Radotina and other tesserate fishes

It is shown that the stratigraphical assignment of Radotina needs considerable revision. Radotina tuberculata Gross is conspecific with Coccosteus primus Barrande and should be known as R. prima (Barrande); this species differs from its contemporary R. tesselata in the same way as extreme forms of R. kosorensis but the question of further synonymy is unsettled. The dermal bones of Radotina are considered to represent a, modified pattern closely related to that of Macropetaliehthyida; to this general grouping may be added the Rhenanida and Stensioellida. It is highly probable that the Radotinida and Acanthothoraci are synonymous.
Consideration of the tesserate condition in arthrodires suggests that this is a secondary condition in the known members. The Psammosteida also show the development of secondary tesseration among the Heterostraci. An hypothesis based on Holmgren's principle of delamination is apparently illustrated by these forms. In certain Rhenanida this delamination goes so far as to produce cartilage bones in the same position, but at a deeper level, as compared with dermal bones in earlier forms.     

Breeding and survival of New Zealand Pigeons Hemiphaga novaeseelandiae

The breeding and survival of New Zealand Pigeons Hemiphaga novaeseelandiae were studied by radiotelemetry at three contrasting native forest sites in the North and South Islands of New Zealand. At each site, mean annual productivity was low (0-0.12 fledglings/adult) in relation to the mean annual rate of adult mortality (0.18-0.53). Losses of eggs and chicks to introduced mammals were the main identified causes of nest failure. Causes of adult mortality included episodic predation by introduced mammals and apparent starvation in spring at one site. At the most intensively-studied site (Pelorus Bridge), where 75 birds were radiotagged over 7 years, there was a marked annual variation in breeding success (0-0.3 fledglings/adult), including one season (1986–1987) when no breeding activity was detected at all. New Zealand Pigeons were legally hunted in the past, but our results indicate that harvesting is unlikely to be sustainable under current ecological conditions.     

Ecosystem responses to water and nitrogen amendment in a California grassland

The world's ecosystems are experiencing simultaneous changes in the supply of multiple limiting resources. Two of these, water and nitrogen (N) can strongly limit grassland production and can affect community composition and biogeochemical cycles in different ways. Grassland ecosystems in California may be particularly vulnerable to current and predicted changes in precipitation and N deposition, and ecosystem responses to potential interactive effects of water and N are not well understood. Here, we show strong colimitation of plant production resulting from factorial addition of water and N. In addition, water and N addition in combination led to increased dominance of the two most abundant grass species, while N addition regardless of water availability led to decreased species diversity. Late season carbon (C) flux response to water addition depended on N. Only plots that received additional water, but not N, still showed net ecosystem C uptake at the end of the experiment. Our results suggest that grassland ecosystem response to N deposition will be strongly dependent on future precipitation patterns.