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Includes abstract., Includes bibliographical references (p. 156-171)., Biogeography is defined as the study of life, in a spatial and temporal context, with respect to the analysis and explanation of patterns for a given area. The tendency for species richness and diversity to increases towards the equator, where both peak, is a much debated and tested pattern. Underlying mechanisms thought to cause this pattern are: gradients in temperature, stress, productivity, competition, predation, stability, effective evolutionary time, niche breadth, range size and area of occupancy. Evidence exists that both supports and negates most of these mechanisms. In addition to the richness gradient, a latitudinal gradient in geographical range size exists, whereby species range sizes decrease with latitude, referred to as Rapoport's Rule. This has been linked to species ability to tolerate changes in climate. The latitudinal gradient in species richness is thought to be a by-product of Rapoport's Rule and the "Rescue Effect".

The adoption of the retention system in much of coastal British Columbia, Canada, has brought with it concern over the windfirmness of the retained trees. The present state of knowledge concerning windthrow risk factors is inadequate for the purposes of risk prediction in partial cuts and in structurally complex forests, such as those that exist in Clayoquot Sound. This study examined the relationship between the occurrence of windthrow after partial-cut harvesting and various stand, neighbourhood, and tree attributes. Measurements of 1215 trees were obtained from 234 sample plots in retention system cutblocks in Clayoquot Sound on the west coast of Vancouver Island, and of 1891 trees from 115 plots in the Silviculture Treatments for Ecosystem Management in the Sayward (STEMS) study site near Campbell River. At the Clayoquot site, 16.5% of trees were windthrown, while at the STEMS site, 5.3% of trees were windthrown. Logistic regression models were fit for both areas using tree, neighbourhood, and stand variables to predict the probability of individual trees being windthrown. The best-fit models for the Clayoquot and STEMS datasets correctly predicted windthrow status of 72% and 94% of the sampled trees, respectively. The proportion of damaged trees at the Clayoquot site increased with increasing tree height-diameter ratio, crown density (sparse, moderate, full), and an index of fetch distance equal to distance multiplied by removal level, and decreased with increasing percent live crown and post-harvest density. At the STEMS site, windthrow decreased with increasing tree diameter. It is recommended that forest managers plan to retain at least 20% of original stand density in areas where windthrow is a concern, and focus retention efforts on trees with low height-diameter ratios, sparse crowns, and high percent live crown.

pre-mRNA splicing is a critical feature of eukaryotic gene expression. Many eukaryotes use cis-splicing to remove intronic sequences from pre-mRNAs. In addition to cis-splicing, many organisms use trans-splicing to replace the 5' ends of mRNAs with a non-coding spliced-leader RNA. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that m6A modification of U6 snRNA A43 by the RNA methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of U6 snRNA m6A modification primarily leads to alternative splicing at 5' splice sites. Furthermore, weaker 5' splice site recognition by the unmodified U6 snRNA A43 affects splicing at 3' splice sites. U6 snRNA m6A43 and the splicing factor SNRNP27K function to recognise an overlapping set of 5' splice sites with an adenosine at +4 position. Finally, we show that U6 snRNA m6A43 is required for efficient SL trans-splicing at weak 3' trans-splice sites. We conclude that the U6 snRNA m6A modification is important for accurate and efficient cis- and trans-splicing in C. elegans .