同域分布3种啄木鸟冬季取食的生态位差异

为了掌握黑啄木鸟、三趾啄木鸟和大斑啄木鸟的冬季取食行为特征,特别是三者之间取食生态位的差异,于2016年1月5-13日,在黑龙江省凉水国家级自然保护区以样线法结合样方法对3种啄木鸟的取食生境和取食行为进行了系统调查,收集了15个生境和行为特征变量数据。共布设45条样线,484个对照样方,收集312组啄木鸟取食数据,其中黑啄木鸟73组,三趾啄木鸟97组,大斑啄木鸟142组。多变量回归树和多分类逻辑斯谛分析结果显示,3种啄木鸟在所调查的15项特征上存在显著分异。采用基于利用-可利用方法的Bailey''s方法和双因子方差分析,分别对3种啄木鸟的生境选择和行为特征进行分析,结果显示：黑啄木鸟和三趾啄木鸟偏好在郁闭度较高的原始云、冷杉林中取食,而大斑啄木鸟则随机地在各种林型、生境中取食。黑啄木鸟、三趾啄木鸟多在树干取食,黑啄木鸟更常在倒木上取食,而大斑啄木鸟则多在树冠层取食。黑啄木鸟基本只在主干上凿洞,其他两种特别是大斑啄木鸟则可以在侧枝上取食。与黑啄木鸟和大斑啄木鸟凿洞取食昆虫不同,三趾啄木鸟多通过扒去树皮获得食物。黑啄木鸟的取食树基本为死树,单树取食时间最长,大斑啄木鸟多在活树上取食,单树取食时间最短,经常更换取食树,而三趾啄木鸟的取食树则死活参半,单树取食时间也较长。黑啄木鸟的冬季取食行为节律表现为双峰形,日出后和日落前各有一个活动高峰,其他两种则于白天持续取食。3种啄木鸟取食生境和行为生态位的差异,使它们能够更有效地利用有限的食物资源,共存于同一森林。     

Interbirth interval variation in three sympatric species of neotropical monkey

Relatively few papers have focused on interbirth intervals in primates, even though the spacing between births is one of the primary determinants of female reproductive success in long-lived mammals. We present life history data from a ten-year field study of Costa Rican capuchins (Cebus capucinus), howlers (Alouatta palliata), and spidei monkeys (Ateles geoffroyi). Analyses of intraspecific variability found no significant differences attributable to individual variation in age, parity, weight, or maternal rank. Loss of an infant significantly shortened the interbirth interval in all three species. There was no correlation between annual rainfall and birth rates, but there was a significant clustering of births in the dry season. Survival analyses demonstrated a significant difference between the median interbirth intervals of the three species. Howlers have the shortest intervals (19.9 months), capuchins exhibit longer intervals (26.36 months), and spider monkeys have the longest intervals (34.72 months;. This comparative pattern does not correspond to relative body weights of the three species, but does correspond to relative brain weights. Comparisons to other primates with similar life history characteristics demonstrate that interbirth intervals are best examined at the level of their three component phases: gestation, lactation, and cycling to re-conception. © 1995 Wiley-Liss, Inc.     

同地共栖三种鼠耳蝠食性差异及其生态位分化

2005年9—11月在贵州省安龙县笃山乡暗河村,分析了共栖同一山洞3种鼠耳蝠的形态特征和食性。在体型上,华南水鼠耳蝠体重为(4.46±0.53)g,前臂长为(34.63±1.45)mm;毛腿鼠耳蝠体重为(5.15±1.76)g,前臂长为(35.20±1.07)mm;西南鼠耳蝠体重为(10.94±0.87)g,前臂长为(45.21±1.15)mm。3种鼠耳蝠的体重两两之间差异显著,西南鼠耳蝠与另外2种鼠耳蝠的前臂长相比两两之间差异显著。在食物组成上,华南水鼠耳蝠主要捕食近水面活动的双翅目及其幼虫,体积百分比和频次百分比分别为79.7%和100%;毛腿鼠耳蝠主要捕食双翅目和小型鞘翅目,体积百分比分别占59.6%和28.8%,频次百分比分别为91.3%和80.1%;西南鼠耳蝠的食物组成主要为近地面或在地表活动的鞘翅目步甲科和埋葬虫科昆虫,体积百分比和频次百分比分别为80.8%和100%;3种鼠耳蝠食物组成存在显著差异。结果表明,同地共栖3种鼠耳蝠除了形态结构上出现差异,食物组成也存在明显的差异。据此,推测3种鼠耳蝠可能采取不同的捕食生境和捕食策略,从而导致捕食生态位分离,避免出现激烈竞争,使得3种近缘鼠耳蝠能够同地共栖。     

同域分布的紫堇属三种植物的繁育系统和传粉差异

为研究近缘物种之间繁育系统分化对传粉环境的适应性意义,本文针对湖北地区的3种紫堇属植物（紫堇Corydalis edulis Maxim.、尖距紫堇C.shearer S.Moore.和小花黄堇C.racemosa（Thunb.） Pers.）进行了传粉生态学研究,对比分析了它们在花部特征、分布模式、花期、交配系统、传粉系统等方面的差异。3种紫堇属植物常见伴生现象,花期有一定重叠;花色、距长、花蜜量等方面均有显著差异;尖距紫堇交配系统为自交不亲和、依靠传粉者异花授粉;而紫堇和小花黄堇交配系统为自交亲和,兼有自交和异交的混合交配系统。3个物种均由蜂类传粉,且花部性器官与传粉者的接触部位一致,但访花频率差异较大。在混合群落中,传粉者访花具有较高的忠实性,花部特征差异可能是传粉者选择性访花的原因。对于紫堇属3个物种,花部特征和交配系统的分化有助于其避免传粉过程的相互干扰,交配系统与传粉环境具有一定相关性,混合交配系统可能有利于提高植物对不同生境和气候的适应性。     

Maintenance of species boundaries in three sympatric Ligularia (Senecioneae,Asteraceae) species

The key process in speciation concerns the formation and maintenance of reproductive isolating barriers between diverging lineages. Although species boundaries are frequently investigated between two species across many taxa, reproductive isolating barriers among multiple species (>2) that would represent the most common phenomenon in nature, remain to be clarified. Here, we use double digest restriction‐site associated DNA (ddRAD) sequencing to examine patterns of hybridization at a sympatric site where three Ligularia species grow together and verify whether those patterns contribute to the maintenance of boundaries among species. The results based on the RAD SNP datasets indicated hybridization Ligularia cyathiceps × L. duciformis and L. duciformis × L. yunnanensis were both restricted to F₁s plus a few first‐generation backcrosses and no gene introgression were identified, giving rise to strong reproductive isolation among hybridizing species. Moreover, hybrid swarm simulation, using HYBRIDLAB, indicated the RAD SNP datasets had sufficient discriminatory power for accurate hybrid detection. We conclude that parental species show strong reproductive isolation and they still maintain species boundaries, which may be the key mechanism to maintain species diversity of Ligularia in the eastern Qinghai‐Tibetan Plateau and adjacent areas. Moreover, this study highlights the effectiveness of RAD sequencing in hybridization studies.     

The demographic basis of population regulation in columbian ground squirrels

Environmental factors influence the dynamics and regulation of biological populations through their influences on demographic variables, but demographic mechanisms of population regulation have received little attention. We investigated the demographic basis of regulation of Columbian ground squirrel (Spermophilus columbianus) populations under natural and experimentally food-supplemented conditions. Food supplementation caused substantial increases in population density, and population densities returned to pretreatment levels when the supplementation ended. Control (untreated) populations remained relatively stable throughout the study period (1981-1986). Because food resources regulated the size of the ground squirrel populations, we used life-table response experiment (LTRE) analyses to examine the demographic basis of changes in population growth rate and thus also demographic influences on population regulation. LTRE analyses of two food-manipulated populations revealed that changes in age at maturity and fertility rate of females generally made the largest contributions to observed changes in population growth rate. Thus, our results suggested that abundance of food resources regulated the size of our study populations through the effects of food resources on age at maturity and fertility rates. Our results also indicated that different demographic mechanisms can underlie population regulation under different environmental conditions, because lower juvenile survival substantially contributed to population decline, but in only one of the populations. Demographic analyses of experimental data, such as those presented here, offer a rigorous and unambiguous means to elucidate the demographic basis of population regulation and to help identify environmental factors that underlie dynamics and regulation of biological populations.     

Measuring fruit patch size for three sympatric indonesian primate species

Food availability is one of the basic factors affecting primate density and socioecology, but food availability is difficult to assess. Two different ways to obtain accurate estimates of food availability have been proposed: using phenology data or using the behaviour of animals. Phenology data can be refined by only including trees that are large enough to be used; including (potential) tree species in which by the concerned primate species forage; or including (fruiting) trees of these species that actually produce fruit. Alternatively, the sizes of the actually visited trees (foraging trees) give an estimate of fruit availability. These measures are compared for three sympatric primate species at the Ketambe Research Station, Sumatra, Indonesia: the Thomas langur, the long-tailed macaque and the orangutan. The sizes of fruiting trees and the foraging trees are larger than the potential trees. The sizes of the potential trees and of the fruiting trees are similar for the three primate species. This, however, is not reflected in the use of trees: the langurs forage on average in trees of similar size to those producing fruit, whereas the macaques and orangutans forage in trees larger than those producing fruit. The use of trees does not necessitate a different cut off point of included dbhs for the three compared primate species. The use of trees of different sizes, however, may be regulated by food competition. This indicates that sympatric primates make different foraging decisions and that behavioural measures of food availability will be less reliable.     

Comparative nest survival of three sympatric loon species breeding in the Arctic

Identifying factors influencing nest survival among sympatric species is important for understanding and managing sources of variation in population dynamics of individual species. Three species of loons nest sympatrically in northern Alaska and differ in body size, life history characteristics, and population trends. We tested the effects of competition, nest site selection, and water level variations on nest survival of Pacific Gavia pacifica, yellow‐billed G. adamsii, and red‐throated loons G. stellata on the Arctic Coastal Plain in Alaska. Although overall nest survival rates did not differ between species, the factors influencing nest survival varied. Nest site selection influenced nest survival for Pacific and yellow‐billed loons, with both species having high nest survival when nesting on islands and peninsulas, likely due to a reduction in access by terrestrial predators. However, on mainland shorelines, Pacific loons had lower nest survival than yellow‐billed loons, and used a higher proportion of vegetation mats for nest sites suggesting that their smaller body size makes them less adept at nest defense. Nest site selection did not influence nest survival of red‐throated loons corresponding to our result of no nest site preferences by this species. Initiation date had a strong influence on nest survival for Pacific and yellow‐billed loons with nests laid earlier having higher survival. Pacific and yellow‐billed loon nests were susceptible to flooding due to precipitation, which contrasted with red‐throated loons that nest on smaller lakes with lower water level variations. Competition did not affect nest survival for any of the species likely due to most territorial encounters occurring prior to incubation. The only influence we found on red‐throated loon nest survival was differences among years. Our results indicate that loons chose nest sites based on predation risk and that factors influencing breeding success of closely related species may differ under similar breeding conditions.     

Social system of round-tailed ground squirrels

The social system of round-tailed ground squirrels, Spermophilus tereticaudus, is quantitatively described in terms of seasonal changes in interaction rates, the effect of age and sex on type and frequency of interaction, the differential response to kin and non-kin, the determinants of dominance, including territoriality, the associations between classes of individuals, and the dispersion of home ranges and core areas. From January to March, the adult squirrels were sociable and nonterritorial. Following copulation in March, they were unsociable and territorial. In May and June, juveniles lived mainly within their mothers' territories. Those juveniles that did not disperse from the study area in late June established territories near their mothers. From September to December, all squirrels were inactive underground.     

Contrasting stress response of male arctic ground squirrels and red squirrels

A hormonal-challenge protocol was used to compare the stress response of males of Arctic ground squirrels and red squirrels during the breeding season (May). These squirrels live in the same boreal forest of the Yukon, but have very different life histories and utilize the forest in markedly different ways. Red squirrels had levels of total cortisol, maximum corticosteroid-binding capacity, and free cortisol that were 5, 7, and 2 times, respectively, those of Arctic ground squirrels. Red squirrels were resistant to suppression by an artificial glucocorticoid, dexamethasone (DEX); Arctic ground squirrels were not. Cortisol levels in red squirrels responded slowly but continuously to the ACTH injection; Arctic ground squirrels responded rapidly and then stabilized. Testosterone levels in red squirrels were extremely sensitive to the challenge, being suppressed by both DEX and ACTH; levels in Arctic ground squirrels were resistant to the challenge, being modestly suppressed by DEX and stimulated by ACTH. Energy mobilization, as measured by glucose and free fatty acid responses, was not affected. Red squirrels had four times the levels of white blood cells and higher proportions of lymphocytes and lower proportions of eosinophils than Arctic ground squirrels, indicating that the latter were in worse condition immunologically. Our evidence suggests that the functions associated with the hypothalamic-pituitary-adrenal axis are compromised in breeding male Arctic ground squirrels, but not in red squirrels. We propose that in male red squirrels this axis has evolved in the context of a stable social system based on long-lived animals with individual territories which are needed to deal with unpredictable winter food supplies. In contrast, Arctic ground squirrels escape the rigors of winter by hibernation and this hormonal axis has evolved in short-lived males in the context of intense intra-sexual competition in a social system based on female kin groups and regular male dispersal to avoid inbreeding. J. Exp. Zool. 286:390-404, 2000.     

Microhabitat affects acorn removal in three sympatric and endangered Neotropical oak species

Acorn removal and predation are processes that can influence forest dynamics and the ecological niche segregation of sympatric oak species. Different factors affect these processes, including differences in acorn germination rate and exposure to predators and/or dispersers. This study evaluated acorn removal and predation patterns in three threatened tropical cloud forest oak species (Quercus germana, Quercus sartorii and Quercus cortesii). Acorns were placed in two accessibility treatments (open to all potential acorn consumers vs. accessible to mice only) and in two types of microhabitat (covered by trunks, shrubs and herbaceous plants vs. uncovered). In addition, acorn germination rate was evaluated in a greenhouse. After 130 days, 76.67 ± 2.45 % of the seeds had been removed and the two accessibility treatments did not differ significantly. Mice were therefore shown as important predators and/or dispersers of acorns. Removal was greater in the covered (93.33 ± 2.04 %) compared to the uncovered (60.00 ± 4.01 %; P < 0.05) microhabitat. Acorn removal and germination were highest for Q. germana (82.00 ± 3.86 %, 91.67 ± 4.41 %, respectively), followed by Q. sartorii (79.00 ± 4.09 %; 50.00 ± 7.64 %) and Q. cortesii (69.00 ± 4.64 %; 13.33 ± 4.41 %); the same trend was recorded in the acorn germination rate (P < 0.05). Our findings suggest that uncovered sites with partial shade might function as regeneration microhabitats where less acorn removal and higher germination occur. The implications of differential acorn trait preferences by rodents for the coexistence of these oak species are discussed.     

Vaginal estrus in unmated Belding's ground squirrels

Belding's ground squirrels are seasonally breeding rodents that have a single annual mating season (ca. 3 weeks long) which begins shortly after their vernal emergence from a 7-month period of hibernation. In this study, changes in vaginal estrus were assessed among unmated captive females. Following a 7-month period in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females were in vaginal estrus within 24-48 hr of removal from the coldroom. Rather than exhibiting repeated cycles, adults (greater than or equal to 2 years old) remained in prolonged estrus (typically 3-4 weeks, but 8-10 weeks in some cases), whereas yearlings exhibited similar but shorter and possibly periodic changes in vaginal condition. The difference between the two age classes persisted in a second year of testing, indicating that the preadult status of yearlings (in the first year of testing) did not primarily account for the difference. In another experiment, removal from the coldroom was delayed for 24 days relative to adults removed at a time coincident with emergence from hibernation of free-living females. The "delayed" adults showed persistent vaginal estrus for a shorter total duration, such that both groups reached anestrus at approximately the same time. This implies that the latency to anestrus is not simply a fixed period from the time of removal from the coldroom.     

Characteristics of auditory brainstem responses in ground squirrels

Summary Auditory brainstem responses (ABRs) were characterized at 37 °C in ground squirrels (Citellus lateralis) which were implanted with recording screws to record ABRs, and a thermistor to record brain temperature. After two weeks ground squirrels were reanesthetized and tone pips and clicks were delivered through a TDH-49 headphone.Recorded ABRs were found to vary in a predictable manner as a function of stimulus frequency and intensity. At intensities above 50 dB SPL, ABRs could be recorded over the range tested (2–32 kHz). An 8 kHz tone pip was the best frequency for recording ABRs at the lowest stimulus intensities. Latencies decreased as stimulus frequencies increased from 4 kHz to 32 kHz.