A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales

The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human-induced changes. Understanding how climate-mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8-year dataset (2013–2020), we show that inter-annual humpback whale pregnancy rates, as determined from skin-blubber biopsy samples (n = 616), are positively correlated with krill availability and fluctuations in ice cover in the previous year. Pregnancy rates showed significant inter-annual variability, between 29% and 86%. Our results indicate that krill availability is in fact limiting and affecting reproductive rates, in contrast to the krill surplus hypothesis. This suggests that this population of humpback whales may be at a threshold for population growth due to prey limitations. As a result, continued warming and increased fishing along the WAP, which continue to reduce krill stocks, will likely impact this humpback whale population and other krill predators in the region. Humpback whales are sentinel species of ecosystem health, and changes in pregnancy rates can provide quantifiable signals of the impact of environmental change at the population level. Our findings must be considered paramount in developing new and more restrictive conservation and management plans for the Antarctic marine ecosystem and minimizing the negative impacts of human activities in the region.     

Litter and soil biodiversity jointly drive ecosystem functions

The decomposition of litter and the supply of nutrients into and from the soil are two fundamental processes through which the above- and belowground world interact. Microbial biodiversity, and especially that of decomposers, plays a key role in these processes by helping litter decomposition. Yet the relative contribution of litter diversity and soil biodiversity in supporting multiple ecosystem services remains virtually unknown. Here we conducted a mesocosm experiment where leaf litter and soil biodiversity were manipulated to investigate their influence on plant productivity, litter decomposition, soil respiration, and enzymatic activity in the littersphere. We showed that both leaf litter diversity and soil microbial diversity (richness and community composition) independently contributed to explain multiple ecosystem functions. Fungal saprobes community composition was especially important for supporting ecosystem multifunctionality (EMF), plant production, litter decomposition, and activity of soil phosphatase when compared with bacteria or other fungal functional groups and litter species richness. Moreover, leaf litter diversity and soil microbial diversity exerted previously undescribed and significantly interactive effects on EMF and multiple individual ecosystem functions, such as litter decomposition and plant production. Together, our work provides experimental evidence supporting the independent and interactive roles of litter and belowground soil biodiversity to maintain ecosystem functions and multiple services.     

Low species turnover of upland Amazonian birds in the absence of physical barriers

Aim

One of the oldest and most powerful ways for ecologists to explain distinct biological communities is to invoke underlying environmental differences. But in hyper-diverse systems, which often display high species richness and low species abundance, these sorts of community comparisons are especially challenging. The classic view for Amazonian birds posits that riverine barriers and habitat specialization determine local and regional community composition. We test the tacit, complementary assumption that similar bird communities should therefore permeate uniform habitat between major rivers, regardless of distance.

Location

Upland (terra firme) rainforests of central Amazonia.

Methods

We conducted intensive whole-community surveys of birds in three pairs of 100-ha plots, separated by 40–60 km. We then used dissimilarity indices, cluster analysis, and ordination to characterize differences among the six avian communities.

Results

In all, we detected 244 forest-dependent birds, with an average of 190 species (78%) per plot. Species turnover was negligible, no unique indicator species were found among plot pairs, and all documented species were already known from a complete inventory at one of the three sites.

Main Conclusions

Our study corroborates the classic biogeographical pattern and suggests that turnover contributes little to regional avian diversity within upland forests. Using a grain size of 100 ha, this implies that upland birds perceive the environment as uniform, at least over distances of ~60 km. Therefore, to maximize both local species richness and population persistence, our findings support the conservation of very large tracts of upland rainforest. Our analyses also revealed that the avifauna at Reserva Ducke, encroached by urban sprawl from the city of Manaus, shows the hallmarks of a disturbed community, with fewer vulnerable insectivores. This defaunation signals that even an enormous preserve (10 × 10 km) in lowland Amazonia is not insulated from anthropogenic degradation within the surrounding landscape.     

Mapping the information landscape of the United Nations Decade on Ecosystem Restoration Strategy

The strategy of the United Nations Decade on Ecosystem Restoration identifies three pathways for action for overcoming six global barriers thought to hamper upscaling. We evaluated 6,023 peer-reviewed and gray literature papers published over the last two decades to map the information landscape underlying the barriers and associated pathways for action across world regions, terrestrial ecosystem types, restorative interventions and their outcomes. Overall, the literature addressed more the financial and legislative barriers than the technical and research-related ones, supporting the view that social, economic and political factors hamper scaling up ecosystem restoration. Latin America, Africa, and North America were the most prominent regions in the literature, yet differed in the number of publications addressing each barrier. An overwhelming number of publications focused on forests (78%), while grasslands (6%), drylands (3%), and mangroves (2%) received less attention. Across the three pathways for action, the action lines on (1) promoting long-term ecosystem restoration actions and monitoring and (2) education on restoration were the most underrepresented in the literature. In general, restorative interventions assessed rendered positive outcomes except those of a political, legislative or financial nature which reported negative or inconclusive outcomes. Our indicative assessment reveals critical information gaps on barriers, pathways, and types of restorative interventions across world regions, particularly related to specific social issues such as education for ecosystem restoration. Finally, we call for refining “strength of evidence” assessment frameworks that can systematically appraise, synthesize and integrate information on traditional and practitioner knowledge as two essential components for improving decision-making in ecosystem restoration.     

Characterization of hemocytes from the marine amphipod Parhyale hawaiensis (Dana 1853): Setting the basis for immunotoxicological studies

Hemocytes are circulating blood cells that play a crucial function in amphipods and other crustacean immune systems. The hemocytes of the marine tropical amphipod Parhyale hawaiensis have been used for the evaluation of DNA damage and micronuclei, but they have not been characterized in the scientific literature. The aim of this study was to describe the hemolymph cells of P. hawaiensis and study their phagocytotic activity. Basic dyes were used to differentiate the cell types and the presence of lipids. The total hemocyte counts (THCs) and the proportion and sizes of the hemocyte types were determined. Hemolymph was exposed to Escherichia coli for verification of the presence of phagocytosis. Three cell types, all containing lipids, were identified in P. hawaiensis: granulocytes (oval shape, 13.4 × 7.6 μm), semi-granulocytes (oval shape, 14.1 × 7.2 μm), and hyalinocytes (round shape, 9.6 × 7.2 μm). Those three cell types were found in different percentages in males (64.8%, 31.1%, and 4.2%) and females (70.1%, 28.2%, and 1.7%). THCs for males were 9007 ± 3800 cells per individual and 4695 ± 1892 cells per individual for females. The cells of E. coli were phagocytized by the hemocytes. Our findings increased the knowledge of hemocytes in P. hawaiensis and is a step forward in using hemocyte-based immune responses as an endpoint in ecotoxicology.     

Fishers' Knowledge Reveals Ecological Interactions Between Fish and Plants in High Diverse Tropical Rivers

Ecosystems - Frugivory and seed dispersal by fish is an important mutualistic interaction in complex and species-rich tropical rivers. The local ecological knowledge (LEK) held by fishers can...