Effect of disturbance on foraging: whelk activity on wave-exposed rocky shores with minimal tidal range

For slow-moving rocky intertidal predators such as whelks, frequent stress can be detrimental. Most studies on the foraging behavior of whelks have been conducted in regions where tidal amplitude is >1 m and on relatively small species. We studied the effects of wave action, desiccation, and water temperature on the foraging behavior of a large (approximately 80 mm) rocky shore whelk, Stramonita haemastoma, at the small-tide (<40 cm) but wave-exposed Israeli Mediterranean coast. We hypothesized that in such conditions foraging activity of this large predator will be greatly limited. Field observations show that when wave height exceeds 0.5 m, activity of whelks decreases by at least threefold relative to that seen under calm-sea conditions, and most whelks remain inside shelters. Wave height data from offshore moorings demonstrate that such conditions occur along the coast >85% of the time. Whelks move into shelters or completely disappear when exposed to prolonged desiccation conditions that can last for days along the shore during spring and autumn. Foraging activity is greater at night than in daytime and might be related to lighter winds and calmer sea conditions at night. Laboratory experiments show that elevated water temperatures during winter do not result in increased predation rates relative to those measured during spring. This indicates that a seasonal endogenous biological rhythm may exist. Our findings demonstrate that the foraging activity of large whelks can be extremely constrained by high rates of disturbance, that is, frequent wave action, and less frequent desiccation. We claim that high rates of disturbance in the eastern Mediterranean explain why large whelks are scarce in intertidal habitats where food is plentiful but suitable shelter is rare.Communicated by G.F. Humphrey, Sydney     

Estimating the complexity of bird song by using capture-recapture approaches from community ecology

Repertoire size, the number of unique song or syllable types in the repertoire, is a widely used measure of song complexity in birds, but it is difficult to calculate this exactly in species with large repertoires. A new method of repertoire size estimation applies species richness estimation procedures from community ecology, but such capture-recapture approaches have not been much tested. Here, we establish standardized sampling schemes and estimation procedures using capture-recapture models for syllable repertoires from 18 bird species, and suggest how these may be used to tackle problems of repertoire estimation. Different models, with different assumptions regarding the heterogeneity of the use of syllable types, performed best for different species with different song organizations. For most species, models assuming heterogeneous probability of occurrence of syllables (so-called detection probability) were selected due to the presence of both rare and frequent syllables. Capture-recapture estimates of syllable repertoire size from our small sample did not differ significantly from previous estimates using larger samples of count data. However, the enumeration of syllables in 15 songs yielded significantly lower estimates than previous reports. Hence, heterogeneity in detection probability of syllables should be addressed when estimating repertoire size. This is neglected using simple enumeration procedures, but is taken into account when repertoire size is estimated by appropriate capture-recapture models adjusted for species-specific song organization characteristics. We suggest that such approaches, in combination with standardized sampling, should be applied in species with potentially large repertoire size. On the other hand, in species with small repertoire size and homogenous syllable usage, enumerations may be satisfactory. Although researchers often use repertoire size as a measure of song complexity, listeners to songs are unlikely to count entire repertoires and they may rely on other cues, such as syllable detection probability.Communicated by A. Cockburn     

Response to perceived predation threat in fiddler crabs: trust thy neighbor as thyself?

Prey require information if they are to respond to predation threat in a risk-sensitive manner. One way that individuals can obtain this information is through the predator-mediated, threat-induced behavior of conspecifics. We examined such a possibility in a refuge-seeking species, the sand fiddler crab (Uca pugilator). Crabs were either exposed directly to a simulated predation threat (a moving cylinder) or the threat-induced response of a near neighbor. We found that fiddler crabs responded to the flight of their neighbors even when they, themselves, were not privy to the stimulus that induced their neighbors response. However, the wider range of behaviors exhibited by these crabs—which included no reaction, freezing, running back to the burrow entrance, and burrow retreat—suggest that non-threatened crabs either (1) perceived the gravity of the predation threat differently from their directly threatened neighbors and/or (2) engaged in behaviors that allowed them to acquire further information in the face of uncertainty. Conspecific behaviors also had an effect on the hiding duration of crabs, with individuals hiding longer if they saw both the predation threat and the flight of their neighbor. Our results suggest that cues provided by conspecifics can play an important role in guiding the antipredator response of refuge-seeking prey.     

Competition and facilitation between germlings of<Emphasis Type="Italic"> Ascophyllum nodosum</Emphasis> and<Emphasis Type="Italic"> Fucus vesiculosus</Emphasis>

Competitive interactions between germlings of Ascophyllum nodosum (L) Le Jolis and Fucus vesiculosus L. were studied both in the laboratory and on a shore of the Isle of Man, in the Irish Sea. Both intra- and interspecific competition were investigated by comparing the performance of algal germlings both in monocultures and mixed populations of the two species. The growth of germlings of both species reduced with increasing density. F. vesiculosus always grew faster than Ascophyllum and did best in mixed cultures, whereas Ascophyllum did least well when mixed with Fucus germlings. Clearly the adverse effects of F. vesiculosus on A. nodosum were greater than those of Ascophyllum cohorts. At the same total density, the survival and growth of Ascophyllum declined with an increasing proportion of Fucus germlings, implying that poor recruitment of A. nodosum results from strong competition with F. vesiculosus. However, under desiccation stress on the shore, F. vesiculosus enhanced the survival of A. nodosum at the early germling stage even though competition may occur again at the late stage. Thus, whether interactions between germlings take the form of competition or facilitation depends on the environmental conditions.Communicated by O. Kinne, Oldendorf/Luhe     

Cadmium accumulation and elimination in tissues of juvenile olive flounder, Paralichthys olivaceus after sub-chronic cadmium exposure

Experiments were carried out to investigate the accumulation and elimination of cadmium (Cd) in tissues (gill, intestine, kidney, liver and muscle) of juvenile olive flounder, Paralichthys olivaceus, exposed to sub-chronic concentrations (0, 10, 50, 100 microg l(-1)) of Cd. Cd exposure resulted in an increased Cd accumulation in tissues of flounder with exposure periods and concentration, and Cd accumulation in gill and liver increased linearly with the exposure time. At 20 days of Cd exposure, the order of Cd accumulation in organs was gill > intestine > liver > kidney > muscle and after 30 days of exposure, those were intestine > gill > liver > kidney > muscle. An inverse relationship was observed between the accumulation factor (AF) and the exposure level, but AF showed an increase with exposure time. During the depuration periods, Cd concentration in the gill, intestine and liver decreased immediately following the end of the exposure periods. No significant difference was found Cd in concentration in the kidney and muscle during depuration periods. The order of Cd elimination rate in organs were decreased intestine > liver > gill during depuration periods.     

PCB and DDT contamination in cultivated and wild sea bass from Ria de Aveiro, Portugal

Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) and metabolites were quantified in muscle and liver of sea bass (Dicentrarchus labrax) collected in Ria de Aveiro and in two fish farms. Sea bass from natural environment showed lower levels than fish from farming, which may be partly attributed to the higher lipid content of cultivated fish. PCB congener distribution in tissues of sea bass from the two farms resembled that of diet pellets suggesting that commercial diet is a major source of PCBs. However, fish in the two sites were fed with diet of similar PCB and DDT contamination but showed distinct levels in its tissues not explained by lipid content.     

Modeling the Entrepe?as Reservoir.

The Entrepe?as Reservoir is a monomictic reservoir located in River Tagus (Spain). The aim of this work is to establish a feasible model to predict the depth of the thermocline that is developed in the reservoir during the period of natural thermal stratification. Entrainment, eddy diffusion, inflow of external energy, and other factors are considered to calibrate the parameters of the model. The methodology involves the measure of actual temperature and electrical conductivity profiles, use of meteorological data and reservoir parameters, and selection and application of several models from the literature. The calculations and predictions are integrated to a software packet that is able to predict thermocline depth and water temperature profile during a 1-year period on a day-by-day basis. In the thermocline depth, the prediction error, on the basis of real data, is less than 6% and, in the water temperature, it is 2 degrees C.     

Dealing with urban noise: vermilion flycatchers sing longer songs in noisier territories

In noisy conditions, several avian species modulate their songs in amplitude and in the temporal or frequency domains, presumably to improve communication. Most studies on how passerine birds perform such adjustments have been carried out in oscines, a group well known for the importance of learning in the development of their songs. On the other hand, suboscines, in which learning appears to have little influence on the development of their songs, have been largely neglected. We evaluated song adjustment to noise in the vermilion flycatcher (Pyrocephalus rubinus), a suboscine bird. We conducted song recordings and noise measurements at several territories within Mexico City during the length of the dawn chorus. Males living in noisier places sang long songs, while those males inhabiting quieter places sang both short and long songs. We also found evidence of individual song plasticity, as males sang less versatile songs (i.e., songs with more introductory elements) later in the morning when noise levels were higher. This individual shift in song seems to be more associated to time of the day rather than to the observed rise in noise. However, we cannot discard an effect of noise, which should be evaluated with an experiment. We discuss our results in the context of other studies with oscine passerines and other taxa and consider implications for signaling in intra- and intersexual contexts.     

The role of canopy structural complexity in wood net primary production of a maturing northern deciduous forest

The even-aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early-successional aspen (Populus spp.) and birch (Betula papyrifera) are senescing at an accelerating rate and are being replaced by middle-successional species including northern red oak (Quercus rubra), red maple (Acer rubrum), and white pine (Pinus strobus). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree-species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine-year period. We found that effects of canopy structural complexity on wood NPP (NPPw) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPPw is mediated primarily through its effect on canopy structural complexity. Stand-level diversity of canopy-tree species was not significantly related to either canopy structure or NPPw. We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests.     

Correlated evolution of male and female testosterone profiles in birds and its consequences

Circulating levels of testosterone in adults have mainly evolved as a consequence of selection on males for increased levels, while levels of circulating testosterone in females may be an indirect consequence of selection on males. A review of the literature revealed that intense directional selection for high levels of circulating testosterone in birds is likely to be mainly due to direct selection on males. A comparative study of testosterone levels in birds revealed a strong positive relationship between peak testosterone levels in adult females and peak levels in males. The slope of this relationship was significantly less than unity, implying that the testosterone levels in females have been reduced in species with high levels in males. An analysis of the order of evolutionary events suggested that peak concentration of testosterone in females changed after peak concentrations of testosterone in males. Females in colonial species of birds had significantly higher circulating peak testosterone levels compared to females of solitary species, and relative levels after controlling for the effects of peak levels in males were also larger, suggesting that any costs of high testosterone levels in females are particularly likely in colonial birds. Direct selection on male circulating testosterone levels may increase the costs that females incur from high testosterone titers. For example, high female levels may negatively affect ovulation and laying and may also affect the levels of testosterone that females deposit in their eggs and hence the exposure of pre- and post-hatching offspring to testosterone. This in turn may affect not only offspring behavior, but also offspring development and the trade-offs between growth, development of immune function, and behavior in offspring.