Reproductive traits of two closely related species-pairs on adjacent, different soil types in South African Fynbos

Abstract

High levels of edaphic endemism and soil-related beta-diversity in Agulhas Plain fynbos communities suggest that reproductive traits of plants growing on different fynbos soils would be related to differences in soil regime. We investigated reproductive traits in two closely related Proteaceae species-pairs growing on adjacent soil types: Protea obtusifolia and Leucadendron meridianum occurring in shallow pockets of limestone-derived soils, and P. susannae and L. coniferum on the adjacent, uniformly deep colluvial sands.We found that species growing on the limestone soil comprised smaller plants, with fewer cones and seeds per plant, than species on the colluvial sands. These differences suggest that the small soil pockets of limestone soil limit plant size, in turn limiting the number of reproductive structures. Annual variation in cones and seed was the same in all species. There were no consistent trends in degree of serotiny, or sex allocation across soil types. The higher cone and seed predation levels of both limestone species than the colluvial sands species were ascribed to the higher plant densities of the former leading to lower insect search times. It was concluded that there were no overall patterns in reproductive traits that could be ascribed to differences in soil regime, other than through size-related effects. Fire regime is likely to have played a more important role in determining reproductive traits.

Root of edaphically controlled Proteaceae turnover on the Agulhas Plain, South Africa: phosphate uptake regulation and growth

“…Edaphic endemism of Proteaceae on the Agulhas Plain is generally considered absolute; for example, Protea obtusifolia and Leucadendron meridianum are restricted to limestone‐derived soils, and rarely mix with Protea compacta , which occurs in close juxtaposition on colluvial sands (Esler et al. 1989; Newton, Cowling & Lewis 1991; Mustart & Cowling 1993; Mustart, Cowling & Dunne 1994). There are several studies of species from these adjacent but contrasting habitats showing significant differences in above‐ground traits, such as seedling establishment, seed germination, seed size and seed nutrient content (Table 2), but those data do not fully explain the lack of overlap between species distributions (Thwaites & Cowling 1988; Esler et al.…”

Equality between the sexes in plants for costs of reproduction; evidence from the dioecious Cape genusLeucadendron(Proteaceae)

“…Also, the spread of such an aggressive male genotype would in any event eventually be terminated by the strong decline in females (leading to 1:3 sex ratio) and the necessary evolution of compensatory female biased sex ratios of seeds (> 2:1), in contradiction of the evolutionary stable 1:1 sex ratio strategy for most dioecious organisms and the ratio expected and found in Leucadendron . Barrett et al (2010) documented 1:1 sex ratios in mature mesic Leucadendron stands and analysis of the data of Mustart et al (1994) indicates no difference in sex ratio from 1:1. Given the argument above that competitive interactions between the sexes are highly likely in fynbos, this sex ratio equality implies competitive symmetry across the sexes.…”

“…Dioecious females achieve higher seedling recruitment in part by having higher seed set and thus seed production than hermaphrodites. For example, seed set (from Mustart et al 1994) in co-occurring Protea obtusifolia (19.5%) is lower than in female L. meridianum (54.7%) as is P. susannae (12.7%) compared to co-occurring L. coniferum (87.1%).…”

“…This back-and-forward scenario from females after every fire is very unlikely. Finally, the data available suggest no habitat specialisation; males and females co-occur equally and at a very fine scale (such as in 5 × 5 m plots in Barrett et al 2010 and 10 × 10 m plots in Mustart et al 1994).…”

“…Numbers of seeds stored in individual serotinous adult Leucadendron canopies can be large (e.g. > 24 000 per female in L. coniferum and > 2500 in L. meridianum in Mustart et al 1994). Since fynbos Proteaceae often occur in mesic areas, dense stands of seedlings typically arise after fire in mature stands.…”