Picture a simmering pot of vegetable broth, the condensed flavors the basis for what will become a hearty corn chowder. Looking at the recipe, you know that before the broth was introduced, onions and garlic were sautéed in olive oil until they grew translucent. Then flour was added to form the roux. And you know after the broth is added, potatoes, corn and other assorted vegetables will be left to simmer. But would you have known all of this just by seeing the list of ingredients alone? Unless you enjoy cooking regularly, you probably would not have known the sequence for preparing corn chowder just by the taste.
According to a study recently published in Science Express, biodiversity is a similar process. Some scientists go about recreating an ecosystem by adding all of the elements at once into an experiment. The results, however, usually do not replicate the original ecosystem that the researchers were trying to reproduce. Jon Chase from Washington University sought to find out why two ecosystems with the same amount of nutrients and number of organisms could have completely different outcomes. In other words, why does biodiversity vary in ecosystems that have the exact same “ingredients”? The answer, it seems, is in the order in which they are introduced.
Chase placed 45 Rubbermaid cattle tanks in a field and added pond water and soil to each. He then introduced nutrients—such as nitrogen and phosphorous—in varying amounts to create a range of productivity. Finally, he collected a number of species (specifically, “zooplankton from each of 15 ponds, 30 insects and small invertebrates such as snails, 9 vascular aquatic plants and 12 kinds of filamentous green algae,” according to a National Science Foundation press release) from nearby ponds to create a species pool.
Each year, for three years, Chase introduced a random selection of species from the species pool, but he kept track of what went where. That is, each container received the exact same number of species, just introduced randomly in three segments of time. Chase found that the low productivity mini-ponds all turned out the same in terms of biodiversity. The high productivity ponds, on the other hand, developed into several different ecosystems. It turns out, said Chase, that the sequence of introducing species to the “ponds” with high nutrient levels mattered for its subsequent biodiversity.
Chase described the process in a press release: “In our pond study we eliminated physical variations and so the beta diversity that emerged was most likely a result of priority effects.” Priority effects show that different arrival times of species could determine species dominance in an ecosystem. He continued,
“Priority effects are probably most important in productive environments such as tropical rainforests and coral reefs and less important in low productivity ones such as grasslands and intertidal habitats.”
Chase’s study suggests that the history of a particular environment—the order in which each species arrived—changes the biodiversity of that ecosystem. Just as the order of steps in a recipe matters in cooking, the history of an ecosystem seems to define its biodiversity.
This post was restored January 12, 2011 after a technical issue removed the post.