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Lizards are important in the biocoenoses of a wide range of habitat types and are politically accepted target species for environmental impact assessments. They play an important part in food chains and are involved in the dynamics of microhabitats (Martens et al. in press). In some states of Germany, the sand lizard became endangered (Heusinger et al. 1992). A decline of the sand lizard, which results mainly from anthropogenic habitat alterations (Blab & Novak 1989), is also reported from England (Corbett 1988), Sweden (Andren et al. 1988), and other countries (Honegger 1981). Despite a large number of descriptive studies on habitat requirements, quantitative habitat models are lacking. This study analyses the significance of habitat quality and heterogeneity for the survival of sand lizards in fragmented landscapes and presents a habitat model to link local demographic data to the landscape level for environmental planning purposes.

The influence of a modified endogenous prostanoid synthesis on circadian rhythmicity at different functional levels (prostanoid formation, behavioural parameters, circulatory indices, hematological parameters, energy metabolism) was investigated. The daily rhythmic changes observed for all parameters were partly modified by the variation of dietary linoleate intake.

Circadian rhythms of eicosanoid formation were investigated in linoleic acid (LA) rich (sunflower seed oil, 13.3 cal% LA) and LA deficient (hydrogenated palm kernel fat, 0.5 cal% LA) diet fed male Wistar rats adapted to an artifical lighting regimen of 12 hours light and 12 hours darkness. Over a period of 24 hours we examined at 4 hour intervals eicosanoid formation in the aorta (PGI 2 , PGE, PGF 2α , in the heart (6-keto-PGF 2α , PGE, PGF 2α TXB 2 ), in the kidney (PGE, PGF 2α ) and in the brain (PGE, PGF 2α ). Two types of circadian variation curves were observed: 1. 1. Low eicosanoid formation in the light period and increase in the dark cycle (PGE in aorta and heart, TXB 2 in heart). The increase in eicosanoid formation in the dark cycle was diminished after an LA deficient diet. 2. 2. Continuous decrease (PGI 2 in aorta) and increase (PGE in the brain), respectively, in the course of the day, without differences between the two dietary groups. We assume that the circadian oscillations of eicosenoid formation might be of importance for the development of the circadian time structure of the organism.