Thresholds for ecological responses to global change do not emerge from empirical data

Area of Science:

• Ecology
• Environmental Science
• Global Change Biology

Background:

• A common framework in global change ecology involves identifying critical thresholds in environmental pressures.
• These thresholds are hypothesized to trigger disproportionately large increases in ecological response magnitudes and variances.
• However, empirical evidence supporting the detectability of such thresholds is limited.

Purpose of the Study:

• To systematically evaluate the extent to which empirical data support the existence of ecological thresholds under global change.
• To assess the prevalence and detectability of threshold effects across numerous studies of global change impacts.

Main Methods:

• Conducted a meta-analysis of 36 studies, synthesizing data from over 4,600 measurements of global change impacts on natural communities.
• Performed sensitivity analyses using modeled data to investigate the influence of response variability on threshold detection.

Main Results:

• Threshold transgressions were infrequently detected in the empirical data, both within individual meta-analyses and across the combined dataset.
• Ecological responses were predominantly characterized by a progressive increase in magnitude and variance with rising pressure levels.
• Simulations indicated that even small response variances can prevent threshold detection, even when thresholds are theoretically present.

Conclusions:

• The findings challenge the widespread assumption that ecological systems exhibit clearly definable thresholds under global change.
• Ecological responses to increasing environmental pressures are often continuous and highly variable, rather than abrupt.
• The concept of 'safe-operating spaces' for nature management may be difficult to quantify due to this inherent variability.