Relative contributions to seed production by floral visitors of slickspot peppergrass, Lepidium papilliferum (Brassicaceae)

Abstract

Assessing the relative contributions to seed production made by different types of floral visitors is fundamental to understanding the evolution of floral morphology and the influence that particular pollinator taxa have on plant fitness and reproduction. This 3-year study examined the pollinator activity and the seed production in three populations of Lepidium papilliferum, a threatened mustard endemic to sagebrush-steppe habitat in southwest Idaho. Relative amounts of time visitor taxa spent foraging on flowers, visitation rates (number of flowers visited per unit time during a foraging bout), and pollination effectiveness (fruit set per single visit to a virgin flower) were recorded for each of 12 insect taxa that visited L. papilliferum flowers. Relative contributions to seed production were calculated as the product of relative interaction frequencies (the relative number of flowers visited by each taxon-the ''quantity'' component of pollination) and pollination effectiveness (fruit set per single visit to a virgin flower-the ''quality'' component of pollination). Despite the superiority of some insect taxa in terms of pollination effectiveness, estimates of relative pollinator contributions to seed production were influenced primarily by an insect taxon's interaction frequency with flowers. Pollinator assemblages varied widely both spatially and temporally, which suggest that L. papilliferum is not under strong selective pressure to shift from its generalist pollination strategy toward greater specialization. For this threatened plant, reliance on a diverse assemblage of insect pollinators may serve as an important buffer against disruption in reproductive success caused by fluctuations in population sizes of individual pollinator taxa.

Generalization versus Specialization in Pollination Systems: Visitors, Thieves, and Pollinators of Hypoestes aristata (Acanthaceae)

“…Because of the shortcomings of using the single-visit method to estimate pollination effectiveness [33], [35], we chose the approach based on 2-hour observation periods. Basing observations on time-defined periods is more suitable to detect the potential effects of the whole spectrum of floral visitors, including occasional visitors; and to reveal both positive and negative effects of individual visitors.…”

“…Indirect techniques, such as estimating visitor frequency rates [25]–[27] or direct measuring the total amount of pollen grains brought onto the stigma during a single visit of a particular visitor [25], [26], [28]–[31], may not sufficiently consider the real contribution of particular visitors to the plant’s reproduction [32]. One possible way to detect the visitor’s actual contribution directly is by using estimates from single visits to virgin flowers [33]–[35]. However, the single-visit approach has several weaknesses.…”

A general framework for effectiveness concepts in mutualisms

“…), fruit and seed set (Mayfield et al . ; Sahli & Conner ; Fagua & Ackerman ; Robertson & Leavitt ; Sánchez‐Lafuente et al . ; Maldonado et al .…”

“…Mayfield et al 2001;Sahli & Conner 2007;Ne'eman et al 2010;Fagua & Ackerman 2011;S anchez-Lafuente et al 2012;Castro et al 2013;Rocca & Sazima 2013), although more complex indices have been used (e.g. Jacobs et al 2010;Robertson & Leavitt 2011;Rader et al 2012;Rodr ıguez-Rodr ıguez et al 2013). Metrics of quality include surrogates thought to affect pollination potential, such as pollen loads (Jacobs et al 2010;Zych et al 2014) or within-vs. between-plant-pollinator movements (Utelli & Roy 2000).…”

The most effective pollinator revisited: pollen dynamics in a spring-flowering herb

“…Honey bees (Apis mellifera L.), for instance, being the most common floral visitors in many anthropogenic habitats, may be efficient in pollen removal, but inefficient in pollen deposition, and thus are quoted in some cases as parasites rather than actual pollinators (Westerkamp 1991;Wilson and Thomson 1991;Buchmann and Nabhan 1996;Willmer 2011;Ollerton et al 2012). Also, the particular components of effectiveness of main floral visitors may be highly variable among years and/or sites (Ollerton 1996;Gómez and Zamora 1999;Lamborn and Ollerton 2000;Ivey et al 2003;Gibson et al 2006;Ollerton et al 2007;Davila and Wardle 2008;Lay et al 2011;Robertson and Leavitt 2011).…”