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The abundance and horizontal distribution of three pteropod species, Limacina helicina, Limacina retroversa and Clione limacina were examined in the western entrance of the Barents Sea (Polar Front region) in August 2011. Sixteen samples were collected from 8 sampling sites located along a latitudinal transect. The southern part of the study area (south of 73°N) was dominated by L. retroversa, while L. helicina was mostly observed north of 73°N. Surface water temperature differences between the coldest and the warmest station were around 8°C. The highest density of L. retroversa was found in the south, near the Norwegian coast (nearly 52 000 ind. 1000 m-3), while the highest density of L. helicina was observed in the region of the Arctic water masses (nearly 13 000 ind. 1000 m-3). The sampled population of pteropods comprised mainly juvenile stages. Redundancy analysis (RDA) of the relationships between environmental factors (mean and surface salinity, mean temperature, sampling depth, chlorophyll concentration) and the population structure showed that mean temperature was the most important factor in the study area, explaining 70.5% of the pteropod community variation. [ABSTRACT FROM AUTHOR]

Aims According to traditional theory, superior competitive ability in plants generally requires relatively large plant body size. Yet even within the most crowded vegetation, most resident species are relatively small; species size distributions are right-skewed at virtually every scale. We examine a potential explanation for this paradox: small species coexist with and outnumber large species because they have greater ‘reproductive economy’, i.e. they are better equipped—and hence more likely—to produce offspring despite severe size suppression from intense competition. Methods Randomly placed plots within old-field vegetation were surveyed across the growing season. Within each plot, the largest (MAX) and smallest (MIN) reproductive individuals of each resident species were collected for above-ground dry mass measurement. We tested three hypotheses: (i) smaller resident species (with smaller MAX size) have generally smaller reproductive threshold sizes; (ii) smaller resident species have greater ‘reproductive economy’, i.e. a smaller MIN relative to MAX reproductive plant size; and (iii) MIN size predicts plot occupancy (species abundance within the community) better than MAX size. Important Findings The results supported the first and third, but not the second hypothesis. However, we could not reject the hypothesis that smaller species have greater reproductive economy, as it was not possible to record data for the largest potential plant size for each species—since even the largest (MAX) plants collected from our sampled plots were subjected to competition from neighbours under these natural field conditions. Importantly, contrary to conventional competition theory, more successful species (in terms of greater plot occupancy) had smaller minimum not larger (or smaller) maximum reproductive sizes. These results suggest that a small reproductive threshold size, commonly associated with relatively small potential body size, is generally more effective in transmitting genes into future generations when selection from neighbourhood crowding/competition is intense—at least within natural old-field vegetation. Accordingly, we propose a simple conceptual model that represents the basis for a fundamental paradigm shift in the predicted selection effects of crowding/competition on plant body size evolution. [ABSTRACT FROM PUBLISHER]

Abstract: The composition of natural vegetation typically includes a wide range of species sizes, but usually, relatively small size classes are represented by the greatest number of resident species. This is the case even within habitat types where traditional theory predicts that the intensity of plant competition should be most severe. Here we show that distributions of species size metrics are generally right-skewed also at the within-genus level. Our analyses are based on published reports of maximum plant height, leaf size, and seed size for an unbiased sample of fourteen angiosperm genera, involving eleven families – including representation of both endemics and cosmopolitans, plus genera that differ widely in both size (number of species) and growth form diversity. Pair-wise relationships for these three traits were, in most cases, also generally positively correlated for con-generic species. These results indicate that the right-skewed species size distributions commonly reported for natural vegetation reflect a pervasive signal for adaptive size metrics, essentially unstructured by phylogenic relationships. From these data therefore, we infer that most episodes of species origination within virtually all angiosperm lineages must have generally involved favouring effects of natural selection associated with relatively small plant body size, leaf size, and seed size. This represents a striking disconnect with the conventional view that superior competitive ability in plants requires relatively large body size/biomass production. Our interpretation of why ‘small is better’ focuses on two recently developed hypotheses – the ‘physical-space-niche’ hypothesis, and the ‘fecundity allocation premium’ hypothesis. In future research, detailed phylogenies at the species level might be used to test the prediction that relatively small size metrics are especially well represented in the most recently evolved species within angiosperm lineages. [Copyright &y& Elsevier]

Abstract: We study the effects of habitat fragmentation on biodiversity patterns by means of a simple spatial model which considers selective geographic colonization, diffusion and mutation. In our model, regions of the lattice are characterized by the amount of resources available to populations of species which are going to colonize that regions. We simulate the fragmentation of the habitat by assuming that a proportion of the sites is not available for colonization, that is, there is no resource availability in those sites. We analyse the patterns of the species–area relationship and the abundance distribution considering two sample methods, in order to simulate the cases in which the habitats are distributed in islands and continents. We have observed that the pattern of the species–area curve is changed when different sample methods are considered. We have also verified that the abundance distribution is bimodal when small mutation probabilities are considered. [Copyright &y& Elsevier]