Individual variation in the foraging strategies of young yellow perch (Perca flavescens) from the Ottawa River

Differences in the foraging strategies among young individuals of the yellow perch (Perca flavescens) were observed in the laboratory by using two kinds of food (Daphnia and brine shrimp) separately and together. Individuals differed significantly in their ability for feeding attempts, time interval between two consecutive feeding attempts, feeding angles, regurgitation rate, and number of unsuccessful attempts and in their food preference. It is concluded that there are individuals with different foraging strategies. Variability in foraging strategies within single species populations is important because it may explain how the conspecific individuals may differ in their overall feeding behaviour.     

Factors influencing the attachment strength of Dreissena polymorpha (Bivalvia)

Abstract

The effects of several factors (shell length, exposure time, substratum orientation in space, illumination, temperature, conspecifics) upon the attachment strength (measured with a digital dynamometer) of the freshwater, gregarious bivalve Dreissena polymorpha were studied under laboratory conditions. A rapid increase in attachment strength was observed on resocart (a thermosetting polymer based on phenol-formaldehyde resin, with paper as filler) substrata during the first 4-d exposure, after which it stabilised at ca 1 N. The attachment strength increased also with mussel size. Mussel adhesion on variously oriented surfaces (vertical, upper horizontal and lower horizontal) was similar. Illumination inhibited attachment strength, as expected for a photophobic species, but only after a 2-d exposure. After 6 d, no effects of light were detected. Thus, illumination seemed to influence the attachment rate, rather than the final strength. The optimum temperature for mussel attachment was 20 – 25°C. At lower and higher temperatures (5 – 15°C and 30°C), their adhesion strength decreased. The presence of conspecifics stimulated mussel attachment strength.     

Insights from social transmission of information in rodents

Direct exposure to stimuli in their environment is not the only way that animals learn about important information. Individuals can infer fear from a social context through observation. Like humans, rats are very social animals, and may learn to infer information about their environment through their interactions with conspecifics. Here, we first review different models for social transmission of information in rodents. Second, we examine different modes of communication that are important to social learning. Then, we cover the different proximate factors that are thought to modulate the social transmission of information. Next, we identify social and environmental conditions that impact social learning, and finally, we conclude by revisiting social transmission through the lens of the Tinbergen framework.     

Alarm calls modulate the spatial structure of a breeding owl community

Animals should continuously assess the threat of predation. Alarm calls inform on predation risk and are often used as cues to shape behavioural responses in birds and mammals. Hitherto, however, the ecological consequences of alarm calls in terms of organization of animal communities have been neglected. Here, we show experimentally that calls of a resident nocturnal raptor, the little owl Athene noctua, triggered a response in terms of breeding habitat selection and investment in current reproduction in conspecifics and heterospecifics. Little owls preferred to settle in territories where calls of conspecifics, irrespective of their type (i.e. alarm versus contact calls), were broadcasted, indicating that either conspecific attraction exists or calls are interpreted as foreign calls, eliciting settlement as a mode of defence against competitors. Also, we found that little owls seemed to invest more in current reproduction in safe territories as revealed by conspecific calls. Innovatively, we reported that a second owl species, the migratory scops owl Otus scops, preferred to breed in safe territories as indicated by little owls' calls. These results evidence that the emission of alarm calls may have, apart from well-known behavioural effects, ecological consequences in natural communities by inducing species-specific biases in breeding habitat selection. This study demonstrates a previously unsuspected informative role of avian alarm calls which may modulate the spatial structure of species within communities.     

Pollution by conspecifics as a component of intraspecific competition among Aedes aegypti larvae

Abstract.  1. The role of pollution by conspecifics in the costs associated with larval intraspecific competition was investigated for Aedes aegypti (Diptera: Culicidae).
2. The growth of larval A. aegypti mosquitoes reared in clean water and water in which another larva had previously grown was compared; this procedure eliminates interactions through food consumption between competitors and allows the effects of other processes to be expressed.
3. A cost of growing in polluted water was found: this cost was expressed as an increase in developmental time and a reduction of adult longevity when starved, starved adult dry weight, and wing length.
4. Contrary to previously reported results of an experiment allowing for competition for food, these costs were not expressed in a sex-specific manner and were independent of the sex of the polluter.
5. It was thus demonstrated that competition arises from both resource depletion and other effects that result in deterioration of the environment, with chemical pollution of the environment being the most likely cause.     

Domestic chicks' runway responses to video images of conspecifics

Because chickens are highly social animals, live conspecifics are often used to provide an incentive or goal in studies of gait, sociality or fear that require the bird to traverse a runway. However, the variable behaviour of the stimulus birds can influence the approach/avoidance responses of the test birds and thereby confound the results. Because chickens modify their behaviour readily and appropriately to a variety of video images, including social stimuli, we asked if video playback might represent easily controllable and standardized alternatives to live birds. Female ISA Brown chicks were housed in groups of eight and then exposed to a blank illuminated television for 10 min per day from 2 to 7 days of age. At 8 or 9 days of age they were placed individually in the start box of a 1.6 m long runway and we recorded their responses to a monitor displaying selected video images that was situated in the goal box at the opposite end of the runway. In Experiment 1 chicks approached a monitor playing the video image and soundtrack of feeding chicks significantly sooner than one of a goal box with the food dish and background noise. In Experiment 2, chicks were exposed to the same video of feeding conspecifics with or without the associated sounds or to a video of the goal box with or without the chick soundtrack. Both the videos of other chicks elicited faster approach than did those of the goal box and the sound and silent versions were equally attractive. Adding the soundtrack of feeding chicks to the goal-box video failed to increase its attractiveness. The present results suggest that chicks are attracted towards televised images of other chicks. They also indicate that the visual and auditory components of the video stimuli did not exert additive effects and that approach reflected attraction to the visual image. Collectively, our findings suggest that video playback of selected social stimuli, such as feeding conspecifics, could be a valuable tool in tests requiring voluntary locomotion along a predetermined path.     

Experimental study on the sensory capabilities of coral-reef fish larvae for the recognition of their settlement location

Some experiments in aquarium and in situ have been carried out to investigate the sensory abilities of coral reef fish larvae in the recognition of their settlement location. Ten out 12 species studied detected their settlement location due to the presence of conspecifics and not by habitat characteristics. Larvae use three senses in this detection: sight, smell and vibratory sense.     

Limited contributions of plant pathogens to density‐dependent seedling mortality of mast fruiting Bornean trees

Fungal pathogens are implicated in driving tropical plant diversity by facilitating strong, negative density‐dependent mortality of conspecific seedlings (C‐NDD). Assessment of the role of fungal pathogens in mediating coexistence derives from relatively few tree species and predominantly the Neotropics, limiting our understanding of their role in maintaining hyper‐diversity in many tropical forests. A key question is whether fungal pathogen‐mediated C‐NDD seedling mortality is ubiquitous across diverse plant communities. Using a manipulative shadehouse experiment, we tested the role of fungal pathogens in mediating C‐NDD seedling mortality of eight mast fruiting Bornean trees, typical of the species‐rich forests of South East Asia. We demonstrate species‐specific responses of seedlings to fungicide and density treatments, generating weak negative density‐dependent mortality. Overall seedling mortality was low and likely insufficient to promote overall community diversity. Although conducted in the same way as previous studies, we find little evidence that fungal pathogens play a substantial role in determining patterns of seedling mortality in a SE Asian mast fruiting forest, questioning our understanding of how Janzen‐Connell mechanisms structure the plant communities of this globally important forest type.     

Strong territoriality and weak density‐dependent reproduction in Lesser Spotted Eagles Clanga pomarina

We assessed whether populations of the migratory, philopatric, territorial Lesser Spotted Eagle Clanga pomarina are regulated through territoriality and density‐dependent reproduction rates. In the north‐western part of the distribution to the east of the Baltic Sea, territories were spaced regularly and consistently between years. We did not find strong support for an improvement of reproductive output with an increase in distance to the nearest neighbour or with a decrease of the number of conspecifics within a 2‐km radius around nest‐sites. Eagles differed greatly in territory spacing across three studied geographical areas, but breeding performance did not follow the same pattern. Performance of birds at the northern limit of their distribution did not differ from that in an adjacent southern area. Moreover, breeding performance fluctuated synchronously across different geographical areas, perhaps indicating climatic spatial autocorrelation or trophic interactions with synchronous vole population fluctuations over large areas. Our data suggest population regulation through territoriality but do not identify density‐dependent breeding performance in this internationally protected raptor. Population density may be a good criterion for the selection of priority sites for conservation, but synchronous fluctuations in reproductive success over large geographical areas suggest that habitat conservation should similarly be focused at large scales.     

Factors influencing tadpole deposition site choice in a frog with male parental care: An experimental field study

Parents have evolved a variety of strategies to minimize risks to their offspring, including complex choices regarding suitable rearing sites, based on abiotic and biotic factors, which differentially affect offspring survival. Because availability and quality of these sites are variable, parents may have to choose between immediately available lower‐quality rearing sites or extended search time. In some frog species with larval transport, parents are known to select bodies of water that are free of predators, cannibalistic tadpoles, or intraspecific competitors for larval deposition and rearing sites. We tested whether abiotic factors and the presence of predators and conspecific tadpoles affect tadpole deposition behavior in a population of smooth guardian frog, Limnonectes palavanensis, on the island of Borneo. Females lay eggs on land and males guard them until they hatch; after hatching, tadpoles climb onto the male's back and are subsequently transported to small pools of water on the forest floor, which are scarce and patchily distributed. We estimated the abundance of natural tadpole rearing sites in our study area and conducted experiments using artificial pools to test whether abiotic characteristics of these pools affect the probability of larval deposition. We also performed choice experiments to test whether males of L. palavanensis avoid pools with conspecific tadpoles or predators. Lastly, we tested whether the tadpoles of this species exhibit cannibalism. The abundance of natural deposition sites was low, and males readily used artificial pools for tadpole deposition. Males were less likely to deposit tadpoles in artificial pools located in steep areas, and males did not avoid depositing tadpoles in pools with conspecifics or with experimentally introduced predators. Males exhibited clutch‐partitioning behavior, dividing tadpoles between adjacent artificial pools. Pool availability, rather than the presence of potential competitors or predators in a pool, affects tadpole deposition decisions in this species.