Intraspecific neighbourhood effect: Population‐level consequence of aggregation of highly defended plants

Abstract

There is increasing evidence that herbivore–plant interactions on a focal plant species are influenced by interspecific neighbourhood effects via neighbouring plants (i.e. an associational effect). However, intraspecific neighborhood effects imposed by plant traits have been less appreciated. Specifically, the significance of intraspecific neighbourhood effects in population‐level consequences of plants has been totally overlooked. Using two varieties of Nicotiana tabacum (high‐ and low‐nicotine), we evaluated the neighbourhood effects based on patch‐level interactions in a split‐plot 3 × 3 factorial experiment that manipulated number of plants (4, 9 and 16 plants) and culture type (monoculture plots with high‐ and low‐nicotine plants, and polyculture plot) in an experimental garden. We found that herbivore visits on plants varied depending on the number of plants per patch and culture type. Presence of more high‐nicotine plants decreased herbivore visits in the four plant plots, and presence of high‐nicotine plants in the nine plant plots decreased herbivore visits on both high‐ and low‐nicotine plants. In contrast, in the 16 plant plots, herbivore visits on high‐nicotine plants in polyculture plots were lower than others, including those on high‐nicotine plants in monoculture plots. Our findings clearly demonstrated that the intraspecific neighbourhood effect could occur depending on the aggregation of highly defended plants (i.e. high density and/or plant‐spacing). This study suggests that multiple mechanisms for the neighbourhood effect simultaneously worked, depending on the patch size and composition of defensive traits of individual plants, and that intraspecific neighbourhood effects may influence population‐level consequences for plant–herbivore interaction. A free Plain Language Summary can be found within the Supporting Information of this article.

Phytochemical drivers of insect herbivory: a functional toolbox to support agroecological diversification

“…Therefore, phytochemistry could provide an interesting perspective to broaden trait-based frameworks generally used to reason biodiversity-based management of crop covers. Although a large body of research interested in associational resistance has focused on interspecific diversity, our results align with recent studies reporting the role of intraspecific diversity in collards [ 79 ] and tobacco [ 80 ]. This is important to take full benefit of phytochemical diversity in mixed crops [ 81 ].…”

“…Taken together, these effects probably explain why trap plants randomly combined with target crops failed to reduce pest infestation as compared with monocultures with trap crop alone (electronic supplementary material, figure S4). This stresses the need to consider the densities and spatial arrangements of trap plants in agronomic systems that attempt to modulate the phytochemical diversity of crop covers [ 80 , 84 ].…”

Effects of the availability of floral resources and neighboring plants on nectar robbery in a specialized pollination system

“…From a phytocentric perspective, the nonlinear relationship we found in H. spathocircinata ( Figure 4 ) indicates that flowers in patches with a greater abundance of flowers may benefit from the attraction of pollinators and the avoidance of nectar robbing. The findings of this study also indicate that the individual probability of a flower being robbed is negatively density-dependent, with a high abundance of resources having a dilutive effect, as observed previously in studies of seed predation ( Ezoe 2017 ), herbivory ( Tamura et al 2019 ), and flower visitation rates ( Robertson 1992 ; Wenninger et al 2016 ). From a zoocentric perspective, the higher frequency of nectar robbing in conspecific H. spathocircinata patches with a low abundance of open flowers ( Figure 4 ) can be explained by the cost-benefit ratio for the nectar robbing hummingbirds of either maintaining a territory or invading an established territory ( Dobkin 1984 ; Heinrich 1975 ; Lanna et al 2017 ).…”

Factors affecting establishment and population growth of the invasive weed Ambrosia artemisiifolia

“…The aggregated distribution of plants is associated with alleviating biological and abiotic environmental stresses (such as drought, low temperatures, wind, and animal feeding) and improving their survival and reproductive ability. Examples include density-dependent hybridization ( Schmitt et al., 1987 ), fairy circles ( Getzin et al., 2016 ), intraspecific facilitation ( Reijers et al., 2019 ), and responses to amplifying and alleviating the effects of environmental pressures ( Hodgson et al., 2017 ; Tamura et al., 2020 ).…”