Chalk streams are among the most species-rich and productive of all temperate ecosystems. Despite this, a few keystone species have the potential to exert disproportionately powerful effects on community structure and ecosystem processes. Two of these are the bullhead Cottus gobio, a small benthic fish that is an extremely abundant, voracious predator, and the freshwater shrimp Gammarus pulex, which dominates the prey assemblage and is the principal detritivore. Field experiments detected a bullheadÁGammarusÁdetritus trophic cascade, with detrital processing rates slowed dramatically in the presence of the predator. In addition, survey data also revealed strong negative density-dependence between bullhead and brown trout, adding a further link in the cascade. However, although bullhead also depressed the abundance of a dominant grazer, the snail Potamopyrgus antipodarum, there was no cascading effect upon algal production, suggesting that autochthonous inputs were not controlled by topÁdown effects. This skewed effect of the predator upon autochthonous versus allochthonous basal resources stresses the need to consider both pathways of energy flux into the food web, whereas many previous studies have potentially overemphasized the importance of predatorÁherbivoreÁprimary producer cascades. The wider community food web contained 142 species and 1383 feeding links. This complex network exhibited ''small world'' properties, such as high clustering (unlike many other food webs) and shortest path lengths between species were small (in common with many other food webs). In particular, each of the four members of the detrital cascade could be connected to any other species by three links or fewer. Our data revealed that powerful cascading effects can be imbedded within even very complex ecological networks.

Research on cognitive ability and affect has indicated that both of them may function at various levels of generality (LG). This study aimed to investigate the possible effects of LG on school mathematics performance and related feelings of difficulty. Two hundred forty-three students of seventh, eighth, and ninth grades of both genders participated in the study. They were tested with cognitive ability tasks, affective questionnaires, and two school mathematics batteries. The difficulty of each of the school mathematics task was also rated on a 4-point scale. The two school mathematics batteries and affective questionnaires were re-administered 1 year after the first testing. Rates of difficulty were also taken. Path analysis showed that performance was mainly influenced by cognitive ability factors, whereas feelings of difficulty were influenced by performance, cognitive ability, and affective factors. The long-term relations between cognitive and affective factors are discussed.

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Aim: Although the ability to recognize emotions through bodily and facial muscular movements is vital to everyday life, numerous studies have found that older adults are less adept at identifying emotions than younger adults. The message gleaned from research has been one of greater decline in abilities to recognize specific negative emotions than positive ones. At the same time, these results raise methodological issues with regard to different modalities in which emotion decoding is measured. The main aim of the present study is to identify the pattern of age differences in the ability to decode basic emotions from naturalistic visual emotional displays. Method: The sample comprised a total of 208 adults from Greece, aged from 18 to 86 years. Participants were examined using the Emotion Evaluation Test, which is the first part of a broader audiovisual tool, The Awareness of Social Inference Test. The Emotion Evaluation Test was designed to examine a person's ability to identify six emotions and discriminate these from neutral expressions, as portrayed dynamically by professional actors. Results:The findings indicate that decoding of basic emotions occurs along the broad affective dimension of uncertainty, and a basic step in emotion decoding involves recognizing whether information presented is emotional or not. Age was found to negatively affect the ability to decode basic negatively valenced emotions as well as pleasant surprise. Happiness decoding is the only ability that was found well-preserved with advancing age. Conclusion: The main conclusion drawn from the study is that the pattern in which emotion decoding from visual cues is affected by normal ageing depends on the rate of uncertainty, which either is related to decoding difficulties or is inherent to a specific emotion.

Feelings ofdifficulty, or subjective estimation oftask difficulty, are on-line metacognitive experiences, which arise as response to the difficulty of the tasks processed by the person. They are related to performance, but little is known about their nature and the factors that influence them. This study aimed to delimit the possible individual differences effects on feelings of difficulty experienced in relation to school mathematics. General and domain-specific cognitive ability, affect, gender and expertise were the individual differences factors studied. The subjects were 299 students of 7th, 8th, & 9th grade and they were tested with mathematical tasks of three levels of difficulty. Upon completion of each task subjects rated its difficulty on a 4-point scale, ranging from J: not difficult at all to 4: very difficult. Testing was repeated one year later. Path analysis showed that feelings of difficulty form a system of their own, which is mainly influenced by performance and cognitive ability rather than affective factors. Only anxiety state had a direct effect on feelings of difficulty. Expertise did not differentiate feelings of difficulty in the Jst testing, but it did so in the second. Gender interacted with both personal and task characteristics, the girls being more atypical in their responses than boys. The educational implications ofthese results are discussed.