Direct and Indirect Effects of Drought on Compensation Following Herbivory in Scarlet Gilia

Abstract

Compensation following herbivory is an important element of plant defense; however, variation in compensation under naturally stressful conditions has yet to be evaluated directly. During Arizona's worst drought on record, we explored compensation following ungulate herbivory in a typically overcompensating population of scarlet gilia (Ipomopsis aggregata) near Flagstaff, Arizona, USA. In a natural survey of browsed and unbrowsed plants, we documented severe undercompensation. We tested two factors that potentially contributed to this atypical pattern: (1) the direct effect of drought stress on the capacity to compensate (following the typical single bout of herbivory) and (2) the indirect effect of drought stress on compensation through increased ungulate browsing. Using a 2 ϫ 2 factorial experiment (with or without supplemental water, with or without clipsimulated herbivory typical of non-drought years), we found that water availability limited compensation (direct effect). In a second experiment examining the indirect effects of drought, we found that ungulates browsed scarlet gilia at unprecedented levels during the drought year, resulting in severe undercompensation. We conclude that, although water was an important limiting factor for compensation during the drought year, the overriding factor determining fitness achieved through compensation was the indirect effect of drought, i.e., drought-year-associated ungulate browsing.

Overcompensation and adaptive plasticity of apical dominance in Erysimum strictum (Brassicaceae) in response to simulated browsing and resource availability

“…Shoot architecture may also be subject to temporally variable selection pressures, e.g. due to fluctuating intensity of herbivory (Crawley 1987, van der Meijden 1990, Vail 1992, Nilsson et al 1996a, Juenger et al 2000, Gómez 2003) or variable climate (Lennartsson et al 1998, Huhta et al 2000a, Levine and Paige 2004) or variable resource availability (Aarssen and Irwin 1991, Bonser and Aarsen 1996, Irwin and Aarssen 1996, Järemo et al 1996, Duffy et al 1999), which operate on fitness effects integrated over generations and which may lead to suboptimal adaptation in the short‐term (Seger and Brockman 1987, Nilsson et al 1996a). Whatever the ultimate causes, the present study suggests that overcompensation in monocarpic herbs occurs in conditions where the intact plants appear to be more meristem rather than resource limited.…”

Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus

“…Several studies show that tolerance of damage is limited by reduced water availability (Poiani & Pozo 1986;Fahnestock & Detling 1999;Hawkes & Sullivan 2001;Levine & Paige 2004;Acuña-Rodríguez et al 2006;Wise & Abrahamson 2007;Gonzáles et al 2008;Atala & Gianoli 2009), but results are seldom discussed considering the interplay between plant functional responses to herbivory and to water stress (Valladares et al 2007). On one hand, some compensatory responses to herbivory, such as increased resource allocation to shoots (Mabry & Wayne 1997;Huhta et al 2000) to replace eaten biomass, counteract plant functional responses to drought, such as increased biomass allocation to roots (Blum 1996;Gianoli & González-Teuber 2005) to enhance water uptake.…”

Impact of simulated herbivory on water relations of aspen (Populus tremuloides) seedlings: the role of new tissue in the hydraulic conductivity recovery cycle

“…The impact of these interactions on plant fitness may be modulated by intensity of herbivory (Staley et al 2006), defoliation frequency (Lasseur et al 2007), water availability (Levine and Paige 2004), changes in light capture (van Staalduinen and Anten 2005), phenological stage of reproductive (Freeman et al 2003) and non-reproductive tissues, (Hanley and May 2006), nutrient availability (Zhao et al 2008), spatial distribution (Avila-Sakar et al 2003) and pattern of herbivory damage (Meyer 1998), palatability of neighbors (Baraza et al 2006) and genetic variation to environmental stress (Stevens et al 2007) among other factors. Furthermore, some of these factors may interact with each other under different levels of competition and resource availability, changing the impact of herbivory on plant fitness (Alward and Joern 1993;Hawkes and Sullivan 2001;Wise and Abrahamson 2005).…”