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Living organisms are constrained by both resource quantity and quality. Ecological stoichiometry offers important insights into how the elemental composition of resources affects their consumers. If resource quality decreases, consumers can respond by shifting their body stoichiometry, avoiding low-quality resources, or up-regulating feeding rates to maintain the supply of required elements while excreting excess carbon (i.e., compensatory feeding). We analyzed multitrophic consumer body stoichiometry, biomass, and feeding rates along a resource-quality gradient in the litter of tropical forest and rubber and oil-palm plantations. Specifically, we calculated macroinvertebrate feeding rates based on consumer metabolic demand and assimilation efficiency. Using linear mixed effects models, we assessed resource-quality effects on macroinvertebrate detritivore and predator communities. We did not detect shifts in consumer body stoichiometry or decreases in consumer biomass in response to declining resource quality, as indicated by increasing carbon-to-nitrogen ratios. However, across trophic levels, we found a strong indication of decreasing resource quality leading to increased consumer feeding rates through altered assimilation efficiency and community body size structure. Our study reveals the influence of resource quality on multitrophic consumer feeding rates and suggests compensatory feeding to be more common across consumer trophic levels than was formerly known.

Parasitic infections are common, but how they shape ecosystem-level processes is understudied. Using a mathematical model and meta-analysis, we explored the potential for helminth parasites to trigger trophic cascades through lethal and sublethal effects imposed on herbivorous ruminant hosts after infection. First, using the model, we linked negative effects of parasitic infection on host survival, fecundity, and feeding rate to host and producer biomass. Our model, parameterized with data from a well-documented producer–caribou–helminth system, reveals that even moderate impacts of parasites on host survival, fecundity, or feeding rate can have cascading effects on ruminant host and producer biomass. Second, using meta-analysis, we investigated the links between helminth infections and traits of free-living ruminant hosts in nature. We found that helminth infections tend to exert negative but sublethal effects on ruminant hosts. Specifically, infection significantly reduces host feeding rates, body mass, and body condition but has weak and highly variable effects on survival and fecundity. Together, these findings suggest that while helminth parasites can trigger trophic cascades through multiple mechanisms, overlooked sublethal effects on nonreproductive traits likely dominate their impacts on ecosystems. In particular, by reducing ruminant herbivory, pervasive helminth infections may contribute to a greener world.

Due to a lack of accurate information for appropriate sturgeon nutrition management, this study was conducted to determine the optimum feeding rate for sub‐yearling great sturgeons (Huso huso) with an average initial weight of 94.01 ± 4.36 g using the desirability function model. The feeding trial lasted for 60 days after acclimatization. This experiment was conducted in a completely randomized design with six different feeding rates (0.5, 1, 1.5, 2, 2.5, and 3% of body weight day−1) and three replicates for each feeding level. Daily diet of each experimental tank was divided into three different meals. The average water flow rate for each experimental tank was 1.5 L min−1 and the water temperature was adjusted to 22.7 ± 1.1.4 °C. To the best of our knowledge, this is the first report on multivariate optimization of feeding rate based on both specific growth rate and feed conversion ratio by the desirability function model. Obtained results indicate that optimum specific growth rate, feed conversion ratio, and economic efficiency for sub‐yearling great sturgeons with a weight range of 94.01 ± 4.36 g up to 350.25 ± 13.18 g occurred at a feeding rate of 1.89% body weight day−1.

Brine shrimp Artemia is able to filter particulate substances non-selectively and continuously, and its filtration capacity is related to various environmental parameters as well as Artemia growth stage. In this study, the filter-feeding rate (FFR) of Artemia franciscana at different temperatures (20°C /25°C /30°C) and stocking densities (200/400/750/1000 ind./L at two earlier growth stages with the body length of 0.91 ± 0.05 mm and 1.53 ± 0.22 mm, respectively; 50/100/200 ind./L at two later growth stages with the body length of 4.72 ± 0.51 mm and 10.26 ± 0.46 mm, respectively) on three unicellular algae ( Chlorella vulgaris , Porphyridium purpureum , Phaeodactylum tricornutum ) and two sizes of polyethylene beads (30 μm and 50 μm) was determined at Artemia four growth stages. In total 144 combinations were tested. The results showed that the FFR was positively correlated with the ambient temperature and Artemia body length, while it was negatively correlated with the Artemia density and particle size. One way ANOVA analysis showed that ambient temperature, Artemia stocking density and particle size mostly had significant effects on FFR (P < 0.05). And the favorable filtration particle size of Artemia increased with its body length. The equation of FFR in function of temperature (T), Artemia body length (BL) and stocking density (SD), and particle size (PS) was obtained using multiple linear regression analysis: FFR = 0.487* BL + 0.067* T-0.01* SD-0.064* PS-1.508 (R 2  = 0.513). Of these four variables, body length had the greatest effect on FFR, followed by ambient temperature, particle size and Artemia density. There were interactions among three factors (T, SD and PS) and the interactive degree varied with Artemia growth. The results of this study provide a valuable guidance for proper feeding in controlled Artemia production and standardization of feeding protocol for ecotoxicity and fundamental Artemia research.

In cooperatively breeding species, helpers take higher risks of getting lower return of investment than breeders due to the incongruity between helping and breeding. Helpers can deal with the risk by curtailing their investment or, if possible, claiming immediate rewards in the cooperation. Given breeders may rely largely on the aid of helpers to raise their offspring, it can be hypothesized that helpers are more likely to make adaptive responses to the incongruity-associated risk in adverse habitats than in good ones. This hypothesis was tested in the giant babax (Babax waddelli) by comparing helpers’ provisioning behaviors between two breeding populations in adverse high-altitude and good low-altitude environments. These two populations differed significantly in their egg size and nestlings’ growth patterns. Helpers in both populations made great contributions to the raising of offspring. During provisioning, helpers in the high-altitude population exhibited significantly higher feeding rates but delivered fewer insects per feeding bout than their counterparts in the low-altitude population. Helpers in both populations displayed a cheating strategy of “non-feeding” to reduce investment in provisioning. They pursued immediate excess rewards via kleptoparasitism of nestling fecal sacs in the high-altitude population but not in the low-altitude one. Accordingly, breeders made different antagonistic actions toward the cheating helpers between populations. Our findings confirm that helpers are prone to deceiving cooperation under poor breeding conditions, and that breeders’ tolerance of the cheating behavior of helpers is determined by their dependence on the helpers’ aid.Significance statementGiant babax is an obligated cooperatively breeding bird that breeds on the Tibetan Plateau. We found that helpers displayed cheating behaviors while they provisioned the brood. Although helpers in both high- and low-altitude populations adopt “non-feeding” strategy to reduce investment in the provisioning, they were more likely to perform contested kleptoparasitism to access the fecal sacs of nestling in the high-altitude population than in the low-altitude one. Our findings suggest that helpers in adverse high-altitude habitats are probable to claim immediate excess reward via cheating strategies.

Anthropogenic climate change poses a serious threat to biodiversity. In marine environments, multiple climate variables, including temperature and CO₂ concentration ([CO₂]), are changing simultaneously. Although temperature has well-documented ecological effects, and many heavily calcified marine organisms experience reduced growth with increased [CO₂], little is known about the combined effects of temperature and [CO₂], particularly on species that are less dependent on calcified shells or skeletons. We manipulated water temperature and [CO₂] to determine the effects on the sea star Pisaster ochraceus, a keystone predator. We found that sea star growth and feeding rates increased with water temperature from 5 °C to 21 °C. A doubling of current [CO₂] also increased growth rates both with and without a concurrent temperature increase from 12 °C to 15 °C. Increased [CO₂] also had a positive but nonsignificant effect on sea star feeding rates, suggesting [CO₂] may be acting directly at the physiological level to increase growth rates. As in past studies of other marine invertebrates, increased [CO₂] reduced the relative calcified mass in sea stars, although this effect was observed only at the lower experimental temperature. The positive relationship between growth and [CO₂] found here contrasts with previous studies, most of which have shown negative effects of [CO₂] on marine species, particularly those that are more heavily calcified than P. ochraceus. Our findings demonstrate that increased [CO₂] will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate change should consider how different types of organisms will respond to changing climatic variables.

We evaluated the possible interaction between feeding frequency (FF) and feeding rate (FR) on growth, nutrient utilization, body composition, and plasma metabolites of juvenile Nile tilapia, Oreochromis niloticus (6.57 g). We tested three FFs: two, four, and six times a day, and two FRs: apparent satiation (AS) or restricted regime (RR), following a completely randomized design in a factorial arrangement, in quadruplicate. The daily weight gain and specific growth rate were 56 and 19% higher in fish fed to AS than in fish fed under the RR, respectively. However, feed efficiency was 14% higher in fish fed in the RR. Fish fed to AS presented the highest body lipid (8.92%), whereas the fish fed in the RR showed the lowest (6.64%). Glucose and triglycerides were also higher in fish fed to AS. The protein retention ratio was highest in the RR (49.17% vs. 42.51%, respectively). Fish fed to AS showed 34% more body protein but 62% more body fat than the fish fed in the RR. There was no difference in feed efficiency or weight gain regarding FF, regardless of the FR. Therefore, feeding Nile tilapia juveniles twice a day is enough to achieve optimum growth.

Feeding rate is an important factor influencing the carbon and nitrogen input and greenhouse gas emission from aquaculture systems. However, the quantitative relationship between feeding rates and GHG emissions is still poorly understood. In this study, we conducted a laboratory-scale experiment to examine the impact of feeding rate (0%, 2%, 4%, 6%, and 8%) on the CH 4 and N 2 O emissions from a pond rice-fish co-culture system. The results showed that the total amount of CH 4 emission did not significantly differ when the feeding rate was no more than 6%, but increased more than four times when the feeding rate reach to 8%. The amount of N 2 O emission showed a linearly increasing trend with the feeding rate. The emission factors of CH 4 and N 2 O was significantly higher for 8% feeding rate than other feeding rates. The variation of CH 4 emission was primarily attributed to the ratio of mcrA/pmoA in the sediment and the contents of biological oxygen demand (COD) and dissolved oxygen (DO) in the water; and the variation of N 2 O was primarily affected by the available nitrogen in the water and sediment and the content of DO in the water. The overall emission of CH 4 and N 2 O showed an exponential relationship with feeding rate. The total yields of fish and rice did not continuously increase when the feeding rate exceeded 4%. The lowest emission intensity per unit yield was reached at the feeding rate of 2.99%. These results can provide a reference for the determination of low-carbon feeding strategy for pond rice-fish co-culture system.

Microplastics are widespread pollutants, but few studies have linked field prevalence in organisms to laboratory uptakes. Aquatic filter feeders may be particularly susceptible to microplastic uptake, with the potential for trophic transfer to higher levels, including humans. Here, we surveyed microplastics from a model freshwater shrimp, common caraidina (Caridina nilotica) inhabiting the Crocodile River in South Africa to better understand microplastic uptake rates per individual. We then use functional response analysis (feeding rate as a function of resource density) to quantify uptake rates by shrimps in the laboratory. We found that microplastics were widespread in C. nilotica, with no significant differences in microplastic abundances among sampled sites under varying land uses, with an average abundance of 6.2 particles per individual. The vast majority of microplastics found was fibres (86.1%). Shrimp microplastic accumulation patterns were slightly higher in the laboratory than the field, where shrimp exhibited a hyperbolic Type II functional response model under varying exposure concentrations. Maximum feeding rates of 20 particles were found over a 6 h feeding period, and uptake evidenced at even the lowest laboratory concentrations (~10 particles per mL). These results highlight that microplastic uptake is widespread in field populations and partly density dependent, with field concentrations corroborating uptake rates recorded in the laboratory. Further research is required to elucidate trophic transfer from these taxa and to understand potential physiological impacts. Microplastics are widespread pollutants, but few studies have linked field prevalence in organisms to laboratory uptakes. Our results highlight that microplastic uptake is widespread in field populations of shrimp and partly density dependent, with field concentrations corroborating uptake rates recorded in the laboratory.

The consequences of defensive secondary metabolite concentrations and interspecific metabolite diversity on grazers have been extensively investigated. Grazers which prefer certain food sources are often found in high abundance on their host and as a result, understanding the interaction between the two is important to understand community structure. The effects of intraspecific diversity, however, on the grazer are not well understood. Within a single, localized geographic area, the Antarctic red seaweed Plocamium sp. produces 15 quantitatively and qualitatively distinct mixtures of halogenated monoterpenes (“chemogroups”). Plocamium sp. is strongly chemically defended which makes it unpalatable to most grazers, except for the amphipod Paradexamine fissicauda. We investigated differences in the feeding and growth rates of both Plocamium sp. and P. fissicauda, in addition to grazer reproductive output, in relation to different chemogroups. Some chemogroups significantly reduced the grazer’s feeding rate compared to other chemogroups and a non-chemically defended control. The growth rate of Plocamium sp. did not differ between chemogroups and the growth rates of P. fissicauda also did not show clear patterns between the feeding treatments. Reproductive output, however, was significantly reduced for amphipods on a diet of algae possessing one of the chemogroups when compared to a non-chemically defended control. Hence, intraspecific chemodiversity benefits the producer since certain chemogroups are consumed at a slower rate and the grazer’s reproductive output is reduced. Nevertheless, the benefits outweigh the costs to the grazer as it can still feed on its host and closely associates with the alga for protection from predation.