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Extreme drought pushes stream invertebrate communities over functional thresholds
Thomas W H Aspin1,2, Kieran Khamis1, Thomas J Matthews1,3
1School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.
Global Change Biology
|October 23, 2018
Summary
Extreme drought events can cause sudden, disproportionate shifts in stream invertebrate communities. Functional traits reveal community vulnerability, highlighting the need for traits-based approaches to predict ecological responses to climate change.
Area of Science:
- Ecology
- Environmental Science
- Climate Change Biology
Background:
- Functional traits predict species' responses to environmental change but are underutilized for extreme events like drought.
- Drought intensification in streams can exceed habitat loss thresholds, causing disproportionate biotic impacts.
- Previous studies focused on structural drought impacts, leaving functional nonlinearities unexplored.
Purpose of the Study:
- To investigate how invertebrate community functional traits respond to drought intensity gradients.
- To identify functional thresholds and nonlinear responses in stream ecosystems under simulated drought.
- To assess the utility of traits-based approaches for predicting drought-induced ecological shifts.
Main Methods:
- Simulated supraseasonal drought in lowland headwater stream mesocosms over 18 months.
- Modeled responses of 16 functional traits and trait profile groups (TPGs) to drought intensity.
- Utilized generalized additive models (GAMs) to detect functional thresholds and nonlinearities.
Main Results:
- Drought significantly impacted 75% of studied functional traits, with behavioral traits (dispersal, diet) sensitive to moderate drought.
- Morphological and physiological traits showed sudden shifts only after surface water loss, affecting body size and thermal tolerance.
- Trait profile groups exhibited varied responses, including population collapses and irruptions of generalist species.
Conclusions:
- Small increases in drought intensity can trigger disproportionately large functional shifts in stream communities.
- Functional nonlinearity exists and is detectable through traits-based analyses.
- Traits-based approaches are valuable for diagnosing and predicting catastrophic ecological responses to global change and extreme drought.
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