Cross-seasonal legacy effects of arthropod community on plant fitness in perennial plants.

Jeltje M Stam,Marcel Dicke,Erik H Poelman,Martine Kos,Matthew Heard

doi:10.1111/1365-2745.13231

Abstract

In perennial plants, interactions with other community members during the vegetative growth phase may influence community assembly during subsequent reproductive years and may influence plant fitness. It is well‐known that plant responses to herbivory affect community assembly within a growing season, but whether plant–herbivore interactions result in legacy effects on community assembly across seasons has received little attention. Moreover, whether plant–herbivore interactions during the vegetative growing season are important in predicting plant fitness directly or indirectly through legacy effects is poorly understood.Here, we tested whether plant–arthropod interactions in the vegetative growing season of perennial wild cabbage plants, Brassica oleracea, result in legacy effects in arthropod community assembly in the subsequent reproductive season and whether legacy effects have plant fitness consequences. We monitored the arthropod community on plants that had been induced with either aphids, caterpillars or no herbivores in a full‐factorial design across 2 years. We quantified the plant traits ‘height’, ‘number of leaves’ and ‘number of flowers’ to understand mechanisms that may mediate legacy effects. We measured seed production in the second year to evaluate plant fitness consequences of legacy effects.Although we did not find community responses to the herbivory treatments, our data show that community composition in the first year leaves a legacy on community composition in a second year: predator community composition co‐varied across years. Structural equation modelling analyses indicated that herbivore communities in the vegetative year correlated with plant performance traits that may have caused a legacy effect on especially predator community assembly in the subsequent reproductive year. Interestingly, the legacy of the herbivore community in the vegetative year predicted plant fitness better than the herbivore community that directly interacted with plants in the reproductive year. Synthesis. Thus, legacy effects of plant–herbivore interactions affect community assembly on perennial plants across growth seasons and these processes may affect plant reproductive success. We argue that plant–herbivore interactions in the vegetative phase as well as in the cross‐seasonal legacy effects caused by plant responses to arthropod herbivory may be important in perennial plant trait evolution such as ontogenetic variation in growth and defence strategies.

Highlights

Despite the absence of an early season herbivore effect on community assembly, our study indicates that insect community assembly on perennial plants is affected by cross‐seasonal legacy effects of community composition across years
The carnivore community in the first vegetative growing season correlated with carnivore community assembly after winter in the second year when plants flowered for the first time
We identified that especially the herbivore community in the vegetative year predicted plant fitness rather than the community that directly interacted with the plant in the reproductive season

Summary

Introduction

To test whether either early‐season herbivory treatments or total arthropod community composition exerted legacy effects on plant fitness, seeds of all monitored plants were harvested. We first tested the effects of early‐season herbivory treatments (aphids, caterpillars or none) on the herbivore or carnivore community composition within and across years on plot level, averaging the abundance of each species over the four plants per plot.

Results

Conclusion