Effects of a trawling moratorium on the breeding success of the Yellow-legged Gull Larus cachinnans

The establishment of a two month commercial fishing moratorium, which overlapped each year with different stages of the breeding cycle of the Yellow-legged Gull Larus cachinnans at the Ebro Delta, Spain, provided the opportunity of testing the effects of food limitation on the breeding success of this species. The study was carried out in 1993, when the chick rearing stage occurred with normal commercial fishing activity and in 1994, when the chick rearing stage overlapped with the trawling moratorium. We recorded diet of the chicks, breeding phenology, clutch size, egg volume, hatching success and productivity of adult birds. There was a highly significant difference in the diet of the chicks between the two years and significantly lower productivity in 1994, whilst the other parameters examined did not change. These results show that a dependence on discards from commercial fishing activities may be a limiting factor in the breeding success of this seabird.     

Habitat fragmentation and population extinction of birds

It has not been established that a major cause of extinction in birds or any other taxa is failure of metapopulation dynamics: the collapse of a network of ephemeral but discrete populations as movement between them becomes increasingly infrequent. The few data on who goes where and who mates with whom suggest that most species are structured as either a single large population or a small set of source populations and a larger set of sinks. The extinction of the latter is irrelevant to the persistence of the species. However, regional decline of a species in the face of habitat destruction and fragmentation can mimic a failure of metapopulation dynamics, because distinct aggregations of individuals will disappear much as they would if populations in an interacting network were eliminated one by one. Any species with highly restricted range is at great risk of extinction from spatially localized forces, such as cyclones or deforestation. Restricted range rather than inherent weakness is the main reason that so many island species have gone extinct or are endangered. Species with small populations in contact with much larger heterospecific ones with which they are interfertile are threatened with extinction by hybridization. Finally, the disappearance of a species from a site may be due to subtle habitat change, even if this observation seems superficially consistent with some general population theory, such as the dynamic equilibrium theory of island biogeography. Current theory is an inadequate substitute for intensive field studies as a means to address the conservation problems of individual species.     

Uptake of DOM by Nemertean Worms: Association of Worms with Arthrodial Membranes

SYNOPSIS. Carcinonemertes errans is a nemertean worm, the juvenilesof which are found as epibionts on the Dungeness crab, Cancermagister, in close association with the arthrodial membranesof the crabs. The juvenile nemerteans appear to have no meansof taking in particulate food but survive for many months onthe surface of the host. We show that the juvenile C. erransare capable of removing amino acids from dilute solution insea water, that the water near the arthrodial membranes wherethe worms are found contains high concentrations of primaryamines, and that there is a low resistance pathway for low molecularweight amino acids across the arthrodial membrane examined invitro.     

Topography and tectonics of the Taconic outer trench slope as revealed through gradient analysis of fossil assemblages

Similarities in stratigraphic sequence, syndepositional topography and tectonics, and regional tectonic setting between the Mohawk Valley, New York, in the Middle Ordovician and the Australian flank of the Timor Trough today support the idea that the Taconic Foreland Basin orginated in an arc-continent collision. The Trenton Group strata studied - a roughly four million year long sequence correlated by bentonite beds along an 83 km downslope transect in the central Mohawk Valley - represent the continental shelf and outer trench slope. Bank limestones pass upward and downslope into deep water black shales in a manner reminiscent of the lateral and vertical sedimentary sequence on the Sahul Shelf and Australian flank of the Timor Trough. In studying topography, relative depth was measured through reciprocal averaging ordination of benthic macroinvertebrate fossil assemblages. Downslope bathymetric profiles show the development of a horst and graben topography coincident with regional tilting and transgression - a pattern associated with downward flexure of the Australian Plate approaching Timor. The net rate of transgression corresponds to an arc-continent convergence rate on the order of 2 cm per year.     

Requirement of Ethylene for Growth of Callus and Somatic Embryogenesis in Medicago sativa L.

The role of ethylene in the growth of callus and somatic embryogenesisin Medicago sativa was examined. The application of 2,5-norbornadiene,a competitive inhibitor of ethylene action, during a 10 d inductionperiod to medium containing 2,4-D and kinetin inhibited thegrowth of callus but did not affect somatic embryogenesis, nordid it affect ethylene production during the induction stage.The exposure of tissue, incubated on differentiation medium,without hormones, to an atmosphere of 2,5-norbornadiene, inhibitedboth growth and embryo maturation and stimulated pigmentation.The inhibition of embryo maturation was observed even in thepresence of norbornadiene at a concentration which did not affectgrowth of tissue. It is suggested that the action of endogenous ethylene is necessaryfor the growth of the callus and embryo maturation. Key words: Medicago sativa, ethylene, callus growth, somatic embryogenesis     

Grasshopper feeding rates, preferences, and growth on safflower

Laboratory experiments were conducted to measure the feeding rates, preferences, survival rates, maturation times, and weight gain of four common species of grasshoppers (Orthoptera: Acrididae) on four lines of safflower (Carthamus tinctorius). When safflower lines were presented individually, all were readily consumed although consumption differed significantly according to grasshopper species, age and sex, and to safflower line. Consumption was greatest on a safflower line devoid of spines. However, grasshoppers also fed readily on spiny lines, and results of experiments in which all safflower lines were presented together indicated preferences that did not necessarily correspond to the results of the single-line feeding trials. Camnula pellucida, a graminivorous species, did feed on safflower, but restricted feeding almost exclusively to stem cambium, whereas Melanoplus bivittatus, M. packardii and M. sanguinipes fed mainly on the heads, flowers and leaves. Highly significant differences in grasshopper maturation time and weight gain were apparent among grasshopper species, and among safflower lines. Seedtec-5, the line which was least digestible, least consumed and least preferred nevertheless yielded rapid development and the greatest body weights of grasshoppers. All species of Melanoplus developed more quickly and gained more weight on safflower than on wheat. One species, M. packardii, was more able to utilise safflower than its congeners, and may gain competitive advantage if safflower becomes widely grown.     

Peroxidases in Relation to Removal of Dormancy and Germination of Apple Embryos

The changes in germination, peroxidase activity and isoperoxidase spectrum have been studied in apple embryos at 5°C (stratification) and at 20°C in the presence or absence of seed coats. The embryo dormancy is progressively released at 5°C, but not at 20°C. The peroxidase activity in embryos covered with seed coats is very low at 5°C as well as at 20°C which corresponds to a restricted number of isoenzymes. In isolated embryos the peroxidase activity increases significantly. This is due to an increase in both the number and the activity of the isoperoxidases and it is more pronounced at 20°C than at 5°C. The obtained results suggest that the soluble peroxidases are not involved in the process of the release of embryo dormancy. The variations observed are attributed to the growth process following germination, which can occur even at low temperature.     

THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS

Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg^–1 shell), nitrogen (µg,N mg^–1 shell) andCaCO_s (%CaCO₃ of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo₃), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl^–1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO₃ and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO₃is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions ¹ Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A. ² Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978;