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

1. Species that persist in small populations isolated by habitat
destruction may experience reproductive failure. Self-incompatible plants
face dual threats of mate-limitation 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 1m 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. 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
results reveal how habitat modification and destruction, which influence
floral neighbourhood and isolation from conspecific mates, can
differentially affect various stages of reproductive biology in
self-incompatible plants. Our results suggest that prairie conservation
and restoration efforts that promote patches of greater floral diversity
may improve reproductive outcomes in fragmented habitats.

1. 因栖息地破坏而形成隔离的小种群存续物种，可能会遭遇生殖失败。自交不亲和（self-incompatible）植物面临双重生存威胁：一是配偶限制，二是与同花期植物竞争传粉服务。这类竞争会降低传粉者访花频率、增加异种花粉传递概率，并降低单次访花成功完成传粉的可能性。
2. 为探究栖息地片段化情境下，配偶隔离与同花期物种竞争如何共同导致生殖失败，我们针对高草草原多年生植物狭叶松果菊（Echinacea angustifolia）开展了一项观测研究。我们量化了目标个体与其配偶的隔离程度，对1米半径范围内的物种丰富度进行表征并统计花序数量，记录传粉者访花行为、采集传粉者样本，定量测定传粉者及狭叶松果菊柱头上的花粉负载量，并评估传粉成功率。整个开花季期间，我们共采样了223株目标植株。
3. 本研究证实，同花期物种竞争与配偶隔离均会显著限制狭叶松果菊的生殖过程。随着开花季推进，目标植株的传粉者访花概率逐渐降低，花粉限制生殖的相关证据愈发充分。传粉者更倾向于访问两类狭叶松果菊植株：一类是生长在物种丰富度较低且潜在配偶距离较近的花域邻区的植株，另一类是生长在物种丰富度较高但潜在配偶距离较远的花域邻区的植株。仅在前一类情境下，频繁访花才能提升传粉成功率，这可能是因为生长在高丰富度花域邻区的狭叶松果菊，其接收到的访花质量较低。
4. 研究总结：狭叶松果菊的生殖过程同时受潜在配偶隔离与同花期物种丰富度的限制。花域邻区的这两项特征会影响传粉者访花行为与传粉成功率，尽管预示高访花频率的环境条件，未必总能带来更高的传粉成功率。本研究结果揭示了栖息地改造与破坏，如何通过改变花域邻区特征及同种配偶隔离程度，对自交不亲和植物生殖生物学的不同阶段产生差异化影响。我们的研究结果表明，通过促进斑块内花卉多样性提升的草原保护与修复举措，或可改善片段化栖息地中植物的生殖表现。