Abstract
1 Environmental fluctuations can hypothetically promote greater species diversity, but this has rarely been experimentally tested in plant communities. We predicted that high temporal variability in soil moisture would promote high diversity in a community of recruiting seedlings. Using a glasshouse experiment designed to imitate field conditions in species-rich limestone pavement habitats, we examined the effects of temporal variability and total quantity of water provided on seedling species richness, evenness and composition within a single growing season. 2 Temporal variability was altered by varying the frequency at which water was added while keeping the total quantity of water constant. Low temporal variability was created by high frequencies of water addition. High variability was associated with more extreme fluctuations between droughted and flooded conditions. Each of three variability treatments was carried out using three total quantities of water added to create a gradient in total soil water availability. 3 Species richness was greatest in higher quantity and lower variability treatments. Higher total quantities of water added buffered the negative effects of higher temporal variability, and lower temporal variability buffered the negative effects of lower quantity. Species richness was negatively correlated with temporal variability in soil moisture content both in the glasshouse and in a field study. Evenness was negatively correlated with richness. Low richness, high evenness communities had low densities and were prone to extinction. Thus, neither richness nor evenness was maintained by higher temporal variabilities within a growing season. 4 Lower species richness under more temporally variable conditions was attributable to both random extinctions due to reductions in total community density and species-specific differences in mortality. Final species relative abundances differed between water treatments, but there were no separate effects of variability in soil moisture content or total quantity of water added. Upland species were more abundant in treatments where drought was more prevalent, either due to low total quantities of water or high temporal variability in soil moisture. Spatial heterogeneity in moisture supply, or interannual fluctuations between dry and wet years, may thus contribute to coexistence of drought-tolerant and flood-tolerant species in the field.
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Claims 11
Claim · model-written summary
Species richness was greatest with more water and lower temporal variability.
- Taxon
- seedlingt0
- Treatment
- higher quantity and lower variability treatmentse0
- Outcome
- Species richnesse0
- Direction
- greateste0
Not reportedComparator
Verbatim
e0“Species richness was greatest in higher quantity and lower variability treatments.”
t0“seedling”
Claim · model-written summary
Higher water quantity buffered the negative richness effect of temporal variability.
Verbatim
e0“Higher total quantities of water added buffered the negative effects of higher temporal variability”
t0“seedling”
Claim · model-written summary
Lower temporal variability buffered the negative effect of lower water quantity.
Verbatim
e0“lower temporal variability buffered the negative effects of lower quantity”
t0“seedling”
Claim · model-written summary
Richness declined as temporal variability of soil moisture rose in glasshouse and field studies.
Verbatim
e0“Species richness was negatively correlated with temporal variability in soil moisture content both in the glasshouse and in a field study”
t0“seedling”
Claim · model-written summary
Evenness was negatively correlated with richness.
Verbatim
e0“Evenness was negatively correlated with richness”
t0“seedling”
Claim · model-written summary
Low-richness, high-evenness communities had low densities and were prone to extinction.
Verbatim
e0“Low richness, high evenness communities had low densities and were prone to extinction”
t0“seedling”
Claim · model-written summary
Lower richness under greater temporal variability was attributed to random extinction from lower community density.
Verbatim
e0“Lower species richness under more temporally variable conditions was attributable to both random extinctions due to reductions in total community density and species-specific differences in mortality”
t0“seedling”
Claim · model-written summary
Lower richness under greater temporal variability was also attributed to species-specific mortality.
Verbatim
e0“Lower species richness under more temporally variable conditions was attributable to both random extinctions due to reductions in total community density and species-specific differences in mortality”
t0“seedling”
Claim · model-written summary
Final relative abundances differed among water treatments.
Not reportedComparatorDirection
Verbatim
e0“Final species relative abundances differed between water treatments”
t0“seedling”
Claim · model-written summary
Variability and total water quantity had no separate effect on final relative abundances.
- Taxon
- seedlingt0
- Treatment
- variability in soil moisture content or total quantity of water addede0
- Outcome
- separate effectse0
- Direction
- no separate effectse0
Not reportedComparator
Verbatim
e0“there were no separate effects of variability in soil moisture content or total quantity of water added”
t0“seedling”
Claim · model-written summary
Upland species were more abundant with more prevalent drought.
- Taxon
- Upland speciese0
- Treatment
- treatments where drought was more prevalente0
- Outcome
- Upland speciese0
- Direction
- more abundante0
Not reportedComparator
Verbatim
e0“Upland species were more abundant in treatments where drought was more prevalent, either due to low total quantities of water or high temporal variability in soil moisture”