Interactive effects of plant neighbourhood and ontogeny on insect herbivory and plant defensive traits

Abstract

Plant ontogenetic stage and features of surrounding plant neighbourhoods can strongly influence herbivory and defences on focal plants. However, the effects of both factors have been assessed independently in previous studies. Here we tested for the independent and interactive effects of neighbourhood type (low vs. high frequency of our focal plant species in heterospecific stands) and ontogeny on leaf herbivory, physical traits and chemical defences of the English oak Quercus robur. We further tested whether plant traits were associated with neighbourhood and ontogenetic effects on herbivory. We found that leaf herbivory decreased in stands with a low frequency of Q. robur, and that saplings received less herbivory than adult trees. Interestingly, we also found interactive effects of these factors where a difference in damage between saplings and adult trees was only observed in stands with a high frequency of Q. robur. We also found strong ontogenetic differences in leaf traits where saplings had more defended leaves than adult trees, and this difference in turn explained ontogenetic differences in herbivory. Plant trait variation did not explain the neighbourhood effect on herbivory. This study builds towards a better understanding of the concurrent effects of plant individual- and community-level characteristics influencing plant-herbivore interactions.

Impacts of urbanization on insect herbivory and plant defences in oak trees

“…Leaf burst in this deciduous species usually occurs during April in southern Europe and in May for northern Europe, whereas leaf senescence and leaf drop typically start in September for northern Europe and in October for southern Europe. In its native range, Q. robur supports a diverse community of specialist (and a few generalist) insect herbivores such as leaf chewers, miners and gallers (Southwood et al 2005, Tack et al 2010, Tack and Roslin 2011, Castagneyrol et al 2012, Giffard et al 2012, Moreira et al 2017, 2018a.…”

“…We chose phenolic compounds as defensive traits because they are widely recognized as herbivore feeding deterrents across many plant taxa (Mithöfer andBoland 2008, Salminen andKaronen 2011), and because they have been previously shown to confer resistance against leaf herbivores in Q. robur (Feeny 1970, Roslin and Salminen 2008, Abdala-Roberts et al 2016b, Moreira et al 2017, 2018a. We extracted phenolic compounds using 20 mg of dry plant tissue with 1 ml of 70% methanol in an ultrasonic bath for 15 min, followed by centrifugation (Moreira et al 2014).…”

Latitudinal variation in plant chemical defences drives latitudinal patterns of leaf herbivory

“…Leaves are approximately 8-12 cm long with four to seven pairs of lobes, and have almost no petiole. In its native range, Q. robur supports a large community of specialist (and some generalist) insect herbivores, mainly leaf chewers, miners and gallers (Southwood et al 2005, Tack et al 2010, Tack and Roslin 2011, Castagneyrol et al 2012, Giffard et al 2012, Moreira et al 2017a.…”

Forest diversity effects on insect herbivores: do leaf traits matter?

“…This phenomenon of associational resistance has often been attributed to a reduced proportion of host plants as diversity increases (resource concentration hypothesis; Root, 1973;Otway et al, 2005;Heiermann & Sch€ utz, 2008;Sholes, 2008;Bj€ orkman et al, 2010;Plath et al, 2012) and to physical and chemical traits of neighbouring plant species (Atsatt & O'Dowd, 1976;Ruttan & Lortie, 2014). However, the possibility that host plant traits involved in plant-herbivore interactions vary according to the diversity of the surrounding plant community has received little attention (but see Kos et al, 2015;Castagneyrol et al, 2017;Kostenko et al, 2017;Moreira et al, 2017). A better understanding of host trait variation across diversity gradients might improve our understanding of the mechanisms underpinning plant diversity effects on herbivores (Moreira et al, 2016) and might also inform the manipulation of stand diversity for sustainable pest management.…”