystems along a gradient of land-use intensity. We tested for response patterns in key properties of the soil food webs in sixteen fields ranging from arable crops to grazed permanent grasslands as part of a long-term management experiment. We found that agricultural intensification drives reductions in trophic group diversity, although taxa richness remained unchanged. Intensification generally reduced the complexity and connectance of soil interaction networks and induced consistent changes in energy pathways, but the magnitude of management-induced changes depended on the variable considered. Average path length (an indicator of food web redundancy and resilience) did not respond to our management intensity gradient. Moreover, turnover of network structure showed little response to increasing management intensity. Our data demonstrates the importance of considering different facets of trophic networks for a clearer understanding of agriculture-biodiversity relationships, with implications for nature-based solutions and sustainable agriculture.

Impact of biochar amendment on soil nematode communities in a West African rain-fed rice cropland

Summary Nematode population and diversity in a West African rain-fed rice cropland amended with biochar (B), biochar plus inorganic fertiliser (B + NPK), inorganic fertiliser (NPK) and control (CK) without amendments were investigated in a 3-year field study. Results demonstrated that significant differences exist between treatments and years of study for total nematode population and nematode trophic groups. Total nematode density, nematode trophic group (bacterivore and plant-parasitic) density were increased and dominant in B + NPK compared with CK after 3 years. Relative abundance of nematode genera according to trophic group across treatments showed Hirschmanniella (23%) as the dominant plant parasites in NPK, and Heterocephalobus (27%), Aphelenchoides (22%) and Eudorylaimus (9%) as dominant bacterivores, fungivores and omnivores-predators, respectively, in B + NPK. Trophic group indicators showed that the fungivore plus bacterivore to plant-parasitic ratio (73%) was significantly increased by B + NPK treatment in comparison to CK. Conversely, treatments exerted no significant effect on the fungivore to bacterivore ratio (F/B) throughout the period of study, which implies less disturbance and adverse impact of biochar on nematode communities. Apart from treatments and environmental factors, changes in nematode trophic groups were strongly related to soil chemical properties, such as soil pH, total nitrogen and available phosphorus, which shows their influence on soil nematode community. Our result shows the positive effect of integrated addition of biochar and inorganic fertiliser in balancing nematode diversity and building a resilient soil ecosystem in a low input rain-fed rice cropping system.

Ecological Traits Influencing Anthropogenic Debris Ingestion by Herbivorous Reef Fishes

One of the most conspicuous marks of the Anthropocene worldwide is the ubiquitous pollution by long lifespan materials (e.g., plastic). In marine habitats, anthropogenic debris are observed from floating on the surface to deposited on the substrate or ingested by wildlife at different food web levels. However, the link between feeding strategy types and debris ingestion by reef fishes remains poorly explored. We analyzed the gut contents of three nominally herbivorous fishes along the Brazilian coast: the doctorfish Acanthurus chirurgus, the parrotfish, Sparisoma axillare, and the chub Kyphosus vaigiensis. Individual [i.e., total length (TL)] and species-level functional traits, as well sites with distinct environmental features (i.e., tourism activity intensity, fishing pressure, and distance from the coast), were tested as predictors of the concentration of debris found inside individual fish guts. Debris found were quantified, measured, and classified accordingly to color and shape. We found debris in 52.7% of individuals. Debris ranged from 0.10 to 11.75 mm, and the frequency of occurrence and ingestion rate (number of debris per individual) varied among species, being higher for the scraper species S. axillare (95.7% and 4.9 ± 1.2, respectively) and A. chirurgus (74.6% and 1.64 ± 0.34), than for the browser K. vaigiensis (55.8% and 0.83 ± 0.24). TL, scraping feeding mode, and the most impacted location were positively related to debris ingestion rate. Our work revealed a higher vulnerability of an ecologically important trophic group to debris ingestion and of an already threatened species according to Brazilian red list. Besides the increasing number of species contaminated by anthropogenic debris, its effect on fish biology and physiology remains poorly understood. Understanding these links would improve conservation planning as species contamination could act as a proxy for environmental pollution on marine habitats.

The Communities of the Nematodes, Bacteria, and Fungi and the Soil’s Organic Matter in an Agroforestry Ecosystem in Croatia

An above‐ground plant diversity affects a below-ground biodiversity. A soil fauna diversity is important for the ecosystems’ sustainability. It reflects both the abiotic conditions and the soil’s biotic activity. This study’s objective was to assess the effect of an agroforestry system on the nematode abundance and trophic group distribution and on the bacterial and fungal abundance in the soil, as well as to analyze the links between a nematode abundance, trophic group patterns, soil’s microbiological status and the organic matter. A field experiment was conducted during two years in three treatments and three sampling periods. The treatments were as follows: an agricultural crop (C), a permanent walnut plantation (W), and a permanent walnut plantation with an agricultural crop (C + W). The nematodes were extracted, counted, processed and mounted on slides and ultimately determined and assigned to the trophic groups. The bacteria and fungi were extracted from the soil, grown on the plates, and counted. Our findings suggest that the studied agroforestry system (C+W) has exerted a positive effect on the soil nematodes, bacteria, and fungi, manifested as the statistically highest abundance of bacteria and fungi, but also as the highest abundance of nematodes and of a diversity of the nematode genera. The highest content of the organic matter was detected in the treatment C + W in the first sampling and in the treatments C + W and W in the second sampling. We have concluded that the combination of an agricultural crop and a permanent plantation has a great potential for better ecosystem stability and sustainability regardless of some deviations in our results. We believe that further research is necessary because the different agroforestry ecosystems may have different impacts on the soil fauna.

Predicting The Sign of Trophic Effects: Individual-Based Simulation Versus Loop Analysis

Food web research needs to be predictive in order to support decisions system-based conservation. In order to increase predictability and applicability, complexity needs to be reduced to simple and clear results. One question emerging frequently is whether certain perturbations (environmental effects or human impact) have positive or negative effects on natural ecosystems or their particular components. Yet, most of food web studies do not consider the sign of effects.Here, we study 6 versions of the Kelian River (Borneo) food web, representing six study sites along the river. For each network, we study the sign of the effect of a perturbed trophic group i on each other j groups. We compare the outcome of the relatively complicated dynamical simulation model and the relatively simple loop analysis model. We compare these results for the 6 sites and also the 14 trophic groups. Finally, we see if sign-agreement and sign-determinacy depend on certain structural features (node centrality, interaction strength).We found major differences between different modelling scenarios, with herbivore-detritivore fish behaving in the most consistent, while algae and particulate organic matter behaving in the least consistent way.

Structure of aquatic macroinvertebrate communities in streams of a sub-basin in the Pampa Biome, Southern Brazil

The Piratinim River is located in the northwest of Rio Grande do Sul, and represents an important effluent from the Uruguay River, with streams located far from urbanized areas, in conditions similar to those of environmental integrity, but under the influence of agricultural activities. In this study, we aim at investigating the structure of the aquatic macroinvertebrate community in streams of the Piratinim river basin by observing both spatial and local scales. The sampling was carried out in six streams distributed in three regions (upper, middle and lower) of the basin, thus exploring its upstream, intermediate and downstream stretches, during spring and autumn. Macroinvertebrates were collected using aquatic dipnets and were identified at the family level; trophic-functional categories were established according to the classification adapted to the state of Paraná. The spatial and temporal variations of the groups and of the biotic attributes (density, richness, diversity and equitability) were subjected to Kruskal-Wallis non-parametric tests and a posteriori Dunn’s tests. The abiotic variables were obtained to verify possible influence on the composition of the macroinvertebrate community, evaluated through a Canonical Correspondence Analysis. We sampled 11,564 macroinvertebrate individuals from 72 taxa, and found a predominance of the collector-filter trophic group. Abundance and richness were different between streams; the highest densities were found in the streams located in the upper region of the watershed (Chuní and Itú). The highest taxon richness was found in the lower region of the watershed (Guaracapa stream), and the lowest richness was found in the two streams for the intermediate region (Santana and Ximbocu). Diversity and equitability did not vary; temporal variations were not found. Canonical correspondence analysis explained 31.7% of the data variability. The main environmental variables that influenced macroinvertebrates distribution were temperature, electrical conductivity, dissolved oxygen, altitude and extension of the riparian forest. Seasonality and the longitudinal gradient along the basin represented determining factors for the structure and distribution of the macroinvertebrate community in the tributary streams of the Piratinim River.

Nematode Community-Based Soil Food Web Analysis of Ferralsol, Lithosol and Nitosol Soil Groups in Ghana, Kenya and Malawi Reveals Distinct Soil Health Degradations

Determining if the vast soil health degradations across the seven major soil groups (orders) of Sub-Saharan Africa (SSA) can be managed on the basis of a one-size-fits-all or location-specific approach is limited by a lack of soil group-based understanding of soil health degradations. We used the relationship between changes in nematode population dynamics relative to food and reproduction (enrichment, EI) and resistance to disturbance (structure, SI) indices to characterize the soil food web (SFW) and soil health conditions of Ferralsol, Lithosol and Nitosol soil groups in Ghana, Kenya and Malawi. We applied bivariate correlations of EI, SI, soil pH, soil organic carbon (SOC), and texture (sand, silt and clay) to identify integrated indicator parameters, and principal component analysis (PCA) to determine how all measured parameters, soil groups, and countries align. A total of 512 georeferenced soil samples from disturbed (agricultural) and undisturbed (natural vegetation) landscapes were analyzed. Nematode trophic group abundance was low and varied by soil group, landscape and country. The resource-limited and degraded SFW conditions separated by soil groups and by country. EI and SI correlation with SOC varied by landscape, soil group or country. PCA alignment showed separation of soil groups within and across countries. The study developed the first biophysicochemical proof-of-concept that the soil groups need to be treated separately when formulating scalable soil health management strategies in SSA.

Do changes in the water regime determine the abundance of the copepod trophic group in a Neotropical floodplain?

Aim Our study evaluated the effects of extreme weather events and environmental conditions on the trophic groups of copepods (herbivores and omnivores) in the upper Paraná River floodplain. Methods The zooplankton were collected and Copepods and Rotifers were analyzed in nine environments of the upper Paraná River floodplain during 2000 and 2010, during which time the La Niña (drought) and El Niño (flood) climatic events occurred, respectively. Results The results suggest that in periods of extreme drought productivity-related variables act as determining forces on abundance of copepod trophic groups due to the contraction of aquatic ecosystems. Although the abundance of trophic groups is associated with system productivity, the responses between them differ, since herbivore abundance was associated with chlorophyll-a and total phosphorus and omnivores with rotifer abundance. In extreme flood (El Niño), no significant relationship was found between environmental variables and any trophic group. Conclusions In general, it is believed that in periods of extreme drought the variables associated with productivity act as determining forces on the abundance of trophic groups of copepods due to the contraction of aquatic ecosystems. According to the results found, it is suggested that other works be carried out with a greater number of extreme events to corroborate our results and, and also to extrapolate to other aquatic communities.