Gradients in the time seeds take to germinate could alter global patterns in predation strength

Aim: Species interactions are predicted to become stronger toward low latitudes and elevations, and these predictions have been supported in large experiments measuring daily predation rates on early life-stages. However, the overall strength and importance of predation depend on both the daily risk of being attacked and how long prey are exposed, and gradients in exposure time are rarely quantified. Here, we test whether time-to-germination, which determines seeds' exposure to post-dispersal attack, is faster in high-predation environments: low latitudes, low elevations, and warmer wetter climates.Location: Global data synthesis.Taxon: Angiosperms.Methods: We synthesized data on time-to-germination from 1410 plant species spanning 118 & DEG; latitude. We divided data by study environment (lab, greenhouse, garden, nature), as we predicted different patterns depending on whether seeds experienced only intrinsic versus intrinsic + extrinsic germination cues. We tested how mean days-to-germination varied with geography (latitude, elevation) and climate (annual mean and seasonality of temperature and precipitation). We also explored whether patterns could be explained by seed size or phylogeny, which vary latitudinally.Results: Seeds germinated faster toward higher latitudes across study environments but slower toward higher elevations when experiencing intrinsic + extrinsic germination cues (in nature). Germination was faster in drier, more seasonal and-when tested in nature-warmer environments. Seed size explained some latitudinal variation in time-to-germination, whereas accounting for phylogeny did not improve predictions. Germination was slower in natural versus lab environments.Main Conclusions: We found little evidence that seeds have commonly evolved faster germination in high-predation environments. While time-to-germination varied with geography and climate, patterns were inconsistent among predictors, and were weaker than those reported for daily seed predation rates. Detected gradients in time-to-germination would partially counter elevational gradients in daily seed predation rates but exacerbate latitudinal gradients in predation rates, such that tropical seeds likely experience much stronger lifetime predation risk than high-latitude seeds.

Automated summary

This study found that seeds germinate faster in higher latitudes, but slower in higher elevations. In drier, more seasonal, and warmer environments, germination is faster. Seed size plays a role in the variation of time-to-germination, but phylogeny does not improve predictions. Overall, time-to-germination is influenced by geography and climate, but patterns are inconsistent and weaker than daily seed predation rates.