Population and social dynamics changes in ring-tailed lemur troops at Berenty,Madagascar between 1989 - 1999 |
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Authors: | Koyama Naoki Nakamichi Masayuki Ichino Shinichiro Takahata Yukio |
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Institution: | (1) The Center for African Area Studies, Kyoto University, Sakyo-ku, 606-8501 Kyoto, Japan;(2) Laboratory of Ethological Studies, Faculty of Human Sciences, Osaka University, Suita, 565-0871 Osaka, Japan;(3) The Center for African Area Studies, Kyoto University, Sakyo-ku, 606-8501 Kyoto, Japan;(4) Kwansei-Gakuin University, Sanda, 669-1324 Hyogo, Japan |
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Abstract: | In the present study, we recorded all births, immigrations, deaths, and emigrations for a population of ring-tailed lemurs
at Berenty Reserve, Madagascar, between September 1989 and August 1999. In September 1989, three troops (C, B, and T) inhabited
the study area of 14.2 ha. During the 10-year period, eight troop divisions, six evictions of females, and three troop takeovers
of ranges by other troops occurred in and around the study area. Consequently, in August 1999, the number of troops in the
same area increased to six (CX, C1, C2A, C2B, T1, and T2). The number of lemurs aged >1 year increased from 63 to 82, which
resulted from 204 births, 58 immigrations, 125 deaths, and 118 emigrations. Of the 204 newborn lemurs during the study period,
103 died, 44 emigrated outside the study area, and 57 remained within the study area. The total number of lemurs that emigrated
from natal troops was 69 (54 males and 15 females). Natal males left their troops around the age of 3. Non-natal males changed
troops after a tenure varying from 1 to 7 years. Survival curves showed a fall in survival rates of both sexes to < 0.5 between
the ages of 2 and 3. For females, the survival rate gradually decreased to < 0.2 at the age of 9. On the other hand, due to
emigration, the survival rate of males could not be determined after the age of 5 yr. Since some males attained high-rank
at the age of 6 – 10 yr, the prime age for male ring-tailed lemurs is thought to be around 7 – 10 yr. Ring-tailed lemurs are
essentially female philopatric, because all cases of females leaving natal troops resulted from troop divisions or forced
evictions. Such social changes may have resulted from competition among females. All cases of troop divisions or evictions
occurred in larger troops consisting of ≥20 lemurs, and only a few females could rejoin their troops. When males joined such
a female-group, a new troop was formed. Although promoted by an increase in population, frequent emigrations of females from
original troops are the characteristics of ring-tailed lemurs at Berenty. |
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Keywords: | Ring-tailed lemurs Demography Age of emigration Survivorship curve Madagascar |
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