A trade off in the absolute magnitudes of seed and microsite limitations and their effects on population regulation

作者：Garcia Meza Diego; Martorell Carlos^*

来源：Oikos, 2016, 125(3): 308-314.

DOI：10.1111/oik.02815

Microsite limitation (ML) occurs when the number of suitable sites for development determines population size. Seed limitation (SL) arises when seeds cannot occupy all microsites. Both limitations have been measured on relative scales, but absolute values would allow analyzing the relationship between them and their contributions to population regulation. A tradeoff is expected because small-seeded species are prolific and thus could have low SL, whereas large seeds perform better under different conditions, lowering ML. We assessed whether there is such tradeoff, and if it is mediated by seed size. We measured the absolute magnitudes of limitations through seed addition experiments, and tested whether they determine population density in 14 herbs with different seed sizes in a semiarid grassland. All species were limited by microsites and seeds. The tradeoff occurred only during germination, but was seemingly not mediated by seed size. Annual species were more limited by microsites than perennials, which suffered more SL. Population densities were smaller for species with greater ML measured over the life cycle, but marginally so when ML was measured during germination. SL only reduced annual-plant density. These negative correlations indicate that our measurements correspond to actual limitations. Microsites limited populations depending on the process analyzed (germination, survival and whole life-cycle) and the life history of species, suggesting that an integral approach to ML is required rather than focusing only on germination. Comparing annuals and perennials, we found that the strongest limitation is the main determinant of population size. The tradeoff was consistent with seed size and competition-colonization tradeoff, but our results were inconclusive. The SL-ML tradeoff seems to arise from still-unidentified evolutionary constraints, and may contribute to the maintenance of species diversity, preventing any single species from becoming dominant and excluding its neighbors.

• 出版日期2016-3