The microspatial distribution of beetles (Coleoptera) on exposed riverine sediments (ERS)

Adam J Bates,Joe N Perry,Adrian P Fowles,Jon P Sadler

doi:10.14411/eje.2007.068

Abstract

Exposed Riverine Sediments (ERS) are often characterised by a high diversity of microhabitats due to strong lateral gradi- ents in temperature, humidity, inundation frequency and availability of aquatic food resources and to variations in the degree of vegetation cover, sediment size and sorting. This variation, potentially in combination with interspecific competitive interactions, is thought to drive the microspatial distribution of ERS invertebrates. This research investigated the microspatial distribution of six ERS specialist beetles across three discreet patches of ERS. In particular it examined the temporal stability of species distributions, and their spatial association with environmental variability and other species. The research used a grid of 204 modified dry pitfall traps over six sampling periods in which weather conditions and water levels were stable, and used the Spatial Analysis by Distance IndicEs (SADIE) method to test the significance of spatial distributions and associations. Strong and significant microspatial zona- tion was observed for all species, and with few exceptions these distributions were remarkably stable across the study period. This zonation was mainly associated with elevation and proximity to the water, and several species were consistently spatially associated or disassociated with one another. This suggests that laterally more extensive patches of ERS support more species. Operations that reduce the size of ERS patches, such as channelisation, aggregate extraction and regulation are therefore likely to reduce ERS inver- tebrate diversity.

Highlights

Species typically show non-random, spatiotemporally heterogeneous distributions, which vary with the scale of observation (e.g. Levin, 1992; Dungan et al, 2002)
This study investigates the stability of the microspatial distribution of Exposed riverine sediments (ERS) specialist beetles and their spatial association with environmental variables and inter-specifics during stable water level and weather conditions
On Bar 1 (Fig. 3) there was clear evidence of spatial zonation in the species distributions, with Z. minimus and C. collaris situated in the “upper” more elevated section of the patch, B. decorum and B. punctulatum situated in the “lower” section of the patch very close to the water’s edge, and Fleutiauxellus maritimus and B. atrocaeruleum situated in the “mid” section of the bar

Summary

Introduction

Species typically show non-random, spatiotemporally heterogeneous distributions, which vary with the scale of observation (e.g. Levin, 1992; Dungan et al, 2002). Exposed riverine sediments (ERS) are areas of relatively unvegetated, alluvial, within-channel, silts, sands and gravels whose vertical distribution lies between the levels of bank-full and the typical base flow of a river. As such, they are situated within the aquatic terrestrial ecotone, which is characterised by a high diversity of microhabitats arranged along gradients of disturbance and succession (Ward et al, 1999). The known movement responses of ERS specialist beetles to variation in sediment, moisture, cover, and light (Andersen, 1978, 1985, 1989) may explain their fairly consistent spatial association with particular microhabitats (c.f. Andersen, 1969, 1983, 1988; Desender, 1989)

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