The proportion of resources which an organism devotes to reproduction has been assumed to be of great evolutionary and ecological significance. However, in previous studies of reproductive allocation (RA) in plants, there has been no consensus of precisely what is being measured nor how it should be measured. An attempt was made to determine the 'best' method of measuring RA and then apply this to a range of species with differing ecological strategies. Under nutrient stress caused by a low N treatment Taraxacum officinale and Poa annua were found to maintain their RA despite up to 4 fold reductions in biomass. Under K and P deficient conditions there was a preferential allocation of these elements to reproductive structures in Taraxacum. Ruderal plants therefore, seem to maintain biomass RA and seed quality despite nutrient stress. Although the nutrient RA in Taraxacum was found to be significantly different from biomass RA (KRA = 71% PRA = 66% BRA= 51.7%) the extent of the difference varied between treatments. There was therefore no obvious alternative currency to biomass. The evolutionary consequences of reproduction may also be measured through a reproductive cost which may take the form of reduced future reproduction, survival or growth. Prevention of flowering in Digitalis purpurea resulted in an increase in the number of axillary buds produced, Similarly in Plantago lanceolata removal of flowers resulted in a 3 fold increase in production of buds. In both species realisation of a reproductive cost was prevented. The importance of individual variability was noted. The importance of plant morphology was evident and was used to explain some of the anomalous RA values in the comparative experiment. RA values were collected for 40 species of Gramineae. RA was a useful ecological index which emphasised the ruderal element of a plant's strategy. When used in conjunction with other parameters particularly Rmax, RA produced a meaningful classification of species in terms of their ecological strategy.

No description available.

Mature oaks covering the full range of the indigenous Quercus species, from the oak woods of Dartmoor and its periphery, were sampled each month during the growing season for the presence of cynipid oak galls. The distributions of galls within sites, within trees and within leaves were recorded, and an investigation into the factors which affect them was made. The distributions of galls on oaks were found to be influenced by climatic and topographical factors as well as by the behaviour of the wasps and the taxonomic status of the host oak. Oaks in exposed situations tended to host more species of gall causing wasps, in higher numbers than oaks in sheltered situations within the woodland canopies. In addition; Q.robur hosts harboured more gall species and larger numbers of an individual species than Q.petraea hosts. Oaks of introgressed hybrid status (Q.x rosacea) had gall populations ranging from levels less than were found for Q.petraea to levels higher than occurred on Q.robur. Partitioning of gall species occurred both vertically and horizontally within the canopy, and within individual leaves. Work on the ecologies of the gall causing wasps indicate that the adults may be able to distinguish between the indigenous oak taxa, when selecting suitable oviposition sites. Some gall species are solely restricted to Q.robur, a situation probably determined by some unidentified physiological property of Q.robur favourable to cynipid gall induction. An investigation into the life cycle of Andricus quercuscalicis Burgsdorff, and its effects on the natural regeneration potential of oaks was also undertaken. Up to 100% of acorns on oaks infested by A.quercuscalicis may be galled, which has serious consequences on the subsequent germination potential of the acorns. Only one or two trees in a wood are infested by A.quercuscalicis in any year, and as long as this pattern exists it is not thought likely to pose a serious threat to the natural regeneration of oaks.

Ecological and productivity responses to agricultural management were studied over eight years in species-rich hay meadows within a Site of Special Scientific Interest on a Somerset peat moor. The vegetation typified that of many wet meadows on the Somerset Levels and elsewhere, definable as MG5 {Cynosurus cristatus-Centaurea nigra meadow) and MG8 {Cynosurus cristatus-Caittia palustris flood pasture) within the National Vegetation Classification. The effects of inorganic fertilizers on species diversity, soil nitrogen loss and agricultural productivity (hay yield and beef production during aftermath grazing), were investigated during 1986-90. These data were subsequently analyzed for the effects of variations in water table depth on productivity and soil N losses. Further studies in 1991-93 covered: (a) soil seed bank composition in relation to above ground vegetation; (b) the effect of different cutting dates on seed rain, vegetation composition and herbage yield and quality; and (c) seed shedding as influenced by hay making operations. The vegetation was sensitive to even small fertilizer inputs, particularly of P and K, both in terms of increased productivity and reduced botanical diversity. Species diversity also declined on unfertilized plots in one experiment, after a change from aftermath grazing to cutting only. Leaching and denitrification of soil N following N application were both high compared with soils elsewhere, due to the high water table. Fertilizers caused a four-fold shift in soil seed bank composition towards nitrophilous species and increased the ratio of short-term to long-term persistent species. Cutting in May or September affected both the total seed rain and the balance of species represented and significantly reduced vegetation diversity, compared with cutting in July or August. The thesis includes an extensive literature review and the results are discussed in the context of (a) current theories on the relationships between species diversity, soil fertility, disturbance and productivity, and (b) hay meadow management within Environmentally Sensitive Areas. It is concluded that production response to fertilizers is not constrained by the species richness of the vegetation, but there is no scope for increasing soil fertility without reducing species diversity. Nitrate leaching risk is increased with N rates above about 75 kg ha'^ year'^ at ambient water table levels, but no N should be applied where high water tables are maintained. Occasional cutting after July is necessary to allow most species to set seed and to maintain a persistent soil seed bank.

Hepatic microsporidia were investigated from 5 species of fish, namely Taurulus bubalis (Euphr.), Crenilabrus melops, (L.), Gaidropsarus mediterraneus (L.), Ciliata mustela (L.). and Scophthalmus maximus (L.) and intramuscular microsporidia from 2 species, namely Taurulus bubalis and Cottus gobio L. Detailed ultrastructural studies carried out on hepatic microsporidia from T. bubalis showed it to be a new species belonging to the genus Microgemma (Ralphs) and it is named here as Microgemma dunkerli sp. n. Although hepatic microsporidia from the other species of fish are included in Microgemma, insufficient data was available to determine whether these were synonomous with M. dunkerli or a separate species. Intramuscular microsporidia were identified as Pleistohora sp. and Pleistophora vermiformis (Leger) from T. bubalis and C. gobio respectively. Unsuccessful attempts were made to experimentally transmit spores by per os and intraperitoneal injection using a variety of experimental hosts. Viability studies indicated that spores survive for at least one month under controlled conditions. A detailed study of host/parasite relations was carried out at Portwrinkle and comparisons made with populations from Roscoff, Wembury, Widemouth and Aberystwyth. Prevalence and intensity of hepatic microsporidiosis in T. bubalis decreased markedly northwards probably due to temperature. Overall infection levels were at their highest in late summer and autumn, 'O' group fish being the most severely affected. The main ecological events of the life cycle of Microgemma dunkerli are presented in the form of a flow diagram. It is hoped that this work will form the basis for an epidemiological model.

The respiratory development of two species of teleost, Oncorhynchus mykiss and Scophthalmus maximus was investigated to identify any possible periods of reduced respiratory fitness during early development. The two species were selected because of their different development strategies to allow any common factors in respiratory development to be identified. The study included determination of the respiratory oxygen demand and the critical oxygen tension (Pc) through early development for both species. Respiratory oxygen demand was measured as a routine rate (rVO2) with individual and weight specific values being determined. The main respiratory surface areas for both species were measured, this included the gills; body area; fin area and yolk-sac area in the case of O. mykiss. Changes in the rate of development was monitored by determining the mass and length specific development relationships. Significant changes in body fin and yolk-sac area occurred at approximately 70mg yolkless wet weight. for O. mykiss, gill area development was found to change at approximately 110mg. Similar changes in rate of fin and body area occurred for S. maximus at approximately 3.5mg wet weight, while gill development changed at 6.8mg. The change in epidermal thickness was measured during the development of S. maximus larvae and fry. During the larval development fin and body epithelium were significantly different up to 4.6mg wet weight with fin area being significantly thinner. Epidermal thickness increased from 2µm to 23µm over the 35 day period of monitoring. The degree of vascularisation of the yolk-sac of O. mykiss larvae was measured and found to remain relatively constant at approximately 41%. up to 70mg wet weight before declining. Mean minimum diffusion distances increased from approximately 13. 5µm to 35µm over the life-span of the yolk-sac. The change in erythrocyte type was also monitored during this period and found to decline in a similar manner to yolk-sac area. O. mykiss larvae reared under hypoxic conditions showed reductions in growth towards the end of the period of endogenous feeding, as well as increased development of gill area and increased levels of vascularisation (up to 10%) of the yolk-sac. compared to normoxic reared larvae. A study of the effects of removal of the respiratory pigment at different stages of development was also undertaken. This allowed the significance of haemoglobin during development of both species of fish to be estimated. Respiratory fitness was inhibited in both species with reductions of up to 2mg02/l in the Pc for O. mykiss, and 2. 5mg02/l for S. maximus. However, S. maximus showed a high level of dependence on haemoglobin for gaseous exchange during a short phase of development from 9.5 to 15mg wet weight were removal of haemoglobin caused 100% mortality in treated fish. Overall the study showed the low level of respiratory flexibility of S. maximus when compared to O. mykiss, especially during early development. This must have significant importance for the intensive mass culture of the larvae of this species. The important role cutaneous respiration plays during the early development of both species was also highlighted.

This study of a population of C.virgo at Burrator, Dartmoor looks for signs of a population regulation mechanism acting through the effects of larval density on larval growth. The consequences of adult body size and emergence time for survival and reproductive success are also examined to look for further regulation mechanisms, and opportunities for natural and sexual selection; in particular the importance of body size to territorial males. Although there were significant differences in patterns of growth and body size within and between year classes of larvae, the differences were were not related to density. Smaller, later developing larvae were present, and the possibility that this was related to late hatching is discussed. Smaller, later developing larvae emerged later as smaller sized adults. Survival to maturity was not influenced by body size. Density-triggered bird predation was a regular feature of the population, and could result in early emergers experiencing higher survival to maturity. The advantage of early emergence could, however, easily be countered by adverse weather patterns. A field experiment showed that ovipositing females were highly aggregated, and that mature males were able to predict and profit from the aggregated distribution of females. Consequently male daily reproductive success was very variable, and was by far the most important component of their lifetime reproductive success. A large body size was an advantage to mature males when levels of competition were high, but not when competition was reduced as a result of bird predation and poor weather. Mature females produced between 85 and 1,615 eggs in their lifetime. The number of sunny days females survived to see was the most important component of their lifetime reproductive success, and was influenced by random predation and weather patterns. Body size was not related to either survival or clutch size. Early emerging females had higher lifetime reproductive success, but only as a result of the timing of the density-triggered bird predation, and this advantage could easily be lost through random weather patterns. The lack of evidence for density dependent feeding competition in larvae, and for a relationship between female body size and fecundity in adults, suggests that feeding competition is not a regulatory mechanism in this population. The difficulties of detecting density dependence in short term studies is discussed. The strong influence of environmental variables on the importance of adult body size and emergence time indicates that the opportunity for selection of these characteristics would be variable and hence weak in the short term. Over the long term, however, there would be a persistent selective pressure, and the possible consequences for larval growth are discussed.

No description available.

No description available.

No description available.