Changes In Food Resources Research Articles

Seasonal variation in the stomach microbiota of two sympatrically breeding Pygoscelis penguin species at Signy Island, South Orkney Islands.

The gut microbiomes of Antarctic penguins are important for the fitness of the host birds and their chicks. The compositions of microbial communities in Antarctic penguin guts are strongly associated with the birds' diet, physiological adaptation and phylogeny. Whilst seasonal changes in food resources, distribution and population parameters of Antarctic penguins have been well addressed, little research is available on the stability or variability of penguin stomach microbiomes over time. Here, we focused on two Pygoscelis penguin species breeding sympatrically in the maritime Antarctic and analysed their stomach contents to assess whether penguin gut microbiota differed over three austral summer breeding seasons. We used a high-throughput DNA sequencing approach to study bacterial diversity in stomach regurgitates of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins that have a similar foraging regime on Signy Island (South Orkney Islands). Our data revealed significant differences in bacterial alpha and beta diversity between the study seasons. We also identified bacterial genera that were significantly associated with specific breeding seasons, diet compositions, chick-rearing stages and sampling events. This study provides a baseline for establishing future monitoring of penguin gut microbiomes in a rapidly changing environment.

Detritivores maintain stoichiometric homeostasis, but alter body size and population density in response to altitude induced stoichiometric mismatches

Maintaining a balance between growth needs and available food resources is critical to the development of any organism. Ecological stoichiometry provides a theoretical basis for studying stoichiometric mismatches between organisms and their food resources. Recent studies have shown that detritivore taxa occupying different multidimensional stoichiometric niches (MSNs) exhibit different stoichiometric mismatch patterns. However, changes in stoichiometric mismatch patterns of different functional groups within the same taxon in response to changes in food resources are poorly understood. Here, we investigated changes in the stoichiometric mismatch between litter as major food resource and five functional groups of soil detritivores (millipedes; Diplopoda) for eleven elements along an altitudinal gradient from 800 to 1850 m on Changbai Mountain, Northeast China. We quantified MSNs and multidimensional stoichiometric mismatch patterns, and investigated changes with altitude and relationships with body size and population density. The concentration of chemical elements of litter varied significantly with altitude and this also was true for the trophic stoichiometric mismatch in millipedes. Furthermore, millipede stoichiometry homeostasis resulted in changing stoichiometric mismatches with changing litter element ratios. Element concentrations in litter, specifically N, Ca, P, Na and Cu, impacted the body size and population density of millipedes, with different elements correlating with individual functional groups. The results indicate that consumer-resource stoichiometric mismatches significantly affect detritivore populations, highlighting the predictive power of the multidimensional stoichiometry framework for detritivore community composition in context of environmental change.

Food resource richness increases seed disperser visitations and seed rain richness.

Within the context of global change, seed dispersal research often focuses on changes in disperser communities (i.e., seed dispersers, such as birds, in an area) resulting from habitat fragmentation. This approach may not be completely illustrative due to certain seed disperser communities being more robust to fragmentation. Additionally, this top-down approach overlooks how changing food resources on landscapes impacts resource tracking and, subsequently, seed dispersal. We hypothesized resource tracking may promote diffuse plant-animal dispersal mutualisms if resource richness is positively linked to disperser and seed rain richness. We predicted increasing food resource richness attracts more visits and species of avian dispersers, resulting in higher counts and greater species richness of seeds deposited at sites (i.e., seed rain). We tested this mechanism in two replicated field experiments using a model system with bird feeders positioned above seed traps. In the first experiment, we demonstrated resource presence skews seed rain. In the second experiment, we explored how species richness of food resources (0, 4, 8, or 12 species) affected the species richness and visitation of avian seed dispersers at feeders and in subsequent seed rain. Collectively, we observed a positive relationship between available food resources and seed rain, likely mediated by resource tracking behavior of avian dispersers. Our findings underscore a potential key mechanism that may facilitate ecological diversity, whereby accumulating species richness in the plant community attracts a more diverse seed disperser community and indirectly promotes more species in seed rain. Importantly, the resource tracking mechanism driving this potential positive feedback loop may also result in negative ecosystem effects if global change diminishes resource availability through homogenization processes, such as invasive species colonization. Future research should explore the bottom-up effects of global change on food resources and seed disperser behavior to complement the literature on changing disperser communities.

An analysis of LULC changes for understanding the impact of anthropogenic activitieson food security: a case study of Dudhganga watershed, India.

Although the Dudhganga watershed is the primary water and food resource of the Kashmir Valley, it has undergone significant changes in food resources and strategies due to rampant urbanization in the area over the past 20years. This urbanization has had a profound impact on the watershed and has also affected land use and land cover (LULC) patterns and environmental changes. The objective of this study is to investigate the effects of urban development on food security parameters in the Dudhganga watershed area, India, from 2000 to 2020, by evaluating LULC changes. Additionally, the study aims to examine the relationship between climate changes and LULC indices, such as the Modified Normalized Difference Water Index (MNDWI), Normalized Difference Vegetation Index (NDVI), and Normalized Difference Built-up Index (NDBI). The results indicate a 21.66% increase in barren areas, at the expense of snow-covered lands, during the 2000-2020 period. The primary land cover transition observed is towards barren areas. The predictions for LULC in 2030 highlight the need for careful management of land use and climate changes in the study area. This study can assist local government officials in reassessing food strategies by identifying areas where urban expansion should be controlled and climate impacts minimized, to prevent local hunger and ecological degradation. Therefore, the development of systematic urban planning approaches and mitigation of climate change sources are crucial. Furthermore, the adoption of advanced agricultural technology should be considered to mitigate the impact of urban expansion.

The putatively high-altitude adaptation of macaque monkeys: Evidence from the fecal metabolome and gut microbiome.

Animals living in high-altitude environments, such as the Tibetan Plateau, must face harsh environmental conditions (e.g., hypoxia, cold, and strong UV radiation). These animals' physiological adaptations (e.g., increased red cell production and turnover rate) might also be associated with the gut microbial response. Bilirubin is a component of red blood cell turnover or destruction and is excreted into the intestine and reduced to urobilinoids and/or urobilinogen by gut bacteria. Here, we found that the feces of macaques living in high-altitude regions look significantly browner (with a high concentration of stercobilin, a component from urobilinoids) than those living in low-altitude regions. We also found that gut microbes involved in urobilinogen reduction (e.g., beta-glucuronidase) were enriched in the high-altitude mammal population compared to the low-altitude population. Moreover, the spatial-temporal change in gut microbial function was more profound in the low-altitude macaques than in the high-altitude population, which might be attributed to profound changes in food resources in the low-altitude regions. Therefore, we conclude that a high-altitude environment's stress influences living animals and their symbiotic microbiota.

Linking changes in individual specialization and population niche of space use across seasons in the great evening bat (Ia io)

BackgroundThe niche breadth of an animal population comprises both within-individual and between-individual variation (individual specialization). Both components can be used to explain changes in population niche breadth, and this has been extensively investigated in dietary niche dimension studies. However, little is known about how changes in food resources or environmental factors across seasons affect changes in individual and population space use within the same population.MethodsIn this study, we used micro-GPS loggers to capture the space use of individuals and of a population of the great evening bat (Ia io) in summer and autumn. We used I. io as a model to investigate how individual spatial niche breadth and spatial individual specialization affect changes in population niche breadth (home range and core area sizes) across seasons. Additionally, we explored the drivers of individual spatial specialization.ResultsWe found that the population home range and the core area of I. io did not increase in autumn when insect resources were reduced. Moreover, I. io showed different specialization strategies in the two seasons: higher spatial individual specialization in summer and lower individual specialization but broader individual niche breadth in autumn. This trade-off may maintain the dynamic stability of the population spatial niche breadth across seasons and facilitate the population response to changes in food resources and environmental factors.ConclusionsLike diet, spatial niche breadth of a population also may be determined by a combination of individual niche breadth and individual specialization. Our work provides new insights into the evolution of niche breadth from the spatial dimension.

Herbivorous dietary selection shown by hawfinch (Coccothraustes coccothraustes) within mixed woodland habitats.

Knowledge of diet and dietary selectivity is vital, especially for the conservation of declining species. Accurately obtaining this information, however, is difficult, especially if the study species feeds on a wide range of food items within heterogeneous and inaccessible environments, such as the tree canopy. Hawfinches (Coccothraustes coccothraustes), like many woodland birds, are declining for reasons that are unclear. We investigated the possible role that dietary selection may have in these declines in the UK. Here, we used a combination of high-throughput sequencing of 261 hawfinch faecal samples assessed against tree occurrence data from quadrats sampled in three hawfinch population strongholds in the UK to test for evidence of selective foraging. This revealed that hawfinches show selective feeding and consume certain tree genera disproportionally to availability. Positive selection was shown for beech (Fagus), cherry (Prunus), hornbeam (Carpinus), maples (Acer) and oak (Quercus), while Hawfinch avoided ash (Fraxinus), birch (Betula), chestnut (Castanea), fir (Abies), hazel (Corylus), rowan (Sorbus) and lime (Tilia). This approach provided detailed information on hawfinch dietary choice and may be used to predict the effects of changing food resources on other declining passerines populations in the future.

Foraging behaviour of the Great Spotted Woodpecker (Dendrocopos major) in the Białowieża National Park

Although the Great Spotted Woodpecker (Dendrocopos major) is the most common of the European woodpecker species, there are no studies detailing its foraging behaviour in the breeding and non-breeding seasons. Our research, conducted in the primeval oak-lime-hornbeam forest of the Białowieża National Park in 1999–2011, compared foraging sites and foraging techniques used by this species in these two seasons. Great Spotted Woodpecker predominantly foraged on standing trees, while lying trees and the ground were occasionally used as foraging sites, but almost exclusively in the breeding season. European hornbeam (Carpinus betulus) and small-leaved lime (Tilia cordata) were the most frequently used for foraging in the breeding season, whereas Norway spruce (Picea abies) and pedunculate oak (Quercus robur) were used in the non-breeding season. Great Spotted Woodpecker foraged more frequently on dead and large trees in the non-breeding season. In the breeding season, Great Spotted Woodpecker collected food mainly from living substrates, predominantly sites on large diameter trunks and at low height, while in the non-breeding season it collected food from thin, dead and upper branches. Searching for food and gleaning it from the tree surface was the most common foraging technique used in the breeding season, whereas seed extraction from cones dominated in the non-breeding season. The percentage of foraging time spent on this type of food was positively correlated with the index of Norway spruce seed production. Our study showed that the foraging behaviour of the Great Spotted Woodpecker in the two seasons differs significantly due to changes in food resources.

Fertilization alters the abundance but not the diversity of soil fauna: A meta‐analysis

AbstractAimSoil fauna, a functionally important group of soil organisms, are greatly affected by fertilization. However, it is still debated whether and how fertilization affects the soil faunal community. Here, we aimed to synthesize the global patterns of soil fauna communities in response to fertilization in terrestrial ecosystems.LocationGlobal.Time period1997–2021.Major taxa studiedSoil fauna.MethodsWe examined the effects of fertilization on the abundance, number of groups and Shannon diversity of soil fauna by synthesizing 1218 observations based on 39 published studies. We also explored the associations between fertilization‐induced changes in the soil faunal community and changes in soil and microbial properties.ResultsFertilization increased the abundance of soil fauna by 56.3%, without significantly affecting the number of groups and the Shannon index. The type of fertilizer affected the responses of soil faunal abundance, and the effects of fertilizer type were altered by climate zones, ecosystem types and soil depths. Both organic and organic–mineral fertilizer treatments significantly increased the abundance of soil fauna in most climate zones, ecosystem types and soil depths, whereas mineral fertilizer treatment had no such effect. Additionally, we found inconsistent responses of soil fauna to fertilization among different taxonomic groups, not only at the order level but also at the class level, providing evidence for the idiosyncratic nature of the effects of fertilization on soil fauna. Furthermore, our regression analysis showed that changes in food resources, including soil nutrients and microbes, were crucial controls for the response of soil faunal abundance to fertilization.Main conclusionsFertilization generally increased soil faunal abundance at the global scale by affecting food resources, and the effects of fertilization were dependent on the specific soil fauna and type of fertilizer. We suggest the use of organic or organic–mineral fertilizers, rather than mineral fertilizers, to increase the benefits on specific soil fauna.

Adaptation of Drosophila larva foraging in response to changes in food resources.

All animals face the challenge of finding nutritious resources in a changing environment. To maximize lifetime fitness, the exploratory behavior has to be flexible, but which behavioral elements adapt and what triggers those changes remain elusive. Using experiments and modeling, we characterized extensively how Drosophila larvae foraging adapts to different food quality and distribution and how the foraging genetic background influences this adaptation. Our work shows that different food properties modulated specific motor programs. Food quality controls the traveled distance by modulating crawling speed and frequency of pauses and turns. Food distribution, and in particular the food-no food interface, controls turning behavior, stimulating turns toward the food when reaching the patch border and increasing the proportion of time spent within patches of food. Finally, the polymorphism in the foraging gene (rover-sitter) of the larvae adjusts the magnitude of the behavioral response to different food conditions. This study defines several levels of control of foraging and provides the basis for the systematic identification of the neuronal circuits and mechanisms controlling each behavioral response.

Modelling the spatial extent of post‐fire sedimentation threat to estimate the impacts of fire on waterways and aquatic species

AbstractAimFires can severely impact aquatic fauna, especially when attributes of soil, topography, fire severity and post‐fire rainfall interact to cause substantial sedimentation. Such events can cause immediate mortality and longer‐term changes in food resources and habitat structure. Approaches for estimating fire impacts on terrestrial species (e.g. intersecting fire extent with species distributions) are inappropriate for aquatic species as sedimentation can carry well downstream of the fire extent, and occur long after fire. Here, we develop an approach for estimating the spatial extent of fire impacts for aquatic systems, across multiple catchments.LocationSouthern Australian bioregions affected by the fires in 2019–2020 that burned >10 million ha of temperate and subtropical forests.MethodsWe integrated an existing soil erosion model with fire severity mapping and rainfall data to estimate the spatial extent of post‐fire sedimentation threat in waterways and in basins and the potential exposure of aquatic species to this threat. We validated the model against field observations of sedimentation events after the 2019–20 fires.ResultsWhile fires overlapped with ~27,643 km of waterways, post‐fire sedimentation events potentially occurred across ~40,449 km. In total, 55% (n = 85) of 154 basins in the study region may have experienced substantial post‐fire sedimentation. Ten species—including six Critically Endangered—were threatened by post‐fire sedimentation events across 100% of their range. The model increased the estimates for potential impact, compared to considering fire extent alone, for >80% of aquatic species. Some species had distributions that did not overlap with the fire extent, but that were entirely exposed to post‐fire sedimentation threat.ConclusionsCompared with estimating the overlap of fire extent with species' ranges, our model improves estimates of fire‐related threats to aquatic fauna by capturing the complexities of fire impacts on hydrological systems. The model provides a method for quickly estimating post‐fire sedimentation threat after future fires in any fire‐prone region, thus potentially improving conservation assessments and informing emergency management interventions.

Diet composition based on stable isotopic analysis of fecal samples reveals the preference of Black-faced Spoonbill (Platalea minor) for natural wetlands and fishponds

The Black-faced Spoonbill (<em>Platalea minor</em>; BFS) is a globally endangered species that is distributed only in the coastal zones of East Asia. Xinghua Bay is one of the main wintering sites and migration stopovers of BFS in mainland China. However, with the reduction and degradation of natural wetlands, it is uncertain whether artificial wetlands can provide habitat for the endangered BFS. Research on the diet of BFS will help to understand their preferences between natural and artificial wetlands and provide a reference for their conservation and habitat restoration. From December 2017 to February 2020, 45 potential food samples and 199 fecal samples of BFS were collected during six sampling periods, of which Cyprinidae, Mugilidae, Portunidae, Gobiidae and Palaemonidae were collected from natural wetlands and Crucian (<em>Carassius auratus</em>) and whiteleg shrimp (<em>Litopenaeus vannamei</em>) were collected from fishponds. Their stable isotope values (e.g., δ¹³C and δ¹⁵N) were measured to obtain the food composition information for BFS. In early winter, the proportion of Palaemonidae in BFS food was as high as 74.4%, while those of other foods were only 3.0% to 6.0%. In late winter, the food contributions for BFS were as follows: Portunidae 39.3% > Palaemonidae 26.1% > Cyprinidae 8.8% > Mugilidae 8.5% > Gobiidae 7.3% > Crucian 5.1% > whiteleg shrimp 4.8%. The proportion of Portunidae exceeded that of Palaemonidae, and together with Palaemonidae, it became the main food of BFS in late winter. The diet compositions of BFS between early and late winter were significantly different, which may be due to seasonal changes in food resources. Natural wetlands are the main feeding grounds of BFS, but fishponds also provide them with supplementary feeding grounds and resting places. Fishponds play an important ecological function in maintaining the overwintering population of BFS in Xinghua Bay.

Seasonality in daily movement patterns of mandrills revealed by combining direct tracking and camera traps.

Movement is a fundamental characteristic of animals, but challenging to measure noninvasively. Noninvasive methods for measuring travel have different weaknesses, so multiple techniques need to be applied multiple techniques for reliable inferences. We used two methods, direct tracking and camera trapping, to examine the variation in time and seasonal differences in movement rates of mandrills (Mandrillus sphinx), an elusive primate that lives in large groups in central Africa. In a 400-km2 rainforest area in Moukalaba-Doudou National Park, Gabon, we tracked unidentified groups 46 times from 2009 to 2013. We systematically placed 157 terrestrial camera traps in the same area from 2012 to 2014 and recorded groups 309 times. Generalized additive mixed models (GAMMs) of the tracking data indicated that the group travel speed varied with time and season. In the fruiting season, the movement rate fluctuated with time in a bimodal pattern, whereas in the nonfruiting season, it increased monotonously with time. The predicted day range was longer in the fruiting season (6.98 km) than in the nonfruiting season (6.06 km). These seasonal differences suggest responses to changes in food resources and temperature. Camera-trap detection rates showed similar temporal and seasonal patterns to the tracking data, allowing us to generalize our findings to the population level. Moreover, cameras never detected mandrills at night, and we observed that they slept high in trees and hardly moved until the next morning, all suggesting their strict avoidance of nighttime movement. This study demonstrated the significance of the multiple-method approach in drawing robust conclusions on temporal patterns of animal movement.

Great tits who remember more accurately have difficulty forgetting, but variation is not driven by environmental harshness

The causes of individual variation in memory are poorly understood in wild animals. Harsh environments with sparse or rapidly changing food resources are hypothesized to favour more accurate spatial memory to allow animals to return to previously visited patches when current patches are depleted. A potential cost of more accurate spatial memory is proactive interference, where accurate memories block the formation of new memories. This relationship between spatial memory, proactive interference, and harsh environments has only been studied in scatter-hoarding animals. We compare spatial memory accuracy and proactive interference performance of non-scatter hoarding great tits (Parus major) from high and low elevations where harshness increases with elevation. In contrast to studies of scatter-hoarders, we did not find a significant difference between high and low elevation birds in their spatial memory accuracy or proactive interference performance. Using a variance partitioning approach, we report the first among-individual trade-off between spatial memory and proactive interference, uncovering variation in memory at the individual level where selection may act. Although we have no evidence of harsh habitats affecting spatial memory, our results suggest that if elevation produced differences in spatial memory between elevations, we could see concurrent changes in how quickly birds can forget.

Analysis of Structural Changes in Food Accessibility Assurance in Russia and Its Macroregions Through Food Security

This article dwells upon the food security of the country in the context of structural changes in national and regional agriculture. The physical availability indicators of food for Russia and its Central and Far Eastern Federal Districts were calculated for the period from 2014 to 2018. The authors analyzed structural changes in the production of the main food types across household categories. The authors determined the intensity and orientation of structural changes in food resources. It is established that structural changes in food accessibility assurance in the Far East (as compared with the country as a whole and the Central district) associated with regional production are by and large regressive. The article shows that the physical availability of food products in the Far Eastern region during the sanctions and countersanctions features negative dynamics. To condition positive structural changes in regional agriculture, it is necessary that the government support agricultural businesses of various legal entity types.

Effects of increased temperature on arctic slimy sculpin Cottus cognatus is mediated by food availability: Implications for climate change

Abstract Lakes are vulnerable to climate change, and warming rates in the Arctic are faster than anywhere on Earth. Fishes are sensitive to changing temperatures, which directly control physiological processes. Food availability should partly dictate responses to climate change because energetic demands change with temperature, but few studies have simultaneously examined temperature and food availability. We used a fully factorial experiment to test effects of food availability and temperature (7.6, 12.7, and 17.4°C; 50 days) on growth, consumption, respiration, and excretion, and effects of temperature (12 and 19.3°C; 27 days) on habitat use and growth of a common, but understudied, mid‐level consumer, slimy sculpin Cottus cognatus, in arctic lakes. We also used bioenergetics modelling to predict consumptive demand under future warming scenarios. Growth rates were 3.4× higher at 12.7°C in high food compared to low food treatments, but the magnitude of differences depended on temperature. Within low food treatments, there was no statistical difference in growth rates among temperatures, suggesting food limitation. Consumption, respiration, and nitrogen excretion increased with temperature independent of food availability. Lower growth rates coincided with lower phosphorus excretion at the highest temperature, suggesting that fish selectively retained phosphorus at high temperatures and low food. In habitat choice experiments, fish were more likely to use the 12°C side of the tank, closely matching their optimal temperature. We predicted a 9% increase in consumption is required to maintain observed growth under a 4°C warming scenario. These results highlight considering changes in food resources and other associated indirect effects (e.g. excretion) that accompany changing temperatures with climate change. Depending on how food webs respond to warming, fish may cope with predicted warming if density‐dependent feedback maintains population sizes.

DNA diet profiles with high-resolution animal tracking data reveal levels of prey selection relative to habitat choice in a crepuscular insectivorous bird.

Given the global decline of many invertebrate food resources, it is fundamental to understand the dietary requirements of insectivores. We give new insights into the functional relationship between the spatial habitat use, food availability, and diet of a crepuscular aerial insectivore, the European Nightjar (Caprimulgus europaeus) by relating spatial use data with high‐throughput sequencing (HTS) combined with DNA metabarcoding. Our study supports the predictions that nightjars collect a substantial part of their daily nourishment from foraging locations, sometimes at considerable distance from nesting sites. Lepidopterans comprise 65% of nightjars' food source. Nightjars tend to select larger species of Lepidoptera (>19 mm) which suggests that nightjars optimize the efficiency of foraging trips by selecting the most energetically favorable—larger—prey items. We anticipate that our findings may shed additional light on the interactions between invertebrate communities and higher trophic levels, which is required to understand the repercussions of changing food resources on individual‐ and population‐level processes.

Responses of soil microarthropod taxon (Hexapoda: Protura) to natural disturbances and management practices in forest-dominated subalpine lake catchment areas

Disturbances are intrinsic drivers of structure and function in ecosystems, hence predicting their effects in forest ecosystems is essential for forest conservation and/or management practices. Yet, knowledge regarding belowground impacts of disturbance events still remains little understood and can greatly vary by taxonomic and functional identity, disturbance type and local environmental conditions. To address this gap in knowledge, we conducted a survey of soil-dwelling Protura, across forests subjected to different disturbance regimes (i.e. windstorms, insect pest outbreaks and clear-cut logging). We expected that the soil proturan assemblages would differ among disturbance regimes. We also hypothesized that these differences would be driven primarily by variation in soil physicochemical properties thus the impacts of forest disturbances would be indirect and related to changes in food resources. To verify that sampling included two geographically distant subalpine glacial lake catchments that differed in underlying geology, each having four different types of forest disturbance, i.e. control, bark beetle outbreak (BB), windthrow + BB (wind + BB) and clear-cut. As expected, forest disturbance had negative effects on proturan diversity and abundance, with multiple disturbances having the greatest impacts. However, differences in edaphic factors constituted a stronger driver of variability in distribution and abundance of proturans assemblages. These results imply that soil biogeochemistry and resource availability can have much stronger effects on proturan assemblages than forest disturbances.

Effects of changes in food resources due to variations in forest cover on stream macroinvertebrate community size structure

Changes in land cover are one of the most extensive and influential human impacts on fluvial ecosystems. In this study, we assessed how changes in food resource quantity and type linked to forest cover affect mountain stream multitrophic macroinvertebrate community size structure. We tested whether the total organism biomass (size spectrum intercept) and the energy transfer efficiency among trophic levels (size spectrum slope) are altered. Community size spectra slopes remained unchanged with variations in food resource type, while intercept increased with resource quantity. This pointed to an internal compensatory regulation of the community size structure for the maintenance of trophic transfer efficiency, only adjusting the total organism biomass to total food resource quantity through variations in organism abundance. Community size structure consistency was related to detritivore-omnivore substitutions, although the shifts in size structure with variations in the degree of allochthony differed between these feeding groups. Omnivore change was numerical (i.e., increase in large organism density with a decrease in allochthony) not related to body size or taxonomic composition. In contrast, detritivores showed a reduction in body size with the decrease in allochthony that did not coincide with a reduction in total biomass or density, but was related to a taxonomic replacement of larger case-building trichopterans by smaller detritivores. These findings elucidate how the size structure of a multitrophic macroinvertebrate community might respond to changes in forest cover, shedding light on the effects of global environmental change on the structure and stability of stream food webs.

The effect of diet on Apis mellifera larval susceptibility to Paenibacillus larvae

Honey bees are threatened by changes in food resources. American Foulbrood (AFB), caused by Paenibacillus larvae, affects Apis mellifera larvae which progressively become more resistant to the disease with age. It has been suggested that nutritional limitations could result in increased susceptibility upon exposure to pathogens. This research, conducted on laboratory-reared honey bee larvae, aimed to analyze the effects of diet quality on the susceptibility of Apis mellifera larvae to P. larvae infections. The values of the lethal dose that killed 50% of the inoculated larvae (LD50) were determined for five strains of P. larvae (ERIC I). Virulence ranged from 2 spores/μl for the N15 strain to 906 spores/μl for the Miramar strain. Different groups of larvae infected with half of the LD50 doses of P. larvae strains were fed Aupinel diet (with daily increases of glucose, fructose, yeast extract and royal jelly) and four different modifications thereof. The results show that the absence of a diet component tends to cause an increase in mortality associated with the infection, depending on the virulence of the strain and the component suppressed. Glucose and fructose suppression, and mainly royal jelly deprivation, affect larval susceptibility to AFB and their survival.