Animal soil food web complexity triggers shifts in microbial communities, including PAH degraders, but without clear effects on phenanthrene phytoremediation

The aim of this study was to determine whether the complexity of the animal soil food web (SFWC) is a significant factor influencing the soil microbial communities, the productivity of the willow, and the degradation rates of 100 mg kg-1 phenanthrene contamination. The SFWC treatment had eight levels: just the microbial community (BF), or the BF with nematodes (N), springtails (C), earthworms (E), CE, CN, EN, CEN. After eight weeks of growth, the height and biomass of willows were significantly affected by the SFWC, whereas the amount of phenanthrene degraded was not affected, reaching over 95% in all pots. SFWC affected the structure and the composition of the bacterial, archaeal and fungal communities, with significant effects of SFWC on the relative abundance of fungal genera such as Sphaerosporella, a known willow symbiont during phytoremediation, and bacterial phyla such as Actinobacteriota, containing many PAH degraders. These SFWC effects on microbial communities were not clearly reflected in the community structure and abundance of PAH degraders, even though some degraders related to the Actinobacteriota and the diversity of Gram-negative degraders were affected by the SFWC treatments. Overall, our results suggest that, under our experimental conditions, SFWC does not affect significantly willow phytoremediation outcomes.

Defensive Symbionts and the Evolution of Parasitoid Host Specialization

Insect host–parasitoid interactions abound in nature and are characterized by a high degree of host specialization. In addition to their behavioral and immune defenses, many host species rely on heritable bacterial endosymbionts for defense against parasitoids. Studies on aphids and flies show that resistance conferred by symbionts can be very strong and highly specific, possibly as a result of variation in symbiont-produced toxins. I argue that defensive symbionts are therefore an important source of diversifying selection, promoting the evolution of host specialization by parasitoids. This is likely to affect the structure of host–parasitoid food webs. I consider potential changes in terms of food web complexity, although the nature of these effects will also be influenced by whether maternally transmitted symbionts have some capacity for lateral transfer. This is discussed in the light of available evidence for horizontal transmission routes. Finally, I propose that defensive mutualisms other than microbial endosymbionts may also exert diversifying selection on insect parasitoids. Expected final online publication date for the Annual Review of Entomology, Volume 67 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Diversity of biological rhythm and food web stability

How ecosystem biodiversity is maintained remains a persistent question in the field of ecology. Here, I present a new coexistence theory, i.e. diversity of biological rhythm. Circadian, circalunar and circannual rhythms, which control short- and long-term activities, are identified as universal phenomena in organisms. Analysis of a theoretical food web with diel, monthly and annual cycles in foraging activity for each organism shows that diverse biological cycles play key roles in maintaining complex communities. Each biological rhythm does not have a strong stabilizing effect independently but enhances community persistence when combined with other rhythms. Biological rhythms also mitigate inherent destabilization tendencies caused by food web complexity. Temporal weak interactions due to hybridity of multiple activity cycles play a key role toward coexistence. Polyrhythmic changes in biological activities in response to the Earth's rotation may be a key factor in maintaining biological communities.

Terrestrial ecosystems of the Antarctic Peninsula and their responses to climate change and anthropogenic impacts

Antarctica and the Southern Ocean are unique natural laboratories where organisms adapted to extreme environmental conditions have evolved in isolation for millions of years. These unique biotic communities on Earth are facing complex climatic and environmental changes. Terrestrial ecosystems in the Antarctic Peninsula Region (APR) have experienced the highest rate of climate warming and, being the most impacted by human activities, are facing the greatest risk of detrimental changes. This review provides an overview of the most recent findings on how biotic communities in terrestrial ecosystems of the Antarctic Peninsula Region (APR) are responding and will likely respond to further environmental changes and direct anthropogenic impacts. Knowledge gained from studies on relatively simple terrestrial ecosystems could be very useful in predicting what may happen in much more complex ecosystems in regions with less extreme temperature changes. The rapid warming of the APR has led to the retreat of glaciers, the loss of snow and permafrost and the increase of ice-free areas, with a consequent enhancement of soil-forming processes, biotic communities, and food web complexity. However, most human activity is concentrated in APR coastal ice-free areas and poses many threats to terrestrial ecosystems such as environmental pollution or disturbances to soilcommunities and wildlife. People who work or visit APR may inadvertently introduce alien organisms and/or spread native species to spatially isolated ice-free areas. The number of introduced non-indigenous species and xenobiotic compounds in the APR is likely to be greater than currently documented, and several biosecurity and monitoring activities are therefore suggested to Antarctic national scientific programs and tourism operators to minimize the risk of irreversible loss of integrity by the unique terrestrial ecosystems of APR.

Food Chain Length Associated with Environmental Factors Affected by Large Dam along the Yangtze River

Food chain length (FCL) is a critical measure of food web complexity that influences the community structure and ecosystem function. The FCL of large subtropical rivers affected by dams and the decisive factors are far beyond clear. In this study, we used stable isotope technology to estimate the FCL of fish in different reaches of the main stream in the Yangtze River and explored the key factors that determined the FCL. The results showed that FCL varied widely among the studied areas with a mean of 4.09 (ranging from 3.69 to 4.31). The variation of FCL among river sections in the upstream of the dam was greater than that in the downstream. Regression analysis and model selection results revealed that the FCL had a significant positive correlation with ecosystem size as well as resource availability, and FCL variation was largely explained by ecosystem size, which represented 72% of the model weight. In summary, our results suggested that ecosystem size plays a key role in determining the FCL in large subtropical rivers and large ecosystems tend to have a longer food chain. Additionally, the construction of the Three Gorges Dam has been speculated to increase the FCL in the impoundment river sections.

Food web complexity weakens size-based constraints on the pyramids of life

Marine ecosystems are generally expected to have bottom-heavy trophic structure (more plants than animals) due to size-based constraints arising from increased metabolic requirements and inefficient energy transfer. However, size-based (allometric) approaches are often limited to confined trophic-level windows where energy transfer is predicted by size alone and are constrained to a balance between bottom-up and top-down control at steady state. In real food webs, energy flow is more complex and imbalances in top-down and bottom-up processes can also shape trophic structure. We expand the size-based theory to account for complex food webs and show that moderate levels of food web connectance allow for inverted trophic structure more often than predicted, especially in marine ecosystems. Trophic structure inversion occurs due to the incorporation of complex energy pathways and top-down effects on ecosystems. Our results suggest that marine ecosystems should be top-heavy, and observed bottom-heavy trophic structure may be a result of human defaunation of the ocean that has been more extreme than presently recognized.

Soil Food Web Complexity Enhances the Link Between Soil Biodiversity and Ecosystem Multifunctionality in Agricultural Systems

Background: Belowground biodiversity supports multiple ecosystem functions and services that humans rely on. However, there is a dearth of studies conducted on a large spatial scale on the topic in intensely managed agricultural ecosystems. Existing studies have overlooked the fact that the functional diversity in other trophic groups within a food web could influence function of an individual in another trophic group. Here, we report significant and positive relationships between soil biodiversity (archaea, bacteria, fungi, protists, and invertebrates) and multiple ecosystem functions (nutrient provisioning, element cycling, and reduced pathogenicity potential) in 228 agricultural fields. Results: The relationships were influenced by (I) the types of organisms with significant relationships in archaea, bacteria, and fungi and not in protists and invertebrates, and (II) the connectedness of dominant phylotypes across soil food webs, which generate different ecological clusters within soil networks to maintain multiple functions. In addition, we highlight the role of soil food web complexity, reflected by ecological networks comprising diverse organisms, which promote the multiple functions and enhance the link between soil biodiversity and ecosystem functions. Conclusions: Overall, our results represent a significant advance in forecasting the impacts of belowground biodiversity within food webs on ecosystem functions in agricultural systems, and suggest that soil biodiversity, particularly soil food web complexity, should not be overlooked, but rather considered a key factor and integrated into policy and management activities aimed at enhancing and maintaining ecosystem productivity, stability, and sustainability under land-use intensification.

Parasites in marine food webs

Parasites have important and unique impacts on marine food webs. By infecting taxa across all trophic levels, parasites affect both bottom-up and top-down processes in marine systems. When host densities are high enough, parasites can regulate or even decimate their populations, causing regime shifts in marine systems. As consumers and resources, parasites are enmeshed in food webs in ways that are different from free-living species. Their unique lifestyle renders parasites more susceptible to perturbations than their free-living hosts. As a result, parasites serve as useful indicators of ecosystem integrity. A theory for how food webs affect parasites will help us better understand why a particular infectious disease has become problematic, give insight into how restoration might reduce a costly marine disease, or let us use parasites as indicators to follow changes in food-web complexity.

Oribatid mites show that soil food web complexity and close aboveground-belowground linkages emerged in the early Paleozoic

The early evolution of ecosystems in Palaeozoic soils remains poorly understood because the fossil record is sparse, despite the preservation of soil microarthropods already from the Early Devonian (~410 Mya). The soil food web plays a key role in the functioning of ecosystems and its organisms currently express traits that have evolved over 400 my. Here, we conducted a phylogenetic trait analysis of a major soil animal group (Oribatida) to reveal the deep time story of the soil food web. We conclude that this group, central to the trophic structure of the soil food web, diversified in the early Paleozoic and resulted in functionally complex food webs by the late Devonian. The evolution of body size, form, and an astonishing trophic diversity demonstrates that the soil food web was as structured as current food webs already in the Devonian, facilitating the establishment of higher plants in the late Paleozoic.