North Temperate Lakes

One of the most intriguing types of population fluctuation is that of regular cyclical change. Recurrent oscillations in the dynamics of natural populations have generated considerable interest in both the occurrence and cause of these cycles. Theoretical models of populations have shown that repeated oscillations can result from a number of factors including combinations of fertility and survival rates, density-dependence, and predator-prey dynamics. Cyclic patterns of abundance have been observed in freshwater fishes, although the ability to detect such cycles is often obscured by the influence of environmental factors. Understanding the extent to which repeated oscillations in fish populations are driven by external factors or internal processes within the population is an important challenge.

At the North Temperate Lakes LTER site, we have observed cyclic dynamics in a population of yellow perch in oligotrophic Crystal Lake. Since 1981, we have observed 3 cases of cohort dominance in which two age-classes dominated the population for roughly 5 years (Figure 1, Sanderson et al. 1999). Across years, the presence of young-of-the-year fish was negatively related to juvenile perch abundance and positively related to adult perch abundance. Conclusions drawn from a statistical dynamic linear model suggest that oscillations in young-of-the-year perch abundance were intrinsically driven by the positive effect of adult perch reproduction and the negative effect of juvenile perch via cannibalism and competition. Young-of-the-year fish were abundant primarily in years when reproductively mature fish were in the lake suggesting that the repeated oscillations are driven predominantly by pulses of abundant reproductive adult perch. As these young perch grow to juveniles, they exclude the possibility of survival by successive cohorts through cannibalistic and competitive interactions. This exclusion occurs until they themselves become reproductively mature and the cycle then repeats. The long-term pattern in Crystal Lake is an exceptional example of cyclic dynamics generated by intraspecific interactions.

Sanderson, B. L., T. R. Hrabik, J. J. Magnuson and D. M. Post. 1999. Cyclic dynamics of a yellow perch population in an oligotrophic lake: evidence for the role of intraspecific interactions. Canadian Journal of Fisheries and Aquatic Sciences. 56:1534-1542.