Dispersal and Germination Patterns of Monterey Spineflower at Fort Ord Natural Reserve.

Abstract:

Some species are rare because they are restricted to certain habitats and/or have small population sizes. Monterey spineflower, a federally listed threatened annual plant, is found in open sandy regions of the California coast, in chaparral vegetation around the Monterey Bay. A model based on previous research suggests that the Monterey spineflower population at Fort Ord Natural Reserve should be rapidly increasing, but it is not. This suggests that the model may be using data that overestimates the percentage of spineflower seeds that successfully germinate. I tested three hypotheses to determine the cause of the difference in population sizes between the predicted model and the field results. First, I predicted that the spineflower seeds are blown by the wind into shrubs such as manzanita, and are unable to germinate due to the lack of a suitable environment. I tested this in two ways. A field experiment showed that seeds are easily blow by wind. Next, I took soil cores and found spineflower seeds within the manzanita shrubs. Secondly, I predicted that the germination rate used by the model (90%) was too high. However, my germination experiments did not support this hypothesis because 91% of new seeds successfully germinated. Lastly, I predicted that the newer seeds are more viable than older seeds and therefore have a higher chance of successfully germinating. After germinating seeds in a controlled environment I observed that the seeds from 2014 had a higher number of successfully germinated seeds compared to the number of successfully germinated seeds from 1995 (91% vs 33%). I conclude that the loss of seeds due to wind decreases germination expectancies and older seeds are less viable than new seeds. Therefore, Monterey spineflower is a rare plant because environmental barriers hinder seeds from dispersing to a suitable habitat and successfully germinating while seeds lose viability as they age.