Increased Frequency of Intergroup Encounters in Wild Bonobos (<Emphasis Type="Italic">Pan paniscus</Emphasis>) Around the Yearly Peak in Fruit Abundance at Wamba

Intergroup interactions in primates vary from nonagonistic to severely aggressive. Food resources and fertile females cause intergroup aggression when groups defend resources and mates from other groups. Peaceful intermingling during intergroup encounters is rare but has been reported in several primates, including bonobos (Pan paniscus). Although intergroup encounters in bonobos occur at both nonprovisioned and provisioned sites, provisioning may be one factor responsible for frequent intergroup encounters. We studied intergroup encounters between one bonobo group (PE) and its neighboring groups, one semihabituated and two habituated groups, under nonprovisioned conditions in 2010–2015 at Wamba, Democratic Republic of Congo. We examined whether fruit abundance and females with sexual swellings influenced encounter frequency. PE group encountered the other groups on 7.1 days (mean, range: 0–19) per month. Up to four different groups met simultaneously at one location. Encounter frequency was highest around the yearly peak in fruit abundance, suggesting that reduced food competition is linked to increased encounter frequency. During periods of relatively low fruit abundance, the probability of an encounter was higher when a higher number of adult females with maximum sexual swellings were present, suggesting that the attractiveness of females with sexual swellings promoted group encounters during periods of relatively low fruit abundance. These findings suggest that both competition for food and the availability of females with sexual swellings influence encounter frequency in bonobos.     

Aggressive intergroup encounters in two populations of Japanese macaques (Macaca fuscata)

It is predicted that variation in intergroup relationships in group living primates reflects the cost and benefit of resource defense. We tested the applicability of the model by examining population difference, group difference, and seasonal difference in behaviors during intergroup encounters in two populations of Japanese macaques (Macaca fuscata), one of six groups from Yakushima Island, and the other of three groups from Kinkazan Island. We found that the nature of intergroup encounter varied with group identity, reproductive seasonality, and population. Yakushima groups showed aggressive behaviors more frequently than did Kinkazan groups and the difference was consistent with the food competition model, both because of the involvement of females, and because home ranges were smaller on Yakushima than on Kinkazan, and thus more defensive. Both sexes of animals participated in aggressive interactions, but males were more aggressive than females. Furthermore, Yakushima population showed more agonistic intergroup behaviors during the mating season than the non-mating season. Also during the encounters, intergroup mating was observed, but only in Yakushima. It is concluded that intergroup relationships reflect the mate guarding behavior by group males. However, the agonistic relationship during non-mating season, especially that of among females, is also consistent with the food competition model. It is also noted that males' behavior toward other groups can also be interpreted as a form of investigative behavior before possible transfer into a new group.     

Searching clusters of community composition along multiple spatial scales: a case study on aquatic invertebrate communities in bamboo stumps in West Timor

We examined spatial heterogeneity at multiple scales in composition of the aquatic invertebrate communities in bamboo stumps in a mountainous area of West Timor. We partitioned the study area (ca. 15,000 m²) at five levels of patchiness: two sites, four sub-sites, eight super-clumps, 14 clumps, and 84 stumps. Similarity of community composition between stumps varied more than expected from independent occurrence of each taxon in comparisons within any levels of patches. Negative association was frequently detected among taxa. These results indicate heterogeneity in community composition at a stump level. At higher levels, similarity among stumps within each site was greater than expected from null models which assumed no spatial heterogeneity, and similarities among super-clumps, sub-sites and between sites in a whole area were lower than expected from the null models. The observed patterns in similarities among subsets of the community and distribution of each taxon were mostly consistent with the models which assumed site-level heterogeneity. Therefore, we conclude that the community in this area was spatially heterogeneous at stump and site levels. The relationship between mean intra- and inter-specific crowding suggested that the site level habitat heterogeneity might reduce the chance of encounters between two predators, the larvae of the Toxorhynchites mosquito and the Brachyceran fly.     

Social dynamics of intergroup encounters in the capped langur (Presbytis pileata)

Data from a 15–month field study of the capped langur (Presbytis pileata) in moist deciduous forest in Bangladesh show that during intergroup encounters males respond more aggressively to extra-group males and to the resident males of unfamiliar one-male groups than they do toward familiar males. Lone males followed established one-male groups and attempted to interact with group females. During intergroup encounters males responded to the approach of unfamiliar males with significantly more displays than were given to familiar (frequently encountered) males. The frequency of displays given to approaching groups showed a negative correlation with the frequency of encounters with those groups. In 50% of intergroup encounters males pushed and bit their group females if the females strayed from the immediate proximity of the group male. Further observations suggest that males obtain females that have emigrated from established groups or attempt to interact with them in established onemale groups. Males had a tenure from at least 13 months to at least 26 months, and between 1986 and 1988 no male changes were seen. Capped langur males defended females from other males, but females did not defend resources or participate in intergroup encounters. The implications of this sex difference in behavior during encounters is discussed with regard to ecological models of female-bonded primate groups.     

Intergroup encounters in wild moor macaques (<Emphasis Type="Italic">Macaca maurus</Emphasis>)

We studied intergroup encounters among moor macaques at the Karaenta Nature Reserve, South Sulawesi, Indonesia. Group B has been observed on the basis of individual identification since 1988. We analyzed 85 encounters between members of Group B and members of neighboring groups from September 1990 to November 1998. The average frequency of intergroup encounters was 0.035/hour. Neither the presence of females in estrus nor rainfall had an effect on encounter frequency. Behaviors of moor macaques during intergroup encounters differed from those of Japanese macaques. In moor macaques, no intergroup interactions with body contact were observed during encounters, and females never directed aggression toward members of different groups. The present study did not confirm the prediction of the model ofvan Schaik (1989). Extension of the existing models is required to explain the difference in female dominance styles among macaques by socioecological factors.     

A field study on the red-bellied tamarin,Saguinus l. labiatus,in Bolivia

A 5-month field study was conducted on red-bellied tamarins,Saguinus labiatus labiatus, in the Pando Department of northern Bolivia. Group sizes ranged from 5 to 10 animals, and each group associated with a group of saddle-backed tamarins,Saguinus fuscicollis weddelli. Members of three groups were trapped and marked and data were collected by radiolocation. The average range size used over 10 days was 19 ha. On average the groups entered about 29% of their range each day and had a mean daily path length of about 1487 m. The groups used a number of different sleeping sites within their ranges. They fed on a variety of different fruits and also on nectar from flowers, resin, and insects. Areas within the home range which were used significantly more than expected were generally those in which one or more of the following existed: a sleeping site, an intergroup encounter site, or a site where the group took shelter during an extended period of heavy rain.     

Variation in Intergroup Encounters in Two Populations of Japanese Macaques

The nature of intergroup encounters differed between two populations of wild Japanese macaques (Macaca fuscata): the Yakushima and Kinkazan populations. In the Yakushima population, intergroup encounters were more likely to result in the displacement of one group, intergroup agonistic interaction was common, and intergroup dominance was usually distinct. When displacement occurred at Yakushima, larger groups tended to dominate smaller ones. Conversely, in the Kinkazan population, intergroup encounters rarely resulted in displacement, intergroup agonistic interaction was rare, and intergroup dominance was usually unclear. Thus, monkeys in Yakushima appear to defend resources actively during encounters, while those in Kinkazan usually did not defend resources. The frequency of encounters was significantly higher in Yakushima than in Kinkazan. The two populations had very different group densities and traveling speeds, both of which directly influence the chance of encounters. Taking these differences into account, we compared the observed frequency with those predicted by the ideal gas model. The observed frequencies in both populations were about one-third of the number expected with the model, which suggests that the differences in encounter frequency were caused by differences in group density and traveling speed. We discuss this intraspecific variation in light of economic defendability in connection to habitat differences and the evolutionary significance of resource defense behavior.     

Predictive modelling of freshwater fish as a biomonitoring tool in New Zealand

SUMMARY 1. A challenge has been issued to ecologists to find quantitative ecological relationships that have predictive power. A predictive approach has been successful when applied to biomonitoring using stream invertebrates with the River Invertebrate Prediction and Classification System (RIVPACS). This approach, to our knowledge, has not been applied to freshwater fish assemblages.
2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.
3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large-scale variables including altitude, distance from the coast, lotic ecoregion and map co-ordinates.
4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.
5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa ( O / E ) ratios were significantly lower than the reference site O / E ratios, indicating a response of the fish assemblages to the known stressors.     

The use of AUSRIVAS predictive models to assess the response of lotic macroinvertebrates to dams in south-east Australia

1. Sites immediately below seven dams in Victoria and 12 in southern New South Wales (NSW) were sampled for macroinvertebrates using rapid bioassessment techniques. Specimens were identified to the lowest taxonomic level. The dams had different operating and discharge regimes and thus potentially different downstream effects on this fauna.
2. The AUStralian RIVer Assessment Scheme (AUSRIVAS) predictive models for macroinvertebrate composition were applied to the families and genera observed at Victorian sites and to the families only at the NSW sites. Lists of predicted taxa, their probabilities of occurrence and ratios of observed to expected taxa (O/E scores) were obtained from these models.
3. The mean O/E score for Victoria was 0.46 at the genus level and 0.63 at the family level; for NSW the mean score at the family level was 0.62. There was no significant difference between family level scores for the two states. Thus about 40% of expected families were missing at all sites. Family level scores were highly correlated ( r =0.84–0.86, P  < 0.001) with numbers of families or species at a site.
4. There was no correlation between family O/E scores (or family and species richness) and the degree to which current discharge levels below a dam differ from the natural patterns. Thus increased hydrological deviation did not result in greater biological degradation. In addition, there was no association between these biological characteristics and whether dams released surface or bottom water.
5. All the dams seemed to cause much the same disruption to the fauna. Of the families predicted to have widespread occurrence, 9–12 were found at most sites (tolerant taxa), while a larger number (14–24) were missing (intolerant taxa). The limited recolonisation below dams may well be because of the fact that dams act as barriers to drift, the most prominent route for invertebrate colonists.     

Against all odds: Numerical assessment by tufted capuchin monkeys

When competitors are able to assess the asymmetry in the resource holding potential before interacting, individuals or groups should avoid interacting with stronger opponents, thereby avoiding the energy costs and risk of injury associated with aggressive intergroup encounters. Thus, escalated aggression is expected only between closely matched competitors. Among Argentine tufted capuchin monkeys (Sapajus nigritus), intergroup dominance is decided by the asymmetry in male group size. Using playback experiments, I simulated intergroup encounters with neighboring groups, manipulating both the apparent numerical asymmetry and the resource context. During experimental trials, I recorded the approach behavior of the focal individual, as well as changes in neighbor density and individual travel speed following the presentation of the playback stimulus, to assess whether individual willingness to participate in resource defense was affected by the probability of winning the encounter. In spite of the competitive disadvantage, neither males nor females showed a decreased probability of approach when the numerical odds strongly favored the opposing group. Instead decisions regarding whether to participate appear to be driven primarily by the resource context. Nevertheless, changes in individual behavior during approaches suggest that tufted capuchin monkeys are sensitive to the relative odds. Individuals accelerated less when approaching a larger group, although no changes in neighbor density were apparent. The absence of an effect of the numerical asymmetry on willingness to approach the playback speaker suggests that subordinate groups benefit from engaging in intergroup aggression with larger neighbors, despite the high probability of losing. These encounters may serve to assess the current subjective resource valuation of the neighboring group or limit territorial expansion by large groups by decreasing the marginal value of home range exclusivity. Because these encounters are riskier, however, individuals appear to alter their approaches, becoming more tentative as the numerical odds increasingly favor the opposing group.     

Characterization and Social Correlates of Fecal Testosterone and Cortisol Excretion in Wild Male <Emphasis Type="Italic">Saguinus mystax</Emphasis>

Reproductive success in male primates can be influenced by testosterone (T) and cortisol (C). We examined them in wild Saguinus mystax via fecal hormone analysis. Firstly, we wanted to characterize male hormonal status over the course of the year. Further we tested the influence of the reproductive status of the breeding female, social instability, and intergroup encounter rates on T levels, comparing the results with predictions of the challenge hypothesis (Wingfield et al., 1990). We also tested for interindividual differences in hormonal levels, possibly related to social or breeding status. We collected data during a 12-mo study on 2 groups of moustached tamarins at the Estación Biológica Quebrada Blanco in northeastern Peru. We found fairly similar T and C levels over the course of the year for all males. Yet an elevation of T shortly after the birth of infants, during the phase of ovarian inactivity of the groups breeding female, was evident. Hormonal levels were not significantly elevated during a phase of social instability, did not correlate with intergroup encounter rates, and did not differ between breeding and nonbreeding males. Our results confirm the challenge hypothesis (Wingfield et al., 1990). The data suggest that reproductive competition in moustached tamarins is not based on endocrinological, but instead on behavioral mechanisms, possibly combined with sperm competition.     

Behaviour of late-instar gypsy moth larvae in high and low density populations

ABSTRACT. 1. Using scaffolding and night-vision equipment, we observed fifth and sixth instars of the gypsy moth, Lymantria dispar (L.), on Quercus velutina Lam. in the field.
2. In low-density populations, larvae fed at night and spent the day resting in sheltered sites away from the canopy. In high-density populations, larvae remained in the canopy throughout the day and night, and the amount of feeding during daylight hours increased with population density.
3. Larvae at all population densities used a similar sequence of behaviours and sampled a number of leaves when selecting feeding sites, but larvae in high-density populations switched feeding sites more frequently and fed continuously for shorter periods.
4. Larvae seldom interfered with each other's feeding in any of the populations.
5. When fifth instars were collected from the field and held for 24 h in an electronic feeding monitor, they maintained feeding rhythms that were characteristic of their source populations. Larvae spent more time crawling and less time feeding when offered foliage from high-density rather than low-density populations.     

Patterns of benthic invertebrate assemblages in rivers of northwestern North America

SUMMARY. 1. Biogeographical and on-site. hydrological variables were evaluated to determine spatial distribution of benthic invertebrate assemblages at 100 river sites in northwestern North America.
2. Results of cluster analysis suggested that the river sites comprised sixgroups (A-F), each supporting a characteristic invertebrate assemblage.Distinct groups were best represented by abundant Tricorythidae (C), Amphipoda (F), Rhyacophilidae and Systellognatha (E), and Elmidae and Hydroptilidae (A). Brachycentridae (B) and Oligochaeta (D) were widespread throughout the study area.
2. Both biogeographical and hydrological features contributed to the correct classification of site groupings characterized by distinctive fauna. However, biogeographical features were more useful than variables measured at the river site in discriminating among the site groupings.Groups C and F were most prevalent within the Hudson Bay drainage.Groups A, C and F were typically located within plains; group E sites were in mountainous regions.
4. The hydrological variables most useful in delineating site groupings were mean current velocity and mean depth. Slow, deep waters characterized amphipod sites; shallow, fast flowing waters occurred at Rhyacophilidae Sysellognatha sites.
5. Results substantiate previous views of a strong association between benthic invertebrates in small rivers and the terrestrial biome through which the river flows.     

Age-dependent clutch size in a koinobiont parasitoid

Abstract.  1. The Lack clutch size theory predicts how many eggs a female should lay to maximise her fitness gain per clutch. However, for parasitoids that lay multiple clutches it can overestimate optimal clutch size because it does not take into account the future reproductive success of the parasitoid.
2. From egg-limitation and time-limitation models, it is theoretically expected that (i) clutch size decreases with age if host encounter rate is constant, and (ii) clutch size should increase with host deprivation and hence with age in host-deprived individuals.
3. Clutch sizes produced by ageing females of the koinobiont gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) that were provided daily with hosts, and of females ageing with different periods of host deprivation were measured.
4. Contrary to expectations, during the first 2 weeks, clutch size did not change with the age of the female parasitoid, neither with nor without increasing host-deprivation time.
5. After the age of 2 weeks, clutch size decreased for parasitoids that parasitised hosts daily. The decrease was accompanied by a strong decrease in available eggs. However, a similar decrease occurred in host-deprived parasitoids that did not experience egg depletion, suggesting that egg limitation was not the only factor causing the decrease in clutch size.
6. For koinobiont parasitoids like M. tristis that have low natural host encounter rates and short oviposition times, the costs of reproduction due to egg limitation, time limitation, or other factors are relatively small, if the natural lifespan is relatively short.
7. Koinobiont parasitoid species that in natural situations experience little variation in host density and host quality might not have strongly evolved the ability to adjust clutch size.     

The impact of patch encounter rate on patch residence time of female parasitoids increases with patch quality

Abstract.  1. For animal species that forage on patchily distributed resources, patch time allocation is of prime importance to their reproductive success. According to Charnov's marginal value theorem (MVT), the rate of patch encounter should influence negatively the patch residence time: as the rate of patch encounter decreases, the patch residence time increases. Moreover, the MVT predicts that animals should stay longer in high quality patches.
2. Using the aphid parasitoid Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), the effects of these two factors (patch encounter rate and host density) were combined in order to test if the increment in patch residence time for a given decrease in patch encounter rate was larger for high quality patches than for low quality patches.
3. The results show a significant effect of the interaction between the two factors. In high host density patches, parasitoids spent more time if they experienced a low patch encounter rate, while in low host density patches, patch encounter rate had no significant effect on the patch residence time. This suggests that the response of A. rhopalosiphi females to patch encounter rate varied with host density in the patch. Moreover, the same interaction effect was observed for the number of ovipositor contacts on aphids.
4. Parasitoid females can use patch encounter rate to estimate patch density in the habitat but the effect of this estimate on their patch residence time is modulated by patch quality. Staying longer in a patch when patches are rare is more advantageous when the fitness gained by doing so is large. In low quality patches, the expected fitness gain is small and the female may gain more by leaving and taking her chance at finding another patch.     

Mayfly locomotory responses to endoparasitic infection and predator presence: the effects on predator encounter rate

SUMMARY. 1. The effects of predaceous stoneflies and endoparasilism by mermithid nematodes on the locomotory behaviour of individual mayflies were studied in the laboratory. The effects of predator- and parasite-induced changes in activity on predator encounter, attack and capture rates were also examined.
2. In response to predator presence non-parasitized mayflies decreased activity, while parasitized mayflies increased activity, in comparison to a control group. As a result, the faster-moving parasitized individuals encountered stonefly predators much more frequently. The frequency of attacks per encounter did not change.
3. In view of this and other studies, two predator-avoidance strategies based on mayfly locomotory and defensive capabilities are proposed: (a) Mayflies that are able effectively to flee a predator's attack and those able to employ a behavioural defence may decrease their mean velocity when a predator is detected, thereby reducing the likelihood of an encounter while allowing foraging to continue; (b) Slower-moving or otherwise defenceless mayflies may immediately move away from the area in which a predator is perceived in order to avoid an encounter.
4. In the absence of a predator, parasitized mayflies demonstrated greatly increased activity. This probably reflects increased foraging in response to the nutritional deficit imposed by the endoparasite. A decrease in upstream movement by parasitized mayflies may also indicate a parasite-imposed energy stress.     

When does diversity fit null model predictions? Scale and range size mediate the mid‐domain effect

Aim  Recently, a flurry of studies have focused on the extent to which geographical patterns of diversity fit mid-domain effect (MDE) null models. While some studies find strong support for MDE null models, others find little. We test two hypotheses that might explain this variation among studies: small-ranged groups of species are less likely than large-ranged species to show mid-domain peaks in species richness, and mid-domain null model predictions are less robust for smaller spatial extents than for larger spatial extents.
Location  We analyse data sets from elevational, riverine, continental and other domains from around the world.
Methods  We use a combination of Spearman rank correlations and binomial tests to examine whether differences within and among studies and domains in the predictive power of MDE null models vary with spatial scale and range size.
Results  Small-ranged groups of species are less likely to fit mid-domain predictions than large-ranged groups of species. At large spatial extents, diversity patterns of taxonomic groups with large mean range sizes fit MDE null model predictions better than did diversity patterns of groups with small mean range sizes. MDE predictions were more explanatory at larger spatial extents than at smaller extents. Diversity patterns at smaller spatial extents fit MDE predictions poorly across all range sizes. Thus, MDE predictions should be expected to explain patterns of species richness when ranges and the scale of analysis are both large.
Main conclusions  Taken together, the support for these hypotheses offers a more sophisticated model of when MDE predictions should be expected to explain patterns of species richness, namely when ranges and the scale of analysis are both large. Thus the circumstances in which the MDE is important are finite and apparently predictable.     

Forests and the temperature of upland streams in Wales: a modelling exploration of the biological effects

SUMMARY. 1. Daily temperature data from six streams in upland Wales were used to explore the thermal effects of afforestation on stream ecology. The data were linked to published biological models to simulate fish and invertebrate development.
2. Mean daily temperatures in forest streams were lower than those of moorland streams in spring and summer, and higher in winter. These spatial comparisons were supported by the results of experimental bank-side clearance at a forest site, where there was evidence that stream temperatures fell in winter and rose in spring following treatment.
3. Simulations indicated that brown trout (Salmo trutta) could weigh over 30% more by the end of their second growing season in a moorland compared with a forest stream. Several species of insects showed slower simulated egg development at forest sites. For two ephemeropteran species simulated nymphal growth was also retarded, suggesting significant alterations to the life cycle. Two plecopteran species were affected only slightly by the different temperature regimes.
4. Overall, the simulations suggested that afforestation, by reducing summer temperatures, could lead to marked reductions in rates of development of some invertebrates and fish.     

Altruistic Punishment and Between-Group Competition

Collective action, or the large-scale cooperation in the pursuit of public goods, has been suggested to have evolved through cultural group selection. Previous research suggests that the costly punishment of group members who do not contribute to public goods plays an important role in the resolution of collective action dilemmas. If large-scale cooperation sustained by the punishment of defectors has evolved through the mechanism of cultural group selection, two implications regarding costly punishment follow: (1) that people are more willing to punish defecting group members in a situation of intergroup competition than in a single-group social dilemma game and (2) that levels of "perverse" punishment of cooperators are not affected by intergroup competition. We find confirmation for these hypotheses. However, we find that the effect of intergroup competition on the punishment of defectors is fully explained by the stronger conditionality of punishment on expected punishment levels in the competition condition.     

Developmental costs of rapid growth in a damselfly

Abstract.  1. Developmental costs of rapid growth in terms of increased fluctuating asymmetry are expected to contribute to the widespread occurrence of growth rates below the physiological maximum, but have rarely been demonstrated. Here, these costs are studied for the first time in an invertebrate, the damselfly Lestes viridis , using a rearing experiment where early- and late-hatched larvae of both sexes were reared at decreasing or permanent water levels.
2. Late-hatched animals were more asymmetrical than early-hatched animals except for males in the drying treatment. Also, females were more asymmetrical than males except in early-hatched animals in the drying treatment.
3. The data presented suggest that in females but not in males treatment groups with higher growth rates have more asymmetrical wings. However, at the individual level no relationship between growth rate and asymmetry was present.
4. Possible reasons why the suggested trade-off between growth and developmental instability was not present at the individual level, and at the group level only in females, are discussed.