Abstract
Plant sexual systems appear to play an important role in community assembly: Dioecious species are found to tend to have a higher propensity to colonize communities in early successional stages. Here, we test two demographic hypotheses to explain this pattern in temperate forests. First, we test demographic differences between hermaphrodite and dioecious species in stressful younger successional stages: Previous theory predicts that hermaphrodite seed production is more harmed in stressful environments than that of dioecious populations leading to an advantage for females of dioecious species. Second, in primary forest, we hypothesized that dioecious species would show demographic advantage over monomorphic ones. We used data from two temperate forest plots in Northeast China surveyed over 10 years to compare the rates of growth and mortality of tree species with contrasting breeding systems in both secondary and primary forests. We assessed the effect of breeding system on the growth‐mortality trade‐off, while controlling for other traits usually considered as correlates of growth and mortality rates. We show that in the secondary forest, dioecious species showed weak advantage in demographic rates compared with monomorphic species; dioecious species showed considerably both lower relative growth and mortality rates compared to the hermaphrodites in the primary forest over 10 years, consistent with a priori predictions. Hermaphrodites showed strong growth‐mortality trade‐offs across forest stages, even when possibly confounding factors had been accounted for. These results suggest that sexual system influences community succession and assembly by acting on the rates of growth and mortality, and the trade‐off between them. As vegetation develops, the demographic differences between breeding systems are much larger. Our results demonstrate the association between breeding system, succession, and community assembly and that this relationship is succession‐stage dependent. Our findings support the suggestion that the demographic advantage of dioecious species facilitates the coexistence of sexual systems in primary forest.
Highlights
Sexual systems are key determinants of the ecological and evolutionary dynamics of plant populations (Barrett & Harder 1996; Charlesworth, 2006) and their links to the succession and assembly of plant communities have gradually become the focus of researchers recently (Queenborough et al, 2009; Sinclair, Korte, & Freeman, 2013; Réjou-Méchain & Cheptou, 2015; Bruijning et al, 2017)
We evaluated growth and mortality rates in two permanent temperate forest dynamics plots at different successional stages in Northeast China and found that demographic rates were linked with variation in breeding system
The analysis presented here revealed that sexual system was one of the key traits correlated with RGR and mortality rate across successional stages of forest (Table 2, Figures 2, Supporting Information Figure S5), which suggests that breeding system played a significant role in driving demographic rates and community dynamics
Summary
Sexual systems are key determinants of the ecological and evolutionary dynamics of plant populations (Barrett & Harder 1996; Charlesworth, 2006) and their links to the succession and assembly of plant communities have gradually become the focus of researchers recently (Queenborough et al, 2009; Sinclair, Korte, & Freeman, 2013; Réjou-Méchain & Cheptou, 2015; Bruijning et al, 2017). The dynamics of plant communities are driven by plant demographic rates (growth and mortality; Pacala et al, 1996; Rees, Condit, Crawley, Pacala, & Tilman, 2001; Silvertown, 2004) Differences in these rates between species are major determinants of ecological succession (Schneider, Ashton, Montagnini, & Milan, 2014) and stand structure (Harper, 1977; Seifert, 2014; Semwal, Nautiyal, Maikhuri, Rao, & Saxena, 2013). Under stressful conditions, hermaphrodite seed production may be more impeded than the female seed production of dioecious populations, leading to a demographic advantage of females over hermaphrodites (Ashman, 2006; Costich, 1995; Litrico, Pailler, & Thompson, 2005) This hypothesis has been often tested in gynodioecious populations (Ashman, 2006), but community-level studies are lacking: If this hypothesis is correct at the community level, we predict dioecious species should have an advantage in demographic performance (in terms of growth and survival) over monomorphic species in the earlier successional stages
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