Монгол еарваганы популяци дакь тахлын эпизоотийн шинж чанар. Mongol tarbagany popoulyatsi dakh’ takhlyn epizootiïn shinj tchanar [Characteristics of a plague epizootic in the Mongolian marmot population. Charactéristiques d’une épizootie de peste chez la population de marmotte de Mongolie].

Résumé

1. The plague epizootic which occurred among the marmot population in the high mountains featured a central plague focal point which appeared in the area where the epizootic stopped the previous autumn. The epizootic then spread through the population along a definite corridor defined by subpopulation boundaries. The plague epizootic moved 11.6 ± 6.0 km and covered 4.2 ± 2.9 thousand hectares every year for the past 8 years. For each of 3 study years the epizootic began with the first case of an infected marmot appearing on the 26th of May. The period of intensive plague epizootism lasted from July through August. 2. Plague passes through 3 stages designated "signal", "peak" and " consequent". The plague pathogen remains in the marmot population for 3 - 4 years. Infected marmots represent 7.0 ± 5.4% of the population during the signal stage, 33.8 ± 6.0% during the peak stage, and 5.9 ± 13.8% during the consequent stage. Attenuation of the epizootic was indicated by a decrease in the percentage of infected marmots, and a drop in of raptors and carnivores densities. 3. Prior to initiation of the plague epizootic, the structure of the marmot population was characterized by a high density (3.27 ± 1.4 marmots/ha) of marmots with a strong male bias (165 males : 100 females), a small number of kits, a low percentage of young marmots, and a low rate of reproduction. Following infection of the population by plague, 34.8% of winter burrows and 52.0% of summer burrows became empty, family size decreased by 52.7% an population density by 76.6%. Male marmot mortality was two times greater than that of females, resulting in a shift to female sex bias. Additional influences of the epizootic included increased immigration into the population and intensified breeding. Over the next 3 years the percentage of kits surpassed that of all other age classes, empty burrows were occupied by marmots, and the number and density of marmot increased.