Effects of Degraded Optical Conditions on Behavioural Responses to Alarm Cues in a Freshwater Fish

Prey organisms often use multiple sensory cues to gain reliable information about imminent predation threat. In this study we test if a freshwater fish increases the reliance on supplementary cues when the reliability of the primary cue is reduced. Fish commonly use vision to evaluate predation threat, but may also use chemical cues from predators or injured conspecifics. Environmental changes, such as increasing turbidity or water colour, may compromise the use of vision through changes in the optical properties of water. In an experiment we tested if changes in optical conditions have any effects on how crucian carp respond to chemical predator cues. In turbidity treatments we added either clay or algae, and in a brown water colour treatment we added water with a high humic content. We found that carp reduced activity in response to predator cues, but only in the turbidity treatments (clay, algae), whereas the response in the brown water treatment was intermediate, and not significantly different from, clear and turbid water treatments. The increased reliance on chemical cues indicates that crucian carp can compensate for the reduced information content from vision in waters where optical conditions are degraded. The lower effect in brown water may be due to the reduction in light intensity, changes in the spectral composition (reduction of UV light) or to a change in chemical properties of the cue in humic waters

Self-regulated learning as a prerequisite for successful distance learning

The relationship between the application of self-regulated learning strategies and the academic achievement of tertiary distance learners from a rural area is explored. The literature review indicated a positive relationship between self-regulation, application of learning strategies and academic achievement. The study focused on investigating the differences in the application of self-regulated learning strategies by a group of successful and non-successful distance learners (n=143). An ex post facto design was used and data were statistically analysed by means of factor analyses and multiple regression analyses. It is argued that distance learners, who are successful in their endeavours to complete an academic module, apply more and/or different self-regulated learning strategies than non-successful learners. South African Journal of Education Vol.24(2) 2004: 141-14

Scaling-up productivity (NPP) using light or water use efficiencies (LUE, WUE) from a two-layer tropical plantation

International audienceNet primary productivity (NPP) is a key driver of ecosystem C balance. ScalingNPP up to larger areas requires indirectmethods: (a) for examble epsilon models based on light use efficiency (LUE = NPP/ APAR, where APAR is the absorbed photosynthetically active radiation by green elements of canopy, or else models based on water-use-efficiency (WUE = NPP/E, where E = evapo-transpiration); (b) remote sensing tools to estimate the fraction ofAPAR(fAPAR) from vegetation indexes, or to estimate E. However, LUE and WUE are suspected to vary in space (edaphoclimatic conditions, planting density) and time (seasonality, age), which needs to be documented before scaling up. Moreover, the application of this scaling approach to agroforestry systems with a stratified canopy may be difficult, since each layer contributes to the overall ecosystem light- and water-use efficiencies. The seasonal and inter-annual variabilities of LUE and WUE was assessed in a very simple bi-layer tropical coconut grove displaying minimum climatic and LAI variations, distinguishing the upper layer of coconuts, the herbaceous under-storey and the whole stand (subscripts C, H and S, respectively). We monitored NPP biometrically during 3 years above and below ground, together with microclimate and ES above the canopy (eddy-covariance), transpiration (TC) by sapflow, and fAPARC by LAI-2000 combined with canopy light absorption models. The partitioning of APAR, NPP and E was very close to the rule-of-thumb of canopy coverage by upper-layer (75%). Also the mean annual value of LUES (1.7 gDM MJPARi -1 ) or mean WUES (3.7 gDM kg_1 H2O) were mainly driven by the upper-layer of coconuts. However, the under-storey experienced around twice as much seasonal variations of NPP, E,LUE andWUE than the upper-storey. Given that NPPS varied by only 23% over the year, the high seasonal variations of WUES (240%) and LUES (250%) were mostly driven by the variations of APARS (230%) and were adjusted successfully using climate, age and density data, as a first step to estimate NPP on larger scales using climate, GIS and remotesensing

Electromyographic Analysis of Selected Muscles during Backhand Throw in Ultimate Frisbee

SOUHRN Název: Elektromyografická analýza vybraných svalů během hodu backhand ve hře ultimate frisbee Title: Electromyographic analysis of selected muscles during a backhand throw in ultimate frisbee Cíl práce: Naše práce se zaměřuje na analýzu svalové činnosti během hodu backhand v jedné z nejnovějších kolektivních her- ultimate frisbee. Sleduje míru společné aktivace extenzorů zápěstí - vykonávajících odhození disku a lopatkových svalů (m.trapezius - kraniální a kaudální porce, m.serratus anterior a m.pectoralis major)- dynamických stabilizátorů lopatky. Dále sleduje rozdíly v zapojení svalů během této aktivity ve skupině trénovaných hráčů ultimate. Metoda: Ke snímání aktivity zmíněných svalů jsme použili metodu povrchové elektromyografie. PEMG zachycuje souvislost mezi svalovou aktivitou na akru a kořenovém kloubu horní končetiny během odhodu disku při backhandu. Výsledky: Experiment ukazuje na rozdílnost v aktivaci svalů ve skupině trénovaných hráčů ultimate frisbee, odvíjející se od individuálního vzoru (resp.stylu) pohybového projevu hráče. Při dalším analyzování však vycházejí do popředí dva pohybové modely, odvíjející se od společných znaků či podob získaných vzorů. l.model je charakteristický dominancí m.pectoralis major, ke kterému se ve dvou případech připojuje aktivita m.serratus anterior a v..