Feeding Competition Research Articles

Comparative analyses of the Pan lineage reveal selection on gene pathways associated with diet and sociality in bonobos.

Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) diverged into distinct species approximately 1.7 million years ago when the ancestors of modern-day bonobo populations were separated by the Congo River. This geographic boundary separates the two species today and the associated ecological factors, including resource distribution and feeding competition, have likely shaped the divergent social behavior of both species. The most striking behavioral differences pertain to between group interactions in which chimpanzees behave aggressively towards unfamiliar conspecifics, while bonobos display remarkable tolerance. Several hypotheses attempt to explain how different patterns of social behavior have come to exist in the two species, some with specific genetic predictions, likening the evolution of bonobos to a process of domestication. Here, we utilize 73 ape genomes and apply linkage haplotype homozygosity and structure informed allele frequency differentiation methods to identify positively selected regions in bonobos since their split from a common pan ancestor to better understand the environment and processes that resulted in the behavioral differences observed today. We find novel evidence of selection in genetic regions that aid in starch digestion (AMY2) along with support for two genetic predictions related to self-domestication processes hypothesized to have occurred in the bonobo. We also find evidence for selection on neuroendocrine pathways associated with social behavior including the oxytocin, serotonin, and gonadotropin releasing hormone pathways.

Energetic management in wild chimpanzees (Pan troglodytes verus) in Ta\xef National Park, C\xf4te d\u2019Ivoire

Socioecological theories predict that, in mammals, feeding and mating competitions affect male and female energetic conditions differently but energetic studies investigating both sexes simultaneously are rare. We investigated the effect of socioecological factors on the energetic conditions of male and female western chimpanzees, a long-lived species with high degrees of male-male competition. We used behavioural data collected on one chimpanzee community in the Taï National Park over 12 months, phenological data and urinary c-peptide (UCP) measures, a marker of energy balance. We found a positive effect of food availability on UCP levels in both sexes. Dominance rank also affected chimpanzee UCP levels. High-ranking females had higher UCP levels than low-ranking ones but only in periods when no oestrus females were present in the community. In contrast, high-ranking males had higher UCP levels than low-ranking males in the presence of oestrus females but lower UCP levels in their absence. Our results suggest that oestrus female presence lessened the competitive advantages of high-ranking females in feeding competition and that low-ranking males bore higher energetic costs related to mating competition than high-ranking ones. Yet caution should apply in interpreting these results since the statistical model was only close to significance. High-ranking male and female chimpanzees spent significantly less energy. Furthermore, all chimpanzees significantly spent less time feeding and spent more energy when food availability was high. Finally, our behavioural measure of energy intake and expenditure did not correlate with UCP levels highlighting the value of non-invasive hormonal markers for field studies.Significance statementGeneral socioecological theories hypothesize that the social grouping dynamic and energetics of females are highly influenced by food competition, whereas in males, competition for sexual partners is more influential for these factors. Recent studies in the non-invasive physiological assessment of energy balance in primates have begun to test the implied relationship between chimpanzee socioecology and individual energetic condition, with inconsistent results. However, only a few studies have investigated this relationship concurrently for both sexes. Here, using non-invasive measures of energy balance in wild western chimpanzees, we found that the energetics of both males and females are related to ecological factors, such as food availability. However, female energy balance appears also to be related to increased male mating competition, as this can result in increased aggression directed from males to females, with apparent energetic costs for females.

Mantled Howler Monkeys (Alouatta palliata) in a Costa Rican Forest Fragment Do Not Modify Activity Budgets or Spatial Cohesion in Response to Anthropogenic Edges

Forest fragmentation increases forest edge relative to forest interior, with lower vegetation quality common for primates in edge zones. Because most primates live in human-modified tropical forests within 1 km of their edges, it is critical to understand how primates cope with edge effects. Few studies have investigated how primates inhabiting a fragment alter their behaviour across forest edge and interior zones. Here we investigate how anthropogenic edges affect the activity and spatial cohesion of mantled howler monkeys (Alouatta palliata) at the La Suerte Biological Research Station (LSBRS), a Costa Rican forest fragment. We predicted the monkeys would spend greater proportions of their activity budget feeding and resting and a lower proportion travelling in edge compared to forest interior to compensate for lower resource availability in the edge. We also predicted that spatial cohesion would be lower in the edge to mitigate feeding competition. We collected data on activity and spatial cohesion (nearest neighbour distance; number of individuals within 5 m) in forest edge and interior zones via instantaneous sampling of focal animals. Contrary to predictions, the monkeys spent equal proportions of time feeding, resting and travelling in forest edge and interior. Similarly, there were no biologically meaningful differences in the number of individuals or the distance between nearest neighbours in the edge (1.0 individuals; 1.56 m) versus the interior (0.8 individuals; 1.73 m). Our results indicate that A. palliata at LSBRS do not adjust their activity or spatial cohesion patterns in response to anthropogenic edge effects, suggesting that the monkeys here exhibit less behavioural flexibility than A. palliata at some other sites. To develop effective primate conservation plans, it is therefore crucial to study primate species’ responses to fragmentation across their geographic range.

Enter the Matrix: Use of Secondary Matrix by Mouse Lemurs

Madagascar is home to many threatened and endemic primate species, yet this island has seen dramatic declines in lemur habitat due to forest loss. This forest loss has resulted in an increasingly fragmented forest landscape, with fragments isolated from each other by grasslands (i.e., matrix). The grassland matrix is not entirely homogeneous containing matrix elements such as isolated trees and shrubs and linear features such as drainage lines. Because most lemurs are predominantly arboreal, they may preferentially use matrix elements to facilitate dispersal between fragments for access to mates or reduce feeding competition, allowing gene flow between fragments of habitat. Therefore, it is important to understand to what degree they use the matrix. We investigated matrix use in two mouse lemurs, the grey mouse lemur (Microcebus murinus) and the golden-brown mouse lemur (Microcebus ravelobensis) in a fragmented landscape in northwest Madagascar. We tested the predictions that: (1) lemurs use matrix less often than forest fragments, (2) if they use the matrix, then they will preferentially use matrix elements compared to grassland, and (3) M. murinus will disperse into the matrix further than M. ravelobensis. In 2011, we visually surveyed line transects in four areas containing matrix elements and four adjacent forest fragments during nocturnal walks. In 2017, we set up traplines in four areas of the matrix containing matrix elements, three areas that were grassland, and six traplines in adjacent fragments. We compared the relative abundance of mouse lemurs in matrix transects to fragmented forest transects, and the relative abundance of captured lemurs in matrix elements, grassland, and fragment traplines. We found that encounter rates of mouse lemurs did not significantly differ between the matrix and fragmented forest transects or traplines. Our sample size was too low to determine if the mean distance from the forest was greater for either Microcebus spp. Our study highlights that mouse lemurs do use matrix elements and there may be interspecific differences in use. Further research is needed to confirm species-specific matrix use, why mouse lemurs use matrix, and how much matrix elements facilitate movement for each species in fragmented landscapes.

196 Feeding and nutritional strategies to improve welfare of group-housed gestating sows

Abstract Gestating sows in group-housing systems usually face two major welfare challenges: aggression when mixing with unfamiliar pen-mates and a lack of satiety due to restricted feeding. The two issues might be related because that hungry animals may be frustrated so that they may be more aggressive than animals that are in satiety. To restricted-fed gestating sows, one of the strategies to reduce aggression at mixing is to increase feed intake for a short period of time around mixing. Research showed that this strategy could reduce aggression among sows during feeding in competitive feeding systems, but had very limited effects on aggression during the initial period of mixing. Likewise, neither providing feed when moving sows in group-pens nor dividing the daily ration into multiple meals affected aggression caused by mixing. There is evidence that supplementation of an excessive amount of Tryptophan in the diet could reduce aggression in growing and finishing pigs. However, effects of dietary Tryptophan on reducing aggression among sows during mixing is less evident. Possibly, sows are more persistent in fighting for dominance hierarchy than young pigs. Although high fiber diets had limited effects on reducing aggression among sows at mixing, providing fermentable fibers in the diet could increase satiety in sows. Increasing satiety could reduce stereotypies, reduce aggression for maintaining dominance hierarchy, and increase resting time, which consequently will improve welfare of group-housed gestating sows.

Small Jellyfish as a Supplementary Autumnal Food Source for Juvenile Chaetognaths in Sanya Bay, China

Information on the in situ diet of juvenile chaetognaths is critical for understanding the population recruitment of chaetognaths and their functional roles in marine food web. In this study, a molecular method based on PCR amplification targeted on 18S rDNA was applied to investigate the diet composition of juvenile Flaccisagitta enflata collected in summer and autumn in Sanya Bay, China. Diverse diet species were detected in the gut contents of juvenile F. enflata, including copepods, small jellyfish, anthozoa, polychaetes, echinoderms, diatoms and dinoflagellates. The diet composition showed obvious differences between summer and autumn. Copepod, such as Temora turbinata, Canthocalanus pauper and Subeucalanus crassus, dominated the diet in summer, representing up to 61% of the total prey items. However, small jellyfish, mainly consisting of Bougainvillia fulva, Solmissus marshalli and Pleurobrachia globosa, was the main food group (72.9%) in autumn. Environmental parameters showed no significant difference between summer and autumn. The mean abundance of juvenile chaetognaths in autumn was about eight times higher than that in summer, while the abundance of potential food prey was similar in both seasons. Our results suggested that juveniles chaetognaths might consume small jellyfish as a supplementary food source under enhanced feeding competition in autumn.

Small shrubs with large importance? Smaller deer may increase the moose-forestry conflict through feeding competition over Vaccinium shrubs in the field layer

The moose (Alces alces) is a dominant large mammalian herbivore in the world’s boreal zones. Moose exert significant browsing impacts on forest vegetation and are therefore often at the centre of wildlife-forestry conflicts. Consequently, understanding the drivers of their foraging behaviour is crucial for mitigating such conflicts. Management of moose in large parts of its range currently largely ignores the fact that moose foraging is influenced by increasing populations of sympatric deer species. In such multispecies systems, resource partitioning may be driven by foraging height and bite size. Feeding competition with smaller species might replace larger species from the field layer and drive them towards higher foraging strata offering larger bites. This bite size hypothesis has been well documented for African ungulate communities. Based on a large diet DNA metabarcoding dataset we suggest that feeding competition from three smaller deer species (red deer Cervus elaphus, fallow deer Dama dama, and roe deer Capreolus capreolus) over Vaccinium shrubs in the forest field layer might drive moose towards increasing consumption of Scots pine (Pinus sylvestris) in Sweden. We found that in areas of high deer density, moose diets consistently contained less Vaccinium and higher proportions of pine over three spring periods. Utilization of these food items by the smaller deer species was either unaffected by deer density or, for Vaccinium showed the opposite pattern to moose, i.e., increases of proportions in the diet of roe and red deer with increasing deer density. Availability of pine and Vaccinium, measured as proportion of available bites, did not explain the observed patterns. Our results suggest that managing key food items like Vaccinium and the populations of smaller deer may play an important role in controlling browsing impacts of moose on pine.

The role of nitric oxide and neuronal nitric oxide synthase in zebrafish (Danio rerio) shoaling.

Nitric oxide (NO)—the product of arginine metabolism catalyzed by nitric oxide synthases (NOS)—is a well-known neurotransmitter which plays an important role in metabolism and amino acid transportation in the nervous system. In particular, it can inhibit monoamine neurotransmitter transportation which affects animal behavior, especially social behavior. Shoaling—is a one kind of social behavior. It is a behavior that individual fish choose to join with their group within two factors; food and predation risk. Shoaling fish has quickly responded to predator and increased the change in feeding competition. In addition, shoaling also effect to stress response on stock density of aquaculture system. The effect of NO molecular signaling on the dopamine pathway was investigated using zebrafish (Danio rerio) as a model organism. Our aim was to understand the role of NOS and NO in shoaling behavior, which is typical of zebrafish. The concentration of NO in the zebrafish brain was modulated using a knockout for the neuronal NOS gene, and NO production was induced through treatment with L-arginine. The existence of NO in the zebrafish brain was confirmed by using a fluorescent probe. Dopamine concentration in the brain was measured by UPLC tandem mass spectrometer. We measured shoaling cohesion of all individual fish of D. rerio, using average distance between all pairs of fish (nearest neighbor distance) and analyzed tracking by Zebralab ViewPoint software. Collectively, our results suggest that a lower level of NO was associated with a higher level of dopamine, which in turn leads to the shoaling behavior.

Overlapping niches between two co-occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus.

Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length-weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.

Feeding competition inferred from patch depletion in a supergroup of Rwenzori black-and-white colobus monkeys (Colobus angolensis ruwenzorii) in Rwanda

Abstract Competition for food is often a cost associated with living in a group, and can occur in an indirect (scramble) or direct (contest) form. We investigated feeding competition in a supergroup of Rwenzori black-and-white colobus monkeys (Colobus angolensis ruwenzorii) in Rwanda, with the aim of establishing whether freedom from scramble competition allows these monkeys to form supergroups. We used the patch depletion method, measuring intake rate coupled with movement rate, to assess if food patches become depleted over the occupancy period. Resource depletion was evident when the colobus fed on young leaves, but not when feeding on mature leaves. Scramble competition was inferred from a negative correlation between group size and change in intake rate over patch occupancy. Between-group contest competition was inferred from displacement from patches. Although feeding competition exists for select resources, limited competition for mature leaves may enable Rwenzori colobus to live in a supergroup of hundreds of individuals in this montane forest.

Switching between Food Patches Suggests a Need to Balance Nutrients while Foraging in Wild Black Howler Monkeys (Alouatta pigra)

Studies of feeding patch choice in primates have traditionally analyzed individual foraging decisions in relation to patterns of social foraging,dominance, and feeding competition. However, information on detailed ecological and nutritional characteristics of the patches also is neededto understand the basis of feeding patch preferences. In particular, recent models of nutritional ecology have stressed the importance of nutrientbalancing as a primary driver of individual foraging decisions. Here we investigated the behavioral and nutritional factors affecting feeding patchchoice in black howler monkeys (Alouatta pigra) during a 15-month field study in Campeche, Mexico. We collected 1300 hours of behavioral dataon 14 focal animals, including full-day follows of one individual/day recording all feeding activities. We carried out nutritional analyses of foodsfrom feeding trees and calculated daily nutrient intake. A total of 690 trees (i.e., patches) were visited throughout the study period. The time spentfeeding and the amount of food consumed differed significantly according to patch type. Individuals consumed more food in mature and immaturefruit patches than in mature leaf, young leaf, and flower patches. Protein intake rates (kJoule/min) were similar in young and mature leaf patches,and higher than in mature fruit, immature fruit, and flower patches, among which the rate was similar. In the majority of the cases (80.3%), thefocal animals left the feeding patch prior to satiation. On those occasions, resource mixing, or moving from one food type to another food type,accounted for 49.4% of the patch leaving events. The fact that black howler monkeys alternated feeding bouts between fruit and leaf patches, aswell as alternating bouts of higher and lower protein intake, suggest that this pattern could be dictated by the need to balance nutrients.

Patterns of urinary cortisol levels during ontogeny appear population specific rather than species specific in wild chimpanzees and bonobos

Compared with most mammals, postnatal development in great apes is protracted, presenting both an extended period of phenotypic plasticity to environmental conditions and the potential for sustained mother-offspring and/or sibling conflict over resources. Comparisons of cortisol levels during ontogeny can reveal physiological plasticity to species or population specific socioecological factors and in turn how these factors might ameliorate or exaggerate mother-offspring and sibling conflict. Here, we examine developmental patterns of cortisol levels in two wild chimpanzee populations (Budongo and Taï), with two and three communities each, and one wild bonobo population (LuiKotale), with two communities. Both species have similar juvenile life histories. Nonetheless, we predicted that key differences in socioecological factors, such as feeding competition, would lead to interspecific variation in mother-offspring and sibling conflict and thus variation in ontogenetic cortisol patterns. We measured urinary cortisol levels in 1394 samples collected from 37 bonobos and 100 chimpanzees aged up to 12 years. The significant differences in age-related variation in cortisol levels appeared population specific rather than species specific. Both bonobos and Taï chimpanzees had comparatively stable and gradually increasing cortisol levels throughout development; Budongo chimpanzees experienced declining cortisol levels before increases in later ontogeny. These age-related population differences in cortisol patterns were not explained by mother-offspring or sibling conflict specifically; instead, the comparatively stable cortisol patterns of bonobos and Taï chimpanzees likely reflect a consistency in experience of competition and the social environment compared with Budongo chimpanzees, where mothers may adopt more variable strategies related to infanticide risk and resource availability. The clear population-level differences within chimpanzees highlight potential intraspecific flexibility in developmental processes in apes, suggesting the flexibility and diversity in rearing strategies seen in humans may have a deep evolutionary history.

Consistent differences in a virtual world model of ape societies

Practical and ethical constraints limit our ability to experimentally test socioecological theory in wild primates. We took an alternate approach to model this, allowing groups of humans to interact in a virtual world in which they had to find food and interact with both ingroup and outgroup avatars to earn rewards. We altered ratios and distributions of high- and low-value foods to test the hypothesis that hominoids vary with regards to social cohesion and intergroup tolerance due to their feeding ecology. We found larger nesting clusters and decreased attacks on outgroup competitors in the Bonobo condition versus the Chimpanzee condition, suggesting a significant effect of feeding competition alone on social structure. We also demonstrate that virtual worlds are a robust mechanism for testing hypotheses that are impossible to study in the wild.

Personality of dairy goats affects competitive feeding behaviour at different feeder heights

The feed bunk is a place of high competition for dairy goats, and high variability in feeding behaviour occurs; thus, it is necessary to understand why individuals respond differently when experiencing different feeding conditions. The objective of this study was to determine how personality traits affect competitive feeding behaviours of goats when feeding at a range of heights. Thirteen goats were provided one of three feeder heights (floor-, head-, and elevated-level) daily in a group pen under competitive feeding conditions and behaviours after feed delivery were recorded. Personality traits were assessed from behavioural responses toward two novelty and two fear tests; principal component analysis revealed four personality traits that were consistent over time: bold, fearful, exploratory and active-escape. These personality traits affected competitive behaviours, and often depended on feeder height. ‘Bold’ goats initiated more aggressive interactions, especially behind the floor-level feeder, and had greater feeding times; the opposite was observed in ‘fearful’ goats, which more often waited for access to the feeder. ‘Exploratory’ goats were less involved in aggressive interactions and spent less time feeding at the floor-level feeder, and more time feeding at the elevated-level feeder. While the findings are limited to a single group of goats, our pilot study suggests that personality traits may explain variability in feeding aggression and feeding time of goats under competitive feeding conditions, and that these differences may be promoted by feed offered at different heights. Further work is needed in larger groups of goats to understand why individuals appear to cope with competitive feeding practices in different ways.

Feed competition reduces heritable variation for body weight in Litopenaeus vannamei

BackgroundCompetition is a common social interaction among shrimp and depending on its intensity, it can affect heritable variation and response to selection. Little is known about the variance of indirect genetic effects (IGE) under competitive and non-competitive conditions in shrimp. In this study, we used extended mixed linear models to estimate genetic parameters for the direct genetic effect (DGE) and IGE on body weight in Litopenaeus vannamei raised under ad libitum (AF, non-competitive environment) and restricted (RF, competitive environment) feeding regimes.ResultsEstimates of heritabilities for body weight obtained with a traditional animal model (i.e. without accounting for IGE) were 0.11 ± 0.09 under AF and 0.25 ± 0.11 under RF. With extended animal models that accounted for IGE, the corresponding estimates for body weight were 0.07 ± 0.08 and 0.34 ± 0.11. Thus, heritabilities were higher under the RF regime than under the AF regime, regardless of whether IGE was accounted for or not. The log-likelihood ratio test revealed significant IGE under the RF regime. Although estimates of indirect genetic variance were low (0.0023 ± 0.0013 for AF and 0.0028 ± 0.0012 for RF), they contributed substantially to the total heritable variance: 66.8% for AF and 692.2% for RF. The total heritable variance was smaller under the RF regime (0.7 ± 1.3) than under the AF regime (5.8 ± 2.6) because of the high contribution of the negative covariance between DGE and IGE (− 7.03). Estimates of the correlation between DGE and IGE were 0.32 ± 0.47 under AF and − 0.93 ± 0.15 under RF, those of DGE and IGE for body weight between both regimes were 0.94 ± 0.07 and 0.67 ± 0.20, respectively, and those of IGE for body weight with DGE for survival were − 0.12 ± 0.22 under AF and − 0.58 ± 0.20 under RF.ConclusionsThese results indicate that strong competitive interactions occurred under the RF regime in L. vannamei. Significant reranking and variation in IGE of individuals were observed between the two feeding regimes. Strong competitive interactions reduced the total heritable variation for body weight when food was restricted. These results indicate that the extent of competition among L. vannamei depends on the feeding regime applied and that this competition affects the genetic basis of body weight.

Using long-term ranging patterns to assess within-group and between-group competition in wild mountain gorillas

BackgroundCompetition within and between social groups determines access to resources and can be inferred from space use parameters that reflect depletion of food resources and competitive abilities of groups. Using location data from 1998 to 2017, we investigated within- and between-group competition in 12 groups of wild mountain gorillas (Gorilla beringei beringei). As within-group feeding competition is expected to increase with group size, an increase in group size is predicted to lead to an increase in the size of annual home ranges and core areas, but to a decrease in fidelity (reuse of an area). Due to asymmetries in competitive abilities, larger groups are expected to have higher exclusivity (degree of non-shared space) of annual home ranges and core areas than smaller groups.ResultsWe found evidence of within-group feeding competition based on a positive relationship between group size and both annual home range and core area size as well as a negative relationship between group size and core area fidelity. Additionally, fidelity of core areas was lower than of home ranges. Between-group competition was inferred from a trend for groups with more members and more males to have more exclusive home ranges and core areas. Lastly, annual core areas were largely mutually exclusive.ConclusionsOur study suggests that non-territorial, group-living animals can have highly dynamic, long-term avoidance-based spacing patterns, both temporally and spatially, to maintain annual core area exclusivity among groups while concurrently shifting these areas annually within overlapping home ranges to avoid resource depletion. Despite ranging in larger home ranges and core areas, larger groups were able to maintain more exclusive ranges than smaller groups, suggesting a competitive advantage for larger groups in between-group competition in a non-territorial species. Together, these findings contribute to understanding how social animals make behavioral adjustments to mitigate the effects of intraspecific competition.

Abundance, horizontal and vertical distribution of epipelagic ctenophores and scyphomedusae in the northern Bering Sea in summer 2017 and 2018: Quantification by underwater video imaging analysis

We examined the abundance and horizontal and vertical distributions of epipelagic ctenophores and scyphomedusae in the northern Bering Sea using an underwater video camera during July of 2017 and 2018. The effects of environmental and biological parameters on the distribution of these species were evaluated by generalized additive modelling (GAM). In 2017, the dominant ctenophore, Bolinopsis infundibulum, was mainly distributed in the north and west of St. Lawrence Island (SLI), and their vertical distribution varied with the region but not by the time of day. We found that B. infundibulum was distributed in the upper pycnocline north of SLI, but below the pycnocline west of SLI. Biological interactions with other gelatinous zooplankton may explain these regional differences in vertical distribution; GAM analysis revealed a negative interaction between B. infundibulum and the large scyphomedusa, Chrysaora melanaster, which occurred in the upper layer in the west of SLI. B. infundibulum may avoid that layer to reduce feeding competition. For the ctenophore, Beroe sp., vertical and horizontal distributions were similar to those of B. infundibulum, and GAM analysis also revealed a positive interaction for both species. As B. infundibulum is an important prey of Beroe sp., a prey-predator interaction may result from their similar horizontal and vertical distributions. Standing stocks of epipelagic ctenophores and scyphomedusae in 2018 were low compared to those in 2017, by a factor of 1/20 (C. melanaster) and1/90 (Beroe sp.). This might be due to annual differences in water mass in this region, in that the thermal conditions characterized by a high abundance of the dominant B. infundibulum in 2017 (<2 and >8 °C) were absent in 2018. As this drastic decrease in standing stock in 2018 was apparent for both ctenophores and scyphomedusae, food availability was hypothesized to be poor that year.

Asymmetric competition between sympatric endangered primates affects their population recovery

Species interactions including predation, competition, and parasitism, matter to species conservation. Sympatric species can have a profound influence on the population recovery of endangered species through a number of ecological processes, but particularly feeding competition. We investigated ranging (spatial pattern) and feeding (trophic overlap) behavior of sympatric critically endangered western black crested gibbons (Nomascus concolor) and endangered Indochinese gray langurs (Trachypithecus crepusculus). Our 1-year study of one group of each species found potential for asymmetric feeding competition between langurs and gibbons on Mt. Wuliang, China, in that: (1) the home range (2 km2) of the gibbon group was nearly entirely within the home range of the langur group (4.2 km2); (2) langurs had a greater niche breadth than gibbons, and their trophic overlap was 0.23; (3) 14 out of 26 primary food items comprising 56.7% of gibbon annual diet were consumed by langurs; and (4) langurs routinely consumed unripe fruits before they ripened sufficiently for gibbons to eat. Differences in group size, feeding habits, and reproductive rate could increase the effects of asymmetric dietary in potential competition, which appears to limit population recovery of gibbons. Rapid recovery of one species may cause unintended conservation consequences through complex interspecific interaction. Thus, it is important that conservation strategies take species interactions into account when designing conservation interventions. To ensure the ongoing survival of gibbons it may be necessary to manage langur populations.

Competitive feeding interactions between native Ostrea edulis and non-native Crassostrea gigas with implications of introducing C. gigas into commercial aquaculture in the eastern Adriatic Sea

In order to detect the possible regulatory effect of non-native C. gigas on the native O. edulis, under aquaculture conditions, feeding interactions between them were investigated in a highly productive environment of Lim Bay (Adriatic Sea). The present study uses a multi-methodological approach, including stomach content, DNA barcoding and stable isotope analysis to elucidate the feeding ecology of two oyster species. The research confirmed a high overlap throughout the year in the feeding traits among native and non-native oyster species. Competition for food was not the only relationship that exists between the investigated species as the presence of O. edulis larvae in C. gigas stomach content was confirmed by DNA analysis. Findings are not in favour of introducing C. gigas to commercial aquaculture in any new areas in the Adriatic Sea and support the need to improve the existing O. edulis aquaculture and conserve its wild stocks.

Female dispersal patterns influenced by male tenure duration and group size in western lowland gorillas

Evaluating the factors influencing the patterns of female dispersal in mammals is critical to understanding its importance for male and female reproductive strategies and the evolution of social systems. In western lowland gorillas, females emigrate from their natal group (natal dispersal) but also disperse between groups multiple times in their life (secondary dispersal). This strategy is uncommon in primates and may reflect females seeking to reduce feeding competition or female choice for males that can provide protection against infanticide. In this study, we test how inbreeding avoidance, group size, and male competitive ability could influence female dispersal in western gorillas, using 25 natal and 285 secondary dispersal events collected over 20 years at Mbeli Bai. We found that while all females dispersed out of their natal group, presumably to avoid inbreeding, females also left their group before having their first offspring when the dominant male was not their father, pointing towards unconditional dispersal by nulliparous females. Regarding secondary dispersal, we found that females were more likely to stay with males that were at the beginning of their tenure than transfer and more likely to disperse away from (presumably old) males that were near the end of their tenure or closer to their death. Females were also more likely to leave larger groups for smaller ones suggesting a potential effect of within-group feeding competition or avoidance of outsider males or predators. This study highlights the intersexual conflict found in gorillas: while female choice for high-quality males may influence the formation of their relatively rare social system, smaller group size may be more important for females than previously thought, which runs counter to the males’ interest of having a high number of females.SignificanceDispersal is a very important life strategy for most group-living mammals. Secondary dispersal by females is a rare behavior but is believed to be a counterstrategy against sexual coercion by males, reduces feeding competition, assists in predator avoidance, and facilitates mate choice. We studied the factors influencing secondary dispersal in western lowland gorillas. We found that the duration of male tenure and the size of the group influences female transfer decisions. This study shows that female reproductive strategies such as secondary dispersal may be very powerful to counter the risk of infanticide through female choice for better protector males but also to reduce the impact of feeding competition or to avoid predators or outsider males.