Initial Dispersal and Breeding Habitat Use of Newly Introduced Mink Frogs in Western Newfoundland, Canada
Insular Newfoundland has no native amphibians. While global amphibian populations are declining at alarming rates, populations of introduced anurans (frogs and toads) continue to expand in western Newfoundland, Canada. We expected the establishment and dispersal of the most recently introduced species, Mink Frog (Lithobates septentrionalis), to be influenced by the presence in the region of the previously introduced and ecologically similar Green Frog (L. clamitans). We used a combination of anuran calling surveys and pond-edge visual surveys to assess the ongoing dispersal, relative regional distribution, and local habitat use for these two species in western Newfoundland. The recently established Mink Frog has dispersed ∼3.8 km/year northeast from the original (2001) discovery location and ∼2.6 km/year southwest; co-occurrence analyses revealed that this population displayed habitat and spatial separation from long-established Green Frog populations, at both landscape and local scales. Although cause and effect is not established, this response appears to be defined, at least in part, by the influence of pH on species occurrence; Mink Frogs may be avoiding acidic environments which are tolerated by Green Frogs.

Presence of Mink Frogs and Green Frogs based on Manual Calling Surveys (NAAMP Protocol) conducted during 2001 (Powell, 2002), 2011 (Stapleton, 2011), and at 40 sites visited between 18 June and 1 July 2014. Noted locations: 1—Gillams, 2—Town of Hughes Brook, 3—Steady Brook, 4—Humber Village, 5—Rapid Pond, 6—Pasadena Beach, 7—Pynn's Brook, 8—Blue Pond, and 9—Moose Pond. Inset represents location of the study area on the Island of Newfoundland.

Visual Encounter Survey sample sites in western Newfoundland (top panel) and encounter rates (frogs/m) of Mink Frogs and Green Frogs detected at 77 sites visited between 9 July and 31 July 2014 (lower panels). Noted locations: 1–Mount Moriah, 2–Moose Pond. Inset represents location of the study area on the Island of Newfoundland.

Water quality parameters for ponds occupied by Green Frogs only, Mink and Green frogs together, Mink Frogs only, and neither species. Values reflected are the median (horizontal line), first and third quartiles (boxes), plus minimum and maximum values that are not outliers (whiskers) for: (A) pH, (B) temperature, (C) conductivity, and (D) dissolved oxygen.
Contributor Notes
Associate Editor: M. J. Lannoo.