Food Limitation Research Articles

Winter is coming: Interactions of multiple stressors in winter and implications for the natural world.

Winter is a key driver of ecological processes in freshwater, marine and terrestrial ecosystems, particularly in higher latitudes. Species have evolved various adaptive strategies to cope with food limitations and the cold and dark wintertime. However, human-induced climate change and other anthropogenic stressors are impacting organisms in winter in unpredictable ways. In this paper, we show that global change experiments investigating multiple stressors have predominantly been conducted during summer months. However, effects of anthropogenic stressors sometimes differ between winter and other seasons, necessitating comprehensive investigations. Here, we outline a framework for understanding the different effects of anthropogenic stressors in winter compared to other seasons and discuss the primary mechanisms that will alter ecological responses of organisms (microbes, animals and plants). For instance, while the magnitude of some anthropogenic stressors can be greater in winter than in other seasons (e.g. some pollutants), others may alleviate natural winter stress (e.g. warmer temperatures). These changes can have immediate, delayed or carry-over effects on organisms during winter or later seasons. Interactions between stressors may also vary with season. We call for a renewed research direction focusing on multiple stressor effects on winter ecology and evolution to fully understand, and predict, how ecosystems will fare under changing winters. We also argue the importance of incorporating the interactions of anthropogenic stressors with winter into ecological risk assessments, management and conservation efforts.

Liver Glycogen as a Sensitive Indicator of Food Limitation in Delta Smelt

AbstractAssessing habitat quality is a major goal of conservationists and restoration practitioners, but to associate habitat quality with biomarkers of vagile animals, the biomarkers must respond rapidly. Here, we identified a biomarker capable of rapidly detecting food limitation in the imperiled Delta Smelt (Hypomesus transpacificus), a pelagic fish endemic to the San Francisco Estuary (SFE). We conducted an experiment with fed and unfed treatments of hatchery-raised, sub-adult Delta Smelt that were sampled at 12 time points: 0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 14, and 21 days. We then compared four biomarkers using Day 21 fish: RNA/DNA in liver, triglycerides in liver, glycogen in liver, and glycogen in muscle. Of the liver endpoints, glycogen had the largest difference between treatments at Day 21, so we compared it to muscle glycogen across all time points. Liver glycogen declined by 60% after 1 day of fasting and remained depressed in the fasting treatment across all subsequent time points. Muscle glycogen also responded rapidly, taking only 2 days to decline by 39% in the fasting treatment, but the difference was inconsistent across subsequent time points. When applied to hatchery-released Delta Smelt collected from the SFE, liver glycogen concentrations were less than half that of the fed hatchery fish, consistent with the hypothesis of food limitation in the wild, but also several other potential causes. This study highlights the utility of liver glycogen as an indicator of recent foraging success in Delta Smelt.

Recent Advances in the Determination of Veterinary Drug Residues in Food.

The presence of drug residues in food products has become a growing concern because of the adverse health risks and regulatory implications. Drug residues in food refer to the presence of pharmaceutical compounds or their metabolites in products such as meat, fish, eggs, poultry and ready-to-eat foods, which are intended for human consumption. These residues can come from the use of drugs in the field of veterinary medicine, such as antibiotics, antiparasitic agents, growth promoters and other veterinary drugs given to livestock and aquaculture with the aim of providing them as prophylaxis, therapy and for promoting growth. Various analytical techniques are used for this purpose to control the maximum residue limit. Compliance with the maximum residue limit is very important for food manufacturers according to the Food and Drug Administration (FDA) or European Union (EU) regulations. Effective monitoring and control of drug residues in food requires continuous advances in analytical techniques. Few studies have been reviewed on sample extraction and preparation techniques as well as challenges and future directions for the determination of veterinary drug residues in food. This current review focuses on the overview of regulations, classifications and types of food, as well as the latest analytical methods that have been used in recent years (2020-2023) for the determination of drug residues in food so that appropriate methods and accurate results can be used. The results show that chromatography is still a widely used technique for the determination of drug residue in food. Other approaches have been developed including immunoassay, biosensors, electrophoresis and molecular-based methods. This review provides a new development method that has been used to control veterinary drug residue limit in food.

Seasonal variation in the relative strength of bottom-up <em>vs</em> top-down effects in pelagic cladoceran populations identified through contribution analysis of birth rate

Pelagic freshwater communities are characterized by the presence of strong trophic interactions, with the dominance of either food limitation (bottom-up effect) or predation pressure (top-down effect) alternating in time. Though this temporal variation should have a major impact on zooplankton dynamics, few studies have examined it. We consider here an approach that involves identifying signatures of food availability and size-selective fish predation based on the demographic characteristics of cladoceran populations. The relative strength of top-down vs bottom-up effects was assessed on short sampling intervals as contributions of the proportion of adults and fecundity, respectively, to the resulting change in birth rate. The dominant effect on each sampling interval was determined based on the absolute value of the ratio of those contributions (R). From previous experiments, we expected that under the dominant effect of food, R should be less than unity, while under fish predation it should be 1 < R < 3.4. We analyzed two datasets – one collected for a pelagic cladoceran community of three species, and another retrieved from the published data for Daphnia catawba in 1986. In the former case, the temporal variation in the dominant effect was assumed from the pattern of cladoceran populationdynamics as well as limited data on zooplankton consumption by planktivorous fish; in the latter case, the seasonal change in predation pressure by fish on the daphnids was known from the original data. Our results show that the probability density functions for R values from the two datasets indicate an increased probability of the ratio values associated with the abovementioned ranges, suggesting that both bottom-up and top-down effects should have been driving cladoceran population dynamics during the study periods. Based on the results of the Generalized Additive Models (GAMs), the fitted R values for the most abundant species from the first dataset - Bosmina longirostris - changed from the values indicative of strong food effect at the beginning of the study period to those indicative of strong top-down effect when fish with substantial numbers of bosminids in the gut were caught. In the second dataset, for the two time intervals associated with increased predation pressure by fish, the fitted R values were predominantly located between 1 and 3.4, as expected. For both datasets, our results indicate that contribution analysis of birth rate can be used as an informative, albeit preliminary, tool to identify trophic interactions driving zooplankton seasonal population fluctuations in freshwater communities.

Study of Proximate Composition and Storage Stability of Selected Bakery Products from Developed Wheat-Sologold Sweet Potato Flour

The proximate composition and storage stability of selected bakery products from composite wheat-sologold sweet potato flour (40:60) were investigated. This is crucial to harness the beneficial attributes of the composite flour coupled with the quality of its baked products. Results of the proximate composition of the baked products (bread, biscuit and cake) from composite wheat-sologold sweet potato flour were as follows: moisture content (10.60, 8.20, 6.80%), crude fiber (0.42, 0.38, 0.40%), ash content (1.20, 1.40, 1.30%), protein content (17.10, 16.50, 18.40%), oil extract (5.83, 5.33, 5.30%) and nitrogen free extract (64.85, 66.79, 67.80%) respectively. These values are within the range of good quality marketable baked products. During storage under room temperature, the total bacterial and fungi count of the baked products were found to be within was within the tolerable limit of edible food. The wheat-sologold sweet potato is therefore, a potential composite flour in the baking industry for improved quality and safety of baked products.

Latitudinal and elevational variation in the reproductive biology of house wrens, Troglodytes aedon.

While cross-species comparisons of birds suggest that as latitude decreases or elevation increases, clutch size decreases and the duration of developmental stages and parental attentiveness increases, studies comparing populations of the same species are rare. We studied populations of house wrens, Troglodytes aedon, at high and low elevations in California and Costa Rica, collecting data on clutch size, the duration of incubation and nestling periods, parental attentiveness, nestling growth rate, and nesting success. Our data support results from cross-species comparisons, but also revealed unanticipated results from low elevation temperate zone house wrens in the southwest. This population had prolonged incubation and nestling periods similar to those found in the tropics. We also found that temperate zone females, especially those at our higher elevation site, spent more of their day incubating than did tropical females. Nest temperature at our high elevation temperate zone site was higher than that at all other tropical sites. Age at fledging did not differ between sites. Total feeding rates per chick and male feedings per chick did not vary between sites. Nest success rates showed the predicted effect of latitude, but not the predicted effects of elevation. Our results extend low elevation house wren research into the southwestern US and contribute the first intraspecific elevational comparison in the Neotropics. Data from our low elevation southwestern site present a unique suite of life history traits that align more with tropical house wrens, although with a larger clutch size, and point to food limitation and/or high predation pressure as being possible drivers of some of these differences. These results highlight the need for additional studies of house wrens and other broadly distributed species at a more diverse array of sites to better understand which forces drive the evolution of different life history strategies across major biogeographical gradients.

A bioenergetics‐based index of habitat suitability: Spatial dynamics of foraging constraints and food limitation for a rare estuarine fish

AbstractObjectivesHabitat suitability models can guide restoration efforts in freshwater and estuarine ecosystems by synthesizing important habitat attributes in a single index. Several important elements of the foraging arena of Delta Smelt Hypomesus transpacificus, a small, zooplanktivorous fish, were quantified using a model that combined bioenergetics with physical habitat attributes. We applied the model to evaluate spatiotemporal variation in the suitability of Delta Smelt foraging habitat as indicated by growth potential.MethodsBioenergetics‐based estimates of daily potential growth, given constraints on daily foraging due to temperature, turbidity, day length, and prey availability, were compared to reference growth, estimated separately from length‐at‐age data. We defined suitable foraging arenas for Delta Smelt as times and places when potential growth equaled or exceeded reference growth.ResultAmong six contiguous regions of the upper San Francisco Estuary, temperature was consistently lowest and turbidity highest in the most seaward locations. As a result, predicted growth rates were greater there compared to landward, upstream regions that were warmer and less turbid.ConclusionSimulated habitat augmentation of prey and turbidity revealed that the effects of potential restoration actions could vary regionally as the factors limiting Delta Smelt foraging varied along longitudinal and seasonal gradients. Models of the spatiotemporal variation in Delta Smelt habitat may be substantially improved by directed laboratory studies; however, this research provided a data‐driven example of how dynamic estuarine habitat attributes interact to influence the suitability of foraging arenas experienced by a pelagic fish.

Occurrence and dietary intake of dioxins, furans (PCDD/Fs), PCBs, and flame retardants (PBDEs and HBCDDs) in baby food and infant formula

This study determines the levels of 49 persistent organic pollutants which were grouped into polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and hexabromocyclododecanes (HBCDDs), in infant formula and varieties of baby food. The analyzed samples (n = 80) came from stores all over Poland.The presence of PCDD/F, PCDD/F/PCB and non dioxin-like (ndl)-PCB congeners above the maximum levels stipulated in Commission Regulation (EU) No 1259/2011 was not detected in any sample. The determined average content of PCDD/Fs/dl-PCBs in the tested baby foods was in the range of 4–10 % of the maximum level, and content of ndl-PCBs was in the range of 2–6 % of the maximum level. Despite these low levels of dioxins, furans, and PCBs, a risk analysis assuming weekly consumption of the recommended food intake showed exceedances of the tolerable weekly intake (TWI).The content of flame retardants was low in all examined categories of food for children and infant formula. The lower-bound concentration of the sum of HBCDD isomers (LB ∑HBCDDs) ranged from below the limit of quantification (LOQ) to 0.0313 ng/g w.w. and the concentration of ∑PBDEs was in a 0.001–1.014 ng/g w.w. range. Neither infant formula nor baby food contributed considerably to infant exposure to HBCDDs or PBDEs.Our research indicates that the safe exposure thresholds for dioxins and PCBs in foods for infants and young children may be too high and perhaps it may be necessary to amend the legislation setting acceptable limits for baby food. It seems reasonable to introduce a recommendation on the frequency of food consumption for children and the control of raw materials for food production, in particular fish and cow milk, should be a permanent control point in the food safety assurance system.

Intra-lake trends and inter-lake comparisons of Mysis diluviana life history variables and their relationships to food limitation

The opossum shrimp, Mysis diluviana, is an important member of the offshore food webs of the Laurentian Great Lakes, but its response to ecosystem changes that have occurred over the past several decades is not well understood. We combined the data of four long-term sampling programs, adding several years of data (post and prior) to previously published analyses to offer a longer-term, cross-basin analysis of M. diluviana populations in the Great Lakes from 1997 to 2019. Densities were high in lakes Superior and Ontario (summer values 100–300/m2), high and variable but declining (from 200–300/m2 in 1997–2004 to less than 100/m2 in 2017–2019) in Lake Michigan, low (∼20–50/m2 since 2005) in Lake Huron, and very low in shallower eastern Lake Erie (<1/m2). Biomass showed similar trends. Life history parameters (mortality, fecundity, and growth) were consistently highest in eastern Lake Erie, followed by lakes Ontario, Michigan, Huron, and Superior. Generation time was 1 year in Lake Erie and 2 years in the other lakes. Cross-basin relationships between annual M. diluviana areal densities and food indices (chlorophyll-a concentration and zooplankton biomass) were non-linear, increasing with food levels up to about 250 mysids/m2 and about 650 mg dry wt/m2. Annual growth rates were also positively correlated to both food indices in the four deep lakes, but fecundity and mortality rates were not. Our results suggest food availability is a primary factor predicting M. diluviana density and biomass. Density-dependent mortality and fish predation could explain some of the inter-lake differences, but these relationships could benefit from further investigations.

Population connectivity and dynamics in early-life stages of Atlantic fish communities

IntroductionMany hypotheses have been suggested to explain recruitment variability in fish populations. These can generally be divided into three groups, either related to: larval food limitation, predation, or transport. Transport mechanisms are central for reproduction in pelagic species and three physical processes, concentration, enrichment, and retention are commonly referred as the fundamental “ocean triads” sustaining larval survival and thus success of reproductive effort. The aim of this study is to investigate linkages between primary production and transport processes of eggs and larvae for the most important commercial fish species in the Atlantic Ocean.MethodsWe simulated eggs and larvae dispersion using an individualbased model and integrating information on the fish ecology of the major fish stocks. Our work included a review on spawning ground locations, spawning time, eggs and larvae duration. Simulations were performed over a 10-year time period for 113 stocks (17 species) in order to assess variability in dispersion and common trends and factors affecting transport.ResultsThe level of primary production from initial to final position, i.e. from spawning to larval settlement, increased for some stocks (n=31), for others it declined (n=64), and for a smaller group (n=18) there was no substantial changes in level of primary production.DiscussionThis result implies that larval transport will not necessarily introduce larvae into areas of enhanced food availability expressed by the primary production at the site. These findings thus suggest marked differences in how physical and biological processes interact in the early life of major fish groups in the Atlantic Ocean. The results provide a further insight into fish larval drift and the potential role of primary production in emergence of spawning strategies.

Lysosomal alteration links food limitation to longevity.

Lysosomal alteration links food limitation to longevity.

Analysis of the Mercury Content in Fish for Human Consumption in Poland.

Mercury (Hg) is a metal with toxic effects on the environment, including living organisms. Organic Hg derivatives readily penetrate biological membranes and pose a particular health risk. Food of aquatic origin is the main source of human exposure to methylmercury (MeHg). In Poland, the consumption of fishery and aquaculture products has been gradually increasing. The aim of this study was to determine the content of Hg in fish intended for human consumption and purchased in Poland. The total Hg content of the edible parts of different species of marine and freshwater fish was analysed. The range of Hg content in all fish was 0.004-0.827 mg/kg, with an arithmetic mean of 0.084 mg/kg. The concentration of Hg in marine fish (0.100 mg/kg) was higher than in freshwater fish (0.063 mg/kg). The highest concentration of Hg was found in tuna. The Estimated Hazard Quotient (EHQ) calculated for the tuna samples analysed was >1. This may represent a potential health risk for consumers. The consumption of the other fish analysed was considered safe on the basis of the EHQ. The Hg content of the analysed fish samples did not exceed the current limits for food.

Post-Migration Changes in Dietary Patterns and Physical Activity among Adult Foreign Residents in Niigata Prefecture, Japan: A Mixed-Methods Study.

The migrant population of Japan is gradually increasing, but it is not well known how and why diet and physical activity (PA) change post-migration. Therefore, this study used a mixed-method approach to investigate the changes in dietary patterns and PA through a web- and paper-based survey (n = 128) and understand the contextual factors for those changes through semi-structured interviews (n = 21). Descriptive and thematic analyses of quantitative and qualitative data were conducted, respectively. The majority of survey (57.8%) and interview (66.7%) participants were female, and the mean duration of stay in Japan was 5 and 3.6 years, respectively. The survey revealed an increased consumption of foods attached to Japanese culture, frozen and microwavable food, and a reduced consumption of fruits. We identified environmental (availability, accessibility, and affordability of foods; food safety and diet-related information; and climate), individual (living status; post-migration lifestyle; and food preferences and limitations), or socio-cultural (relationships with Japanese people; cultural differences; and religious influences) factors that impact diet changes. Language proficiency and the duration of stay shape dietary behaviors. Determinants of PA changes were climate, lifestyle, and the influence of Japanese culture. In conclusion, immigrants in Japan experience post-migration diet and PA changes, and this study adds knowledge about how and why such changes occur.

Cadmium speciation in cacao beans changes during a fermentation-like incubation

Cadmium (Cd) concentrations in cacao often exceed food limits. Recently, it was shown that cacao bean fermentation enhances Cd solubility, opening potential for Cd mitigation in cacao products. This study was set-up to identify changes in Cd speciation during fermentation. X-Ray absorption spectroscopy (XAS) complemented with speciation calculations, were used on samples collected from high and low Cd farms, that were subjected to a fermentation-like incubation that reached high temperatures (>45 °C) and acidic pH (<5). Incubation decreased nib Cd concentration up to a factor 1.5 and changed Cd complexation in high Cd beans from sulphur to oxygen ligands, likely due to pH changes. In beans with lower Cd concentrations, Cd was complexed before and after incubation with oxygen-ligands. A combination of pH changes and/or phytate breakdown may explain the migration of Cd outward from the nib. XAS and speciation calculations proved complimentary techniques and indicated similar speciation changes during fermentation.

A LC-MS/MS procedure for the analysis of 19 perfluoroalkyl substances in food fulfilling recent EU regulations requests

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are synthetic, stable, fluorinated molecules widely used in consumer products. They are non-biodegradable, persistent and bio-accumulating. In 2020 European Food Safety Authority (EFSA) lowered the Tolerable Weekly Intake (TWI) for the four PFASs (PFOA, PFOS, PFNA, PFHxS) and in 2022, the EU issued a Recommendation asking to monitor twenty-one PFASs in food. Since 1st January 2023 limits in food were set. Here we report a sensitive, straightforward and robust procedure enabling the determination of 19 PFAS in food matrices using a liquid chromatography mass spectrometer (LC–MS/MS). Few are the published methods applicable to the different food matrices and covering the molecules listed in Recommendation 2022/1431, fulfilling the LOQs requested. The method was satisfactory validated (UNI CEI EN ISO/IEC 17025:2018 and Regulation (EU) 2022/1428) and used to investigate hen egg samples, highlighting home-produced eggs as the more critical egg farming process for PFAS accumulation.

Gut microbiome resilience of green-lipped mussels, Perna canaliculus, to starvation

Host gut microbiomes play an important role in animal health and resilience to conditions, such as malnutrition and starvation. These host-microbiome relationships are poorly understood in the marine mussel Perna canaliculus, which experiences significant variations in food quantity and quality in coastal areas. Prolonged starvation may be a contributory factor towards incidences of mass mortalities in farmed mussel populations, resulting in highly variable production costs and unreliable market supplies. Here, we examine the gut microbiota of P. canaliculus in response to starvation and subsequent re-feeding using high-throughput amplicon sequencing of the 16S rRNA gene. Mussels showed no change in bacterial species richness when subjected to a 14-day starvation, followed by re-feeding/recovery. However, beta bacteria diversity revealed significant shifts (PERMANOVA p-value < 0.001) in community structure in the starvation group and no differences in the subsequent recovery group (compared to the control group) once they were re-fed, highlighting their recovery capability and resilience. Phylum-level community profiles revealed an elevation in dominance of Proteobacteria (ANCOM-BC p-value <0.001) and Bacteroidota (ANCOM-BC p-value = 0.04) and lower relative abundance of Cyanobacteria (ANCOM-BC p-value = 0.01) in the starvation group compared to control and recovery groups. The most abundant genus-level shifts revealed relative increases of the heterotroph Halioglobus (p-value < 0.05) and lowered abundances of the autotroph Synechococcus CC9902 in the starvation group. Furthermore, a SparCC correlation network identified co-occurrence of a cluster of genera with elevated relative abundance in the starved mussels that were positively correlated with Synechococcus CC9902. The findings from this work provide the first insights into the effect of starvation on the resilience capacity of Perna canaliculus gut microbiota, which is of central importance to understanding the effect of food variation and limitation in farmed mussels.

Infant food formulations based on cereals (millet, maize) and caterpillar powder (Imbrasia oyemensis): Nutritional composition and sensory evaluation

Malnutrition is a real public health problem, particularly in low-income households. Therefore, the objective of this work is to improve nutritional quality of complementary foods based on maize and millet flours intended for children during diversification period of low-income households. Thus, biochemical and phytochemical composition of ten cereal-based formulations (maize and millet) incorporated or not with Imbrasia oyemensis caterpillar powder were studied using standard and conventional methods. In addition, these formulations were subjected to a hedonic test by a panel of fifty people. It was found that incorporation of Imbrasia oyemensis powder improved contents of protein (11.97±0.03-16.4±0.03%), lipids (7.65±0.49-11.08±0.20%), ash (2.07±0.05-3.20±0.05%) and energy value (402.97±13.9- 483.63±35.71 kcal/100g) of maize (FMa0) and millet (FMi0) based flours. In addition, these formulations showed excellent contents of total polyphenols (160.19±2.80-256.16±0.00 mg/100g), flavonoids (10.95±0.07-25.64±0.15mg/100g) and tannins (109.45±0.68- 225.54±0.90 mg/100g). In addition, anti-nutritional contents such as phytates (97.24±0.08-128.60±0.08 mg/100g) and oxalates (215.81±1.67-370.65±9.29 mg/100g) are below the acceptable limit in human food. Thus, these incorporated formulations of Imbrasia oyemensis caterpillar powder were highly appreciated by panelists. Incorporation of Imbrasia oyemensis powder in maize and millet-based supplementary foods constitutes a cheaper and healthier alternative in children diet during diversification period of low-income households in Côte d'Ivoire.

Carcinogenic and Non-Carcinogenic Health Risks Assessment of Elemental Contaminants in &lt;I&gt;Laminariae thalli&lt;/I&gt;

Scientific relevance. Laminariae thalli are a native herbal preparation used to prevent or treat multiple diseases. To achieve the optimal effect, this herbal preparation is usually taken for several weeks or months. The control of Laminariae thalli should extend beyond the element content in the herbal drug limited by specifications; additionally, it is important to assess the health risks of ingesting heavy metals with the medicinal product during the exposure period.Aim. The study aimed to assess the carcinogenic and non-carcinogenic risks of consuming elemental contaminants with therapeutic doses of herbal medicinal products based on Laminariae thalli.Materials and methods. The study investigated the content of elemental contaminants (Al, As, Cd, Cr, Co, Cu, Fe, Hg, Mn, Mo, Ni, Se, Pb, Sr, V, and Zn) in Laminaria saccharina and Laminaria japonica. The content of inorganic arsenic was determined by solid-phase extraction using inductively coupled plasma mass spectrometry (ICP-MS).Results. When averaged at the 90th percentile level, the mean concentrations of the specified elements did not exceed the limits for seaweed and seagrass foods. The total hazard index from exposure to all analysed elements amounted to 0.173 at the median level and 0.616 at the 90th percentile level. The leading contributors to the total hazard index were As, Fe, Cd, and Sr. The individual carcinogenic risk (CR) values for the potential carcinogens (As, Cd, Pb, and Cr) fell within the range of 1×10-6&lt;CR&lt;1×10-4.Conclusions. If the elements analysed are ingested with a daily therapeutic dose of Laminariae thalli for the exposure period, their total negative effect will not cause harm to the human body. To eliminate the risk of developing neoplasms when the studied medicinal product (Laminariae thalli) is taken at its maximum recommended therapeutic dose for a month or more, the Cr content should be controlled along with the elements limited by specifications for herbal medicines.

Sibling cannibalism in the false widow spider is dependent on spiderling density and the reliable availability of fresh prey

AbstractAdult female spiders lay batches of eggs in silken egg sacs, and after hatching, the spiderlings live for transient periods in their mother's web before dispersing. Sibling cannibalism is frequently observed among spiderlings of many species under conditions of food deprivation. Here, we conducted assays in small Petri dishes with different densities of newly hatched (second instar) spiderlings of the false widow spider, Steatoda grossa, using a split‐clutch design. Prey (freshly killed fruit flies) availability was manipulated both numerically and temporally. Offspring from 10 different females were separated as siblings into densities of two, four, or eight spiderlings per Petri dish and these were provided with either 0 flies (starvation control), two flies, four flies, or eight flies that were replenished weekly or every 3 weeks. A further control was conducted with solitary spiderlings in Petri dishes deprived of flies. The number of surviving spiderlings per Petri dish was counted every 3 days until only one remained (or until death of the solitary spiderling). Our results show that the rate of cannibalism was lower with increasing spiderling density and when fresh flies were replenished more frequently, whereas the number of flies that were provided did not affect cannibalism. In S. grossa, juvenile cannibalism occurs primarily under conditions of extreme food limitation, although in synanthropic habitats where the spider is abundant, it may be an adaptive strategy owing to the potential scarcity of prey. Under certain conditions, cannibalism in spiderlings is adaptive by eliminating competitors and providing nutrient‐rich food.

TEMPORAL DYNAMICS IN PANTANAL HUMMINGBIRD ASSEMBLAGES IS TRIGGERED BY FLOOD PULSE

Abstract ∙ Hummingbirds (Trochilidae) are highly specialized New World birds that depend on nectar as their major food source. In response to seasonal food limitations, many trochilids develop dispersal and long-distance migration patterns, but these patterns are understudied for many continental South American species. In this study, conducted in the Brazilian Pantanal, we investigated the movement patterns of hummingbirds in a highly variable environment, where an annual flood pulse leads to four distinctive seasonal periods (high water, receding water, dry period, and rising water). Our objective was to verify how these four periods affected the hummingbird community according to habitat occupation in savannas or forests. This study was conducted in the northeastern Pantanal of Mato Grosso, Brazil (16° 39'S, 56°47'W, 119–131 m a.s.l.), covering two annual inundation periods (2014–2016). Data were collected using mist net sampling. Two migrant and seven resident species were identified. The results indicated significant differences in hummingbird species richness and abundance between habitats; savanna habitats were the richest habitats during rainy seasons (rising and high water). Higher hummingbird abundance in these seasonal periods was seemingly related to higher food availability since these seasons corresponded to the main flowering period of ornithophilous plants and other angiosperms.