Male-male relationships among wild bonobos (Pan paniscus) at Wamba,Republic of Zaire

Male-male relationships among wild bonobos (Pan paniscus) in two adjacent unitgroups (E1 and E2 groups), which were formed by division of the E group, were studied at Wamba, in the Central Zaire Basin, by analyzing the proximity and social interactions among males. Dominant-subordinate relationships between a male-male dyad were easily recognized from the directions of individual agonistic interactions. Male bonobos rarely joined forces in aggression. Clear differences in social status existed between adult and adolescent male bonobos in both groups, as reported in the case of chimpanzees (Pan troglodytes). The presence of mothers in the unit-group greatly influenced the dominant-subordinate relationships among males through strong mother-son bonds in both groups. However, the extent of the mother-son bonds differed between the groups. Males in the E2 group participated more frequently in agonistic or affinitive interactions than did males in the E1 group. Males in the E1 group were divided spatially into several clusters, while there were cohesive relationships among the adult males in the E2 group. The difference in intensities of mother-son bonds between the groups may be explained by the distribution of males at the time of the division of the E group. Differences in male-male relationships between bonobos and chimpanzees seem to be related to differences in intra- and inter-unit-group competition among males between the two species. Male chimpanzees may achieve coexistence by manipulating ambivalent relationships that are caused by intra- and inter-unit-group competition among them, while male bonobos may achieve coexistence by decreasing intra- and inter-unit-group competition among them.     

Habitat Use and Ranging of Wild Bonobos (Pan paniscus) at Wamba

The relationship between vegetation and ranging patterns of wild bonobos at Wamba, Democratic Republic of the Congo, was examined. Via Landsat data, we distinguished three types of vegetation—dry forest, swamp forest, and disturbed forest—at Wamba. The home ranges of the study groups changed considerably from year to year, due mainly to intergroup relationships. The population density of each group varied between 1.4 and 2.5 individuals per km ² and was lowest during a period of population increase. Home ranges consisted mainly of dry forest. The bonobos used dry forest more frequently than the other forest types, though they also used swamp and disturbed forest almost every day. The latter types of forest seemed to be important resources for the bonobos, owing to the abundant herbaceous plants that are rich in protein and constantly available. The bonobos tended to use dry forest more frequently in the rainy season than in the relatively dry season, probably because the favored fruits in the dry forest were mostly available in the rainy season. There was no seasonal difference in the size of the daily ranging area.     

The relationship between socio‐sexual behavior and salivary cortisol in bonobos: tests of the tension regulation hypothesis

Bonobos are known for their pacifistic behavior and their large repertoire of behaviors that are thought to serve conflict resolution. One is an unusual form of ventro‐ventral mounting that facilitates genital contacts (GC). Various hypotheses have been proposed to explain its function. In this study we tested predictions of the tension regulation hypothesis using salivary cortisol as a marker for social stress. The results indicate a temporal relationship between GC and cortisol levels. Compared with baseline data and matched samples of unrestricted food access, rates of GC increased when access to food sources was restricted. Cortisol levels were highest when access to food was constrained. However, because the behavioral and hormonal responses occurred when viewing the stimulus at a distance and preceded the physical presence of the stimulus, we conclude that the anticipation of a competitive situation was sufficient to induce social stress. Contrary to our prediction, targets of aggression did not have higher rates of GC nor did they solicit GC more often than others. Furthermore, higher GC rates did not correlate with a more pronounced decrease in cortisol levels. Not all results obtained in this study supported the predictions concerning the regulatory function of GC on social tension and further research is needed to explore this question. However, the results indicate that the anticipation of competition may be sufficient to induce a costly physiological response, and that high levels of resource competition may have lasting effects on physical stress and stress management. Am. J. Primatol. 71:223–232, 2009. © 2008 Wiley‐Liss, Inc.     

Non-antagonistic relations between wild bonobos and two species of guenons

Interspecific relations between wild bonobos (Pan paniscus) and two species of guenons (Cercopithecus wolfi andC. ascanius) were studied at Wamba in the Central Zaire Basin from September 1989 to January 1990. Data on the guenons were collected while following parties of bonobos or when searching for them. The guenons were observed directly 59 times during the study period. In about half of these observations, the guenons were found within 20 m from the bonobo parties. The encounters between the bonobos and the guenons sometimes lasted over an hour. The guenons mainly initiated the encounters by approaching the bonobos. During the encounters, no aggressive interactions were observed between the bonobos and the guenons. Evidence of hunting by wild bonobos has been restricted to small mammals, and there has been no evidence of hunting of primates by wild bonobos. These findings and the results of the present study strongly suggest that wild bonobos do not hunt sympatric primates.     

Habitat use of the white‐headed langurs in limestone forest of Southwest Guangxi,China: Seasonality and group size effects

Understanding how animals cope with habitat‐specific environmental factors can assist in species conservation management. We studied the habitat use of four groups (two large and two small groups) of white‐headed langurs (Trachypithecus leucocephalus) living in the forest of southwest Guangxi, China between September 2016 and February 2017 via instantaneous scan sampling. Our results showed that the langurs primarily used hillsides (55.91% ± 6.47%), followed by cliffs (29.70% ± 5.48%), hilltops (7.26% ± 3.55%), flat zones (6.99% ± 6.58%), and farmlands (0.14% ± 0.28%). The langurs moved most frequently on hillsides (49.35% ± 6.97%) and cliffs (35.60% ± 9.17%). The hillsides were more frequently used (66.94% ± 7.86%) during feeding, and the langurs increased the use of hilltops during the rainy season, and the use of cliffs in the dry season. The langurs frequently rested on hillsides (49.75% ± 8.16%) and cliffs (38.93% ± 8.02%). The larger langur group used cliffs more frequently when moving and resting, whereas the small langur group used hillsides more frequently while resting. Langurs in all groups avoided the flat zones for feeding. Their use of habitat reflected the balancing of foraging needs, thermoregulation, and predator avoidance. We conclude that the ecological factors are determinants of habitat use for white‐headed langurs. Our findings suggest that conservation efforts should focus on protecting the vegetation on the hillsides and restoring the vegetation on the flat zones.     

Factors underlying party size differences between chimpanzees and bonobos: a review and hypotheses for future study

Differences in party size and cohesiveness among females have been primary topics in socio-ecological comparisons of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). This paper aims to review previous studies that attempted to explain these differences and propose some hypotheses to be tested in future studies. Comparisons of recent data show that relative party size (expressed as a percentage of total group size) is significantly larger for bonobos than chimpanzees. Although the prolonged estrus of females, close association between mother and adult sons, female social relationships including unique homosexual behavior, and high female social status might be related to the increased party size and female cohesiveness of bonobos, these social and behavioral factors alone do not appear to explain the differences between the two species. Differences in ecological factors, including fruit-patch size, density of terrestrial herbs, and the availability of scattered foods that animals forage as they travel between large fruit patches could also contribute to the differences between chimpanzees and bonobos. However, these factors cannot fully account for the increased party size and female cohesiveness of bonobos. The higher female cohesiveness in bonobos may be explained by socio-ecological systems that reduce the cost in feeding efficiency incurred by attending mixed-sex parties. These systems may include female initiatives for party ranging movements as well as the factors mentioned above. Because of their geographical isolation, the two species probably evolved different social systems. Chimpanzees, whose habitats became very dry during some periods in the Pleistocene, likely evolved more flexible fission–fusion social systems to cope with seasonal and annual variation in food availability. On the other hand, bonobos had a large refugia forest in the middle of their range even during the driest periods in the Pleistocene. Therefore bonobos, whose habitats had more abundant food and smaller variation in food availability, probably evolved systems that help females stay in mixed parties without incurring large costs from contest and scramble competition.     

Factors affecting party size and composition of chimpanzees (Pan troglodytes verus) Bossou,Guinea

I studied the party sizes of western chimpanzees (Pan troglodytes verus)and factors assumed to affect them at Bossou, Republic of Guinea, West Africa. Party size is negatively correlated with feeding ratio, and larger parties tend to be formed in more dangerous situations (i.e. crossing roads with much traffic). When parties included estrous females, young (i.e., late juvenile and adolescent) males tended to forage with them, independently from their mothers. Lactating females with infants tended to spend more time alone, but the trend was not as apparent as it is in P. t. schweinfurthiat Gombe, Tanzania. These facts suggest that several factors, in addition to food availability, affect party formation, or fission-fusion, of chimpanzees. I also briefly discuss comparatively the pattern of party formation in P. paniscus.     

Temporal variation in dwarf sperm whale (Kogia sima) habitat use and group size off Great Abaco Island, Bahamas

Dwarf sperm whales (Kogia sima) are among the most commonly stranded yet least known pelagic cetaceans. Few studies have occurred at sea, and none have quantified temporal and spatial variation in dwarf sperm whale abundance and group size. We assessed seasonal and spatial variation in dwarf sperm whale group size and abundance off Great Abaco Island, Bahamas using surveys within a 126 km² study area with depths between 2 and 1,600 m. After correcting for survey effort and variation in sighting efficiency among sea states, we found that dwarf sperm whale group size and habitat use varied seasonally. In summer, dwarf sperm whale groups were small (median = 2.5, range = 1–8) and were found only in the two deep habitats within the study area (slope 400–900 m, deep 900–1,600 m). In winter, group sizes increased (median = 4, range = 1–12) and sightings were almost six times higher in the slope habitat, where vertical relief is highest, than other habitats. Our results suggest that studies of pelagic cetaceans and conservation plans must explicitly account for seasonal variation in group size and habitat use.     

The group size effect and synchronization of vigilance in the Tibetan wild ass

Vigilance behavior is considered as an effective strategy for prey species to detect predators.An individual benefits from living in a group by reducing the time spent being vigilant without affecting the probability of detecting a predator.However,the mechanism producing a decrease in vigilance with increasing group size is unclear.Many models of vigilance assume that group members scan independently of one another.Yet in recent studies,the other 2 patterns of vigilance,coordination and synchronization,were reported in some species.In 2 summers(2018 and 2019),we studied the group-size effect on vigilance and foraging of Tibetan wild ass in Chang Tang Nature Reserve of Tibet.We also tested whether individuals scan the environment independently,tend to coordinate their scans,or tend to synchronize their vigilance.The results showed that individuals decreased the time spent on vigilance with increasing group size,while increased the time spent foraging.Group members scanned the environment at the same time more frequently and there was a positive correlation between group members'behaviors,indicating that Tibetan wild asses tend to synchronize their vigilance.     

Mate preference for multiple cues: interplay between male and nest size in the sand goby, Pomatoschistus minutus

Female mating preferences are often based on more than one cue.In empirical studies, however, different mate choice cues aretypically treated separately ignoring their possible interactions.In the current work, we studied how male body size and sizeof the male's nest jointly affect mate preferences of femalesand gobies, Pomatoschistus minutus. The females were givena binary choice between males that differed either in body sizeor size of their nest or both. We found that neither body sizenor size of the nest alone affected male attractiveness, buttogether these 2 cues had a significant effect. Specifically,large males were more popular among females when they had alarge nest than when they occupied a small nest. The resultssuggest that if interaction effects between multiple mate choicecues are not considered, there is a danger of ignoring or underestimatingthe importance of these cues in sexual selection by female choice.     

Perch selection in Sympetrum species (Odonata: Libellulidae): importance of vegetation structure and composition

1. Perching dragonflies are closely associated with the physical structure of vegetation because adults utilise plants when foraging, thermoregulating, and mate-seeking. However, little attention has been given to which structural attribute of vegetation is playing a key role within foraging habitat use. 2. This study focused on the influence of different features of perches on their selection by adult dragonflies. As a model group, a typical percher behavioural guild of Sympetrum was used and experimental plots with artificial perches and different structural properties were established. 3. It was found that adults preferred perch sticks with a wider diameter and larger spacing. It is assumed that these perching sites are advantageous because their base is more stable, they provide the best view for successful foraging, and there is no interference among individuals. 4. This study also revealed significant differences between male and female preferences. Females used less structured vegetation formed by thin perches in high densities. It is suggested that female discrimination is influenced by the higher competitiveness of males, which is related to their agonistic behaviour. 5. These results suggest that the availability of perches in the foraging habitat might be an essential requirement for adults. However, within the terrestrial surroundings of breeding sites, the structure of vegetation providing conditions for perching may be associated only with certain habitats. In intensive landscapes, physically structured vegetation can be limited or completely absent.     

Nest size affects clutch size and the start of incubation in magpies: an experimental study

Nest size has been suggested to be a sexually selected traitindicating parental ability of both males and females. To testwhether a female's reproductive decisions (e.g., clutch sizeand starting incubation) change in relation to experimentalmanipulation of nest size, as would be predicted if nest sizeis a sexually selected signal reflecting the male's parental quality, we manipulated nest size in a population of monogamousmagpies before laying by adding or removing about 20 cm oflarge sticks in the roof of magpie nests. On the one hand,we found that clutch size of reduced nests was smaller thanthat of control or enlarged nests. Moreover, clutch size was significantly related to nest size after manipulation, whichindicates that females adjust clutch size to the final sizeof the nest, nest size thereby being a good candidate for asexually selected trait. On the other hand, number of eggshatched during the first day is hypothesized to be related to the expected available resources during nestling growth, andsubsequent nestlings hatched are likely to die due to broodreduction if resources are not sufficient to raise well-developednestlings. Nest size is hypothesized to inform females abouta male's willingness to invest in reproduction, and we foundthat in broods of experimentally reduced nests, females startedto incubate earlier in the laying sequence than they did inbroods of control or enlarged nests. Moreover, in experimentallyreduced nests, fewer nestlings hatched during the first day,and the difference in body mass between the first and the fourthnestling hatched increased. This result is in accordance withthe hypothesis that the female's decision of when to start incubationin the laying sequence is mediated by nest size, a sexuallyselected trait signaling parental quality. We discuss alternativeexplanations for the results such as the possibility that nestsof different treatments may differ in their thermoregulationproperties or in their protection against predators.     

Species richness and the proportion of predatory animal species in temporary freshwater pools: relationships with habitat size and permanence

The proportion of predatory animal species is often believed not to vary systematically across communities. However, we predict that larger temporary freshwater pools, and pools that are more permanent, will contain a higher proportion of predatory animal species. In 24 temporary rockpools in Northern Israel (supporting communities dominated by ostracods, copepods, cladocerans, flatworms, dipterans and amphibians), the mean proportion of macroscopic predatory species (averaged over a series of samples) increased with increasing pool area. For the highest possible proportion of predatory species (including microscopic species with uncertain diets), the relationship with pool area was not statistically significant. We did not find significant relationships between permanence and the proportion of either macroscopic or all possible predatory species. Larger pools and pools that were more permanent had more species. Species richness and the proportion of macroscopic predators were positively correlated. These patterns imply that species-poor ecosystems are likely to be functionally different from species-rich systems.     

清凉峰不同海拔木本植物小枝内叶大小-数量权衡关系

权衡关系是生活史对策理论的基础, 叶大小-数量的权衡关系对理解叶大小进化具有重要的意义。该研究以单叶面积和单叶片干重表示叶大小, 用小枝干重和小枝茎干重表示小枝大小, 采用标准化主轴估计(standardized major axis estimation, SMA)和系统独立比较分析(phylogenetically independent contrast analysis, PIC)的方法, 对浙江省清凉峰自然保护区3个不同海拔落叶阔叶木本植物当年生小枝内的叶大小与数量间的关系进行研究。结果显示, 无论叶大小和小枝大小是用面积或干重表示, 在每个海拔, 叶大小与出叶强度均存在显著的等速负相关关系, 表明在落叶阔叶木本植物中发现的叶大小与出叶强度之间的权衡关系在不同生境物种中是普遍存在的, 植物在叶大小方面的种间变化, 可能不是自然选择的直接产物, 而是叶片数量变化权衡关系的一个副产物。不同海拔间的比较显示, 高海拔物种的叶面积或干重与出叶强度相关关系的y轴截距比中、低海拔物种小, 表明在出叶强度一定的情况下, 高海拔物种比低海拔物种具有更小的叶大小。与高海拔物种相比, 中海拔物种的共同斜率沿共同主轴有一个向上的位移, 表明中海拔物种比高海拔物种具有更大的叶大小, 但出叶强度更小。这些结果表明生境对叶大小-数量的权衡关系具有显著的影响, 中海拔生境具有更适宜植物生长的气候及养分条件, 而高海拔的低温等不利影响使得叶片变小。