Species found
Nine species of anurans were found during visual and audio sampling of adults (Table 1). Overall, agricultural and natural sites both yielded the same nine species but the species present varied at each site. At agricultural sites, species richness varied from three to eight, and while species richness was seven at both natural sites. The mined sites had only five species, four at one site and five at the second. Only one agricultural site (A1) had more than six species.
Based on overall occurrences, there may be three clusters of species. Cluster one included species generally found at all three groups of sites: the southern leopard frog (Rana sphenocephala), western chorus frog (Pseudacris triseriata), American toad (Bufo americanus), Blanchard’s cricket frog (Acris crepitans), and the bullfrog (Rana catesbeiana) [Table 1]. Cluster two included species not found at the mined sites, less common at the agricultural sites, and common at the natural sites: northern spring peeper (Pseudacris crucifer) and gray treefrog (Hyla versicolor / chrysoscelis). Cluster three included species uncommon at all sites: northern crawfish frog (Rana areolata) and eastern narrowmouth toad (Gastrophryne carolinensis).
Adult density
Total audio density was significantly greater in natural sites (1048.7 / ha) than in the agricultural and mined sites (Table 2), but there was no significant difference between the agricultural (519.0 / ha) and mined (164.8 / ha) sites. Total visual density did not vary significantly among the groups of sites, but the rank order was the same as for audio density. Overall, estimates of audio density were about twice the visual densities at agricultural and natural sites, but just over half at the mined sites.
The densities of some species varied with land use group. P. triseriata audio density was significantly higher in agricultural sites than in mined and natural sites (Table 2). Natural sites had no P. triseriata in the audio census. Visual density was also higher at the agricultural sites, but not significantly so, and P. triseriata were found during the visual census at one natural site. The density of R. sphenocephala was also higher at agricultural sites in both audio and visual census (Table 2), although the differences were not significant. Visual density of the H. versicolor/chrysoscelis complex was significantly higher in natural sites compared to agricultural sites (Table 2). The same pattern existed for audio density, but was not significant. Audio and visual density of P. crucifer approached being significantly higher in natural sites (P = 0.06) compared to agricultural sites (Table 2). Mined sites had no P. crucifer or H. versicolor / chrysoscelis complex individuals in either audio or visual census.
Field-collected tadpoles
Tadpole density was significantly higher in natural sites (137.6/m2) compared to agricultural (59.4/m2) and mined sites (28.5/m2, Table 3). Natural sites also had significantly lower percentage of tadpoles with malformations in the field (0.4%) compared to agricultural (4.6%) and mined sites (8.3%, Table 3). Four different types of malformations were found on tadpoles in the field (Table 4). Spinal cord malformations were the most prevalent in all land use categories varying from 67.5% of malformations found on tadpoles in agricultural sites to 92.8%at natural sites. Optic malformations varied from 5.3% at mined sites to 12.5% at agricultural sites. No tadpoles with edema were found at natural sites compared to 10.5% of tadpoles at mined sites and 13.8% at agricultural sites. No tumors were found on tadpoles at natural sites, but tumors were found on 5.3% of tadpoles with malformations at mined sites and on 6.3% at agricultural sites.
Laboratory-hatched tadpoles
The percentage of eggs hatching successfully in the laboratory was significantly higher in natural and agricultural sites (98.8% and 88.2%, respectively), compared to mined sites (40.4%, Table 5). Natural sites also had the lowest percentage of tadpoles with malformations from eggs incubated in the laboratory (17.5%), compared to agricultural sites (51.0%) and mined sites (76.1%, Table 5); however, these differences were not statistically significant.
Five different types of malformations were found on tadpoles hatched from eggs incubated in the laboratory: notochord / spinal cord, head / face, edema, stunted, and severe (having three or more different malformations) [Table 6]. Notochord / spinal cord and stunted malformations were most prevalent on tadpoles from eggs collected at mined and agricultural sites, and edema was the most prevalent malformation from natural sites.
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