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Anne L. Engh Rebekah R. Hoffmeier Robert M. Seyfarth Dorothy L. Cheney 《Behavioral ecology and sociobiology》2009,64(1):97-104
Males in sexually dimorphic species like baboons appear to have surprisingly little influence on the reproduction and dominance
ranks of their female kin, even though they could potentially increase their fitness by helping their relatives improve their
ranks. Male baboons are able to dominate females several years before they emigrate, but their presence has no effect on relatives’
dominance ranks, at least when female kin are present. As a result, females usually acquire ranks within their matriline,
above their older sisters. We describe the process of rank acquisition among orphaned and non-orphaned juvenile and adolescent
females in a group of free-ranging baboons. Orphaned females were significantly more likely than non-orphaned females to acquire
unexpected ranks. Orphaned females with older sisters often acquired ranks within the matriline, but below their older sisters’.
Orphaned females with older brothers were likely to rise in rank above their matriline. Females’ interventions on behalf of
younger sisters always supported the existing female dominance hierarchy, while males’ interventions tended to act against
it. Similarly, in playback experiments, females appeared to be willing to support their younger sister only in disputes with
lower-ranking females. In contrast, males appeared to be willing to support their sister even in disputes with higher-ranking
females. Fraternal support enables females to improve their dominance ranks, but only if their mothers have died. It remains
a puzzle why males have so little influence on their female relatives’ ranks when female kin are present, and so much when
they are absent. 相似文献
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Most studies on feeding by herring larvae (Clupea harengus) have taken place in clear, open waters, but several herring stocks around the world spawn in inshore and estuarine regions.
An example is the spring-spawning Blackwater Estuary (Essex, England) stock. Samples were collected in this estuary to examine
prey selectivity and feeding levels in relation to biological and environmental conditions. Herring larvae negatively selected
copepod nauplii, but positively selected the copepodite and adult stages of Acartia spp. Gastropod larvae were also positively selected. Particles >150 μm width were preferred, whilst particles smaller than
this value were preferentially rejected. Concentrations of potential prey items in the water were in the range of 6.0 to 49.7
organisms l−1 with a median concentration of 15.0 organisms l−1 (n = 26). These values are towards the low end of prey concentrations quoted in the literature as being required to sustain
herring larval growth and survival. However, theoretical considerations suggest that, in this environment, levels of tidally-induced
turbulence enhance encounter rates between larval herring and their prey. On the other hand, turbidity is also related to
tidal current speed and might reduce feeding success by decreasing underwater light levels. Measurements at two sites in the
estuary confirmed that tidally-induced turbidity reduced the effective water depth in which herring larvae could visually
feed by up to 50% at times of peak current speed. However, with the gut-content data available in the present study, it was
not possible to discern any clear relationships between feeding success and the state of the tide. Feeding success appeared
to be more strongly influenced by surface light-levels.
Received: 24 June 1998 / Accepted: 17 February 1999 相似文献