Seed demographic comparisons reveal spatial and temporal niche differentiation between native and invasive species in a community of desert winter annual plants

Question: What is the evidence for spatial and temporal niche differentiation to stabilize co-existence between invasive and native species over broad environmental conditions? Hypothesis: Two key elements for stable co-existence via environmental niche differentiation - species-specific responses to the environment and buffered population growth - are present in an invaded plant community when the seed demography of these plants is compared over time and space. Organisms: A community of invasive and native winter annual plants in the Sonoran Desert. Field site: A complex landscape in the Mohawk Valley in southwestern Arizona. Methods: We surveyed ~180 plant neighbourhood clusters and sampled the adjacent seed bank for three years over three types of habitat to obtain data on germination and seed survival. We used the data to determine both species-specific germination responses to the varying environment and buffered population growth through seed banking. We also conducted a growth-chamber experiment to assess the influence of temperature and light availability on species-specific germination responses. Conclusions: The findings supported our hypothesis. Species-specific germination responses were observed for both spatial and temporal environmental variation in the field. Germination responses were differentiated for both temperature and light in growth chambers. The native species and one of the invasive species had persistent seed banks, an outcome of low germination and high seed survival, which strengthened their buffered population growth over time. The other invasive species had a weak seed bank in two habitats but a stronger one in the third habitat, and thus relied on spatial population structure to buffer population growth.