| Humans are impacting many aspects of the biological world on a scale that has rarely occurred before. One of our impacts, the loss and redistribution of species, may have serious consequences for the ecosystem services that humans depend on. In my dissertation research, I have investigated part of the relationship between biological diversity and ecosystem functioning in two experiments which directly manipulated plant diversity.; In the first experiment, I manipulated plant species diversity in greenhouse plots in order to investigate the effects of losing an "average" species as compared to losing specific species from a community. I showed that, although productivity decreased as species richness decreased on average, the effect of deleting a single, specific species from an average community ranged from a 10-fold decrease in productivity to a 5-fold increase. Effects of deleting a single, specific species from specific communities had an even wider range of effects. Thus, although it may be possible to predict the average effect of losing a species from an average ecosystem, predicting the effect of losing a certain species from a specific ecosystem will require extensive knowledge of how the species interacts with the rest of the community.; I also investigated the effect of plant diversity on community and ecosystem properties in a field experiment in which I investigated the effects of plant functional group richness and composition on primary productivity, nitrogen cycling and retention, arthropod community structure, drought resistance and resilience, and community invasibilty. For most of these properties, my work confirmed other studies that have shown that which organisms are in an ecosystem (composition) has greater influence than does how many kinds of organisms are present (richness). However, the uncommon approach of removing functional groups from an already existing ecosystem that I used in this experiment, as opposed to the more common method of constructing communities from bare ground, showed that losing species or types of species can produce unexpected results because of long-lasting transitional effects. These effects are important for understanding how the loss of species will affect ecosystem functioning while a community adjusts to its new structure. |
