The importance of patch shape at threshold occupancy: functional patch size within total habitat amount.

Area of Science:

• Ecology
• Conservation Biology
• Ornithology

Background:

• The habitat amount hypothesis (HAH) posits that total habitat area, not individual patch size, dictates species richness.
• This hypothesis may not account for species-specific territory requirements and minimum viable patch sizes.

Purpose of the Study:

• To test HAH predictions regarding threshold patch occupancy and species richness.
• To investigate the role of functional patch size versus total habitat amount in determining bird diversity.

Main Methods:

• Characterized 16 patch types at high spatial resolution for 19 insectivorous bird guilds.
• Measured functional patch size using the largest inscribed circle within each patch.
• Used regression models to assess the predictive power of functional patch size and total patch amount on species richness.

Main Results:

• Functional patch size was the primary predictor of species richness for 15 out of 19 bird guilds.
• Total patch amount was the primary predictor for only 2 guilds.
• Demonstrated that smaller patches exclude larger species and that very small patches are unoccupied.

Conclusions:

• Functional patch size is a critical metric for understanding habitat availability and species distribution.
• This metric helps explain variations in species composition and richness, informing conservation and restoration efforts.
• The findings challenge the HAH by highlighting the importance of individual patch size and shape for species occupancy.