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1.
Solitary foragers can balance demands for food and safety by varying their relative use of foraging patches and their level of vigilance. Here, we investigate whether colonies of the ant, Formica perpilosa, can balance these demands by dividing labor among workers. We show that foragers collecting nectar in vegetation near their nest are smaller than are those collecting nectar at sites away from the nest. We then use performance tests to show that smaller workers are more likely to succumb to attack from conspecifics but feed on nectar more efficiently than larger workers, suggesting a size-related trade-off between risk susceptibility and harvesting ability. Because foragers that travel away from the nest are probably more likely to encounter ants from neighboring colonies, this trade-off could explain the benefits of dividing foraging labor among workers. In a laboratory experiment, we show that contact with aggressive workers results in an increase in the mean size of recruits to a foraging site: this increase was not the result of more large recruits, but rather because fewer smaller ants traveled to the site. These results suggest that workers particularly susceptible to risk avoid dangerous sites, and suggest that variation in worker size can allow colonies to exploit profitably both hazardous and resource-poor patches.Communicated by L. Sundström 相似文献
2.
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
3.
Although contemporary animal contest theory emphasises the importance of physical asymmetries in resolving disputes, such
asymmetries do not obviously settle fights in all groups. Territorial male butterflies, for example, compete via elaborate
non-contact aerial interactions in which success is determined by relative persistence. Prior research suggests that the resolution
of these contests is not clearly related to physical variables such as body size or energy reserves. However, given that the
contests involve elaborate aerial manoeuvres, one long-standing suggestion is that asymmetries in flight performance, and
thus flight morphology, may be important. We addressed this hypothesis via a manipulative investigation into the biophysical
correlates of contest success in the speckled wood butterfly, Pararge aegeria. This species possesses the ability for significant adaptive phenotypic plasticity in relevant flight morphological parameters.
We took advantage of this plasticity to rear 90 individuals of markedly varying flight morphologies, which we then pitted
against each other in a semi-controlled experimental fashion. Multiple logistic and lognormal analyses provided little evidence
for the relevance of morphological parameters, including relative flight musculature, wing loading and wing aspect ratio (wing
length relative to area), to the outcome and/or duration of experimental contests. Instead, we found a positive effect of
age upon contest success. Given that ability for high acceleration is strongly linked to variation in these morphological
parameters, our findings suggest that flight performance is not a strong determinant of resource-holding potential in this
notably territorial butterfly. 相似文献
4.
How animals divide space can have fundamental implications for the population dynamics of territorial species. It has recently been proposed that space can be divided if animals tend to avoid fight locations, rather than the winner of fights gaining access to exclusive resources, behaviour that generates exclusive territories in two-dimensional space. A game-theory model has shown that this avoidance behaviour can be adaptive, but the adaptiveness has not been investigated in a spatially realistic context. We present a model that investigates potential strategies for the acquisition of territories when two-dimensional space must be divided between individuals. We examine whether exclusive territories form when animals avoid all encounters with others, or only those encounters that have led to losing fights, under different fighting costs and population densities. Our model suggests that when fighting costs are high, and the population density is low, the most adaptive behaviour is to avoid fight locations, which generates well-defined, exclusive territories in a population that is able to resist invasion by more aggressive strategies. Low fighting costs and high population densities lead to the break-down of territoriality and the formation of large, overlapping home ranges. We also provide a novel reason as to why so-called paradoxical strategies do not exist in nature: if we define a paradoxical strategy as an exact mirror-image of a common-sense one, it must respond in the opposite way to a draw as well as to wins and losses. When this is the case, and draws are common (fight outcomes are often not clear-cut in nature), the common-sense strategy is more often adaptive than a paradoxical alternative.Communicated by P. Bednekoff 相似文献
5.
Contests often occur between members of the same sex when they compete for access to mates, but inter-sexual contests may
occur over access to other essential resources such as food or shelter. Despite the possibility that such contests are common,
most studies focus on male fighting, and very few have analysed fights between males and females. Because males and females
differ physically and physiologically, fighting ability or resource-holding potential (RHP) may also be subject to inter-sexual
variation. In this study, we investigate size-controlled inter-sexual contests over the ownership of empty gastropod shells
in the hermit crab Pagurus bernhardus. During these fights, there are two roles, attacker and defender, and we use a fully orthogonal experimental design to compare
the performance of males and females in each role, when fighting either a male or female opponent. Although females fight
more intensely, male attackers have an advantage when compared to females playing the attacker role, as they are more likely
to evict the defender from its shell and thus win the resource. Further, in the defender role, male defenders are subject
to shorter attacks than female defenders. The differences in agonistic performance could not be attributed to differences
in perceived resource value between the sexes or to differences in body or weapon size. There are clear differences in the
agonistic behaviour of males and females, and this possibility should be incorporated into models of contest behaviour. In
particular, evolutionarily stable strategies may be expected to vary with sex ratios. 相似文献
6.
The establishment of fighting rules and the ability to recognise individual conspecifics and to assess their fighting ability
and/or roles may help to reduce costs of fighting. We staged encounters between males of the lizard Podarcis hispanica to examine whether lizards used fighting strategies and whether a previous agonistic experience affects the outcome and characteristics
of a subsequent encounter. The results showed that simple rules such as body size differences and residence condition were
used to determine the outcome of agonistic interactions as quickly as possible. Thus, larger males were dominant in most encounters.
However, when size differences between opponents are smaller, they may be more difficult to estimate and, then, residence
condition was more important. In addition, the intensity of interactions between males could be explained according to the
”sequential assessment game”, supporting the idea that P. hispanica males acquire information about fighting ability gradually during the progress of a fight. Our results also showed that the
second fight of the same pair of males was less aggressive, even when its outcome was the opposite of the first. This result
suggests that male P. hispanica can recognise individual opponents and that they use this information to reach a contest outcome more quickly, thus reducing
unnecessary aggression levels in subsequent interactions. These fighting strategies and assessment mechanisms may help to
stabilise the social system of this lizard.
Received: 2 November 1999 / Revised: 26 August 2000 / Accepted: 4 September 2000 相似文献
7.
The elongated eye span of male Diopsid flies is a sexually selected character that scales positively with body size. Previously,
the duration of agonistic contests was found to increase as rival body size and eye span disparities decreased. Hence, along
with its role in mate choice, eye span seems to facilitate mutual assessment of rival size. However, such results are also
expected in the absence of rival assessment, when each individual persists according to its own size-dependent internal threshold.
Here, we reanalyze these contests to distinguish between these two hypotheses using two measures of size: body length and
eye span. Mutual assessment predicts that contest duration should increase with loser size and decrease with winner size.
In contrast, our results were more consistent with self-assessment: We found a positive relationship between loser size and
contest duration, whereas winner size did not affect contest duration. Thus, flies did not appear to assess the size of their
rivals, indicating that the mutual assessment function of eye span elongation may be less important than previously suspected.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Francesca Gherardi 《Behavioral ecology and sociobiology》2006,59(4):500-510
A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence
dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of
equal/different RHP (i.e. ‘body size’) and equal/different RV (i.e. ‘shell size’ and ‘shell quality’). In a fifth experiment,
dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality
than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min.
As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were
directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with
the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during
fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell
quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic
modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses
and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and
oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory
of the previously held resource and behaved accordingly. 相似文献
9.
Michael P. Haley 《Behavioral ecology and sociobiology》1994,34(6):427-434
The effect of resource-holding power (RHP) and prior residency asymmetries on fight outcome and subsequent seasonal copulatory success was analyzed for fights between marked male northern elephant seals (Mirounga angustirostris). RHP asymmetries were measured as differences in estimated mass and prior residency asymmetries were measured as differences in beach tenure prior to the fight. The principal results were: (a) Neither differences in mass nor differences in beach tenure had any effect on fight outcome as separate factors. (b) Mass and tenure differences had an interactive effect on fight outcome; fight winners were either heavier males present for shorter periods (intruders) or lighter males present for longer periods (prior residents). (c) Winners of fights copulated more often than losers after a fight throughout the breeding season; this difference was smallest for low-ranking males, larger for high-ranking males in short fights, and greatest for high-ranking males in long fights. (d) Prior resident males who won long fights obtained significantly more copulations after a fight than the males they defeated, but this was not true for intruder males who won long fights. These results suggest that male northern elephant seals will incur greater contest costs (i.e., fight for longer periods and/or against heavier males) for higher reproductive payoffs. They also imply that, at least for males in long fights, differences in prior residence represent payoff asymmetries, with higher reproductive payoffs for winning prior residents than for winning intruders. 相似文献
10.
Thomas J. Valone 《Behavioral ecology and sociobiology》2007,62(1):1-14
Public information (PI), a form of indirect social information, is used by individuals to estimate the quality of environmental
parameters. It can be acquired in two ways. One way is by noting the performance of others. The other way it can be acquired
is by noting the behavioral decisions of other individuals. Performance-based PI has been observed most often in the context
of food and breeding patch estimation, as well as by individuals eavesdropping on contests between others in the context of
assessing the fighting ability of opponents and the quality of mates. Evidence for the acquisition of PI from behavioral decisions
of others comes mostly from studies of copying behavior, although recent work suggests that it also occurs when individuals
estimate the tendency of others to be altruistic. PI use appears to be widespread across many taxa, although most work has
been conducted on birds and fish. Absent from the literature are clear examples of PI use in mammals. The use of PI appears
to often depend on its cost of acquisition and whether it contradicts an individual’s personal prior experience. PI can be
an important benefit of associating with others. 相似文献