CAUSES OF VARIATION IN BIOTIC INTERACTION STRENGTH AND PHENOTYPIC SELECTION ALONG AN ALTITUDINAL GRADIENT

Understanding the causes of variation in biotic interaction strength and phenotypic selection remains one of the outstanding goals of evolutionary ecology. Here we examine the variation in strength of interactions between two seed predators, common crossbills (Loxia curvirostra) and European red squirrels (Sciurus vulgaris), and mountain pine (Pinus uncinata) at and below tree limit in the Pyrenees, and how this translates into phenotypic selection. Seed predation by crossbills increased whereas seed predation by squirrels decreased with increasing elevation and as the canopy became more open. Overall, seed predation by crossbills averaged about twice that by squirrels, and the intensity of selection exerted by crossbills averaged between 2.6 and 7.5 times greater than by squirrels. The higher levels of seed predation by crossbills than squirrels were related to the relatively open nature of most of the forests, and the higher intensity of selection exerted by crossbills resulted from their higher levels of seed predation. However, most of the differences in selection intensity between crossbills and squirrels were the result of habitat features having a greater effect on the foraging behavior of squirrels than of crossbills, causing selection to be much lower for squirrels than for crossbills.     

The influence of abrupt climate change on the ice‐age vegetation of the Central American lowlands

Aim To investigate the effects of abrupt climate change in the North Atlantic on the vegetation history of lowland Central America. We use palynological evidence from a Central American lake on the Yucatan Peninsula to evaluate the effects of rapid climate changes during the last ice age, between 65 and 8 ka. Location Lake Petén‐Itzá, lowlands of northern Guatemala. Methods Sediment core PI‐6 was sampled at c. 170‐year resolution for pollen and charcoal analysis in order to construct a temporal sequence of environmental change. Uni‐ and multivariate statistical analyses were performed on the pollen dataset to test whether there was an association between Heinrich events in the North Atlantic and vegetation changes in the Central American lowlands. Results Pollen analysis revealed that the composition of plant assemblages on the Yucatan Peninsula varied in phase with rapid changes in North Atlantic climate. Pine savannas were the main vegetation type between c. 60 and 47 ka. These savannas gave way to pine–oak (Pinus–Quercus) forests in the latter half of the last ice age. Marked episodes of replacement of the pine–oak assemblage by xeric‐tolerant taxa occurred during Heinrich events. The Last Glacial Maximum (LGM) was characterized by mesic conditions. Main conclusions The pollen record from Lake Petén‐Itzá showed that vegetation changes associated with Heinrich events were more significant than those associated with the LGM. Each Heinrich event produced a characteristic shift towards xeric taxa. Although colder than Heinrich events, the LGM on the Yucatan Peninsula was relatively moist, and the presumed savannization of the landscape during the maximum cooling of the last glacial was not supported by our data. Our findings suggest alternative scenarios for plant diversification and genetic interchange during glacial times, and also indicate that vegetation in tropical continental settings was not as stable as previously thought.     

Metabolic and structural responses of pine buds under climate chamber conditions

Scots pine ( Pinus sylvetris L.) plants, about 2 m high, were placed in controlled conditions for 2 weeks in January, April and November. During the experiments made in January, the conditions in the climate chambers simulated either a gradual or abrupt advancement of spring. In April they simulated either the advancement of the season or its reversal back to January. In November the plants were transferred to conditions that resembled spring. In January, pieces of buds collected at the end of the experiment were also fixed for electron microscope studies.
Isolation of the ribosomes and the determination of their in vitro translation capacity revealed that in January the response to environmental changes was evident. An increase in synthesized proteins was caused by a rise in the translation capacity of ribosome assemblies rather than by an increase in their quantity. The cellular ultras-structure changed in conformity with the changes characteristic of the spring. In April, the plants transferred to the climate chambers maintained their ability to synthesize proteins, but the buds were judged to be under stress. In November die ability of the buds to respond to environmental changes was retarded or inhibited.     

马尾松林向香樟林改造林下植物功能多样性研究

在生物多样性研究中,功能多样性比物种多样性可以更直接地反映生态系统的结构和功能,从而在群落生态学研究中受到越来越多的推崇。马尾松次生纯林是一种亟待改造的森林类型,而在亚热带地区香樟是马尾松林改造的理想树种之一。为了完善马尾松林向香樟林改造的研究,以更好地指导马尾松林改造的实践,本文用空间代替时间的方法,选取马尾松林向香樟林改造过程中4种不同阶段群落为研究对象,对林下灌木层和草本层植物的功能性状及其多样性展开了研究。结果表明:(1)随着森林改造的进行,林下植物的物种数目、功能性状多样性均表现为先上升后下降的变化趋势,其中功能丰富度和功能均匀度在改造前期达到峰值,而物种数目和功能离散度则在改造中期表现最高。(2)比较森林改造的4个时期,林下植物功能多样性的综合表现大致为:改造前期改造中期改造后期未改造时期。(3)森林改造过程中,林下植物"光响应性状"和"繁殖性状"的功能多样性变化趋势相似,但前者比后者对改造的响应更敏感。(4)在森林改造过程中,林下植物的生长、发育和扩散受到林下光照资源的影响,并在长时间的生物竞争中逐渐表现为物种种类、多度和空间分布格局的变化,最终影响生态系统功能。(5)马尾松林向香樟林的改造加速了群落的演替进程,提升了群落的功能,但仍存在林下植物功能多样性下降等问题。在对马尾松次生纯林改造过程中,应选择合适的造林密度和混交林的改造模式。     

Purification of Acetyl Coenzyme A: Deacetylacephalosporin C O-Acetyltransferase from Acremonium chrysogenum

Acetyl CoA: deacetylcephalosporin C O-acetyltransferase, which catalyzes the final step of the biosythetic pathway to cephalosporin C, was stabilized by a buffer solution containing 7-aminocephalosporanic acid and purified over 1300-fold from Acremonium chrysogenum. The purified enzyme has a molecular weight of 55,000 as measured by gel filtration. SDS-polyacrylamide gel electrophoresis showed two subunit bands corresponding to molecular weights of 27,000 and 14,000. The enzyme has an isoelectoric point at pH 4.0 and optimum activity at pH 7.5.     

Ultraviolet penetration of pine trees and insect virus survival

Solar UV light entering Lodgepole pine,Pinus contorta (Loud.) canopy was measured by radiometer and polysulphone film. It was found to be much attenuated among lower branches and nuclear polyhedrosis virus exposed there was significantly more infective to Pine beauty moth,Panolis flammea (D.+S.) than virus from upper branches. S. J. Warden died April 1989     

减雨对南亚热带马尾松人工林凋落物分解的影响

为探究气候变化背景下降雨格局改变对马尾松人工林凋落物分解及养分释放过程的影响,以南亚热带马尾松(Pinus massoniana)人工林为研究对象,设置穿透雨减少50%和不减雨(对照)处理,开展连续观测野外降水控制实验。采用凋落物分解袋法,研究了减雨处理对南亚热带马尾松人工林凋落叶分解速率及养分释放的影响,以及凋落叶分解速率的影响因素。结果表明:凋落叶分解2年后,减雨处理和对照林凋落叶残留率分别为38.09%和38.06%;凋落叶分解过程中碳元素表现为淋溶-富集-释放,而氮元素表现为富集,减雨50%在一定程度上促进了氮的富集,但未达到显著水平。相关分析表明,凋落叶的残留率与氮浓度和月积温呈显著负相关,与碳/氮呈显著正相关。本研究发现,减雨50%并未改变马尾松凋落叶分解速率和养分释放模式,凋落叶的残留率与氮浓度、碳/氮及月积温密切相关。