Imagine you are hiking up a mountain, say… Mt Rainier in Washington state. It is a 10,000 foot slog from the forests at the base of the mountain to the summit crater. As you lace up your boots you admire the tall Douglas firs that dominate the forest, the pink lips of the lady slipper orchids, and the grotesquely fascinating banana slugs coasting through the litter on the forest floor. You begin to ascend and when you stop to take a breather the forest has opened up. The trees are small and stunted and huddle together amidst colorful meadows packed with blue lupine flowers and studded with bear grass. Small bees flower-hop on both sides of the trail. You continue upward and eventually the trail turns to packed snow as you step onto the snout of a glacier. Even in this white world there is life. Pink photosynthetic algae collects in depressions on the surface of the snow and is feasted upon by tiny black ice worms. Finches hop around the trail catching worms.
The birds, worms, and algae make up a community, which is just a group of things living together and interacting, much like people in a city neighborhood. And just like city neighborhoods, communities change as you move around in space. You probably already knew that the things that live at the tops of mountains are different from the things that live at the bottoms. And the forest community in Washington is quite different from the rainforest in Costa Rica. We are used to thinking on these kinds of scales.
But what if, instead of looking up at towering Douglas firs, we look down at microscopic organisms living in pools of water that collect in plants. In the tropical forests of Costa Rica there is a plant, the beehive ginger, that forms bright yellow structures reminiscent of beehives from which flowers emerge. These beehives don’t house bees but instead many small pools of water, each about a tablespoon in volume, which thousands of microorganisms call home. The pools at the top of the beehive are different from the pools at the bottom, which are more open and receive water that has flowed down from the top.
So, imagine that you are about 0.1mm tall, which is quite a bit smaller than a grain of sand. You are going scuba diving through the pools of the beehive ginger, swimming with transparent paramecium, moving aside clouds of algae, and dodging giant ravenous mosquito larvae, then climbing up the plant to higher and higher pools. What will you find? Is the beehive like a mountain?
We (Megan Blanchard of CU Boulder and Shelley Sianta of UC Santa Cruz) recently discovered that communities of microorganisms do change from the bottom to the top of beehive gingers. And the communities in the bottom pools of one beehive are more similar to the bottom pools of other beehives than they are to the top pools within their own hive. If you were to hike up another mountain in Washington you would see that the forests at lower elevations would also be dominated by Douglas firs and would remind you of the start of your hike up Mt. Rainier.
To learn more about how we explored these tiny aquatic pools (and see some of what we found there), watch this video:
So beehive gingers are like mountains, at least if you are 0.1mm tall. In the mountains, weather and temperature change dramatically from lower to higher elevations, and these are important factor for determining what lives where. In the beehives, the temperature of a bottom pool is probably not different from a top pool. But other factors like the pH of the water or the amount of decaying plant material in a pool may vary consistently from the bottoms to the tops of beehives and drive the differences in communities that we see.
It will likely take many more journeys into these tiny mountains to understand what determines who lives in each aquatic neighborhood. In the meantime, biologists are exploring communities on smaller and smaller scales and realizing that there are microscopic neighborhoods all around us.