How Evolutionary History Shapes Ecosystem Resilience
The key to successful prairie restoration may lie not in the number of species planted, but in their evolutionary relationships.
Imagine planting a prairie from scratch. You carefully select a mix of native species, expecting them to grow into a resilient, self-sustaining ecosystem. Years later, something is missing. The restoration looks lush but lacks the stability and diversity of natural prairies. For decades, scientists have struggled to understand why restorations often fall short, even when species richness appears adequate.
Recent research has uncovered a crucial missing piece: phylogenetic diversity—the measure of how broadly species are drawn from across the evolutionary "Tree of Life." This revolutionary concept suggests that the evolutionary relationships between planted species may be just as important as the number of species introduced.
In the simplest terms, phylogenetic diversity measures the breadth of evolutionary history represented in a community. Think of it as a family tree for all the plants in a prairie. A phylogenetically diverse community contains species from many different branches of this tree, while a less diverse community contains closely related species, much like a family reunion attended only by immediate cousins.
Because species that have evolved separately for millions of years tend to develop different traits and strategies for survival. They may respond differently to drought, resist various diseases, or support distinct soil microorganisms. When environmental conditions change—as they increasingly do in our climate crisis—a phylogenetically diverse community has better odds that at least some species possess traits needed to withstand new challenges 2 .
This concept represents a significant shift from traditional restoration approaches, which have primarily focused on species richness (the number of different species) without considering their evolutionary relationships. The emerging science suggests this may be like stocking a toolbox with multiple screwdrivers but no hammer or wrench—plenty of items but limited functional diversity.
To test whether phylogenetic diversity could improve restoration outcomes, a collaborative team of scientists from the Chicago Botanic Garden, The Morton Arboretum, and several universities launched an ambitious, NSF-funded experiment in 2014 1 2 5 .
The researchers established nearly 400 experimental plots, each measuring 2×2 meters, where they carefully manipulated the phylogenetic diversity and functional-trait diversity of planted species 5 . This experimental design allowed them to isolate the effects of evolutionary relationships from other factors.
Researchers assigned each plot a specific mix of plant species, varying both the evolutionary distances between species and the diversity of their functional traits 5 .
For five years, the team tracked key indicators of restoration success, including resistance to invasion by non-native species, primary productivity (biomass production), maintenance of species diversity over time, and effects on soil properties 5 .
The scale and duration of this experiment provided unprecedented insights into how evolutionary relationships influence the development of restored ecosystems.
The findings challenged many long-held assumptions in restoration ecology:
Contrary to expectations, higher phylogenetic diversity did not consistently preserve species diversity or boost productivity 5 . Instead, all plots tended to settle toward similar species diversity by the third year, with productivity driven more by the most productive species than by diversity itself.
The most significant effect emerged in community dynamics over time. Plots with greater phylogenetic diversity changed more rapidly because they contained representatives from across the plant tree of life, providing more opportunities for species with competitive advantages to emerge based on site conditions 5 .
Perhaps the most encouraging finding for practical restoration was that plots established from seed maintained phylogenetic diversity as effectively as those planted with more expensive young plants (plugs) 5 . This suggests that restoration practitioners can achieve evolutionary diversity goals while containing costs.
The study also revealed a complex relationship with invasion resistance. Higher diversity plots appeared somewhat more susceptible to invasion by unplanted species, though planting species with dominant traits, particularly from the aster family (Asteraceae), helped resist invasion 5 .
| Research Question | Expected Outcome | Actual Finding |
|---|---|---|
| Does phylogenetic diversity preserve species richness? | Higher diversity would maintain more species | All plots settled to similar richness by year 3 |
| Does phylogenetic diversity boost productivity? | More diverse plots would produce more biomass | Productivity depended on dominant species, not diversity |
| How does diversity affect community change? | Unknown | Higher diversity plots changed more rapidly over time |
| Seed vs. plug establishment | Plugs might better maintain diversity | Seeds performed equally well at lower cost |
Another fascinating piece of the phylogenetic diversity puzzle comes from research on rare species. For years, ecologists hypothesized that rare species persist in communities because they occupy distinct evolutionary niches, making them functionally different from their more common relatives.
A 2022 study examining 21 plant communities across the Prairie Coteau ecoregion delivered a surprising contradiction to this theory 4 6 9 . The research found that rare species in tallgrass prairies do not contribute higher levels of phylogenetic diversity than common species. Instead, they tend to be closely related to both common species and other rare species 4 .
This discovery suggests high functional redundancy between rare and common species—a potentially promising finding for ecosystem resilience. If rare species were to disappear, their evolutionary and functional roles would likely be filled by their more common relatives 4 . However, this insurance policy only works if enough species remain in the system overall.
| Characteristic | Niche Differentiation Theory Prediction | Actual Observation in Tallgrass Prairies |
|---|---|---|
| Evolutionary distinctiveness | Rare species evolutionarily distinct | Rare species closely related to common species |
| Functional role | Unique ecological functions | High functional redundancy with common species |
| Contribution to phylogenetic diversity | Higher than common species | Similar to common species |
| Response to environmental change | Differential responses | Similar responses within evolutionary lineages |
Further evidence of the importance of evolutionary patterns comes from research on endangered and threatened grass species in Illinois. Using advanced DNA sequencing techniques, scientists analyzed complete plastid genomes from herbarium specimens to reconstruct evolutionary relationships with remarkable precision 8 .
The findings revealed that endangered and threatened grass species show significant phylogenetic clustering—they are more closely related to each other than would be expected by chance 8 . This pattern suggests that certain evolutionary lineages may be particularly vulnerable to the threats that have decimated tallgrass prairies, primarily habitat loss due to agriculture and development.
This clustering has important implications for conservation: the loss of these species would not represent random biodiversity loss but would disproportionately affect certain branches of the grass evolutionary tree . Protecting these species means preserving unique evolutionary history that could be crucial for future ecosystem resilience.
| Community Type | Phylogenetic Pattern | Conservation Implication |
|---|---|---|
| Remnant prairies | Higher phylogenetic diversity | Reference targets for restoration |
| Restored prairies | Reduced phylogenetic diversity | May lack resilience of natural prairies |
| Rare species assemblages | Phylogenetically clustered | Functional redundancy provides resilience |
| Endangered grasses | Phylogenetically clustered | Vulnerable lineages require targeted protection |
The growing understanding of phylogenetic diversity represents a paradigm shift in restoration ecology. We're moving beyond simply counting species to considering the deep evolutionary relationships that shape how species interact and function within ecosystems.
Designing phylogenetically diverse seed mixes appears to be a promising strategy for creating restorations that can adapt to changing conditions 7 .
The finding that seeds perform as well as plugs for maintaining phylogenetic diversity makes this approach more financially feasible 5 .
Identifying evolutionary lineages missing from restorations allows for targeted introductions to fill phylogenetic gaps 7 .
Perhaps most importantly, this research highlights the incredible value of remnant prairies. These ecosystems, with their higher phylogenetic diversity developed over millennia, serve not only as conservation targets but as living libraries of evolutionary history that can guide our restoration efforts 7 .
As we face the interconnected challenges of climate change and biodiversity loss, understanding the deep evolutionary relationships within ecosystems may prove crucial to building resilient landscapes capable of weathering an uncertain future.
The research continues, with scientists now investigating how plant roots influence soil microbial communities—another layer of the complex puzzle of ecosystem function and resilience 5 .