Small-scale spatial and temporal interactions among benthic crustaceans and one fish species in the Bay of Biscay

In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasière) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus suggested reduced competition for food but also space as both are burrowing species. The observed temporal and spatial activity patterns may contribute to regulating assemblage structure as competing species may be actively foraging at different times and locations thus reducing direct competition.     

Effects of Neutral Posture on Muscle Tension During Computer Use

This study focused on developing a new approach to seated work positions as conducted on 67 office workers who use a Visual Display Terminal (VDT) as a major function of their working day. Muscle tension was measured by surface electromyography (sEMG) while participants were asked to adopt 4 selected working postures. Pain was measured before and after ergonomic intervention on the Nordic scale, which was modified for this study. Adjustable workstations were used to place participants in desired positions during the clinical testing sessions and the extended intervention period. Results indicate the effects of this ergonomic intervention may have positive effects on muscle tension and pain, significant enough to encourage employers to implement training and workstation modifications following these guidelines.     

Black spots and female association preferences in a sexual/asexual mating complex (Poecilia, Poeciliidae, Teleostei)

We investigated whether female association preferences for males are influenced by black spot disease (BSD), a parasite induced change of the host phenotype. We compared three different species of fish: a gynogenetic hybrid species, Poecilia formosa (amazon molly) and two sexual species (Poecilia latipinna and Poecilia mexicana), which were involved in the natural hybridisation leading to the amazon molly. Contrary to their sexual relatives, asexual amazon mollies significantly avoided images of males infected with black spot disease. We propose that amazon molly females have direct fitness benefits from choosing healthy males. The adaptive significance of the preference for BSD-uninfected males in the asexual amazon molly is yet unclear but may involve avoidance of predation or parasite infection as well as increased sperm availability.     

视屏显示终端对精神心理和神经行为的影响

本文进行了视屏显示终端(VDT)对操作人员精神心理和神经行为影响的调查研究。初步显示VDT作业可对操作人员造成情绪、感知、记忆、操作及复合功能诸多方面的不良影响。通过职业应激源的调查评价,显示VDT作业本身独特的作业性质、环境和要求形成了VDT作业的主要应激源。对从事VDT作业时间较长和作业负荷较大者则产生较高的职业性紧张度。从而说明VDT作业引起操作人员的某些心身疾患的可能性。     

Development and application of a video-mosaic survey technology to document the status of coral reef communities

The recent decline in the condition of coral reef communities worldwide has fueled the need to develop innovative assessment tools to document coral abundance and distribution rapidly and effectively. While most monitoring programs rely primarily on data collected in situ by trained divers, digital photographs and video are used increasingly to extract ecological indicators, provide a permanent visual record of reef condition, and reduce the time that divers spend underwater. In this study, we describe the development and application of a video-based reef survey methodology based on an algorithm for image registration and the estimation of image motion and camera trajectory. This technology was used to construct two-dimensional, spatially accurate, high-resolution mosaics of the reef benthos at a scale of up to 400 m². The mosaics were analyzed to estimate the size and percent cover of reef organisms and these ecological indicators of reef condition were compared to similar measurements collected by divers to evaluate the potential of the mosaics as monitoring tools. The ecological indicators collected by trained divers compared favorably with those measured directly from the video mosaics. Five out of the eight categories chosen (hard corals, octocorals, Palythoa, algal turf, and sand) showed no significant differences in percent cover based on survey method. Moreover, no significant differences based on survey method were found in the size of coral colonies. Lastly, the capability to extract the same reef location from mosaics collected at different times proved to be an important tool for documenting change in coral abundance as the removal of even small colonies (<10 cm in diameter) was easily documented. The two-dimensional video mosaics constructed in this study can provide repeatable, accurate measurements on the reef-plot scale that can complement measurements on the colony-scale made by divers and surveys conducted at regional scales using remote sensing tools.     

Underwater video as a monitoring tool to detect change in seagrass cover

To date seagrass monitoring has involved the removal of seagrass from its environment. In fragile or highly disturbed systems, monitoring using destructive techniques may interfere with the environment or add to the burden of disturbance. Video photography is a form of non-destructive monitoring that does not require the removal of seagrass or interference with the environment and has the potential to be a valuable tool in monitoring seagrass systems. This study investigated the efficacy of video photography as a tool for detecting change in seagrass cover, using the temperate Australian species Amphibolis antarctica (Labill.) Sonder ex Aschers. Using visual and random point estimates of seagrass cover from video footage, it was possible to determine the minimum sample size (number of random video frames) needed to detect change in seagrass cover, the minimum detectable change in cover and the probability of the monitoring design committing a Type II error. Video footage was examined at three scales: transects (m apart), sites (km apart) and regions (tens of km apart). Using visual and random point estimation techniques, a minimum sample size of ten quadrats per transect was required to detect change in uniform and variable seagrass cover. With ten quadrats it was possible to identify a minimum detectable change in cover of 15% for uniform and 30% for variable seagrass cover. Power analysis was used to determine the probability of committing a Type II error from the data. Region level data had low power, corresponding to a high risk of committing a Type II error. Site and transect level data had high power corresponding to a low risk of committing a Type II error. Based on this study's data, managers using video to monitor for change in seagrass cover are advised to use data from the smaller scale, for example, site and transect level data. By using data from the smaller scale, managers will have a low risk of incorrectly concluding there has not been a disturbance when one has actually occurred.     

Predicting functional response and size selectivity of juvenile Notonecta maculata foraging on Daphnia magna

A mechanistic model was developed to assess the impact of predation of juvenile Notonecta maculata on size structured Daphnia magna populations and to provide a framework for quantifying the backswimmers uptake of food. Results of experiments and model predictions clearly demonstrate selective predation of backswimmers when fed with a choice of daphnid size classes, with patterns of selectivity differing across N. maculata instars. The model describes the foraging process empirically on the base of a general predation cycle including four conditional events instead of using classic functional response curves. For model parameterisation components of predation, namely probability of encounter, attack and success as well as time spent on handling prey was directly observed by means of video tracking experiments. Since attack rate, capture success and handling time appeared to be a function of prey size differing between Notonecta instars, the model takes into account ontogenic changes in both predator and prey characteristics. Independent data of functional response and size selectivity experiments were used for model validation and proved the model outcome to be consistent with observations.     

Evaluating Visitor-Monitoring Techniques: A Comparison of Counting and Video Observation Data

Two visitor-monitoring methods, video monitoring and counts by human observers, were compared in order to identify and evaluate their respective advantages and disadvantages. The analysis considered user numbers, user type (walkers, dog walkers, bicyclists, and joggers) and group size of visitors. Remarkable differences were found between the two methods for user type and use levels. At low use levels, evaluations based on video monitoring resulted in fewer single bicyclists compared to counts by human observers, whereas at high use levels, human observers counted fewer walkers and bikers than video-interpreters. Based on this comparative analysis, we derive recommendations for more effective visitor-monitoring approaches. All data were collected during a visitor-monitoring project in the Danube Floodplains National Park in Austria between 1998 and 1999.     

Combining motions into complex displays: playbacks with a robotic lizard

Complex displays composed of multiple, seemingly independent, units can result from sexual selection for increasingly variable, but redundant, displays and from potentially opposing selective pressures imposed by use of the display in multiple contexts. Our playback results support the latter, multireceiver hypothesis by confirming that two aspects of the sagebrush lizard headbob display (number of headbobs and use of display-specific body postures) are independently-meaningful components that are interpreted differently by different receivers. Male receivers use species-typical body postures to distinguish between aggressive and broadcast forms of the display, whereas female receivers are more attentive to the number of headbob motions, using these to distinguish male courtship from a challenge from a female competitor. Thus, display components are likely subject to different selective pressures and the display as a whole is evolving in response to a complex selective regime. Our example differs from other complex signals that have been considered in that both display elements involve dynamic motions (turned on and off by the display producer) as opposed to static signal elements (e.g., color, size). In addition, we found evidence that display structure is highly malleable, and that lizards both produce and respond to artificial displays that violate syntactic rules identified from field observations. Finally, our experiments demonstrate that a robotic lizard can be used effectively in playback studies of visual display behavior in lizards.Electronic Supplementary Material: S1. Movie clip of the robotic lizard producing a species-typical headbob display as in Fig. 1a.