Contest Competition Research Articles

Female-Female Competition in Bornean Orangutans

The mostly solitary ranging of orangutans and the large areas over which they traverse have hampered quantification of Bornean orangutan ranging patterns and feeding competition. Because of their semisolitary existence, female orangutans have few competitive interactions among themselves. However, contest and scramble types of competition occur, and researchers consider both to be important for the species. Using 9 yr of data and >22,300 h of observation of adult female orangutans in Gunung Palung National Park in Indonesian Borneo, we examined both forms of competition. Based on our analyses, we have 4 conclusions: 1) Adult female orangutans have highly overlapping home ranges, and thus there is potential for scramble competition to impose a cost. 2) Adult female orangutans actively avoid each other, suggesting that scramble competition indeed imposes a cost. 3) Adult females have distinct core areas that overlap to a lesser degree than home ranges do. 4) Analyses of contest competition reveal a slight spatial component to female competition for the first time. Preliminary evidence for core area defense and passive range exclusion may be among the mechanisms responsible for maintaining distinct adult female core areas.

Mating strategies and aggressive combat in wingless neotropical fig wasp males

The aim of this work was to study the wingless males of pollinating (Pegoscapus tonduzi) and two nonpollinating fig wasp species, genus Idarnes, associated with figs (Ficus citrifolia) in Brazil to answer the following questions: 1) Do wingless males of Idarnes spp. and P. tonduzi show different male-male competition strategies?; and, 2) Do the injury within-species variables correlate with fig/population features? Consistently higher injury levels were observed in the two species of Idarnes than in the pollinator species. The results suggested that aggressive confrontations were involved in the mating strategies of Idarnes, whereas non-aggressive strategies were shown by males of P. tonduzi. Generally, injury variables in Idarnes spp. correlated positively with the male encounter rate and negatively with the fig size, thus supporting the contest competition theory. The results pointed out that different species under similar local conditions might follow distinct evolutionary histories. Within species, natural-history particularities might have some influence upon quantified injury levels in wingless males.

Feeding Competition and Agonistic Relationships Among Bwindi Gorilla beringei

Testing predictions of socioecological models, specifically that the types of feeding competition and social relationships female primates exhibit are strongly influenced by the distribution, density, and quality of food resources, requires studies of closely related populations of subjects living under different ecological conditions. I examined feeding competition and the resulting female social relationships in mountain gorillas (Gorilla beringei beringei) of Bwindi Impenetrable National Park, Uganda, which has ecological conditions distinctive from those where other gorilla populations live. I observed 1 group of gorillas for 29 mo to examine the proportion of time spent foraging on fruit, the relationship between patch size and occupancy patterns of fruit trees, and agonistic interactions. Patch occupancy time while foraging in fruit trees decreased with increasing number of gorillas in a tree and decreasing tree size, suggesting that fruit trees represent limiting patches and can lead to intragroup scramble competition. Gorillas exhibited higher levels of aggression while feeding on fruit versus other food resources, which indicates intragroup contest competition. I observed a linear dominance hierarchy with no bidirectionality via displacements, and a similar hierarchy via aggression, though a notable proportion of the dyads contained 2-way interactions. However, most aggression was of low intensity (vocalizations) and the recipient typically ignored it. Despite differences in ecological conditions and diet between the Virunga Volcanoes and Bwindi, agonistic relationships among females are largely similar in the 2 populations and are best characterized as dispersal individualistic.

Female Competition over Core Areas in Pan troglodytes schweinfurthii, Kibale National Park, Uganda

Aggression is rare among wild female chimpanzees. However, in the Kanyawara chimpanzee community in Kibale National Park, Uganda, stable use of food-rich core areas is linked to increased reproductive success, suggesting that contest competition might occur over access to the highest-quality ranges. To examine this hypothesis, we studied aggression and dominance relationships among Kanyawara females during a 10-yr period that included the immigration of 5 females into the community. We tested 2 predictions: 1) that female-female aggression should intensify when immigrants enter the community because this is when core area access is determined and 2) that the quality of core areas should reflect relative female dominance relationships. In support of the first prediction, female-female aggression increased 4-fold when new immigrants were in the community, with rates peaking when there were multiple immigrants. This pattern was due primarily to aggression by resident mothers toward immigrants and featured coalitionary aggression, a rare behavior among female chimpanzees. In support of the second prediction, females occupying core areas high in foraging quality ranked high overall and higher than expected for their ages, whereas females occupying low-quality core areas were lower-ranking and ranked lower than expected for their ages. Together, the data indicate that though female aggression does not regularly occur in chimpanzees, contest competition continues to play an important role in determining long-term access to resources, an important correlate of reproductive success.

Simultaneous polyandry increases fertilization success in an African foam-nesting treefrog

In many animals females mate with multiple males during a single breeding season (polyandry), but the benefits of this mating system remain poorly understood. One hypothesis is that polyandry ensures the fertilization of a female's ova (fertilization insurance hypothesis). We tested the fertilization insurance hypothesis in a natural population of African foam-nesting treefrogs, Chiromantis xerampelina, a species lacking male contest competition and in which females routinely mate with multiple males. We observed matings involving from one to 12 males and found that fertilization success was positively correlated with the number of mating males, but was unaffected by variance in clutch size or ambient temperature. Variance in fertilization success was also unrelated to the body size ratio of mating pairs. Critically, females that mated with more males also produced more tadpoles. These findings provide the first evidence that polyandry can benefit female frogs by increasing fertilization success and offspring production. We propose that fertilization insurance may account for the high incidence of simultaneous polyandry in frog species that use foam nests during breeding.

A paradox in discrete single species population dynamics with harvesting/thinning

We analyze a general time-discrete mathematical model of single species population dynamics with the intraspecific density effect and the harvesting/thinning effect. We harvest a portion of the population at a moment in each year. We investigate the condition under which the harvesting/thinning causes an eventual increase of its population at the equilibrium, and show that such a paradoxical increase could occur for the discrete single species population dynamics with a large family of density effect functions. Some typical models are analyzed in detail according to the possibility of the paradox emergence. Our result implies that the contest competition would never cause the paradox, while the scramble competition would be likely to cause it.

Formal submission, tolerance and socioecological models: a test with female Hanuman langurs

Patterns of agonistic relationships among group-living mammalian females are suggested to reflect differences in feeding competition. Socioecological models predict that within-group contest (WGC) competition leads to despotic relationships that are linear, consistent, and stable, in which subordinate individuals use formal submission to acknowledge rank. Between-group contest (BGC) competition and risk of infanticide are predicted to add tolerance, as evidenced by frequent reconciliation, low-intensity aggression and counteraggression. We examined the predicted effects for formal submission and two criteria of tolerance for a group of Hanuman langurs ( Semnopithecus entellus ) in a population known to experience WGC and BGC as well as high rates of infanticide. Results were based on focal animal sampling of eight of 13 adult females (419 h) and ad libitum sampling of all 13 females (711 contact hours) in the group Kailana I (Jodhpur, India). The behaviour ‘presenting’ ( N = 281) qualified as formal submission, adhering to most proposed criteria (e.g. linear, consistent, predictive of other agonistic relationships and hierarchies, 40.9% spontaneous). Thus, regarding formal submission, the predicted effects of WGC hold, and support the explanatory value of this aspect of socioecological models. In contrast, agonistic relationships were nontolerant, with frequent high-intensity aggression (48.9% of N = 231) and almost no counteraggression (

Invasion under a trade‐off between density dependence and maximum growth rate

AbstractThe invasion of alien species and genotypes is an increasing concern in contemporary ecology. A central question is, what life‐history traits enable invasion amidst populations of wild species and conventional cultivars? In order to invade, the initially rare species must perform better than their resident competitors. We conducted a mathematical analysis and simulation of a two‐species extension of the Maynard Smith and Slatkin model for population dynamics in discrete time to study the role of density dependence as different types of competition in the invasion of new species. The type of density dependence ranged from scramble to contest competition. This led to intrinsic dynamics of the species range from point equilibrium to cycles and chaos. The traits were treated either as free parameters or constrained by a trade‐off resulting from a common fixed strength of density dependence or equilibrium density. Resident and intruder traits had up to ten‐fold differences in all of the parameters investigated. Higher equilibrium density of the intruder allowed invasion. Under constrained equilibrium density, an intrinsically stable intruder could invade an unstable resident population. Scramble competition made a population more susceptible to invasion than contest competition (e.g., limitation by light or territory availability). This predicts that a population which is mainly limited by food (or nutrients in plants) is more likely to be invaded than a population limited by a hierarchical competition, such as light among plants. The intruder population may have an effect on the resident population's dynamics, which makes the traditional invasion analysis unable to predict invasion outcome.

Punishment and competition over food in captive rhesus macaques, Macaca mulatta

Current socioecological models predict that clumped food resources influence aggression, yet definitions of clumped resources often include two concepts: time spent at the resource and distance between resources. To disentangle these two aspects of clumping, we conducted an experiment on 15 multimale–multifemale groups (range 50–110 individuals) of captive rhesus macaques at the California National Primate Research Center in which we varied both food size and interfood distance independently to test which factor more significantly influenced two forms of feeding competition, contest competition and punishment. At interfood distances of 1–6 m, two same-sized apple pieces of 1 g, 5 g, 15 g or 30 g were offered to the monkeys simultaneously during each of 297 trials. Aggression was recorded 5 min before the arrival of the food, when the food arrived and 5 min after. Results of the independent effects of food size revealed that larger food size was significantly associated with both contest competition and punishment. Interfood distance was not significantly associated with either contest competition or punishment. These results suggest that the size or handling time of food may be a better predictor of within-group aggression than is the spatial distribution of food.

Male reproductive skew, paternal relatedness, and female social relationships

Female social relationships among primates are thought to be shaped by socio-ecological factors and phylogenetic constraints. We suggest that patterns of paternal relatedness among females influence measures of social tolerance that have been used to classify species into different social relationship categories. As kin support and kin preference have only been measured for matrilineal kin and related individuals exchange less aggression and have a higher conciliatory tendency, the observed low nepotism levels and high tolerance levels may be an artifact of hidden paternal relatedness among the nonkin category. Using comparative data on macaques, we investigate this hypothesis using male reproductive skew as a proxy for paternal relatedness. Within the limitations of the study we show that populations classified as being less nepotistic, and more tolerant exhibit higher levels of reproductive skew. This first result and the reasoning behind may motivate future students of social relationships to take paternal relatedness into consideration. Potential implications of this finding if repeated with larger samples include that variation in aspects of macaque social relationships may be explained without considering phylogeny or the strength of between-group contest competition for food.

Competition between larvae in a butterfly Pieris napi and maintenance of different life‐history strategies

1. In scramble competition all individuals suffer equally from competition, whereas in contest competition some individuals outperform the others. Generally, larger individuals gain asymmetric advantage in competition over smaller ones. Given the positive correlation between age and size, asynchronous birth may result in asymmetric competition among juveniles. 2. In Pieris napi (Lepidoptera: Pieridae), reproductive rate is determined by the females' intrinsic mating tactic. The early reproductive rate is high in females with a low mating frequency and low in females with a high mating frequency, whereas lifetime fecundity shows the opposite pattern. Thus, offspring of monandrous females start to develop in relatively low densities and they are relatively large when the offspring of highly polyandrous females start to hatch. 3. The purpose of this study was to explore if asymmetry in larval competition could outweigh the late-life benefits of polyandry. In a laboratory experiment, P. napi larvae of different ages were reared together in different densities. 4. Increasing density decreased both larval survival and reachable pupal mass, but had no effect on duration of larval period. Younger larvae suffered from high mortality and reduced size compared with the older larvae. Mortality decreased in the older cohort with increasing age difference between the cohorts, and the reverse occurred in the younger cohort. Increasing age difference between the cohorts was associated with increase in pupal mass in both cohorts. All the variables showed a lot of variation between broods of different females. 5. The results suggest that polyandrous females, or more generally females with a low early reproductive rate, may lose a great proportion of their late-life benefits, which may partly explain the maintenance of polymorphism in reproductive strategies within species.

Aerial Contests, Sexual Selection and Flight Morphology in Solitary Pompilid Wasps

AbstractAerial contest competition has proven to be a challenging phenomenon to interpret in many territorial insects. Because the duels often consist of elaborate and/or high speed ascending maneuvers, the hypothesis that they are settled due to asymmetries in flight performance is intuitively appealing. We evaluated this hypothesis by contrasting differences in known morphological determinants of flight performance between (1) residents vs. non‐residents of the territorial wasp, Hemipepsis ustulata and between (2) H. ustulata vs. a non‐territorial relative, Pepsis thisbe. In the first contrast, resident male H. ustulata were seen to be larger, and had a tendency for reduced wing loading, but they did not possess greater flight musculature or wing aspect ratios (i.e., more elongated wings) than their non‐resident counterparts. In the second contrast, male H. ustulata exhibited clearly greater flight musculature and greater sexual dimorphism in this parameter (males more muscular), and also exhibited a slight tendency for greater wing loading and smaller aspect ratios than males of the patrolling species P. thisbe. Interestingly, although size is linked with territorial success in H. ustulata, males of this species were not larger than male P. thisbe, nor did the former species exhibit greater sexual size dimorphism. These results do not support the hypothesis that the repeated ascending contests of H. ustulata require, and select for, a high acceleration design. However, the observed intraspecific patterns of flight musculature suggest that high acceleration is favored in males of the perching species, perhaps for the ability to intercept passing receptive females.

Intragroup aggression, fission–fusion dynamics and feeding competition in spider monkeys

Scramble competition is related to animals depleting resources before others can use them, whereas contest competition is associated with the monopolization of resources and food-related aggression. One hypothesized major benefit of fission–fusion sociality is the reduction of scramble feeding competition between community members. We studied intragroup aggression in a community of spider monkeys. Despite seasonal variation in food availability, we found no seasonal difference in aggression rates, which, in combination with a basic lack of aggression among adult females, suggests that fission–fusion dynamics may reduce not only scramble, but also the intensity of contest competition. There were, however, numerous attacks from adult females towards subadult females, especially new immigrants. This aggression, although it occurred mainly during feeding, may not reflect contest competition. Instead, it may be used by resident females to limit scramble competition at the community level, which is ultimately affected by the number of community members. The aggressive harassment of subadult females by long-term resident females can be a means to encourage dispersal of natal subadult females and discourage immigration of new subadult females who are both potential future resource competitors.

Variation in kin bias over time in a group of Tibetan macaques at Huangshan, China: contest competition, time constraints or risk response?

We examine variation in grooming kin bias intensity (KBI) among wild female Tibetan macaques ( Macaca thibetana huangshanensis ) in one group over time. We test three hypotheses based on socioecological theory, time constraints and risk-related responses. Only the time constraints hypothesis was supported. Grooming KBI was higher when the group was larger, but was unrelated to other indicators of within-group competition. Allies were not necessarily frequent grooming partners; thus, support did not depend on maintaining strong grooming relationships. Females groomed similar amounts, regardless of group size, but groomed smaller percentages of available partners when the group was larger, suggesting that they were unable to maintain grooming relationships with all females as the group expanded. Females with several close kin groomed each of them less than females with few. The lowest ranking females tended to groom close kin almost exclusively, as expected if they had less grooming time to spare than other females. Although grooming KBI was higher when stressful external risks (many humans) were present, the correlation was unsustained when group size was controlled. We suggest that kin-focused grooming networks are shaped at least in part by time constraints and may not be linked directly or indirectly to within-group competition.

Social factors enhancing foraging success of a wild group of Japanese macaques (Macaca fuscata) in a patchy food environment

We evaluated the effects of social factors and food quality on patch use by a wild group of Japanese macaques (Macaca fuscata) that experienced no inter-group feeding competition or predation risk. We obtained the following results: (1) Food patch depletion and within-group scramble competition for food apparently did not affect patch use. (2) Within-group contest competition (aggressive interactions related to social-dominance rank) also did not strongly affect patch use. (3) The number of co-feeders in the same patch consistently showed positive effects on patch use, while food quality did not have consistent effects. These results suggest that the presence of co-feeders enhances foraging success in a patchy food environment.

Food conditions, competitive regime, and female social relationships in Japanese macaques: within-population variation on Yakushima

Feeding conditions, competitive regime, and female social relationships of Japanese macaques (Macaca fuscata) on Yakushima were compared between the two habitats at two different altitudes (coniferous forest, 1,000-1,200 m and coastal forest, 0-200 m). Fruit availability was higher in the coastal forest. There was no consistent difference in the frequency of agonistic interactions within a group during feeding between the two habitats. The coastal forest evoked stronger inter-group contest competition compared to the coniferous forest as evidenced by a higher inter-group encounter rate and a higher proportion of aggressive encounters to non-aggressive ones. Birth rate was higher in larger groups compared to smaller ones in the coastal forest, but did not differ in the coniferous forest. In spite of these differences in competitive regime, no variation in female social relationships was observed, such as direction and concentration on particular individuals in grooming, linearity in dominance rank, counter-attack, and support of juvenile kin during agonistic interactions. The present results indicate that the female social relationships of Japanese macaques are robust and do not change according to changes in the current environment.

Sperm Competition and Optimal Timing of Matings in Microcebus murinus

Female promiscuity is common in mammals and leads to sperm competition: the sperm of ≥2 males compete for ova. Scientists understand the possible role of optimal insemination periods for male reproductive success in many species as well as the impact of monopolization of receptive females. Information from experiments combined with detailed observations from the field that allow determining the relative impacts of the elements in the same species are rare. We studied sperm competition and the role of optimal insemination periods in gray mouse lemurs (Microcebus murinus), a small solitary nocturnal primate from Madagascar. We used controlled matings to identify the relative impact of both contest and scramble competition, which characterize their mating system, on paternity. Fifteen females mated with 3–6 males in quick succession. Our experiments revealed that the optimal insemination period is during early receptivity. Early but not first mating males are more likely to sire offspring. Comparison with our field data indicate that the timing of male monopolization efforts correspond with the optimal insemination period.

Larval competition within seeds: From the behaviour process to the ecological outcome in the seed beetle Callosobruchus maculatus

Abstract Environmental conditions experienced by organisms during development can have profound impacts on adult fitness and behaviour. Internally feeding larvae unable to leave the seed selected by their mother face limitations of resource suitability and competition. The host seed may guide the larval behaviour within the seed leading to differential intensity of competition and determining its process and outcome, which varies in strains of the legume seed beetle Callosobruchus maculatus (Coleoptera: Bruchidae). However, the intensity, process and outcome of larval competition in different hosts have yet to be simultaneously considered, the objective of the present study. Here we assessed the intensity, process and outcome of intrastrain larval competition as related to host type, and how they are interrelated. Larval competition was faced with two distinct strategies – scramble and contest competition depending on the insect strain and host seed species. The intensity of competition did not show any straight link with the process and outcome of competition. Only a single strain showed a contest competition process with likely interference between larvae, while the four other strains studied showed the process of scramble competition. The process of scramble competition, however, led to variable outcomes in mung beans based on larval competition curves. Such differences were not apparent on cowpea seeds and either the plateau or the peak expected on the larval fitness curves were not reached preventing the distinction of the competition outcome, a likely consequence of the egg laying behaviour of these strains limiting the maximum number of eggs laid per seed. Seed host species rather than seed size are the likely cause of the differences observed from the initial expectation. The strain showing the process of contest competition increased larval fitness with density of larvae emerged per seed regardless of the host species, an unexpected outcome based on theoretical models. In this case the egg laying behaviour of the adult female is probably the main fitness determinant of its progeny.

Controversy over the application of current socioecological models to folivorous primates: Colobus vellerosus fits the predictions

We explore the applicability of the current socio-ecological model to characterize the social structure of Colobus vellerosus, a folivorous primate. The current socio-ecological model predicts that female social relationships should respond in predictable ways to food abundance and distribution and associated competitive regimes. It appears to successfully explain variation in social structure in some primate species; however, recent research indicates that several folivorous or folivore-frugivorous species seem to be exceptions. We present data on social relationships and social structure in two groups of C. vellerosus over 15 months at Boabeng-Fiema, Ghana. As predicted by the model, our results indicate the co-occurrence of 1) low levels of grooming between female C. vellerosus when compared with other species, 2) an absence of female coalitions over food, and 3) female dispersal. Taken together, these traits suggest a "Dispersal-Egalitarian" species. However, our results also indicate female-female affiliation was higher than male-female affiliation, which was more indicative of a "female resident" species. Our data also suggests inter-sexual affiliation varied among groups. This variation in inter-sexual affiliation could be due to variation in the intensity of infanticidal threats between groups. The combination of these social characteristics lead us to conclude that C. vellerosus' social structure is largely congruent with the ecological indicators of food distribution and female competitive regime that we have previously documented, which indicated high quality foods were not monopolizable or usurpable and behavioral evidence of within-group contest competition (i.e. supplantations over food) was rare. But the combination of higher female-female affiliation (compared to male-female) and female dispersal is difficult to explain in light of predictions, unless future work reveals female residency is more predominant than female dispersal in our population. We also discuss reasons why some folivores do not appear to fit the predictions of the current socio-ecological model.

Wall-making behavior as a proximate mechanism to generate variation in larval competition in Callosobruchus maculatus (Coleoptera: Bruchidae)

Variation from contest to scramble in larval competition types was observed among laboratory lines derived from a geographic strain of Callosobruchus maculatus. In contest competition, only one adult can emerge from a small bean because the successful larva monopolizes resources. In scramble competition, however, multiple adults can emerge from the bean because larvae share resources. To explain the variation in competition types, we used six lines of the geographic strain to test the hypothesis that the larval competition type is determined by the larval behavior of building walls, which prevent larvae from interfering with each other, allowing multiple adults to emerge from a single bean. We also investigated the proportions of wall-making in contest-scramble hybrid lines to test whether the formation of a wall structure was genetically determined. Results support our hypothesis that wall-making behavior determines the type of larval competition within a geographic strain, and that the behavior is genetically determined. Scramble-type lines exhibited higher frequencies of wall-making than contest-type lines when two larvae of the same line infested a bean. Larval competition type and the tendency towards wall formation in contest-scramble hybrid lines ranged intermediate of parental lines. We concluded that the variation in larval competition type is determined by the variation in larval wall-making behavior among laboratory lines derived from the geographic strain. We will discuss the evolution of scramble-type larvae in C. maculatus based on our results.