Fluent Essays

Please read the article closely, answer the following questions: 1. What is the motivation for the study – what is the broad problem in the field that the study helps to address? 2. What is the specific hypothesis being tested? 3. What is the experimental approach to testing the hypothesis?  What was measured? 4. What were the important quantitative results? 5. Explain whether the results support or contradict the hypothesis. 6. What do the results mean in terms of the broader issues that motivated the study?Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance A. Randall Hughes* and John J. Stachowicz Section of Evolution and Ecology, One Shields Avenue, University of California, Davis, CA 95616 Edited by G. David Tilman, University of Minnesota, St. Paul, MN, and approved May 4, 2004 (received for review April 14, 2004) Motivated by recent global reductions in biodiversity, empirical and theoretical research suggests that more species-rich systems exhibit enhanced productivity, nutrient cycling, or resistance to disturbance or invasion relative to systems with fewer species. In contrast, few data are available to assess the potential ecosystem- level importance of genetic diversity within species known to play a major functional role. Using a manipulative field experiment, we show that increasing genotypic diversity in a habitat-forming species (the seagrass Zostera marina) enhances community resis- tance to disturbance by grazing geese. The time required for recovery to near predisturbance densities also decreases with increasing eelgrass genotypic diversity. However, there is no effect of diversity on resilience, measured as the rate of shoot recovery after the disturbance, suggesting that more rapid recovery in diverse plots is due solely to differences in disturbance resistance. Genotypic diversity did not affect ecosystem processes in the absence of disturbance. Thus, our results suggest that genetic diversity, like species diversity, may be most important for enhanc- ing the consistency and reliability of ecosystems by providing biological insurance against environmental change. There is growing recognition that humans are highly depen-dent on natural ecosystems for a variety of goods and services (1). Maintaining the provision of these goods and services in the face of natural and anthropogenic disturbances is critical to achieving both conservation and economic goals. Motivated by accelerating rates of worldwide decline in biodi- versity (2), considerable research has focused on the conse quences of local species loss for goods and services provided by ecosystems (2– 8). Much of this work focuses on the effects of declining species richness on short-term processes such as pro- duction, community respiration, and nutrient cycling (2). Al- though the results are far from unequivocal and subject to varying interpretation (e.g., ref. 9), it does appear that, in some systems, reductions in local species diversity contribute to a decline in ecosystem properties such as productivity and resis- tance to disturbance (see review in ref. 2). Nevertheless, many important ecosystems, such as kelp forests, cattail marshes, and fir forests, are dominated by, and dependent on, one or a few key plant species (10). Furthermore, individual predator and herbivore species often play a disproportionate role in determining ecosystem processes, overwhelming any effect of spe- cies diversity (11). Dominant, numerically abundant speci