Spectral Transmission and the Aerial Profile in Mature Stands of Mercurialis perennis L.

The passage of light through mature stands of the woodland perennialherb Mercurialis perennis L. is investigated. Less than 3 percent of each of seven discrete wavelengths in the visible wavebandreach the herb layer in the sites considered. Percentage transmissionof the 750 nm wavelength was far greater, and the proportionof this light passing deep into the herb profile increased astotal light transmission decreased. Mean specific leaf area of M. perennis is negatively correlatedwith shoot height and weight. Leaf area/shoot increases exponentiallywith shoot height, but linearly with shoot weight. Shoot leafweight ratio remains virtually constant over a range of shootsizes, but shoot leaf area ratio is negatively correlated withshoot height and shoot weight. Most leaf pairs are borne between10–30 cm above ground level and 71 per cent of the totalleaf area occurs between 15–30 cm above ground. Averageleaf area/leaf pair increases from the lowest layers in theprofile upwards except for the highest strata where many leavesare not fully expanded. Chlorophyll content of leaves, expressedon either a weight or an area basis, increases from the bottomto the top of the herb profile; the ratio of chlorophyll a:bdoes not alter through the stand.     

Genetic differentiation amongst fragrant orchids (Gymnadenia conopsea s.l.) in the British Isles

Genetic variation was examined in five microsatellite loci to seek evidence of genetic differentiation and restricted gene flow that would support the taxonomic division of Gymnadenia into three species ( G. borealis , G. conopsea , and G. densiflora ). A total of 107 alleles was detected in 17 populations from England, Scotland, and Ireland. The mean expected heterozygosities ranged from 0.48 to 0.81. The differentiation in allele frequencies amongst populations that had been assigned to each taxon on the basis of morphology was sufficiently large to support the taxa as distinct species. Phylogenetic trees based on microsatellite allele frequencies, as well as assignment tests, supported the existence of three distinct groups with at least partial restriction of gene flow between them. There was substantial homozygote excess, leading to high F _IS estimates, for most loci in most populations. This is unlikely to have been a result of widespread null alleles, and more probably reflects a high level of inbreeding in G. conopsea . This inference requires further investigation. The implications of the results of this and other taxonomic studies for the conservation of Gymnadenia in Britain are discussed.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 349–360.     

Advances in laying date and increasing population size suggest positive responses to climate change in Common Eiders Somateria mollissima in Iceland

Models of climate change predict that its effects on animal populations will not always be negative, but most studies indicate negative associations between changes in climate and the phenology of animal migration and reproduction. For some populations, however, climate change may render particular environments more favourable, with positive effects on population growth. We used a 30-year population dataset on over 2000 Common Eiders Somateria mollissima at a colony in southwest Iceland to examine the response of this species to climate fluctuations. Eiders are strongly dependent on suitable climatic conditions for successful reproduction and survival. Temperatures in southwest Iceland, in both winter and summer, have generally increased over the past 30 years but have shown considerable fluctuation. We show that females laid earlier following mild winters and that year-to-year variation in the number of nests was related to the temperature during the breeding season 2 years previously. Milder summers could have positive effects on breeding success and offspring survival, producing an increase in nest numbers 2 years later when most Eiders recruit into the breeding population. In this part of their range, Eiders could benefit from a general warming of the climate.