Emergence of size-structured dominance hierarchies through size-dependent feedback

Size-based dominance hierarchies influence fitness, group size and population dynamics and link dominance structure to evolutionary and ecological outcomes. While larger individuals often gain dominance, social status may influence growth and size in return, resulting in feedbacks among status, growth and size. Here, we present two models evaluating how these feedbacks influence the emergence of size structure in a dominance hierarchy. In the first, size influences competition for food and investment in suppressing growth of groupmates. Stable size differences emerged when suppression was greatest for similarly sized individuals and size had little effect on competition for food. The model predicted size divergence when size strongly affected competition for food. In the second model, we used a dynamic game to solve for optimal investment in growth suppression as a function of size structure. Investment in growth suppression was favoured only when dominants and subordinates were similar in size, generating size ratios different than those expected by chance. Variation in the feedbacks among growth, size and status can explain variation in emergent size structure of dominance hierarchies and its consequences for conflict within groups. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

KOMPOSISI DAN LUAS RELUNG MAKANAN IKAN PALUNG (Hampala macrolepidota C.V.1823) DI WADUK PB. SOEDIRMAN BANJARNEGARA, JAWA TENGAH

This study aims to determine the composition and value of the natural feed niche of trough fish caught from the waters of the PB Reservoir. Sudirman. The research method used is a survey method with a sampling technique using purposive random sampling. The research location was divided into three stations, namely I (Karang Kemiri), II (Wanadadi), and III (Karang Jambe). Sampling was carried out three times (19 February, 07 March, and 2 August 2020). Data were analyzed descriptively comparatively. The results showed that the composition of the trough fish diet was dominated by Chlorophyta and plant debris. Based on the selectivity index and the most significant part of trough fish, including omnivorous fish. Large trough fish have a high food niche area. Small, medium and large trough fish have stiff competition for food in the waters

Foraging Interference and Fruit Palatability in Pteropus Scapulatus (Megachiroptera: Pteropodidae): Management Implications

<p>The “residents and raiders” theory emphasizes the importance of conspecific feeding interference in seed dispersal by frugivorous megachiropterans. Agonistic interactions at fruiting trees frequently result in the “ejection” of one bat, which has often first obtained some fruit. The ejected bat then flies to an unoccupied tree, thus dispersing non-consumed seeds. For seeds too large to be swallowed this may be the sole method of dispersal. Raiding and subsequent seed spread only occur when bat populations are sufficiently large, relative to resources, to cause competition for food. If competition similarly affects nectarivorous bats and their floral resources, decline in a bat population could lead to reduced seed set and genetic diversity in their food-plant species. Pteropus scapulatus (Little Red Flying Fox) visit the flowers of dozens of Australian and New Guinean species and are believed to play an important role in the pollination of Eucalyptus and Melaleuca. Feeding-interference and raiding “success” by P. scapulatus eating fruit at Wellington Zoo (New Zealand) was studied to infer the importance of population size on cross-pollination. Decrease in population-to-resource ratio was correlated with decrease in raiding frequency, suggesting a decreased likelihood of cross pollination. These results highlight the value of management practices that promote the maintenance of large populations of nectarivorous megachiropterans. The effects of dominance and food preference on these behaviours were also evaluated. Dominance was inversely correlated to both dispersal and maturity. Contrary to many reports, females were not always subordinate to males. Fruit preference data may be useful for selecting “distracter” trees in orchards prone to damage by fruit bats and for ex situ husbandry concerns. Implications for population-, orchard-, and captive-management are discussed.</p>

Foraging Interference and Fruit Palatability in Pteropus Scapulatus (Megachiroptera: Pteropodidae): Management Implications

<p>The “residents and raiders” theory emphasizes the importance of conspecific feeding interference in seed dispersal by frugivorous megachiropterans. Agonistic interactions at fruiting trees frequently result in the “ejection” of one bat, which has often first obtained some fruit. The ejected bat then flies to an unoccupied tree, thus dispersing non-consumed seeds. For seeds too large to be swallowed this may be the sole method of dispersal. Raiding and subsequent seed spread only occur when bat populations are sufficiently large, relative to resources, to cause competition for food. If competition similarly affects nectarivorous bats and their floral resources, decline in a bat population could lead to reduced seed set and genetic diversity in their food-plant species. Pteropus scapulatus (Little Red Flying Fox) visit the flowers of dozens of Australian and New Guinean species and are believed to play an important role in the pollination of Eucalyptus and Melaleuca. Feeding-interference and raiding “success” by P. scapulatus eating fruit at Wellington Zoo (New Zealand) was studied to infer the importance of population size on cross-pollination. Decrease in population-to-resource ratio was correlated with decrease in raiding frequency, suggesting a decreased likelihood of cross pollination. These results highlight the value of management practices that promote the maintenance of large populations of nectarivorous megachiropterans. The effects of dominance and food preference on these behaviours were also evaluated. Dominance was inversely correlated to both dispersal and maturity. Contrary to many reports, females were not always subordinate to males. Fruit preference data may be useful for selecting “distracter” trees in orchards prone to damage by fruit bats and for ex situ husbandry concerns. Implications for population-, orchard-, and captive-management are discussed.</p>

Ecology and Conservation of the Laotian langur Trachypithecus laotum in a Protected Area of Laos (Southeast Asia)

Terrestrial species from the Lao People’s Democratic Republic (PDR) are under high threat due to deforestation and overhunting. Previous studies have even defined these forests as subjected to an “empty forest syndrome”, a condition in which forests that are apparently well preserved are instead almost deprived of vertebrate faunas due to extreme exploitation by local communities. Forest specialists, including several primates, are among the most threatened species in the country. The Laotian langur (Trachypithecus laotum) is endemic to Lao PDR, is listed as Endangered by the IUCN Red List, and it is one of the least studied species in the region. A survey on the local distribution, life history and conservation status of the Laotian langur was carried out in Phou Hin Poun National Protected Area, Khammouane Province of Lao PDR. The survey consisted of an initial phase with interviews to select key informants on the Laotian langur and the other primate species of the area. Then, a phase of field surveys along forest transects, totaling 64.1 km of 21 transects, yielded a record of 35 individuals in 9 groups. The highest encounter/detection rate of the Laotian langur was 1 group per km at one sector of the park. In contrast, it was much lower (0.18–0.34 groups/km) in the rest of the protected area. The group sizes were much lower than those observed in the same area between 1994 and 2010, thus suggesting a decline in the population size of langurs. This decline may be linked to habitat loss (timber extraction and mining). Still, also overhunting, as signs of poaching were observed during our field surveys. This was also supported by the reports of our interviewees. Laotian langurs were observed to be sympatric and interact while foraging with the Assamese macaque (Macaca assamensis). In the cases of sympatric occurrence between the two species, we observed that subtle mechanisms of niche partitioning may occur to reduce interspecific competition for food. Further research on the population and ecology of this endangered langur should be conducted to understand the species and aid its conservation.

Intra- and inter-specific density dependence of body condition, growth, and habitat temperature in chub mackerel (Scomber japonicus)

The density dependence of growth and body condition have important impacts on fish population dynamics and fisheries management. Although population density is known to affect the temperature of the habitat selected, how this affects the density dependence of growth and body condition remains unclear. Here, we investigated annual changes in body condition, habitat temperature, and cohort-specific growth of chub mackerel (Scomber japonicus) in the western North Pacific and examined quarterly changes in the density dependence of body condition. We hypothesized that chub mackerel body condition is affected both directly (e.g., through competition for food) and indirectly (through changes in habitat temperature) by the abundance of both conspecifics (i.e., chub mackerel) and heterospecifics (the Japanese sardine Sardinops melanostictus). Indeed, chub mackerel body condition, habitat temperature, and growth all decreased with increasing conspecific and heterospecific abundance. Mean annual growth rates in chub mackerel were positively corelated with body condition. The best model showed that conspecific and/or heterospecific abundance had strong negative effects on chub mackerel body condition in all seasons, and influenced habitat temperature in some seasons. By contrast, temperature effects on body condition were weak. Therefore, direct effects likely have more impact than indirect effects on density-dependent body condition and growth.

TROPHOLOGY OF CTENOPHORE MNEMIOPSIS LEIDYI AFTER NATURALIZATION IN ECOSYSTEM OF CASPIAN SEA

Trophological studies of ctenophore Mnemiopsis leidyi conducted in the Caspian Sea more often included species at the later stage of development, as a result, juveniles, metamorphic larvae and larvae were ignored. Ctenophore is known to start feeding since the moment the larva emerges from the egg. Studying the availability of food resources and their size range allowed to trace a certain dependence in the diet of ctenophore, and to determine at which stage of development the jellylike organism in the population feeds most intensively. During the period of naturalization of invasion in the Caspian Sea (1998-2016) there has been registered an increasing number of species with an empty gastrovascular cavity (GVC) in the Mnemiopsis population. According to the analysis results obtained during the study period, the share of individuals with empty GVC in the North Caspian increased to 77.8%, which is associated not with the climatic or hydrological factors, as in 2015 and 2016, but with the availability of food items and internal competition for food resources. There has been found the diversity of the items making food stuff of Mnemiopsis in nature. The main food component is mesozooplankton, as well as meroplankton (cirriped nauplii, larvae of polychaete worms). In food requirements ctenophore does not show selectivity of food resources, the basis of its food make the most available forms of zooplankters.

Tandem communication improves ant foraging success in a highly competitive tropical habitat

Tropical ants experience intense intra- and interspecific competition for food sources, which influences their activity pattern and foraging strategies. Even though different ant species can coexist through spatial and temporal niche partitioning, direct competition for food cannot be avoided. Recruitment communication is assumed to help colonies to monopolize and exploit food sources successfully, but this has rarely been tested under field conditions. We studied if recruitment communication helps colonies of the Neotropical ant Pachycondyla harpax to be more successful in a highly competitive tropical environment. Additionally, we explored if temporal and spatial niche differentiation helps focal colonies to avoid competition. Pachycondyla harpax competed with dozens of ant species for food. Mass-recruiting competitors were often successful in displacing P. harpax from food baits. However, when foragers of P. harpax were able to recruit nestmates they had a 4-times higher probability to keep access to the food baits. Colonies were unlikely to be displaced during our observations after a few ants arrived at the food source. Competition was more intense after sunset, but a disproportionate increase in activity after sunset allowed focal colonies to exploit food sources more successfully after sunset. Our results support the hypothesis that recruitment communication helps colonies to monopolize food sources by helping them to establish a critical mass of nestmates at large resources. This indicates that even species with a small colony size and a slow recruitment method, such as tandem running, benefit from recruitment communication in a competitive environment.