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1.
Nga Nguyen Russell C. Van Horn Susan C. Alberts Jeanne Altmann 《Behavioral ecology and sociobiology》2009,63(9):1331-1344
Close associations between adult males and lactating females and their dependent infants are not commonly described in non-monogamous
mammals. However, such associations [sometimes called “friendships” (Smuts 1985)] are regularly observed in several primate species in which females mate with multiple males during the fertile period.
The absence of mating exclusivity among “friends” suggests that males should invest little in infant care, raising questions
about the adaptive significance of friendship bonds. Using data from genetic paternity analyses, patterns of behavior, and
long-term demographic and reproductive records, we evaluated the extent to which friendships in four multi-male, multi-female
yellow baboon (Papio cynocephalus) groups in Amboseli, Kenya represent joint parental care of offspring or male mating effort. We found evidence that mothers
and infants benefited directly from friendships; friendships provided mother–infant dyads protection from harassment from
other adult and immature females. In addition, nearly half of all male friends were the genetic fathers of offspring and had
been observed mating with mothers during the days of most likely conception for those offspring. In contrast, nearly all friends
who were not fathers were also not observed to consort with the mother during the days of most likely conception, suggesting
that friendships between mothers and non-fathers did not result from paternity confusion. Finally, we found no evidence that
prior friendship increased a male’s chances of mating with a female in future reproductive cycles. Our results suggest that,
for many male–female pairs at Amboseli, friendships represented a form of biparental care of offspring. Males in the remaining
friendship dyads may be trading protection of infants in exchange for some resources or services not yet identified. Our study
is the first to find evidence that female primates gain social benefits from their early associations with adult males.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
Offspring size can have pervasive effects throughout the life history stages of many marine invertebrates. Although maternal
offspring investment is largely determined by the environmental conditions experienced by the mother, egg size might additionally
vary in response to the number and quality of previous mating partners. Positive effects of mating multiply with several different
males (polyandry) have been confirmed for a variety of species, whereas such investigations are lacking for marine invertebrates.
Here we differentiated between the effects of ejaculate amount (repeatedly mated) and ejaculate diversity (polyandry) on maternal
offspring investment in the simultaneously hermaphroditic sea slug Chelidonura sandrana. We found that focal “females” mated with four different “males” produced significantly larger egg capsules and larger veligers,
while focal “females” mated four times with the same “male” suffered from reduced mid-term fecundity. We found no effect of
veliger size on veliger survival. Our results show that female mating patterns are an important addition to understanding
the variation in offspring size in internally fertilizing marine invertebrates. 相似文献
3.
Manuela Panzacchi Ivar Herfindal John D. C. Linnell Morten Odden John Odden Reidar Andersen 《Behavioral ecology and sociobiology》2010,64(8):1267-1278
The choice of neonatal hiding place is critical for ungulates adopting hiding anti-predator strategies, but the consequences
of different decisions have rarely been evaluated with respect to offspring survival. First, we investigated how landscape-scale
choices made by roe deer fawns and their mothers affected predation risk by red foxes in a forest–farmland mosaic in southeastern
Norway. After, we examined the effect of site-specific characteristics and behaviour (i.e. visibility, mother–fawn distance
and abundance of the predator’s main prey item—small rodents) on predation risk. The study of habitat use, selection and habitat-specific
mortality revealed that roe deer utilised the landscape matrix in a functional way, with different habitats used for feeding,
providing maternal care and as refugia from predation. Mothers faced a trade-off between foraging and offspring survival.
At the landscape-scale decisions were primarily determined by maternal energetic constraints and only secondarily by risk
avoidance. Indeed, forage-rich habitats were strongly selected notwithstanding the exceptionally high densities of rodents
which increased fawn predation. At fine spatial scales, a high visibility of the mother was the major factor determining predation
risk; however, mothers adjusted their behaviour to the level of risk at the bed site to minimise predation. Fawns selected
both landscape-scale refugia and concealed bed sites, but failure to segregate from the main prey of red foxes led to higher
predation. This study provides evidence for the occurrence of spatial heterogeneity in predation risk and shows that energetically
stressed individuals can tackle the foraging-safety trade-off by adopting scale-dependent anti-predator responses. 相似文献
4.
We investigated the effects of population fluctuation on the offspring’s sex allocation by a weakly polygynous mouse, Apodemus argenteus, for 3 years. In acorn-poor seasons, heavier mothers invested more in sons, and lighter mothers invested more in daughters.
In acorn-rich seasons, heavier mothers invested more in daughters, and lighter mothers invested more in sons. Maternal body
condition and litter size affected the sex allocation. Furthermore, there was a maternal investment trade-off between a son’s
birth mass and the number of daughters. Based upon the effect of population fluctuation on the lifetime reproductive success
of each sex, we proposed the new “safe bet hypothesis”. This hypothesis predicts that frequent and unpredictable change in
female distribution, which is often caused by abrupt fall in food condition, favors female-biased maternal investment to offspring
by polygynous mammals and is applicable to many small mammals inhabiting in unstable environments. 相似文献
5.
Predictions of the model of van Schaik (1989) of female-bonding in primates are tested by systematically comparing the ecology,
level of within-group contest competition for food (WGC), and patterns of social behaviour found in two contrasting baboon
populations. Significant differences were found in food distribution (percentage of the diet from clumped sources), feeding
supplant rates and grooming patterns. In accord with the model, the tendencies of females to affiliate and form coalitions
with one another, and to be philopatric, were strongest where ecological conditions promoted WGC. Group fission in the population
with strong WGC was “horizontal” with respect to female dominance rank, and associated with female-female aggression during
a period of elevated feeding competition. In contrast, where WGC was low, females’ grooming was focused on adult males rather
than other females. Recent evidence suggests that group fission here is initiated by males, tends to result in the formation
of one-male groups, and is not related to feeding competition but to male-male competition for mates. An ecological model
of baboon social structure is presented which incorporates the effects of female-female competition, male-male competition,
and predation pressure. The model potentially accounts for wide variability in group size, group structure and social relationships
within the genus Papio. Socio-ecological convergence between common baboons and hamadryas baboons, however, may be limited in some respects by phylogenetic
inertia.
Received: 22 April 1994/Accepted after revision: 9 December 1995 相似文献
6.
M. Thiel 《Marine Biology》1998,132(1):107-116
The reproductive traits of a deposit-feeding amphipod that engages in extended parental care were examined. At the study
site in Lowes Cove, Maine, USA, Casco bigelowi (Blake, 1929) occurred in highest densities in soft sediments just below mean low water (MLW). During most months, the sex
ratio was ≃1. Many females hosted males in their burrows throughout the summer, but after fertilization of females in September,
all adult males disappeared from the study area. In October almost 80% of the females were ovigerous, and in November about
the same percentage was parental, i.e. caring for juveniles in their burrows. The females produced only one brood each in
late fall which they accommodated in their burrows for 2 mo or longer. The average number of juveniles per female was ∼20
in November, and continuously decreased until January. Juveniles reached sizes >10 mm length in the maternal burrows. In early
December the first juveniles were found in their own burrows, but major recruitment took place in late December and January.
It is concluded that for C. bigelowi, the delay of recruitment into the winter months with low predation pressure and the large offspring size at this time are
major advantages gained by extended parental care. C. bigelowi is host to the peritrich ciliate Cothurnia sp. on its gills, and during the summer months >70% of all amphipods had ciliates on their gills. Juveniles still living
in their mother's burrows showed infestation rates similar to that of the parent; those of highly infested mothers were more
heavily infested than those of “clean” mothers. Facilitated epibiont transmission during intimate and long-lasting (2␣mo)
parent–offspring associations may be a consequence of extended parental care.
Received: 25 November 1997 / Accepted: 14 April 1998 相似文献
7.
Gine Roll Skjærvø Bård G. Stokke Eivin Røskaft 《Behavioral ecology and sociobiology》2009,63(8):1133-1140
The aim of this study was to test the hypothesis that parent–offspring conflict over parental investment might have led to
the rarity of dizygotic twins in humans. We explored the theoretical prediction that twins maximize their inclusive fitness
by the death of a co-twin, while mothers of twins maximize fitness by raising both twins to independence. We used life history
data (1700–1900) from two parishes in Central Norway to compare differences in inclusive fitness (measured as number of children
reared to the age of 16 years, using Hamilton's rule) between twins and mothers of twins. Our results show that twins maximize
their inclusive fitness by the death of a co-twin, while mothers of twins raise more children by rearing both twins to adulthood.
However, because twins growing up as singletons may produce higher or at least equal number of offspring than the sum of the
two twins growing up together, mothers might gain more grandchildren by allowing twins to grow up as singletons. To conclude,
both selfish twins and their mothers might benefit by the death of a co-twin, indicating that there is no parent–offspring
conflict responsible for the rareness of twins in these human populations. Finally, we discuss the results in the light of
“The Insurance Egg Hypothesis” and “The Natural Selection Hypothesis”. 相似文献
8.
Close association between an anoestrous female at the time of lactation and adult male(s) is relatively rare in mammals, but
common in baboons (Papio hamadryas subsp.). The functional significance of these “friendships” remains unclear, however. In chacma baboons (P. h. griseipes), friendships are a counter-strategy to infanticide by immigrant males. Experimental playback of female distress calls in
chacma baboons revealed that male friends are more motivated to protect females and infants than are control males. Olive
baboons (P. h. anubis) also exhibit friendships, but infanticide is rare, suggesting that friendships provide females with protection from non-lethal
aggression (anti-harassment hypothesis) or serve to promote male–infant bonds that later benefit the maturing juvenile (future
male caretaker hypothesis). We replicated these playback experiments on a group of olive baboons to test between these hypotheses
and to evaluate if the lower costs of non-lethal harassment lessens male protective responsiveness relative to protection
from (more costly) infanticide. Spatial data revealed that most lactating females had one to four friend males. Relative to
non-friends, friend dyads were characterized by higher rates of allogrooming and infant handling, but less agonism. Female
rank was correlated with the number of male friends. Just as in chacma baboons, playback of female screams elicited stronger
responses from male friends than control males in support the anti-harassment hypothesis. Compared to the chacma baboon, male
olive baboons appeared to exhibit similarly high levels of protective solicitude for female friends although they protect
against non-lethal harassment rather than infanticide. 相似文献
9.
Assisting the genetic parents in the rearing of young, a widespread phenomenon in many birds and mammals, is usually regarded
as an altruistic or mutualistic behavior. Infant handling by females other than the mother is also common in many primates,
but due to high within- and between-species variation and limited knowledge about fitness consequences there is no consensus
about its evolutionary and functional significance. Analysis of female infant-handling patterns and its reproductive consequences
in three groups of semifree-ranging Barbary macaques revealed that nulliparous females significantly more often handled infants
than parous females, but infant handling experience did not affect survival of their own first live-born offspring. Females
interacted preferentially with closely related infants, but infant handling frequency improved neither infant survival nor
maternal fecundity. Reciprocation of infant handling by mothers was rare. Although “aunting to death” occurred in the population,
the hypothesis that infant handling serves to reduce the fitness of competitors was not supported. Limited evidence suggests
that females at least sometimes use infants as strategic tools in the course of alliance formation. In concert with this poor
evidence for a functional basis of the behavior, several lines of evidence support the hypothesis that infant handling evolved
as a non-adaptive by-product of a strong selection for mother-offspring bonding. (1) Rates of infant handling were highest
among females that experienced early infant loss. (2) Females caring for infants or yearlings of their own handled other infants
significantly less often than females without dependent offspring. (3) Infant handling by females was most prevalent during
the infants’ first month of life. (4) Both “aunting to death” and a successful adoption occurred irrespective of kinship relations.
Although the by-product hypothesis appears to be the only one able to explain all results of this study, the apparent rarity
of infant handling in non-female-bonded species suggest that kin selection is a possible alternative explanation for the evolution
of female infant-handling in primates.
Received: 30 December 1995/Accepted after revision: 10 May 1996 相似文献
10.
Martha M. Robbins Andrew M. Robbins Netzin Gerald-Steklis H. Dieter Steklis 《Behavioral ecology and sociobiology》2007,61(6):919-931
Over the past few decades, socioecological models have been developed to explain the relationships between the ecological
conditions, social systems, and reproductive success of primates. Feeding competition, predation pressures, and risk of infanticide
are predicted to influence how female reproductive success (FRS) depends upon their dominance rank, group size, and mate choices.
This paper examines how those factors affected the reproductive success of female mountain gorillas (Gorilla beringei beringei) of the Virunga Volcanoes, Rwanda from 1967–2004. Reproductive success was measured through analyses of interbirth intervals,
infant survival, and surviving infant birth rates using data from 214 infants born to 67 females. Mountain gorillas were predicted
to have “within-group scramble” feeding competition, but we found no evidence of lower FRS in larger groups, even as those
groups became two to five times larger than the population average. The gorillas are considered to have negligible “within-group
contest” competition, yet higher ranked mothers had shorter interbirth intervals. Infant survival was higher in multimale
groups, which was expected because infanticide occurs when the male dies in a one-male group. The combination of those results
led to higher surviving birth rates for higher ranking females in multimale groups. Overall, however, the socioecological
factors accounted for a relatively small portion of the variance in FRS, as expected for a species that feeds on abundant,
evenly distributed foliage. 相似文献
11.
Parent–offspring conflict theory predicts the evolution of offspring solicitation signals that can influence the amount and/or
the duration of parental investment. Short-term effects of offspring solicitation signals on parental food provisioning have
been widely demonstrated, but persistent effects of offspring signals on the maintenance of parental care have been rarely
studied. Also, the relation between the amount of care provided to the brood and how it is distributed among individual offspring
within a brood is not well enough understood. Here, we investigated in the European earwig (Forficula auricularia) the effects of offspring condition-dependent chemical signals on the maintenance of maternal care among broods and the distribution
of maternal food within broods. Mothers were isolated from their brood for 3 days and continuously exposed to chemical signals
extracted from broods of experimentally manipulated nutritional state. After re-introducing mothers to their brood, a range
of maternal behaviours were quantified. We found that earwig mothers groomed their offspring significantly more after exposure
to chemical extract from high-food brood in comparison with mothers exposed to extract from low-food brood, which in turn
displayed significantly more aggressive behaviour. Furthermore, we manipulated offspring individual nutritional condition
within the brood to evaluate the effect of offspring state on the within-brood food distribution. Within broods, poorly fed
individuals received significantly more food than well-fed individuals, probably due to scramble competition. These results
show that earwig nymphs express multi-component condition-dependent signals and behaviours differentially affecting maternal
care provisioned to the brood and the distribution of care within broods. 相似文献
12.
Andrea L. Baden Patricia C. Wright Edward E. Louis Jr. Brenda J. Bradley 《Behavioral ecology and sociobiology》2013,67(12):1939-1950
Communal nesting, where several mothers regularly pool and cooperatively rear offspring, is unusual in mammals. This type of crèching behavior is especially rare among primates, with the notable exceptions of humans, some nocturnal strepsirrhines, and—as we show in this study—black-and-white ruffed lemurs (Varecia variegata). Here, we combine data on nesting behavior, genetic relatedness, and infant survivorship to describe variation in ruffed lemur infant care and to examine the potential benefits of ruffed lemur communal breeding. Reproductive events were rare, and females produced litters (synchronously) only once in 6 years of observation. We show that not all mothers participate in communal crèches, but those that did had greater maternal success; communal breeders spent more time feeding and their offspring were more likely to survive. Although cooperating mothers were often related, females also cooperated with non-kin, and those who shared infant care responsibilities had greater maternal success than mothers who did not participate. If there is indeed a causal link between maternal cooperation and reproductive success, this unusual behavior, like that of human communal rearing, may have evolved via some combination of kin selection and mutualism. 相似文献
13.
Socialization of young is an important component of maternal care in social mammals. It is therefore perplexing that female
chimpanzees with dependent offspring spend more time alone than females without dependent offspring, and than males. We propose
that chimpanzee mothers are less gregarious than nonmothers and males to reduce the risk of injury that aggressive males pose
to their offspring. We predict that mothers will associate less with males, associate with fewer males, and reduce mother−infant
proximity in the presence of males, and that these effects will reduce with increasing offspring age. We test whether the
pattern of gregariousness and mother−offspring proximity support these predictions in the Kanyawara chimpanzee community in
Uganda. The probability that a female was found in the presence of males was lower for mothers than nonmothers and increased
with offspring age. The probability that a female was found with other females did not differ between mothers and nonmothers.
Mother-to-offspring distance was higher when a mother was in an all-female group than in a mixed-sex group and increased with
her offspring's age. Mother-to-offspring distance was greatest when there were relatively low numbers of males and relatively
high numbers of females in a subgroup. We propose that mothers avoid grouping with males because of the vulnerability of their
young, and that the presence of males in a subgroup increases a female's protectiveness of her young. We discuss the implications
of our findings and the relevance of fission−fusion group formation to chimpanzee mothers. 相似文献
14.
There is growing evidence that the sex ratios of wild vertebrate populations are determined by mechanisms that are directly
influenced by environmental characteristics. The Trivers–Willard (TWH) and extrinsic modification (EMH) hypotheses postulate
differing determinants of mammalian offspring sex ratios. TWH states that mothers allocate resources according to their current
condition and sex-specific offspring costs. EMH states that environmental forces that affect maternal condition determine
offspring sex ratios, independently of maternal tactics of sex-biased allocation. We statistically assessed support for each
of these hypotheses using long-term life histories of the allied rock-wallaby, Petrogale assimilis; a continuously breeding, polygynous, weakly dimorphic marsupial. We showed that birth sex ratios were equal and independent
of maternal and environmental conditions. However, secondary sex ratios were male-biased under good environmental conditions
and for high quality mothers or mothers in good condition. Sex differences in offspring survival contributed to these biases:
(1) environmental conditions strongly influenced survival to pouch emergence (in support of EMH) and (2) maternal quality
affected survival to the end of maternal care (in support of TWH). Environmental effects on survival were more important than
maternal factors over the entire period of maternal care and contributed most to male-biased sex ratios at pouch emergence.
In contrast, maternal mass was the best predictor of sex ratios at the end of maternal care—the life history stage where offspring
body mass differed between the sexes. 相似文献
15.
Length of maternal care, i.e. the interval between successfully raised litters, is the most important factor explaining the variation in reproductive rate among brown-bear (Ursus arctos) populations. In this paper, we examine the variation in length of maternal care in radio-marked brown bears and its effect on their offspring in northern Sweden. Young stayed with their mothers for 1.4–1.5 or 2.4–2.5 (in one case 3.5) years and were weaned with body masses varying from 17 to 69 kg. The probability of yearling litters staying with their mother for a 2nd year increased with decreasing yearling body mass, and was higher for litters with two offspring than for litters with one or three to four offspring. Staying with their mothers for a 2nd year had a positive effect on mass gain in yearlings and this effect was more pronounced in litters with two than three to four offspring. Body mass of 2-year-olds was not related to age of weaning, suggesting that keeping offspring for an additional year mainly compensated for low yearling body mass. If large offspring body mass positively affects later offspring survival and reproduction, mothers may be able to optimize the length of maternal care according to the litter size and the size of their yearlings.Communicated by F. Trillmich 相似文献
16.
Maternal investment in rhesus macaques (Macaca mulatta): reproductive costs and consequences of raising sons 总被引:1,自引:0,他引:1
Maternal investment in offspring is expected to vary according to offspring sex when the reproductive success of the progeny
is a function of differential levels of parental expenditure. We conducted a longitudinal investigation of rhesus macaques
to determine whether variation in male progeny production, measured with both DNA fingerprinting and short tandem repeat marker
typing, could be traced back to patterns of maternal investment. Males weigh significantly more than females at birth, despite
an absence of sex differences in gestation length. Size dimorphism increases during infancy, with maternal rank associated
with son’s, but not daughter’s, weight at the end of the period of maternal investment. Son’s, but not daughter’s, weight
at 1 year of age is significantly correlated with adult weight, and male, but not female, weight accounts for a portion of
the variance in reproductive success. Variance in annual offspring output was three- to fourfold higher in males than in females.
We suggest that energetic costs of rearing sons could be buffered by fetal delivery of testosterone to the mother, which is
aromatized to estrogen and fosters fat accumulation during gestation. We conclude that maternal investment is only slightly
greater in sons than in daughters, with mothers endowing sons with extra resources because son, but not daughter, mass has
ramifications for offspring sirehood. However, male reproductive tactics supersede maternal investment patterns as fundamental
regulators of male fitness.
Received: 23 July 1999 / Received in revised form: 23 February 2000 / Accepted: 13 March 2000 相似文献
17.
Paula A. White 《Behavioral ecology and sociobiology》2008,62(3):377-361
Among spotted hyenas, Crocuta crocuta, neonatal aggression in twins is a well-known phenomenon and serves to establish intra-litter dominance soon after birth.
As the stronger more aggressive cub presumably attains dominance over its twin, intra-litter dominance presents mothers with
an ideal opportunity to assess individual cub fitness and, thereafter, to selectively favor one cub over the other. This study
quantified maternal response to sibling conflict in 26 sets of twins born to 16 wild-living females to determine whether mothers
of different social ranks exhibited favoritism towards sons or daughters, or in the case of same-sex twins, the dominant or
subordinate cub. Maternal response to sibling conflict did not vary with litter sex composition, suggesting that mothers do
not favor offspring of one sex over the other. All mothers intervened when their cubs fought and sometimes punished their
cubs. Higher-ranking mothers more often punished both cubs, while lower-ranking mothers were more selective and punished the
dominant cub. Where sibling aggression was most extreme, rather than favor the dominant sibling, mothers of all ranks made
concessions to the subordinate cub that included procuring private nursing bouts for the subordinate and temporarily housing
twins in separate dens, presumably to decrease sibling conflict. These findings represent a complex example of parent–offspring
conflict and support both the insurance cub hypothesis and resource tracking hypothesis that mothers endeavor to keep all
offspring alive for as long as possible in the event that the dominant sibling dies or that resources provide for the rearing
of twins.
This contribution is part of the special issue “Sibling competition and cooperation in mammals” (guest editors: Robyn Hudson
and Fritz Trillmich). 相似文献
18.
Common goldeneyes adjust maternal effort in relation to prior brood success and not current brood size 总被引:3,自引:0,他引:3
Parental investment theory predicts that parental effort should be related to the reproductive value of the current brood.
This depends on both the number of young and the survival prospects of each of them. Thus parents may provide more care to
larger broods either because of (1) the direct effect of brood size per se on reproductive value (the “brood size” hypothesis)
or because (2) past mortality, reflected in current brood size, predicts future mortality of the brood and hence its reproductive
value (the “brood success” hypothesis). Earlier studies have not attempted to distinguish between these alternatives. We tested
the hypotheses in the precocial, nidifugous common goldeneye Bucephala clangula, a species with uniparental female care. Maternal effort was measured as the time spent by the female in rearing the brood.
We found that brood size itself is not associated with maternal effort, but that females modify their maternal effort according
to the mortality already experienced by the brood, supporting the prediction of the brood success hypothesis. We also found
that brood mortality varied considerably between broods and that previous mortality predicts future mortality within broods,
basic assumptions of the brood success hypothesis.
Received: 30 January 1996 / Accepted after revision: 27 October 1996 相似文献
19.
Risk taking during parental care: a test of three hypotheses applied to the pied flycatcher 总被引:2,自引:0,他引:2
According to life-history theory, there will often be a conflict between investment in current versus future reproduction.
If a predator appears during breeding, parents must make a compromise between ensuring the growth and survival of offspring
(nest defence, feeding and brooding of young), and reducing the risk of predation to ensure their own survival. We model three
hypotheses for the outcome of this conflict which are particularly relevant for altricial birds. They are not mutually exclusive,
but focus on different costs and benefits. (1) Parental investment is determined by the parents’ own risk of predation. This
hypothesis predicts that a lone parent should take smaller risks than a parent that has a mate. (2) Parental investment is
related to the reproductive value of the offspring: Parents are predicted to take greater risks for larger broods, larger-sized
or older offspring. (3) Finally, we present the new hypothesis that parental investment is related to the harm that offspring
would suffer during a period of no parental care (incubation, brooding, feeding). This hypothesis predicts that parents should
take greater risks for younger offspring, or for offspring in poorer condition, because the marginal benefit of parental care
is largest in such cases. Hence, one may also expect that lone parents should take greater risks than two parents because
their offspring are more in need of care. We tested these hypotheses on the pied flycatcher (Ficedula hypoleuca) by presenting a stuffed predator of the parents (a sparrowhawk, Accipiter nisus) close to the nest when parents were feeding the young. Risk taking was measured as the time that elapsed until the first
visit to the nest. Most support was found for the ‘‘harm to offspring’’ hypothesis. Previous studies have usually measured
the intensity of nest defence against typical nest predators, and have found evidence for the ‘‘reproductive value of offspring’’
hypothesis. However, our model predicts that the importance of the reproductive value of the offspring should decrease relative
to the harm that offspring would suffer if they were not cared for when the predator type changes from a nest predator to
a predator of adults, and when conditions for breeding turn from good to bad.
Received: 13 April 1995/Accepted after revision: 11 March 1996 相似文献
20.
Group sizes are often considered to be the result of a trade-off between predation risk and the costs of feeding competition. We develop a model to explore the interaction between different ecological constraints on group sizes, using a primate (baboons) case study. The model uses climatic correlates of time budgets to predict maximum ecologically tolerable group size, and climatic predictors of predation risk (reflected mainly in predator density and female body mass) to predict minimum tolerable group size for any given habitat. As well as defining the range of sustainable group sizes for a given habitat, the model also allows us to reliably predict our exemplar taxon's biogeographical distribution across Africa. We also explore the life history implications of the model to ask whether baboons form group sizes which maximise survival or fecundity in the classic trade off between these two key life history variables. Our results indicate that, within the range of study sites in our sample, baboons prefer to maximise fecundity. However, the data indicate that in higher predation risk habitats they would switch to maximising survival at the expense of fecundity. We argue that this is due to the fact that interbirth interval and developmental rates have a ceiling that cannot be breached. Thus, while females can shorten interbirth intervals to compensate for increased predation risk, there is a limit to how much these life history variables can be altered, and when this is reached the best strategy is to maximise survivorship. 相似文献