Good years and good days: Mating synchrony at multiple temporal scales in a long-lived organism

Background/Question/Methods

The ability of individuals to successfully reproduce in small, isolated populations is a key factor in population dynamics and persistence. Reproductive failure due to isolation from potential mates is a current prospect for many long-lived, perennial plants that live in fragmented habitats. The extent to which mating effort (flowering) is synchronized influences the proximity of potential mates and the likelihood of successful mating. Mating can synchronize at distinct temporal scales, including within and among seasons. Among-season synchrony, also known as masting, has been widely studied in trees, especially those that are wind-pollinated, while little is known about the extent of masting in herbaceous perennial plants. Within-season synchrony, a consequence of flowering phenology in plants, has been studied more, yielding evidence that phenology sometimes influences reproductive success. Here we investigate mating synchrony at both of these distinct temporal scales in Echinacea angustifolia, a long-lived plant native to the grasslands of central North America. Echinacea now exists in many small, isolated remnant populations. In summer 2014 we characterized the flowering phenology (start and end dates) of over 1200 heads on 870 plants in 27 remnant prairie populations in an agricultural landscape western Minnesota. We compare fine-scale measures of synchrony of these individuals to long-term longitudinal records of annual reproduction.

Results/Conclusions

Annual mating potential, as characterized by distance from an individual to its 7th-nearest potential mate (another individual that flowered in 2014), varied from less than one meter to over 50 meters in 2014. Proximity to potential mates predicted annual reproductive success, quantified as seed set, and the effect depended on temporal synchrony as evidenced by significant temporal and spatial interaction terms in statistical models. We compare proximity to potential mates measured at an annual scale to proximity measured among years and within years. We demonstrate how measures of spatial isolation and mating potential depend on the temporal scale of resolution. Our results indicate that both proximity to and synchrony with potential mates influence reproduction in fragmented populations with likely consequences for populations dynamics and persistence.