Multivariate ordination identifies vegetation types associated with spider conservation in brassica crops.

Hafiz Sohaib Ahmed Saqib,Geoff M Gurr,Minsheng You

doi:10.7717/peerj.3795

Hafiz Sohaib Ahmed Saqib, Geoff M Gurr + Show 1 more

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https://doi.org/10.7717/peerj.3795

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Abstract

Conservation biological control emphasizes natural and other non-crop vegetation as a source of natural enemies to focal crops. There is an unmet need for better methods to identify the types of vegetation that are optimal to support specific natural enemies that may colonize the crops. Here we explore the commonality of the spider assemblage—considering abundance and diversity (H)—in brassica crops with that of adjacent non-crop and non-brassica crop vegetation. We employ spatial-based multivariate ordination approaches, hierarchical clustering and spatial eigenvector analysis. The small-scale mixed cropping and high disturbance frequency of southern Chinese vegetation farming offered a setting to test the role of alternate vegetation for spider conservation. Our findings indicate that spider families differ markedly in occurrence with respect to vegetation type. Grassy field margins, non-crop vegetation, taro and sweetpotato harbour spider morphospecies and functional groups that are also present in brassica crops. In contrast, pumpkin and litchi contain spiders not found in brassicas, and so may have little benefit for conservation biological control services for brassicas. Our findings also illustrate the utility of advanced statistical approaches for identifying spatial relationships between natural enemies and the land uses most likely to offer alternative habitats for conservation biological control efforts that generates testable hypotheses for future studies.

Highlights

IntroductionAnthropogenic activities—such as land clearing, environmental pollution and agricultural intensification—have led to adverse effects on the occurrence, diversity and evenness (Bengtsson, Ahnström & Weibull, 2005; Benton, Vickery & Wilson, 2003; Landis, Wratten & Gurr, 2000; Sunderland & Samu, 2000; Thies et al, 2011; Thies & Tscharntke, 1999), and even the outright extinction of numerous species (Thomas et al, 2004)
We identified the response of spider abundance and diversity (H ) against different vegetation types and weighted principal coordinates of neighbor matrices (PCNM) as explanatory variables using the ‘‘varpart’’ and ‘‘pcnm’’ functions of package ‘‘vegan’’ (Oksanen et al, 2016) in R, which allowed variance partitioning to separate the effects of weighted PCNM and vegetation types on spider abundance and diversity (H ) (Peres-Neto et al, 2006)
In Minqing, variance partitioning results showed that vegetation type (X1) alone explained 13% of variation in abundance of spiders, and the total effect of X1 and PCNM (X2) was 6% (Fig. 1A)

Summary

Introduction

Anthropogenic activities—such as land clearing, environmental pollution and agricultural intensification—have led to adverse effects on the occurrence, diversity and evenness (Bengtsson, Ahnström & Weibull, 2005; Benton, Vickery & Wilson, 2003; Landis, Wratten & Gurr, 2000; Sunderland & Samu, 2000; Thies et al, 2011; Thies & Tscharntke, 1999), and even the outright extinction of numerous species (Thomas et al, 2004). An alternative approach is to manipulate the availability of nearby donor habitat in field margins or adjacent fields and uncropped zones. This avoids the need to reduce to the extent of the focal crop. There is a need, to develop approaches that will help understand specific interactions between crops, adjacent vegetation types and natural enemies (predators and parasitoids) (Furlong, 2015; Furlong et al, 2008; Furlong & Zalucki, 2010; Szendrei et al, 2014; Tscharntke et al, 2012)

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