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The relative importance of plant intraspecific diversity in structuring arthropod communities: a meta-analysis 

Julia Koricheva, Dexter Hayes

Abstract

1.Understanding how plant diversity influences higher trophic levels is important for predicting the consequences of global biodiversity loss. While early studies have focused on the effects of plant species richness, more recently a growing number of experiments have explored the effects of plant intraspecific diversity by manipulating the genotypic richness of plant communities.

2.By combining 162 estimates of effect size from 60 experimental studies, we examined the effects of plant genotypic richness on arthropods, one of the most diverse and abundant taxa which play a crucial role in many ecosystem processes and services. We have also compared the effects of plant genetic and species diversity on arthropods when both were manipulated within the same study.

3.Species richness and abundance of most trophic groups of arthropods was higher in genetically diverse plant stands. Interestingly, the effects of plant genetic diversity on natural enemies of herbivores were stronger than the effects of plant genetic diversity on herbivores, suggesting that plant genetic diversity effects on predators might be driven by mechanisms independent of herbivores.

4.Herbivore and predator abundance increased with plant genetic diversity in studies using wild plants whereas predator abundance was unaffected and herbivore abundance was reduced by crop genetic diversity. Damage by generalist herbivores was reduced by plant genetic diversity whereas damage by specialist herbivores was not affected.

5.When the effects of plant genetic and species diversity on arthropods were compared within the same study, the magnitude of plant genetic diversity effects was comparable to that of plant species diversity.

6.Our results suggest that plant genetic diversity has significant effects on the diversity of arthropods across several trophic levels, thus highlighting the importance of maintaining high levels of both plant species and genetic diversity for arthropod conservation. However, the potential of using crop genetic mixtures in agriculture for pest control appears to be limited as even though herbivore abundance was reduced in genetically diverse plots, herbivore damage and predator abundance were not affected by crop genotypic richness.

Figure 1. Effects of plant genetic diversity on different trophic groups of arthropods. Error bars represent 95% confidence intervals. Numbers next to error bars indicate number of studies in each category. Numbers in parentheses are Rosenberg’s fail-safe numbers which indicate how many additional studies with effect size of 0 and of the same weight as the average of those already being used would need to exist to reduce the significance of the mean effect to 0.05. Effects are considered significantly different from 0 if 95% confidence intervals do not cross 0 (dashed line).

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http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13062/full

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