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1.
Summary Risk-sensitive foraging theory predicts that predators which face starvation if there is a temporary shortfall in their food supply should choose feeding sites on the basis of variation in as well as mean expected reward rate. For a given mean reward rate they should choose high variance feeding sites (be risk-prone) if they are running below energy requirement, but low variance sites (be risk-averse) if they are running above.Common shrews presented with a choice between constant and variable feeding stations were more likely to visit the variable station when they were running below energy requirement and more likely to visit the constant station when they were running above. However, the tendency towards risk-aversion above requirement was greater than that towards risk-proneness below.When all shrews were considered together, the probability of visiting the variable station correlated negatively and continuously with intake relative to requirement. 相似文献
2.
C. J. Barnard C. A. J. Brown A. I. Houston J. M. McNamara 《Behavioral ecology and sociobiology》1985,18(2):139-146
Summary A model of risk-sensitive foraging based on a continuously foraging but interruptable predator is developed and tested in a simple choice experiment using common shrews.Given a choice of two feeding stations, shrews behaved in accordance with the broad predictions of the model. Having been trained below their estimated food requirement, shrewss preferred the station y elding the higher mean reward rate, but prefereence for a constant (constant reward rate) or risky variable reward rate) station was influenced by experience of variance in reward rate at the risky station.Preference was influenced most clearly by experience of reward rate variance during tests rather than training. 相似文献
3.
We examined the risk-sensitive foraging behaviour of the round-eared elephant shrew by open-economy choice experiments, in which animals were deprived of food immediately prior to experiments but given food ad libitum afterwards, to test the energy budget rule. The energy budget rule states that if an animal's (daily) energy budget is negative it should behave in a risk-prone manner. A risk-prone elephant shrew should select food from a more variable rather than a constant feeding station, although both feeding stations yield the same average return. The choice of a variable station can indicate the degree to which an animal is an energy-shortfall minimizer. Elephant shrews running below energy requirement did not choose feeding stations in accordance with the rule. Under laboratory conditions, approximating either average summer or winter temperatures, elephant shrews showed risk-averse behaviour. A polycyclic activity profile, the ability to switch the diet, and greater than expected physiological control over energy balance, may favour a continuously foraging animal such that short-term energy deficits are minimized. We argue that, under these conditions, a risk-averse response to reward-size variance is expected, because an elephant-shrew may not reliably perceive those circumstances under which risk-prone behaviour should be adopted. 相似文献
4.
Monique Liesenjohann Thilo Liesenjohann Lenka Trebaticka Marko Haapakoski Janne Sundell Hannu Ylönen Jana A. Eccard 《Behavioral ecology and sociobiology》2011,65(11):2079-2089
Indirect exploitative competition, direct interference and predation are important interactions affecting species coexistence.
These interaction types may overlap and vary with the season and life-history state of individuals. We studied effects of
competition and potential nest predation by common shrews (Sorex araneus) on lactating bank voles (Myodes glareolus) in two seasons. The species coexist and may interact aggressively. Additionally, shrews can prey on nestling voles. We studied
bank vole mothers’ spatial and temporal adaptations to shrew presence during summer and autumn. Further, we focused on fitness
costs, e.g. decreased offspring survival, which bank voles may experience in the presence of shrews. In summer, interference
with shrews decreased the voles’ home ranges and they spent more time outside the nest, but there were no effects on offspring
survival. In autumn, we found decreased offspring survival in enclosures with shrews, potentially due to nest predation by
shrews or by increased competition between species. Our results indicate a shift between interaction types depending on seasonal
constraints. In summer, voles and shrews seem to interact mainly by interference, whereas resource competition and/or nest
predation by shrews gain importance in autumn. Different food availability, changing environmental conditions and the energetic
constraints in voles and shrews later in the year may be the reasons for the varying combinations of interaction types and
their increasing effects on the inclusive fitness of bank voles. Our study provides evidence for the need of studies combining
life history with behavioural measurements and seasonal constraints. 相似文献
5.
Andrea Romano Giuseppe Boncoraglio Diego Rubolini Nicola Saino 《Behavioral ecology and sociobiology》2013,67(5):851-859
In species with parental care, competition among siblings for access to limited parental resources is common. Sibling competition can be mediated by begging behaviour, a suite of different visual and acoustic displays by which offspring solicit parental care. These are mostly addressed to the parents upon food provisioning, but can also be performed in the absence of the attending parents. This so-called parent-absent begging (PAB) may function as an intrabrood communication signal and potentially affect intrabrood competition dynamics for access to food. We investigated the role of PAB in moulding sibling interactions and its effect on food intake among altricial barn swallow (Hirundo rustica) nestlings, both under normal and experimentally reduced food intake. Frequency of PAB increased after food deprivation. Nestlings that had performed PAB increased their begging intensity upon the subsequent parental feeding visit, while siblings reduced their own begging level, but only when they had not been food-deprived. As a consequence, nestlings which had performed PAB before parental arrival had larger chances of receiving food. However, nestlings did not benefit from displaying PAB when competing with food-deprived siblings. Our findings show that PAB reliably reflects need of food, indicating that a nestling will vigorously compete for the subsequent food item. By eavesdropping siblings' PAB displays, nestlings may optimally balance the costs of scrambling competition, the direct fitness gains of being fed and the indirect fitness costs of subtracting food to needy kin. However, large asymmetries in satiation between competitors may lead individual offspring to monopolize parental resources, irrespective of PAB displays. 相似文献
6.
Summary Interactions between pairs of shrews on a foraging grid were analysed to test for the effects of prior residence, food density and differences in competitive ability between individuals on the outcome.Prior residence was an important factor influencing the outcome of interactions but the degree of resident advantage varied both with food density on the grid and the difference in competitive ability between shrews.Payoff and resource holding power (R.H.P.) asymmetry effects can be implied from the influence of food density and competitive ability differences but prior residence may operate as an uncorrelated asymmetry only under certain conditions determined by combinations of the other two asymmetries. 相似文献
7.
Summary Local concentrations of migrating, fat-depleted birds with similar diets can lead to increased competition for food at a time when energy demand is high. Results of a predator-exclosure experiment indicate that intercontinental passerine migrants depress food abundance during stopover following migration across the Gulf of Mexico. Moreover, migrants that stop when a high number of potential competitors are present replenish energy reserves more slowly than migrants that stop under low density conditions. Competition increase the rate of food depletion and may decrease the probability that a migrant will meet its energetic requirements and complete a successful migration. 相似文献
8.
Kit Magellan Lars B. Pettersson Anne E. Magurran 《Behavioral ecology and sociobiology》2005,58(4):366-374
Although many studies have examined the effects of male size on attractiveness and mating behaviour, few have taken genetic background into consideration. Phenotypic manipulation permits the experimental adjustment of morphological traits while keeping genetic background constant. Here, male guppies, Poecilia reticulata, an ideal model for this type of manipulation, were raised at different temperatures to produce sibling pairs that differed in size. These were then used to investigate male mating behaviour and male attractiveness, assessed through female mate choice, in relation to this size dimorphism. Further, male–male competition, which is intrinsic to male mating behaviour, is also likely to be affected by their size. Through the use of repeated measures analyses we demonstrate that females significantly prefer larger males and male size and competition significantly affect several aspects of male mating behaviour. Larger siblings perform more sneaky mating attempts and spend more time chasing females. The frequencies of both these behaviours increase with competition. While display frequency is unaffected by male size and competition, display duration and the amount of time spent attending females are reduced in the presence of competitors. This study highlights the use of phenotypic manipulation as a valuable tool for investigating behavioural interactions and confirms that both male size and competition are significant factors in the guppy mating system. 相似文献
9.
When endoparasitoid wasps oviposit into hosts which have already been parasitized (= superparasitism), this results in potentially
lethal interlarval competition. For solitary species, the decision to lay additional eggs should therefore be based on the
probability of superparasite survival in any superparasitized host. In this study, in vitro contests staged between three larval instars of Venturia canescens Grav. (Hymenoptera: Ichneumonidae) reveal that the age difference between competitors affects the outcome of interlarval
competition. Three parameters were used to assess parasitoid performance: the number of fights initiated, the number of bites
inflicted, and the duration of each bite. When fighting takes place between two first instars, then both competitors were
found to be evenly matched. However, at greater age differences, first-instar competitors appeared to win more fights than
their larger second instar rivals. The advantage shown by younger competitors is most pronounced in contests staged between
first and third instar larvae. These findings are consistent with the increasingly high levels of conspecific superparasitism
shown by V. canescens in the first 5 days after initial host attack, suggesting that this parasitoid can deploy her use of deliberate superparasitism
in an adaptive way.
Received: 13 December 1995/Accepted after revision: 5 March 1996 相似文献
10.
Kurt Kotrschal Josef Hemetsberger John Dittami 《Behavioral ecology and sociobiology》1993,33(5):289-295
Summary To investigate the dynamics of the winter flock patch exploitation, feeding experiments were performed with 140 semi-tame, free-roaming greylag geese (Anser anser). Three different initial densities of barley were offered on a 50-m2 patch: low (1600 grains/m2), intermediate (3300/m2) and high (I 1500/m2). Goose numbers on the patch, peck rates, and frequencies of agonistic encounters and of alert postures were observed by scanning the flock and in focal individuals. At low and intermediate initial food densities, peck rates decreased with food density, whereas at high food density, peck rates decreased only slightly over the feeding bout. Agonistic interactions increased as food decreased. A switch from exploitation to interference competition occurred at a threshold of approximately 900 remaining grains per square meter. With high initial food density, agonistic encounters began to increase gradually after 20–30 min. The same general patterns were observed for frequency of alertness. Family members occupied the patch for the longest time periods. The family female and the offspring fed most intensely. The family gander however, fed significantly less but was more aggressive and vigilant than all other social categories. Solitary geese spent their time on the patch doing little else but feeding and were the first to leave. It seems that high-ranking families and low-ranking singles adopt different competitive strategies, the former being superior interference competitors whereas the latter are forced scramble competitors.This study is dedicated to the memory of Konrad Lorenz
Correspondence to: K. Kotrschal 相似文献
11.
Abi Tamim Vanak Maria Thaker Matthew E. Gompper 《Behavioral ecology and sociobiology》2009,64(2):279-287
The structure of mammalian carnivore communities is strongly influenced by both intraguild competition and predation. However, intraguild interactions involving the world’s most common carnivore, the domestic dog (Canis familiaris), have rarely been investigated. We experimentally examined the behavioural responses of a small canid, the Indian fox (Vulpes bengalensis), to the presence of dogs and dog odours. Resource competition between dogs and Indian foxes is low, so it is unclear whether foxes perceive dogs as interference competitors. To test this, we exposed foxes to neutral, live dog, and animal odour stimuli at food trays, and recorded the time spent at food trays, the amount of food eaten, and vigilance and non-vigilance behaviours. When dogs were visible, foxes continued to visit the food trays, but reduced the amount of time spent and food eaten at those trays. Foxes were more vigilant during dog trials than during neutral and odour trials and also exhibited lower levels of non-vigilance behaviour (resting and playing). In contrast, dog odours did not affect fox foraging and activity. These results show that vigilance/foraging trade-offs due to interference competition can occur between native and domestic carnivores despite low dietary overlap. These negative effects of dogs on a smaller member of the carnivore guild raise conservation concerns, especially for endangered carnivores. In many parts of the world, free-ranging dog densities are high due to human subsidies, and these subsidized predators have the potential to exacerbate the indirect effects of human presence. 相似文献
12.
We investigated competition for food among two groups of six clone amagos (salmonids), Oncorhynchusmasoumacrostomus, in a laboratory experiment with different rates of food input. We examined the effect of temporal clumping of food resources
on the inequality of food sharing between competitors. Monopolization of food by dominants was greater at a low input rate
(one food item per 10 s) than at a high input rate (1 food item per 1 s). Aggressive behavior by dominants was more frequent
at the low input rate than at the high input rate; its purpose was presumably to interfere with the feeding behavior of subordinates.
We assessed the relative importance of three foraging factors (the number of approaches to food items, the chance per approach
and the gain per chance) in enhancing inequality in food gain between individuals. Dominants had a disproportionately high
chance per approach and gain per chance at the low input rate, but not at the high input rate. The chance of obtaining a food
item per approach depended on how many competitors approached simultaneously. The gain per chance depended on the competitive
ability of the approaching fish. There was an interaction between these components, such that the number of approaches affected
the chance per approach and gain per chance. We evaluated the independent effect of the chance per approach, and showed that
it was higher for dominants than for subordinates at the low input rate, but not at the high input rate. This implies that
subordinates changed their behavior and became more likely to avoid approaching food at the same time as dominants at the
low input rate.
Received: 13 August 1996 / Accepted after revision: 30 November 1996 相似文献
13.
Does local competition increase the coexistence of species in intransitive networks? 总被引:1,自引:0,他引:1
Competitive intransitivity, a situation in which species' competitive ranks cannot be listed in a strict hierarchy, promotes species coexistence through "enemy's enemy indirect facilitation." Theory suggests that intransitivity-mediated coexistence is enhanced when competitive interactions occur at local spatial scales, although this hypothesis has not been thoroughly tested. Here, we use a lattice model to investigate the effect of local vs. global competition on intransitivity-mediated coexistence across a range of species richness values and levels of intransitivity. Our simulations show that local competition can enhance intransitivity-mediated coexistence in the short-term, yet hinder it in the long-term, when compared to global competition. This occurs because local competition slows species disaggregation, allowing weaker competitors to persist longer in the shifting spatial refuges of intransitive networks, enhancing short-term coexistence. Conversely, our simulations show that, in the long-term, local competition traps disaggregated species in unfavorable areas of the competitive arena, where they are excluded by superior competitors. As a result, in the long-term, global intransitive competition allows a greater number of species to coexist than local intransitive competition. 相似文献
14.
We present a model of error-prone female choice on leks, and investigate the effects of different degrees of error on the
distribution of mating success among males present at leks of different sizes. At higher levels of error, the best male is
predicted to gain a smaller share of matings, while low-ranking males gain a larger share. Males who are of high rank but
not the most desirable on the lek do best at intermediate levels of error, since the top-ranked male does not then claim all
the matings, but assessment is still sufficiently accurate for females to discriminate between high-ranking and low-ranking
competitors. The effects of error are shown to be more pronounced on larger leks, due to smaller expected differences in mating
value between males of adjacent ranks. This interaction between lek size and error suggests that observed negative relationships
between lek size and mating skew need not be attributed solely to intrasexual competition, as previously suggested, but could
also be a result of imperfect choice.
Received: 20 February 1998 / Accepted after revision: 25 October 1998 相似文献
15.
Conservation Implications of Introduced Game Birds in High-Elevation Hawaiian Shrubland 总被引:1,自引:0,他引:1
F. Russell Cole Lloyd L. Loope Arthur C. Medeiros Jane A. Raikes Cynthia S. Wood 《Conservation biology》1995,9(2):306-313
The Ring-necked Pheasant ( Phasianus colchicus ) and the Chukar ( Alectoris chukar ) are the dominant avifauna in high-elevation shrubland (2070–3000 m) of Haleakala National Park, Maui, Hawaii. We studied the food habits, ecological niche, and effects of these alien game birds on the native biota in this Hawaiian ecosystem. Analyses of crop contents indicated that pheasant and Chukar consumed predominantly fruits of native, woody dicots (39% and 47% respectively) and leaves (29% and 24% respectively) and flower parts (12% and 17% respectively) of alien, herbaceous dicots. Both species generally selected food items according to their relative availability, although other factors influenced choice of certain items. Invertebrates were a minor component of the game-bird diet, suggesting that their impact on native invertebrate populations is minimal. Pheasant and Chukar occupy, at least partially, an ecological niche once held by now-extinct or rare birds, and they appear not to be significant competitors with the endangered Nene. The role of these alien birds in facilitating seed dispersal and germination of native plant species is beneficial in restoring degraded ecosystems. 相似文献
16.
Peter Korsten Oscar Vedder István Szentirmai Jan Komdeur 《Behavioral ecology and sociobiology》2007,61(12):1933-1943
Structurally based ultraviolet (UV)-reflective plumage parts can be important cues in mate choice. However, it remains largely
unknown if UV plumage variation can also function as a signal of social status during competitive interactions. In blue tits
(Cyanistes caeruleus), the UV-reflective crown plumage functions as a female mate choice cue that probably indicates male quality, as males with
higher UV reflectance have been shown to have better chances of over-winter survival. Possibly, the UV crown plumage acts
as a status signal in the competition over scarce food sources during winter. To test this idea, we related dominance of individuals
at an artificial food source during adverse winter conditions to spectrophotometric measurements of their crown plumage. However,
while controlling for the confounding effects of sex, age, and distance from territory, we found no significant effect of
crown UV reflectance on dominance. Consistent with this result, we also found no relation between crown UV reflectance and
over-winter survival. We conclude that the structurally based UV reflectance of the blue tit crown feathers plays little role
in competition between individuals during winter despite its importance as a cue in mate choice. 相似文献
17.
The importance of species interactions and recruitment variability was examined during the first year and a half of primary succession (1988–1989) on an exposed rocky seashore near Halifax, Nova Scotia. Previous work suggested that emergent rock on these shores is normally dominated by fucoid rockweeds because predatory whelks control the sessile animal competitors, mussels and barnacles, and because herbivorous littorinids control ephemeral algal competitors. Abundances of all species except seasonal ephemeral algae were very small throughout this experiment and we found no significant effects of carnivory, herbivory, plant-animal competition or plant-plant competition. A slight facilitation of Fucus recruitment is attributed to a thin mat of ephemeral, blue-green algae. Very few other studies have directly manipulated intertidal ephemeral algae. As primary succession may be very rare in this assemblage, these results may be specific to these circumstances, but they highlight the varying importance of species interactions with variable recruitment. In particular, it appears that variations in recruitment success may be important to community structure, even when recruitment is not limited by propagule supply. The scale of the study also provides insight into successional processes occurring after the recent, extensive ice-scour of exposed seashores in this region. 相似文献
18.
Elizabeth A Leger 《Ecological applications》2008,18(5):1226-1235
Changes in the species composition of biotic communities may alter patterns of natural selection occurring within them. Native perennial grass species in the Intermountain West are experiencing a shift in the composition of interspecific competitors from primarily perennial species to an exotic, annual grass. Thus traits that confer an advantage to perennial grasses in the presence of novel annual competitors may evolve in invaded communities. Here I show that such traits are apparent in populations of a native perennial grass, big squirreltail (Elymus multisetus M.E. Jones), exposed to cheatgrass (Bromus tectorum L.) competitors. Dormant big squirreltail plants were collected from cheatgrass-invaded and uninvaded sites near Bordertown, California, USA, a mid-elevation (1600 m) sagebrush community, and transplanted into pots in a greenhouse. Individual plants were split into equal halves. One half was grown with competition from cheatgrass, and the other half was grown without competition. Plants collected from invaded sites responded more quickly to watering, growing more leaves in the first 10 days after transplanting. In addition, big squirreltail plants collected from invaded areas experienced a smaller decrease in plant size when grown with competition than did plants collected from uninvaded areas. Accordingly, while there were fewer big squirreltail individuals in the invaded sites, they were more competitive with cheatgrass than were the more abundant conspecifics in nearby uninvaded areas. It is possible that annual grasses were the selective force that caused these population differences, which may contribute to the long-term persistence of the native populations. While it is tempting to restore degraded areas to higher densities of natives (usually done by bringing in outside seed material), such actions may impede long-term adaptation to new conditions by arresting or reversing the direction of ongoing natural selection in the resident population. If hot spots of rapid evolutionary change can be identified within invaded systems, these areas should be managed to promote desirable change and could serve as possible sources of restoration material or reveal traits that should be prioritized during the development of restoration seed material. 相似文献
19.
Ilka M. Kureck Beate Nicolai Susanne Foitzik 《Behavioral ecology and sociobiology》2013,67(8):1369-1377
Sexual selection has led to male morphologies and behaviours that either increase male attractiveness or their success in male–male competition. We investigated male traits under selection in the ant Hypoponera opacior, in which wingless males mate with pupal queens inside their natal colony and guard their partners for hours. The lack of female choice and fights among adult males makes this species an ideal study system to investigate sexual selection in the absence of these selective forces. We hypothesised that males, which emerge first and live longer, should have a higher mating success because of more mating opportunities, reduced competition and the ability to kill pupal competitors. We recorded the number and length of matings and tested whether these measures of male-mating success were associated with emergence order, lifespan and body size. Indeed, early emerged males mated more often and longer than their later-emerging rivals. Furthermore, longer-lived and larger males obtained more matings. Body size might be important because larger males either produce more sperm or perform better in mounting females. We found no evidence for a trade-off between body size and emergence time. Moreover, male removal manipulations revealed that males quickly adapt their guarding behaviour to changes in the competitive environment. Under reduced competition, males guarded their partners for shorter periods. In conclusion, these sib-mating ant males are under selection to develop fast, to live long, to be large and to be able to respond to the competitive situation in the nest. 相似文献
20.
Erika Nilsson Anders Persson P. Anders Nilsson 《Behavioral ecology and sociobiology》2010,64(5):729-736
Predation and competition are both strong structuring forces in community dynamics, but their relative importance is disputed.
In a laboratory experiment, we evaluated the relative importance of competition and predation from juvenile and adult brown
trout, respectively, on foraging performance of groups of three stone loaches. We observed loach consumption rate, time spent
inactive, and aggressive interactions between juvenile trout and loach in artificial stream sections. The controlled experiments
were complemented by examining stone loach population densities in natural systems as functions of juvenile and adult trout.
In the laboratory experiments, increasing numbers of competitors decreased prey availability, which ultimately led to lower
consumption rates for loach. Loach responded to predation risk by increasing time being inactive, thereby decreasing consumption
rates. However, there were no effects of juvenile trout competitors on loach consumption rates in treatments with adult trout
presence, suggesting no additive effect of predation and competition on loach foraging success. Partial regressions of loach
and trout densities in natural streams revealed a positive relationship between juvenile trout and loach, and a negative relationship
between adult trout and loach. Our laboratory and field data thus suggest that predation is a limiting factor for loach success,
and predator presence could mediate species coexistence at high interspecific densities. 相似文献