The Distribution of Soil Insects across Three Spatial Scales in Agricultural Grassland

Abstract

The effects of specific environmental factors on abundance and distribution of some individual soil insect taxa is known, but how scale influences spatial distribution is less well evaluated, particularly at the community level. However, given that many soil insects are pests or beneficial natural enemies, and that collectively they play a role in soil processes, this information is of potential value for predictive modeling and in furthering our understanding of soil ecology and management. The objectives of this study were to characterize the spatial distribution, relative population sizes, effect of sampling scale and taxa co-occurrence on a range of soil insects at the family level over 2 years. Soil cores were taken from agricultural grassland soils across three different sampling scales (farm, field, and core) using a systematic sampling approach. Spatial distribution was assessed using the variance-to-mean (VMR) ratio and taxa distribution plots and the contribution of scale, spatial (geographical location), and biotic (presence-absence of other species) factors determined using deviance partitioning. Tipulid larvae (leatherjackets) were the most abundant taxa in both years, but the composition of other Dipteran and Coleopteran taxa varied between years. The VMRs revealed differences in spatial distribution between taxa across scales and years, showing a range of underlying distributional patterns. Scale was the most important factor influencing species distributions, but a large proportion of deviance remained unexplained and there was much variation between taxa, suggesting biological and scale-specific factors are driving distributions, in agreement with a previous study.

Molecular identification and distribution of leatherjackets (Diptera: Tipulidae) in U.K. agricultural grassland

“…haplotype 4) are common throughout the study site, and that AMOVA results suggest a panmictic population with little evidence of spatial structuring [in accordance with Benefer et al . () who, in a broader assessment, found little evidence of scale or space affecting tipulid larvae presence/absence in general], a lack of dispersal ability in T. paludosa in general does not appear to be the case, at this scale of study at least. For example, field 1 and field 19 are separated by a distance of approximately 1.6 km but share haplotype 1.…”

“…(), who reported 4% of larvae to be this species in a survey of 75 agricultural grass fields in Northern Ireland. Adults were not directly surveyed in the present study, although, based on observational data, both species were abundant aboveground, which could suggest that there are species‐specific oviposition preferences and/or differences in dispersal ability (Blackshaw et al ., ; Benefer et al ., ). Although the limited data from surveys in U.K. agricultural grassland suggest T. oleracea may not be present in damaging proportions, in North America this species is becoming more common in turfgrass (Rao et al ., ) and so it is important to be able to separate damaging species reliably.…”

“…Leatherjackets recovered in the surveys described in Benefer et al . () were used as source material. Briefly, larvae were heat‐extracted from soil cores that were collected using a systematic sampling approach (a 25‐m grid across 19 fields) in two sampling periods over 2 years.…”

“…The samples collected in the present study were used as a baseline survey to assess the distribution of soil insects across the site, as described in Benefer et al . (). Using DNA barcoding to identify leatherjackets collected to the species level, our specific objectives were to: (i) determine the relative proportion of leatherjacket species present; (ii) investigate the intra‐ and inter‐specific genetic variation of the species identified; and (iii) assess the spatial relationships between tipulid haplotypes.…”

Novel approaches to sampling pollinators in whole landscapes: a lesson for landscape-wide biodiversity monitoring

“…Up to now, examples of grid-based sampling at multiple spatial scales come e.g. from a sampling campaign for soil insects, where Benefer et al (2016) showed detailed maps of the distribution of various taxa on sites measuring about 1 9 1 km. Similar approaches were used in the pan-European project ''Greenveins'' for insects and birds (Dormann et al 2007b;Le Féon et al 2010), and grid-based approaches in general are widely employed in biodiversity monitoring schemes (e.g.…”