Effects of Herbivores on Seed Banks of Grass and Shrublands at the Sevilleta National Wildlife Refuge, New Mexico (2004)

Grazers and granivores have the potential to affect seed banks. Several studies have examined the impact of these herbivores on the aboveground vegetation, but few have looked at how they influence the seed bank. I asked whether both grazers and granivores alter the seed bank at the Sevilleta National Wildlife Refuge. Long-term experimental plots were installed in 1996 to exclude grazers and granivores from a grassland and shrubland. Soil samples were collected from these plots and seeds were germinated in a greenhouse. The grassland had significantly more species in its seed bank than the shrubland. Also, the seed bank composition differed significantly between the two sites. However, the number of species in the seed bank did not vary among herbivore treatments nor did total seed numbers vary among treatments at the grassland. At the shrubland, in contrast, plots that excluded both herbivores had fewer total seeds than control plots and plots where only grazers were excluded. Therefore, although herbivores play some role in the shrubland, herbivores do not reduce seed numbers at either site. Thus, seed bank size is not controlled by the consumption of seeds from these herbivores, but by some other factor (e.g. disturbance or abiotic events).植食动物与种子捕食者均可对土壤种子库产生潜在影响。现有多项研究已探讨此类草食动物对地上植被的影响，但针对其如何作用于土壤种子库的相关研究仍较为匮乏。本研究旨在探究：在塞维利塔国家野生动物保护区（Sevilleta National Wildlife Refuge）内，植食动物与种子捕食者是否均会改变当地的土壤种子库。研究团队于1996年在草原与灌丛生境中设立长期实验样地，设置多组处理以分别排除植食动物、种子捕食者或同时排除二者。研究人员从上述样地采集土壤样本，并在温室中开展种子萌发实验。结果显示，草原生境的土壤种子库物种丰富度显著高于灌丛生境；同时，两处生境的土壤种子库群落组成亦存在显著差异。但在草原生境中，不同草食动物处理组间的种子库物种丰富度并无显著差异，总种子量亦未出现明显变化。与之相对，灌丛生境中同时排除两类草食动物的样地总种子量显著低于对照组与仅排除植食动物的样地。由此可见，尽管草食动物在灌丛生境中发挥了一定作用，但两类生境中草食动物均未导致种子总量减少。因此，土壤种子库的规模并非由此类草食动物的种子取食所调控，而是受其他因素（如干扰事件或非生物胁迫）影响。