Ecological equivalency as a tool for endangered species management

Area of Science:

• Conservation Biology
• Ecology
• Genetics

Background:

• The use of taxon substitutes for endangered species is a contentious conservation strategy.
• The endangered California tiger salamander (Ambystoma californiense; CTS) is being replaced by hybrids with the invasive barred tiger salamander (Ambystoma mavortium).

Purpose of the Study:

• To develop and apply a strategy for evaluating the ecological equivalency of taxon substitutes.
• To assess the ecological role of pure CTS, full hybrids, and superinvasives in experimental pond communities.

Main Methods:

• Experimental mesocosms were stocked with realistic densities of tiger salamander larvae (pure CTS, full hybrids, superinvasives) and their prey.
• Community structure was analyzed using multivariate and univariate statistical approaches.
• A control treatment with no salamanders was included to assess baseline community dynamics.

Main Results:

• Pure CTS and superinvasive larvae were found to be ecologically equivalent, with statistically indistinguishable positions in multivariate community space.
• Full hybrids were ecologically similar but not equivalent to pure CTS and superinvasives.
• The absence of Ambystoma larvae resulted in the most divergent community structure.

Conclusions:

• Superinvasives, with only 4% nonnative genes, are adequate taxon substitutes for the larval stage of pure CTS.
• Superinvasives may warrant protection under the Endangered Species Act.
• The conservation status of full hybrids, with 70% nonnative genes, remains uncertain.