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1.
The adaptive significance of male subadult plumage in purple martins: plumage dyeing experiments 总被引:1,自引:0,他引:1
Bridget J. Stutchbury 《Behavioral ecology and sociobiology》1991,29(4):297-306
Summary I tested two hypotheses for the adaptive significance of subadult plumage in male purple martins (Progne subis) : the female mimicry and subordinance signaling hypotheses. Subadult males were at a competitive disadvantage in obtaining territories, as they arrived later in the spring than adult males. Contrary to the predictions of both hypotheses, adult male territory owners were not less aggressive toward subadult male than adult male intruders. The subadult plumage was not effective in mimicking females, as adult male owners were significantly more aggressive toward subadult male than female intruders. Summer adaptation hypotheses predict that young males in subadult plumage are more successful in acquiring territories and mates than they would be with an adult plumage. I tested this prediction by dyeing the plumage of floater subadult males to mimic the appearance of adult males. In 13/17 paired experiments, dyed subadults obtained territories before control subadults. There was no difference in the time it took dyed and control males to attract a mate after they obtained a territory. These results suggest that the subadult plumage is not an advantage to young males in competing with adult males for breeding resources. In late winter, subadult males were growing mostly femalelike feathers on their underside, suggesting that the subadult plumage is not the result of a molt constraint. The subadult plumage could enhance survival of yearlings in winter roosts if it improves access to good roost sites or reduces the risk of predation. 相似文献
2.
We studied sexual selection in the red bishop, Euplectes orix, a colonial, polygynous weaverbird widely distributed over sub-Saharan Africa. Male reproductive success measured in terms
of the number of nests accepted by females and the number of eggs and nestlings in all the nests on a male's territory varied
considerably. The standardized variance (variance/mean2) in male reproductive success ranged from 0.505 to 1.737 in different years, indicating a high potential for sexual selection
in this species. An analysis of genetic parentage for 432 nestlings by non-radioactive, multilocus DNA fingerprinting confirmed
that male reproductive success (number of young sired on the territory) in this species can be reliably estimated by the measures
introduced above. In all 4 study years there was a strong positive correlation between male mating success and the total number
of nests that males built in their territories. The number of nests built can be partitioned into the number of weeks a male
held a territory and his nest-building performance. Both factors exert a significant positive effect on male mating success
and in combination explained between 53.3 and 86.3% of the variation in male reproductive success. Male morphological characters
were found to be of no importance. Males that established a territory in the following season built more nests and held their
territories for longer than males that did not establish a territory in the following season, suggesting that these measures
might be indicators of male condition and quality. Male nest-building performance (number of nests built per week) seems to
be unrelated to male condition or quality.
Received: 8 January 1999 / Received in revised form: 7 June 1999 / Accepted: 13 June 1999 相似文献
3.
Isobel Booksmythe Richard N. C. Milner Michael D. Jennions Patricia R. Y. Backwell 《Behavioral ecology and sociobiology》2010,64(3):485-491
Mimicry of females enables weaker males in many species to avoid intrasexual aggression. In fiddler crabs (Uca annulipes), males use their major claw in aggressive interactions to acquire and defend a territory. Males that have autotomised their
major claw will be disadvantaged in fighting, but might use their temporary resemblance to females to avoid costly aggressive
encounters with other males. We investigated whether: (1) courting males mistake clawless male fiddler crabs for females;
(2) clawless males are able to acquire, defend and retain territories as successfully as intact males; and (3) clawless males
are more cautious than intact males. Clawless and intact males differed in burrow acquisition methods and fighting behaviour,
but were equally successful at acquiring and retaining burrows. While courting males treated clawless males as female, we
found no evidence that clawless males mimic the behaviour of females, or that they exploit the advantage of their mistaken
identity. Clawless males further appear to avoid male aggression by altering their territorial strategies to minimise the
potential for conflict. 相似文献
4.
Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio 总被引:1,自引:0,他引:1
We studied the effect of relative parental investment on potential reproductive rates (PRRs) to explain sex differences in
selectivity and competition in the dart-poison frog Dendrobates pumilio. We recorded the reproductive behavior of this species in a Costa Rican lowland rainforest for almost 6 months. Females spent
more time on parental care than males, and `time out' estimates suggest that PRRs of males are much higher than than those
of females, rendering females the limiting sex in the mating process. Males defended territories that provide suitable calling
sites, space for courtship and oviposition, and prevent interference by competitors. Male mating success was highly variable,
from 0 to 12 matings, and was significantly correlated with calling activity and average perch height, but was independent
of body size and weight. Estimates of opportunity for sexual selection and variation in male mating success are given. The
mating system is polygamous: males and females mated several times with different mates. Females were more selective than
males and may sample males between matings. The discrepancy in PRRs between the sexes due to differences in parental investment
and the prolonged breeding season is sufficient to explain the observed mating pattern i.e., selective females, high variance
in male mating success, and the considerable opportunity for sexual selection.
Received: 9 June 1998 / Received in revised form: 27 March 1999 / Accepted: 3 April 1999 相似文献
5.
The evolution of male breeding aggregations is difficult to explain because males may reduce their reproductive success by
associating with their closest competitors. We examined aggregative behavior by male New Mexico spadefoot toads, Spea multiplicata, which form breeding choruses in rain-filled pools. We specifically asked whether males are attracted to conspecific calls
and, if so, whether they preferentially associate with those male calls that are also attractive to females. Field observations
revealed that males showed significant clustering with conspecifics within breeding ponds, whereas laboratory phonotaxis experiments
revealed that males preferentially associated with conspecific male calls. Moreover, when males were presented with conspecific
calls that differed in call rate, smaller males associated with the stimulus preferred by females (average call rate). Thus,
males appear to evaluate the attractiveness of competitors using the same trait employed by females to assess potential mates,
and males adjust their positions relative to competitors depending on their size. We discuss these results in the light of
several current hypotheses on the adaptive significance of male breeding aggregations.
Received: 20 December 1999 / Accepted: 18 March 2000 相似文献
6.
Migratory stonechats (Saxicola torquata) spend the winter in the northern Negev desert in Israel. After arrival in October most birds defend territories throughout the winter either as heterosexual pairs or as single birds. In this population we examined: (1) aggressive behaviour of pairs; (2) the functional significance of pair territoriality; and (3) hormonal correlates of territorial behaviour. Pairs were aggressive towards both conspecific intruders and stonechat dummies, particularly in autumn when territories were established. Males were more aggressive than females and aggression was primarily intrasexual. More frequent than intraspecific interactions were interspecific encounters, with 94% involving the local mourning wheatear (Oenanthe lugens). With one exception these encounters consisted of attacks of mourning wheatears against stonechats, mainly males. Two functions of winter territoriality of migrant pairs are proposed: (a) a reduction of individual defense costs associated with the maintenance of a territory; (b) an increase of the net vigilance to reduce the risk of attacks by competitors or predators. The levels of testosterone (males and females) and estradiol (females only) were close to or below the lower detection limit of the assay throughout the winter. Therefore, high levels of gonadal steroids are not required for pair formation and aggression in the non-reproductive context. The results indicate that both the function and the proximate control mechanisms of territoriality during the non-breeding season in winter are different from those during the breeding season in spring. 相似文献
7.
Alison M. Muldal J. David Moffatt Raleigh J. Robertson 《Behavioral ecology and sociobiology》1986,19(2):105-114
Summary Nestling feeding by males is less common among birds with polygynous mating systems than in monogamous species, because of the pronounced trade-off between parental behavior and the attraction of additional mates. In this study, however, we found that male red-winged blackbirds (Agelaius phoeniceus) commonly assisted females in feeding nestlings in several Ontario marshes. Male parental care was additional to that provided by females, and it significantly enhanced the fledging success of nests (Table 2). Male redwings did not help to feed all nests on their territories: primary and secondary nests were much more likely to receive male parental care than tertiary and later nests. Contrary to expectation, male parental care was not restricted to the nests of primary females: a greater proportion of secondary than primary nests were assisted (Tables 4a and b). The presence of new females settling on the territory at the same time that a resident female had nestlings, resulted in males deferring parental care until a later brood. This suggests that males trade off the recruitment of females against parental care to an existing brood. Although the number of nestlings fledging from a male's territory was strongly influenced by the number of females in the harem, males could additionally increase their reproductive success by feeding nestlings in one or more nests on their territories (Fig. 2). The reproductive success of females was significantly enhanced by male assistance in feeding nestlings (Table 3). However, those females not receiving male assistance on territories of feeding males did not suffer a significantly reduced reproductive success in comparison to females on territories of non-feeding males (Table 2). Males varied considerably in the quality of brood care given. We therefore suggest that the quality of male parental care may be a factor considered by females in choosing a breeding situation. 相似文献
8.
In monogamous species, females often choose between males according to the quality of the territories they defend, but the
extent to which females themselves contribute to territory defence is frequently underestimated. Here we test for differences
in male and female roles during paired scent-marking bouts, a key component of territorial defence, in a monogamous antelope.
In two populations (Kenya, Zimbabwe) of klipspringer, Oreotragus oreotragus, both males and females usually scent-marked at the same site, but there were significant differences between sexes in terms
of investment within bouts. Females initiated most bouts, thus dictating the marking strategy of the pair. Males initiated
relatively few bouts, but deposited more scent marks per bout than females and were usually the last to scent-mark before
leaving the site; they marked on the same branches as the female and thus overmarked her scent. Both sexes deposited more
marks during paired than solo visits. Immediately preceding and following scent-marking bouts, males approached females and
females left males more often than expected. Female scent-marking rates were higher when they were receptive than at other
times, and this increase was matched by elevated marking rates of males. Females may increase marking rates when they are
receptive in order to test the quality of their mate or to incite male competition. However, these ideas are unlikely to explain
female scent-marking behaviour outside the mating season, which appears to be related primarily to territorial defence. We
suggest that these differences in investment in scent-marking bouts are consistent with predictions that females may be autonomously
territorial and that overmarking of female scent by males is a form of mate-guarding.
Received: 17 November 1999 / Received in revised form: 24 February 2000 / Accepted: 13 March 2000 相似文献
9.
Many species of territorial animals are more aggressive toward strangers than neighbors, a pattern of aggression referred
to as the ’dear-enemy phenomenon.’ In many cases, the mechanism by which neighbors are discriminated from strangers and the
function of neighbor-stranger discrimination remain controversial. We investigated the spatial patterns of inter-colony aggression
within and between two Pheidole species of seed-harvesting ants in the Mojave Desert of California by quantifying aggression between colonies in standardized
staged encounters. We also tested whether the level of fighting between workers of two colonies is affected by previous exposure
to each other. We show that neighbors (i.e., colonies less that 2.6 m away) of either species are treated less aggressively
than more distant colonies and that habituation may be a mechanism by which this discrimination is achieved. The variation
in aggression among spatially distant colonies also suggests that additional genetic or environmental factors are involved
in recognition. The function of the dear-enemy phenomenon in these ant species may be related to the greater risk to the resources
of a colony presented by strange workers than workers from a neighboring colony.
Received: 18 November 1999 / Received in revised form: 3 April 2000 / Accepted: 3 May 2000 相似文献
10.
Kooji Hayashi 《Behavioral ecology and sociobiology》1985,16(4):301-306
Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution. 相似文献
11.
Female control of offspring paternity in a western population of red-winged blackbirds (Agelaius phoeniceus) 总被引:9,自引:0,他引:9
E. M. Gray 《Behavioral ecology and sociobiology》1996,38(4):267-278
Extra-pair copulations, which occur when individuals that have formed social relationships to breed copulate outside their
pairbond, now are recognized as an important component of reproductive success in many species. In situations where both males
and females benefit from extra-pair copulations without incurring much risk, an inevitable conflict arises between pairbonded
mates. In this study I investigated the conflict of interest between male and female reproductive strategies in a western
population of red-winged blackbirds (Agelaius phoeniceus). Female red wings in this population initiate extra-pair copulations, which resulted in a 35% rate of extra-pair fertilization.
Females initiated the majority (78%) of extra-pair copulations away from their nesting territory where pairbonded individuals
typically copulate, and females that engaged in extra-pair copulations spent a significantly greater amount of time off the
marsh during peak fertilization compared to females that did not. In addition, females that nested in areas with a large number
of potential extra-pair partners produced significantly more extra-pair fertilized young compared to females that nested on
marshes with few male neighbors. Males’ strategies to protect paternity were limited primarily to patrolling territory boundaries
and to opportunistically preventing extra-pair copulations off the marsh when they were visible. In this population females
appear to use behavioral means to control nestling paternity, which in turn directly affected their mate’s reproductive success,
and males were restricted to using strategies that were largely ineffective at preventing the threat of extra-pair paternity.
Received: 23 December 1994/Accepted after revision: 17 December 1995 相似文献
12.
Tradeoffs between courtship, fighting, and antipredatory behavior by a lizard, Eumeces laticeps 总被引:4,自引:0,他引:4
W. E. Cooper Jr. 《Behavioral ecology and sociobiology》1999,47(1-2):54-59
Male fitness in many species depends strongly on social behaviors needed to obtain fertilizations and prevent loss of fertilizations
to other males, but courtship, copulation, and fighting may incur increased risk of predation. When demands for reproductive
and antipredatory behaviors conflict, fitness may be maximized by accepting some degree of risk to enhance reproductive success.
To examine such tradeoffs, I introduced tethered conspecific males or females to adult male broad-headed skinks, Eumeces laticeps, in the field and observed how close they allowed a simulated predator (me) to approach before fleeing, or their latency
to approach an introduced female located at different distances from the predator. When conspecific males were introduced,
isolated and mate-guarding males initiated agonistic behaviors and permitted closer approach than control males, and mate-guarding
males permitted closer approach than isolated males. When females were introduced, both isolated and mate-guarding males courted
the introduced females and isolated males permitted closer approach than did mate-guarding males. These results for introduced
males and females suggest that increasing risk was accepted when reproductive benefits were greater. Latency for isolated
males to approach a conspecific female was greater when the predator was closer to the female, further suggesting sensitivity
to predation risk during a reproductive opportunity. Relationships between reproductive and antipredatory behaviors have been
studied much less than those between feeding and antipredatory behaviors, but this study indicates that animals balance increased
risk of predation with the opportunity to perform several reproductively important behaviors.
Received: 5 March 1999 / Received in revised form: 15 July 1999 / Accepted: 25 July 1999 相似文献
13.
Territoriality is of great significance for many species and a characteristic of most group-living animals. Territoriality is thought to lead to increased reproductive success by defending a particular area containing critical resources. I describe several factors that influence territorial aggression in free-ranging striped mice (Rhabdomys pumilio), a group-living solitary forager. I induced territorial aggression by attracting mice of different groups using bait either at territory boundaries or in front of nests. Striped mice are territorial and make decisions about whether or not to attack a mouse from another group based upon several factors: (1) the sex of the opponent: males are much more likely to attack strange males than strange females, whereas no sex specific aggression was observed in females; (2) the body size of the opponent: striped mice are much more likely to attack a strange mouse that is lighter than themselves; and (3) the location of encounters: striped mice are much more likely to attack strangers, even those significantly heavier than themselves, in front of the nest than at territory boundaries. These variations in territorial responses between different types of individuals may be due to the different ultimate consequences of territorial aggression for different animals.Communicated by S. Alberts 相似文献
14.
N. Rauch 《Behavioral ecology and sociobiology》1985,16(2):125-134
Summary The reproductive behaviour of marine iguanas (Amblyrhynchus cristatus) was studied to answer the following questions: Which physical factors determine the number of females found on a male's territory? Do males select territories according to preferences for physical conditions or according to the number of females there? What causes the strong correlation between the number of females on a territory and the number of copulations achieved there? Females preferred as their resting places territories with the following characteristics, in order of importance: High number of shady/shelter places, low temperature of rocks at noon, proximity to the sea, sun-basking places in the afternoon. Other factors measured (probability of being wetted by spray, sun-basking places in the morning and at noon) showed no significant correlation with the number of females. Males, however, preferred territories further from the sea (within about 7 m), with high rock temperatures and a high number of basking places in the morning (in order of importance). Males primarily followed their site preferences and not female density in their choice of a territory. The site choice of females determined the number of copulations achieved on a territory, as females copulated preferentially on their resting places. A shift of females from one territory to another within one colony between two succeeding years was correlated with the change in relative weight of territory owners. This result was interpreted as an indication of female choice. Site preferences of males and females are discussed in relation to the animals' physiological requirements. Possible influences of ecological factors on the evolution of this mating system are considered. 相似文献
15.
Five hypotheses have been proposed to explain polygyny in the red-winged blackbird (Agelaius phoeniceus). We categorized the hypotheses into three groups based on female preference for unmated versus monogamously mated males:
(1) the “polygyny threshold” model, “sexy son” hypothesis and the “asynchronous settlement” model, which assume that females
prefer unmated males to mated males on breeding situations of homogeneous quality; (2) the “neutral mate choice” hypothesis,
which assumes that females have no preference; and (3) the “cooperative female choice” model, which assumes that females prefer
monogamously mated males to unmated males. We tested the direction of female preference in two field experiments. In both
experiments, newly settling females were given a choice of two adjacent territories, one defended by an unmated male and the
other by a monogamously mated male. Male mating status was randomized with respect to the variation in territory quality and
male quality. Early in the breeding season, significantly more females settled with the unmated males than with the mated
males. Although more females settled with the unmated males than with the mated males late in the breeding season, the difference
was no longer significant. Female settlement late in the season appeared to be related to the tenure of the resident females:
the new females avoided territories where the resident females were in early stages of their nesting, but settled on territories
where the resident females were in late stages. The pattern of female settlement shows that females prefer unmated males to
mated males. The preference is consistent with the polygyny threshold model, sexy son hypothesis and the asynchronous settlement
model, and inconsistent with the neutral mate choice hypothesis and the cooperative female choice model. For this reason,
the latter two hypotheses are unlikely to explain the occurrence of polygyny in our population of red-winged blackbirds.
Received: 1 December 1994 / Accepted after revision: 28 October 1995 相似文献
16.
Relative importance of male and territory quality in pairing success of male rock ptarmigan (Lagopus mutus) 总被引:4,自引:0,他引:4
We studied pairing success in male rock ptarmigan (Lagopus mutus) in northern Alaska to learn whether males obtaining more females possessed phenotypic traits that influenced female choice
directly, whether these traits permitted males to obtain territories favored by females, or whether both processes occurred.
The number of females per male varied from zero to three. Several male and territory traits were significantly correlated
with number of females per male. We used multiple regression to obtain a single measure of male quality and a single measure
of territory quality. These measures of male and territory quality correlated with each other and with male pairing success.
We used path analysis to separate direct effects of male quality on pairing success from indirect effects due to high-quality
males obtaining high-quality territories. Both direct and indirect pathways had significant effects on pairing success, and
direct and indirect effects of male traits on pairing success were about equal. This study illustrates an analytical approach
for estimating the relative importance of direct and indirect causal relationships in natural systems.
Received: 13 January 1998 / Accepted after revision: 7 November 1998 相似文献
17.
Kin-biased social tolerance among house mice has been interpreted in terms of kin discrimination. However, several lines of evidence suggest it may instead be an incidental artifact of group member discrimination. This leads to very different predictions about the social consequences of relatedness within and between social groups. Social interactions between wild-stock adult female and juvenile house mice (Mus domesticus) established in neighbouring territorial groups within enclosures reveal relatedness to dominant males within groups as the major factor determining social tolerance of juveniles by females. Relatedness to the female herself had no significant independent effect on responses indicating tolerance. Females were generally more aggressive toward neighbouring-group juveniles (all unrelated to females) compared with those from their own group (all related to females), but were most aggressive toward neighbouring juveniles sired by the neighbouring dominant male. They were also more aggressive toward their own-group juveniles that had been sired by the neighbouring dominant but only when encountered in the neighbouring territory and with a greater bias against female juveniles. Females were least aggressive toward own-group juveniles sired by their own-group dominant male. The sire-bias in tolerance among females is similar to that reported among the dominant males themselves in an earlier study. As a result of the combined sire-bias in tolerance by adult males and females, juveniles sired by their own-group dominant males become less likely to intrude into a neighbouring territory with time. Overall, the results suggest that differences in social tolerance reflect discrimination on the basis of social group membership rather than relatedness between interactants and thus provide strong experimental evidence in support of incidental kin bias rather than kin discrimination. 相似文献
18.
Russell C. Titus C. Ray Chandler Ellen D. Ketterson Val Nolan Jr. 《Behavioral ecology and sociobiology》1997,41(3):165-169
Frequency of singing by birds may vary with reproductive stage in ways that reflect variation in the functions of song in
intersexual and intrasexual communication. In dark-eyed juncos (Junco hyemalis) high-amplitude song is produced only by males. To investigate the function of this song, we tested whether fertility of
females affected singing by their mates or by neighboring males. Using focal observations, song censuses, and radiotracking
data, we determined whether song production varied between and among periods when females were fertile and non-fertile. Our
findings show that males do not increase song production when their mates are fertile, nor do they increase song production
when neighboring females are fertile. These results suggest that male juncos do not signal their intent to defend territories
(or mates) more when females are fertile and that they do not use song to advertise to specific potential participants in
extra-pair fertilizations.
Received: 13 February 1997 / Accepted after revison: 2 May 1997 相似文献
19.
T. R. Pope 《Behavioral ecology and sociobiology》2000,48(4):253-267
Evaluation of evolutionary mechanisms proposed to promote cooperative behavior depends on the relative influence of the behavior
on the reproductive success of individuals, the reproductive success of the group in which they interact behaviorally, and
the degree of gene correlation among cooperators. The genetic relationship within cooperative coalitions of female red howler
monkeys was examined for three populations with different densities and growth rates. Patterns of gene correlation change
within coalitions is documented using data from the mitochondrial and nuclear genomes, and long-term census monitoring. Differences
in fecundity and infant survivorship within and between groups of unrelated (rˉ=0) and related (rˉ≥ 0.25) females are compared. Females that emigrate from their natal groups form coalitions with other migrant females. These
coalitions attempt to establish a territory and, once successful in producing offspring, exclude other females from feeding
resources. Females in these coalitions had different mtDNA haplotypes and a genetically estimated mean r of 0, supporting demographic data on emigration patterns indicating that these females rarely have the opportunity to form
coalitions with kin. Patterns of recruitment and rate of matriline development within social groups supported behavioral data
indicating that females actively attempt to promote their own matriline as breeders over that of other females, and that some
matrilines are more successful at this than others. Mean r among females was significantly higher in coalitions established as social groups for several generations (rˉ=0.44). In these groups, females all shared the same mtDNA haplotype, and mtDNA haplotype divergence was significantly higher
between than within groups. Females in coalitions with kin had significantly higher reproductive success than females in unrelated
coalitions in all populations. This difference was not a function of coalition size, number of males, socionomic sex ratio,
or primiparity, although anecdotal evidence suggests that allomothering may compensate for inept new mothers in related coalitions
more often than in unrelated ones. Differences in territory quality could not be ruled out as a potential causal factor in
the saturated populations, but were unlikely in the low-density, growing population. There were substantial differences among
long-established coalitions in overall reproductive output in all three populations, and this was significantly correlated
with the number of breeding females. Increase in coalition size was a function of both group age and the behavioral tolerance
among females. Regardless of the underlying reasons for the patterns observed, reproductive success clearly increases with
degree of gene correlation among females within cooperative coalitions, and coalitions that recruit more daughters produce
more offspring. The nature of the cooperative relationship among group females directly influences both of these outcomes.
This is associated with substantial genetic differentiation among social groups within populations, creating conditions in
which genetic tendencies towards cooperative behavior can become tightly associated with group reproductive success.
Received: 15 September 1999 / Revised: 27 April 2000 / Accepted: 27 May 2000 相似文献
20.
We examined adult-juvenile conflict in the guanaco (Lama guanicoe). During spring, territorial males become increasingly aggressive toward all juveniles born the previous year and begin expelling them from family groups. In an apparent effort to reduce aggression, juveniles display submissive crouches when being observed, approached, or attacked by the territorial male. Therefore, we assessed the influence of juvenile submissive behavior on the timing of dispersal and also examined if dispersal time was related to survival and reproductive performance as adults. We also evaluated hypotheses regarding the evolution of juvenile mammalian dispersal in the context of if and how each may favor the forced dispersal of juvenile guanacos by territorial males. Juveniles generally dispersed in late spring and early summer, and a nearly equal proportion of females (n=46; 48%) and males (n=49; 52%) dispersed. More-submissive animals generally dispersed later than less-submissive animals. Juvenile sex and dispersal time were not related to survival. In contrast, juvenile sex and dispersal time were related to reproductive performance. The probability of reproducing was highest when juveniles dispersed early and decreased with increasing time in family groups prior to dispersal. The largest proportion of juveniles was forced to disperse during a 2-week interval following the peak of the breeding season. Competition for food resources is likely very intense at this juncture and territorial males may force older juveniles to disperse in order to divert food resources to younger neonates. Additionally, juveniles may be forced to disperse after territorial males mate their mothers to prevent lost mating opportunities, because females leave territories when their offspring disperse and possibly prior to mating with males. We conclude that the forced dispersal of juvenile guanacos by territorial males is ultimately driven by competition for food resources on territories. The timing of dispersal, however, may be tempered by the chronology of matings between territorial males and particular adult females, and/or genetic relatedness between territorial males and juveniles. 相似文献