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Summary 0[ The present study investigated breeding success and causes of breeding failure of curlew\ a species for which the UK holds internationally important breeding numbers[ Studies were undertaken between 0882 and 0884 in two areas of Northern Ireland\ where the species| breeding range has recently contracted and breeding numbers are declining[ Avian nest predators were abundant in both areas\ whereas foxes were abundant on the Antrim study area but generally were absent from the Lough Erne study area\ which was mainly islands[ 1[ Productivity was estimated to be 9=03Ð9=15~edglings per pair in Antrim and 9=19Ð 9=36~edglings per pair on Lough Erne[ These _gures are lower than most estimates of productivity from other studies of breeding curlew[ The di}erences between the recorded productivity levels and those estimated to be required to maintain a stable population are su.cient to account for the observed decline in Northern Ireland|s breeding curlew population[ 2[ Predation was the main proximate cause of breeding failure\ with nest predation being of most importance in reducing productivity[ Only 2=5Ð08=9) of all nests hatched on each study area in each year\ with nest predation accounting for 74Ð86) of failures[ Survival of chicks from hatching to 20 days of age was 27=4) in Antrim and 08=0Ð18=1) on Lough Erne[ Predation accounted for 63) of chick mortality[ 3[ Nest failure rates were not related to the vegetation height around nests nor to clutch laying date on either study area[ They di}ered among the islands and one shoreside site on Lough Erne[ Almost all nest predation on Lough Erne was attribu! table to avian predators\ but in Antrim foxes probably accounted for most nest predation[ The likelihood of predation on chicks was not related to their hatching date\ hatching weight or body condition[ 4[ The results from this study suggest that predation rates on curlew nests in Northern Ireland may have increased in recent decades[ Levels of predator control in Northern Ireland have declined but there have also been considerable changes in land!use that could bene_t generalist predator species or increase the vulnerability of curlew nests to predation[ It is recommended that large!scale trials of legalized predator control and land!use manipulation should be undertaken to identify appropriate conservation management methods[ Key!words] breeding waders\ nesting success\ population decline\ predation[ Journal of Applied Ecology "0888# 25\ 48Ð63

This is a study of the molecular mechanisms employed by Tetrahymena pyriformis to change the lipid composition and thereby the fluidity of its various membranes during temperature acclimation. By quantitatively measuring the intramembrane particle aggregation using freeze-fracture electron microscopy, membrane physical properties in 39.5 degrees C grown cells shifted to 15 degrees C were found to be correlated with the degree of phospholipid fatty acid desaturation. Alteration of the phospholipid polar head group distribution from that of 39.5 degrees C-grown cells to the significantly different pattern of 15 degrees C grown cells appeared not to be of critical importance in the acclimation process. Changes in fatty acid desaturation during acclimation from high to low temperatures and vice versa were analyzed using normal cells and cells fed large amounts of polyunsaturated fatty acids. Fatty acid desaturase activity corresponded to the degree of membrane fluidity but not to the cell temperature. All evidence was compatible with the hypothesis that membrane fluidity is self-regulating, with the action of fatty acid desaturases being modulated by the physical state of their membrane environment.

We have developed a rapid procedure for isolating a fraction enriched in plasma membrane from DunalielIa salUna using an aqueous two-phase system (dextran/polyethylene glycol, 6.7%/ 6.7%). An enriched plasma membrane fraction, free of chloroplast and mitochondrial contamination, could be obtained in 2.5 hours. Plasma membrane proteins, which accounted for approximately 1% of the total membrane protein, contained a number of unique proteins compared with the other cell fractions, as shown by gel electrophoresis. The lipids of the plasma membrane fraction from 1.7 molar NaCI-grown cells were extracted and characterized. Phosphafidylethanolamine and phosphatidylcholine were the two most prevalent phospholipids, at 20.6% and 6.0% of the total lipid, respectively. In addition, inositol phospholipids were a significant component of the D. salina plasma membrane fraction.Phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate accounted for 5.2% and 1.5% of the plasma membrane phospholipid, respectively. Diacylglyceryltrimethylhomoserine accounted for 7.9% of the plasma membrane total lipid. Free sterols were the major component of the plasma membrane fraction, at 55% of the total lipid, and consisted of ergosterol and 7-dehydroporiferasterol. Sterol peroxides were not present in the plasma membrane fraction. The lipid composition of enriched plasma membrane fractions from cells grown at 0.85 molar NaCI and 3.4 molar NaCI were compared with those grown at 1.7 molar NaCI. The concentration of diacylglyceryltrimethylhomoserine and the degree of plasma membrane fatty acid saturation increased in 3.4 molar plasma membranes. The relative concentration of sterols in the plasma membrane fraction was similar in all three NaCI concentrations tested.

The metabolic regulation of membrane lipid composition has been examined using the cell wall-less, unicellular green alga Dunwaiela salina (UTEX 1644) as a model system. Low temperature stress was employed to initiate and study the We have undertaken a comprehensive study of membrane metabolism and physical properties in the eukaryotic plant cell, using the unicellular green alga Dunaliella salina as a model system. This alga has many unique properties which make it a useful experimental system. For example, it grows rapidly under axenic conditions to yield a population of very homogeneous cells. Being naturally wall-less, Dunaliella is easily disrupted, facilitating cell fractionation. The lipid composition of Dunaliella is typical of green algae and similar to that of higher plants. It is able to tolerate a wide range of temperatures and salinities (6), making it useful for investigating the role of the membrane in response to environmental stresses.A certain amount of information concerning the lipids of Dunaliella is already available (13). In this communication we report additional data of the type needed for a detailed analysis of intracellular membrane lipid dynamics. We have employed a shift in growth temperature as a means of altering membrane properties and lipid metabolism. Although a thorough understanding of the effects of low temperature on plant cells is lacking, it is clear that the cell membranes and their constituent lipids change in response to chilling (14). Studying the rate and the extent of lipid change in chloroplasts and microsomes during low temperature acclimation affords a sensitive tool for identifying the contributions of the two lipid synthesizing organelles to the plant cell's membrane economy.In recent years, much progress has been made in understanding the lipid metabolism, physical properties, and physiological role of biological membranes (25). Experimental evidence, derived mainly from microorganisms and higher animals, strongly suggests that the physiological functioning of a membrane is dependent upon its physical state (fluidity) and that the physical state is itself a function of the membrane lipid composition (24).Progress toward understanding the role of lipids in determinin'g properties of plant membranes has been more difficult for several reasons. The cellular heterogeneity of plant tissues and the pres-