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Group Size (group + size)
Kinds of Group Size Selected AbstractsHeterogeneity, Group Size and Collective Action: The Role of Institutions in Forest ManagementDEVELOPMENT AND CHANGE, Issue 3 2004Amy R. Poteete Collective action for sustainable management among resource-dependent populations has important policy implications. Despite considerable progress in identifying factors that affect the prospects for collective action, no consensus exists about the role played by heterogeneity and size of group. The debate continues in part because of a lack of uniform conceptualization of these factors, the existence of non-linear relationships, and the mediating role played by institutions. This article draws on research by scholars in the International Forestry Resources and Institutions (IFRI) research network which demonstrates that some forms of heterogeneity do not negatively affect some forms of collective action. More importantly, IFRI research draws out the interrelations among group size, heterogeneity, and institutions. Institutions can affect the level of heterogeneity or compensate for it. Group size appears to have a non-linear relationship to at least some forms of collective action. Moreover, group size may be as much an indicator of institutional success as a precondition for such success. [source] The Effect of Group Size on Interfaith Marriage Among Catholics1JOURNAL FOR THE SCIENTIFIC STUDY OF RELIGION, Issue 3 2002James D. Davidson This article examines the relationship between the religious composition of Catholic dioceses and interfaith marriage rates among Catholics. Building on Blau's(1977) theory of intergroup relations and previous research on intermarriage, we argue that Catholics are most likely to marry outside their group when they comprise a relatively small percent of the population in their dioceses. They are most likely to marry other Catholics when they are a large percentage of the population. Research in the 1940s and 1950s supports this hypothesis, as do diocesan,level data reported in the 1960, 1965, 1970, 1975, 1980, 1985, 1990, and 1995 editions of the Official Catholic Directory. We conclude with a discussion of what these findings imply for future research on interfaith marriage among Catholics and among members of other religious groups. [source] Lotteries, Group Size, and Public Good ProvisionJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 3 2007PAUL PECORINO We analyze the effect of group size on public good provision under the Morgan (2000) lottery mechanism. For a pure public good, the lottery performs quite well as public good provision is found to increase in group size, even when the lottery prize is held constant. By contrast, for fully rival public goods, per capita provision is found to decrease in group size, even when the lottery prize is proportional to group size. Further, the per capita level of provision will approach zero when group size is sufficiently large. [source] Free Riding on Altruism and Group SizeJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 3 2002Jean Hindriks It is shown that altruism does not affect the equilibrium provision of public goods although altruism takes the form of unconditional commitment to contribute. The reason is that altruistic contributions completely crowd out selfish voluntary contributions. That is, egoists free ride on altruism. It is also shown that public goods are less likely to be provided in larger groups. The only qualification to our results is when the probability of altruism is so high that it is a dominant strategy for all egoistic players to free ride. In this case, actually, both altruism and the larger group facilitate public good provision. [source] Dynamic social system in Nubian ibex: can a second mating season develop in response to arid climate?JOURNAL OF ZOOLOGY, Issue 3 2008A. Massolo Abstract We studied a population of Nubian ibex Capra ibex nubiana in the eastern extreme of its range, the hyper-arid central desert of the Sultanate of Oman. Long-term data were collected from January 1983 to December 1997 by direct observation, as well as VHF telemetry on 12 animals (eight from 1987 to 1990; four from 1994 to 1996). We recorded 884 sightings: 40.4% of single animals and 59.6% of groups. Although no significant monthly variation of group size (Jarman's Typical Group Size) was found, there were distinct peaks in March (4.0 ind. group,1) and September (5.1 ind. group,1). Groups of males and females formed especially in March and November, and female,kid groups in February and July,August. Our data may suggest two mating periods: the first one in autumn (similar to the rut of ibex in temperate mountain areas), with kids born in spring/early summer, after winter,spring rainfall, and the second one in spring, with kids born in late summer/autumn, before winter,spring rainfalls. We suggest that the second rutting period may have evolved as a micro-evolutionary process, with the local population adapting to hyper-arid environment constraints. The spring mating season may favour only females in prime conditions, who can afford a pregnancy in the local severe summers and will deliver kids when plant greening begins, in the autumn, whereas the autumn (original) mating season may be afforded by any female, but kids will be born in an unfavourable period, before the summer drought. [source] Group Size Regulates Self,Assertive versus Self,Deprecating Responses to Interpersonal CompetitionCHILD DEVELOPMENT, Issue 6 2002Joyce F. Benenson The current study examined the hypothesis that group size can influence whether children display self,assertive versus self,deprecating responses to interpersonal competition, especially under stress. Twenty same,sex playgroups (N= 120) of 9, to 10,year,old children played a competitive game in groups and in dyads. Stress was induced by causing some of the children to lose the game and watch as their opponents received psychological and material rewards. Results demonstrated that both the dynamics of the game and individual reactions to stress varied consistently as a function of the social context. Individuals displayed more assertive behaviors in groups than in dyads. In contrast, individuals exhibited more self,deprecating behaviors in dyads than in groups. Given that under naturalistic conditions males are more likely than are females to interact in groups and females are more likely than are males to interact in dyads, group size provides one possible mechanism for the development of sex differences in self,assertive versus self,deprecating behaviors. [source] Heterogeneity, Group Size and Collective Action: The Role of Institutions in Forest ManagementDEVELOPMENT AND CHANGE, Issue 3 2004Amy R. Poteete Collective action for sustainable management among resource-dependent populations has important policy implications. Despite considerable progress in identifying factors that affect the prospects for collective action, no consensus exists about the role played by heterogeneity and size of group. The debate continues in part because of a lack of uniform conceptualization of these factors, the existence of non-linear relationships, and the mediating role played by institutions. This article draws on research by scholars in the International Forestry Resources and Institutions (IFRI) research network which demonstrates that some forms of heterogeneity do not negatively affect some forms of collective action. More importantly, IFRI research draws out the interrelations among group size, heterogeneity, and institutions. Institutions can affect the level of heterogeneity or compensate for it. Group size appears to have a non-linear relationship to at least some forms of collective action. Moreover, group size may be as much an indicator of institutional success as a precondition for such success. [source] Cooperative Breeding and Group Structure in the Lake Tanganyika Cichlid Neolamprologus savoryiETHOLOGY, Issue 11 2005Dik Heg As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding cichlid Neolamprologus savoryi. Breeding groups typically consisted of a large breeding male with one to four breeding females and three to 33 helpers (mean group size: 14.3 members). Group size was significantly related to breeding male and female body sizes, and larger males had more breeding females and larger sized male helpers. The size of the largest female in the group was positively related to the number and sizes of secondary breeding females and female helpers. In case of multiple breeding females, these females usually divided the group's territory into sub-territories, each with its own helpers (subgroups). Interspersed between groups, independent fish were detected defending an individual shelter (4.4% of all fish). In 9% of the groups no breeding female was present. All group members participated in territory defence and maintenance, and showed submissive behaviours to larger group members. As expected, the level of between-subgroup conflicts was high compared with the level of within-subgroup conflicts. We compare these results with data available from other cooperatively breeding fishes. [source] Ethnophaulisms for ethnic immigrant groups: the contributions of group size and familiarityEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 3 2001Brian Mullen An archival analysis was conducted on the ethnophaulisms for ethnic immigrant groups as a function of the size and the familiarity of those groups. Cognitive representation was operationalized as the degree of complexity in, and the valence of, the ethnophaulisms applied to ethnic immigrant groups in the United States during each of 15 consecutive 10-year time periods. Group size was operationalized as the number of first-generation persons in these ethnic groups during each of these same 15 10-year time periods. Familiarity was operationalized in terms of the number of times each ethnic immigrant group was mentioned in social histories and popular songs for each of these same 15 10-year time periods. Ethnophaulisms for smaller groups tended to be less complex and more negative and ethnophaulisms for less familiar groups tended to be less complex and more negative. Analyses delineate the interrelations between ethnic immigrant group size, ethnic immigrant group familiarity, and the cognitive representations of these groups. The implications of these results for research on intergroup perceptions are discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens: a model for cooperatively breeding birds?JOURNAL OF ANIMAL ECOLOGY, Issue 3 2001Robert D. Magrath Summary 1,Many studies of cooperatively breeding birds have found no effect of group size on reproductive success, contrary to predictions of most adaptive hypotheses. A model is proposed for variation in group-size effects: group size has a reduced effect on success when conditions for breeding are good, such as in good environmental conditions or in groups with older breeders. This hypothesis is tested with a case study of white-browed scrubwrens Sericornis frontalis and a review of the literature. 2,The scrubwren is a cooperatively breeding passerine with male helpers. Previous analyses revealed no effect of group size on reproductive success, but those analyses were restricted to groups with older females (Magrath & Yezerinac 1997). Here 7 years' data are used to contrast the effect of group size on reproductive success for yearling and older females. 3,Yearling females breeding in groups had more than double the seasonal reproductive success than those breeding in pairs, even after controlling for territory quality. However, group size still had no effect on the reproductive success of older females. Yearling females tended to survive better in groups, but older females tended to survive better in pairs, emphasizing this pattern. 4,Yearlings breeding in pairs were more likely to be found on poor-quality territories than those breeding in groups, exaggerating the already-strong effect of group size on yearling success. Older females were not affected significantly by territory quality. 5,Group size, territory quality and female age affected different components of seasonal reproductive success. Group size increased the success of individual nesting attempts, while both territory quality and female age affected the length of the breeding season, and thus the number of breeding attempts. 6,A sample of the literature on cooperative breeders shows that group size has a larger effect on reproductive success in poorer conditions, caused either by younger, inexperienced breeders or poorer environmental conditions. Scrubwrens therefore illustrate a widespread pattern, which provides an explanation for much of the variation in group-size effects among and within species. Clearly single estimates of group-size effects for species can be inadequate to test ideas about the evolution of cooperative breeding. [source] Mexican Jay social group size varies with habitat in northeastern MexicoJOURNAL OF FIELD ORNITHOLOGY, Issue 2 2006Nirmal K. Bhagabati ABSTRACT We evaluated the hypothesis that social group size in Mexican Jays (Aphelocoma ultramarina) varies with habitat structure. We counted the social group size of Mexican Jays over a range of elevations and forest types in a single mountain range in northern Mexico (Sierra El Carmen, Coahuila). Group size increased significantly with elevation, in contrast to a population of Mexican Jays in Arizona that showed no such trend in another study. Among the vegetation variables measured, those relating to size of pines and oaks were especially important in explaining variation in group size. Because acorns and pine nuts are a major part of the diet of Mexican Jays, sites with larger oaks and pines may produce larger nut crops and support larger groups of jays. Elevation did not significantly explain variance in group size after taking vegetation into account. We compared group size and habitat variation across different parts of the geographic range of Mexican Jays. Our analysis indicates that variation of social group size in Mexican Jays is influenced by habitat quality at both local and geographic scales. Detailed studies on habitat structure and demographics of this population are needed to further clarify aspects of habitat quality important to these jays, and the mechanisms by which variation in social structure is maintained. SINOPSIS Evaluamos la hipótesis en donde se indica que el tamaño de los grupos en el Azulejón Mexicano (Aphelocoma ultramarina) varía con la estructura del hábitat. Determinamos el tamaño del grupo social a través de elevaciones variadas y tipos de bosques a lo largo de una cordillera en la Sierra El Carmen, Coahuila, del norte de México. El tamaño del grupo incremento significativamente con la elevación, en contraste con una población de azulejones estudiada en Arizona. Entre las variables medidas en la vegetación, encontramos unas relacionadas al tamaño de los pinos y los robles que fueron especialmente importante en la explicación del tamaño de los grupos. Dado el caso de que las semillas y nueces son un componente principal en la dieta de las aves, los lugares con árboles de mayor tamaño pudieran producir más alimento y a su vez sostener grupos mayores de azulejones. La elevación no explicó significativamente la variación en el tamaño de los grupos, una vez incluido en el análisis la vegetación. Comparamos tamaño de grupos y la variación en hábitat a través de diferentes partes de la distribución geográfica del ave. Nuestro análisis indica que la variación de tamaño de los grupos esta influenciada por la calidad del hábitat tanto al nivel local como geográfico. Estudios detallados en la estructura del hábitat y estudios demográficos son necesarios para determinar el mecanismo a través del cual se mantiene la variación en grupos. [source] Socioecological correlates of facial mobility in nonhuman anthropoidsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009Seth D. Dobson Abstract Facial mobility, or the variety of facial movements a species can produce, is likely influenced by selection for facial expression in diurnal anthropoids. The purpose of this study is to examine socioecological correlates of facial mobility independent of body size, focusing on social group size and arboreality as possible evolutionary agents. Group size was chosen because facial expressions are important for group cohesion, while arboreality may limit the utility of facial expressions. Data for 12 nonhuman anthropoid species were taken from previous studies and analyzed using a phylogenetic generalized least-squares approach. Regression results indicate that group size is a good predictor of facial mobility independent of body size. No statistical support was found for the hypothesis that arboreality constrains the evolution of facial mobility. The correlation between facial mobility and group size may be a consequence of selection for more effective facial expression to help manage conflicts and facilitate bonding in larger groups. These findings support the hypothesis that the ultimate function of facial expression is related to group cohesion. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] Geographic distribution and demography of Pithecia aequatorialis (pitheciidae) in Peruvian AmazoniaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 12 2009Rolando Aquino Abstract To study the geographic distribution and demographic characteristics of Pithecia aequatorialis in Peruvian Amazonia, we undertook surveys and transect census in three river basins (Río Itaya, Río Tigre and Río Curaray) between 2004 and 2008. A total of 123 groups of P. aequatorialis was encountered during 1623,km of transect walks. Group size was uniform among the three areas (3.4,3.6 individuals), but surprisingly, population densities were higher in the area with strong hunting pressure (Río Itaya: 7.8,ind./km2, vs. 5.6 and 5.9,km2 in the Río Tigre and Río Curaray basins, respectively). The most common group composition included an adult pair with one offspring. Groups with more than one adult male and/or female accounted for 35% of sightings. Our observations extend P. aequatorialis range in Peru further south to the area between the Río Tigre and Río Corrientes, but exclude the area to the north between the Río Curaray and Río Napo. These findings are in contrast to previous distribution maps. P. aequatorialis was rarely seen in interspecific association during our censuses. Am. J. Primatol. 71:964,968, 2009. © 2009 Wiley-Liss, Inc. [source] Habitat fragmentation and population size of the black and gold howler monkey (Alouatta caraya) in a semideciduous forest in Northern ArgentinaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 9 2007Gabriel E. Zunino Abstract A population of black and gold howler monkeys (Alouatta caraya) living near the southern limit of its distribution in a semideciduous forest located in northern Argentina was studied in 2003 to evaluate the possible effects of habitat fragmentation , owing to logging , on its density and social organization within it. Aerial photographs taken in 1982, 1992, and 2001 were used to compare maps of vegetation. These maps were used to evaluate changes in the area covered by forest fragments. From March to June 2003, 10-day monthly surveys of howlers were made in each fragment. A total of 232 individual howlers were counted, belonging to 34 groups plus a solitary adult female. Groups ranged from 2 to 19 individuals (mean = 6.82, SD = 4.23), and 21% of the groups contained more than one adult male. Adults accounted for 55% of the individuals, immatures for 45%, and infants represented 13% of the total. Data obtained were compared with information available for the same population for 1982 and 1995. Results revealed no significant changes in the area of fragments, the crude and ecological density of howlers, and group composition. Group sizes and group composition of howlers suggest that the population remained stable over the past 22 years. The density, number of groups, and individuals appears not to be affected by fragmentation and logging, but crude density was low compared with other less-disturbed habitats. The status of the population remains uncertain owing to isolation, and because there are no protected areas to ensure its stability for the future. Am. J. Primatol. 69:966,975, 2007. © 2007 Wiley-Liss, Inc. [source] Noninvasive Stress and Reproductive Measures of Social and Ecological Pressures in Free-Ranging African ElephantsCONSERVATION BIOLOGY, Issue 4 2001C. A. H. Foley This, coupled with political pressures to delist the elephant, has created a need for noninvasive physiological measures that can quantify the long-term effects of past mortality patterns of this long-lived species. We collected fresh fecal samples from 16 female elephants in three different groups over 23 months at Tarangire National Park, Tanzania, and analyzed them for fecal progesterone and cortisol metabolites. Social and ecological measures were collected concurrently. Fecal progesterone metabolite measures corresponded significantly with stage of gestation, and appear to be able to confirm pregnancy in female elephants from as early as 3 months of gestation. We found that progesterone metabolite concentrations were significantly lower during the dry season than during the wet season after controlling for stage of gestation. Fecal cortisol metabolite concentrations showed the opposite seasonal pattern, being significantly higher in the dry season and inversely correlated with rainfall across seasons. Fecal cortisol metabolite concentrations also increased with group size and were correlated positively with dominance rank in the largest group. Our results suggest that measures of progesterone and cortisol metabolites in feces provide indices of reproductive function and physiological stress that can quantify both natural and human disturbances in African elephants. These measures are ideally suited for monitoring the long-term effects of social disruption from poaching and a variety of other management concerns. Resumen: Debido a la cacería furtiva, la población de elefante africano ( Loxodonta africana) declinó en un 60%, principalmente adultos, entre 1979 y 1988. Esto, aunado a presiones políticas para eliminar al elefante de las listas de especies en peligro, ha creado la necesidad de medidas fisiológicas no invasivas que puedan cuantificar efectos a largo plazo de patrones de mortalidad en el pasado de esta especie longeva. Recolectamos muestras fecales de 16 elefantes hembras en tres grupos diferentes en el Parque Nacional Tarangire, Tanzania a lo largo de 23 meses, y las analizamos para detectar metabolitos de progesterona fecal y de cortisol. Al mismo tiempo se recolectaron medidas sociales y ecológicas. Las medidas de metabolitos de progesterona fecal correspondieron significativamente con la etapa de gestación, y parecen permitir la confirmación de preñez en elefantes hembras tan temprano como a los tres meses de gestación. Las concentraciones de metabolitos de progesterona fueron significativamente menores durante la época de sequía que en la de lluvias después de controlar para la etapa de gestación. Las concentraciones de metabolitos de cortisol fecal mostraron un patrón estacional opuesto, siendo significativamente más altas en la época de sequía e inversamente correlacionados con la precipitación en todas las estaciones. Las concentraciones de metabolitos de cortisol fecal también incrementaron con el tamaño del grupo y se correlacionaron positivamente con el rango de dominancia en el grupo más grande. Nuestros resultados sugieren que las medidas de metabolitos de progesterona y cortisol en las heces proporcionan índices de la función reproductiva y del estrés fisiológico que puede cuantificar perturbaciones, tanto naturales como humanas, en elefantes africanos. Estas medidas son idealmente adecuadas para monitorear efectos a largo plazo de la disrupción social por la cacería furtiva y así como una variedad de aspectos del manejo. [source] Heterogeneity, Group Size and Collective Action: The Role of Institutions in Forest ManagementDEVELOPMENT AND CHANGE, Issue 3 2004Amy R. Poteete Collective action for sustainable management among resource-dependent populations has important policy implications. Despite considerable progress in identifying factors that affect the prospects for collective action, no consensus exists about the role played by heterogeneity and size of group. The debate continues in part because of a lack of uniform conceptualization of these factors, the existence of non-linear relationships, and the mediating role played by institutions. This article draws on research by scholars in the International Forestry Resources and Institutions (IFRI) research network which demonstrates that some forms of heterogeneity do not negatively affect some forms of collective action. More importantly, IFRI research draws out the interrelations among group size, heterogeneity, and institutions. Institutions can affect the level of heterogeneity or compensate for it. Group size appears to have a non-linear relationship to at least some forms of collective action. Moreover, group size may be as much an indicator of institutional success as a precondition for such success. [source] Predicting global abundance of a threatened species from its occurrence: implications for conservation planningDIVERSITY AND DISTRIBUTIONS, Issue 1 2009Marcos S. L. Figueiredo Abstract Aim, Global abundance is an important characteristic of a species that is correlated with geographical distribution and body size. Despite its importance these estimates are not available since reliable field estimates are either expensive or difficult to obtain. Based on the relationship between a species' local abundance and distribution, some authors propose that abundance can be obtained through spatial distribution data from maps plotted at different scales. This has never been tested over the entire geographical range of a species. Thus, the aim of this study was to estimate global abundance of the Neotropical primate Brachyteles hypoxanthus (northern muriqui) and compare the results with available field estimates. Location, From southern Bahia to Minas Gerais and Espírito Santo states, in the Brazilian Atlantic rain forest. Methods, We compiled 25 recent occurrence localities of B. hypoxanthus and plotted them in grid cells of five different sizes (1, 25, 50, 75 and 100 km per side) to evaluate the performance and accuracy of abundance estimates over a wide range of scales. The abundance estimates were obtained by the negative binomial distribution (NBD) method and corrected by average group size to take into account primate social habits. To assess the accuracy of the method, the predicted abundances were then compared to recent independent field estimates. Results, The NBD estimates were quite accurate in predicting B. hypoxanthus global abundance, once the gregarious habits of this species are taken into account. The predicted abundance estimates were not statistically different from those obtained from field estimates. Main conclusions, The NBD method seems to be a quick and reliable approach to estimate species abundance once several limiting factors are taken into account, and can greatly impact conservation planning, but further applications in macroecological and ecological theory testing needs improvement of the method. [source] Aggression in imported fire ants: an explanation for shifts in their spatial distributions in Southern United States?ECOLOGICAL ENTOMOLOGY, Issue 4 2009HENRY Y. FADAMIRO Abstract 1.,The imported fire ants, Solenopsis invicta Buren (red), S. richteri Forel (black), and their hybrids (S. invicta × S. richteri) are sympatric congeners with overlapping but shifting spatial distributions in northern Alabama and Mississippi, United States. 2.,The abilities of workers of the three ant forms (or species) to recognise non-nestmate conspecifics and heterospecifics were compared in separate aggression bioassays using three group sizes of competitor numbers (battles): 1-1, 5-1, and 5-5 resident,intruder battles. 3.,Workers of all three forms showed significant aggression toward non-nestmate conspecifics and heterospecifics. The results of the intra-specific aggression bioassays showed that S. invicta had the lowest aggression threshold, whereas S. richteri was the least aggressive. Survival rates 1 day after intra-specific encounters were higher for S. richteri than for S. invicta or hybrids, consistent with its lower aggressiveness. 4.,In inter-specific interactions, S. invicta workers showed the greatest aggression and were more aggressive towards S. richteri than to hybrids. Furthermore, survival 1 day after inter-specific encounters was highest for S. invicta workers, whether they were the intruders or residents. The hybrid form was intermediate between both parental forms in aggression and post-aggression survival. 5.,The live 1-1 and 5-5 battles produced similar and consistent results, but differences were amplified in the 5-5 battles, suggesting an effect of group size on aggression. These results may explain the observed shifts in the spatial distributions of the three forms and range restriction of S. richteri in southern United States. [source] Life-history, genotypic, and environmental correlates of clutch size in the Glanville fritillary butterflyECOLOGICAL ENTOMOLOGY, Issue 2 2007MARJO SAASTAMOINEN Abstract 1.,Glanville fritillary butterfly (Melitaea cinxia) females lay up to 10 clutches of 50,300 eggs in their lifetime. Clutch size is an important life-history trait as larval group size affects survival throughout larval development. 2.,Two experiments were carried out in a large population cage in the field to investigate the life-history and environmental correlates of clutch size. 3.,Clutch size decreased with the cumulative number of eggs laid previously, increased with both female body weight and the number of days between consecutive clutches. 4.,Genotypic differences among females in the glycolytic enzyme phosphoglucose isomerase had a significant influence on clutch size, partly because females of particular genotypes were able to initiate oviposition earlier in the day and thereby take advantage of the most favourable environmental conditions for oviposition. 5.,Factors influencing clutch size were partly different in two summers, indicating the modulating effect of prevailing environmental conditions on reproductive performance. [source] No Plastic Responses to Experimental Manipulation of Sperm Competition per se in a Free-Living FlatwormETHOLOGY, Issue 4 2010Peter Sandner In the absence of sperm competition evolutionary theory predicts low mating rates and low ejaculate expenditure per mating, and sex allocation theory for simultaneous hermaphrodites predicts a strongly female-biased sex allocation. In the presence of sperm competition a shift towards a more male-biased sex allocation and a higher ejaculate expenditure are predicted. The free-living flatworm Macrostomum lignano has been shown to respond plastically in mating rate, testis size, and sperm transfer to manipulation of the social group size, a proxy of the strength of sperm competition. However, manipulation of social group size may manipulate not only sperm competition, but also other factors, such as food supply and metabolite concentration. In this study we therefore manipulated sperm competition per se by repeatedly exposing individuals to partners that have either mated with rivals or not, while keeping the social group size constant. Our results suggest that M. lignano does not have the ability to detect sperm competition per se, as worms experimentally exposed to the presence or absence of sperm competition did not differ in sex allocation, sperm transfer or mating behavior. A response to our manipulation would have required individual recognition, the ability to detect self-referencing tags, or tags or traces left by rivals on or in the mating partners. We first discuss the possibility that highly efficient sperm displacement may have decreased the difference between the treatment groups and then propose three alternative cues that may allow M. lignano to respond plastically to the social group size manipulation used in earlier studies: assessment of the mating rate, chemical cues, or tactile cues. [source] Scent-Marking of Giant Otter in the Southern Pantanal, BrazilETHOLOGY, Issue 3 2009Caroline Leuchtenberger Giant otters live in social groups, consisting of a mating pair and one or two litters. Groups are territorial and mark their territories often with scent-marks. Our objectives were to evaluate the frequencies of marking and over-marking according to the social status of the individuals and to define the different postures used during the marking. We observed four groups, totaling 25 individuals (five alpha males, four alpha females, seven adult females, one adult male and eight juveniles) with group size ranging between four and 13 individuals. The study was conducted between July 2006 and July 2007 in the Vermelho River and in a stretch of the Miranda River, in the Southern Pantanal. We observed the groups for a total of 2006 min and recorded 95 events of marking totaling 84.9 min. Time spent marking varied between groups and ranged from 4.3 to 44.7 min. The alpha males marked more frequently (62% of marking events, 55 min) than the alpha females (17% of marking events, 13.6 min). Of the 59 events of scent-marking by the alpha males, 32 over-marked the marks of other individuals from the group. Of the 16 events of scent-marking of the alpha females, five over-marked that of other females from the same group. When scent-marking, alpha males used the ,stepping' posture most frequently (63%), then ,fore-paw rubbing' (24%), ,latrine use' (7%), and ,body rubbing' (6%). Alpha females used the ,stepping' posture most frequently (65%), then ,latrine use' (19%) and ,fore-paw rubbing' (12%), with only one event of ,body rubbing' observed during marking. Subordinate females used the ,stepping' posture (76%) and ,latrine use' (24%) during marking. Scent-marking can play many roles in mammals and for giant otters, and the main roles appear to be communication of social and sexual status and territorial defense. [source] Cooperative Breeding and Group Structure in the Lake Tanganyika Cichlid Neolamprologus savoryiETHOLOGY, Issue 11 2005Dik Heg As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding cichlid Neolamprologus savoryi. Breeding groups typically consisted of a large breeding male with one to four breeding females and three to 33 helpers (mean group size: 14.3 members). Group size was significantly related to breeding male and female body sizes, and larger males had more breeding females and larger sized male helpers. The size of the largest female in the group was positively related to the number and sizes of secondary breeding females and female helpers. In case of multiple breeding females, these females usually divided the group's territory into sub-territories, each with its own helpers (subgroups). Interspersed between groups, independent fish were detected defending an individual shelter (4.4% of all fish). In 9% of the groups no breeding female was present. All group members participated in territory defence and maintenance, and showed submissive behaviours to larger group members. As expected, the level of between-subgroup conflicts was high compared with the level of within-subgroup conflicts. We compare these results with data available from other cooperatively breeding fishes. [source] Vocalizations of Amazon River Dolphins, Inia geoffrensis: Insights into the Evolutionary Origins of Delphinid WhistlesETHOLOGY, Issue 7 2002Jeffrey Podos Oceanic dolphins (Odontoceti: Delphinidae) produce tonal whistles, the structure and function of which have been fairly well characterized. Less is known about the evolutionary origins of delphinid whistles, including basic information about vocal structure in sister taxa such as the Platanistidae river dolphins. Here we characterize vocalizations of the Amazon River dolphin (Inia geoffrensis), for which whistles have been reported but not well documented. We studied Inia at the Mamirauá Sustainable Development Reserve in central Brazilian Amazônia. During 480 5-min blocks (over 5 weeks) we monitored and recorded vocalizations, noted group size and activity, and tallied frequencies of breathing and pre-diving surfaces. Overall, Inia vocal output correlated positively with pre-diving surfaces, suggesting that vocalizations are associated with feeding. Acoustic analyses revealed Inia vocalizations to be structurally distinct from typical delphinid whistles, including those of the delphinid Sotalia fluviatilis recorded at our field site. These data support the hypothesis that whistles are a recently derived vocalization unique to the Delphinidae. [source] Anti-Predator Strategies and Grouping Patterns in White-Tailed Deer and Mule DeerETHOLOGY, Issue 4 2001Susan Lingle White-tailed deer (Odocoileus virginianus) and mule deer (O. hemionus) are closely related species of similar size that differ in their anti-predator behavior. White-tails flee from coyotes (Canis latrans), whereas mule deer typically stand their ground and attack this predator. I used observations of coyotes hunting deer to identify: (i) changes in group structure made in response to coyotes; and (ii) the relationship between group structure and the risk of predation for each species. In response to coyotes, groups of mule deer merged with other groups and individuals bunched together. Predation attempts were more likely to escalate when groups split and individuals failed to bunch. Coyotes typically attacked mule deer that were in outlying positions, and these deer had to move to central positions to end attacks. Due to the high frequency of attacks on small groups as well as to the level of dilution of risk, individuals in small mule deer groups were at high risk of being attacked compared with those in larger groups. In contrast to mule deer, white-tails made no consistent changes in group size or formation, and coyotes attacked individuals in central as well as in outlying positions. Variation in aspects of group cohesion was not related to the vulnerability of white-tails, and there was no obvious difference in the risk of attack facing individuals in groups of different size. These results suggest that coyote predation selects for relatively large, cohesive groups in mule deer, apparently because this type of group improves their ability to deter coyotes. Coyote predation does not have similar effects on groups formed by white-tails, which use flight rather than deterrence to avoid predation. The benefits of responding cohesively, occupying certain positions within groups, and forming groups of a certain size can vary widely depending on the anti-predator strategies used by an animal. [source] Detection and Avoidance of Predators in White-Tailed Deer (Odocoileus virginianus) and Mule Deer (O. hemionus)ETHOLOGY, Issue 2 2001Susan Lingle In this paper, we investigate the relationship between early detection of predators and predator avoidance in white-tailed deer (Odocoileus virginianus) and mule deer (O. hemionus), two closely related species that differ in their habitat preferences and in their anti-predator behavior. We used observations of coyotes (Canis latrans) hunting deer to test whether the distance at which white-tails and mule deer alerted to coyotes was related to their vulnerability to predation. Coyote encounters with both species were more likely to escalate when deer alerted at shorter distances. However, coyote encounters with mule deer progressed further than encounters with white-tails that alerted at the same distance, and this was not due to species differences in group size or habitat. We then conducted an experiment in which a person approached groups of deer to compare the detection abilities and the form of alert response for white-tails and mule deer, and for age groups within each species. Mule deer alerted to the approacher at longer distances than white-tails, even after controlling for variables that were potentially confounding. Adult females of both species alerted sooner than conspecific juveniles. Mule deer almost always looked directly at the approacher as their initial response, whereas white-tails were more likely to flee or to look in another direction with no indication that they pinpointed the approacher during the trial. Mule deer may have evolved the ability to detect predators earlier than white-tails as an adaptation to their more open habitats, or because they need more time to coordinate subsequent anti-predator defenses. [source] Defence of Females by Dominant Males of Artibeus jamaicensis (Chiroptera: Phyllostomidae)ETHOLOGY, Issue 5 2000Jorge Ortega Defence of females by dominant males of the Jamaican fruit-eating bat Artibeus jamaicensis was observed in two natural colonies over 2 yr. A log-linear model was used to evaluate the frequency distribution of visits to harems by sex, season and agonistic interaction of dominant males. Harem group size varied from four to 18 females, with one adult male in the small and medium-sized groups and two males in the large groups (> 14 females). A highly significant interaction was noted between the age and sex of the visitor and the response of the dominant male. Male visitors were attacked more often than female and juvenile visitors. Aggressive defence increased during the reproductive seasons, with dominant males showing more agonistic responses towards male visitors. An increase in the frequency of visits by male visitors was noted in harem groups that ranged in size from four to 12 females, but the frequency of male visits declined in harem groups that contained more than 14 females. [source] The extent of dissent: The effect of group composition and size on Israeli decisions to confront low intensity conflictEUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 4 2002Ranan D. Kuperman This article tests a number of hypotheses about foreign policy decision making within parliamentary democracies. First it explores the origins of debates among decision-makers. Are deliberations provoked by alternative organizational perspectives or by conflicting ideological orientations? Second, it asks how debates are resolved. On the one hand, it has been suggested that, because each minister has an equal vote, a compromise between decision-makers must be reached. On the other hand, it has been argued that the Prime Minister exerts considerable control and power in foreign policy matters in relation to other decision-makers. These questions were studied with the aid of data collected from a sample of 97 decision episodes between 1949 and 1982, where the Israeli government discussed how to respond to low-intensity aggression against Israeli citizens and soldiers. The results of this research demonstrate that internal debates are poorly associated with organizational or political diversity. Instead group size seems to be more important, although the relationship is not linear. In any case, the discussions usually concluded in a consensus around the Prime Minister's policy of choice, thus indicating that he or she is the paramount decision-maker. [source] Informational intra-group influence: the effects of time pressure and group sizeEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 1 2008Bryan L. Bonner The judgments of groups have immense impact on our daily lives. This paper theorizes that three families of intra-group influence affect the collective estimation process. These different forms of influence map to different levels of task demonstrability, or the extent to which correct answers are transparent to problem-solvers. When demonstrability is low, group estimates are disproportionately influenced by proposals closer to the intra-group mean (centrality). When demonstrability is high and groups are small, group decisions are disproportionately influenced by proposals closer to the correct answer (accuracy). Finally, when demonstrability is high and groups are larger, group decisions are disproportionately influenced by proposals offered by generally more accurate individuals across a set of judgments (expertise). Three laboratory studies support our predictions with regard to informational influence in cooperative groups. Copyright © 2006 John Wiley & Sons, Ltd. [source] Ethnophaulisms for ethnic immigrant groups: the contributions of group size and familiarityEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 3 2001Brian Mullen An archival analysis was conducted on the ethnophaulisms for ethnic immigrant groups as a function of the size and the familiarity of those groups. Cognitive representation was operationalized as the degree of complexity in, and the valence of, the ethnophaulisms applied to ethnic immigrant groups in the United States during each of 15 consecutive 10-year time periods. Group size was operationalized as the number of first-generation persons in these ethnic groups during each of these same 15 10-year time periods. Familiarity was operationalized in terms of the number of times each ethnic immigrant group was mentioned in social histories and popular songs for each of these same 15 10-year time periods. Ethnophaulisms for smaller groups tended to be less complex and more negative and ethnophaulisms for less familiar groups tended to be less complex and more negative. Analyses delineate the interrelations between ethnic immigrant group size, ethnic immigrant group familiarity, and the cognitive representations of these groups. The implications of these results for research on intergroup perceptions are discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] PROMISCUITY AND THE RATE OF MOLECULAR EVOLUTION AT PRIMATE IMMUNITY GENESEVOLUTION, Issue 8 2010Gabriela Wlasiuk Recently, a positive correlation between basal leukocyte counts and mating system across primates suggested that sexual promiscuity could be an important determinant of the evolution of the immune system. Motivated by this idea, we examined the patterns of molecular evolution of 15 immune defense genes in primates in relation to promiscuity and other variables expected to affect disease risk. We obtained maximum likelihood estimates of the rate of protein evolution for terminal branches of the primate phylogeny at these genes. Using phylogenetically independent contrasts, we found that immunity genes evolve faster in more promiscuous species, but only for a subset of genes that interact closely with pathogens. We also observed a significantly greater proportion of branches under positive selection in the more promiscuous species. Analyses of independent contrasts also showed a positive effect of group size. However, this effect was not restricted to genes that interact closely with pathogens, and no differences were observed in the proportion of branches under positive selection in species with small and large groups. Together, these results suggest that mating system has influenced the evolution of some immunity genes in primates, possibly due to increased risk of acquiring sexually transmitted diseases in species with higher levels of promiscuity. [source] | |||||||||||||||||||||||||||||||||||||