Evaluation of population densities of the common wolf spider Pardosa agrestis (Araneae: Lycosidae) in Hungarian alfalfa fields using mark-recapture

Balázs Kiss,Ferenc Samu

doi:10.14411/eje.2000.036

Abstract

The absolute population density of adult Pardosa agrestis (Westring, 1862), the dominant epigeic spider species in many arable lands in Central Europe, was quantified in two alfalfa fields using a multiple mark-recapture method. The resulting density estimates are presented together with catch data from simultaneously performed suction sampling and pitfall trapping. Two week long mark-recapture surveys were conducted in August 1995 and 1996 using grids of 11 × 11 live-catching pitfall traps covering a square area of 400 m2 in the first, and 900 m2 in the second survey. The trap checking and marking procedure, using individual codes, was done daily. Over 5,000 spiders were marked in the two surveys. The number of spiders caught varied greatly between days. The recapture rate was also variable, ranging between 5-19%. Recaptured animals moved considerable daily distances, marked animals left the area of the trapping grid within a few days. Population sizes were estimated for 3 day time windows during which period the population could be considered closed. Spider densities were calculated from the estimated abundances and the capture area, which consisted of the grid area plus a boundary strip calculated from the estimated movement ranges of spiders. The resulting densities were close to 2 males and 1 female per m2 in the first, and 4.5 males and 4.5 females per m2 in the second experimental site. Suction sampling caught very few adult individuals and gave unsatisfactory data for statistical comparison. Live catching pitfall trap catches did not correlate with the derived mark-recapture density estimates across the short time windows, but for the entire trapping sessions the catches were consistent with the density estimates.

Highlights

The estimation of population density is important for a wide range of ecological studies concerning spiders
In the present study we tried to answer the question of what population density might adult wolf spiders reach in alfalfa fields, by conducting two intensive mark-recapture surveys
We applied this method because the reliability of traditional density and abundance estimating methods, such as pitfall trapping and suction sampling, was ques tionable for studying population densities in wolf spider populations

Summary

Introduction

The estimation of population density is important for a wide range of ecological studies concerning spiders. In Central Europe one species, Pardosa agrestis, is by far the most dominant epigeic spi der in many arable cultures, such as cereals or alfalfa (Samu et al, 2000). Even though this spider species is ob viously abundant (Samu et al, 1996b; Toth & Kiss, 1997), there have been no attempts to estimate its popula tion densities. Studies to asses densities of other wolf spiders in agricultural areas have been unsuc cessful so far (Dinter, 1995; reviewed in Sunderland & Topping, 1995).

Methods

Results

Conclusion