Cryptic Declines in a Widespread Australian Frog Complex

Area of Science:

• Amphibian ecology and conservation biology.
• Disease ecology and wildlife pathology.
• Environmental science and climate change impacts.

Background:

• Amphibian populations worldwide, especially in uplands, face severe declines.
• The Pseudophryne bibronii complex in eastern Australia, once common, now has an uncertain status.
• Limited surveys hinder understanding of amphibian population dynamics and threats.

Purpose of the Study:

• To assess contemporary occupancy, relative abundance, and disease prevalence of the Pseudophryne bibronii complex across an elevational gradient.
• To investigate the role of the fungal pathogen Batrachochytrium dendrobatidis (Bd) in population declines.
• To identify factors contributing to amphibian population changes in eastern Australia.

Main Methods:

• Surveyed 70 historically occupied sites for the Pseudophryne bibronii complex over two breeding seasons.
• Monitored sites across an elevational gradient from near sea level to ~1700 m.
• Swabbed adult male amphibians to test for Batrachochytrium dendrobatidis (Bd) infection and intensity.

Main Results:

• Amphibian occupancy and abundance significantly decreased with increasing elevation.
• Batrachochytrium dendrobatidis (Bd) prevalence and infection intensity rose sharply in upland areas.
• Occupancy declined from 71% at low elevations to 28% in upland sites.

Conclusions:

• Batrachochytrium dendrobatidis (Bd) is implicated as a key factor in amphibian declines at higher elevations.
• Unrecognized population contractions can occur in common species without targeted monitoring.
• Time-lagged declines associated with chytrid fungus may affect amphibian populations.