Diet and divergence of introduced smallmouth bass (Micropterus dolomieu) populations

We examine the degree and causes of divergence in growth and reproduction in two populations of smallmouth bass (Micropterus dolomieu) introduced a century ago. Despite a common source, the Provoking Lake population now has a higher population density and slower growing individuals than the Opeongo Lake population. Using this system, we test the predictions of life history theory that delayed maturation and reduced reproductive investment are expected in high density populations with slow individual growth rates. Observations on both populations run directly counter to the aforementioned expectations. Instead, Provoking males have smaller sizes and younger ages at nesting and higher gonad masses than Opeongo males; Provoking females have smaller sizes at maturity, larger egg sizes, and higher ovarian dry masses than Opeongo females. Temperature, food availability, diet ontogeny, young-of-the-year mortality, and adult mortality were examined as plausible contributors to the divergence. Results suggest that low food availability, likely caused or mediated by intraspecific competition for prey, and lack of large prey in the diet are contributing to the slow growth, increased reproductive investment, and higher mortality following reproduction in Provoking. This study provides insight into the processes that produce rapid divergence of life history in a species exhibiting parental care

Demography of fluctuating populations: temporal and phase-related changes in vital rates of Microtus ochrogaster

1. Small mammal population fluctuations, cyclic or not, have been an ecological puzzle and a source of heated debate among ecologists. Identifying the demographic parameters that covary closely with density changes can help elucidate the underlying causes of population fluctuations, but few studies have reported rigorous estimates of these parameters. 2. We applied capture-mark-recapture analysis to twice-weekly trapping data from a long-term study of a fluctuating Microtus ochrogaster (prairie vole) population in Illinois, USA to estimate stage-specific apparent survival and maturation rates. We also estimated population density, fecundity rate, age at maturity and life span on a weekly basis. 3. Survival, maturation and fecundity rates exhibited phase-related changes during major density fluctuations, but they showed density-independent temporal variations during the prolonged low-density phases. Among these variables, maturation and juvenile survival rates covaried most closely with population density. 4. These results suggest that phase-related changes in maturation and juvenile survival rates are likely to be the main demographic factors driving the dynamics of our study population. 5. Phase-related changes in maturation rates provide a plausible demographic explanation of density fluctuations in our study population. Our results suggest that direct predation may not be necessary for large-scale fluctuations in M. ochrogaster abundance