Species, functional groups, and thresholds in ecological resilience

Area of Science:

• Ecology
• Ecological modeling
• Conservation biology

Background:

• Ecological resilience is key to ecosystem stability and is influenced by the distribution of functions across scales.
• The cross-scale resilience model posits that functional group distribution within and across scales generates ecological resilience.
• Species' functional roles link ecosystem processes to resilience, with body mass reflecting resource distribution.

Purpose of the Study:

• To apply the cross-scale resilience model to avian species in a grassland ecosystem.
• To assess how threatened species loss impacts cross-scale resilience metrics.
• To determine if functional diversity is retained more than expected after species loss.

Main Methods:

• Utilized log-transformed, rank-ordered body masses of grassland breeding birds to identify patterns.
• Assessed cross-scale resilience using metrics: total functional groups, functional groups per aggregation, and inter-aggregation functional redundancy.
• Simulated threatened species loss and compared observed functional retention against random loss using Monte Carlo methods.

Main Results:

• Analysis of bird body mass distributions revealed aggregations and discontinuities.
• The loss of threatened species did not disproportionately affect the distribution of functions within and across aggregations.
• Observed functional retention after species loss exceeded that expected from random extinction events.

Conclusions:

• Ecosystems can withstand significant species loss without altering functional distribution across aggregations, albeit with reduced overall resilience.
• Species loss is likely nonrandom, conserving functional distribution and retention mechanisms.
• The distribution of function within and across aggregations appears conserved despite extinctions.