ß-diversity decreases with increasing trophic rank in plant - arthropod food chains on lake islands.

Contrasting trophic theories of island biogeography try to link spatial patterns in species distribution and richness with dietary preferences, arguing that the spatial turnover of species among habitat patches changes with trophic rank causing a systematic change in the proportion of plants, herbivores, and predators across habitats of different size. Here we test these predictions using quantitative surveys of plants, spiders, and herbivores as well as of omnivorous and predatory ground beetles on undisturbed Polish lake islands. We found decreased proportions of predators and habitat generalists on larger islands. Environmental niches and niche overlap were highest in predators. Variability in environmental niche width among species increased at higher trophic levels. Our results confirm models that predict a decrease in spatial species turnover (ß-diversity) with increasing trophic level. We speculate that the major trigger for these differences is a reduced dispersal ability in plants at basal trophic ranks when compared to higher trophic levels.

Do David and Goliath Play the Same Game? Explanation of the Abundance of Rare and Frequent Invasive Alien Plants in Urban Woodlands in Warsaw, Poland.

Invasive Alien Plants occur in numbers differing by orders of magnitude at subsequent invasion stages. Effective sampling and quantifying niches of rare invasive plants are quite problematic. The aim of this paper is an estimation of the influence of invasive plants frequency on the explanation of their local abundance. We attempted to achieve it through: (1) assessment of occurrence of self-regenerating invasive plants in urban woodlands, (2) comparison of Random Forest modelling results for frequent and rare species. We hypothesized that the abundance of frequent species would be explained better than that of rare ones and that both rare and frequent species share a common hierarchy of the most important determinants. We found 15 taxa in almost two thirds of 1040 plots with a total number of 1068 occurrences. There were recorded 6 taxa of high frequency-Prunus serotina, Quercus rubra, Acer negundo, Robinia pseudoacacia, Impatiens parviflora and Solidago spp.-and 9 taxa of low frequency: Acer saccharinum, Amelanchier spicata, Cornus spp., Fraxinus spp., Parthenocissus spp., Syringa vulgaris, Echinocystis lobata, Helianthus tuberosus, Reynoutria spp. Random Forest's models' quality grows with the number of occurrences of frequent taxa but not of the rare ones. Both frequent and rare taxa share a similar hierarchy of predictors' importance: Land use > Tree stand > Seed source and, for frequent taxa, Forest properties as well. We conclude that there is an 'explanation jump' at higher species frequencies, but rare species are surprisingly similar to frequent ones in their determinant's hierarchy, with differences conforming with their respective stages of invasion.