Risky decisions: a test of risk sensitivity in socially foraging flocks of Lonchura punctulata

Group foraging allows for individuals to exploit the food discoveriesof other group members. If searching for food and searchingfor exploitation opportunities within a group are mutually exclusivealternatives, the decision to use one or the other is modeledas a producer-scrounger game because the value of each alternativeis frequency dependent. Stochastic producer-scrounger modelsgenerally assume that producer provides a more variable anduncertain reward than does the scrounger and hence is a riskierforaging alternative. Socially foraging animals that are attemptingto reduce their risk of starvation should therefore alter theiruse of producer and scrounger alternatives in response to changesin energy budget. We observed flocks of nutmeg mannikins (L.punctulata) foraging in an indoor aviary to determine whethertheir use of producer and scrounger alternatives were risk sensitive.Analyses of the foraging rewards of three flocks of seven birdsconfirm that producer is a riskier foraging strategy than isscrounger, although the difference in risk is rather small.We then submitted two other flocks to two different energy budgetsand observed the foraging decision of four focal birds in eachflock. All but one bird increased their relative use of theriskier producer strategy in the low food reserve treatment,but the overall use of producer did not differ significantlybetween treatments, providing evidence for a small but consistenteffect.     

Mimicry in hoverflies (Diptera: Syrphidae): a field test of the competitive mimicry hypothesis

Although most studies on the evolution of mimicry and warningcoloration in insects have considered predators as the majorselective force, it is possible that competition for food resourcescould also facilitate selection for these conspicuous signals.For example, when warningly colored social wasps visit flowers,then they frequently behave aggressively toward heterospecifics,and they also attack and feed on other flying insects. Underthese conditions, a resemblance to a wasp might provide a mimetichoverfly with improved access to floral resources by reducingthe frequency with which it is disturbed by other pollinators.We experimentally evaluated whether wasp-like colors and patternswere important in preventing other flower visitors from sharingthe same flower resource, using pairwise presentations of bothnatural and artificial prey in the field. Flower visitors weremore likely to visit unoccupied flowers compared with the flowerspinned with either natural or artificial specimens in 2 plantspecies with different inflorescences. However, flower visitorsdid not show a significantly reduced rate of visitation to flowerspinned with specimens bearing wasp-like colors and patternscompared with the flowers occupied by similar-sized specimensthat were nonmimetic. Overall, we found no compelling evidencein this study to support the contention that wasp-like warningsignals of hoverflies prevent other flower visitors from sharingflower resources, although insects showed a greater tendencyto avoid visiting flowers pinned with a wasp compared with flowerspinned with a nonmimetic fly.     

Patch assessment in foraging flocks of European starlings: evidence for the use of public information

A field experiment was carried out to determine whether group-foragingstarlings (Sturnus vulgaris) use public information to helpthem estimate the quality of an artificial resource patch anddepart accordingly. Three kinds of information are potentiallyavailable in a group: patch-sample information, pre-harvestinformation, and public information. These three types of informationcan be combined into four patch assessment strategies: (1) patch-samplealone; (2) patch-sample and pre-harvest; (3) patch-sample andpublic; and (4) patch-sample, pre-harvest, and public. Dependingon the foraging environment we presented to the starlings, eachassessment strategy made a unique set of predictions concerningthe patch departure decisions of pairs of birds based on differencesin their foraging success. The environment was manipulated intwo ways: by altering the variability in patch quality and bychanging compatibility, the ease with which individual birdscould simultaneously acquire both patch-sample and public information.Our observations on patch persistence and departure order demonstratethat the starlings used a combination of patch-sample and publicinformation, but not pre-harvest information, to estimate thequality of the experimental patch. Moreover, our results suggestthat starlings use public information only when it is easilyavailable and ignore it under incompatible conditions. Thisstudy provides the first evidence of public information usein a patch assessment problem.     

Foraging Behaviour and Patch Exploitation by Campoplex dubitator (Hymenoptera: Ichneumonidae), a Parasitoid of Bark-mining Larvae

This study examines the foraging behaviour of Campoplex dubitator Horstmann (Hymenoptera: Ichneumonidae), a parasitoid of the highly concealed bark-mining host, Enarmonia formosana Scopoli (Lepidoptera: Tortricidae), and how this foraging behaviour is affected by host density. The ultimate aim was to determine whether foraging behaviour and patch fidelity could explain patterns of parasitism in the field. An ethogram was first constructed to portray C. dubitator behaviour prior to and immediately following host attacks. The pre-attack behavioural sequence was highly structured whereas behavioural transitions became less predictable after a sting event. Females spent more time on patches with higher host densities and host encounters caused a significant reduction in the leaving tendency. The giving up time was only slightly affected by host encounters. Campoplex dubitator did not demonstrate the ability to distinguish between occupied and empty host mines. The results show that C. dubitator forages more efficiently at lower host densities and this behavioural phenomenon may result in the patterns of parasitism observed in the field.     

Intensity and Importance of Competition for a Grass (Festuca rubra) and a Legume (Trifolium pratense) Vary with Environmental Changes

How plant competition varies across environmental gradients has been a long debate among ecologists. We conducted a growth chamber experiment to determine the intensity and importance of competition for plants grown in changed environmental conditions. Festuca rubra and Trifolium pratense were grown in monoculturs and in two- and/or three-species mixtures under three environmental treatments. The measured competitive variations in terms of growth (height and biomass) were species-dependent. Competition intensity for Festuca increased with decreased productivity, whilst competition importance displayed a humpback response. However, significant response was detected in neither competition intensity nor importance for Trifolium. Intensity and importance of competition followed different response patterns, suggesting that they may not be correlated along an environmental gradient. The biological and physiological variables of plants play an important role to determine the interspecific competition associated with competition intensity and importance. However, the competitive feature can be modified by multiple environmental changes which may increase or hinder how competitive a plant is.     

Sexual interference in the Golden snub-nosed monkey (Rhinopithecus roxellana): a test of the sexual competition hypothesis in a polygynous species

Sexual interference (SI), which is defined as any disturbance directed to a mating pair by other individuals, has been reported in several primate species. It is widely suggested that successful harassers experience improved mating success by increasing their access to reproductive partners as well as by reducing the mating success of rivals. Although theories of primate sexual conflict highlight male intra-sexual mating competition, females also are reported to actively disrupt copulations between mating partners. In this study, we investigated SI in a multilevel troop of Golden snub-nosed monkeys (Rhinopithecus roxellana) inhabiting the Qinling Mountains, China. Behavioral observations of 11 one-male units (OMU) that comprised the multilevel troop were conducted from September 2007 to May 2008. During this period 17.1% of 652 documented intra-OMU sexual encounters were characterized either by mild or aggressive forms of harassment. Sexual harassment was typically performed by a single individual (91.9%), and in 75.7% of cases the harasser was an adult or sub-adult female. The frequency of female harassment was positively correlated with the number of adult and sub-adult females residing in an OMU, and resulted in a significant decrease in matings ending in ejaculation. We found that the amount of SI a female received was not a significant predictor of her reproductive success. However, females who conceived during the mating season directed higher levels of harassment at other females than females who did not conceive. We evaluate the strength of the sexual competition hypothesis and the hormonally modulated aggression hypothesis in explaining patterns of SI in female Golden snub-nosed monkeys.     

Sexual swelling in mandrills (Mandrillus sphinx): a test of the reliable indicator hypothesis

Various hypotheses have been proposed to account for the functionof sexual swellings in female primates, but few empirical dataexist to test predictions arising from these hypotheses. Controversyhas recently arisen over a field study that appeared to supportthe predictions of the reliable indicator hypothesis. This hypothesisproposes that females compete for males or matings, that differencesin swelling size between females reliably advertise female quality,and that males use swelling characteristics to differentiallyallocate mating effort to females with certain swelling characteristics,hence to females of higher quality. To provide an independenttest of this hypothesis, we collected data concerning the sizeand coloration of 40 sexual swellings for 29 semi-free-rangingfemale mandrills, varying in age and parity, along with dataconcerning the behavior of males toward the females, and comparedthese with the long-term reproductive history of the females.We examined the following predictions: (1) swelling characteristicsare consistent across subsequent cycles for individual females,(2) swelling characteristics indicate aspects of female reproductivequality, and (3) males prefer to mate with females that showparticular swelling characteristics. Our results support prediction1; we found little change in swelling characteristics acrossswellings for individual females. However, we found no significantrelationships between female reproductive history and swellingcharacteristics and, thus, no support for prediction 2. Finally,we found only limited support for prediction 3; females withlarger (wider) sexual swellings were more likely to have a spermplug when maximally swollen. However, male mate-guarding wasnot significantly related to female swelling characteristics.Furthermore, in situations in which more than one female wasmaximally swollen, the alpha male (who has "free" choice) didnot show the most interest in the female with the largest swelling.We conclude that the reliable indicator hypothesis does notexplain variation in sexual swellings in female mandrills.     

Short-and long-term sperm precedence in the beetle Tenebrio molitor: a test of the 'adaptive sperm removal' hypothesis

Abstract. Sperm removal in Tenebrio molitor L. (Coleoptera: Tenebrionidae) has been proposed as an adaptation to sperm competition and has been documented when the remating interval between successive copulations is short, but not when it is long (Gage, 1992). If sperm removal is adaptive, it follows that there should be different fertilization outcomes from double matings with different remating intervals.
Sperm precedence patterns were assessed using reciprocal double matings of normal and γ-irradiated (sterile) virgin males of controlled size and age with virgin females of controlled size and age.
Immediate last male sperm precedence was high whether the remating interval was short (<10 min) (P_2,= 0.89) or long (24h) (P₂= 0.92).
Sperm precedence in eggs laid in a 16-day period after the last copulation showed no difference in the pattern of change between females with short and long remating intervals.
By examining the aedeagus of males we show that sperm are removed at the end of copulation by the first and the second male to mate with a virgin female regardless of whether the remating interval is short or long.
We conclude that sperm removal is unlikely to be the primary mechanism by which males gain such high levels of last male sperm precedence.     

Monogamy to communal breeding: exploitation of a broad resource base by burying beetles (Nicrophorus)

Abstract.

• 1 To investigate the range of resource size that burying beetles (Nicrophorus) exploit, small (21–33 g), medium (50–90 g) and large (120–210g) carcasses, were placed in the field and then exhumed after 1, 4, 8, 12 or 18 days.
• 2 Nicrophorus attempts to utilize carcasses over this entire size range but has greater success on smaller carcasses.
• 3 Larger carcasses were more difficult to exploit because: (a) they took longer to conceal beneath the leaf litter; (b) they were less likely to be rounded into brood balls; (c) they were more likely to be utilized by dipterans; and (d) they were occupied by greater numbers of congeners.
• 4 Larger carcasses, however, did support greater numbers of larvae and contained broods of greater total mass than smaller carcasses.
• 5 Beetles sometimes bred communally on larger carcasses in the field and same-sex adults were observed to feed young.
• 6 Two follow-up experiments were conducted in the laboratory. On a large carcass N.defodiens, N.tomentosus or N.orbicollis can raise a maximum of 35–50 young. Nicrophorus pustulatus, in contrast, appears to be unique among Nicrophorus in that it can raise nearly 200 young on larger carcasses.
• 7 Nicrophorus orbicollis and Nicrophorus sayi are extremely dependent on parental regurgitations and young fail to survive to the second instar if parents are removed. Young of Nicrophorus defodiens, N.tomentosus and N.pustulatus can develop normally without parental regurgitations.
• 8 I discuss these results in the context of reproduction on carcasses of different size and hypothesize that this breeding system is facultatively quasisocial.

     

Effects of exploitation on reproductive capacity of blackspot snapper, Lutjanus fulviflamma (Pisces: Lutjanidae) in Mafia Island, Tanzania

There is paucity of information on the effects of exploitation on reproductive characteristics of blackspot snapper, Lutjanus fulviflamma (Forsskål 1775) in Tanzanian coastal waters. We compared size at first sexual maturity (L_M50), sex ratio, fecundity, and breeding season of L. fulviflamma in least fished Mafia Island Marine Park (MIMP) and intensively fished areas (IFA) between May 1999 and April 2001. Fish in MIMP matured at significantly smaller size (female: L_M50 = 206.3 mm; male: L_M50 = 195.5 mm) than in IFA (female: L_M50 = 216.7 mm; male: L_M50 =212.1 mm) total body length. Sex ratio was balanced at 1.03 : 1 (female : male) in MIMP, but it was skewed 0.9 : 1 (female : male) in IFA. Size‐related differences in sex ratio were observed with males predominating in the smaller sizes and females in the larger sizes. Total fecundity of fish in MIMP was determined at 45,200–430,200 oocytes in females of between 207 and 293 mm total length. Lutjanus fulviflamma in MIMP has a prolonged spawning season lasting from September to March peaking in December. None of the fish from IFA were in breeding state, suggesting recruitment overfishing is an added matter of concern for the long‐term sustainability of the fishery at the current exploitation level.     

Testosterone effects on the immune system and parasite infestations in the barn swallow (Hirundo rustica): an experimental test of the immunocompetence hypothesis

The immunocompetence hypothesis predicts that testosterone (T)enhances the expression of male secondary sexual characterswhile exerting a suppressive effect on the immune system therebyexposing hosts to higher intensities of parasite infestations.In a natural population of barn swallow (Hirundo rustica) males,the intensity of infestation by some ectoparasites was negativelycorrelated with tail length and was positively correlated withimmunoglobulin levels, but no clear relationship was observedbetween immune responses (leukocyte counts, immunoglobulins)and tail length. Males implanted with T had higher intensitiesof parasite infestations at the time of recapture than controlmales, and T-implanted males experienced an increase in countsof eosinophils. In T-implanted males, immunoglobulin levelsinitially decreased and then increased as time from implantationelapsed. Among T-implanted males, those with longer tails hada smaller increase in eosinophil counts, tended to experiencea smaller increase of parasite infestations, and were more likelyto survive until the following breeding season than those withshorter tails. The relationships between parasite burden, immunesystem, and exaggeration of tail length in the natural populationof males are consistent with some aspects of the immunocompetencehandicap hypothesis. The results from the manipulation of Tplasma levels are also partly consistent with the hypothesis,since T-implantation resulted in higher levels of parasite infestations,but contradict the assumption of an obligatory immunosuppressiveeffect of T. Higher activation of the immune system of T-implantedmales indicate that high T plasma levels imposed a two-foldcost because of the effects on parasites and the immune responseto parasites, and this suggests that the effect of T on parasitesmight not be mediated by the immune system of the host. Theresults of the manipulation of T plasma levels support the handicapversion of the immunocompetence hypothesis since high quality,long-tailed males paid less in terms of activation of the immunesystem, change in parasite infestations, and chances of survivalthan low-quality, short-tailed males.     

Extrapair paternity in the great tit (Parus major): a test of the "good genes" hypothesis

In 1993 and 1994 we determined the frequency of extrapair paternityin broods of great tits, Parus major using multilocus DNA fingerprinting.We found no instances of intraspecific brood parasitism, but40% of broods (31/78) contained extrapair-fathered young and83% of offspring (58/681) were xtrapair We identified the geneticfathers of 60% of the extrapair nestlings (35/ 58). Males withfull and lost paternity did not differ significantly in traitsthat have been suggested to indicate male quality, nor did thegenetic and social fathers of extrapair offspring. In 1993,cuckolded males sired more offspring that recruited to the subsequentbreeding season than males with full paternity. Moreover, eventhough genetic fathers of extrapair young (EPY) sired more fledglingsthan the males they cuckolded, genetic and social fathers ofEPY did not differ in the number of recruits sired. Also, theEPY of a brood did not survive better than their half sibs.Thus, our results do not supportthe hypothesis that femaleschoose better quality males for extrapair matings ("good genes"hypothesis). Further, the level of extrapair paternity differedmarkedly between the two years. Our data show that females areconstrained in their extrapair activities by the availabilityof extrapair mates. This is at least partly due to yearly differencesin breeding synchrony.     

The effect of intra- and interspecific aggression on patch residence time in Negev Desert gerbils: a competing risk analysis

We observed patch-use behavior by two gerbil species in a fieldsetting and investigated how aggression and intrinsic decision-makinginteract to influence patch residence times. Results were interpretedby using a competing risk analysis model, which uniquely enabledus to estimate the intrinsic patch-leaving decisions independentlyof external interruptions of foraging bouts by aggression. Theexperiment was conducted in two 1-ha field enclosures completelysurrounded by rodent-proof fences and included allopatric (onlyGerbillus andersoni allenbyi) and sympatric (G. a. allenbyiand G. pyramidum) treatments. We predicted that increased foodpatch quality (i.e., habitat quality) should decrease intrinsicpatch-leaving rates and increase rates of aggressive interactionsinvolving the forager feeding in the patch (i.e., the occupantindividual). We also anticipated that increasing populationdensity should result in an increase in the rate of aggressiveinteractions involving the occupant individual. Our resultssupported the first two predictions, indicating a trade-offbetween foraging and aggression. However, the third predictionwas realized only for G. a. allenbyi in allopatry. Furthermore,in allopatry, occupant G. a. allenbyi individuals with highcompetitive ranks were involved in aggressive interactions atlower rates than those with low competitive ranks. However,in sympatry, patch-use behavior of occupant G. a. allenbyi individualswas mainly influenced by aggressive behavior of G. pyramidum,which did not respond to their competitive rank. Thus, it shouldpay less for G. a. allenbyi to be aggressive in sympatric populations.The observed reduction in intraspecific aggression among individualG. a. allenbyi in the presence of G. pyramidum supports thisassertion. We suggest that this reduction likely weakens thenegative effect of intra- and interspecific density on the percapita growth rate of G. a. allenbyi. Because this would changethe slope of the isocline of G. a. allenbyi, it could be animportant mechanism promoting coexistence when habitat selectionis constrained.     

Live for the moment—Adaptations in the male genital system of a sexually cannibalistic spider (Theridiidae, Araneae)

Monogyny in spiders culminates in extreme traits, like dramatic male self-sacrifice and emasculation of the male by the female during copulation. Here we show that monogynous males can be highly adapted for this fatal sexual behaviour. Dwarf males of the one-palped theridiid spider Tidarren argo, which are cannibalised immediately after the insertion of their single copulatory organ, stop spermiogenesis when reaching adulthood. Their testes atrophy, which might economise the energy expenditures of these males. We also found that the amount of seminal fluid produced is stored in an enlarged seminal vesicle until the single sperm induction takes place. The volume of the seminal vesicle is similar to the sperm droplet taken up into the copulatory organ (palpal organ). Sperm uptake takes much longer than in related species most likely due to the large amount of seminal fluid. As shown by histological observations males are able to fill one of the paired female sperm storage organs during copulation thereby presumably impeding subsequent charging by rival males.     

Carotenoid limitation and mate preference evolution: a test of the indicator hypothesis in guppies (Poecilia reticulata)

Under the indicator models of mate choice, female preferences evolve to exploit the condition-dependence or "indicator value" of male traits, which in turn may cause these traits to evolve to elaborate extremes. If the indicator value of a male trait changes, the payoff function of the female preference for that trait should change and the preference should evolve to a new optimum. I tested this prediction in the guppy, Poecilia reticulata, a species in which the indicator value of a sexually selected male trait, carotenoid coloration, varies geographically. Carotenoid coloration is thought to be an indicator of foraging ability and health because animals must obtain carotenoid pigments from their diet. The primary dietary source of carotenoids for guppies is unicellular algae, the abundance of which varies among natural streams because of variation in forest canopy cover. Carotenoid availability limits male coloration to a greater extent in streams with greater forest canopy cover. Thus, the indicator value of male coloration covaries positively with canopy cover. To test the indicator model prediction, I measured genetic divergence in the strength of female preferences for carotenoid coloration between high- and low-carotenoid availability streams in each of three river drainages. Second-generation laboratory-born females were given a choice between full-sib males raised on three different dietary levels of carotenoids. For all six populations, male attractiveness (as determined from the responses of females to male courtship displays) increased with dietary carotenoid levels. However, the strength of female preferences differed between populations in the predicted direction in only one of three river drainages. These results fail to support a crucial prediction of the indicator model. More studies taking an interpopulation approach to studying mate preference evolution are needed before the explanatory value of the indicator models can be rigorously assessed.     

Predation-imposed selection on threespine stickleback (Gasterosteus aculeatus) morphology: a test of the refuge use hypothesis

The transition from marine to freshwater life in the threespine stickleback (Gasterosteus aculeatus) is accompanied by complex morphological changes-including reduction in bony armor and change in body shape-but experimental evidence for the selective agents behind these evolutionary transitions is sparse. We investigated whether selection by predatory fish affects threespine stickleback morphology differentially when refuge is absent (pelagic lifestyle-ancestral condition) or present (benthic lifestyle-derived condition). Our results show that selection favors low numbers of lateral plates in habitats with refuge, whereas fully plated individuals have a selective advantage in habitats without refuge. We also found that a decrease in the length of the caudal peduncle increased survival probability, irrespective of habitat. The effect of spine lengths on survival was evident only in a multivariate analysis of selection, implying that it is essential to account for phenotypic and genetic correlations between traits before drawing conclusions about the effects of selection on single traits. Apart from uncovering targets and patterns of predator-induced selection on threespine stickleback morphology, our results provide direct evidence to support the hypothesis that differences in antipredator strategies in pelagic versus benthic sticklebacks could play a role in the repeated, independent cases of plate number reduction following freshwater colonization in this species.     

Fluctuating asymmetry and genetic variability in the roe deer (Capreolus capreolus): a test of the developmental stability hypothesis in mammals using neutral molecular markers

Fluctuating asymmetry (FA), used as an indicator of developmental stability, has long been hypothesized to be negatively correlated with genetic variability as a consequence of more variable organisms being better suited to buffer developmental pathways against environmental stress. However, it is still a matter of debate if this is due to metabolic properties of enzymes encoded by certain key loci or rather to overall genomic heterozygosity. Previous analyses suggest that there might be a general difference between homeo- and poikilotherms in that only the latter tend to exhibit the negative correlation predicted by theory. In the present study, we addressed these questions by analysing roe deer (Capreolus capreolus) from five German populations with regard to FA in metric and non-metric skull and mandible traits as well as variability at eight microsatellite loci. Genetic variability was quantified by heterozygosity and mean d2 parameters, and although the latter did not show any relationship with FA, we found for the first time a statistically significant negative correlation of microsatellite heterozygosity and non-metric FA among populations. Because microsatellites are non-coding markers, this may be interpreted as evidence for the role of overall genomic heterozygosity in determining developmental stability. To test if the threshold character of non-metric traits is responsible for the metric vs non-metric difference we also carried out calculations where we treated our metric traits as threshold values. This, however, did not yield significant correlations between FA and genetic variability either.     

区域生态经济系统的物质输入与输出分析——以常州市武进区为例

运用物质流分析（MFA）方法,对江苏省常州市武进区生态经济系统中物质输入与输出进行了系统的分析,结果表明：（1）随着社会经济发展和人口增长,武进区物质输入总量及人均物质输入量也在增加,但递增速率均远小于GDP增长速率,而物质输出总量及人均物质输出量则呈现递减趋势;（2）在不考虑水的因素情况下,武进区物质输入量保持较快的上升速度,其中固体物质的增长速率远远大于气体物质的增长速率;物质输出量则呈总体下降趋势,其中以气体物质输出量的贡献最大,对环境造成污染的物质以气体特别是以化石燃料燃烧排放的废气和工业废气为主;（3）排除占大部分比例农业用水的上升,工业用水、城镇生活用水和地下水总量及人均利用强度都在减少;同时,总的废水排放量及人均排放量在减少,其中又以生活废水排放量的减少最快,其次是工业废水;（4）单位GDP物质输入量的变化处于波动状态,同期的单位GDP物质输出量则呈递减趋势,单位GDP用水量和单位GDP废水排放量则有相同的递减趋势,表征了武进区资源利用效率的稳步提高,区域经济增长和环境压力也在逐步脱钩。上述结果体现了武进区近年来循环经济发展模式的优势,但还存在较多问题,说明武进区在调整物质利用强度和提高资源利用效率方面还需下更大的功夫,并采取相关措施,以期提高实施循环经济战略与建设节约型社会的地位和意义。文章最后结合研究区实际情况就区域环境一经济的协调发展进行了展望,指出了物质流分析方法在应用中的一些缺陷,为今后该领域的进一步研究提供了借鉴。