Interactions between nectar robbers and seed predators mediated by a shared host plant, Ipomopsis aggregata

Abstract

Animals that consume plant parts or rewards but provide no services in return are likely to have significant impacts on the reproductive success of their host plants. The effects of multiple antagonists to plant reproduction may not be predictable from studying their individual effects in isolation. If consumer behaviors are contingent on each other, such interactions may limit the ability of the host to evolve in response to any one enemy. Here, we asked whether nectar robbing by a bumblebee (Bombus occidentalis) altered the likelihood of pre-dispersal seed predation by a fly (Hylemya sp.) on a shared host plant, Ipomopsis aggregata (Polemoniaceae). We estimated the fitness consequences of the combined interactions using experimental manipulations of nectar robbing within and among sites. Within sites, nectar robbing reduced the percentage of fruits destroyed by Hylemya. However, the negative effects of robbing on seed production outweighed any advantages associated with decreased seed predation in robbed plants. We found similar trends among sites when we manipulated robbing to all plants within a local population, although the results were not statistically significant. Taken together, our results suggest that seed predation is not independent of nectar robbing. Thus, accounting for the interactions among species is crucial to predicting their ecological effects and plant evolutionary response.

Additive effects of herbivory, nectar robbing and seed predation on male and female fitness estimates of the host plant Ipomopsis aggregata

“…However, they found that the effects of pre-dispersal seed predators and florivores were non-additive. Brody et al (2008) found primarily additive effects of robbing and seed predation on the female function of I. aggregata, despite finding some reduction of pre-dispersal seed predation on plants that incurred high levels of robbing, but only robbing and not seed predation was manipulated. These results underscore that diverse species interactions can combine with different outcomes, although findings of additive effects are more common than non-additive effects for multispecies interactions with I. aggregata.…”

“…We focused on the damage imposed by three antagonists-an ungulate herbivore, a nectar-robbing bumble bee, and a dipteran predispersal seed predator-that each feed on the hummingbird-pollinated host Ipomopsis aggregata. The effect of each of the antagonists on I. aggregata fitness has been studied independently (e.g., Paige and Whitham 1987;Brody 1992;Irwin and Brody 2000) or in two-way interactions (e.g., Juenger and Bergelson 1998;Sharaf and Price 2004;Brody et al 2008). However, the combined effects of herbivores, nectar robbers, and seed predators on male and female function have remained unexplored.…”

When resources don't rescue: flowering phenology and species interactions affect compensation to herbivory in Ipomopsis aggregata

“…by Juenger et al 2005), and nectar‐robbing bumble bees (Apidae: Bombus occidentalis ). Plants can experience damage from all of these antagonists within one flowering season, and the extent to which the outcomes of these interactions are independent is not fully known (Juenger and Bergelson 1997, Brody et al 2008, Irwin and Brody 2011).…”

“…Plants with larger fl oral displays (those not clipped and provided supplemental resources) experienced higher rates of predation and robbing and outperformed their clipped counterparts. A positive link between seed predation and fl owering success, although counter-intuitive, is not unprecedented (Brody andMitchell 1997, Brody andMorita 2000). High rates of attack in plants with large fl oral displays…”

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

“…Studies on ecological and evolutionary consequences of species interactions have been mainly focusing on single pairwise effects, such as pollinator-mediated (Campbell et al 1996;Alexandersson and Johnson 2002;Sandring and Å gren 2009;Cuartas-Domínguez and Medel 2010; or nectar robber-mediated (Lara and Ornelas 2001;Urcelay et al 2006;Castro et al 2008;Young 2008;Navarro and Medel 2009) selection on floral traits. However, single pairwise interaction seldomly exists in isolation and can be interfered by other community members (Gómez 2003;Cariveau et al 2004;Lavergne et al 2005;Brody et al 2008;Sánchez-Lafuente 2007;Bartkowska and Johnston 2012). For example, mutualisms between plants and pollinators can be changed by nectar robbers through competing with pollinators or altering floral attractants or rewards (Strauss and Irwin 2004;Irwin et al 2010 and references therein).…”