Competition for pollination and isolation from mates differentially impact four stages of pollination in a model grassland perennial

Abstract

1. Species that persist in small populations isolated by habitat destruction may experience reproductive failure. Self-incompatible plants face dual threats of matelimitation and competition with co-flowering plants for pollination services. Such competition may lower pollinator visitation, increase heterospecific pollen transfer and reduce the likelihood that a visit results in successful pollination. 2. To understand how isolation from mates and competition with co-flowering species contribute to reproductive failure in fragmented habitat, we conducted an observational study of a tallgrass prairie perennial Echinacea angustifolia. We quantified the isolation of focal individuals from mates, characterized species richness and counted inflorescences within 1 m radius, observed pollinator visitation, collected pollinators, quantified pollen loads on pollinators and on Echinacea stigmas, and measured pollination success. Throughout the season, we sampled 223 focal plants across 10 remnant prairie sites. 3. We present evidence that both co-flowering species and isolation from mates substantially limit reproduction in Echinacea. As the flowering season progressed, the probability of pollinator visitation to focal plants decreased and evidence for pollen-limited reproduction increased. Pollinators were most likely to visit Echinacea plants from low-richness floral neighbourhoods with close potential mates, or plants from high-richness neighbourhoods with distant potential mates. Frequent visitation only increased pollination success in the former case, likely because Echinacea in high-richness floral neighbourhoods received low-quality visits. 4. Synthesis. In Echinacea, reproduction was limited by isolation from potential mates and the richness of co-flowering species. These aspects of the floral neighbourhood influenced pollinator visitation and pollination success, although conditions that predicted high visitation did not always lead to high pollination success. These | 1357

Fire influences reproductive outcomes by modifying flowering phenology and mate‐availability

“…speciosa , which had a neutral relationship between flowering synchrony and seed set. Competition for pollination in these populations may also influence the relationship between individual within‐year flowering synchrony and reproductive success (Richardson et al ., 2021). Seed set probably reflects pollination rather than resource availability in L .…”

“…Second, small or isolated populations, which are common in fragmented habitat, are more likely to experience mate‐finding Allee effects (Davis et al ., 2004; Wagenius et al ., 2007). Third, when individuals of a given species flower infrequently, such that only a fraction of adult plants flower in any given year, they are vulnerable to reduced reproductive success (Waananen et al ., 2018), despite pollinator visitation (Wagenius & Lyon, 2010; Richardson et al ., 2021). Many prairie perennials flower infrequently, are self‐incompatible, and persist in fragmented habitat, making them vulnerable to mate‐finding Allee effects.…”

Extensive pollinator sharing does not promote character displacement in two orchid congeners

“…The presence of co‐flowering species has been found to decrease the pollination success of focal species in several systems (Caruso 1999; Landry 2013; Richardson et al. 2021), but some studies have shown the opposite trend (i.e., facilitation) in other species pairs (Moeller 2004; Tur et al. 2016; Bergamo et al.…”

“…This result suggests that despite extensive pollinator sharing, the presence of G. densiflora does not increase competition for pollinator visits in G. conopsea (and vice versa). The presence of co-flowering species has been found to decrease the pollination success of focal species in several systems (Caruso 1999;Landry 2013;Richardson et al 2021), but some studies have shown the opposite trend (i.e., facilitation) in other species pairs (Moeller 2004;Tur et al 2016;Bergamo et al 2020). Moreover, the sign of pollinator-mediated interactions between plant species may be context dependent.…”

A meta‐analysis of single visit pollination effectiveness comparing honeybees and other floral visitors

“…Over 70% of plants depend to some degree on animal pollinators to successfully reproduce (Ollerton et al, 2011). Among the diversity of pollinators, taxa vary in their contributions to pollination in multiple intricate dimensions, some quantitative (e.g., numbers of visits, numbers of pollen grains transferred: Herrera, 1987; King et al, 2013), others qualitative (e.g., proportion selfed vs. outcrossed pollen, diversity of mates, spatial distances of mating: Valverde et al, 2019; Richardson et al, 2021). At its core, the functional contributions of different pollinator taxa can be measured by the quantity (frequency) and quality (effectiveness) of visits to plant reproductive success (Inouye et al, 1994; King et al, 2013).…”