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Population Dynamics of Microtus Ochrogaster in Eastern Kansas
Author(s) -
Gaines Michael S.,
Rose Robert K.
Publication year - 1976
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1935041
Subject(s) - microtus , biology , population , seasonal breeder , juvenile , population density , zoology , reproduction , prairie vole , ecology , density dependence , vole , demography , vital rates , population growth , sociology
Four eastern Kansas populations of the prairie vole, Microtus ochrogaster were live trapped from 1970—73 to gain insight into the population regulation of this species. All four populations exhibited a 2—yr cycle in numbers with peak densities generally occurring in June 1972. Peak densities were followed by a decline in numbers, a recovery, and a population crash in spring 1973. Reproductive parameters changed dramatically as density rose and fell. The summer breeding season in the crash year of 1973 was shortened by at least 3 mo. A reduction in breeding activity occurred during the summer of every year of the study. The highest amount of reproduction occurred during the spring and fall. More voles were breeding during the winter before the peak year (1971—72) than during either the preceding or succeeding winter. There was no deviation from a sex ratio of 1 in the populations. Mortality rates had a strong impact on changes in numbers. Survival rates of juveniles and subadults in the population were significantly lower than adults in the summer breeding season. Adults survived better during winter than during summer. Survival of ♂ ♂ and ♀ was correlated and was relatively low during episodes of decreasing density. The survival of voles between weaning and trappable size was high during periods of increasing density and low during periods of declining density. A multiple regression analysis was performed to determine the relative usefulness of four demographic variables in predicting mean rate of population increase. The analysis indicated that early juvenile and ♀ survival are the best predictors of population growth. Growth of voles in the populations was assessed from body weight distributions and instantaneous growth rate per body weight. There was no shift in body weight toward heavier animals in peak populations and instantaneous growth rates were erratic. Finally, inconsistencies in these results compared with other microtine studies, such as the short peak phase, lack of a well—defined breeding season, a summer breeding depression, and the absence of a shift towards heavier animals in the peak phase, are discussed in relation to a single or multifactor hypothesis for explaining population cycles.