Condition, growth, and reproductive styles of fishes exposed to different environmental regimes in a prairie drainage

To investigate effects of environmental variability on fish populations, we compared three species from two different stream segments that differed in their magnitudes of environmental fluctuations. Fish from the upper and lo wer basin of an Oklahoma prairie stream were sampled bi-weekly from 19 Apri l to 12 October 1997. Along with condition factors of Campostoma anomalum ( adults and juveniles), Etheostoma spectabile, and Notropis boops, growth ra tes of juvenile C. anomalum, and gonadal somatic indices (GSI) from adult C . anomalum were calculated. Individuals occupying the upper basin experienc ed the greatest environmental fluctuations, but also had condition factors that were similar or higher than conspecifics in the more stable lower basi n for each species. Changes in length-frequency distributions suggested the existence of 2-3 cohorts and relatively rapid growth in the upper basin an d a single slower-growing cohort in the lower basin. Additionally, reproduc tive styles, measured in terms of GSI and appearance of juveniles, varied a mong the two sites, suggesting that reproductive plasticity over small scal es may result from the different environmental regimes of each stream segme nt. Overall results demonstrate that although large fluctuations in the env ironment may produce conditions that appear to be detrimental to an individ ual, in actuality, they may not be. In fact, areas with the largest environ mental fluctuations produced robust individuals, and thus may offer some un seen benefit that counterbalances or outweighs the costs associated with a variable environment. Additionally, there is evidence that at least some re sident taxa have sufficient life history plasticity to exploit these opport unities wherever or whenever they may arise.