Starns Heath D, Weckerly Floyd W, Ricca Mark A, Duarte Adam
Department of Biology, Texas State University San Marcos, Texas, 78666.
U.S. Geological Survey, Western Ecological Research Center 800 Business Park Drive, Suite D, Dixon, California, 95620.
Ecol Evol. 2015 Jan;5(1):109-20. doi: 10.1002/ece3.1327. Epub 2014 Dec 7.
Interactions between large herbivores and their food supply are central to the study of population dynamics. We assessed temporal and spatial patterns in meadow plant biomass over a 23-year period for meadow complexes that were spatially linked to three distinct populations of Roosevelt elk (Cervus elaphus roosevelti) in northwestern California. Our objectives were to determine whether the plant community exhibited a tolerant or resistant response when elk population growth became irruptive. Plant biomass for the three meadow complexes inhabited by the elk populations was measured using Normalized Difference Vegetation Index (NDVI), which was derived from Landsat 5 Thematic Mapper imagery. Elk populations exhibited different patterns of growth through the time series, whereby one population underwent a complete four-stage irruptive growth pattern while the other two did not. Temporal changes in NDVI for the meadow complex used by the irruptive population suggested a decline in forage biomass during the end of the dry season and a temporal decline in spatial variation of NDVI at the peak of plant biomass in May. Conversely, no such patterns were detected in the meadow complexes inhabited by the nonirruptive populations. Our findings suggest that the meadow complex used by the irruptive elk population may have undergone changes in plant community composition favoring plants that were resistant to elk grazing.
大型食草动物与其食物供应之间的相互作用是种群动态研究的核心。我们评估了加利福尼亚州西北部与三个不同罗斯福马鹿（Cervus elaphus roosevelti）种群在空间上相关联的草甸复合体在23年期间草甸植物生物量的时空模式。我们的目标是确定当马鹿种群增长爆发时，植物群落是表现出耐受还是抗性反应。使用归一化植被指数（NDVI）测量了马鹿种群栖息的三个草甸复合体的植物生物量，该指数由陆地卫星5号专题制图仪图像得出。在整个时间序列中，马鹿种群呈现出不同的增长模式，其中一个种群经历了完整的四个阶段的爆发式增长模式，而其他两个种群则没有。爆发式增长种群所使用的草甸复合体的NDVI时间变化表明，旱季末期饲料生物量下降，5月植物生物量峰值时NDVI的空间变化随时间下降。相反，在非爆发式增长种群栖息的草甸复合体中未检测到此类模式。我们的研究结果表明，爆发式增长的马鹿种群所使用的草甸复合体可能经历了植物群落组成的变化，有利于那些对马鹿啃食具有抗性的植物。
