Pollinators, mates and Allee effects: the importance of self‐pollination for fecundity in an invasive lily

Abstract

Summary1. Ability to self-fertilize is correlated with invasiveness in several introduced floras, and this has been attributed to its mitigating effect on fecundity when pollinator visitation and mate availability are inadequate. Cross-pollination opportunities are expected to be most limited in isolated individuals and small populations, both typical of the leading edge of an invasion. Thus, self-pollination may promote invasion in part by mitigating pollen-limitation Allee effects. 2. We used emasculation and pollen supplementation experiments to test whether the importance of self-pollination for fecundity increased as plant abundance decreased and isolation increased, in the hawkmoth-pollinated and autonomously self-pollinating invasive lily Lilium formosanum, in its introduced range in KwaZulu-Natal, South Africa. As inbreeding depression is negligible in these populations, seed production through selfing is likely to be demographically important. 3. In naturalized populations of L. formosanum, varying in size and degree of isolation, emasculation reduced seed production by two-thirds, indicating strong reliance on self-fertilization for fecundity due to inadequate pollinator visitation. However, this was not related to population size and was only greater for more isolated populations in one of the 3 years in which the experiment was carried out. Pollen supplementation experiments showed that pollen limitation was low -12% on average -and significant in only one of 3 years, demonstrating that autonomous self-pollination was highly effective. 4. In artificial arrays, consisting of plants placed inside naturalized populations or in pairs isolated (3-702 m) from populations, the effect of emasculation on fecundity was greater in isolated plants than those inside the population in one of two populations. Isolation reduced fecundity when emasculated plants were placed next to a second emasculated plant, but not when emasculated plants were partnered with an intact plant, from which they could receive pollen. 5. We conclude that self-fertilization in L. formosanum compensates for inadequate pollinator visitation across all levels of population size and for a pollen-limitation Allee effect due to decreased mate availability in isolated plants, and may thus play an important role in invasion.

Selfing ability and dispersal are positively related, but not affected by range position: a multispecies study on southernAfricanAsteraceae

“…Rambuda & Johnson, 2004;Van Kleunen et al, 2008). Self-fertilization also alleviates the effects of inadequate pollinator and mate availability on fecundity during invasion (Davis et al, 2004;Van Kleunen et al, 2007;Rodger et al, 2013). Even in native plants, recently established populations may be more outcross-pollen limited than well-established populations (e.g.…”

Relative ranges of mating and dispersal modulate Allee thresholds in sessile species

“…Isolated individuals remain likely to suffer from reproductive costs through pollen limitation, and may compensate through self-fertilisation (e.g. Rodger et al, 2013). Plants which are unable to do so are likely to be particularly vulner- Spatial patterns formed by trees are contingent on their mechanism of seed dispersal (Seidler and Plotkin, 2006); similar impacts may arise through pollination and drive both the spatial patterns of populations and the density at 335 which they are able to maintain themselves.…”

Plantas, polinizadores e algumas articulações da biologia da polinização com a teoria ecológica

“…Dessa forma, o efeito deve ser visto como o saldo líquido dos efeitos positivos e negativos da densidade no valor adaptativo total. Um teste do efeito Allee relacionado com a biologia da polinização de plantas foi feito com a planta invasora, Lilium formosanum, que se reproduz tanto pela polinização por mariposas quanto por autogamia (Rodger et al 2013). Através de emasculação e suplementação de pólen, os autores demonstraram que a importância da autogamia aumenta com a diminuição do tamanho populacional e aumento do isolamento.…”