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Introduction: The crude protein level in the diet will affect the fermentation parameters, microflora, and metabolites in the rumen of ruminants. It is of great significance to study the effect of crude protein levels in supplementary diet on microbial community and metabolites for improving animal growth performance. At present, the effects of crude protein level in supplementary diet on rumen fermentation parameters, microbial community, and metabolites of Jersey-Yak (JY) are still unclear. Methods: The purpose of this experiment was to study the appropriate crude protein level in the diet of JY. The rumen fermentation indexes (volatile fatty acids and pH) were determined by supplementary diets with crude protein levels of 15.16 and 17.90%, respectively, and the microbial community and metabolites of JYs were analyzed by non-target metabonomics and metagenome sequencing technology, and the changes of rumen fermentation parameters, microbial flora, and metabolites in the three groups and their interactions were studied. Results and Discussion: The crude protein level in the supplementary diet had significant effects on pH, valeric acid, and the ratio of acetic acid to propionic acid (p < 0.05). The protein level had no significant effect on the dominant microflora at the phylum level (p > 0.05), and all three groups were Bacteroides and Firmicutes. The results of metabolite analysis showed that the crude protein level of supplementary diet significantly affected the metabolic pathways such as Bile secretion and styrene degradation (p < 0.05), and there were different metabolites between the LP group and HP group, and these different metabolites were related to the dominant microbial to some extent. To sum up, in this experiment, the effects of crude protein level in supplementary diet on rumen microorganisms and metabolites of JY and their relationship were studied, which provided the theoretical basis for formulating a more scientific and reasonable supplementary diet in the future. [ABSTRACT FROM AUTHOR]

Three experimental groups with different feeding frequencies, different feeding rates and compensatory feeding were set up to study their effects on the growth of Micropterus salmoides. The results showed that different feeding rates of 2%, 3% and 4% had no significant effects on the growth of M. salmoides. Therefore, before the individual weight of 50 g, the fish could be fed with a feeding rate of 4%, which could be gradually decreased to 2% in the later period. Under the condition of relatively fixed feeding rate, different feeding frequencies had an impact on the growth of M. salmoides. Under the conditions of suitable water temperature, it is reasonable to feed twice daily. The experimental fish fed for 5 d and then deprived of feed for 1 d showed fully compensatory growth, and there were no significant differences in weight gain rate, daily weight gain and specific growth rate compared with the continuous feeding group (P >0.05). Therefore, according to the feeding conditions of fish in the breeding process, stopping feeding for 1 d every 5 d could save feed and labor and improve breeding efficiency. [ABSTRACT FROM AUTHOR]

In the present Anthropocene, wild animals are globally affected by human activity. Consumer fireworks during New Year (NY) are widely distributed in W‐Europe and cause strong disturbances that are known to incur stress responses in animals. We analyzed GPS tracks of 347 wild migratory geese of four species during eight NYs quantifying the effects of fireworks on individuals. We show that, in parallel with particulate matter increases, during the night of NY geese flew on average 5–16 km further and 40–150 m higher, and more often shifted to new roost sites than on previous nights. This was also true during the 2020–2021 fireworks ban, despite fireworks activity being reduced. Likely to compensate for extra flight costs, most geese moved less and increased their feeding activity in the following days. Our findings indicate negative effects of NY fireworks on wild birds beyond the previously demonstrated immediate response. [ABSTRACT FROM AUTHOR]

Abstract In the present Anthropocene, wild animals are globally affected by human activity. Consumer fireworks during New Year (NY) are widely distributed in W‐Europe and cause strong disturbances that are known to incur stress responses in animals. We analyzed GPS tracks of 347 wild migratory geese of four species during eight NYs quantifying the effects of fireworks on individuals. We show that, in parallel with particulate matter increases, during the night of NY geese flew on average 5–16 km further and 40–150 m higher, and more often shifted to new roost sites than on previous nights. This was also true during the 2020–2021 fireworks ban, despite fireworks activity being reduced. Likely to compensate for extra flight costs, most geese moved less and increased their feeding activity in the following days. Our findings indicate negative effects of NY fireworks on wild birds beyond the previously demonstrated immediate response.

Global environmental change exerts growing pressure on biodiversity. Anthropogenic climate and land use change are particularly important drivers of biodiversity loss. While their effects on biodiversity have been widely studied individually, interactions among them are poorly understood. Here, we investigate the effects of two common drivers of global change, increased temperature and nitrogen fertilization, on host‐plant quality and herbivore performance in the butterfly Lycaena tityrus. We show that butterfly performance was positively affected by plants grown at increased temperatures and nitrogen fertilization, the latter being in line with the nitrogen limitation hypothesis. Effects were largely consistent across treatments; that is, nitrogen deposition and temperature did not interact strongly to affect herbivore performance. Overall, females suffered more strongly than males from poor host‐plant quality. Our study demonstrates changes in host‐plant quality caused by variation in temperature and nitrogen availability, which induced indirect effects in an herbivore. Such indirect effects of global environmental change are an important source of variation and should be considered in order to reduce uncertainties with regard to the effects of global change on biodiversity. [ABSTRACT FROM AUTHOR]

In the Neotropical region, euphonias (Euphonia spp., Fringillidae) are the quintessential example of specialized bird frugivores, making the bulk of feeding visits to certain mistletoes (Phoradendron spp., Santalaceae) and epiphytes in the genus Rhipsalis (Cactaceae), whose fruits have high water and low sugar and protein concentrations. Surprisingly, a mechanistic explanation for such specialized, otherwise rare, relationships is lacking. Using captive birds and artificial diets, we contrasted euphonias with frugivorous tanagers in the genus Thraupis (Thraupidae), which rarely eats Rhipsalis fruits, to test the hypothesis that the digestive capacity of euphonias entails them to exploit such low‐energy fruits. We expected that compensatory feeding in response to decreasing energy density would occur only in euphonias, whose higher reliance on fruits would entail a lower nitrogen requirement than the tanagers. Euphonias and tanagers were both able to compensate energy intake as sugar density decreased, and both species had the same mass‐corrected energy intake at any given sugar concentration. Similarly, euphonias and tanagers did not differ in mass‐corrected maintenance nitrogen requirement. Therefore, the physiological traits we investigated do not explain euphonias' specialization on Rhipsalis fruits. The fast rates of fruit passage typical of specialized avian frugivores as euphonias that entail the processing of a large volume of fruits and the putative better abilities of such birds to deal with secondary compounds likely present in Rhipsalis fruits are other possible mechanisms that should be considered in future studies to unveil the mechanisms underlying the intriguing specialized relationships between euphonias and certain fruits. [ABSTRACT FROM AUTHOR]

Abstract Global environmental change exerts growing pressure on biodiversity. Anthropogenic climate and land use change are particularly important drivers of biodiversity loss. While their effects on biodiversity have been widely studied individually, interactions among them are poorly understood. Here, we investigate the effects of two common drivers of global change, increased temperature and nitrogen fertilization, on host‐plant quality and herbivore performance in the butterfly Lycaena tityrus. We show that butterfly performance was positively affected by plants grown at increased temperatures and nitrogen fertilization, the latter being in line with the nitrogen limitation hypothesis. Effects were largely consistent across treatments; that is, nitrogen deposition and temperature did not interact strongly to affect herbivore performance. Overall, females suffered more strongly than males from poor host‐plant quality. Our study demonstrates changes in host‐plant quality caused by variation in temperature and nitrogen availability, which induced indirect effects in an herbivore. Such indirect effects of global environmental change are an important source of variation and should be considered in order to reduce uncertainties with regard to the effects of global change on biodiversity.

The use of biochar as a soil amendment in forest ecosystems can be beneficial in the restoration of degraded soils. Forest insects such as the Douglas-fir tussock moth, Orgyia pseudotsugata (McDonnough) (Lepidoptera: Erebidae), may be exposed to biochar when the material is applied. Two experiments were conducted using biochar either (1) applied to the surface of the diet at three rates (0, 5, and 10 mg) or (2) incorporated into synthetic diet at four rates (0, 10, 20, and 40% volume/volume). The objective of both experiments was to determine if biochar on the surface or incorporated into a synthetic diet affected development and survival of O. pseudotsugata larvae. In both experiments, there was a significant decrease in estimated time to larval mortality in all biochar treatments compared to untreated controls. In the surface-applied biochar experiment, there was a significant difference in larval weight gain at day 12 between the control and 10 mg biochar treatments. In the experiment with biochar incorporated into the diet, mean larval weight at day 12 was highest in the low (10%) biochar treatment compared to all other treatments, although weight gain was only significantly different between the low- and high-concentration (40%) biochar treatments. Our results suggest that larvae, feeding on a low amount of biochar in the synthetic diet, may respond by engaging in compensatory feeding behavior. Fewer surviving larvae in the biochar treatment groups may contribute to the lack of significance found in the comparison of weight gain at day 24 in each experiment.

Anthropogenic activities have reshaped the relative supply rates of essential elements to organisms. Recent studies suggested that consumer performance is strongly reduced by food that is either very high or very low in relative phosphorus content. However, the generality of such 'stoichiometric knife‐edge' and its underlying mechanisms are poorly understood. We studied the response of a planktonic rotifer to a 10‐fold food carbon : phosphorus (C : P) gradient and confirmed the existence of the stoichiometric knife‐edge. Interestingly, we observed a complete homeostatic breakdown associated with strong growth reductions at high food C : P. In contrast, at low food C : P, animals maintained homeostasis despite pronounced performance reductions. Our results suggest that the mechanisms underlying adverse effects of stoichiometric imbalance are determined by both the identity of elements that are limiting and those that are present in excess. Negative effects of excess P reveal an additional way of how eutrophication may affect consumers. [ABSTRACT FROM AUTHOR]

Abstract Background Mass occurrences of cyanobacteria frequently cause detrimental effects to the functioning of aquatic ecosystems. Consequently, attempts haven been made to control cyanobacterial blooms through naturally co-occurring herbivores. Control of cyanobacteria through herbivores often appears to be constrained by their low dietary quality, rather than by the possession of toxins, as also non-toxic cyanobacteria are hardly consumed by many herbivores. It was thus hypothesized that the consumption of non-toxic cyanobacteria may be improved when complemented with other high quality prey. We conducted a laboratory experiment in which we fed the herbivorous freshwater gastropod Lymnaea stagnalis single non-toxic cyanobacterial and unialgal diets or a mixed diet to test if diet-mixing may enable these herbivores to control non-toxic cyanobacterial mass abundances. Results The treatments where L. stagnalis were fed non-toxic cyanobacteria and a mixed diet provided a significantly higher shell and soft-body growth rate than the average of all single algal, but not the non-toxic cyanobacterial diets. However, the increase in growth provided by the non-toxic cyanobacteria diets could not be related to typical determinants of dietary quality such as toxicity, nutrient stoichiometry or essential fatty acid content. Conclusions These results strongly contradict previous research which describes non-toxic cyanobacteria as a low quality food resource for freshwater herbivores in general. Our findings thus have strong implications to gastropod-cyanobacteria relationships and suggest that freshwater gastropods may be able to control mass occurrences of benthic non-toxic cyanobacteria, frequently observed in eutrophied water bodies worldwide.

The modulation of nutritional intake by animals to combat pathogens is a behaviour that is receiving increasing attention. Ant studies using isolated compounds or nutrients in artificial diets have revealed a lot of the dynamics of the behaviour, but natural sources of medicine are yet to be confirmed. Here we explored whether Formica fusca ants exposed to a fungal pathogen can use an artificial diet containing foods spiked with different concentrations of crushed aphids for a medicinal benefit. We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented foods during the acute phase of the infection, reducing the mortality caused by the disease. However, the benefit was only attained when having access to a varied diet, suggesting that while aphids contain nutrients or compounds beneficial against infection, it is a part of a complex nutritional system where costs and benefits of compounds and nutrients need to be moderated.

Benthic algal biomass and distribution in freshwater ecosystems are determined by both nutrient availability (bottom‐up control) and grazing activity by herbivores (top‐down control). Fluctuations in algal nutrient ratios may cause grazers to optimise their food intake through behavioural strategies in order to maintain a constant soft body stoichiometry. Such linkages between nutrient availability and grazing control of algal biomass are as yet poorly understood.In this study, we tested whether the stream‐dwelling freshwater gastropod Ancylus fluviatilis would increase its food consumption rate with decreasing periphyton nutrient content, a behaviour known as compensatory feeding. We performed a fully factorial microcosm experiment in which two levels of periphyton phosphorus content (low versus high) were crossed with grazer presence/absence in 12 circular flumes. After 1 week of grazing, food consumption rates were measured by determining the periphyton difference between grazed and ungrazed flumes, and the periphyton biomass variability in every flume was described with a coefficient of variation.The food consumption rate of A. fluviatilis was significantly higher in the low phosphorus compared to the high phosphorus treatment, supporting the compensatory feeding hypothesis. As a result, in the presence of grazers, periphyton biomass was significantly lower under low phosphorus availability, while biomass was not affected by nutrient enrichment in the grazer‐free flumes.Despite the strong difference in periphyton phosphorus content, A. fluviatilis soft body stoichiometry did not differ between the two nutrient treatments, suggesting strong stoichiometric homeostasis. Furthermore, the distribution of algal biomass was significantly more heterogeneous in the grazed phosphorus‐poor than in the phosphorus‐rich periphyton.Our findings suggest that nutrient enrichment may lead to a weaker top‐down control of algal biomass in stream ecosystems and to reduced spatial heterogeneity of periphyton abundance. [ABSTRACT FROM AUTHOR]

Nutritional intake and reproductive allocation are strongly associated and dietary energy restriction (ER) or surpluses can affect reproductive capacity. The objective of this study was to investigate the effect of energy levels on sheep testicular development. Three-month old Hu sheep were assigned to four groups, and fed diets containing different levels of energy (Control, maintenance energy; ER1, 85% maintenance energy; ER2, 70% maintenance energy; ER3, 55% maintenance energy). Two months later, half the sheep in each group were euthanized, whereas the remaining sheep were euthanized after a further 3 months feeding on a compensatory energy diet. The testicular weight and reproductive hormone levels of the Hu sheep were investigated. Differences in the testes of ER3 and control group sheep were investigated at the transcriptional level using high-throughput sequencing. The results showed that the testicular weights had decreased in the energy-restricted rams compared with the controls, and that the testosterone concentration in ER3 group rams was significantly lower than that in other compared groups ( P  < 0.05). After the period of compensatory feeding, however, ER3 sheep testicular weight and testosterone concentrations were similar to those of the control group sheep. In addition, the RNA sequencing results revealed that 81 genes were upregulated and 180 genes were downregulated in the ER3 group compared with the control group. Moreover, based on the enriched steroidogenesis, meiosis and kinases pathways, a number of candidate genes potentially involved in the regulation of testicular development or reproduction of Hu sheep, including CYP11A1, ALDH3B1, FDFT1, WNT2, PGR and INSR , were screened. Quantitative real-time polymerase chain reaction analysis results correlated well with the sequencing data. Taken together, this study provides a first insight into the development of the testis with dietary energy restriction in sheep and shows that these changes are associated with alterations in transcriptomic. The sheep testis mRNA database were extended in this study will provides novel candidate regulators for future genetic and molecular studies on sheep testicular development associated with energy restriction, which will contribute to improving the reproductive performance of sheep. [ABSTRACT FROM AUTHOR]

Resources are a core currency of species interactions and ecology in general (e.g., think of food webs or competition). Within parasite-infected hosts, resources are divided among the competing demands of host immunity and growth as well as parasite reproduction and growth. Effects of resources on immune responses are increasingly understood at the cellular level (e.g., metabolic predictors of effector function), but there has been limited consideration of how these effects scale up to affect individual energetic regimes (e.g., allocation trade-offs), susceptibility to infection, and feeding behavior (e.g., responses to local resource quality and quantity). We experimentally rewilded laboratory mice (strain C57BL/6) in semi-natural enclosures to investigate the effects of dietary protein and gastrointestinal nematode (Trichuris muris) infection on individual-level immunity, activity, and behavior. The scale and realism of this field experiment, as well as the multiple physiological assays developed for laboratory mice, enabled us to detect costs, trade-offs, and potential compensatory mechanisms that mice employ to battle infection under different resource conditions. We found that mice on a low-protein diet spent more time feeding, which led to higher body fat stores (i.e., concentration of a satiety hormone, leptin) and altered metabolite profiles, but which did not fully compensate for the effects of poor nutrition on albumin or immune defenses. Specifically, immune defenses measured as interleukin 13 (IL13) (a primary cytokine coordinating defense against T. muris) and as T. muris-specific IgG1 titers were lower in mice on the low-protein diet. However, these reduced defenses did not result in higher worm counts in mice with poorer diets. The lab mice, living outside for the first time in thousands of generations, also consumed at least 26 wild plant species occurring in the enclosures, and DNA metabarcoding revealed that the consumption of different wild foods may be associated with differences in leptin concentrations. When individual foraging behavior was accounted for, worm infection significantly reduced rates of host weight gain. Housing laboratory mice in outdoor enclosures provided new insights into the resource costs of immune defense to helminth infection and how hosts modify their behavior to compensate for those costs.

Abstract: Ecological stoichiometry suggests that herbivore growth is limited by phosphorus when this element in the diet is < 8.6 μg P mg C−1 (C : P atomic ratio > 300). However, in nature, it is not necessarily related to the relative phosphorus content in diets. This may be the result of complex feeding and assimilation responses to diets. We examined these possibilities using herbivorous plankton fed mono‐specific and mixed algae varying in phosphorus content of 1.6 to 8.1 μg P mg C−1. The herbivores showed a 10‐fold growth rate difference among the diets. Growth rates related poorly with phosphorus content in the diets (r2 = 0.07), better with P ingestion rate (r2 = 0.41) and best with phosphorus assimilation rate (r2 = 0.69). Inclusion of assimilation rates for carbon and fatty acids increased 7% of the explained growth variance. These results indicate that the feeding and assimilation flexibilities play pivotal roles in acquiring a deficient element and in regulating growth rate. [ABSTRACT FROM AUTHOR]

Resources are a core currency of species interactions and ecology in general (e.g., think of food webs or competition). Within parasite-infected hosts, resources are divided among the competing demands of host immunity and growth as well as parasite reproduction and growth. Effects of resources on immune responses are increasingly understood at the cellular level (e.g., metabolic predictors of effector function), but there has been limited consideration of how these effects scale up to affect individual energetic regimes (e.g., allocation trade-offs), susceptibility to infection, and feeding behavior (e.g., responses to local resource quality and quantity). We experimentally rewilded laboratory mice (strain C57BL/6) in semi-natural enclosures to investigate the effects of dietary protein and gastrointestinal nematode (Trichuris muris) infection on individual-level immunity, activity, and behavior. The scale and realism of this field experiment, as well as the multiple physiological assays developed for laboratory mice, enabled us to detect costs, trade-offs, and potential compensatory mechanisms that mice employ to battle infection under different resource conditions. We found that mice on a low-protein diet spent more time feeding, which led to higher body fat stores (i.e., concentration of a satiety hormone, leptin) and altered metabolite profiles, but which did not fully compensate for the effects of poor nutrition on albumin or immune defenses. Specifically, immune defenses measured as interleukin 13 (IL13) (a primary cytokine coordinating defense against T. muris) and as T. muris-specific IgG1 titers were lower in mice on the low-protein diet. However, these reduced defenses did not result in higher worm counts in mice with poorer diets. The lab mice, living outside for the first time in thousands of generations, also consumed at least 26 wild plant species occurring in the enclosures, and DNA metabarcoding revealed that the consumption of different wild foods may be associated with differences in leptin concentrations. When individual foraging behavior was accounted for, worm infection significantly reduced rates of host weight gain. Housing laboratory mice in outdoor enclosures provided new insights into the resource costs of immune defense to helminth infection and how hosts modify their behavior to compensate for those costs. [ABSTRACT FROM AUTHOR]

Food processing affects the way animals behave with important implications in their ecology and community structure. Despite numerous studies of food processing by nectar-feeding bats have been done, these have been focused on species living in tropical climates, whereas the information about species inhabiting high altitude environments is scarce. Here, we investigated food processing of the nectar-feeding bat Anoura geoffroyi, a species that can be found in places above 2, 500 m a.s.l. To do this, we evaluated the capacity of bats to assimilate the energy content in seven sucrose solutions ranging from 5 to 35%. We measured: 1) nightly food/energy intake, and 2) changes in body mass of seven captive individuals feeding from the different experimental solutions. Bats increased food intake nearly seven times (from 16.9 ± 4.7 to 111.6 ± 18.7 g) when sucrose concentration decreased from 35 to 5% (wt/vol). By doing this, animals were able to obtain a constant energy intake of 101.07 kJ ± 5.4 (mean ± SD) and a mean body mass gain of 1.31 g ± 0.1 (mean ± SD). Both values were independent of sugar concentration. This response (known as compensatory feeding) may enable bats the access to many feeding sources present in their environment, increasing their feeding niche-breadth and their ability to live in cold environments. [ABSTRACT FROM AUTHOR]

Invertebrate-mediated leaf litter decomposition is frequently used to assess stress-related implications in stream ecosystem integrity. In situ measures such as the mass loss from leaf bags or the feeding of caged invertebrates deployed for days or weeks may, however, fail to detect transient effects due to recovery or compensatory mechanisms. We assessed the relevance of transient effects using the peak exposure towards an insecticide (i.e., etofenprox) as a model scenario at three levels of complexity. These were 1) the assessment of the decomposition realised by invertebrate communities in stream mesocosms over 21 days via leaf bags, 2) 7-days lasting in situ bioassays quantifying the leaf consumption of Gammarus fossarum , and 3) a laboratory experiment determining the daily feeding rate of the same species over 7 days. Etofenprox did not trigger a significantly altered decomposition by invertebrate communities during the leaf bag assay, while in situ bioassays detected a significant reduction in gammarids’ feeding rate at the highest tested concentration. The laboratory bioassay suggests that observed mismatches might be explained by recovery and post-exposure compensation. As leaf-shredding invertebrates are likely in a vulnerable state following transient effects, biomonitoring for implications of peak exposures and other pulsed stress events must happen at an adequate temporal resolution. [ABSTRACT FROM AUTHOR]

Research on parasite-altered feeding behavior in insects is contributing to an emerging literature that considers possible adaptive consequences of altered feeding behavior for the host or the parasite. Several recent ecoimmunological studies show that insects can adaptively alter their foraging behavior in response to parasitism. Another body of recent work shows that infection by parasites can change the behavior of insect hosts to benefit the parasite; manipulations of host feeding behavior may be part of this phenomenon. Here, we address both the functional and the underlying physiological frontiers of parasite-altered feeding behavior in order to spur research that better integrates the two. Functional categories of parasite-altered behavior that are adaptive for the host include prophylaxis, therapy and compensation, while host manipulation is adaptive for the parasite. To better understand and distinguish prophylaxis, therapy and compensation, further study of physiological feedbacks affecting host sensory systems is especially needed. For host manipulation in particular, research on mechanisms by which parasites control host feedbacks will be important to integrate with functional approaches. We see this integration as critical to advancing the field of parasite-altered feeding behavior, which may be common in insects and consequential for human and environmental health. [ABSTRACT FROM AUTHOR]

Background: Mass occurrences of cyanobacteria frequently cause detrimental effects to the functioning of aquatic ecosystems. Consequently, attempts haven been made to control cyanobacterial blooms through naturally co-occurring herbivores. Control of cyanobacteria through herbivores often appears to be constrained by their low dietary quality, rather than by the possession of toxins, as also non-toxic cyanobacteria are hardly consumed by many herbivores. It was thus hypothesized that the consumption of non-toxic cyanobacteria may be improved when complemented with other high quality prey. We conducted a laboratory experiment in which we fed the herbivorous freshwater gastropod Lymnaea stagnalis single non-toxic cyanobacterial and unialgal diets or a mixed diet to test if diet-mixing may enable these herbivores to control non-toxic cyanobacterial mass abundances. Results: The treatments where L. stagnalis were fed non-toxic cyanobacteria and a mixed diet provided a significantly higher shell and soft-body growth rate than the average of all single algal, but not the non-toxic cyanobacterial diets. However, the increase in growth provided by the non-toxic cyanobacteria diets could not be related to typical determinants of dietary quality such as toxicity, nutrient stoichiometry or essential fatty acid content. Conclusions: These results strongly contradict previous research which describes non-toxic cyanobacteria as a low quality food resource for freshwater herbivores in general. Our findings thus have strong implications to gastropod-cyanobacteria relationships and suggest that freshwater gastropods may be able to control mass occurrences of benthic non-toxic cyanobacteria, frequently observed in eutrophied water bodies worldwide. [ABSTRACT FROM AUTHOR]

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m-2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer=resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems. [ABSTRACT FROM AUTHOR]

Introduction: The crude protein level in the diet will affect the fermentation parameters, microflora, and metabolites in the rumen of ruminants. It is of great significance to study the effect of crude protein levels in supplementary diet on microbial community and metabolites for improving animal growth performance. At present, the effects of crude protein level in supplementary diet on rumen fermentation parameters, microbial community, and metabolites of Jersey-Yak (JY) are still unclear., Methods: The purpose of this experiment was to study the appropriate crude protein level in the diet of JY. The rumen fermentation indexes (volatile fatty acids and pH) were determined by supplementary diets with crude protein levels of 15.16 and 17.90%, respectively, and the microbial community and metabolites of JYs were analyzed by non-target metabonomics and metagenome sequencing technology, and the changes of rumen fermentation parameters, microbial flora, and metabolites in the three groups and their interactions were studied., Results and Discussion: The crude protein level in the supplementary diet had significant effects on pH, valeric acid, and the ratio of acetic acid to propionic acid ( p < 0.05). The protein level had no significant effect on the dominant microflora at the phylum level ( p > 0.05), and all three groups were Bacteroides and Firmicutes. The results of metabolite analysis showed that the crude protein level of supplementary diet significantly affected the metabolic pathways such as Bile secretion and styrene degradation ( p < 0.05), and there were different metabolites between the LP group and HP group, and these different metabolites were related to the dominant microbial to some extent. To sum up, in this experiment, the effects of crude protein level in supplementary diet on rumen microorganisms and metabolites of JY and their relationship were studied, which provided the theoretical basis for formulating a more scientific and reasonable supplementary diet in the future., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Dai, Ma, Dingkao, Huang, La, Li, Ma, Wu, Chu, Guo, Pei, Yan and Liang.)

Frequency and severity of insect outbreaks in forest ecosystems are predicted to increase with climate change. How this will impact canopy leaf area in future climates is rarely tested. Here, we document function of insect outbreaks that fortuitously and rapidly occurred in an ecosystem under free-air CO2 enrichment. Over the first 2 years of CO2 fumigation of a naturally established mature Eucalyptus woodland, we continuously assessed population responses of three sap-feeding insect species of the psyllid genera Cardiaspina, Glycaspis and Spondyliaspis for up to ten consecutive generations. Concurrently, we quantified changes in the canopy leaf area index ( LAI). Large and rapid shifts in psyllid community composition were recorded between species with either flush ( Glycaspis) or senescence-inducing ( Cardiaspina, Spondyliaspis) feeding strategies. Within the second year, two psyllid species experienced significant and rapid population build-up resulting in two consecutive outbreaks: first, rainfall stimulated Eucalyptus leaf production increasing LAI, which supported population growth of flush-feeding Glycaspis without impacting LAI. Glycaspis numbers then crashed and were followed by the outbreak of senescence-feeding Cardiaspina fiscella that led to significant defoliation and reduction in LAI. For all three psyllid species, the abundance of lerps, protective coverings excreted by the sessile nymphs, decreased at e[ CO2]. Higher lerp weight at e[ CO2] for Glycaspis but not the other psyllid species provided evidence for compensatory feeding by the flush feeder but not the two senescence feeders. Our study demonstrates that rainfall drives leaf phenology, facilitating the rapid boom-and-bust succession of psyllid species, eventually leading to significant defoliation due to the second but not the first outbreaking psyllid species. In contrast, e[ CO2] may impact psyllid abundance and feeding behaviour, with psyllid species-specific outcomes for defoliation severity, nutrient transfer and trophic cascades. Psyllid populations feeding on Eucalyptus experience rapid boom-and-bust cycles depending on availability of suitable foliage driven by rainfall patterns and leaf phenology. [ABSTRACT FROM AUTHOR]

Frequency and severity of insect outbreaks in forest ecosystems are predicted to increase with climate change. How this will impact canopy leaf area in future climates is rarely tested. Here, we document function of insect outbreaks that fortuitously and rapidly occurred in an ecosystem under free-air CO2 enrichment. Over the first 2 years of CO2 fumigation of a naturally established mature Eucalyptus woodland, we continuously assessed population responses of three sap-feeding insect species of the psyllid genera Cardiaspina, Glycaspis and Spondyliaspis for up to ten consecutive generations. Concurrently, we quantified changes in the canopy leaf area index ( LAI). Large and rapid shifts in psyllid community composition were recorded between species with either flush ( Glycaspis) or senescence-inducing ( Cardiaspina, Spondyliaspis) feeding strategies. Within the second year, two psyllid species experienced significant and rapid population build-up resulting in two consecutive outbreaks: first, rainfall stimulated Eucalyptus leaf production increasing LAI, which supported population growth of flush-feeding Glycaspis without impacting LAI. Glycaspis numbers then crashed and were followed by the outbreak of senescence-feeding Cardiaspina fiscella that led to significant defoliation and reduction in LAI. For all three psyllid species, the abundance of lerps, protective coverings excreted by the sessile nymphs, decreased at e[ CO2]. Higher lerp weight at e[ CO2] for Glycaspis but not the other psyllid species provided evidence for compensatory feeding by the flush feeder but not the two senescence feeders. Our study demonstrates that rainfall drives leaf phenology, facilitating the rapid boom-and-bust succession of psyllid species, eventually leading to significant defoliation due to the second but not the first outbreaking psyllid species. In contrast, e[ CO2] may impact psyllid abundance and feeding behaviour, with psyllid species-specific outcomes for defoliation severity, nutrient transfer and trophic cascades. Psyllid populations feeding on Eucalyptus experience rapid boom-and-bust cycles depending on availability of suitable foliage driven by rainfall patterns and leaf phenology. [ABSTRACT FROM AUTHOR]

Animals have several strategies to contend with nutritionally poor diets, including compensatory consumption and enhanced food utilization efficiencies. Plants produce a diversity of defense compounds that affect the ability of herbivores to utilize these strategies in response to variation in food nutritional quality. Little is known, however, about effects of allelochemicals on herbivores utilizing integrated behavioral and morphological responses to reduced food quality. Our objectives were to (1) examine how variation in diet nutritional quality influences compensatory responses of a generalist insect herbivore, and (2) determine how plant defenses affect these processes. Gypsy moth ( Lymantria dispar) larvae were administered one of nine combinations of diet having low, moderate, or high nutritional quality and 0, 2, or 4 % purified aspen ( Populus tremuloides) salicinoids. We quantified larval growth, consumption, frass production, and biomass allocation to midgut tissue over a 4-day bioassay. In the absence of salicinoids, larvae compensated for reduced nutritional quality and maintained similar growth across all diets through increased consumption, altered midgut biomass allocation, and improved processing efficiencies. Dietary salicinoids reduced larval consumption, midgut biomass allocation, digestive efficiencies, and growth at all nutritional levels, but the effect size was more pronounced when larvae were fed nutritionally suboptimal diets. Our findings demonstrate that integrated behavioral and morphological compensatory responses to reduced food quality are affected by plant defenses, ultimately limiting compensatory responses and reducing larval performance. [ABSTRACT FROM AUTHOR]

Temporary malnutrition during juvenile development often negatively influences the life-history decisions of adults. Hence, individuals should avoid this effect by compensatory feeding on the limited resource when the food situation improves. In a feeding experiment, bush-crickets (Pholidoptera griseoaptera) responded to nine days depression of animal food supply by increasing their feeding activities on insect carcasses when a full-nutritional diet was available. As a short-term reaction, treated individuals of both sexes took 3.4 times more food from carcasses (0.084 g / 9 h) than control individuals. The increased carcass intake levelled off at 0.025 g / 9 h after an interval of nine hours, indicating that bush-crickets can rapidly compensate for an experimentally increased demand for animal diet. The general daily carcass intake of male and female bush-crickets was 0.07 g fresh weight, corresponding to 16.4% of the bush-cricket's body mass. Carcass intake and body mass development was correlated over the complete period (7 d), but no correlation was found for the time of short-term reaction. We conclude that animal diet is essential for the growth of dark bush-crickets. They were able to compensate for short depressions in animal food supply by increasing feeding frequencies and feeding rates of the limited resource. Hence, bush-crickets can cope with short periods of limited animal food supply, e.g. periods of rainfall, which regularly occur in their natural habitat.

Frugivorous animals may face an osmoregulatory challenge due to the watery nature of their food and low concentration of electrolytes therein. We examined the effects of salt content (NaCl) and sugar type (sucrose vs. glucose) on the intake rate of dilute sugar solutions by the Egyptian fruit bat ( Rousettus aegyptiacus ). Increased salt content did not bring about an increase in energy intake by bats fed dilute sucrose diets and the bats did not compensate by hyperphagia to achieve the energy intake of bats fed concentrated sucrose solution without salt. Moreover, increasing salt content had a negative effect on the total energy intake of Egyptian fruit bats fed equicaloric sucrose solutions. There were no differences in hematocrit in bats fed the diets of different sucrose concentration, but plasma osmolality was higher in those bats fed more concentrated sugar solutions, and urine osmolality was higher in those fed on high-salt diets. Food and energy intake did not differ between bats that were fed dilute glucose and sucrose solutions. Our findings indicate that Egyptian fruit bats do not modulate food intake when salt content of dilute sugar solutions is increased, and that increasing salt content might constrain their food intake rate. Sugar type did not affect food intake by Egyptian fruit bats, indicating that sucrose hydrolysis alone does not limit the intake of dilute sugar nectar. [ABSTRACT FROM AUTHOR]

This study examined diet, prey quality and growth for a generalist fish predator, grey snapper Lutjanus griseus, at five sites across an estuarine gradient in the Loxahatchee River estuary, Florida, U.S.A. Lutjanus griseus diets shifted from dominance by low quality, intertidal crabs upstream to an increased reliance on higher quality shrimp, fishes and benthic crabs downstream. Frequency of L. griseus with empty stomachs was higher at downstream sites. Lutjanus griseus growth rates did not vary among sites. Results indicate that L. griseus may be able to compensate for lower quality prey upstream by consuming more, and thus individuals are able to maintain similar levels of energy balance and growth rates across the estuarine gradient. Elucidating mechanisms, such as compensatory feeding, that enable generalist species to remain successful across habitat conditions are critical to understanding their organismal ecology and may facilitate predictions about the response of generalists to landscape alteration. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of low levels of Bt exposure on Trichoplusia ni resistant and susceptible to Bt was examined. [•] Larvae were fed diet with Bt or were pre-exposed to Bt and transferred to diet with or without Bt. [•] Resistant larvae exhibited increased diet consumption at the lowest tested Bt concentration. [•] Growth of resistant larvae increased when exposed to some Bt concentrations. [•] Susceptible larvae exhibited reductions in growth at all tested Bt concentrations. [Copyright &y& Elsevier]

According to stoichiometric principles, the ratios at which consumers recycle nutrients depend on the elemental compositions of the consumer and its food. However, nutrient assimilation efficiencies and ingestion rates can vary among consumer species and, thus, can affect the rates of consumer-mediated nutrient recycling (CNR). The grazer Theodoxus fluviatilis has high nutrient excretion rates of either P or N, depending on grazer growth limitation, and has a high body N. I examined how a grazer with a high proportion of N in its body tissues can assimilate enough N to maintain that N content despite high N excretion rates by estimating the mass balance for nutrient recycling including nutrient excretion through fecal pellets. I used the snail species Theodoxus fluviatilis and Lymnea peregra fed nutrient-enriched periphyton in a 2-d grazing experiment done in 48 experimental units. I estimated periphyton and grazer nutrient stoichiometry and nutrient excretion rates and ratios in dissolved and fecal-pellet form, and calculated nutrient assimilation efficiencies of the limiting nutrient (N). Theodoxus fluviatilis had higher N excretion rates, lower N assimilation efficiency, and higher ingestion rates than L. peregra. Thus, T. fluviatilis recycled more N by ingesting and processing a larger amount of food per unit time than L. peregra. My study shows that grazers with low nutrient assimilation efficiencies and high nutrient demands can assimilate sufficient nutrients via high ingestion rates. The consequence of this strategy (high ingestion and excretion rates) could be a more rapid nutrient turnover in ecosystems dominated by these grazers. [ABSTRACT FROM AUTHOR]

Availability and quality of food resources limit consumer performance and modulate food webs, which in turn, can affect ecosystem functioning. Availability and quality of food resources can be especially important in streams, where consumers depend on allochthonous organic matter whose availability and quality can differ markedly both spatially and throughout the year. Most studies of the relationships between food quality and detritivore performance have been based on standardized food types and have not been designed to allow consideration of interactions between resource quantity and quality. Our goal was to evaluate the effects of quality and quantity of resource on shredder performance. We raised larvae of the caddisfly Sericostoma vitattum in the laboratory with food taken from a stream reach. We controlled food type (conditioned Alnus glutinosa leaves, natural leaf packs from riffles, and deposits within thick debris jams) and quantity (low: 2 mg individual-1 d-1; high: 10 mg individual-1 d-1). Consumption rate tended to be higher for lower- than for higher-quality materials, and the differences were more marked at high resource quantity. However, this compensatory mechanism was not enough to compensate growth in the case of lowest-quality food. In addition, food quality and quantity interacted to determine the energy allocation to body condition or growth. Our results show that the interaction between resource quality and quantity can influence invertebrate condition and life cycles. Stored organic matter in large jams, despite their poor quality, could enable consumers to survive until the next high-input season. [ABSTRACT FROM AUTHOR]

The article discusses research on Neotropical frugivorous bat Sturnira (S.) ludovici concerning food intake changes in relation to food quality. It states that core plant taxa is the basis of diet diversity in such bat species. It mentions that fruits with high sugar concentration are eaten by S. bats while fruits with lower sugar content are eaten by Artibeus (A.) species. In such study, the intake sugar response of S. ludovici was compared with that of A. jamaicensis. It offers information on the results, revealing the failure of S. ludovici to achieve compensatory feeding.

Abstract: This work tested if carbohydrates and proteins ingestion is regulated in the South American fruit fly, Anastrepha fraterculus, to optimize survival and reproduction. Adult food treatments were established by providing sugar and hydrolyzed yeast in various combinations either alone or mixed at a standard 3:1 ratio (sugar:hydrolyzed yeast). Individual food consumption was assessed and related to survival patterns. The effects of adult feeding on fecundity and fertility patterns were investigated in groups of flies. Sugar consumption was the lowest in the treatment where it was provided with hydrolyzed yeast at a fixed 3:1 ratio. Consumption of hydrolyzed yeast did not differ between this treatment and the one in which this solution was complemented with one solution of sugar. It seems that a mixture of sugar and hydrolyzed yeast at a fixed ratio of 3:1, respectively, restricts extra ingestion of sugar; most probably because of negative response of the fly to overconsumption of protein. Survival was affected by the treatments, being lower in those cases where protein was at the fixed ratio. Group experiments revealed that protein restriction expanded longevity and decreased egg production. In contrast, egg production was enhanced when flies were kept continuously with a mixture of yeast and sugar plus an extra source of sugar, and this was not in detriment of survival. Our results suggest that fixed sugar-protein ratios in which protein is in excess affects fitness components such as longevity and reproduction. These findings are discussed from a theoretical and applied perspective in the context of pest control by means of the sterile insect technique. [Copyright &y& Elsevier]

Abstract: There is increasing evidence that insecticidal transgenic crops can indirectly cause detrimental effects on arthropod predators or parasitoids when they prey on or parasitize sublethally affected herbivores. Our studies revealed that Chrysoperla carnea is negatively affected when fed Bt-susceptible but not Cry1Ac-resistant Helicoverpa armigera larvae that had fed Bt-transgenic cotton expressing Cry1Ac. This despite the fact that the predators ingested 3.5 times more Cry1Ac when consuming the resistant caterpillars. In order to detect potential differences in the nutrient composition of prey larvae, we evaluated the glycogen and lipid content plus the sugar and free amino acid content and composition of caterpillars fed non-Bt and Bt cotton. The only change in susceptible H. armigera larvae attributable to Bt cotton feeding were changes in sugar concentration and composition. In case of the Cry1Ac-resistant H. armigera strain, feeding on Bt cotton resulted in a reduced glycogen content in the caterpillars. The predators, however, appeared to compensate for the reduced carbohydrate content of the prey by increasing biomass uptake which caused an excess intake of the other analyzed nutritional compounds. Our study clearly proves that nutritional prey-quality factors other then the Bt protein underlie the observed negative effects when C. carnea larvae are fed with Bt cotton-fed prey. Possible factors were an altered sugar composition or fitness costs associated with the excess intake of other nutrients. [ABSTRACT FROM AUTHOR]

The article presents a laboratory study that evaluates the effects of environmental temperature, body mass, and food quality on phosphorus (P) efflux in whitemarked tussock moth or Orygia leucostigma. It reveals the correlation of larval mass and of environmental temperature in the individual phosphorus efflux rate. It suggests that compensatory feeding in larvae that eats low quality leaves affects food phosphorous concentration.

Simple Summary: The novel use of carbon-rich biochar as a soil amendment in forest systems may be beneficial in the restoration of disturbed sites due to its ability to increase soil water holding capacity, potentially reduce drought stress in surrounding vegetation and aid in long-term carbon sequestration. As biochar is utilized in forest management, it is necessary to establish the potential effects that it may have on insects and other invertebrate assemblages. The results of recent laboratory studies demonstrate a potential for negative impacts on insects. Examining direct exposure of insects to biochar in a laboratory experiment may help us understand what effects biochar may have on insects that come into direct contact with the material. Along with direct exposure, biochar applications in the field would result in the surface and possible contamination of insect nutrient sources. To determine the impacts of ingesting biochar, we reared Douglas-fir tussock moth, Orgyia pseudotsugata, on synthetic diet to examine the insect's survival and longevity. The use of biochar as a soil amendment in forest ecosystems can be beneficial in the restoration of degraded soils. Forest insects such as the Douglas-fir tussock moth, Orgyia pseudotsugata (McDonnough) (Lepidoptera: Erebidae), may be exposed to biochar when the material is applied. Two experiments were conducted using biochar either (1) applied to the surface of the diet at three rates (0, 5, and 10 mg) or (2) incorporated into synthetic diet at four rates (0, 10, 20, and 40% volume/volume). The objective of both experiments was to determine if biochar on the surface or incorporated into a synthetic diet affected development and survival of O. pseudotsugata larvae. In both experiments, there was a significant decrease in estimated time to larval mortality in all biochar treatments compared to untreated controls. In the surface-applied biochar experiment, there was a significant difference in larval weight gain at day 12 between the control and 10 mg biochar treatments. In the experiment with biochar incorporated into the diet, mean larval weight at day 12 was highest in the low (10%) biochar treatment compared to all other treatments, although weight gain was only significantly different between the low- and high-concentration (40%) biochar treatments. Our results suggest that larvae, feeding on a low amount of biochar in the synthetic diet, may respond by engaging in compensatory feeding behavior. Fewer surviving larvae in the biochar treatment groups may contribute to the lack of significance found in the comparison of weight gain at day 24 in each experiment. [ABSTRACT FROM AUTHOR]

Nectarivorous birds encounter varying nectar concentrations while foraging on different food plants and must adjust their consumption to maintain constant energy intake. We determined how rapidly captive whitebellied sunbirds ( Cinnyris talatala) adjust their volumetric intake and feeding patterns after changes in diet concentration. On four consecutive days, birds were fed sucrose diets alternating between a standard diet of 16% w/w and test diets of 2.5, 8.5, 16 or 30% w/w, respectively, for 1.5 h periods. Feeding events were recorded with an infrared photo-detection system and food intake and body mass were monitored continuously by electronic balances interfaced to a computer. Generally, birds demonstrated a measurable increase in feeding frequency and food intake within 10 min after a decrease in sucrose concentration. However, individuals responded differently to the most dilute diet (2.5%): while most increased their food intake, others stopped feeding for a short while, appearing to dislike this diet. Furthermore, the number and duration of feeding events increased in the first 5 min after the switch from 2.5% back to 16%, as the birds attempted to compensate for previous reduced sugar intake. Daily sugar intake was lower when birds alternated between 2.5 and 16% diets than on other test days, but birds were able to maintain body mass, presumably through behavioural adjustments. [ABSTRACT FROM AUTHOR]

Ants and all social insects are faced with a nutritional challenge: the food entering the colony is brought by only a small number of its workers but is shared among all members of the colony. In this study, we investigated how ants maintain carbohydrates supply at both a collective and an individual level in response to changes in the concentration of available sucrose solution, colony demography and larval growth. We manipulated the concentration of sugar solutions available to ant colonies (dilute, medium and concentrated solutions) over extended periods and measured the capacity of colonies to maintain sugar supply through compensatory feeding. First, we demonstrated that ants regulated carbohydrate intake at a collective and individual level. Initially, ants consumed most and recruited fastest in response to more concentrated than to dilute sugar solutions, but over time this pattern reversed, such that the number of ants that fed and the volume ingested by each ant was a negative function of sugar concentration in the diet. Second, we found that ants became better at regulating their carbohydrate intake with the production of larvae in the nest. When the number of larvae was experimentally doubled, the ants regulated their consumption of carbohydrates more accurately than when the number of adult workers was doubled, suggesting that larvae play an important role in providing nutritional feedback to workers. Finally, we showed that ants defended a carbohydrate intake target' by allowing them to select among sugar solutions of different concentration. [ABSTRACT FROM AUTHOR]

Abstract: Observational studies on leaf damage, gut content analyses, and crab behaviour have demonstrated that like numerous other mangrove and salt-marsh generalists, the mangrove tree crab Aratus pisonii feeds on a variety of food resources. This study is the first that experimentally tests feeding preferences of A. pisonii, as well as the first to test experimentally whether chemical composition of food resources is responsible for food selection. Feeding preferences were determined among a variety of plant, algal, and animal resources available in the field both in Florida and Belize, using multiple-choice feeding assays, where male and female crabs simultaneously were offered a variety of food items. To test whether chemistry of food resources was responsible for feeding preferences, chemical extracts of food resources were incorporated in an agar-based artificial food, and used in feeding assays. Results of feeding assays suggest that crabs prefer animal matter from ∼ 2.5 to 13× more than other available resources, including leaves of the red mangrove Rhizophora mangle, which contribute the most to their natural diet. Artificial feeding assays also demonstrated that chemical cues were responsible for selection of animal matter, up to 25× more than other available resources. Non-polar extracts (derived from extraction in 1:1 ethyl actetate:methanol) stimulated feeding the most, suggesting that fatty acids, triglycerides, or sterols may be important for growth, reproduction, or survival. Results for both sexes were similar across most assays. While chemical composition of food resources appears to play some role in selection, this does not discount the potential role of other factors, such as resource availability, competition, predation, or reproductive requirements in influencing feeding preferences. Bioassay-guided fractionation of extracts should aid in determining chemical constituents that play the greatest role in determining feeding preferences. [Copyright &y& Elsevier]

Avian nectarivores show compensatory feeding by adjusting their volumetric intake in response to variation in nectar concentration. This study used an infrared photo-detection system to investigate the short-term feeding patterns of whitebellied sunbirds (Nectarinia talatala) consuming three different sucrose concentrations (10, 20 and 30% w/w). Sunbirds increased their feeding frequency on the most dilute diet, but there was no change in feeding duration. Thus, the increase in total time spent feeding on the dilute diet was due to the increased feeding frequency. No difference in short-term feeding patterns was found between the 20% and 30% diets. Total time spent feeding was extremely short on all diets (96–144 s in every hour). Birds maintained the same steady increase in body mass over the course of the day on all three diets. Daily rhythms in feeding patterns were evident, with longer feeding duration and lower feeding frequency in the early morning and evening than during the rest of the day. Because ingestion rates on a particular diet may vary through the day, caution must be exercised in using feeding duration as a surrogate for meal size. Individual birds varied greatly in their feeding patterns irrespective of diet concentration. [ABSTRACT FROM AUTHOR]

Nutritional regulation is a powerful mechanism used by generalist feeders to obtain the balance of nutrients they require from nutritionally diverse, perhaps unbalanced, foods. We examined nutritional regulation in a species with a narrow individual diet breadth: the forest tent caterpillar, Malacosoma disstria. Fourth instar caterpillars were provided with artificial foods consisting of different ratios of protein to digestible carbohydrate in no-choice, choice and compensatory feeding experiments. In the no-choice test, caterpillars were confined to a single food source of varying protein/carbohydrate ratio for the duration of the fourth larval stadium. Caterpillars performed best on equal-ratio and slightly protein-biased diets. Significant reductions in performance were only observed on extremely protein- or carbohydrate-biased diets. Daily consumption of the three acceptable intermediate diets was consistent with volumetric regulation, but the timing of the moult to the next instar appeared linked instead to protein intake. In the choice test, caterpillars were provided with two complementary foods, one biased toward protein and the other toward carbohydrate, for the duration of the stadium. The caterpillars fed randomly from the two food sources presented to them, except for the extremely protein-biased diet (P:C ratio of 35:7), which they avoided. The compensatory feeding experiment tested whether forest tent caterpillars deprived of either protein or digestible carbohydrate would select a food containing the deficient nutrient. Insects were conditioned on either protein-only, carbohydrate-only, protein-and-carbohydrate or no-nutrient foods, then offered a choice between protein-only and carbohydrate-only foods. Unlike previously studied generalist feeders, our caterpillars did not compensate for protein deficiency and showed only very weak evidence of compensation for carbohydrate deficiency. Forest tent caterpillars are colonial trail-laying forest folivores that are generally confined to a single host plant and hence do not experience much diversity in food nutrient ratios. We show that forest tent caterpillars do not independently regulate protein and carbohydrate intake. These findings are consistent with predictions that nutritional regulation abilities should be less important in animals with narrower diet breadths. [ABSTRACT FROM AUTHOR]

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur. [ABSTRACT FROM AUTHOR]

Because plant nitrogen content varies within and between plants, insects must often compensate for low nitrogen levels by consuming more or suffer decreased performance. To test the effects of varying nitrogen content and plant characteristics that are affected by nitrogen content on monarch butterfly (Danaus plexippus L.) growth and development, we applied high and low nitrogen fertilizer treatments to common milkweed grown in a glasshouse. High nitrogen fertilization resulted in increased leaf nitrogen and plant height, but also higher disease and pest levels. Monarchs fed plants in the low nitrogen fertilization treatment showed higher relative consumption rates. Monarch performance, measured with development time and relative growth rate, was affected differently in different larval stadia, but larvae of all stadia fed leaves from the low nitrogen fertilization treatment weighed as much as or more than those fed high nitrogen leaves. These results suggest that monarch larvae compensate for lower plant quality by consuming more. If increased consumption is costly because of increased exposure to natural enemies or increased expenditure on consuming and processing food, low nitrogen host plants may result in decreased fitness, despite the monarchs' ability to compensate. [ABSTRACT FROM AUTHOR]

Leaf maturation in mountain birch (Betula pubescens ssp. czerepanovii) is characterized by rapid shifts in the types of dominant phenolics: from carbon-economic flavonoids aglycons in flushing leaves, via hydrolysable tannins and flavonoid glycosides, to carbon-rich proanthocyanidins (condensed tannins) in mature foliage. This shift accords with the suggested trade-offs between carbon allocation to plant defense and growth, but may also relate to the simultaneous decline in nutritive leaf traits, such as water, proteins and sugars, which potentially limit insect growth. To elucidate how birch leaf quality translates into insect growth, I introduce a simple model that takes into account defensive compounds but also acknowledges insect demand for nutritive compounds. The effects of defensive compounds on insect growth depend strongly on background variation in nutritive leaf traits: compensatory feeding on low nutritive diets increases the intake of defensive compounds, and the availability of growth-limiting nutritive compounds may modify the effects of defenses. The ratio of consumption to larval growth (both in dry mass) increases very rapidly with leaf maturation: from 2.9 to 9.8 over 2 weeks in June–July, and to 15 by August. High concentrations in mature birch leaves of "quantitative" defenses, such as proanthocyanidins (15–20% of dry mass), presumably prevent further consumption. If the same compounds had also protected half-grown leaves (which supported the same larval growth with only one third of the dry matter consumption of older leaves), the same intake of proanthocyanidins would have demanded improbably high concentrations (close to 50%) in young leaves. The model thus suggests an adaptive explanation for the high levels of "quantitative" defenses, such as proanthocyanidins, in low-nutritive but not in high-nutritive leaves because of the behavioral responses of insect feeding to leaf nutritive levels. [ABSTRACT FROM AUTHOR]