LOWER DEVONIAN GRAPTOLITES FROM SOUTHEASTERN ALASKA

The youngest zones of Monograptus occur in Devonian black shale and slate along the western shore of Prince of Wales Island and on Noyes Island, southeastern Alaska. The following five species of Monograptus, in close association with vascular plants and marine shelly faunas, indicate a Praguian, (Siegenian to Early Emsian), late Lower Devonian and possibly early Middle Devonian age: M. yukonensis Jackson & Lenz, M. n. sp. aff. yukonensis ? Jaeger & Stein, M. aeqimbilis notoaequakilis Jaeger & Stein, M. pacificus Jaeger n. sp. and M. craigensis Jaeger n. sp. The yukonensis zone containing M. craigensis in its upper part is followed stratigraphically higher by the M. pacificus zone – the youngest occurrence of Monograptus. The new species belong to the M. uncinatus group and, like most Praguian monograptids, have long dorsal tongues on their siculae. M. craigensis and M. pacificus increase to seven the number of species of Monograptus known from the Praguian. On the basis of the Alaskan material, the geographical distribution of M. aequabilis notoaequabilis now includes North America in addition to previously recorded occurrences in Australia, Southeast Asia, and Europe. This broad geographic distribution suggests that the last survivors of Monograptus had worldwide distribution and a rather uniform assemblage of species.     

Seasonal dynamics, movements and the effects of experimentally increased female densities on a population of imaginal Calopteryx aequabilis (Odonata: Calopterygidae)

Abstract. 1. A population of Calopteryx aequabilis Say was sampled daily on a tributary of Canard River, Kings County, Nova Scotia, for the entire flight season in 1983 (29 May to 13 August), using capture–mark–recapture techniques.
2. 2701 sightings of 678 individuals were obtained along a 635 m segment of the stream. A maximum daily count of 174 imagines was reached on 11 June, after which the population gradually declined.
3. More females than males were marked but sexually mature males outnumbered females at the water on all but four days.
4. Immigration rather than local emergence accounted for a large proportion of the population after 20 June.
5. Females were consistently vagile; males were site–specific but occasionally moved long distances between captures.
6. Males and females first marked as tenerals became reproductively mature after about 5 days.
7. We experimentally increased female density on a partially isolated section of the study stream to see how increased female numbers affected the demographics and movement patterns of the population.
8. Residence times for introduced and resident females were similar. In contrast, during a similar introduction of males a year earlier, most introduced males disappeared quickly.
9. Males decreased the distance they travelled daily between captures, their total distance travelled and their range following the introduction, and females showed a tendency (not statistically significant) toward increased movements and dispersal, as predicted.     

Trophic relationships in the soil microfood-web: predicting the responses to a changing global environment

In this article, we evaluate how global environmental change may affect microfood-webs and trophic interactions in the soil, and the implications of this at the ecosystem level. First we outline how bottom-up (resource control) and top-down (predation-control) forces regulate food-web components. Food-web components can respond either positively or negatively to shifts in NPP resulting from global change, thus creating difficulties in developing general principles about the response of soil biota to global change phenomena. We also demonstrate that top-down effects can be important in soil food-webs, creating negative feed-backs which may partially counter bottom-up effects. Secondly, we determine how soil food-webs and the processes they regulate respond to various global change phenomena. Enhanced atmospheric CO₂ levels can have two main effects on plants which are relevant for the soil food-web, i.e. enhanced NPP (often positive) and diminished organic matter quality (with negative effects, at least in the short term). Climate change effects resulting from elevated CO₂ levels may be mainly secondary through alteration of vegetation, as shown by examples. Intensification of land management is usually associated with greater disturbance, which alters soil food-web composition and key processes; this is particularly apparent in comparisons of conventionally tilled and nontilled agroecosystems. Global change involves shifts in plant species composition and diversity, possibly affecting soil food-webs; we interpret this in terms of theories relating biodiversity to ecosystem function. We conclude that a more detailed understanding of interactions between NPP, soil organic matter and components of the soil food-web, as well as their regulation of biogeochemical processes and ultimately ecosystem-level properties, is essential in better understanding long-term aspects of global change phenomena.     

Development of taxon‐specific markers for high‐throughput screening of microbial‐feeding nematodes

In an effort to assess the taxonomic identity of large‐scale samplings of nematodes from the Konza Tallgrass Prairie, we sequenced a portion of the 18S rRNA gene and its associated internally transcribed spacer (ITS1) from 74 nematodes encompassing four taxonomic families. From these sequences, we have developed a series of molecular probes to distinguish 16 distinct microbivorous nematode taxa. Using a combination of low power microscopy and taxon‐specific real‐time probes, the 74 nematodes were correctly assigned to their respective taxonomic groups. This optimized method provides a high‐throughput assay to determine nematode identities across larger data sets.     

Acidification of three moorland pools in The Netherlands by acid precipitation and extreme drought periods over seven decades

SUMMARY. 1. Relations between acidification by atmospheric deposition, water depth and the occurrence of dry summers in this century, as well as their effects on chemistry, macrophytes and diatoms in three moorland pools, are described.
2. Direct observations and biological data indicate a decrease of pH by c. 0.5 unit over a period of seven decades in a pool where 20% of the bottom desiccates in extremely dry years, and 2 pH units over the same period in a pool where 70% of the bottom is exposed to the atmosphere in such years.
3. Acidification promotes the growth of Juncus bulbosus L., Sphagnum and the acidobiontic diatom Eunotia exigua (Bréb.) Rabenh. and suppresses the growth of isoetids (e.g. Lobelia dortmanna L.) and of acidophilus and circumneutral diatoms. Also the acidobiontic Frustulia rhomboides var. saxonica (Rabenh.) Toni and Navicula subtilissima Cleve, characteristic of humic waters, decline by acidification.
4. In two pools where more than half of the bottom desiccated in 1976, observed concentrations of sulphate were highest in 1977–78 and decreased later on. Juncus bulbosus had a maximum in 1977–80. Eunotia exigua became the dominant diatom after 1976 and decreased after 1981 in the pool with the shortest residence time (3 years).
5. In desiccating pools the long-term decrease of pH is apparently much larger than in softwater lakes in Scandinavia and North America. During the last 50 years, pH dropped rapidly after dry summers, probably due to oxidation of sulphur and nitrogen compounds which were originally derived from the atmosphere, reduced and stored in the sediments. Rapid falls in pH were followed by an increase, presumably due to alkalinity production during sulphate reduction and denitrification.