Bright ideas about parasites

The Hamilton-Zuk hypothesis for parasite-mediated sexual selection in animals has generated much controversy. To resolve the arguments it will be necessary to incorporate many more details of the biology, ecology and evolution of hosts and parasites into studies of sexual selection.     

Factors controlling fruit set in hermaphroditic plants: Studies with the Australian proteaceae

The number of fruits produced by many hermaphroditic plants is usually far fewer than the number of flowers available for fertilization. There are various possible explanations for the low fruit:flower ratio, some proximate and others ultimate. Recent studies, especially in northern hemisphere systems, have used field experiments to test some of them, but there are potential difficulties with the methodology of some experiments and with the testing of ultimate hypotheses. It is important to examine the possible explanations for low fruit: flower ratios with a range of different systems. This article reviews studies on Australian species of woody, perennial shrubs in the family Proteaceae; this evolutionarily distinct group of plants and pollinators has several unusual and interesting characteristics, and provides a valuable addition to the better-known northern hemisphere studies.     

Short-term instabilities and long-term community dynamics

Competition in a temporally variable environment leads to sequences of short-term instabilities that in some cases are the mechanism of long-term coexistence; in other cases they promote long-term instability. Recent work associates long-term stability with a positive relationship between environmental and competitive effects and with population growth rates that are buffered against jointly unfavorable environmental and competitive events. Buffered growth rates arise from population subdivision over life-history stages, microenvironments or phenotypes. A distinct but related mechanism of long-term stability relies on population growth rates that are nonlinear functions of competition. New ways of understanding and investigating species diversity follow from these results.     

The changing solar ultraviolet climate and the ecological consequences for higher plants

There is compelling evidence that a general erosion of the global ozone layer is occurring. Since ozone in the stratosphere absorbs much of the shortwave solar ultraviolet radiation (UV-B), diminished ozone means that more UV-B of a very specific wavelength composition will be received at the earth's surface. Evaluating the implications for vegetation involves consideration of the wavelength specificity of biological photochemical reactions and their sensitivity to the extant and future solar spectrum. Recent research suggests the occurrence of direct damaging reactions and of indirect morphological and chemical responses with implications at the community and ecosystem levels.     

Supply-side ecology and benthic marine assemblages

Many marine invertebrates have a planktonic stage of their life history during which widespread dispersal and much mortality occur. The numbers surviving to recruit into habitats occupied by adults are therefore very variable in time and space. Models for the structure and dynamics of benthic assemblages tend to focus on processes causing death - often assuming consistent arrivals of recruits. Supply-side ecology is a newly fashionable term to describe recent interest in the long-realized consequences of variations in recruitment. Such variations have important influences on theory and empirical research in these assemblages.     

Are ecological systems chaotic - And if not, why not?

Chaotic dynamics emerge when positive/negative feedback systems are dominated much of the time by positive feedback growth processes. Although all ecological systems contain the seeds of chaos (positive feedback), empirical evidence and evolutionary/ecological reasoning support the view that ecosystems do not normally behave chaotically. They may, however, be driven to chaos by human actions that increase growth rates or induce delays in the regulatory (negative feedback) processes.     

鸟类核型研究集形目9种

本文报道了蜂鹰、鸢,苍鹰、雀鹰、松雀鹰、普通鸷、鹊鹞、燕隼和猎隼9种鸟类的核型。鹰科鸟类具有与其它鸟类截然不同的核型。其特点为多而短的大染色体,长度匀称的棱型。谜种匀称的核型是由一般鸟类不匀称核型的大染色体发生了一系列着丝点分裂而形成     

两种捕食马尾松毛虫鸟类的初步研究

大山雀和白颊噪鹛是马尾松毛虫的最重要捕食性天敌。大山雀营巢于墙洞、土洞和树洞中,每窝产卵4—9枚。孵卵期平均14.8天,育雏期15—18天,幼鸟出窝率56.06％。白颊噪鹛营巢于浓密的杉树树冠及荆刺丛中,每窝产卵2—5枚,孵卵期平均14.6天,幼鸟出窝率36.36—44.26％。大山雀对1龄松毛虫为吞食,对2龄以上的松毛虫只啄食虫体的一部分;白颊噪鹛对各龄松毛虫均为吞食。在林间松树上人工放虫后3—4天,鸟对松毛虫的最高捕食率达94.84％。对已驯化的鸟在笼内做捕食量测定,大山雀和白颊噪鹛对1龄松毛虫每小时的捕食量分别为187和951条。