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Breeding ecology and mating patterns of the western toad, Bufo boreas, were examined in three large explosively breeding populations in the Oregon Cascade Mountains. Two mating patterns occurred variably within and among the three populations. First, a large male mating advantage was observed in two of the three populations when data from all the days of data collection were combined. When each day of breeding was analyzed separately, there was a large male mating advantage on 3 of 5 days at one population, and mating was random on all days at the two other populations. The second mating pattern, positive assortative mating by size, was observed at two of the three populations. This pattern was found on separate days of breeding as well as when data from all days were combined at one population, and on only one day of breeding at the second population.In a survey of anuran amphibian mating patterns, intraspecific variation was found in 13 of 15 species, including the present study of the western toad. Intrapopulation variation in mating patterns among breeding years has been observed in 5 of 8 anurans, whereas within-site, within-year mating pattern variation has only been reported for the western toad. These results strongly suggest that anuran mating patterns are frequently neither species-specific nor population-specific attributes. Variable mating patterns were most commonly observed in explosively-breeding anurans. Explosive breeders may be susceptible to variable mating patterns because they may be more sensitive to fluctuations in environmental conditions, demographic parameters, and the intensities of intrasexual competition and mate choice.

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