Advertisement call duration indicates good genes for offspring feeding rate in gray tree frogs (Hyla versicolor)

Indicator or ”good genes” models of sexual selection predict that mating preferences allow females to choose mates that are genetically superior. Female gray tree frogs (Hyla versicolor) prefer male advertisement calls of long call duration, which can be indicators of enhanced offspring growth performance. We tested the effects of father’s call duration and the presence of a caged predator (dragonfly naiad) on tadpole activity and growth in a factorial experiment, controlling for maternal and environmental effects. The effect of food availability (a repeated measure) on tadpole activity was also examined. Tadpoles responded to predator presence and to high food availability by decreasing activity and feeding. Tadpoles exposed to a caged predator were smaller after 14 days than those exposed to an empty cage, suggesting that spending less time feeding carries the cost of reduced growth. Offspring of males with long versus short calls responded similarly to the presence of a predator. Nonetheless, offspring of long-calling males spent more time feeding than did offspring of short-calling males, except when a predator was present but no food was available. Increased time spent feeding may contribute to enhanced offspring growth and, therefore, to the indirect benefit that a female may realize by selecting a mate with long calls. However, because the behavioral differences depended on the environment, and because the fitness consequences of such behavioral differences should also vary with the environment, the benefit of mating with a long-calling male may depend on the conditions encountered by the offspring. Received: 15 February 2000 / Revised: 24 September 2000 / Accepted: 16 October 2000     

Novel features of an inducible defense system in larval tree frogs (Hyla chrysoscelis)

Organisms in aquatic ecosystems must often tolerate variable environmental conditions, including an uncertain risk of predation. Individuals that can maintain plastic defenses against predation will increase their survival when predators are present, but will not incur the costs of these defenses when the risk of predation is low and the defense is not induced. Larvae of the pond-breeding anuran Hyla chrysoscelis develop a conspicuous phenotype in the presence of predators consisting of a brightly colored tail and a deeper tail fin. In this study, I attempted to identify the source of the chemical signal that induces this defensive morphology in this species. I tested whether metabolites alone, originating from the prey but passing through the predator, were able to induce the same morphological response as the combination of alarm signals released directly by attacked conspecifics, and metabolites. I used morphometric and tail conspicuousness data to assess tadpole response to the perceived risk of predation by larval odonate predators (Anax junius). I also tested whether this inducing cue could be recognized across species by measuring the morphological response of H. chrysoscelis tadpoles exposed to cues emitted when tadpoles of a closely related genus (Pseudacris crucifer) were consumed. Tadpoles exhibited a clean graded response of both overall shape and tail morphology in response to all cues, corresponding to their relative reliability as indicators of a risk of predation. H. chrysoscelis tadpoles were also able to respond to cues emitted when tadpoles of a closely related genus were consumed by predators. These results illustrate that tadpoles of this species are able to respond to metabolites alone without alarm signals, and that interspecific chemical communication is a primary mechanism for predator avoidance in this inducible defense system.     

The effect of social interactions on calling energetics in the gray treefrog (Hyla versicolor)

Summary The vocal behavior of Hyla versicolor was studied in the field by means of behavioral observations and playback experiments, and these data were coupled with measurements of oxygen consumption in calling frogs to estimate the effect of social interactions on calling energetics. Male gray treefrogs have intense calls (median peak SPL=109 dB, fast RMS SPL=100 dB at 50 cm). At an air temperature of 23° C, males produced an average of 1,200–1,300 calls/h for 2–4 h per night. Calling rates and call durations differed among individuals, but were relatively constant for each male during periods of sustained calling. Males in dense choruses gave calls about twice as long as isolated males, but produced calls at about half the rate. Consequently, total calling effort and estimated aerobic costs were largely independent of chorus density. Playbacks of recorded calls to males in the field elicited increases in call duration and decreases in calling rate, regardless of the rate or duration of the stimulus. Males gave longer calls in response to long calls or to stimuli presented at high rates, but they did not precisely match either stimulus rate or duration. Calling effort and estimated oxygen consumption changed only slightly during stimulus playbacks. These results indicate that male-male competition elicits pro-found changes in the vocal behavior of calling males, but these changes have little effect on energy expenditure. We estimated that most calling males had metabolic rates of about 1.7–1.8 ml O₂/(g\h), or about 280 J/h for an average size (8.6 g) male at 20° C. Although changes in call duration and calling rate did not affect aerobic costs of calling, males producing long calls at slow rates called for fewer hours per night than males producing shorter calls at higher rates. This suggests that calling time may be limited by the rate at which muscle glycogen reserves are depleted.     

Begging calls and parental feeding decisions in tree swallows (Tachycineta bicolor)

We conducted playback experiments to examine how parent tree swallows (Tachycineta bicolor) use nestling begging calls to distribute feedings to individuals within broods. In a first study, we used a paired-choice test to determine if parents discriminated between the taped begging calls of nestlings deprived of food and those of nestlings that had been recently fed. Our results showed that parents directed their first feeding attempt towards model nestlings near speakers playing deprived calls significantly more often than to models near speakers playing fed calls. They also made more feeding attempts overall to models with deprived calls. In the second study, we varied call rate and amplitude to examine which call features parents might use to discriminate begging calls. Parents directed significantly more first feeding attempts and more feeding attempts overall towards non-begging nestlings near speakers playing high call rates than to nestlings near speakers playing low call rates. They did not, however, discriminate between calls differing in amplitude. Previous studies have shown that parent birds use begging calls to regulate overall feeding rates to the brood. Our results suggest that parent tree swallows also use begging calls when feeding individual nestlings and, in particular, prefer calls associated with increased levels of nestling hunger. Received: 14 February 2000 / Revised: 6 October 2000 / Accepted: 16 October 2000     

Complex brood care and reproductive behaviour in captive poison-arrow frogs,Dendrobates pumilio O. Schmidt

Summary Brood care in Dendrobates pumilio not only involves egg attendance and tadpole transport, but also tadpole attendance and feeding. Each tadpole is carried by the attending female to a water-filled bromelial leaf axil and regularly fed on unfertilized eggs. The tadpole responds to an approaching adult with a specialized, conspicuous behavior signalling its presence. Male-male competition includes fighting, egg eating, and male tadpole transport. D. pumilio is the first frog known to feed its free-living larvae.     

Male response to an aggressive visual signal, the wing wave display, in swamp sparrows

Signaling often involves complex suites of behaviors that incorporate different sensory modalities. Whatever modality is used to establish that a signal functions in communication researchers must demonstrate that receivers respond to it. The territory defense response of male swamp sparrows involves a variety of behaviors that includes both vocal and visual displays. One of these, the “wing wave” display, is a distinctive movement that predicts physical attack. Here, we use robotic taxidermic mounts paired with song to test the hypothesis that wing waving is a signal and, specifically, that male receivers respond to wing waving as a signal of aggressive intent. As predicted, subjects responded more aggressively to the mount during wing waving trials than during stationary trials. A second experiment demonstrated that this effect cannot be attributed simply to increased attention to movement. Less expectedly, subjects did not alter their own display behavior in response to wing waving as compared to a static mount. We conclude that the wing wave display in the context of singing is a signal that functions in male–male aggressive communication. Questions remain, including whether wing waving functions as a signal in the absence of singing and whether wing waving and song are redundant signals or communicate different information.     

Platinum pollution in road dusts,roadside soils,and tree barks in Seoul,Korea

This study presents the level of platinum in urban environment in and around Seoul, the capital city of Korea. Road dust, roadside soil, and tree bark samples were collected from the sites of various traffic volumes and from control sites in the suburbs. The above samples were analyzed for Pt by ICP-MS and other heavy metals by ICP-OES. Platinum levels in road dusts and roadside soils from Seoul were in the range of 3.8–444 ng/g (av. 115.0 ng/g) and 0.7–221 ng/g (av. 49.7 ng/g), respectively, whereas those in the suburbs were in the range of 2.3–5.2 ng/g (av. 3.9 ng/g) in road dusts and 0.4–5.1 ng/g (av. 2.4 ng/g) in roadside soils. The highest Pt levels in road dusts were found from major roads with high traffic volume. The remarkable difference in average Pt level between heavy traffic roads (av. 132.2 ng/g) and light traffic roads (av. 22.8 ng/g) reflects that an important source of Pt in roadside environment is automobile catalytic converter. High Pt level in road dust was found from the site of erratic stop–start driving condition, for example, 178 ng/g Pt in road dust around a vehicle crossing gate. Platinum level in tree barks ranged from 0.9 to 4.5 ng/g, which indicates the existence of Pt-containing particulate matter in the atmosphere. Road dusts with high Pt level were enriched in traffic-related heavy metals.     

Alternative mating tactics in the Italian treefrog, <Emphasis Type="Italic">Hyla intermedia</Emphasis>

As in many lekking anurans, Italian treefrog males use two mating tactics: they can attract females by calling vigorously or be satellites, that is, they can remain silent in proximity of a calling male and try to intercept females attracted by their neighbour. We investigated the factors that affected the expression of this mating tactic. Consistent with the conditional mating tactic hypothesis, satellites were smaller than average and smaller than their parasitised calling males. They spent a larger-than-average number of nights at the breeding site, where most of them were also observed calling. Moreover, satellites showed lower call rates and lower mating success than those of males they parasitise but not lower than those of males they did not parasitise. Overall, these results, together with those derived from the analyses of the seasonal and spatial distribution of males, provide evidence for a non-random association between satellites and calling males and are consistent with the hypothesis that satellites have spectral and temporal acoustic preferences that parallel those of females. By adopting the less-successful satellite mating tactic, competitively inferior males can nevertheless maximise their potential reproductive fitness by sexually parasitising the most attractive chorusing males.     

Advertisement-call modification,male competition,and female preference in the bird-voiced treefrog <Emphasis Type="Italic">Hyla avivoca</Emphasis>

Senders and receivers influence dynamic characteristics of the signals used for mate attraction over different time scales. On a moment-to-moment basis, interactions among senders competing for a mate influence dynamic characteristics, whereas the preferences of receivers of the opposite gender exert an influence over evolutionary time. We observed and recorded the calling patterns of the bird-voiced treefrog Hyla avivoca to assess how the dynamic characters of calls vary during interactions among groups of males in a chorus. This question was also addressed using playback experiments with males. Playback experiments with females showed how changes in dynamic call properties are likely to affect male mating success. Frogs calling in pairs, groups, or in response to playbacks produced longer calls than did isolated males. During call overlap, males often increased the duration of the silent interval (gaps) between the pulses of their calls so that the pulses of the calls of two neighbors interdigitated. This change resulted in increased variability of pulse rate, a traditionally static acoustic property; however, males also produced high proportions of non-overlapped calls in which variability in pulse rate was low and had species-typical values. Females preferred long calls to short- and average-duration calls, and non-overlapped calls to overlapped calls. Given a choice between pairs of overlapped calls, females preferred pairs in which the proportion of overlap was low and pairs in which the pulses of such calls interdigitated completely. The observed patterns of vocal competition thus reflect the preferences of conspecific females, which have influenced the evolution of the calling behavior of H. avivoca. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Behavioural responses of Diana monkeys to male long-distance calls: changes in ranging,association patterns and activity

Although much is known about the relationship between vigilance, group size and predation risk, behavioural responses to predation risk and their resultant costs are less clear. We investigated the response of Diana monkeys to increased predation risk by looking at behavioural changes associated with male long-distance calls, which are reliably given to certain predators. After male long-distance calls, group spread and nearest-neighbour distance decreased whilst travel and association rates for the group increased. The average height and exposure level of individuals in the group did not change after calls. Individual Diana monkeys changed their behaviour and were more likely to be vigilant or travel and less likely to engage in social or resting behaviours after long-distance calls. In addition, movement rates increased with the number of species the Diana monkeys were associated with. Diana monkey long-distance calls facilitate the joining of groups of other species. Black and white colobus and lesser spot-nosed monkeys were more likely to be in an association following a long-distance call than before. Behavioural responses, such as increased travel or association rates, that reduce foraging efficiency are interpreted as evidence of a non-lethal impact of increased predation risk.     

Vertical migrations in the tree crab Sesarma leptosoma (Decapoda,Grapsidae)

Sesarma leptosoma, somewhat similar to the Atlantic related species, Aratus pisonii, is an East-African mangrove crab which spends its entire life on the roots and branches of mangrove trees (mostly Rhizophora mucronata, Bruguiera gymnorhiza and Ceriops tagal). S. leptosoma never enters the water, nor does it ever venture onto the free mud surface at low tide. Part of the day and night it remains on the lower parts of the mangrove aerial roots, which are often encrusted with a wet algal mat of Bostrichia spp., searching for food and water. Twice a day, from ca. 06:00 to 08:00 hrs in the morning and 16:00 to 18:00 hrs in the afternoon, many of the crabs migrate as far as the leaves at the top of the tree on which they feed. However, they only spend a brief period among the leaves, from ca. 07:00 to 10:00 and 17:00 to 19:00 hrs, after which time they make their way back towards the roots again in two downward migrations. In the morning, the downward migration brings all the crabs back to the roots, but in the evening not all the crabs take part in the downwards migration and some of them pass the whole night in the tree tops. A comparison of the migration time patterns for two different periods of the year (June–July and November) shows that the number of crabs migrating along the tree trunk is modulated by the spring-neap tidal cycle, while the onset of daily migration seems to be controlled mostly by the light level and/or other climatological cues. The adaptive significance of this migratory behaviour is discussed. Observations reported in our study were made in Mida Creek, Dabaso, Kenya in 1991 and 1992.     

Predator choice in the field; grouping guppies, Poecilia reticulata, receive more attacks

Capture success of many predator species has been shown to decrease with increasing prey group size and it is therefore suggested that predators should choose to attack stragglers and/or small groups. Predator choice in the laboratory has shown mixed results with some species preferentially attacking large groups and others preferring to attack stragglers over groups. Such predator choices have not been tested in the field. In our study we presented a binary choice between a shoal of guppies and a single guppy to predators in pools in the Arima river, Trinidad. We observed attacks in 11 different pools from a total of 53 predators (20 acara cichlids, Aequidens pulcher, 32 pike cichlids, Crenicichla frenata, and one wolf-fish, Hoplias malabaricus) and found that all predators showed a strong preference for the shoal of guppies in terms of both first choice and total number of attacks. We discuss the implications of these preferences with regards to predator–prey interactions.     

北京西山地区不同林分健康状况比较研究

以不同树种林分健康状况比较研究为切入点,以北京西山地区同一时期的油松×侧柏混交林、油松（Pinus tabulaeformis）林、侧柏（Platycladus orientalis）林和栓皮栎（Quercus variabis）林为研究对象。通过构建林分健康评价指标体系,计算林分综合健康指数,分别对不同林分的健康状况进行了分析和比较,探讨不同林分开展森林健康经营的关键环节,同时也从森林健康的角度说明造林树种选择的重要性。研究结果表明：各林分综合健康指数都为正值但数值都不高,这表明目前各林分都处于健康状态,但对外界扰动反应较为敏感,按健康状况排序：油松×侧柏林0．234〉栓皮栎林0．186〉油松林0．145〉侧柏林0．128;从单个指标看,各林分中都有负值指标出现,由此揭示,对负值指标的调整和增加正向指标的指标值是森林健康经营的关键。     

惠州绿化乔木叶片及其叶面降尘对大气SO2污染的生物监测

采用常规采样及碱片挂片法同步监测广东省惠州市大气SO2体积分数,用ICP-AES测定了惠州市不同功能区的2种主要绿化树种大叶榕(Ficus virens Ait var.sublanceolata(Miq.) Corner)、紫荆(Bauhinia blakeana)叶片及其叶面降尘的硫质量分数。结果表明,不同功能区植物叶片和降尘的硫质量分数差异显著,其综合污染指数(PI)以商业交通区、工业区、居住区、清洁区的趋势递减。叶片中硫的质量分数随春、夏、秋季而增长,季节差异显著。植物叶片、降尘中硫质量分数随交通流量的减少而降低。叶片和叶面降尘中硫的质量分数与大气硫酸盐化速率三者显著相关,大叶榕和紫荆与降尘协同生物监测大气SO2的二元数学模型的相关系数分别为R=0.995和R=0.990,明显优于植物与硫酸盐化速率监测SO2的常规一元数学模型。表明大叶榕、紫荆叶片及其叶面降尘均可作为城市区域大气SO2污染的有效指示剂,叶片的长期效益和季节效益显著,降尘则短期效益显著;两者协同监测,可靠性和灵敏度更高,应用前景广阔,可为地方和区域环境监测和评价提供参考。     

Seed terminal velocity, wind turbulence, and demography drive the spread of an invasive tree in an analytical model

Little is known about the relative importance of mechanistic drivers of plant spread, particularly when long-distance dispersal (LDD) events occur. Most methods to date approach LDD phenomenologically, and all mechanistic models, with one exception, have been implemented through simulation. Furthermore, the few recent mechanistically derived spread models have examined the relative role of different dispersal parameters using simulations, and a formal analytical approach has not yet been implemented. Here we incorporate an analytical mechanistic wind dispersal model (WALD) into a demographic matrix model within an analytical integrodifference equation spread model. We carry out analytical perturbation analysis on the combined model to determine the relative effects of dispersal and demographic traits and wind statistics on the spread of an invasive tree. Models are parameterized using data collected in situ and tested using independent data on historical spread. Predicted spread rates and direction match well the two historical phases of observed spread. Seed terminal velocity has the greatest potential influence on spread rate, and three wind properties (turbulence coefficient, mean horizontal wind speed, and standard deviation of vertical wind speed) are also important. Fecundity has marginal importance for spread rate, but juvenile survival and establishment are consistently important. This coupled empirical/theoretical framework enables prediction of plant spread rate and direction using fundamental dispersal and demographic parameters and identifies the traits and environmental conditions that facilitate spread. The development of an analytical perturbation analysis for a mechanistic spread model will enable multispecies comparative studies to be easily implemented in the future.     

Combining a generic process-based productivity model and a statistical classification method to predict the presence and absence of tree species in the Pacific Northwest,U.S.A.

Although long-lived tree species experience considerable environmental variation over their life spans, their geographical distributions reflect sensitivity mainly to mean monthly climatic conditions. We introduce an approach that incorporates a physiologically based growth model to illustrate how a half-dozen tree species differ in their responses to monthly variation in four climatic-related variables: water availability, deviations from an optimum temperature, atmospheric humidity deficits, and the frequency of frost. Rather than use climatic data directly to correlate with a species’ distribution, we assess the relative constraints of each of the four variables as they affect predicted monthly photosynthesis for Douglas-fir, the most widely distributed species in the region. We apply an automated regression-tree analysis to create a suite of rules, which differentially rank the relative importance of the four climatic modifiers for each species, and provide a basis for predicting a species’ presence or absence on 3737 uniformly distributed U.S. Forest Services’ Forest Inventory and Analysis (FIA) field survey plots. Results of this generalized rule-based approach were encouraging, with weighted accuracy, which combines the correct prediction of both presence and absence on FIA survey plots, averaging 87%. A wider sampling of climatic conditions throughout the full range of a species’ distribution should improve the basis for creating rules and the possibility of predicting future shifts in the geographic distribution of species.