Fire induced stem death in an African acacia is not caused by canopy scorching

Abstract The death of smaller stems of trees due to fire is widespread in savannas. There are currently two hypotheses as to how tree stems avoid stem death; by (i) growing tall and enabling the terminal buds to escape being scorched; and (ii) growing a larger stem diameter and thus being buffered against the heat of the fire. Laboratory‐based tests of these hypotheses on one savanna tree species, Acacia karroo Haynes, support the contention that the important parameter is stem diameter. In addition, anatomical evidence of heat impacts to xylem suggests that damage to the xylem of a stem may play a mechanistic role in causing stem death.     

Spatial patterns of range contraction in British breeding birds

We use ornithological atlas data to assess evidence for the existence of a number of spatial patterns of range contraction in British breeding birds. For 18 of the 25 species which suffered the greatest range contractions between 1968 and 1991, there wais a greater likelihood of local extinction in areas where the species was initially less widespread, so ranges tended to contract towards their cores. However there was evidence for a number of other patterns, with some species having a greater likelihood of local extinction in the centres of their ranges and others suffering random local extinctions throughout their range. The different spatial patterns identified were largely independent of the overall range contraction suffered by each species nationally. We suggest that range contractions in British birds can generally be explained better by a general decline in habitat quality or other factors than by contagious anthropogenic effects, as might be expected in a country with a long history of human environmental modification.     

Adipokinetic hormone of the true armyworm, Pseudaletia unipuncta: immunohistochemistry, amino acid analysis, quantification and bioassay

Abstract A cluster of five to seven AKH-like immunoreactive cells lie in each lobe of the paired corpora cardiaca of the true armyworm, Pseudaletia unipuncta. These cells form a mesh work of immunoreactive processes within the corpora cardiaca, and immunoreactive tracts projecting posteriorly over the aorta.
Reversed-phase high performance liquid chromatography of extracts of the corpora cardiaca of P.unipuncta revealed a single large U.V. absorbent peak with a retention time identical to synthetic Manduca- AKH. Amino acid analysis of the contents of this peak yielded a composition identical to that of synthetic Manduca-AKH which was analysed in a parallel manner. Furthermore the material within the peak possessed adipokinetic activity when bioassayed in day 2 adult male P. unipuncta. The corpora cardiaca of similar individuals were found to contain approximately 17.6ng (17.6pmol) of Manduca-AKH equivalents per pair.
Injection of Manduca-AKH into 2-day-old adult male P.unipuncta resulted in a dose-dependent elevation in haemolymph lipid levels with a maximum level of 80–90μmg/μl obtained with 5–10 ng of Manduca-AKH. Continuous flight also elevated haemolymph lipid levels in day 4 adult males with a significant elevation evident in the first samples taken after 15 min of flight and lipid levels plateauing at approximately 100 μg/μl by about 60 min of flight.     

Effects of density-dependence and weather on population changes of English passerines using a non-experimental paradigm

The Common Birds Census documents changes in the populations of the more abundant British land birds. Here we analyse the CBC data for various English passerines to discover the separate effects of weather and of density-dependent feedback on their annual population changes. Density dependence is generally apparent in the data from woodland plots, less so in those from farmland. There are clear effects of weather, particularly in farmland. Prolonged snowfall in winter reduces populations of most species; frost and low temperatures appear much less important. Rainfall in March and April increases numbers censused in the spring but this may be an artefact. We discuss ways in which analyses such as these should be taken forward.
We consider whether this work is respectable science, arguing that monitoring through the CBC goes much further than mere surveillance of numbers, that such monitoring is important in wildlife management, and that density dependence is not a bankrupt paradigm. Long-term data gathering is an essential part of ecological science, even in programmes not designed at the outset to test specific hypotheses.     

The colonization of Scottish islands by the common shrew, Sorex araneus (Eulipotyphla: Soricidae)

In this paper we apply molecular methods to study the colonization of islands off the west coast of Scotland by the common shrew ( Sorex araneus L.), and current gene flow. We collected 497 individuals from 13 islands of the Inner Hebrides and Clyde Island groups and six mainland regions. Individuals were genotyped at eight microsatellite loci, and the mitochondrial cytochrome b sequence (1140 base pairs) was obtained for five individuals from each island/mainland region. Based on these molecular data, island colonization apparently proceeded directly from the mainland, except for Islay, for which Jura was the most likely source population. Raasay may also have been colonized by island hopping. Most island populations are genetically very distinct from the mainland populations, suggesting long periods of isolation. Two exceptions to this are the islands of Skye and Seil, which are geographically and genetically close to the mainland, suggesting in each case that there has been long-term gene flow between these islands and the mainland. We consider possible methods of island colonization, including human-mediated movement, swimming, and land and ice bridges.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 797–808.