Intraspecific competition influences the symmetry and intensity of aggression in the Argentine ant

Cooperative social groups rely on the ability to distinguishmembers from nonmembers. Accordingly, social insects have evolveda variety of systems that allow discrimination of nest matesfrom non–nest mates. In this study, we show that experiencecan modify patterns of intraspecific aggression in Argentineants (Linepithema humile). In laboratory experiments, we foundthat aggression between colonies was often asymmetrical, butin all five cases, this asymmetry shifted to symmetrical aggressionafter contact with a hostile colony. Moreover, in the field,aggression between workers collected from colony borders wassymmetrical, whereas polarized aggression occurred between workerscollected 500 m away from colony borders. Coinciding with thisshift in aggression symmetry, we also observed an increase inboth the overall level of aggression and the frequency of aggressionin both the field and laboratory bioassays. We found littleevidence for colony-level competitive asymmetries stemming frompolarities in aggression at the worker level, either in thelaboratory or in the field. These results illustrate that recognitionsystems in Argentine ants are surprisingly dynamic and provideexperimental evidence for how recognition can be adjusted inresponse to specific circumstances—in this case the presenceof intraspecific competitors.     

Biodiversity of vespid wasps in spatial and temporal dimensions in northern Zanjan Province of Iran

Vespidae is one of the major families of Hymenoptera with more than 115000 described species. In the present paper, Simpson and Shannon-Wiener diversity indices, Simpson,Camargo, Smith and Wilson, and modified Nee evenness indices, and richness index based on rarefaction method were adopted to study the biodiversity of vespid wasps in spatial and temporal dimensions in northern Zanjan Province of Iran. In spatial dimension, Zanjan and Gilvan showed the highest and the lowest species diversity, evenness, and richness, respectively; while in tem-poral dimension, 16 July-6 August showed the highest species diversity and richness, and 18 May -27 May and 23 August -2 September showed the highest and the lowest species evenness,respectively. Significant differences in species abundance between localities of study area were observed by Kruskal-Wallis nonparametric test.     

Effects of short-term hunger and competitive asymmetry on facultative aggression in nestling black guillemots Cepphus grylle

Siblings in a diversity of species are facultatively aggressive,yet the proximate control of the aggressive response and theecological conditions selecting for such systems are poorlyunderstood. In this study, we investigated the effects of foodamount (food amount hypothesis) and competitive asymmetry onsibling aggression in black guillemot broods. Parental provisioningrates were experimentally manipulated in broods comprisinga range of hatching intervals over a 12-h period. Aggressionbecame evident only after parental provisioning rates wereexperimentally reduced. When parental provisioning resumed,adults did not increase their feeding rate to compensate forthe induced food deficit, and the result of sibling rivalrywas a change in the allocation of parental deliveries from oneof equality to one in favor of the dominant chick. Food-deprivedchicks from synchronous broods were more aggressive than thosefrom asynchronous broods, suggesting that one benefit of hatchingasynchrony in the black guillemot is to establish an efficientcompetitive hierarchy among siblings which minimizes the needfor costly aggressive interactions. On the following day, siblingaggression ceased, and chicks regained an equal share of parentalfeeds. Our results provide the first evidence that short-termfood shortage per se acts as an initial trigger for aggressionand also show that the aggressive response is complicated byfactors associated with hatching and laying order.     

Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

Background and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan.Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively.Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species.Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.     

Temporal partitioning and aggression among foragers: modeling the effects of stochasticity and individual state

In many natural systems, individuals compete with conspecificsand heterospecifics for food and in some cases, individualshave been observed to partition their foraging times or fightover food. In this study, I investigated when it is optimalfor a consumer to partition time and be aggressive. I formulatedan individual-based model of foraging and used game theoryto find evolutionarily stable strategies (ESSs) that maximizethe probability that consumers survive each day and acquiretheir daily food requirements. Consumers choose when to forageand when to behave aggressively during confrontations overfood. Consumers are each associated with a state variable,representing the amount of food eaten, and a dominance ranking,which describes how likely they are to forage and fight forfood. The ESS is sensitive to food abundance, consumer state,and the dominance ranking. When food is abundant, temporalpartitioning is often an ESS where the dominant consumer foragesfirst; however, partitioning is unlikely to be an ESS whenfood abundance is low. Fights over food are typically avoidedbut may be part of an ESS when food abundance is low, bothconsumers are hungry, or the time available for foraging eachday is drawing to a close. Because the ESS is sensitive toconsumer state, the stochastic nature of finding food oftenresults in considerable variation in observed foraging dynamicsfrom one day to the next, even when consumers adopt the samestate-dependent strategy each day. Results are compared withempirical observations, and I discuss implications for consumercoexistence.     

Variation in spatial and temporal gradients in zooplankton spring development: the effect of climatic factors

1. We examined the temporal and spatial heterogeneity of zooplankton in lake surface waters during the spring of 3 years in Lake Washington, U.S.A., a large lake with a high production of sockeye salmon fry. 2. We show large within‐season and among‐year variation in the horizontal distribution of temperature, chlorophyll a concentration, and zooplankton in the lake. The main pattern, a delay in zooplankton population increase from the north‐ to the south‐end of the lake, recurred in each year and was persistent within each spring. 3. The delay is primarily caused by the development of a temperature gradient during spring warming, as cold mountain water enters the south end of the lake, while warm water enters the north end via a river draining a nearby lake. Climate factors, such as air temperature and precipitation during winter and spring, appear to influence the extent of the delay of zooplankton increase. 4. If the climate continues to warm, the temporal disconnection in zooplankton development between lake areas immediately influenced by cold river inflow and areas that are influenced by spring warming may increase in magnitude. Thus, the different areas of the lake may not contribute equally to fish production.     

Relative importance of temporal and spatial heterogeneity in the zooplankton community of an artificial reservoir

Zooplankton samples were collected monthly at three stations in Ogochi Reservoir during 1980, and the temporal and horizontal variations in the density of dominant taxa were evaluated by a standard 2-way ANOVA with random effects. The analysis revealed that horizontal is greater than temporal variation in the warm water season (> 18 °C), whereas temporal variation is greater in the cold water season (< 18 °C). Horizontal heterogeneity of the zooplankton community found in the warm water season seems to be associated with differences in site-specific conditions.     

Effects of forced migrations on spatial and temporal changes in genetic structure of two local populations in Bosnia

Ten qualitative traits were observed in two isolated human populations in Bosnia for prewar and postwar periods. Due to recent war in Bosnia and Herzegovina two million citizens was forced to migrate. Dramatic migration effects occurred in the investigated populations. Population characteristics found were geographic isolation, high levels of marital distance “zero”, patrilocality and propagation isolation. Relative recessive allele frequencies of ten qualitative traits were calculated. Average heterozigosity, genetic differentiation, total heterozigosity, within populations heterozigosity, genetic distance and relative measures based on results of genetic distance analysis were observed. The total number of observed individuals was 1875. We have observed 1209 individuals in prewar period (Bijela population 731 and Memici population 478) and 666 individuals in the postwar period (Bijela population 248 and Memici population 478). Results ofFst andGst analysis showed changed degree of genetic differentiation across observed loci. Significant changes in differentiation were recorded for crooked little finger and PTC tasting. Modest changes of gene differentiation were recorded for ear lobe type and thumb proximal extensibility. Genetic distance analisis between Bijela and Memici has lower value after then before the war, but genetic distance between Bijela-prewar and Bijela-postwar has higher value, as well as Memici-prewar and Memici-postwar genetic distance. Genetic distance between Bijela-prewar and Memiciprewar, as well as Bijela-postwar and Memici-postwar showed similarity. Constructed dendrogram based on results of genetic distance analyses indicated two clusters groups (1. Bijela-prewar, Memici-prewar; 2. Bijela-postwar, Memici-postwar). Changed genetic differentiation and results of genetic distance analyses indicated possibility of significant impact of forced migration in genetic structure of observed populations.     

Negative effect of ayu on the growth of omnivorous pale chub in experimental pools

The growth rate of pale chub Zacco platypus was negatively correlated with the number and biomass of ayu Plecoglossus altivelis in experiment pools regardless of their body weight. Both species were omnivorous, feeding upon both benthic algae and invertebrates; ayu fed principally upon algae whereas pale chub consumed invertebrates. Pale chub shifted their moving tactics from bottom moving to surface moving or sit-and-wait when they coexisted with numerous ayu, presumably due to occasional attack by ayu. It seems likely that the reduced pale chub growth rate was due to interspecific aggression and exploitation of benthic algae and invertebrates by ayu.     

Competitor-to-resource ratio, a general formulation of operational sex ratio, as a predictor of competitive aggression in Japanese medaka (Pisces: Oryziidae)

Operational sex ratio (OSR), the number of potentially matingmales divided by the number of fertilizable females, playsa central role in the theory of mating systems by predictingthe intensity of intra-sexual competition and sexual selection.We introduce a general version of OSR, competitor-to-resourceratio (CRR, the number of potential competitors divided bythe number of resource units), as a potential way of predictingthe intensity of competition for any resource. We manipulatedCRR over a broad range (0.5-8) by varying both the number ofcompeting male Japanese medaka fish (Oryzias latipes) and thenumber of resources, either females or food items. We testedwhether the rate of male—male aggression differed dependingon resource type and whether it increased monotonically or followed a dome-shaped relationship with increasing CRR. The patternsof competitive aggression in relation to CRR did not differsignificantly between resource types. In addition, the percapita rate of aggression followed a dome-shaped curve; itwas low when CRR was less than one, initially increased as CRR increased, was highest at a CRR of about two, and then decreasedwhen CRR was greater than two. However, competitor number,independent of CRR, had a significant and negative effect onrate of aggression. We suggest that CRR is a valuable predictorof the rate of competitive aggression and may be a useful conceptfor synthesizing ideas about resource competition and monopolization that are currently dispersed in the separate bodies of literatureon mating systems, social foraging and territoriality.     

Effects of rearing on aggression and subordination in papio monkeys

The objective of this study is to assess the effects of short-term maternal deprivation (birth to 12 weeks) followed by peer group rearing on the development of aggressive and subordinate behaviors in papio monkeys (superspecies – Papio cynocephalus). Nursery reared monkeys (34 males and 30 females) were compared with mother-peer reared monkeys (11 males and 12 females) in late infancy (6 to 12 months of age) and at the end of their juvenile stage (36 to 42 months of age) in social groups composed of 75% nursery reared subjects and 25% mother reared subjects. Focal animal data were analyzed with a repeated measure ANOVA model. In general, the nursery reared infants tended to be less aggressive than mother-peer reared infants and performed less dominance behaviors, such as displace. Significant sex differences were present in the performance of aggressive (♂ > ♀) and subordinate (♂ > ♀) behaviors. Significant age differences were observed, with infants having consistently higher rates of performance.     

Effects of cortisol on aggression and locomotor activity in rainbow trout

Noninvasive administration of cortisol through the diet resulted in relatively rapid (<1.5 h) and highly reproducible increases in plasma cortisol in rainbow trout, comparable to changes seen in fish subjected to substantial stress. Juvenile rainbow trout were reared in isolation for 1 week, before their daily food ration was replaced by a meal of cortisol-treated food corresponding to 6 mg cortisol kg(-1). All fish were observed for 30 min, beginning at 1 or 48 h following the introduction of cortisol-treated food. Additional cortisol (75% of the original dose on Day 2, and 50% on Day 3) was administered to the long-term cortisol-treated group. The resulting blood plasma concentrations of cortisol were similar in short- and long-term treated fish, and corresponded to those previously seen in stressed rainbow trout. Controls were fed similar food without cortisol. Half of the fish from each treatment group (controls and short- and long-term cortisol) were subjected to an intruder test (a smaller conspecific introduced into the aquarium), while half of the fish were observed in isolation. In fish challenged by a conspecific intruder, short-term cortisol treatment stimulated locomotor activity, while long-term treatment inhibited locomotion. Aggressive behavior was also inhibited by long-term cortisol treatment, but not by short-term exposure to cortisol. Cortisol treatment had no effect on locomotor activity in undisturbed fish, indicating that the behavioral effects of cortisol were mediated through interaction with other signal systems activated during the simulated territorial intrusion test. This study demonstrates for the first time that cortisol has time- and context-dependent effects on behavior in teleost fish.     

Reconciling the influence of global climate phenomena on macrofaunal temporal dynamics at a variety of spatial scales

Determining the relative importance of environmental forces on population dynamics is a fundamental question for ecologists. Growing concern over the ecological effects of climate change emphasizes the importance of defining whether broad-scale environmental forces uniformly act upon local populations (hierarchy theory) or cross-scale interactions influence local responses (multiscale theory). This study analyses 13 years of data on species abundances at six sites within a large harbour to determine the effect of the El Niño Southern Oscillation (ENSO). Environmental variables both directly and indirectly related to ENSO were observed to be important predictors of the temporal dynamics of abundance in many species, but the observed effects were not consistent across sites or species. While nearly all species were affected by large temporal and spatial scale variability, smaller temporal scale, location-specific environmental variables (such as wind-generated wave exposure and turbidity) were also generally important, increasing the variability explained by our models by up to 25%. As with many other broad-scale variables, generality of response to ENSO is affected by interactions across time and space with smaller scale heterogeneity. This study therefore suggests that the degree of interaction between broad-scale climatic factors, such as ENSO, with smaller scale variability, will determine the consistency of responses over large spatial scales, and control our ability to predict effects of climate change on coastal and estuarine communities.     

Effects of kinship on aggression and RNA content in juvenile Arctic charr

The behaviour of juvenile Arctic charr Salvelinus alpinus was studied in groups of four siblings composed of familiar and unfamiliar individuals or in mixed groups of four where both siblings and unrelated individuals were present. The frequency of aggressive acts was significantly higher in the mixed groups compared to the pure sibling groups and the difference was present at all levels of the hierarchy rank order, based on a dominance index, except the lowest ranked individuals. The difference was significant after but not before feeding, implying that competition with non-kin for a food resource increased the aggression. No significant difference in weight gain was observed between sibling and mixed groups during the 6 days of the experiment, but the RNA contents of lateral musculature in dominant individuals from sibling groups were significantly higher than the corresponding fish in the mixed group, suggesting a difference in growth rate when the experiments ended. No significant difference in RNA content was observed between subordinate fish of the two treatments, i.e. siblings v . mixed.     

The effect of depletion and predictability of distinct food patches on the timing of aggression in red deer stags

For group-foraging ungulates, forage is generally widely and relatively evenly dispersed. However, for free-ranging red deer Cervus elaphus supplementary winter feeding provides distinct patches of predictable food. These patches differ in size, but also in temporal distribution and depletion rate. Interference competition is known to increase with increasing spatial clumping (decreasing patch size), but the influence of temporal clumping and the predictability of food occurrence has received much less attention. Therefore in this study we investigated the effects of different degrees of spatial and temporal clumping of food on interference competition during feeding. Patch size was the main parameter influencing participation in feeding as well as interference competition during feeding on the respective patch. Temporal dispersion and the predictability of food occurrence were however, important parameters for the timing of aggressive interactions. Generally, aggression occurs during feeding and increases with decreasing patch size. But when depletion rate was high food availability was predictably short and the patch occurred predictably (such as hay), middle ranking stags increased aggression already prior to feeding at the respective patch. We suggest that in this way they confirmed hierarchy outside feeding on the quickly depleted patch and as a result gained actual feeding time when feeding on the respective patch. With the patch occurring predictably but varying in size the number of participating subordinates varied concomitantly with variation in patch size. Subordinates assessed patch profitability and left without having fed when patch size was too small for an efficient participation. When patch size was predictably small enough to be defended exclusively (feed blocks), subordinate stags did not assess profitability each time but did not participate at all in feeding at the respective patch. The relative importance of these various food-related parameters (patch size depletion rate, predictability) influencing feeding competition and the timing of aggression will vary with group size, rank, alternative food sources, physical characteristics of the food as well as different hierarchy systems of the feeding animals.     

Activity and Ranging Patterns of Guerezas in the Kakamega Forest: Intergroup Variation and Implications for Intragroup Feeding Competition

From March 1997 to February 1998, I investigated the activity patterns of 2 groups and the ranging patterns of 5 groups of eastern black-and-white colobus (Colobus guereza), aka guerezas, in the Kakamega Forest, Kenya. Guerezas at Kakamega spent more of their time resting than any other population of colobine monkeys studied to date. In addition, I recorded not one instance of intragroup aggression in 16,710 activity scan samples, providing preliminary evidence that intragroup contest competition may be rare or absent among guerezas at Kakamega. Mean daily path lengths ranged from 450 to 734 m, and home range area ranged from 12 to 20 ha, though home range area may have been underestimated for several of the study groups. Home range overlap was extensive with 49–83% of each group's range overlapped by the ranges of other groups. Despite the high level of home range overlap, the frequently entered areas (quadrats entered on 30% of a group's total study days) of any one group were not frequently entered by any other study group. Mean daily path length is not significantly correlated with levels of availability or consumption of any plant part item. Mean daily path length is also not significantly correlated with group size, though the largest group did have the longest mean daily path length. This finding suggests that intragroup scramble competition may have been rare or absent among guerezas at Kakamega except perhaps in the largest group, which was unusually large.     

东北地区近50年来极端降水和干燥事件时空演变特征

利用东北地区93个国家常规气象观测站1951~2002年逐日降水资料,分析了东北地区的暴雨、严重干燥事件等极端降水事件的时空演变特征,从极端降水事件发生频率和强度变化的角度解释旱涝灾害加剧的原因。结果表明,近52年来,小雨事件发生频次显著减少;暴雨发生频次变化不大,但强度增强;严重干燥事件显著增加;严重湿润事件显著下降。因此,在东北地区降水总量具有减少趋势的背景下,降水事件还有向极端化发展的倾向,降水分布变得更不均匀,从而可能引起更多、更强的旱涝灾害,尤其是旱灾,从而对东北地区的生态环境,尤其是农业生产带来不利的影响,这应引起重视。