Testing the Resource Hypothesis of Species-Area Relationships: Extinction Cannot Work Alone

Area of Science:

• Ecology
• Biogeography
• Microbial Ecology

Background:

• The species-area relationship (SAR) is fundamental to biogeographic theory and conservation.
• The resource hypothesis suggests ecosystem resource richness reduces extinction rates, influencing SAR.
• Previous tests were hindered by difficulties in quantifying resources, extinction, and controlling for confounding factors like area, habitat diversity, dispersal, and history.

Purpose of the Study:

• To experimentally test the resource hypothesis's prediction that richer resources lower extinction rates and shape SAR.
• To overcome previous limitations by using controlled microbial microcosm systems.

Main Methods:

• Two sets of microbial microcosm experiments were established with manipulated correlations between total resources and microcosm volume (positive and negative).
• High-throughput sequencing was used for monitoring over 30 days across 11 time points (157 sessions total).
• Analysis focused on detecting significant SAR and correlations between extinction rates and resource levels.

Main Results:

• No significant species-area relationship (SAR) was observed in either the positive or negative resource-volume correlation groups.
• Extinction rates did not show a significant negative correlation with resource availability.
• Microcosm volume did not significantly influence SAR.

Conclusions:

• In this experimental microbial system, resource availability does not appear to influence extinction rates or shape the species-area relationship.
• The findings challenge the resource hypothesis as a primary driver of SAR in this context.
• If the resource theory is correct, dispersal may be the principal mechanism, as it was not manipulated in this study.