Abstract

This paper summarizes the mechanisms behind the patterning of the intra-population abundance distribution of the land snail Vallonia pulchella (Müller, 1774). The molluscs were collected in recultivated soil formed on red-brown clays (Pokrov, Ukraine). Data obtained in this study reveal that V. pulchella population abundance ranges from 1 to 13 individuals per 100 g of soil sample. To obtain estimates of the mean, three models were used: the model of the arithmetic mean, the Poisson model and a log-normal model. The arithmetic mean of the occurrence of this species during the study period was 1.84 individuals/sample. Estimation of the average number of molluscs in one sample calculated using the Poisson model is lower and equals 1.40 individuals/sample. The distribution of the number of individuals in a population was described by the graphics "rank – abundance". The individual sample plot sites with molluscs may be regarded as equivalents of individual species in the community. For the analysis, the following models were used: broken sticks model, niche preemption model, log-normal model, Zipf model, and Zipf-Mandelbrot model. Applying the log-normal distribution gives a lower estimate of the mean density at 1.28 individuals/sample. Median value and mode is estimated at 1.00 individuals/sample. The Zipf-Mandelbrot model was shown as the most adequate to describe distribution of the V. pulchella population within the study area. The Zipf-Mandelbrot model belongs to the family of so-called non-Gaussian distributions. This means that the sample statistics do not possess asymptotic properties and by increasing the sample size, they tend to infinity, and are not close to the values of the general population. Therefore, the average value of the random variable that describes the non-Gaussian distribution has no statistical meaning. From an environmental point of view, this means that within the study area the capacity of the habitat is large, and for some combination of environmental conditions the rapid growth of the abundance of a given species is possible.

Highlights

  • There are plenty of publications devoted to habitat selection by land snails based on the investigation of mollusc communities from spatially different biotopes which differ in vegetation cover, soil type, moisture level (Millar & Waite, 1999; Martin & Sommer, 2004; Müller et al, 2005; Weaver et al, 2006)

  • Ellenberg phytoindication scales have been effectively used to explain the habitat preferences of the land snail Vertigo geyeri in Poland and Slovakia (Schenková et al, 2012)

  • The difference consists in the fact that the x-axis will not be delayed in the rank of species abundance and species abundance levels in the locus of a given population

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Summary

Introduction

There are plenty of publications devoted to habitat selection by land snails based on the investigation of mollusc communities from spatially different biotopes which differ in vegetation cover, soil type, moisture level (Millar & Waite, 1999; Martin & Sommer, 2004; Müller et al, 2005; Weaver et al, 2006). Ondina et al (2004) noted the restrictions of the importance of soil moisture data at any given moment because of the considerable changeability of this parameter. To help address this situation phytoindication data application is an appropriate method for assessment of land snails’ ecological characteristics and community properties (Horsák et al, 2007; Dvořáková & Horsák, 2012). The importance of soil factors in the spatial distribution, abundance and diversity of mollusc communities has been revealed on a large-scale level of research (Nekola & Smith, 1999; Juřičková et al, 2008; Szybiak et al, 2009). The issue of the spatial scale and the hierarchy of factors acting on molluscs are of special interest (Nekola & Smith, 1999; Bohan et al, 2000; McClain & Nekola, 2008; Myšák et al, 2013)

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