Effects of Floral Herbivory on Maternal Reproduction in Sanicula Arctopoides (Apiaceae)

Abstract

Although numerous studies have addressed plant compensatory responses to removal of vegetative tissue by herbivores, only a few have determined the effect of floral removal on subsequent seed production in natural populations. In Sanicula arctopoides, a perennial monocarp, removal of inflorescences (umbels), both naturally by deer (Odocoileus hemionus) and by artificial clipping early in the flowering season, led to no loss of maternal reproduction as measured by seed number and seed mass. Full compensation occurred when umbels bearing up to one—third of a plant's flowers were removed at the stage when plants are normally grazed. However, there are thresholds both in timing and severity of removal beyond which plants were unable to compensate fully. Compared to controls, artificial removal of developing fruits 20 d later than the normal stage resulted in a 42% decrease in seed production. Successive clippings that removed °55% of each plant's flowers resulted in a 52% decrease in seed production relative to controls; however, a single clipping of the same intensity resulted in full compensation. Differential reactions to clipping of different umbel ranks provided information about the mechanism of the response. Removal of secondary umbels resulted in decreased seed abortion rates in later developing umbels, while removal of tertiary umbels resulted in decreased abortion rates in both earlier and later formed umbels. These responses indicated that delayed abortion of developing seeds may be common in secondary umbels, that removal of secondary umbels by herbivores may relieve plants of some costs of abortion, and that S. arctopoides uses flexible allocation to achieve full compensation at typical levels of floral herbivory.

Overcompensation in response to simulated herbivory in the perennial herb Sedum maximum

“…This is the first report of overcompensation in an iteroparous perennial plant in which future costs of herbivore-induced reproduction are explicitly measured. Previously, this phenomenon was known in monocarpic plants such as Ipomopsis aggregata (Paige and Whitham 1987), Sanicula arctopoides (Lowenberg 1994), Gentianella campestris (Lennartsson et al 1997), Raphanus raphanistrum (Agrawal et al 1999) and Erysimum strictum (Rautio et al 2005). Studies on iteroparous perennials that report a positive effect of herbivores on plant reproduction are usually based on the data from a single growing season and overlook future consequences of enhanced reproduction (Hicks and Turkington 2000;Gao et al 2008).…”

“…In spite of this, overcompensation has been documented a number of times (e.g. Paige and Whitham 1987;Lowenberg 1994;Lennartsson et al 1997;Agrawal et al 1999). The first evidence of overcompensation provoked controversy about the possibility of mutualistic relationships between plants and herbivores.…”

“…All the above models were constructed for monocarps. The empirical evidence of overcompensation mostly concerns plants with a single bout of seed production (Paige and Whitham 1987;Lowenberg 1994;Lennartsson et al 1997;Agrawal et al 1999;Rautio et al 2005), the reason being that comparing reproductive output of grazed plants with that of non-grazed plants is relatively straightforward in monocarps. The aim of this study was to examine whether overcompensation in terms of current and future performance can be observed in iteroparous perennial plants.…”

Differences in growth and yield responses to Aphis gossypii Glover between different okra varieties

“…The damage levels were variable and depended on the variety. Variety Local was less vulnerable to aphid feeding, presumably due to its high compensatory growth (Dyer et al 1993;Lowenberg 1994). Varieties Perkins dwarf and Lee suffered most from aphid damage, probably because aphids developed massive populations early on the still young plants where the ratio between assimilate removed by aphids to that produced by the plant is perhaps more advantageous for aphid growth (Prütter & Zebits 1991).…”

Overcompensation through the paternal component of fitness in Ipomopsis arizonica

“…To date, the majority of studies on plant-herbivore interactions have focused on the maternal, as opposed to the paternal, side of fitness (Gronemeyer et al 1997;Strauss et al 1996). Because there are many plants that produce more flowers following apical damage where fruit and seed set is reduced or unaffected (Hendrix 1979;Inouye 1982;Lowenberg 1994;Paige 1999;Reichman and Smith 1991), the paternal component of fitness could be enhanced, resulting in an increase in total fitness. We provide the first example of such a case.…”