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Findings > Cycles
in Perch Populations
Cycles
in Perch Populations Revealed by Long-Term Data
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.
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