Harem size and oviposition behaviour in a polygynous bark beetle

Abstract. 1. Harem polygyny can have fitness benefits and costs on females. In bark beetles of the genus Ips the latter may include within‐harem competition between larvae. However, earlier competition between females for male care and mating opportunities may also influence oviposition behaviour. There has been relatively little investigation into the relationship between harem size and initial egg output. The present study investigated this relationship in the bark beetle Ips grandicollis. 2. The measure of egg output used was the number of eggs in the gallery with the most eggs in each harem. Mean (±SE) harem size of 242 observed harems was 3.25 ± 0.10. A curvilinear relationship was found between egg output and harem size, with females in smaller harems (one to four females) laying more eggs with increased harem size. However, females in larger harems (five to seven females) laid fewer eggs as harem size increased. The optimal harem size (in terms of number of eggs laid) was close to four females. 3. We found no evidence from a behavioural assay that females could preferentially choose unmated males over mated males with harems of two females. Additionally, the distribution of harem sizes suggests that females distribute themselves among males randomly. 4. The results suggest that harem size has effects on female reproduction that extend beyond larval competition and influence patterns of oviposition. The mechanism that determines why egg laying is greatest at intermediate levels is unknown. There is no evidence that smaller harems belong to lower quality males, but females may adjust egg‐laying behaviour in large harems as a result of reduced male attendance or anticipated larval competition.     

Reproductive Consequences of Male Arrival Order in the Bark Beetle, Ips grandicollis

For group-living animals the choice of whether to join aggregations or initiate their own is influenced by potential benefits such as group protection and reduced energetic expenditure, as well as costs such as competition for food and mates. The bark beetle Ips grandicollis is an invasive pest species that colonises recently felled timber in Australian pine (Pinus spp.) plantations. Male beetles initiate colonies by burrowing under the bark of trees and emitting an aggregation pheromone which attracts conspecifics, including a harem of females with whom they mate. We predicted that males that initiated colonies, or who arrived early, would have larger harems than later arrivals (due to decreased competition for females). However, we found the opposite effect with early-arriving males actually associated with fewer females than later arriving males, although this may have resulted from some females leaving harems as they get older. We conclude that pioneering does not improve male likelihood of attracting females in Ips grandicollis, at least initially, but it may provide advantages for offspring when competing for food during development.     

Reproductive performance of clonal and sexual bark beetles (Coleoptera: Scolytidae) in the field

In Ips acuminatus (Gyll.) parthenogenetic females occur together with sexual females and with sexual males upon which they depend for sperm. In a reciprocal‐transplant experiment, I studied fecundity differences among parthenogenetic and sexual females from two populations that differ dramatically in the proportion of clonal females. In a second experiment, I studied competition between larvae from different mothers and between females from the two source populations. Fecundity measured by the number of eggs per egg tunnel was influenced by the ambient environment at the sites of the experiment as well as the origin of the female, and was generally higher for clonal than for sexual females at both sites. In experimental groups where larvae competed with larvae from their own population (pure treatments), the number of surviving pupae was significantly lower than in groups where females from the two source populations were mixed. The high fecundity of clonal females makes coexistence of the two types of females difficult to explain. It makes the reproductive advantage associated with clonality in I. acuminatus even higher than the two‐fold difference due to asexuality per sé. The significant differences in the number of pupae in mixed vs. pure groups suggest ecological divergence between sexual and clonal females. This would make the mortality of larvae not only density dependent, but also frequency dependent, which could explain the coexistence of sexual and clonal females.     

Reconstruction of Parentage in a Band of Captive Hamadryas Baboons

The male leaders of free-ranging harem groups of hamadryas baboons are believed to mate exclusively with the female members of their harems, which typically contain no more than 2–3 females. Using no-parent parentage exclusion analysis (PEA) we identified the paternity of 25 offspring born in a captive band of hamadryas baboons (Papio hamadryas hamadryas) containing five adult males, each with a stable harem of about five females. Nine of 13 microsatellite (SSR) loci known to be highly polymorphic in rhesus macaques (Macaca mulatta) were successful in identifying the sires of all but two offspring without knowledge of the dams' genotypes, and we were able to determine the sires of all offspring when the dams' genotypes were considered. Mating success of the males ranged between 2 and 7 offspring and bore no clear relationship to the males' ages, ranks or the number of females in their harems. The males sired 7 of the 25 offspring with females outside their own harems, with higher-ranking males exhibiting greater success monopolizing access to females in their harem than lower-ranking males did. More surprisingly, the females assigned as the dams of 14 of the 25 offspring could be unequivocally excluded from parentage. The identity of the true dam could be determined for each of these 14 offspring using single-parent PEA and was uncorrelated with the ranks of these offsprings' sires and whether the offspring were born to dams outside the sires' harem groups. The combined effect of this extraharem mating and kidnapping was that only 12 of the 25 offspring were raised within their sires' harem groups. A second group of hamadryas baboons of identical structure exhibited the same high incidences of infant kidnapping and mating outside the harem group. It is unclear whether these behaviors provide an adaptive advantage or represent aberrant behavior resulting from captivity or other circumstances.     

The evolution of mating systems in bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae)

The extraordinary array of mating systems in the Scolytidae and Platypodidae has been largely overlooked by researchers interested in the evolution of sexual behaviour. This paper provides the first overview of reproductive behaviour in this important and widespread group, known to most biologists only by the reputations of tree-killing taxa. Referred to generally as ‘bark beetles’, these insects chew egg tunnels inside a variety of (usually dead) plant tissues, though most species are either phloeophagous (breeding in the inner bark of woody plants) or xylomycetophagous (all stages feeding on mutualistic fungi growing on sapwood or heartwood). In most species, permanent records of many aspects of reproductive behaviour are etched in the host; in many, engravings reveal female fecundity, eggs sired per male, hatching success, and offspring survivorship. Each gallery arm represents a good portion of a given female's lifetime reproduction, but in many species females commonly re-emerge to reproduce in one or two additional sites. In most species of bark beetles, each female initiates her own gallery, to be joined later by a male. These monogynous gallery systems are associated with mating systems defined by how long males stay with females: in a few species, males seldom if ever join females under the bark; in the vast majority of species, males stay for part or all of the oviposition period then leave to seek other mates; and a few groups exhibit permanent monogamy, in that both sexes die in their only gallery system. While these patterns emerge from an overview of the world scolytid fauna, the length of male residency has seldom been quantified, and the costs and benefits associated with male mating strategies have not been measured for any bark beetle. Male-initiated monogyny is uncommon in Scolytidae, though the rule in Platypodidae; all instances of which I am aware are summarized from a phylogenetic perspective. Inbreeding polygyny with highly biased sex ratios has arisen at least seven times in Scolytidae. These taxa are usually characterized by males being dwarfed, flightless, and uncommon. Sex determination is known for only a few examples, but both haplodiploidy and diplodiploidy have been reported. Multiple origins of harem polygyny (otherwise rare in invertebrates) add an exciting dimension to the comparative and experimental study of scolytid mating systems. In harem polygynous taxa, males initiate gallery construction. I summarize what little can be learned from the literature about the fine structure of harem polygynous mating systems in bark beetles, and the problem of measuring reproductive success. Data on the nature of harem polygyny in Pityophthorus lautus are presented, illustrating (a) the fluidity of harems; (b) that average eggs laid per gallery arm is relatively unaffected by harem size, but strongly influenced by resource quality; (c) that male egg-gain is strongly correlated with territory quality (a consequence of (b) above); and (d) the temporal patterning of immigration and emigration and its effects on gallery system sex ratios. The second half of this paper is a discussion of the evolution of bark and ambrosia beetle mating Mating systems, emphasizing sexual selection and the role of resources. Male, residence is interpreted as postcopulalory guarding—preventing sexual liaisons with wandering males. Operational sex ratio, encounter rate, synchrony of breeding, ejaculate competition, and spatiotemporal distribution of resources are discussed as evolutionary forces moulding scolytid and platypodid male postmating behaviour. The nature of male male competition is reviewed. The paucity of information on male behaviour in gallery systems is mentioned; whether or not males significantly aid females is not known. Three hypotheses are presented for why females re-emerge, a feature which strongly affects operational sex ratios. Finally, I summarize features of bark beetle existence predisposing them to the evolution of post-inseminative guarding. Male-initiated monogyny presents a puzzle. I propose that most uncontested examples can be explained by monogyny re-evolving from (male-initiated) harem polygyny, and I present an argument for the evolution of harem polygyny leading to the development of male gallery initiation. The evolution of harem polygyny in birds and mammals has attracted considerable attention. The Verner Willson Orians polygyny threshold model is discussed with respect to bark beetles in general and P. lautus in particular. Resource quality is a major factor in P. lautus harem dynamics: the cost to females of joining harems is apparently slight compared to benefits accrued from moving into sites with higher quality inner bark. Female-biased adult sex ratios have been suggested to lead to harem polygyny, and literature and original data pertinent to this hypothesis are examined. The geometric constraints model, based on the polygyny threshold concept but tailored to bark beetles, is proposed to account for the failure of most species to evolve harem polygyny, and testable predictions are derived that interrelate breeding systems, habitat quality, and progeny size. The evolution of Inbreeding is briefly covered, and two routes to inbreeding polygyny are suggested.     

Pairs and Harems in a Cichlid Fish,Lamprologus brichardi1

L. brichardi is a substrate brooding cichlid with facultative polygamy. The social organization was studied in the field for a 6-week period. The mating structure was examined in detail in the laboratory. Two types of social groupings are described:

• 1 Aggregations of sexually mature but nonterritorial fish, also frequently visited by territory holders in the vicinity.
• 2 Reproductive units (families) mainly consisting of the reproducing pair members and offspring from several broods. All family members defend a common territory around the shelter site. Occasionally a male has access to two females each with a separate territory (harem).

The factors influencing mating structure were investigated in the laboratory:

• 1 Females select breeding sites rather than partners.
• 2 Without competitors for breeding sites, and with an equal or nearly equal sex ratio, harems were established nearly as often as pairs.
• 3 Young males are physically able to mate and form a harem; but they are usually prevented from doing so by more competitive (larger) males.
• 4 Competition for breeding sites is not a prime influence on harem formation, although it is of great importance in determining the composition and size of the breeding population.
• 5 Just as many pairs as harems were formed with and without predators, even though, with predators, no young survived.
• 6 In L. brichardi the formation of harems is not predominantly determined by the distribution of suitable spawning sites. The monopolization of females is only slightly influenced by the distance between their territories.
• 7 In L. brichardi it is not necessary for harem formation that the male is bigger than the female.
• 8 Behavioural protocols and data on growth rates, as well as spawning intervals, did reveal any consistent difference between pairs and harmes.

Of the variables tested, male competition for females was therefore the sole determinant of who should mate.     

Transition of nonharem male to harem male status in the short-nosed fruit bat Cynopterus sphinx

The short-nosed fruit bat Cynopterus sphinx is known to exhibit resource defence polygyny as its primary mating strategy. Tent construction by harem males to recruit females represents a heavy investment of time and effort, which is not done by nonharem males. The previously unobserved mode of harem formation by the solitary males was studied using mark-recapture and radio-telemetry. In our observation, the solitary males roosting near to harems started recruiting females by occupying the tent abandoned by the harems. This result suggests that the transition of nonharem male to harem male status possibly by a previously unobserved mode and the female recruitment is associated with resource (roost). It implies that the solitary males are actively involving in female recruitment and also presumably mating.     

Individual variation in perfume blending in male greater sac-winged bats

Male greater sac-winged bats, Saccopteryx bilineata, use hovering flights to court females in their harem territory. While hovering, males fan a fragrant perfume from sac-like organs in the wing membrane towards the females. Each afternoon, males renew the perfumes of their wing sacs during a stereotypical and time-consuming behavioural sequence, which includes blending secretions from genital and gular glands. I investigated whether male perfume-blending behaviour varies between the mating and the nonmating season, and whether successful males, those with large harems, have different patterns of perfume blending than less successful males. I measured variation in perfume-blending behaviour in 21 adult males. The pattern of perfume blending was not significantly different between the mating and the nonmating season. However, the time at which perfume blending began and terminated differed between seasons. During the mating season, males spent about the same time cleaning their wing sacs during phase I of perfume blending, irrespective of the number of females in their harem. During phase II, males with large harems spent significantly less time refilling and blending perfume than males with small harems. In addition, males with large harems took up fewer droplets of secretion from the genital region. Overall, male-male interactions were rare during perfume blending, and the decrease in duration in phase II was not attributable to more disturbance in large harems. There was also no evidence that males prevented each other from transferring secretions into their wing sacs. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Male reproductive success in harem troops of hanuman langurs (Presbytis entellus)

Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably. Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such competition is more intense in larger harems.     

Monogamy in the bark beetle Ips latidens: ecological correlates of an unusual mating system

Abstract. 1. The diversity of mating systems in bark beetles (Coleoptera: Scolytidae) is poorly understood. Ips latidens (LeConte) is a small-bodied species of a harem polygynous genus whose mating system in nature had not been established previously. This study examines the breeding biology of I. latidens breeding in recently dead ponderosa pine ( Pinus ponderosa ) in California. It was expected that both the heterogeneous habitat quality inherent in dead trees and small body size would favour polygyny.
2. Contrary to expectations, I. latidens was found to be monogamous on the basis of excavations of 131 galleries conducted throughout the oviposition period at two wind-felled trees and at four sites composed of freshly-cut logs. Males left the galleries much sooner than females (50% gone by 24 and 36 days, respectively).
3. Individual females made up to four egg gallery arms extending from the male nuptial chamber, with the number of arms and the length of individual arms increasing with the age of the gallery. The relationship between total gallery length and gallery age was consistent among the trees and log sites, and did not depend on the presence of the male.
4. Ips latidens bred in a wide range of tree diameters (10–24 cm), and occurred in both pure aggregations and in aggregations with two other bark beetle species, Dendroctonus brevicomis and I. paraconfusus . The presence of the other species did not appear to influence negatively the density of I. latidens .
5. Monogamy in I. latidens may be due to lower male mortality during dispersal associated with a greater range of suitable breeding habitat than occurs for other Ips species, resulting in an even sex ratio at breeding sites.     

Alternative spawning tactics of female angelfish according to two different contexts of sex change

Social conditions for sex change and reproductive success werestudied in the haremic marine angelfish, Centropyge ferrugatus,in the coral reefs of southern Japan. In this species the largestfemale in a harem changed sex not only after disappearance ofthe dominant male but also occasionally in his presence. Inisolated harems containing two to three females, strict socialcontrol by the dominant male resulted in females changing sexonly after the male disappeared (takeover sex change). In haremsadjacent to each other, however, takeover sex change did notoccur even when one of the males disappeared. Instead, largeharems including more than four females were formed by fusionof two adjacent harems. In such large harems, the dominant malewas unable to socially prevent the largest female from changingsex later to acquire a portion of the harem (harem-fission sexchange). Females in adjacent harems spawned less frequentlyand tended to grow faster than those in isolated harems, probablyto gain an advantage in dominance status over neighbors of similarsize. Thus, females changed spawning frequencies according tothe two different contexts of sex change. The takeover tacticresults in higher fitness than the harem-fission tactic, whichshould be the best in the bad situation of adjacent harems.     

Social organization of the spotted sharpnose puffer,Canthigaster punctatissima (Tetraodontidae)

Synopsis Tagged individuals of the Eastern Pacific sharpnose puffer, Canthigaster punctatissima, were studied at Punta Santa Inez, Baja California Sur. Territories were maintained by both sexes in this sexually dimorphic fish. Male puffers appear to have harems; one large male interacts with one to four smaller females. Puffers from different harems were not seen to interact except for occasional aggressive contact. Removal of a male puffer resulted in the overnight takeover of his harem by a neighboring male. Harem-forming behavior is discussed, as well as the possible role of predation.     

Harem structure of the protogynous angelfish, Centropyge ferrugatus (Pomacanthidae)

Social structure of the protogynous angelfish, Centropyge ferrugatus, was examined on the coral reefs of Sesoko Island, Okinawa, Japan. Each individual male monopolized a harem of 1-6 females. Harems could be categorized as linear-type or branching-type based upon spatial and dominance relationships among the females. A linear harem consisted of different-sized females whose home ranges overlapped each other with a linear dominance order based on body size. Branching harems were composed of two linear sub-groups dividing a male's territory. Females of similar size did not have overlapping home ranges, which resulted in branching harems. These two systems appear to be a result of competition for opportunities of sex change, as only the largest fish of a harem (or a sub-group) can become a male. Comparison of the harem structures of some reef fishes suggests that the two harem structures may occur broadly in protogynous haremic fishes.c/o Prof. T. Kuwamura     

Defence of Females by Dominant Males of Artibeus jamaicensis (Chiroptera: Phyllostomidae)

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.     

Queuing for harem access in colonies of the greater sac-winged bat

Colonies of the greater sac-winged bat, Saccopteryx bilineata, consist of nonterritorial males and males that defend harem territories in which females roost. The traits of nonterritorial males that define their success in harem take-overs are so far unknown. We predicted that the time nonterritorial males spent in the colony and their proximity to harems would be important factors. We temporarily removed harem holders from a colony of 60 greater sac-winged bats on consecutive days and observed which of the nonterritorial males took over the harem. To test for consistency of results, we repeated the experiments in some of the territories. In a second set of experiments, we removed both the harem holder and the corresponding usurper from the first experiment. On average, usurping males preferred territories with a large harem over territories with a small harem and they belonged to groups of males who spent the daytime near the corresponding harems. Usurpers in the second experiment were present in the colony for a shorter time than usurpers in the first experiment. Overall, the results support the hypothesis that nonterritorial males form overlapping peripheral groups for harems and that they live in a hierarchy according to their tenure in the group. Group membership and hierarchy seemed to be the factors that determined whether a male occupied a vacant harem. Hence, instead of floating, the pattern of harem succession in greater sac-winged bats is best described by queuing of nonterritorial males for access to a harem. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Intracolonial social distance, signaling modality and association choice in the greater sac-winged bat (Saccopteryx bilineata)

Understanding patterns and motivations for social spacing greatly illuminates the structure and internal dynamics of given groups or social systems. The highly social, polygynous greater sac-winged bat, Saccopteryx bilineata, represents an excellent model for social spacing analysis, since the choice of individual roost-sites within a day-roost constitutes an enduring, often repeated decision about relative proximity to conspecifics. Day-roost colonies consist of one or multiple harem groups, each with several females and a single male. Additionally, non-harem males without females may be present. A social-distance–time-budget metric revealed that harem males, females, and non-harem males differed significantly in their respective spatial associations while roosting. Harem males and females were most closely associated, with harem males located at the center of harems instead of at the borders. Non-harem males associated significantly closer with one another than with harem females that they were trying to access. The signaling modality mediating social interactions depended on the respective social distances between communicating bats. Our results suggest a concentric social organization based around harem males, which may select roost sites in closest possible proximity to females to enhance courtship signal strength. This constitutes an interesting deviation from the normative form of harem maintenance, patrolling borders, in mammals.     

Density-related changes in sexual selection in red deer.

In sexually dimorphic mammals, high population density is commonly associated with increased mortality of males relative to females and with female-biased adult sex ratios. This paper investigates the consequences of these changes on the distribution of male breeding success, the intensity of competition for females and the opportunity for sexual selection. After the red deer (Cervus elaphus L.) population of the North Block of Rum (Inner Hebrides) was released from culling, female numbers rose and male numbers declined, leading to an adult sex ratio of around one male to two females. This change was the result of increased mortality of males relative to females during the first two years of life; of increased emigration rates by young males; and of reduced immigration by males from outside the study area. The increasing bias in the adult sex ratio affected the timing of breeding as well as the distribution of mating success in males. As the adult sex ratio became increasingly biased towards females, the degree of skew in mating success (calculated across all harem-holders) increased, but mature males defended harems for shorter periods and a higher proportion of males held harems. In addition, a higher proportion of calves were fathered by immigrant males and the proportion fathered by males born in the study area declined. These results support the contention that, where high population density is associated with a female-biased adult sex ratio, competition for mates is likely to decline.     

Social Organisation of the Bat Tadarida (Chaerephon) pumila (Chiroptera: Molossidae) in Ghana,West Africa

The social organisation of the polyoestrous bat, Tadarida pumila, was studied in northern Ghana (W. Africa). Although this small (8.5 g) free-tailed bat is not sexually dimorphic in size, adult males develop an odorous inter-aural crest of long hairs. A social system based on female defense polygyny was found which, however, also involved elements of resource defense. Harems, each generally established in the roof space of separate dwelling houses with restricted access, consisted of an adult male and up to 21 females, with their young, and the larger harems were held by heavier males. Harem composition was stable and both harem males and females showed high site fidelity over the study span of 16 months. Some female young were recruited to their natal harems, at a sufficient rate to replace the annual loss of harem females. However, most young, which were born in three successive cohorts during the rainy season, apparently dispersed over the dry season, following early sexual maturation. The potential causes and benefits of female associations are discussed.     

One-male harems and female social dynamics in Guinea baboons

Little is known about the mating system and social organization of Guinea baboons. This study investigated whether Guinea baboons have a harem-based mating system similar to that of hamadryas and gelada baboons and whether one-male mating units also correspond to social units. Ten adult females in a captive multi-male multi-female group of Guinea baboons were focally observed 2 h per week for 12 weeks, and all observed copulations within the group were recorded. Some males copulated with a single female while others had harems of 2-4 females. All females copulated with a single male except 1 female that switched harems early in the study. The focal females had higher rates of social interaction with their harem members, especially their harem male, than with individuals outside the harem. Females appeared to be subordinate to the harem male but little or no physical aggression or herding behavior from the male was observed. Variation in female social interactions within the harem was not accounted for by their sexual interactions with the male or their genetic relatedness with the females. Females, however, appeared to maintain social relationships with their female relatives in other harems. Taken together, the results of this study show that both mating and affiliative interactions in Guinea baboons are concentrated within one-male units and that the social dynamics within and between these units share some similarities as well as differences with those of hamadryas and gelada baboons.     

Subordinate Males in Harem Groups of Jamaican Fruit‐Eating Bats (Artibeus jamaicensis): Satellites or Sneaks?

In the caves of Yucatan, Mexico, the Jamaican fruit‐eating bat, Artibeus jamaicensis, forms harems consisting of four to 18 females and a dominant male that defends the group against foreign males. Large groups (>14 females) contain an additional subordinate male. In theory, subordinate males can associate with harem groups either as satellites, if they provide at least some benefits to the dominant male, or as sneaks, if they only impose costs on the dominant male. We assessed the costs and benefits of subordinate males in three removal experiments. In the first experiment, when a dominant male was removed from its group, its role was occupied by the subordinate male (in large groups) or by a foreign male (in small groups). Former subordinate males took less time to gain control of the harems and stayed longer with the groups than foreign males. In the second experiment, when a subordinate male was removed, the rate of visitation by foreign males and the number of agonistic displays by the dominant male both increased. In the third experiment, when the number of females in large groups was reduced, subordinate males spent less time with their groups and the rate of visitation by foreign males increased. However, the frequency of agonistic displays by dominant males towards subordinate males did not change. Dominant males invest large amounts of energy in defending the harems, but obtain direct and immediate benefits from the presence of subordinate males in the form of access to a larger number of females, and suffer no obvious costs. Subordinate males apparently invest little energy in defending the harems, obtain no obvious immediate benefit, but gain long‐term benefits by having priority access to vacant positions left by dominant males. Subordinate males in harem groups of the Jamaican fruit‐eating bat can be considered satellites because their presence brings immediate benefits to the dominant males.