Microhabitat characteristics of the critically endangered big-headed turtle Platysternon megacephalum.

Understanding the microhabitat requirements of an animal is vital for ensuring the success of targeted conservation and microhabitat restoration measures. The big-headed turtle (Platysternon megacephalum) is a freshwater species that is distributed across Southeast Asia. Owing to the human threats posed by illegal pet trade and overharvesting for food and medicinal purposes, the species has undergone rapid decline. However, in Hainan, their microhabitat characteristics are still unknown, which is neither conducive to the conservation of the species nor to the establishment of the Hainan Tropical Rainforest National Park. This study examined the microhabitat characteristics of P. megacephalum using sample plot methods in the Diaoluo Mountain area of Hainan Tropical Rainforest National Park. Our results indicated that P. megacephalum prefers stream microhabitats with rocky substrates, several caves, and a high diversity of food sources. Microhabitat characteristics did not differ significantly between adults and juveniles. Our results suggest that protecting microhabitats and main food sources is important for the conservation of P. megacephalum. Our findings provide a reference for the protection of this species in Jianfeng Ridge, Yingge Ridge, and other areas in Hainan Tropical Rainforest National Park.

Physiological effects of food availability times in higher vertebrates.

Food availability is a crucial ecological determinant of population size and community structure, and controls various life-history traits in most, if not all, species. Food availability is not constant; there are daily and seasonal differences in food abundance. When coupled to appetite (urge to eat), this is expressed as the eating schedule of a species. Food availability times affect daily and seasonal physiology and behaviour of organisms both directly (by affecting metabolic homeostasis) and indirectly (by altering synchronization of endogenous rhythms). Restricted food availability times may, for example, constrain reproductive output by limiting the number or quality of offspring or the number of reproductive attempts, as has been observed for nesting frequency in birds. Consuming food at the wrong time of day reduces the reproductive ability of a seasonal breeder, and can result in quality-quantity trade-offs of offspring. The food availability pattern serves as a conditioning environment, and can shape the activity of the genome by influencing chromatin activation/silencing; however, the functional linkage of food availability times with epigenetic control of physiology is only beginning to emerge. This Review gives insights into how food availability times, affected by changes in eating schedules and/or by alterations in feeding environment or lifestyle, could have hitherto unknown consequences on the physiology and reproductive fitness of seasonally breeding vertebrates and those that reproduce year round.

Winter coexistence in herbivorous waterbirds: Niche differentiation in a floodplain, Poyang Lake, China.

The classical niche theory supports the idea that stable coexistence requires ecological differences between closely related species. However, information on waterbirds coexistence in the entirely landlocked freshwater system of Poyang Lake is not well understood, especially when the available biomass of their food in the area decreases. In this study, we tested the ecological segregation mechanisms in the 2015/2016 and 2016/2017 wintering periods among eight herbivorous waterbirds (including the Siberian crane Grus leucogeranus, hooded crane Grus monacha, white-naped crane Grus vipio, common crane Grus grus, greater white-fronted goose Anser albifrons, bean goose Anser fabalis, swan goose Anser cygnoides, and tundra swan Cygnus columbianus) at Poyang Lake. Using field observations and species niche and foraging habitat selection models, we investigated the abundance, distribution, and food sources of these eight waterbird species to quantify and compare their habitat use and ecological niches. Our results showed that niche segregation among the waterbirds, with respect to food types, time, and spatial location, allow them to coexist and use similar resources. The water level gradually receded in the sub-lakes of the Poyang Lake, which could provide food sources and various habitats for wintering herbivorous waterbirds to coexist. We demonstrated that the differences in habitat use could mitigate interspecific competition, which may explain the mechanism whereby waterbirds of Poyang Lake coexist during the wintering period, despite considerable overlap in the dietary niches of herbivorous waterbirds.

Arthropod biomass increase in spring correlates with NDVI in grassland habitat.

Data from remote sensing are often used as proxies to quantify biological processes, especially at large geographical scales. The normalized difference vegetation index (NDVI) is the most frequently used proxy for primary productivity. Assuming a direct, positive interrelation between primary and secondary production in terrestrial habitats, NDVI is often used to predict food availability for higher trophic levels. However, the relationship between NDVI and arthropod biomass has rarely been tested. In this study, we analyzed extensive datasets of arthropod communities from semi-natural grasslands in central Europe to test the relationship between arthropod biomass of consumer trophic levels ("herbivores," "mixed," and "carnivores") in grassland communities and NDVI during the spring season. We found that arthropod biomass generally increased with NDVI. The same positive relationship between biomass and NDVI was observed for each individual trophic level. Cross-correlation analyses did not show statistically significant lags between the NDVI and biomass of herbivores and carnivores. All in all, our study provides correlational evidence for the positive relation of primary and secondary productivity in temperate terrestrial habitats during spring. Moreover, it supports the applicability of NDVI data as a suitable habitat-specific proxy for the food availability of insectivores during spring.

Understanding resource driven female-female competition: ovary and liver size in sand gobies.

The operational sex ratio (OSR, ready-to-mate males to females) is a key factor determining mating competition. A shortage of a resource essential for reproduction of one sex can affect OSR and lead to competition within the opposite sex for resource-holding mates. In the sand goby (Pomatoschistus minutus), a fish with paternal care, male readiness to mate depends on acquiring a nest-site, whereas food abundance primarily impacts female egg production. Comparing body condition and gonadal investment of fish from two populations with different availability in resources (Baltic Sea: few nest-sites, more food; North Sea: many nest-sites, less food), we predicted females carrying more mature eggs in the Baltic Sea than in the North Sea. As predicted, ovaries were larger in Baltic Sea females, and so was the liver (storage of energy reserves and vitellogenic compounds) for both sexes, but particularly for females. More females were judged (based on roundness scores) to be ready to spawn in the Baltic Sea. Together with a nest colonization experiment confirming a previously documented difference between the two areas in nest-site availability, these results indicate a more female-biased OSR in the Baltic Sea population, compared to the North Sea, and generates a prediction that female-female competition for mating opportunities is stronger in the Baltic population. To our knowledge, this is the first time that female reproductive investment is discussed in relation to OSR using field data.

Effects of insect infestation on rodent-mediated dispersal of Quercus aliena: results from field and enclosure experiments.

Rodents influence plant establishment and regeneration by functioning as both seed predators and dispersers. However, these rodent-plant interactions can vary significantly due to various environmental conditions and the activity of other insect seed predators. Here, we use a combination of both field and enclosure (i.e. individual cage and semi-natural enclosure) experiments, to determine whether rodents can distinguish sound seeds from those infested with insects. We also demonstrate how such responses to insects are influenced by food abundance and other environmental factors. We presented rodents with 2 kinds of Quercus aliena seeds (sound and insect-infested seeds) in a subtropical forest in the Qinling Mountains, central China, from September to November of 2011 to 2013. The results showed that rodents preferred to hoard and eat sound seeds than infested seeds in the field and semi-natural enclosure, while they preferred to eat infested seeds over sound seeds in the individual cages. In addition, both hoarding and eating decisions were influenced by food abundance. Rodents hoarded more sound seeds in years of high food abundance while they consumed more acorns in years of food shortage. Compared with field results, rodents reduced scatter-hoarding behavior in semi-natural enclosures and ate more insect-infested seeds in smaller individual cages. These results further confirm that rodents distinguish infested seeds from non-infested seeds but demonstrate that this behavior varies with conditions (i.e. environment and food abundance). We suggest that such interactions will influence the dispersal and natural regeneration of seeds as well as predation rates on insect larvae.

The effects of social context and food abundance on chimpanzee feeding competition.

Feeding competition is thought to play a role in primate social organization as well as cognitive evolution. For chimpanzees (Pan troglodytes), social and ecological factors can affect competition, yet how these factors interact to affect feeding behavior is not fully understood; they can be difficult to disentangle in wild settings. This experiment investigated the differential effects of food quantity, the presence of a co-feeding partner, and the contestability of a food patch on feeding rate. We presented tolerant pairs of chimpanzees from a semi-captive social group with an apparatus comprising a matrix of transparent tubes between two adjacent rooms, of which, either all (abundant condition) or only a small proportion (scarce condition) were baited with peanuts. Dyads were either grouped into the competitive treatment, in which peanuts were accessible from both sides of the apparatus simultaneously, or the non-competitive treatment, in which the peanuts were pre-divided; half of the tubes were accessible to one chimpanzee from one side, and the other half were accessible only from the opposite side of the apparatus. We compared dyadic tolerance levels with individual feeding rates across quantity conditions and between competitive treatments. While tolerance and food quantity had no effect on feeding rate, partner presence significantly increased feeding rate relative to individual feeding. This increase was much larger when the dyads directly competed over the peanuts than when they were co-feeding on a pre-divided set of peanuts. Thus, in a co-feeding situation, the presence of another individual and, to an even larger extent, the contestability of the food source play a larger role in chimpanzee feeding behavior than dyadic tolerance or food quantity. These findings highlight the relative impact of social facilitation and direct competition on co-feeding behavior between pairs of chimpanzees.

Gyrfalcons Falco rusticolus adjust CTNS expression to food abundance: a possible contribution to cysteine homeostasis.

Melanins form the basis of animal pigmentation. When the sulphurated form of melanin, termed pheomelanin, is synthesized, the sulfhydryl group of cysteine is incorporated to the pigment structure. This may constrain physiological performance because it consumes the most important intracellular antioxidant (i.e., glutathione, GSH), of which cysteine is a constitutive amino acid. However, this may also help avoid excess cysteine, which is toxic. Pheomelanin synthesis is regulated by several genes, some of them exerting this regulation by controlling the transport of cysteine in melanocytes. We investigated the possibility that these genes are epigenetically labile regarding protein intake and thus contribute to cysteine homeostasis. We found in the Icelandic population of gyrfalcon Falco rusticolus, a species that pigments its plumage with pheomelanin, that the expression of a gene regulating the export of cystine out of melanosomes (CTNS) in feather melanocytes of developing nestlings increases with food abundance in the breeding territories where they were reared. The expression of other genes regulating pheomelanin synthesis by different mechanisms of influence on cysteine availability (Slc7a11 and Slc45a2) or by other processes (MC1R and AGRP) was not affected by food abundance. As the gyrfalcon is a strict carnivore and variation in food abundance mainly reflects variation in protein intake, we suggest that epigenetic lability in CTNS has evolved in some species because of its potential benefits contributing to cysteine homeostasis. Potential applications of our results should now be investigated in the context of renal failure and other disorders associated with cystinosis caused by CTNS dysfunction.

Using urinary parameters to estimate seasonal variation in the physical condition of female white-faced capuchin monkeys (Cebus capucinus imitator).

OBJECTIVES: The physical condition of females depends on access to resources, which vary over space and time. Assessing variation in physical condition can help identify factors affecting reproductive success, but noninvasive measurement is difficult in wild animals. Creatinine concentration relative to the specific gravity (i.e., density) of urine has promise for noninvasively quantifying the relative muscle mass (RMM) of wild primates. We verified the relationship between these urinary parameters for wild white-faced capuchin monkeys, and assessed temporal changes in the RMM of females across groups and between periods of high and low resource abundance. MATERIALS AND METHODS: We collected urine from 25 adult females in three groups across varying seasons at Sector Santa Rosa, Costa Rica. We measured the specific gravity and creatinine concentration of 692 samples and the effect of specific gravity on creatinine concentration. We used the residuals of this relationship to measure effects of group and season using mixed-effects models. RESULTS: Specific gravity significantly predicted creatinine concentration. Season, group membership and the interaction between these variables were significant predictors of residual creatinine variation. Specifically, RMM was higher during months with high fruit energy density, lower in one social group, and less variable among females in the smallest group. DISCUSSION: Our findings suggest that specific gravity and creatinine may be used as urinary parameters to make inferences about the RMM of capuchins. Using this technique, we infer that females experienced changes in muscle mass according to variation in resource energy availability and social group variation.

Marked reduction in demographic rates and reduced fitness advantage for early breeding is not linked to reduced thermal matching of breeding time.

Warmer springs may cause animals to become mistimed if advances of spring timing, including available resources and of timing of breeding occur at different speed. We used thermal sums (cumulative sum of degree days) during spring to describe the thermal progression (timing) of spring and investigate its relationship to breeding phenology and demography of a long-distant migrant bird, the northern wheatear (Oenanthe oenanthe L.). We first compare 20-year trends in spring timing, breeding time, selection for breeding time, and annual demographic rates. We then explicitly test whether annual variation in selection for breeding time and demographic rates associates with the degree of phenological matching between breeding time and thermal progression of spring. Both thermal progression of spring and breeding time of wheatears advanced in time during the study period. But despite breeding on average 7 days earlier with respect to date, wheatears bred about 4 days later with respect to thermal spring progression. Over the same time period, selection for breeding time changed from distinct within-season advantage of breeding early to no or very weak advantage. Furthermore, demographic rates (nest success, fledgling production, recruitment, adult survival) and nestling weight declined markedly by 16%-79%. Those temporal trends suggest that a reduced degree of phenological matching may affect within-season fitness advantage of early breeding and population demographic rates. In contrast, when we investigate links based on annual variation, we find no significant relationship between either demographic rates or fitness advantage of early breeding with annual variation in the degree of phenological matching. Our results show that corresponding temporal trends in phenological matching, selection for breeding time and demographic rates are inconclusive evidence for demographic effects of changed phenological matching. Instead, we suggest that the trends in selection for breeding time and demographic rates are due to a general deterioration of the breeding environment.

The ecological and physiological bases of variation in the phenology of gonad growth in an urban and desert songbird.

Birds often adjust to urban areas by advancing the timing (phenology) of vernal gonad growth. However, the ecological and physiological bases of this adjustment are unclear. We tested whether the habitat-related disparity in gonad growth phenology of male Abert's towhees, Melozone aberti, is due to greater food availability in urban areas of Phoenix, Arizona USA or, alternatively, a habitat-related difference in the phenology of key food types. To better understand the physiological mechanism underlying variation in gonad growth phenology, we compared the activity of the reproductive system at all levels of hypothalamo-pituitary-gonadal (HPG) axis. We found no habitat-associated difference in food availability (ground arthropod biomass), but, in contrast to the seasonal growth of leaves on desert trees, the leaf foliage of urban trees was already developed at the beginning of our study. Multiple estimates of energetic status did not significantly differ between the non-urban and urban towhees during three years that differed in the habitat-related disparity in gonad growth and winter precipitation levels. Thus, our results provide no support for the hypothesis that greater food abundance in urban areas of Phoenix drives the habitat-related disparity in gonad growth phenology in Abert's towhees. By contrast, they suggest that differences in the predictability and magnitude of change in food availability between urban and desert areas of Phoenix contribute to the observed habitat-related disparity in gonad growth. Endocrine responsiveness of the gonads may contribute to this phenomenon as desert - but not urban - towhees had a marked plasma testosterone response to GnRH challenge.

Diet and cannibalism in plainfin midshipman Porichthys notatus.

The macroscopic and microscopic diversity of potential food items available in the nests of plainfin midshipman Porichthys notatus were quantified and compared with items that were found in the stomach and intestine (digestive tract) of the guarding males. In this species, males occur as one of two possible reproductive morphs: guarder males that care for young and sneaker males that parasitize the courtship and care of guarder males. Although it was predicted that guarder males would have fewer feeding opportunities due to their confinement to the nest, they in fact had more food items in their digestive tracts than did sneaker males and females. Date in the breeding season (a proxy of care duration) and body condition were not correlated with the amount of food consumed by guarder males. The main type of food consumed was P. notatus embryos; 69% of all guarder males sampled had cannibalized offspring. By comparing the diet of both sexes and tactics, this study sheds light on some of the strategies designed to cope with the costs of providing parental care.

Ranging and site fidelity in northern pigtailed macaques (Macaca leonina) over different temporal scales.

Space-use patterns are crucial to understanding the ecology, evolution, and conservation of primates, but detailed ranging data are scarce for many species, especially those in Southeast Asia. Researchers studying site fidelity to either home ranges or core areas have focused mainly on territorial species, whereas less information is available for non-territorial species. We analyzed the ranging patterns and site fidelity of one wild troop of northern pigtailed macaques over 16 months at different temporal scales. We used characteristic hull polygons in combination with spatial statistics to estimate home ranges and core areas. The total home range and core areas were 449 ha and 190 ha, respectively. Average daily path length was 2,246 m. The macaques showed a high defendabili--ty index according to the expected ranging of a non-territorial species in which movement does not theoretically permit the defense of a large territory. Overall, the study troop ranged more extensively than conspecific groups and closely related species studied elsewhere. These differences may reflect variable troop size, degree of terrestriality and habitat characteristics, but could also reflect methodological differences. The location, size and shape of home ranges and core areas, and extent of daily path lengths changed on a monthly basis resulting in low site fidelity between months. The macaques also showed clear shifts in the location of daily home ranges with low site fidelity scores between consecutive days. Daily home range and daily path length were related to seasonality, with greater values during the fruit-abundant period. Low site fidelity associated with lack of territoriality is consistent with macaques structuring their movement based on available food sources. However, ranging patterns and site fidelity can also be explained by macaques feeding on the move, a foraging strategy that hinders frequent and long visits to the same location.

Vocal output predicts territory quality in a Neotropical songbird.

Females who choose highly ornamented mates may gain resources that improve offspring production and survival. Studies have focused on the relationship between male quality and the complexity of sexual ornaments; however, less is known of the communicative content of courtship displays, and whether they indicate the quality of resources males can provide to mates. Here, we used blue-black grassquits (Volatinia jacarina) to test the relationship between male display attributes and territory quality, measured as food availability. Our main hypothesis was that territory quality would be better predicted by dynamic displays than by static ornaments. During four breeding seasons in central Brazil, we quantified display song attributes (output and consistency) and the timing of nuptial molt. We measured territorial seed density, body condition, and ectoparasite infestation. We found a positive relationship between song output and territory seed density, suggesting this attribute provides a reliable indicator of territory quality. However, the timing of molt was unrelated to territory quality. Additionally, no other male attribute was associated with seed density. The link between song output and territory quality might reflect variation in male condition in response to territorial resources, or extra time males on higher quality territories have to invest in territorial defense. This article is part of a Special Issue entitled: Neotropical Behaviour.

Short-term fluctuations in cellular immunity of tree swallows feeding nestlings.

We examined cellular immunity of adult tree swallows feeding nestlings under variable weather conditions. Birds received an injection of phytohaemagglutinin (PHA), which causes a local swelling, reflecting the strength of T-cell-mediated immunocompetence. There was a negative relationship between the immune response and the number of nestlings in the brood (range 3-6 young) which suggests that parental effort suppresses the immune function. However, there was also a strong effect of ambient temperature and food abundance (aerial insects) on immune response. Parents that received the PHA injection during cold weather and at low food abundance showed a suppressed immune response compared to birds treated during more favourable conditions. They also lost more body mass during the 24 h inoculation period, and their offspring showed reduced growth. When controlling for ambient temperature and food abundance in a multivariate analysis, there was no longer any significant effect of brood size on the parents' immune response. Three of 39 pairs deserted their broods after PHA injection. All three desertions took place when the mean ambient temperature fell below 13°C. The PHA response is known to have both heritable and environmental components; our study emphasizes its condition-dependency. Previous studies of other passerine birds have shown that high levels of parental effort may have an immunosuppressive effect. Our study indicates that weather conditions may override the effects of natural variation in parental effort, and that the PHA response is particularly influenced by short-term fluctuations in energy balance.

Rainfall, food abundance and timing of parturition in African bats.

We used published results from studies in Africa to test the hypothesis that the timing of parturition in the Chiroptera is constrained by rainfall. Comparison of year-round rainfall and insect data at various latitudes showed that insect abundance peaks approximately a month after peak rainfall. A similar comparison of parturition time to rainfall showed that with the possible exception of the molossids, the Microchiroptera commonly give birth a month before peak rainfall. With an average 6-week lactation period in the Microchiroptera, the timing of parturition is such that young bats are weaned just before the period of maximum insect abundance. We suggest that the needs of the young in this post-weaning period may be more important than the energetic demands of lactation on the mother in determining the timing of parturition on an evolutionary scale. A similar conclusion is implied for the African Megachiroptera, but there is insufficient information on their reproduction to adequately test the main hypothesis for these bats.

Linking individual foraging behavior and population spatial distribution in patchy environments: a field example with Mediterranean blue tits.

In spite of recent theoretical interest, few field studies have addressed the links between individual behavioral decisions and population distribution. This work analyzes the foraging behavior of individuals and the spatial distribution of a population of blue tits (Parus caeruleus) just before the main breeding season, when blue tit foraging was not affected by central-place or flocking behaviors. The study was carried out in open holm oak Quercus ilex woodlands (dehesas) that are patchy for canopy-foraging birds because of the scattered arrangement of trees. Residence time on each tree was not correlated either with previous flight time or with prey abundance in trees. Flight distances between trees were larger than average distances estimated in random samples of holm oaks taken close to foraging birds. Trees were not selected by birds on the basis of their expected energy costs and rewards. Bird abundance was not related to food availability in trees or to tree size across dehesas. However, bird abundance was strongly correlated with tree density and with the availability of tree holes for nesting, to the extent that the proportion of tits matched the proportions of both tree abundance and hole abundance across study plots. Overall, neither the behavior of individuals nor the distribution of the population of blue tits corresponded with food resources, which appeared superabundant; instead, tits appeared to behave and be distributed according to the distribution of structural resources such as trees and tree holes for nesting.

FITNESS CONSEQUENCES OF VARIATION IN EGG SIZE AND FOOD ABUNDANCE IN BROOK TROUT SALVELINUS FONTINALIS.

Relationships between egg size and juvenile survival in brook trout, Salvelinus fontinalis, were determined experimentally at two levels of food abundance and then incorporated into a model that related maternal fitness to egg size and food supply. Egg volume was positively correlated with juvenile size at hatching and size at yolk sac resorption but had no significant effect on embryonic survival or development time. Juvenile survival was linearly related to egg size throughout the first 50 days of exogenous feeding at high and low food levels. The effects of egg size and food abundance on juvenile survival were not additive. Decreased food abundance significantly increased mortality among the smallest eggs but had a negligible effect on the largest eggs. Model simulations indicate that maternal fitness is a curvilinear function of egg size and that food supply influences both the height and the shape of the function. The fitness functions provide empirical support for the hypothesis that selection favors an increase in offspring size with reductions in resource abundance.