Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range

Abstract

Herbivory can negatively affect several components of plant reproduction. Yet, because of a lack of experimental studies involving multiple populations, the extent to which differences in herbivory contribute to among-population variation in plant reproductive success is poorly known. We experimentally determined the effects of insect herbivory on reproductive output in nine natural populations of the perennial herb Lythrum salicaria along a disturbance gradient in an archipelago in northern Sweden, and we quantified among-population differentiation in resistance to herbivory in a common-garden experiment in the same area. The intensity of leaf herbivory varied >500-fold and mean female reproductive success >400-fold among the study populations. The intensity of herbivory was lowest in populations subject to strong disturbance from ice and wave action. Experimental removal of insect herbivores showed that the effect of herbivory on female reproductive success was correlated with the intensity of herbivory and that differences in insect herbivory could explain much of the among-population variation in the proportion of plants flowering and seed production. Population differentiation in resistance to herbivory was limited. The results demonstrate that the intensity of herbivory is a major determinant of flowering and seed output in L. salicaria, but that differences in herbivory are not associated with differences in plant resistance at the spatial scale examined. They further suggest that the physical disturbance regime may strongly influence the performance and abundance of perennial herbs and patterns of selection not only because of its effect on interspecific competition, but also because of effects on interactions with specialized herbivores.

Phenological shifts of native and invasive species under climate change: insights from the Boechera–Lythrum model

“…Herbivory by G. calmariensis and G. pusilla can cause extensive damage to the host plant in the native range [68,69], and in the introduced range where the beetles have been widely introduced as biological control agents [70]. The number of herbivore species decrease with increasing latitude in the native range [71], but it is not clear if the same is true in North America.…”

“…(b) Interactions with specialist herbivores with regards to size and phenology Specialist insect herbivores strongly affect the demographic structure and seed production of L. salicaria populations in its native range [68,69,78]. Both resistance and tolerance to herbivore damage vary with latitude, which may be related both to divergent selection on resistance traits as well as pleiotropic effects of growth and phenology [76].…”

Native insect herbivory overwhelms context dependence to limit complex invasion dynamics of exotic weeds

“…) and other environmental gradients (Louda , ; Lehndal et al . ). A variety of mechanisms, often unknown, could underlie context‐dependent variability (Maron et al .…”

“…Context-dependence is a pervasive feature of interspecific interactions (Bradley et al 2003;Agrawal et al 2007;Chamberlain et al 2014). For example, herbivore effects on plants can be affected by vegetation type (Lambrinos 2002), proximity to stand edges (Lambrinos 2006), soil characteristics (Louda et al 1987;von Euler et al 2014), elevation (Miller et al 2009) and other environmental gradients (Louda 1982(Louda , 1983Lehndal et al 2016). A variety of mechanisms, often unknown, could underlie context-dependent variability (Maron et al 2014).…”

Cumulative herbivory outpaces compensation for early floral damage on a monocarpic perennial thistle

“…Such herbivory can dramatically and quantitatively reduce plant-reproductive success (Louda and Potvin 1995;McCall and Irwin 2006;LucasBarbosa 2016) and directly affect plant population growth rate (Rose et al 2005;Tenhumberg et al 2008;von Euler et al 2014) and population density (Louda 1983;Jongejans et al 2008;Lehndal et al 2016). Floral herbivore impacts should, therefore, favor plant growth and allocation strategies that can reduce losses, or even improve fitness, under herbivory pressure (Fornoni 2011;Agrawal et al 2012;Carmona and Fornoni 2013).…”