Inter-annual variation in amphibian larval interspecies interactions

Area of Science:

• Ecology
• Amphibian Biology
• Conservation Biology

Background:

• Species interaction outcomes are influenced by life stage, environmental conditions, and yearly variations.
• Amphibian larvae, particularly tadpoles, are expected to experience intense competition due to high densities.
• The Fowler's toad (Anaxyrus fowleri) exists at the northern limit of its range in Long Point, Ontario, overlapping with the American toad (Anaxyrus americanus).

Purpose of the Study:

• To investigate the competitive interactions between Fowler's toad and American toad tadpoles.
• To determine if competition effects are consistent across different years and environmental conditions.
• To assess the potential for competitive exclusion of Fowler's toads by American toads at the species' range edge.

Main Methods:

• Tadpoles of both Fowler's toad and American toad were raised together and separately in mesocosms during 2018 and 2021.
• Key metrics including survivorship, weight at metamorphosis, and time to metamorphosis were recorded for both species.
• Experimental design accounted for inter-annual variation in pond conditions.

Main Results:

• American toad tadpoles consistently exhibited a detrimental effect on Fowler's toad tadpoles.
• The specific manifestation of this competitive effect varied between the study years (2018 and 2021).
• Survivorship, growth, and developmental timing were impacted by the presence of competing tadpoles.

Conclusions:

• The findings suggest that American toads may competitively exclude Fowler's toads at the northern edge of the Fowler's toad's distribution.
• Ecological studies must incorporate multi-year observations to fully capture the dynamics of species interactions.
• Understanding these interactions is vital for the conservation of range-limited species like the Fowler's toad.