Exploitation Of Food Resources Research Articles

Cave amphipods reveal co‐variation between morphology and trophic niche in a low‐productivity environment

Abstract Identifying the relationships between morphology and trophic niche is at the core of functional morphology. Low resource diversity and fluxes of organic carbon are expected to constrain trophic specialisation of morphological structures because food resources are too scarce to promote trophic differentiation. However, species from low‐productivity habitats often exhibit specialised biological traits such as resistance to starvation and high food‐finding abilities, which may in turn release constraints on trophic and morphological differentiation among species. Groundwaters are food resource‐limited because of the lack of photosynthetic production and limited inputs of organic carbon from surface ecosystems. We tested for co‐variation between morphology and trophic habits in co‐occurring Niphargus amphipods from five groundwater caves of the Dinaric Karst, Europe. We predicted that the size of gnathopods—the accessory feeding appendages—would positively co‐vary with trophic position: species with larger gnathopods should more easily grab and immobilise prey. We quantified gnathopod size and shape by means of morphometric measurements and assessed isotopic niche, trophic position, and carbon signatures using nitrogen (δ15N) and carbon (δ13C) stable isotopes. We tested for correlation between morphological traits and trophic position and δ13C signatures while accounting for phylogenetic relationships among species. All co‐occurring species differed morphologically in at least one gnathopod measurement and all of them differed in their isotopic niches. As predicted, gnathopod size increased with the increasing trophic position. This co‐variation probably reflects differences in detritivorous and predatory habits among species: amphipods with larger gnathopods, hence larger muscle and more powerful grip, could more easily subdue prey. Moreover, we found a significant correlation between gnathopod shape and the normalised δ13C values, indicating that shape of the gnathopods may be related to exploitation of different food resources. We show that low‐productivity subterranean habitat species can exhibit strong trophic specialisation of morphological structures. Gnathopod size and shape of Niphargus amphipods are functional traits that co‐vary with trophic habits. Our findings pave the way for investigating how co‐variation of morphological and trophic traits may control energy flow and species’ coexistence at lower bounds of habitat productivity.

Fundamental dietary specialisation explains differential use of resources within a koala population.

The diets of individual animals within populations can differ, but few studies determine whether this is due to fundamental differences in preferences or capacities to eat specific foods, or to external influences such as dominance hierarchies or spatial variation in food availability. The distinction is important because different drivers of dietary specialisation are likely to have different impacts on the way in which animal populations respond to, for example, habitat modification. We used a captive feeding study to investigate the mechanisms driving individual dietary specialisation in a population of wild koalas (Phascolarctos cinereus) in which individuals predominantly ate either Eucalyptus viminalis or Eucalyptus obliqua foliage. All six koalas that primarily ate E. viminalis in the wild avoided eating E. obliqua for more than 1 month in captivity. In contrast, all seven koalas that primarily ate E. obliqua could be maintained exclusively on this species in captivity, although they ate less from individual trees with higher foliar concentrations of unsubstituted B-ring flavanones (UBFs). Our results show that fundamental differences between individual animals allow some to exploit food resources that are less suitable for others. This could reduce competition for food, increase habitat carrying capacity, and is also likely to buffer the population against extinction in the face of habitat modification. The occurrence of fundamental individual specialisation within animal populations could also affect the perceived conservation value of different habitats, translocation or reintroduction success, and population dynamics. It should therefore be further investigated in other mammalian herbivore species.

Foraging Behaviour of Heterotrigona itama (Apidae: Meliponini) in Residential Areas

This study aims to investigate the foraging behaviour of Heterotrigona itama in exploiting food resources at a residential area, and the viability of this species to adapt to urban microclimatic conditions. Heterotrigona itama prefers to forage at areas closer to their nesting site, where diverse food sources are found. The marked bees of H. itama prefer to forage on various resources available at a 500-metre radius from the house yard. The obtained results indicate that the active foraging pattern of H. itama is negatively correlated to the time phases of a day (p < 0.05). This phenomenon was contributed by the three peaks of foraging hours, which reached a peak in the early morning (6:30 to 8:00 a.m.), moderately peaked towards the evening (2:30 to 3:30 p.m.), and was greatest towards the afternoon (10:30 a.m. to 12:00 p.m.). The ambient temperature and relative humidity were not the primary factors influencing the average number of foragers exiting from and returning to the hives (temperature, p > 0.05; and humidity, p > 0.05). There was a difference between the varieties of content resources collected by the bees (p < 0.05). The nectar or water sources was the highest material (51.39%) that was brought back to the hive by foragers, followed by resin (34.73%) and pollen (13.87%). There was a significant difference in foraging time phases by returning foragers for collecting resin (p < 0.05) and nectar or water (p < 0.02), but there was no significant difference in foraging time phases found for pollen (p > 0.05). We concluded from the results that H. itama is able to withstand urban microclimate conditions, and successfully incorporated pollen, nectar or water, and resin obtained from floral and non-floral resources into their diet.

Lipid residue analysis on Swifterbant pottery (c. 5000–3800 cal BC) in the Lower Rhine-Meuse area (the Netherlands) and its implications for human-animal interactions in relation to the Neolithisation process

This paper focuses on the functional analysis of Swifterbant pottery (c. 5000–3800 cal BC) in the Lower Rhine-Meuse area (the Netherlands). It examines pottery use across the transition to agriculture and aims to assess temporal changes in human-animal relations during the 5th millennium BC in the Lower Rhine-Meuse area through lipid residue analysis. We conducted lipid residue analysis of 49 samples from four Swifterbant sites: Hardinxveld-Giessendam Polderweg, Hardinxveld-Giessendam De Bruin, Brandwijk-het Kerkhof, and Hazendonk. A combined approach using both GC-MS and GC-C-IRMS of residues absorbed into the ceramic was employed to identify their context. Their context was then compared to published faunal datasets to present the relative abundance of taxa detected in the lipid residues. Evidence of processing freshwater fish was found in all sites, presenting that it was a continuous and primary function of Swifterbant pottery in the Lower Rhine-Meuse area starting from its first appearance at c. 5000 cal BC till the end of 5th millennium BC regardless of vessel form, size, decoration or temper. The results of our analysis also present temporal changes in the exploitation of food resources from the early to the late 5th millennium BC. From the mid 5th millennium BC onwards, vessels were also used to process different ranges of foodstuffs such as terrestrial resources and dairy products. The identification of dairy residue is the first direct evidence so far from Swifterbant pottery. We tentatively explain these results as an indication of presence of different culinary practices that had developed through the 5th millennium in the Lower Rhine-Meuse area and that the use of Swifterbant pottery is a direct reflection of changing cultural preferences on food preparation and consumption.

Stunning Facts of Bird Migration: Mini-Review

Migration is a unique phenomenon that millions of birds perform annually. It includes various aspects such as preparation for the long journey, migratory patterns, problems faced during migration, figuring out routes, etc. Some more interesting things are genetics behind migration and urge for migration. Zugunruhe , a period for migratory restlessness, has been observed well in caged birds or those restricted to Zoos. The analysis of population studies in European blackcaps evidences that ADCYAP1 gene is one of the major genes which regulate the expression of migratory behavior. It is instinctively known to young birds which way to go and how to adapt complex migratory patterns of movement as this knowledge is genetically imprinted some way or the other. Astronomical cues such as solar and stellar compasses in conjunction with the earth’s magnetic compass provide aid of senses in migration and this is very well received by the eyes of migrant birds to overcome the long routes of journey. Ecological implications of migration include adequate exploitation of food resources in some regions, which won’t be possible otherwise. Also, migrant birds favour regions having productivity that varies with seasons as in these regions there may be food surpluses. Anthropogenic actions pose serious threats to migratory birds and also the diverse developments (mostly commercial and deforestation) of the human habitats are the worst threats the birds face during migration.

Mobile (after-)lifeways: People at pre- and protopalatial Sissi (Crete)

This paper discusses the first integrated strontium and oxygen isotope ratio results from human remains from Pre- and Protopalatial Crete, spanning the period circa 2500–1750 BCE, with a view to offering a more nuanced understanding of past populations, their diets, potential origins and aspects of their mobility: in particular, the extent to which mobility was part of these people’s lives.Twenty-six human individuals from the site of Sissi were sampled for strontium and oxygen isotope ratio in tooth enamel, while five of them were also analysed for corresponding strontium isotope signatures in bone samples. The human tooth enamel strontium isotope signatures follow a broad distribution that is in overall agreement with the diverse substrate geology reported for the site and its immediate range within a radius of 5 km, as well as with strontium isotope results from snail samples also collected from the broader Sissi region. Strontium data variation can be explained by access to different feeding territories in close proximity to the site and possibly also as a result of variation in the composition of childhood diet, while some short-range immigration cannot be excluded either. In a fashion similar to the strontium data, the human oxygen isotope signatures are also consistent with a provenance from within the island.Isotope data variation and the inferred maximization of the exploitation of arable land to extend the agricultural resource base is largely in tune with contemporary socio-economic developments, settlement nucleation and population growth on Crete towards the late Prepalatial period. Use of multiple production zones by the people at Sissi may also be seen as a buffer against climate instability and vulnerability of coastal sites, while settlement nucleation is supported by evidence for the abandonment of contemporary sites in the bay of Malia with the exception of Sissi and Malia.Based on these data we conclude that mobility was part of the life of people at Sissi. They were either moving as part of their daily routine to exploit food resources, or in relation to settlement nucleation with some of them having moved to Sissi from nearby sites. It is also possible that people from nearby sites were buried in the Sissi cemetery. Owing to the overlapping strontium and oxygen isotope signatures in the context of this study, it is currently impossible to choose between the above three scenarios.

Convective circulation influences horizontal movement by planktonic crustaceans in the littoral zone of a mesotrophic lake

Abstract Crustacean zooplankton perform diel vertical and horizontal migrations in lakes to avoid predators and/or exploit food resources more efficiently. Crustaceans may also move passively with convective flows that are generated by the nocturnal cooling of the surface water. Water in the shallow littoral zone cools faster than deeper pelagic waters. Therefore, bottom water moves from inshore to the pelagic zone while surface water moves in the opposite direction. The purpose of this study was to determine if crustaceans performed horizontal movements in the bottom and surface layers of a mesotrophic lake, Lake Obsterno in north‐west Belarus. We installed plankton nets horizontally in the bottom and surface layers of the lake at three sites located at different distances from the shore. We hypothesised that (1) if crustaceans performed diel horizontal migration, they would move in identical directions in the bottom and surface layers either from nearshore to open waters in the evening and back in the morning, or vice versa; (2) if crustaceans moved with convective flows, they would be carried to the shore in the surface layer and to the open waters in the bottom layers. Day and night air temperatures differed by more than 10°C over 24 hr. We assumed that the rates of convective currents were similar to those reported for other lakes exposed to a similar range of air temperatures. Rates of convective currents were also measured in Lake Obsterno and varied between 0.6–0.7 cm/s. These rates of convective currents were shown to exceed the cruise speed of planktonic crustaceans. The direction of movement of the most abundant taxa coincided with the direction of convective currents in more than 90% of the cases in the bottom layer and 70–80% of the cases in the surface layer. The abundance of invertebrate predators (mainly predatory cladocerans and boatmen (Hemiptera, Heteroptera) was negatively related to the abundance of crustaceans in the surface layer. Deviations in the distribution patterns of some crustacean species compared to distributions induced by convection currents in the upper layers may have been associated with the avoidance of invertebrate predators and/or predator grazing. Abundances of crustaceans were positively correlated between the sites located at different distances from the shore, and individual taxa were positively related to each other indicating that they moved in the same direction. Based on the fact that the directions of crustacean movements and convective currents mostly coincided, we concluded that convective currents passively carried the crustaceans. At low light intensities and low predation pressure (by visual fish predators), the direction of horizontal movement by zooplankton was mainly determined by convective circulation generated by cooling of the lake surface. Actively swimming planktonic invertebrate predators are likely to move in the same direction as herbivorous crustaceans. Therefore, predators could influence zooplankton distribution regulated by convective flows. We suggest that studies of horizontal migration and coupling between pelagic and littoral zones need to account for diurnal water currents in lakes.

Soldiers of the termite Nasutitermes corniger (Termitidae: Nasutitermitinae) increase the ability to exploit food resources

The performance of eusocial insect colonies is optimized by the division of labor among castes. Throughout the evolution of termites, there was an evident increase in the proportion of soldiers in the colonies. In derived termite species, the soldiers have a crucial role in defense and the initial phases of foraging. Here, we evaluated whether the soldiers of the Neotropical termite Nasutitermes corniger improve the foraging decisions. We tested the hypotheses that groups with soldiers (i) are more efficient searching for food, (ii) more efficiently recruit individuals, and (iii) a higher proportion of soldiers results in a more efficient balance between exploitation and exploration of food resources. Using behavioral bioassays under laboratory conditions, we show that the presence of soldiers in termite groups promotes a faster exploitation of the environment that allows them to encounter more food sources simultaneously. However, the presence of soldiers did not significantly increase the attraction of termite groups. Despite that, termite groups with higher soldier proportions were more able to perceive changes in the resource offerings by redirecting individuals to explore more profitable sources. Our results show that the role of soldiers in N. corniger increases the efficiency of termite groups in the exploration and exploitation of food resources.

Intentional partial beaching in a coral reef fish: a newly recorded hunting behaviour of titan triggerfish, Balistoides viridescens.

Coral reef fishes use a multitude of diverse feeding behaviours to increase their ability to successfully capture a wide range of prey. Here, this study reports a novel hunting behaviour in a coral reef fish, the titan triggerfish, Balistoides viridescens, where an individual was seen partially beaching itself while attempting to catch a Red Sea ghost crab, Ocypode saratan. This is the first report of this behaviour in the order Tetraodontiformes and represents an astonishing capability of this species to exploit food resources outside their typical assumed ecological niche.

For emergency only: terrestrial feeding in Coimbra-Filho’s titis reflects seasonal arboreal resource availability

Terrestriality in Platyrrhine primates is primarily associated with low arboreal resource availability, low predation risk when on the ground and increased contact time with human observers. To test the relationship between these variables and ground use frequency, we studied a group of endangered Coimbra-Filho's titi monkeys (Callicebus coimbrai) in a 14-ha forest fragment in north-eastern Brazil. Terrestriality data were collected on a monthly basis (33months) using scan sampling procedures from July 2008 to July 2012. Overall, Coimbra-Filho's titi monkeys were recorded during 0.6% of observation time (113 out of 18,164 scans) on the ground. Most of the time on the ground was spent feeding on young leaves (71 records) and the least amount of time on fruits (14 records). Availability of arboreal foods, rainfall, and time of contact with human observers did not influence overall terrestrial behaviour (ground use). However, the timing and nature of the monkeys' terrestrial feeding was strongly related to the absence of arboreal fruit (β-estimate = -3.078) and young leaf (β-estimate = -3.515) food resources. We suggest that terrestrial feeding by Coimbra-Filho's titi monkeys could be an adaptation to low arboreal fruit availability and the exploitation of alternative food resources.

Early Marine Isotope Stage 5 sea levels, coastal dune palaeoenvironments, and human occupation on the southeast coast of South Africa

Quaternary-age human and animal footprints have been reported from coastal deposits along the South African coast. These footprints and their sedimentary contexts can inform on Quaternary palaeoenvironments and processes stratigraphically associated with the palaeoanthropological record of past human occupation in the coastal zone, and exploitation of its resources. This study examines the palaeoenvironmental context and sedimentology of Marine Isotope Stage 5 aeolianite at Nahoon Point, southeastern coast of South Africa, where preserved human footprints have been previously recorded. This study identifies seven sedimentary facies from 20 logged profiles through the coastal aeolianite in order to develop a landscape-scale stratigraphic framework for coastal palaeoenvironmental reconstruction during the period of the MIS 5 highstand. Two phases of aeolianite deposition are identified, which bracket a single stepped sea-level transgression phase up to +7.82 ± 0.82 m asl, evidenced by intraformational beachrock facies and marine benches. This correlates with the second known global MIS 5e highstand; no evidence for the first highstand reported from the literature was found in the study area. Aeolianite bed geometries and sedimentary structures indicate that wind regimes and rainfall seasonality were similar to present. Newly discovered faunal tracks in aeolianites of the first depositional phase suggest the presence of unidentified bovids of varying sizes. Evidence for human activity is preserved in all three recorded depositional phases, suggesting people were present throughout the early MIS 5 sequence despite changing environmental conditions. This evidence suggests that human occupation of coastal areas, and the exploitation of marine food resources was more widespread than generally thought in southern Africa during early MIS 5.

Black Soldier Fly Larvae Adapt to Different Food Substrates through Morphological and Functional Responses of the Midgut.

Modulation of nutrient digestion and absorption is one of the post-ingestion mechanisms that guarantees the best exploitation of food resources, even when they are nutritionally poor or unbalanced, and plays a pivotal role in generalist feeders, which experience an extreme variability in diet composition. Among insects, the larvae of black soldier fly (BSF), Hermetia illucens, can grow on a wide range of feeding substrates with different nutrient content, suggesting that they can set in motion post-ingestion processes to match their nutritional requirements. In the present study we address this issue by investigating how the BSF larval midgut adapts to diets with different nutrient content. Two rearing substrates were compared: a nutritionally balanced diet for dipteran larvae and a nutritionally poor diet that mimics fruit and vegetable waste. Our data show that larval growth performance is only moderately affected by the nutritionally poor diet, while differences in the activity of digestive enzymes, midgut cell morphology, and accumulation of long-term storage molecules can be observed, indicating that diet-dependent adaptation processes in the midgut ensure the exploitation of poor substrates. Midgut transcriptome analysis of larvae reared on the two substrates showed that genes with important functions in digestion and absorption are differentially expressed, confirming the adaptability of this organ.

Thermal effects on red muscle contractile performance in deep-diving, large-bodied fishes.

Bigeye thresher sharks (Alopias superciliosus) and swordfish (Xiphias gladius) are large, pelagic fishes, which make long-duration, diurnal foraging dives from warm, surface waters (18-24°C) to cold waters beneath the thermocline (5-10°C). In bigeye thresher sharks, the subcutaneous position of the red, aerobic swimming muscles (RM) suggests that RM temperature mirrors ambient during dives (i.e., ectothermy). In swordfish, the RM is closer to the vertebrae and its associated with vascular counter-current heat exchangers that maintain RM temperature above ambient (i.e., RM endothermy). Here, we sought to determine how exposure to a wide range of ambient temperatures (8, 16, 24°C) impacted peak power output and optimum cycle (i.e., tailbeat) frequency (0.25, 0.5, 1Hz) in RM isolated from both species. Bigeye thresher shark RM did not produce substantial power at high cycle frequencies, even at high temperatures; but it did produce relatively high power at slow cycle frequencies regardless of temperature. Swordfish RM produced more power when operating at a combination of fast cycle frequencies and higher temperatures. This suggests that swordfish RM benefits considerably more from warming than bigeye thresher shark RM, while the RM of both species was able to produce power at cold temperatures and slow cycle frequencies. Despite different thermal strategies (i.e., ectothermy vs. RM endothermy), the ability of the RM to power sustained swimming during foraging-related search behaviors may contribute to the unique ability of these fishes to successfully exploit food resources in deep, cold water.

Use of microhabitat and activity patterns of two lizard species from a seasonal dry forest in northern Colombia

In this work, the microhabitat use and activity patterns of two lizard species with sympatric distribution were evaluated in a dry forest fragment within the department of Sucre, northern Colombia. Data was collected in May, June, September and October of 2017, using the active search method limited by time (7:00 and 19:00 hours). Substrates used, spatial distribution and time of capture were recorded for individuals of the species Loxopholis rugiceps (Cope 1869) and Lepidoblepharis sanctaemartae (Ruthven 1916). Complementarily, environmental and physical parameters were recorded, which allowed us to characterise the microhabitats of the species. A total of 276 lizards were recorded, 177 belonging to the species Loxopholis rugiceps and 99 to Lepidoblepharis sanctaemartae. The results showed similar resource use by the two species for the spatial dimension, with both exploiting different terrestrial elements mainly from the interior forest, followed by the riverbed stream and forest edge. Differences were found in the daily activity patterns between species, with individuals of L. sanctaemartae more frequently recorded in the morning hours and L. rugiceps in the afternoon hours. The activity patterns did not differ by age groups: juveniles and adults. Both species were more frequently found in the litter substrate within the forest, followed by rocks and bare ground. Our results indicate that both species are tolerant to matrix conditions, however, they require internal forest conditions to exploit food resources and refuge.

Local community perceptions toward livelihood and water–energy–food nexus: A perspective on food security

AbstractWhile water–energy–food (WEF) nexus is a major livelihood sources for local community, its security issues grow continually and there is limited information on how nexus resource management is effective at delivering livelihoods and food security. These difficulties are related to the lack of local community knowledge of the use and exploitation of water, energy, and food resources; this limited awareness leads to trade‐offs, especially in local and marginalized areas. On the basis of data collected from a local community through a survey‐based approach, this study examines local community perception of nexus resources and their contribution to livelihoods. The results indicate that community perceptions of nexus resources can be understood through social, natural, economic, human, physical, and environmental livelihood indicators. According to our findings, the perception of nexus resources is based on the benefits of individual resources rather than their interlinkages. This could be the result of community perceptions of a particular nexus resource from three nexus sector, that is, food. Food is the center of nexus resources for the community in the study area. This indicates, that there is a missing link between cross‐sectorial resource utilization and management, and full‐scale adoption of the WEF nexus to enhance living conditions. Our findings suggest that there is a low understanding of WEF nexus resource use and management, and the livelihood benefit of individual nexus resources is the primary focus in the studied community. From these results, we recommend more action to be taken by the government and other stakeholders to improve the local community perception of nexus resources for their livelihoods.

Foraging behavior of the Greater White-fronted Goose (Anser albifrons) wintering at Shengjin Lake: diet shifts and habitat use

BackgroundThe habitat use and foraging behaviors of waterbirds are closely related to the distribution and abundance of their food resources. Reductions in food supply can cause waterbirds to shift their habitats and adjust their foraging behaviors to meet their nutritional requirements and increase fitness. Seasonal withdraw of the water levels in the river-connected lakes in the middle and lower Yangtze River floodplain provides abundant food resources for the wintering Greater White-fronted Goose (Anser albifrons). Sedge (Carex) meadows are critical foraging habitats for herbivorous waterbirds in the hydro-fluctuation belt, which changes with hydrological conditions and climate. This study aimed to examine the behavioral responses of the Greater White-fronted Goose to temporal- spatial changes of food availability in the Sedge meadows.MethodsFields surveys were carried out at Shengjin Lake from November 2017 to April 2018. According to the phenology of Shengjin Lake, we divided the wintering season into three periods. The food density, minimum temperature, food items, grass height, and number of foraging geese were surveyed, and samples of the foraging behavior were collected. We analyzed the relationship of the foraging behavior and habitat use relative to the food resources, using correlation and linear regression analyses.ResultsAlong with the temporal-spatial variation and exploitation of food resources, the food abundance and items varied widely among the foraging sites. Over the whole wintering period, the foraging habitat with the highest utilization rate was the meadows, followed by the paddy fields, and then mudflats. Furthermore, the utilization of the meadows showed a bimodal distribution trend, while the paddy fields showed a unimodal trend, and a decreasing trend was seen in the mudflats over the whole wintering period. The results of the generalized linear model showed that the foraging rate was related to the food density and grass height, with a linearly increasing trend during the winter.ConclusionsWith the change of food resources in the three habitats, the habitats used by the Greater White-fronted Geese shifted from meadows in the hydro-fluctuation belt to the paddy fields, and then back to the meadows. The time budget for foraging activities increased correspondingly, and there was an increase in the foraging rate to compensate for food shortages.

Feeding habits of Bigeye Houndshark, Iago omanensis (Elasmobranchii; Triakidae); a typical deep water shark from the Gulf of Oman

In this study, the feeding habits of Bigeye Houndshark, Iago omanensis , a typical deep water shark, were examined in the Gulf of Oman by analyzing of stomach contents. In addition, the effects of sex and seasons (spring and summer) on its feeding habits were evaluated. Bigeye Houndshark diet consists of mostly teleost fishes, and to a lower extent on crustaneans, molluscs and sea snakes. The great importance of teleost in the diet of Bigeye Houndshark may be due to the fact that teleosts are the dominant in terms of biomass and abundance in the area where Bigeye Houndshark exist, allowing them to exploit food resources available in the environment. No significant differences were found between sexes and seasons. This species occupy high trophic position within the food webs. These results present new data that will allow us to understand the role of Bigeye Houndshark in the deep water of Gulf of Oman to effect of fishing activity on its population dynamics in the future.

Facultative amphidromy involving estuaries in an annual amphidromous fish from a subtropical marginal range.

Variation in the life cycle of diadromous fishes can be explained by differential food availability between marine and freshwater habitats, since migration is often interpreted as a mechanism for exploiting food resources. Theoretically, a migration pattern of mainly remaining in freshwater occurs in tropical and subtropical habitats where fluvial productivity possibly exceeds marine productivity. However, in Yakugachi River, Amami-Oshima Island, southern Japan, low nutrient concentrations in the river suggest that food availability is limited for the subtropical Ryukyu-ayu Plecoglossus altivelis ryukyuensis. Since Ryukyu-ayu is an amphidromous fish that mainly grows in rivers after spending 2 months in the sea, limited food availability in rivers would force this species to migrate to other habitats with better food availability. Otolith increment and Sr:Ca analyses of 48 adult Ryukyu-ayu collected from the Yakugachi River revealed that all individuals visited estuaries more than three times after moving upstream. Although the specific growth rates of this species in the river had no correlation with the salinity profile in the fluvial period, this movement may be an adaptive choice because the salinity profile significantly affected the body size at maturity. Our results highlighted individual-based variations in amphidromous migration for utilizing estuaries, which could be explained by relatively higher productivity in estuarine than in freshwater and marine habitats.

Food resource exploitation and functional resilience in ant communities found in common Mediterranean habitats

Understanding how ecosystems may cope with future environmental change is a key challenge in modern ecology. Ecosystem resilience depends on both functional redundancy (the number of species making a similar contribution to a given ecosystem function) and response diversity (variability in the responses of functionally similar species to disturbance). Ants provide numerous important ecosystem functions that are rooted in their dietary ecology. We focused on food resource exploitation and analyzed how functional redundancy and response diversity changed across common habitats for Mediterranean ant communities. Our aim was to assess the vulnerability of ant-furnished ecosystem functions to future environmental change. We used cafeteria experiments to identify ant functional groups: we offered ants a variety of seeds, insects, and liquid sugars. Then, using more general baits, we estimated ant species richness and abundance. We also examined 12 ant traits (morphological, social, ecobehavioral, and physiological) thought to reflect responses to disturbance. We found that most Mediterranean ant species are dietary generalists. Functional redundancy was highest and lowest for sugar and seed consumers, respectively, a consistent trend across habitats that was unrelated to species richness. Response diversity did not depend on ant functional group. Interestingly, both functional redundancy and response diversity were higher in pine forests and shrublands than in oak forests, a pattern that was consistent regardless of whether the functional groups were examined collectively or individually. Variation in functional redundancy and response diversity was strongly driven by site-specific species richness. Response diversity also varied based on trait type. Ecosystem functions mediated by seed-consuming ants should be the most vulnerable to environmental change, and habitat type and local species richness should affect the vulnerability of any ecosystem functions mediated by ant dietary ecology. Species-poor communities in forests should be the most vulnerable, while species-rich communities in open habitats should be the most resilient.

Avian frugivory rates at an abundant tree species are constant throughout the day and slightly influenced by weather conditions

Birds, like most animals, are expected to adjust their foraging activity in response to biotic and abiotic variations to optimize energy intake and reduce costs associated with finding and ingesting food. This may lead to temporal variation in the exploitation of food resources, which has been investigated for birds of different feeding guilds but remains poorly understood for frugivorous species. Here, we tested whether the frugivory activity of birds on Schinus terebinthifolia trees varies throughout the day during the austral autumn and winter and whether variation is related to weather conditions. For two consecutive years, we quantified frugivory events for 304 h in 19 individuals of S. terebinthifolia observed across four time periods throughout the day. We found that the number of frugivory events was similar irrespective of the time period, both for the entire assemblage (all species pooled together) and for the most common species analyzed individually. We additionally found that frugivory activity was slightly influenced by temperature and wind. The lack of any effect of daytime period on fruit consumption may relate to the high and prolonged levels of fruit availability in S. terebinthifolia and the short photoperiod of the autumn–winter, which favors frequent feeding throughout the day. Such constant removal of fruits by a diverse assemblage of generalist fruit consumers probably enhances seed dispersal and may have important implications for the population dynamics of this abundant plant. Our results also demonstrate that data on avian frugivory in temperate, open-vegetation environments can be quantified throughout the entire daytime during the cold season without temporal bias, which has important methodological implications for studies on bird–plant interactions.