Variation in hypothallus width and the growth of the lichen Rhizocarpon geographicum (L.) DC.

Variations in hypothallus width were studied in relation to radial growth in the lichen Rhizocarpon geographicum (L.) DC. in South Gwynedd, Wales, UK. Variations were present both within and between thalli and in successive three-month growth periods, but there was no significant variation associated with thallus size. In individual thalli, there were increases and reductions in hypothallus width in successive three-month growth periods attributable to hypothallus growth and changes at the margin of the areolae. Total radial growth over 18 months was positively correlated with initial hypothallus width. These results suggest: 1) individual thalli of similar size vary considerably in hypothallus width, 2) fluctuations in the location of the margin of the areolae in successive three month periods is an important factor determining this variability, 3) hypothallus width predicts subsequent radial growth over 18 months, and 4) variation in hypothallus; width is a factor determining between thallus variability in radial growth rates in yellow-green species of Rhizocarpon.

Egg quality and fecundity in rainbow trout: the determining factors and mechanisms of control

This thesis considers the factors involved in the determination of egg quality and fecundity in farmed stocks of rainbow trout ( Salmo gairdneri R) • Measurements of egg quality, ie. percentage survivals of eggs and fry, from the production batches of eggs of seven fish farms, showed mean survivals of 70% to eying but levels of only 35% to 4.5g fry (approx. 130 days post-fertilisation). Under optimum conditions survivals may reach 85% suggesting that husbandry methods exert significant influences on egg quality. Chemical analyses of the protein, fat, vitellogenin, ash, amino acids, free fatty acid and mineral levels of eggs of varying quality and from parents of different strains showed compositional differences even between individuals of the same stock. However, none of these differences were correlated with egg quality. Egg size showed similar variations but, again under hatchery conditions there was no correlation with differences in egg quality. The only factor which has been shown to exert a significant influence on egg quality is the time of stripping after ovulation. At 1 0°C eggs should be removed from gravid females within ten days of ovulation to achieve optimum egg and fry survival. Studies of egg production from approximately 10,000 broodstock revealed that total fecundity and egg size increased and relative fecundity decreased with increasing fish size. In general, most fish appeared to produce a constant volume of eggs. This is consistent with a hypothesis that egg size can only be increased by parallel reductions in fecundity. Feeding broodstock at half-ration (0.35% body weight day- 1 ) did not affect egg quality but reduced total fecundity and egg size and increased relative fecundity when compared with eggs produced by fish on full-ration. Comparisons of regressions of total fecundity against fish weight for three strains using ANOCO revealed that one strain was significantly more fecund than two other strains considered. Trout of the same strain maintained on different farms behaved similarly suggesting there was some reproducibility of strain characteristics.

An international cohort comparison of size effects on job growth

The contribution of different-sized businesses to job creation continues to attract policymakers’ attention; however, it has recently been recognised that conclusions about size were confounded with the effect of age. We probe the role of size, controlling for age, by comparing the cohorts of firms born in 1998 over their first decade of life, using variation across half a dozen northern European countries Austria, Finland, Germany, Norway, Sweden and the UK to pin down size effects. We find that a very small proportion of the smallest firms play a crucial role in accounting for cross-country differences in job growth. A closer analysis reveals that the initial size distribution and survival rates do not seem to explain job growth differences between countries, rather it is a small number of rapidly growing firms that are driving this result.