Clan Size Research Articles

Multilevel sociality in the spotted hyaena: How to live in large groups without falling prey to the infertility trap

AbstractSpotted hyaenas live in unusually large social groups for a carnivore. Since, all else equal, the ‘infertility trap’ (a negative relationship between fertility and the number of females in a group) limits social group sizes to ~5 reproductive females in mammals, hyaena must, like other very social species, have found a way to mitigate the stresses involved in order to do so. From a comparative analysis of data from 19 well‐studied Crocuta crocuta populations, I show (1) that the distribution of hyaena clan sizes is multimodal, with a fractal scaling ratio close to 3 and a base unit of 12–15 individuals (3–5 reproductive females), (2) that fertility is a negative function of number of females in the group and (3) that there is a trade‐off between the benefits of having more males in the group and the costs incurred by having more females. Although females do buffer themselves against the infertility trap by forming matrilineal alliances (thereby creating a primate‐like multilevel structure), males seem to play an important role, such that, in areas with a low density of males, clan sizes are much smaller.

Aggregation of clans to speed-up solving linear systems on parallel architectures

The paper further refines the clan composition technique that is considered a way of matrix partitioning into a union of block-diagonal and block-column matrices. This enables solving the individual systems for each horizontal block on a separate computing node, followed by solving the composition system. The size of minimal clans, obtained as a result of matrix decomposition, varies considerably. For load balancing, early versions of ParAd software were using dynamic scheduling of jobs. The present paper studies a task of static balancing the clan size. Rather good results are obtained using a fast bin packing algorithm with the first fit on a sorted array which are considerably improved applying a multi-objective graph partitioning with software package METIS. Aggregation of clans allows us to obtain up to three times extra speed-up, including systems over fields of real numbers, on matrices from Model Checking Contest and Matrix Market.

Seasonal movements and site utilisation by Asian water buffalo (Bubalus bubalis) in tropical savannas and floodplains of northern Australia

Abstract ContextThe Asian water buffalo (Bubalus bubalis) is an introduced herbivore of the savannas and floodplains of northern Australia. Despite the significant environmental damage caused by water buffalo, important cultural and commercial stakeholders request this species is managed rather than eradicated. However, gaps in knowledge of buffalo ecology limit effective policy and planning. AimsTo better understand how buffalo, at current population densities, respond to seasonally changing resources in the two key habitat types that they occupy in northern Australian – upland eucalypt savanna and seasonally inundated floodplain. MethodsSatellite telemetry was used to record the location of a single female buffalo from each of 11 independent clans every hour over a 12-month period. Generalised linear mixed modelling was used to assess the extent to which buffalo movements, activity-space and site revisitation correlated with forage quality (inferred from the normalised difference vegetation index – NDVI) and localised buffalo density. Key resultsAs the dry season progressed, forage quantity and quality within the activity-space of buffalo clans decreased. In response, buffalo inhabiting floodplain exhibited increased rates of movement and enlarged the size of their activity-space. This resulted in low repeated visitation of foraging areas in the late dry season and NDVI remained relatively high within these areas. In comparison, buffalo in upland savanna maintained similar rates of activity and occupied the same activity-space size throughout the year. This resulted in frequent revisitation of the same areas in the late dry season and NDVI reached as low as zero in these foraging areas. Clan size and localised buffalo density had no significant effect on measured movement parameters. ConclusionsBuffalo exhibited a behavioural strategy in upland savanna that resulted in acute removal of green herbaceous vegetation within a few kilometres of the clan’s permanent water source. Buffalo inhabiting the floodplain used multiple wallows that reduced grazing impacts, but likely resulted in hoof-derived impacts over a broad area. ImplicationsCurrent buffalo densities in Kakadu National Park appear to be well below carrying capacity but localised environmental degradation around permanent water sources remains severe in upland savanna.

Dyadic associations reveal clan size and social network structure in the fission–fusion society of spotted hyaenas

AbstractEstimating the size and dynamics of populations is of paramount importance in ecology. In species with uniquely marked individuals, capture–recapture methods can be used to establish population size and to explore associations between individuals. However, very few studies have used cameras traps to focus on group composition in social carnivores, despite being of particular interest in species characterised by “fission–fusion” formation of sub‐groups. Here, we provide estimates of (a) population size, (b) density, (c) clan size, (d) association patterns and (e) social network structure in spotted hyaenas (Crocuta crocuta) based on images from camera traps deployed at waterholes on Ongava Game Reserve (northern Namibia). In a 15 week study period, we identified 32 individuals. Dyadic associations and the resulting social network showed that all but two hyaenas associated directly or indirectly with each other, indicating the presence of one clan of at least 30 individuals, resulting in a density of 8.1 hyaenas/100 km2. We found a very high variability in the tendency of individuals to associate with others. This study confirms a highly dynamic fission–fusion society in spotted hyaenas. We argue that camera traps can provide relevant insights into large carnivore social network structure where associations between individuals are difficult to observe directly.

Solving Linear Diophantine Systems on Parallel Architectures

Solving linear Diophantine systems of equations is applied in discrete-event systems, model checking, formal languages and automata, logic programming, cryptography, networking, signal processing, and chemistry. For modeling discrete systems with Petri nets, a solution in non-negative integer numbers is required, which represents an intractable problem. For this reason, solving such kinds of tasks with significant speedup is highly appreciated. In this paper we design a new solver of linear Diophantine systems based on the parallel-sequential composition of the system clans. The solver is studied and implemented to run on parallel architectures using a two-level parallelization concept based on MPI and OpenMP. A decomposable system is usually represented by a sparse matrix; a minimal clan size of the decomposition restricts the granulation of the technique. MPI is applied for solving systems for clans using a parallel-sequential composition on distributed-memory computing nodes, while OpenMP is applied in solving a single indecomposable system on a single node using multiple cores. A dynamic task-dispatching subsystem is developed for distributing systems on nodes in the process of compositional solution. Computational speedups are obtained on a series of test examples, e.g., illustrating that the best value constitutes up to 45 times speedup obtained on 5 nodes with 20 cores each.

Spotted hyaena survival and density in a lion depleted ecosystem: The effects of prey availability, humans and competition between large carnivores in African savannahs

Interspecific competition between large carnivores is not well understood due to the complexity of carnivore guild dynamics and the array of ecological and human factors affecting them. The loss of a carnivore guild's dominant species can therefore provide considerable insights. We evaluated spotted hyaena density and demography from Zambia's Liuwa Plain National Park, a recovering ecosystem where the hyaena's main competitor, the African lion, was severely reduced to 3–5 animals. Using data from 233 individuals in five clans and mark-resight robust design models we estimated population size, density, age and sex-specific annual survival rates for the hyaena population from 2010 to 2013 and tested for the effect of human settlements, prey density, competition with lions and hyaena clan size on mean hyaena survival. We estimated a minimum density of 0.13 hyaenas/km2 and maximum density of 0.52 hyaenas/km2. Density fluctuated with seasonal migrations of the main prey species, the blue wildebeest. Mean annual survival across all age classes was 0.93 (95%CI: 0.79–0.99). With high survival rates across all sex and age classes, we found no detectable effects of ecological or anthropogenic factors on survival. These results suggest that the combination of abundant prey, weak human-carnivore conflict, and weak competition from lions provide very favourable conditions for hyaena survival. Additional investigations of hyaena demography concurrent with lion population recovery efforts can provide considerable insights into the dynamics of carnivore competition and predation in African savannahs and the human and ecological factors affecting them.

Spotted, striped or brown? Taphonomic studies at dens of extant hyaenas in eastern and southern Africa

We compare taphonomically relevant aspects of 6 bone accumulations produced by extant spotted hyaenas Crocuta crocuta, striped hyaenas Hyaena hyaena, and brown hyaenas Parahyaena brunnea) from eastern and southern Africa (Republic of Djibouti and Namibia) and published accounts. We highlight similarities and differences in the bone-cracking/consumption and bone collecting habits of each hyaena species with a view to revealing criteria that might be used to distinguish these species. Four parameters are described: i) the prey taken and preferences, ii) the skeletal part distribution, iii) the long bone fragmentation, iv) the tooth mark diversity and frequency. Information from hyaena ecology and the ungulate remains recovered from each bone accumulation reveals differences (or a lack thereof) related to environment, anthropogenic pressure and ethology. Spotted hyaena hunting strategy and clan size suggest a low degree of inter-group competition, but high levels of intra-group on-carcass competition; fewer osteological remains are brought back to dens. In contrast, striped and brown hyaenas are primarily scavengers (removing carcass remnants) and produce significant accumulations of bones at their dens. These differences are likely to be related mainly to inter-specific competition and serve to reduce interaction with other carnivores and to limit kleptoparasitism; the composition of accumulations at dens is determined by food availability and foraging behaviour to a greater or lesser degree. Modern analogues are essential baseline tools for elucidating characteristics that might distinguish each species. The development of neo-taphonomic models is the first step towards comparison and greater understanding of the palaeo-ethology of extinct Pleistocene hyaenids.

The Socioecology of Network Scaling Ratios in the Multilevel Society of Hamadryas Baboons (Papio hamadryas hamadryas)

Multilevel or modular societies characterize a range of mammalian taxa, allowing social groups to fission and fuse in response to ecological factors. The modular society of hamadryas baboons has previously been shown to consist of 4 levels: troop, band, clan, and one-male unit (OMU). A recent study by Hill et al. (Biology Letters 4:748–751, 2008) revealed a mean scaling ratio across successive levels of multilevel societies of ca. 3; this was consistent across elephants, orca, geladas, and hamadryas baboons. Here we reanalyze the scaling ratio for hamadryas baboons with previously unavailable data from Filoha. Our analysis revealed a mean scaling ratio for hamadryas of 3.28 without data on the hamadryas clan layer of organization at Filoha, but a ratio of 6.17 with these data included. This discrepancy is due to the large clan and band sizes at Filoha yielding a larger than average gap between the OMU and the clan. Further analysis revealed subsets of OMUs within clans, suggesting a 5th level of society in this population. When this 5th layer of social structure is included in the analysis, the scaling ratio at Filoha is consistent with that of other hamadryas populations and other taxa. These results suggest that a consistent mammalian scaling ratio can be used to detect previously hidden levels of organization within societies and to predict their sizes in taxa for which detailed behavioral data are not available.

Network cohesion, group size and neocortex size in female-bonded Old World primates

Most primates are intensely social and spend a large amount of time servicing social relationships. In this study, we use social network analysis to examine the relationship between primate group size, total brain size, neocortex ratio and several social network metrics concerned with network cohesion. Using female grooming networks from a number of Old World monkey species, we found that neocortex size was a better predictor of network characteristics than endocranial volumes. We further found that when we controlled for group size, neocortex ratio was negatively correlated with network density, connectivity, relative clan size and proportional clan membership, while there was no effect of neocortex ratio on change in connectivity following the removal of the most central female in the network. Thus, in species with larger neocortex ratios, females generally live in more fragmented networks, belong to smaller grooming clans and are members of relatively fewer clans despite living in a closely bonded group. However, even though groups are more fragmented to begin with among species with larger neocortices, the removal of the most central individual does cause groups to fall apart, suggesting that social complexity may ultimately involve the management of highly fragmented social groups while at the same time maintaining overall social cohesion. These results emphasize a need for more detailed brain data on a wider sample of primate species.

The fourth level of social structure in a multi‐level society: ecological and social functions of clans in hamadryas baboons

Hamadryas baboons are known for their complex, multi-level social structure consisting of troops, bands, and one-male units (OMUs) [Kummer, 1968. Social organization of hamadryas baboons. Chicago: The University of Chicago Press. 189p]. Abegglen [1984. On socialization in hamadryas baboons: a field study. Lewisburg, PA: Bucknell University Press. 207p.] observed a fourth level of social structure comprising several OMUs that rested near one another on sleeping cliffs, traveled most closely together during daily foraging, and sometimes traveled as subgroups independently from the rest of the band. Abegglen called these associations "clans" and suggested that they consisted of related males. Here we confirm the existence of clans in a second wild hamadryas population, a band of about 200 baboons at the Filoha site in lowland Ethiopia. During all-day follows from December 1997 through September 1998 and March 2005 through February 2006, data were collected on activity patterns, social interactions, nearest neighbors, band fissions, and takeovers. Association indices were computed for each dyad of leader males, and results of cluster analyses indicated that in each of the two observation periods this band comprised two large clans ranging in size from 7 to 13 OMUs. All band fissions occurred along clan lines, and most takeovers involved the transfer of females within the same clan. Our results support the notion that clans provide an additional level of flexibility to deal with the sparse distribution of resources in hamadryas habitats. The large clan sizes at Filoha may simply be the largest size that the band can split into and still obtain enough food during periods of food scarcity. Our results also suggest that both male and female relationships play a role in the social cohesion of clans and that males exchange females within clans but not between them.

Taphonomic and zooarchaeological implications of spotted hyena (Crocuta crocuta) bone accumulations in Kenya: a modern behavioral ecological approach

The significant impact of extant carnivores, particularly spotted hyenas, on the depositional history and physical characteristics of archaeofaunal and paleontological assemblages is well recognized. We focus on the behavioral ecology of extant spotted hyenas (Crocuta crocuta) in relation to bone accumulations produced by one East African clan at communal dens. Limbs and skulls of prey animals more frequently appear at dens than do other carcass portions. These items reflect the relative abundance of prey species near dens; carnivore remains are poorly represented. Comparative analysis reveals that bones are deposited far more slowly (<7 carcass portions per month) and accumulations tend to be smaller atCrocutadens than at dens of either brown (Parahyaena brunnea) or striped (Hyaena hyaena) hyenas. We propose that extantCrocutabone accumulation rates and sizes are likely affected by prey species abundance, clan size, social interactions within the clan, and the type and availability of den sites. We also suggest that the potential for intraspecific behavioral variability in bone accumulation patterns is important when comparisons are made among spotted hyena populations and across hyena species. For example, accumulation patterns may be dramatically influenced by the temporal span, potentially ranging from days to hundreds or thousands of years, in which bones are collected, depending on the species-specific history of occupation at a given site. Understanding the behavioral and ecological variability likely to influence bone accumulation patterns at dens used by different hyaenids will allow taphonomists and zooarchaeologists to refine their knowledge of mechanisms underlying site formation processes and potential causes of variability in deeper-time den assemblages.

Competitive interactions between spotted hyenas and lions in the Etosha National Park, Namibia

AbstractSpotted hyenas are successful hunters, but they also scavenge. Their main food competitors are lions. In the Etosha National Park, Namibia hyenas are unable to prevent kleptoparasitism by lions and fail to acquire kills from lions. The reasons are the small ratio of hyenas to female and subadult lions at kills and the presence of adult male lions. Because of the hyenas’ small clan sizes and large territories they seem to be unable to recruit sufficient clan members to take over lion kills or deter lions from their own kills. In Etosha, 71% of hyena mortality was due to lions; four cubs and one adult female hyena were killed by male lions during a 1‐year study. Hyenas have evolved adaptations against lions and initiate aggressive interactions with lions without the immediate availability of food, which is termed mobbing behaviour. Etosha hyenas initiated mobbing attempts when lions were near the hyena's communal den. Possibly, Etosha hyenas mobbed lions to distract lions from the hyenas’ den and their cubs and to warn their dependent offspring to hide from lions.

The effect of prey abundance and foraging tactics on the population dynamics of a social, territorial carnivore, the spotted hyena

We used naturally occurring spatial and temporal changes in prey abundance to investigate whether the foraging behavior of a social, territorial carnivore, the spotted hyena (Crocuta crocuta), conformed to predictions derived from the ideal free distribution. We demonstrate that hyenas in the Ngorongoro Crater, Tanzania, redistributed themselves from less profitable to more profitable areas, even when this required them to undertake foraging trips to areas beyond their clan territory boundary, or required normally philopatric females to emigrate. As expected for a system with rank related access to food resources in the territory, females of low social status foraged more often outside their territory and were more likely to emigrate than dominant females. Probably because Crater hyenas regularly foraged outside their territories, there was no correlation between clan size and prey density within territories, suggesting that clan sizes may have exceeded the carrying capacity of territories. A substantial decline of the hyena population in the Crater from 385 adults in the mid 1960s to 117 in 1996 was most likely due to a substantial decline of their main prey. The decline in the hyena population was associated with a decline in the size of clans but not in the number of clans. The number of clans probably remained constant due to emigration by females from large clans into vacant areas or clans with no adult females, and because hyenas regularly fed in areas containing concentrations of prey beyond their territory boundary. Between 1996 and 2003 annual recruitment rates of Crater hyenas consistently exceeded annual mortality rates, resulting in an almost doubling of the adult population. This increase was most likely due to an increase in prey abundance, a relatively low level of predation on hyenas by lions (Panthera leo), and an absence of high levels of disease related mortality.

Philopatry, Dispersal, and Social Organization of Gunnison's Prairie Dogs

I examined dispersal and social organization of Gunnison's prairie dogs (Cynomys gunni­ soni) for 7 years at Petrified Forest National Park, Arizona. Within colonies, individuals lived in harem-polygynous family groups called clans. The number of clans at the study site each year ranged from 21 to 23, with a mean of 22.3. Clan size (the number of adults living in the same territory) ranged from 1 to 19, with a mean of 5.30. Clans contained 1.06 ± 0.39 (SD) breeding males, 3.01 ± 2.08 breeding females, and 1.23 ± 1.65 non­ breeding yearling males. Some clans contained two breeding males, and others contained no resident breeding male. The area of clan territories ranged from 0.16 ha to 1.82 ha, with a mean of 0.67 ha. Females were more likely than males to copulate as yearlings (100% versus 24%). Ninety-five percent of females (340/358) remained in the natal clan territory for life, but only 5% of males (3/66) remained in the natal clan territory for> 1 year after weaning. Dispersal of both sexes was most commonly to an adjacent clan territory. Infan­ ticide at the study colony was rare or absent.

Rapid Change in Offspring Sex Ratios After Clan Fission in the Spotted Hyena

We describe the rapid reversal in juvenile sex ratio that occurred after fission of our study clan of free-living spotted hyenas (Crocuta crocuta). Juvenile sex ratios were strongly male biased before fission, when clan size was at or slightly above the habitat's carrying capacity (K). Clan size after fission fell below K, and juvenile sex ratios became female biased within a single reproductive cycle. The change in juvenile sex ratio appeared to be due to altered sex bias in cubs recruited through births. The observed change in secondary sex ratio was only significant among offspring of high-ranking females. Our observations were consistent with predictions of existing sex allocation theories based on local resource competition and enhancement. Our data suggest secondary sex ratios in spotted hyenas are influenced by conflicting demands of competition and cooperation among philopatric individuals.

The commuting system of Serengeti spotted hyaenas: how a predator copes with migratory prey. I. Social organization

Abstract. The social organization and space use of spotted hyaenas, Crocuta crocuta Erxleben, in the Serengeti, Tanzania is described. In contrast to Kruuk (1972, The Spotted Hyena. Chicago: University of Chicago Press), spotted hyaenas in the Serengeti live in large stable groups (clans); median clan size for seven clans was 47 adults and subadults. Clans defended permanent territories that contained the communal den. The size of one well-known territory was 55·5 km 2. Territories contained low densities of resident herbivores (mean 3·3 animals/km 2) throughout the year, but experienced very high densities (mean 219 animals/km 2) of migratory herds, principally wildebeest, Connochaetes taurinus , zebra, Equus burchelli, and Thomson's gazelle, Gazella thomsoni, for only 26% of the year. The most important prey killed inside territories were migratory species. When the migratory herds were away from a clan's territory, clan members regularly left the territory to forage on nearby migratory herds ('commuting trips'). Clan sizes were maintained above the carrying capacity of the territory, estimated from populations of resident herbivores, by year-round exploitation of migratory herbivores. This suggests that, in contrast to many other carnivores, group sizes of Serengeti hyaenas are not limited by resources on the territory and feeding ranges are decoupled from territoriality.

Red-cockaded woodpecker use of seed-tree/shelterwood cuts in eastern Texas: R. N. Conner, A. E. Snow & K. A. O'Halloran, Wildlife Society Bulletin, 19(1), 1991, pp 67–73

Establishment or maintenance of suitable habitat for any wildlife species is an important aspect of its management, especially for endangered species such as the red-cockaded woodpecker (Picoides borealis). Populations of the red-cockaded woodpecker are declining over much of the bird's current range, most likely because of the lack of suitable habitat (Carter et al. 1983, Conner and Rudolph 1989, Costa and Escano 1989). Jackson (1982), Locke et al. (1983), and others anecdotally noticed that red-cockaded woodpeckers used residual pines (mature pines left uncut during a harvest) for cavity excavation in seed-tree and shelterwood reproduction cut areas. Seed-tree and shelterwood reproduction cutting methods remove most trees but leave some residual pines to provide seeds and in some cases shelter for the next generation of pines. Conner and O'Halloran (1987) suggested that shelterwood cuts would produce trees similar to red-cockaded woodpecker cavity trees. Conner and Rudolph (1989) reported that fragmentation caused by clear-cutting was associated with small clan size. Shelterwood cutting may reduce fragmentation if residual pines are not eventually removed, thus reducing the

Territorial Behaviour by a Clan of Spotted Hyaenas Crocuta crocuta

AbstractTerritorial behaviour of a clan of spotted hyaenas, Crocuta crocuta, was investigated in the Kruger National Park over a period of 27 months. These hyaenas were highly territorial, spending ⅕ of their total activities on territory patrol by scent‐marking intensively and monitoring 64 marking posts, particularly in border regions. Females, the more philopatric sex, were most active in territory defence. Local intensity of territorial activities by residents within their 130‐km2 territory was directly proportional to intrusion pressure by neighbours. When clan size was reduced, the ability to defend disputed land declined and larger neighbouring clans appropriated parts of the territory. We propose a relationship between resource distribution, intrusion pressure and territory defence.