Overgrowth competition in encrusting bryozoan assemblages of the intertidal and infralittoral zones of Alaska

Almost 2000 cheilostomatid–cheilostomatid (bryozoan) interactions were recorded from 110 rocks from intertidal and infralittoral zone locations at Kodiac Island in the Alaskan Boreal–Arctic. Intraspecific interactions were unusually rare; this may have resulted from inhibition of con-specific settlement by adult colonies. In one species, rank did vary as a function of depth. The proportion of determinate-species encounter-pairings (a pairing in which one competitor/species wins all encounters) and tied outcomes (whereby neither competitor/species wins or loses but are involved in a “standoff” or mutual overgrowth) increased from the upper midlittoral to the lower infralittoral. The assemblage of bryozoans formed a clear hierarchy, with a score of 0.83 on Tanaka and Nandakumar's transitivity index. Overgrowth dominants did not monopolise the assemblage. The most abundant species were mid- or lower-ranked competitors. The identity of the competitive species had a major influence on the outcome of encounters. Zooidal height and colony growth morphology were important factors determining overall overgrowth rank. The greatest number of interaction types was recorded on medium-sized (surface area >300 and <600 cm²) rocks, and the overall diversity of intertidal species was very high compared with studies conducted elsewhere. The high interaction and species diversity recorded may both have resulted from intermediate levels of disturbance. Received: 16 July 1998 / Accepted: 14 December 1999     

A Systemic Approach to Scoping of Factors Influencing More Sustainable Land Use in Herefordshire

Abstract

Defining and putting into practice sustainable land use is a complex, systemic problem. Systems models and techniques were used in a study of Herefordshire to clarify the situation and identify the potential for a more locally focused, learning-based approach to land use. Issues included: (i) uncertainty about the boundary of a ‘system of sustainable Herefordshire land use’; (ii) the complexity of economic flows in the county and the absence of some critical data; (iii) the importance of the Herefordshire landscape to tourism and the role of agriculture as a determinant of the state of that landscape; (iv) weakness of the institutional linkage between tourism and agriculture; (v) the current lack of inclusion of many relevant stakeholders in concerted action. Factors favouring a learning approach included a strong local identity, local food-related developments, and educational initiatives. Barriers to such an approach included questions of power and landholding, government policies, and attitudes and skills within organizations. These findings are considered in relation to the wider debate over approaches to sustainability.     

A review: long-term effects of agricultural systems on soil biochemical and microbial parameters

This paper provides a review of recent developments on assessing the effect of agricultural systems on long-term productivity of soils. Cultivation of soils, besides affecting soil chemistry and structure, reduces biological activity due to the reduction of macroaggregates which provides an important microhabitat for microbial activity. Indirect evidence suggests that soil amendments such as animal and green manures, and plant diversity (crop rotations) may be more important in maintaining soil microbial activity/diversity than conservation tillage in monocultural systems. There is increasing evidence that crop rotation promotes crop productivity by suppressing deleterious microorganisms that flourish under monoculture. Additions of inorganic fertilizers can increase soil biological activity because of an increased plant biomass production which upon incorporation stimulates soil biological activity. Conversely, limited evidence suggests that repeated applications of inorganic fertilizer nutrients can suppress production of certain soil enzymes that are involved in cycling of a given nutrient. The observed transitory decrease in crop productivity during conversion from chemical intensive input to alternative systems (greater reliance on biological resources) may be due to the initial diminished biological potentials of conventionally managed soils to efficiently cycle and mineralize organic nutrient sources. This review reaffirms the continuing need for the maintenance of existing long-term experimental sites and establishment of new studies in major agroecosystems throughout the world.     

Prenatal diagnosis of spina bifida aperta after first-trimester valproate exposure

In the context of a prospective study on the adverse effects of anti-epileptic drugs on fetal outcome, we evaluated our experience with prenatal diagnosis by ultrasonography and α- fetoprotein (AFP) determination in amniotic fluid. We compared these results with AFP values in maternal serum obtained prior to amniocentesis. From November 1985 to July 1990, amniocentesis at 16–18 weeks of gestation was performed in 267 pregnancies of 237 different women using anti-epileptic drugs. Among 92 pregnancies with maternal valproic acid use, five (including one concordantly affected monozygotic twin-pair) were terminated because of a spina bifida aperta, all prenatally diagnosed by AFP determination and acetylcholinesterase electrophoresis in amniotic fluid. The maternal serum AFP level was raised (⩾ 2.5 multiples of the median (MOM) for singleton pregnancies and ⩾ 4.5 MOM for twin pregnancies) in only two of these five affected pregnancies. We emphasize that maternal serum AFP levels may be unreliable for prenatal screening for fetal neural tube defects in women taking valproate and recommend that amniocentesis and fetal ultrasound examination should be offered directly.