Consequences of herbivore extinction for plant population and community dynamics

点击翻译按钮获取中文摘要

Human activities are causing extinctions to occur at unprecedented rates. Although we often possess detailed knowledge about their causes, a dearth of information exists regarding the consequences of extinction for ecological systems. My research group and I work to understand how extinctions of large herbivores affect plant populations in African savannas. Our study sites in Laikipia, Kenya comprise an ideal system in which to study the ramifications of such extinctions. Laikipia consists of a 10,000 square km mosaic of private properties, where each property is associated with one of three scenarios reflecting the progressive, size-biased extinction typical of vertebrate communities: 1) elephant (~3000 kg) + impala (~70 kg) + dik-dik (~5 kg); 2) impala + dik-dik; or 3) dik-dik only. Using a series of semi-permeable, electrified fences, my research group and I are simulating the above extinction scenarios to address how large mammalian herbivores influence the abundance and distribution of Acacia trees, critical determinants of savanna fire frequency, nutrient cycles, and biodiversity. Specifically, we are working to answer the following questions: 1) How do extinctions of large mammalian herbivores change pollination of savanna trees?; 2) How do impacts of large mammalian herbivores on seed production, germination, and recruitment of savanna trees influence population growth of trees?; and 3) How important are large mammalian herbivores in driving population growth of trees, relative to variation in abiotic factors (e.g., rainfall)? To address the first two questions, my research group and I are combining field experiments with spatial statistics and matrix models. To address the third question, we are "ground truthing" projections from our matrix models across a five-fold gradient in rainfall in central Kenya. Thus, my research group and I will shed light on understanding the ramifications of extinctions for ecosystems. Moreover, through a combination of field experiments, long-term observations, and statistical modeling, we will develop and refine tools that predict the consequences of extinction for plant populations and communities.