Trade‐offs in seedling growth and survival within and across tropical forest microhabitats

For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade‐offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade‐offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade‐offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51–53%) followed by substrate type (35–37%) and light (11–12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade‐offs among species during regeneration are common in low‐diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.     

Fitness-related benefits of dominance in primates

Dominance hierarchies are thought to provide various fitness-related benefits to dominant individuals (e.g., preferential access to food or mating partners). Remarkably, however, different studies on this topic have produced contradictory results, with some showing strong positive association between rank and fitness (i.e., dominants gain benefits over subordinates), others weak associations, and some others even revealing negative associations. Here, we investigate dominance-related benefits across primate species while controlling for phylogenetic effects. We extracted data from 94 published studies, representing 25 primate species (2 lemur species, 4 New World monkeys, 16 Old World monkeys, and 3 apes), to assess how dominance affects life-history and behavior. We used standard and phylogenetic meta-analyses to analyze the benefits of dominance in primates. Dominant females had higher infant survival to first year, although we found no significant effect of dominance on female feeding success. Results for female fecundity differed between the two meta-analytical approaches, with no effect of dominance on female fecundity after controlling for phylogeny. Dominant males had a higher fecundity and mating success than subordinate males. Finally, the benefits of dominance for female fecundity were stronger in species with a longer lifespan. Our study supports the view that dominance hierarchies are a key aspect of primate societies as they indeed provide a number of fitness-related benefits to individuals.     

若尔盖高原退化沼泽群落植物多样性及种间相关性沿排水梯度的变化

植物多样性与种间相关性是植物群落生态学和生物多样性研究的核心问题, 然而有关二者之间关系的综合研究尚不多见。该文以若尔盖高原排水干扰下不同退化阶段的沼泽湿地植被为研究对象, 应用Spearman秩相关、回归分析等方法, 分析了沼泽植物群落物种多样性和种间相关性的变化及二者相互关系。结果表明: 沿排水梯度, 从相对原生沼泽至极度退化沼泽, 不同植物种群均有其特定的生态分布范围; 群落总种数、样方物种丰富度、Shannon-Wiener指数和Whittaker指数均单调增加; 植物种间相关强度增加; 正相关种对比例呈逐渐增加的趋势, 以极重度和极度退化阶段的较高, 相对原生沼泽和轻度退化阶段的较低, 负相关种对比例的变化趋势与之相反; Shannon-Wiener指数与正负相关种对比例均具有显著线性关系(p < 0.05), Whittaker指数均无显著关系(p > 0.05)。人为排水作用通过提高群落生境异质性, 促进正相关种对的共存, 增加沼泽群落植物多样性。     

Social status and cortisol levels in singing rock hyraxes

Many mammals use acoustic signals to communicate with conspecifics. Rock hyraxes (Procavia capensis) are social mammals whose vocal communication is usually restricted to quiet sounds used between nearby individuals. Loud repetitive warning trills are an exception. In our study site, a third of the adult male hyraxes also produces a rich, complex and loud vocalization we term 'singing'. In this study, we examine whether singers, which are more conspicuous by the act of singing, have higher cortisol (i.e. basal stress; C) levels than non-singers, and whether there is an association between social status and stress hormones in male hyraxes. We show that 'singing' males are different from the general adult male population in that their C levels are higher than those of silent males. Only in singers, C levels are associated with social rank, with dominants showing the highest levels. Singers are also on average older and more dominant than most other sexually mature non-singing males. Further, they copulate more than non-singers, suggesting that singing males may have higher reproductive success. Our results support the ‘stress of domination’ hypothesis and indicate that in the rock hyrax singing may reflect high competitive ability, designating singers as a distinct class of males, unique in their personal attributes and behavior.     

Social correlates of fecal testosterone in male ursine colobus monkeys (Colobus vellerosus): the effect of male reproductive competition in aseasonal breeders

Male testosterone (T) levels are thought to be linked with the mating system, degree of parental care, and male–male aggression in reproductive contexts (The ‘challenge hypothesis’; Wingfield et al., 1990). In many species though, T increases associated with mating behavior cannot be separated from those associated with male–male aggression. We tested the challenge hypothesis on aseasonally breeding ursine colobus (Colobus vellerosus), where male–male competition is intense outside of mating contexts. Fecal samples (N = 109) were collected from > 27 subadult and adult males in seven groups during 13-months of research in Ghana in 2004–2005. Fecal T (fT) levels were determined by enzyme immunosorbant assays. Behavioral data was collected using focal-animal and ad libitum sampling. The number of receptive females in each group did not positively correlate with male fT. There was a trend for adult males to have higher fT than subadult males; however there was no effect of rank on fT. The level of male–male aggression experienced was positively correlated with fT and individual males showed higher mean fT during ‘challenge’ than during ‘non-challenge’ periods. The number of male incursions experienced positively correlated with fT whereas the number of between-group encounters did not. Males attempt to gain reproductive opportunities during incursions, thus these results support the ‘challenge hypothesis’ in C. vellerosus. Outside of mating contexts, higher male fT levels are associated with increased aggression. Male parental investment in the form of infant defense was associated with increased fT, rather than the decline expected from other forms of paternal care.     

Diel activity and home range size in relation to food supply in a drift-feeding stream fish

Individuals within a species often compete for resources inboth space and time. In dominance hierarchies individuals withthe greatest competitive ability will occupy prime locationsduring optimal periods. We compared spatial and temporal useof habitat, aggression, and feeding success among giant kokopu(Galaxias argenteus) in dominance hierarchies under normal andreduced food supply. Under normal food supply conditions dominantfish were predominantly nocturnal and maintained large homeranges at night. Conversely, subdominant fish were diurnal andoccupied large home ranges by day but were generally not observedat night. When the food supply was limited, the utilizationof pools was determined by social rank. Dominant fish from eachpool increased diurnal activity, home range size, aggressiveness,and the capture of food items offered by day while simultaneouslyreducing the spatial and temporal activity and habitat use ofsubdominant fish. These results indicate that behavioral changesin large dominant fish influence and reduce the amount of resourcesavailable to subdominant fish.     

Is there a relationship between dominance rank and condition in captive male bank voles, Clethrionomys glareolus?

The sexual selection theory predicts that traits associated with male–male competition or female mate choice honestly reflects individual quality when they are costly and condition dependent. Dominance seems to be a reliable signal of male quality. The aim of this study was to investigate whether dominance rank, measured in terms of agonistic interactions and trait correlated with dominance, such as preputial gland mass, depends on condition in captive male bank voles. We used five physiological measures to characterize condition: body mass, neutrophils to lymphocytes ratio (N/L ratio), spleen mass, thymus mass and adrenal gland mass. Additionally, the condition of males was challenged with a T cell-dependent antigen, sheep red blood cells. Dominance rank was not significantly related to body mass, N/L ratio and adrenal gland mass but was positively correlated with immune defence organ mass. Moreover, testes mass was positively related to the N/L ratio. However, after Bonferroni correction, only the relationship between preputial gland mass and thymus mass remained significant. Results of this experiment showed condition dependence of dominance in captive male bank voles.     

Patterns of extrapair mating in relation to male dominance status and female nest placement in black-capped chickadees

In sexually promiscuous animals, females may benefit by nestingclose to the edge of their partner's territory to facilitateextrapair copulations. In the present study, we describe theextrapair mating system of black-capped chickadees, Poecileatricapillus, and test whether nest locations are influencedby conspecific attraction to extrapair partners. We conducteda spatial analysis of female mating strategies by using microsatellitepaternity analysis in conjunction with geographic informationsystem (GIS) analysis of nest and territory locations. Extrapairoffspring comprised 52 of 351 offspring (14.8%) and were presentin 19 of 57 broods (33.3%). Females paired to males with lowdominance status in the previous winter's flock hierarchy weremore likely to engage in a mixed reproductive strategy thanwere females paired to males with high dominance status. Femaleshad extrapair copulations and extrapair fertilizations withhigh-ranking males more often than with low-ranking males. Notall extrapair copulations resulted in extrapair fertilizations.Females constructed their nests within 16.8 ± 1.0 m ofthe edge of their partner's territory, significantly closerto the edge of their nearest neighbor's territory than to thecenter of their own partner's territory. Extrapair males usuallyshared territory boundaries with cuckolded males. Females pairedto low-ranking males constructed nests near the territory edgesof neighboring high-ranking males. However, females did nothave extrapair copulations with the neighbor nearest to theirnest or even with the high-ranking neighbor nearest to theirnest. We conclude that conspecific attraction to neighbors mayinfluence nesting location in black-capped chickadees; however,it does not operate by facilitating extrapair copulations.