Studies on the feeding biology of thalassinidean mud-shrimps

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Piddocks (Mollusca: Bivalvia: Pholadidae) increase topographical complexity and species diversity in the intertidal

Bioerosion increases the topographic complexity of soft rock habitats, thereby increasingspecies diversity. This increase in species diversity may either be associated with an increase incomplexity or may simply be a consequence of the increase in available surface area for colonisation.The influence of habitat modification by piddocks on intertidal species richness was investigatedthrough field survey using fractal geometry to assess topographical complexity. The relationshipbetween topographical complexity and species diversity was examined using the species spacingtechnique, which uses fractal dimensions to normalise the species richness data in relation to topographicalcomplexity. Six sites were chosen, comprising either clay or chalk substratum, which had arange of rock hardness. Through their rock-boring activities, piddocks significantly increased thetopographical complexity of the shore. Associated with this increase was an increase in species richnessat all sites. Using species spacing, at 5 of the 6 sites, the increased species richness was found tobe area-independent, with more species being observed than would be expected for a simpleincrease in surface area alone. However, piddocks are also known to significantly increase the erosionof soft rock habitats, many of which are regarded as being of particular conservation importancebecause of their rarity within Europe. Piddocks thus increase intertidal biodiversity while at the sametime significantly contributing to erosion of the substratum

Reproductive features of Celmisia species (Asteraceae) in relation to altitude and geographical range in New Zealand

A range of seed and flower characters was examined in 37 species of the New Zealand genus Celmisia (Asteraceae) to determine whether there were any relationships between reproductive features and the geographic or altitudinal ranges of the species. Using published sources and herbarium material, flower attractiveness to pollinators was measured in terms of capitulum size and ray/disc length ratio. Dispersibility was measured in terms of seed dry weight, seed terminal velocity, pappus/seed length ratio, and scapdeaf length ratio. Altitude (minimum and maximum) and geographic ranges (number of 1" latitude x 1" longitude squares occupied) were obtained from published sources. A multivariate principal components analysis using 12 morphological characters revealed the presence of five groups of species differing in capitulum size, seed weight, pappus length, number of pappus bristles, leaf length and scape length. Linear regressions showed that altitude was significantly and negatively related to seed dry weight and capitulum size, and positively to scapdeaf length ratio. Geographic range is negatively related to capitulum size, and positively to ray/disc ratio and altitudinal range. Amongst the seed features measured, seed weight was the best predictor of terminal velocity (an inverse measure of dispersability), but lighter seeds also had a higher pappudseed length ratio. The frequency distribution of the geographic ranges of the species is highly skewed, with many local species (86% occurring in 15 or fewer one-degree squares) and very few common ones. Two species (C. gracilenta and C. grarninifolia) are notably more common than all the others. A comparison of these species with the others shows that, on average, they have lighter seeds with more bristles, taller scapes and higher ray/disc ratios, but have smaller capitula. The low geographic abundance of the rare species could not readily be attributed to any specific reproductive feature, possibly because of the multiple types of rarity represented within the genus