On Friday, Matthew Leibold of the University of Texas gave a presentation at the Dartmouth Medical School on the significance of diversity in the resilience of pond ecosystems. The two studies he presented sought to illuminate three questions: (1) Does diversity affect the resistance of pond ecosystems to outside perturbations? (2) Do recurrent environmental fluctuations affect the variety of ecosystem attributes and species? (3) How do divergence and the accessibility of the pond to outside influence affect such variety?
Matthew Leibold from the University of Texas spoke on Friday. Image retrieved from http://www.biosci.utexas.edu/ib/faculty/leibold.htm
For his two experiments, Leibold used cattle tanks to create pond mesocosms. Each tank was given the essential components of a stable pond ecosystem: water, algae, zooplankton, tadpoles, snails, nutrients, and other freshwater organisms. The tanks were then aged for a period of 40 days, allowing these populations to mature and form a stable system.
For Leibold’s first experiment, the diversity of these species was varied across three groups of tanks and a control. Following the 40-day maturation period, a perturbation of acid was added to these systems, reducing the pH of the pond water to 4.5; the control tanks had salt added to them. The tanks were neutralized after 48 hours. The recovery of the pond ecosystems was then monitored for 60 days.
Leibold’s results showed that populations with greater diversity recovered more effectively than those with less diversity. However, in no set of tanks did any particular species go extinct—all survived. Even snail species, which are particularly vulnerable to acid, were able to maintain a population.
Leibold’s second experiment further investigated the findings from his first experiment. He again varied the diversity of his tanks, but this time exposed them to nitrogen and phosphorus, UV light, or acid. Members of each test group were divided into those that were exposed every week, every two weeks, or every three weeks. Controls were given salt at the same frequencies as the tested populations.
Leibold found that while initially the variety of the pond ecosystem was stable, they became asynchronous after about 60 days of harmful exposure. In other words, the attributes of the ecosystem became less varied. Nonetheless, concurrent with the results of his first experiment, Leibold, found that the individual populations of species still stabilized with time, regardless of weakened biodiversity.
Leibold admitted that his studies appear to challenge previous theories about pond ecosystems. Poor diversity while harmful does not necessarily doom a particular species.
Leibold, however, would only go to say that his research illuminated new aspects of the dynamics of pond ecosystems. Many more experiments would be needed for conclusive deductions to be made.