Scientists set up 45 artificial ponds near St. Louis and studied them for 7 years; even when ponds got the same species, the order they arrived changed the outcome

Imagine forty-five plastic cattle tanks, all sitting out in a field outside St. Louis and all filled with the same water, mud, and then eventually a roughly equal combination of a hundred species of plants, insects, algae, and micro animals. You’d expect them to all create similar miniature ponds, but according to a 2010 study titled “Stochastic Community Assembly Causes Higher Biodiversity in More Productive Environments,” published in the journal Science by ecologist Jonathan Chase from Washington University in St. Louis, the order in which species arrived was enough on its own to send otherwise identical ecosystems down different paths. For a generation constantly switching careers, raised on the saying "it’s never too late to start again," or moving across the country and building new personal brands, this shows that, in some situations, timing is everything.

A soup of 100 species, 45 tanks, seven summers

The investigation began in 2002 and involved filling 300-gallon tanks with well water and adding low, medium, or high nutrients. Over three years, students added a third of the species to each tank in a random order, so each tank received the same species but in a different order. The remaining species (dragonflies, snails, zooplankton, and algae) were allowed to colonise naturally. Students then continued monitoring species counts across the following summers, extending the study to a full seven years of data by the time it concluded; the “seven years” in the headline refers to this complete span, not just the three-year planting phase

Interestingly, in the low nutrient tanks it did not matter what order the species were added; they all created relatively similar communities. However, in the high nutrient tanks, the order in which the species arrived made a difference. Tadashi Fukami’s widely cited 2015 research article titled “Historical Contingency in Community Assembly: Integrating Niches, Species Pools, and Priority Effects,” published in the journal Annual Review of Ecology, Evolution, and Systematics, found that some species can become dominant due to a high growth rate if they arrive before others; this is known as a ‘priority effect’. Priority effects can create very different stable communities.

Why restoration ecologists should be concerned

This isn’t just interesting information for dragonfly lovers. It means that when trying to restore degraded ecosystems, such as wetlands and coral reefs, we can’t rely on the idea known as the "myth of the carbon copy." This idea suggests that if you damage an ecosystem and remove the pressure, nature will predictably restore itself.

Chase’s findings suggest this assumption often breaks down in resource-rich environments, where history (who showed up first) shapes the outcome more than the species pool itself. But that doesn’t contradict the pattern in the low-nutrient tanks; it clarifies it. Priority effects need slack to operate: a tank has to be rich enough that an early arrival can actually crowd out a later one. Strip that slack away, through scarcity or stress, and the field narrows to whichever few species can tolerate the conditions at all, regardless of when they turned up. That’s the mechanism a separate 2007 PNAS study by Chase, “Drought Mediates the Importance of Stochastic Community Assembly” points to: drought erases the “historical” advantage of early arrivals by filtering the pool down to drought-tolerant survivors, pushing ponds back toward uniformity.

Why should this matter to us?

It’s worth being cautious about stretching a pond study too far; ecosystems aren’t people, and zooplankton don’t carry student debt. Still, the underlying idea travels: in high-pressure, resource-rich situations, what arrives first can shape everything that follows, which is a useful check on the assumption that a good setup will sort itself out over time regardless of sequence. Overall, the study argued that order, not just presence, deserves more weight in how we think about ecological outcomes.