Fahnestock Jace T, Detling James K
Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado, 80523, USA.
Department of Biology, Colorado State University, Fort Collins, Colorado, 80523, USA.
Oecologia. 2002 Jun;132(1):86-95. doi: 10.1007/s00442-002-0930-8. Epub 2002 Jun 1.
Both bison and prairie dogs have multiple and dramatic effects on grassland landscapes and both are considered by many to be keystone herbivores. Numerous studies have documented their independent or combined impact on grassland ecosystem processes, but there have been few attempts to simultaneously assess the individual and interactive effects of bison and prairie dogs where they co-occur. We began a long-term study in late 1994 in Badlands National Park, South Dakota, USA, to evaluate the ecological consequences of the presence or exclusion of prairie dogs, bison, or both, upon various aspects of plant community dynamics and N cycling. Five different treatments were established at three separate mixed-grass prairie sites in the park: (1) off the prairie dog colony with bison excluded, (2) off colony with continued bison utilization, (3) on colony with bison excluded but continued prairie dog use, (4) on colony with utilization by prairie dogs and bison, and (5) on colony with both excluded. There were few differences in aboveground biomass or plant species composition between the two off-colony treatments or among the three on-colony treatments, even after 3 years of treatment imposition. However, aboveground biomass was >2 times greater in off-colony sites than on-colony sites, primarily due to the near elimination of grasses on prairie dog colonies. Off-colony sites were dominated by a few grass species, resulting in lower plant species diversity, while on-colony sites were dominated by several forb species. Net N mineralization early in the growing season was 4 times greater on prairie dog colonies than at off-colony sites, but all sites exhibited net immobilization by the latter half of the growing season. The results of this study indicate distinct differences in several ecosystem properties between on- and off-colony treatments. Whether these patterns represent relatively stable alternate states or whether distinct changes will emerge in the different herbivore treatments after several additional years is of considerable interest.
野牛和草原犬鼠对草原景观都有多重显著影响，许多人都认为它们是关键食草动物。大量研究记录了它们对草原生态系统过程的独立或综合影响，但很少有人尝试同时评估野牛和草原犬鼠在共生区域的个体影响和交互作用。1994年末，我们在美国南达科他州的恶地国家公园开展了一项长期研究，以评估草原犬鼠、野牛或两者的存在或缺失对植物群落动态和氮循环各个方面的生态影响。在公园内三个不同的混合草原地点设置了五种不同的处理方式：（1）草原犬鼠群落外且排除野牛，（2）群落外且野牛持续存在，（3）群落内且排除野牛但草原犬鼠持续活动，（4）群落内且草原犬鼠和野牛都存在，（5）群落内且两者都排除。即使在施加处理三年后，两种群落外处理方式之间或三种群落内处理方式之间，地上生物量或植物物种组成的差异都很小。然而，群落外地点的地上生物量比群落内地点大两倍多，主要原因是草原犬鼠群落上的草几乎被吃光。群落外地点以少数几种草类为主，导致植物物种多样性较低，而群落内地点则以几种草本植物为主。生长季节早期，草原犬鼠群落的净氮矿化量比群落外地点高四倍，但到生长季节后半期，所有地点都表现为净固定。本研究结果表明，群落内和群落外处理方式在几个生态系统属性上存在明显差异。这些模式是代表相对稳定的替代状态，还是在再过几年后不同食草动物处理方式中会出现明显变化，这是一个相当有趣的问题。
