Breeding activity, estimated age-structure, and growth in Sonoran Desert anurans

We investigated breeding activity of a community of desert anurans at two s ites in north-central Phoenix, Maricopa County, Arizona during 1990-1995. F our species used these sites for breeding during the summer monsoon season: Colorado River toad, Bufo alvarius, Great Plains toad, B, cognatus, red-sp otted tend, B. punctatus, and Couch's spadefoot toad, Scaphiopus couchii. B reeding activity was restricted primary to 1990 and 1992 when significant r ainfall events (>25 mm of rainfall within 24 h) occurred repeatedly. No bre eding (i.e., oviposition) occurred during 1991 or 1993, and only S. couchii bred on a single night in 1994 and B. alvarius on a single night in 1995. We undertook a skeletochronologic analysis of lines of arrested growth in d igits and femurs with all four study species. Conservative estimates of age based on lines of arrested growth (LAC's) suggest that populations of all four taxa were relatively young (average age between two and four years) at both sites in 1994 and 1995. Growth, as indicated by the amount of bone de posited between LAG's, was greatest during the second year in B. alvarius a nd B. cognatus, but not B. punctatus or S. couchii. These results indicate rapid growth to maturity but do not support the notion that these anuran am phibians are long-lived organisms that exhibit an extended reproductive lif espan as adults in response to a highly variable, harsh desert environment.