环境因子对硬骨鱼类性腺发育成熟及其排卵和产卵的调控

对影响硬骨鱼类性腺发育成熟及其排卵和产卵的诸多环境因子进行了综述（如水温、光照、降雨和水流、水体化学因子、水体生物因子以及环境污染（环境胁迫）等）,并对其调控机制进行了阐述,侧重强调了环境胁迫对硬骨鱼类生殖的影响,旨在从生态学角度为保护鱼类种质资源提供对策。     

一类食饵种群中具有传染病的捕食-被捕食系统

对疾病仅在食饵种群传播的有比例依赖的捕食-被捕食系统的动力学进行了分析,给出了每个平衡点附近系统的性态,定义了决定疾病灭绝和成为地方病的阁值R_0．得出的结论是:在比例依赖的捕食-被捕食系统中,染病食饵种群可以充当一个生物控制量,以抑制种群的绝灭．     

一个捕食-被捕食-互惠模型反应扩散系统的稳定性条件

本文利用Lyapunov直接方法讨论了一类捕食-被捕食-互惠模型的正值常态平衡解的稳定性．稳定性条件中包含对捕食与互惠种群扩散强度比例的限制．     

具有反馈控制的非自治多种群捕食-被捕食系统的持久性与全局吸引性

研究具有反馈控制的非自治多种群捕食-被捕食系统的持久性与全局吸引性.通过引入函数上、下平均的概念,得到系统持久和全局吸引的均值条件,同时将文献[7]的结果推广到了时滞非自治系统上.     

一类非自治捕食-被捕食系统的全局渐近稳定性

本文研究了一类非自治捕食-被捕食的周期系统．当周期为ω＞0时,在某些条件下证明了该系统正周期解的存在唯一性和全局渐近稳定性．     

不同迁移能力和竞争能力的集合种群竞争模式及其模拟

种群竞争是影响生态系统演化的莺要生态过程之一。本文是在徐彩琳和Tilman研究工作的基础上,将竞争系数引入集合种群动力模式,建立了集合种群之间竞争的数学模型,并对5-集合种群的竞争动态进行了计算机模拟研究。结果表明：种群竞争排除与共存受迁移扩散能力和竞争能力影响很大,排除原理在理论上是存在的,在广域集合种群和实际中物种是竞争共存的．共存的条件是其竞争能力与扩散能力呈非线性负相关关系,竞争的结果使物种的强弱序列发生变化。     

具有时滞和密度制约基于比率的捕食-被捕食系统的稳定性

考虑了一类具有时滞和密度制约基于比率的捕食-被捕食系统的稳定性.证明了系统在一定条件下的一致持久性,并且得到了系统正平衡位置局部稳定和全局稳定的充分条件     

非线性奇摄动多种群生态竞争-捕食系统的渐近解

利用局部坐标系统和边界层函数。讨论了一类多种群生态竞争——捕食非线性奇摄动系统的渐近性,得出了其任意r阶的渐近估计。     

具有捕食正效应的捕食-食饵系统

在经典的捕食食饵系统中考虑到由于捕食效应对食饵种群带来的正向调节作用后,提出了具有捕食正效应的捕食-食饵系统.通过对模型的动力学行为的分析,从理论上说明了正向调节作用对系统的影响,并就第一象限内平衡点存在时的相图解释了捕食正效应的作用.结果表明:(1)捕食系统中适当的正向调节作用会增加系统的稳定性;(2)当捕食正效应达到一定的程度后系统拥有一个不稳定的极限环;(3)当捕食正效应过大时会使系统的稳定性发生变化,使捕食者种群与食饵种群同时趋向无穷,出现了调节放纵现象.这些结果在保护生物学中具有重要的意义.     

一类捕食-被捕食系统周期解的存在性

对于二维非自治捕食-被捕食系统,本文讨论了它的解的有界性,进而得到周期解和正周期解的存在性。     

Costly dispersal can destabilize the homogeneous equilibrium of a metapopulation

I investigate the stability of the homogeneous equilibrium of a discrete-time metapopulation assuming costly dispersal with arbitrary (but fixed) spatial pattern of connectivity between the local populations. First, I link the stability of the metapopulation to the stability of a single isolated population by proving that the homogeneous metapopulation equilibrium, provided that it exists, is stable if and only if a single population, which is subject to extra mortality matching the average dispersal-induced mortality of the metapopulation, has a stable fixed point. Second, I demonstrate that extra mortality may destabilize the fixed point of a single population. Taken together, the two results imply that costly dispersal can destabilize the homogeneous equilibrium of a metapopulation. I illustrate this by simulations and discuss why earlier work, arriving at the opposite conclusion, was flawed.     

Competitive ability of maize pollen. Intergametophytic effects

Summary Intergametophytic influences on pollen competitive ability were studied by means of the pollen mixture technique: mixtures of pollen from different genetic sources, marked for the presence of the normal or the mutant allele of the opaque-2 gene, were used to pollinate o2o2 female plants. The variation of relative frequency of one of the two kernel types from apex to base of the resulting ear, made it possible to measure the competitive ability by regression coefficients.The effect of the pollen marker on the character was estimated by analyzing the progeny of heterozygous o2/+ plants self-pollinated through four generations. The o2 allele-bearing pollen revealed a slower germination rate than the dominant counterpart; no differences between the two pollen types were observed with regard to tube growth rate.The occurrence of intergametophytic interactions was confirmed: the competitive ability of a line varied according to the genotype of the competing pollen. Thus, this component has to be taken into account in considering male gametophyte fertilization ability.     

Joint evolution of specialization and dispersal in structured metapopulations

We study the joint evolution of dispersal and specialization concerning resource usage in a mechanistically underpinned structured discrete-time metapopulation model. We show that dispersal significantly affects the evolution of specialization and that specialization is a key factor that determines the possibility of evolutionary branching in dispersal propensity. Allowing both dispersal propensity and specialization to evolve as a consequence of natural selection is necessary in order to understand the evolutionary dynamics. The joint evolution of dispersal and specialization forms a natural evolutionary path leading to the coexistence of generalists and specialists. We show that in this process, the number of different patch types and the resource distribution are essential.     

The effect of habitat fragmentation on dispersal patterns, mating behavior, and genetic variation in a pika (Ochotona princeps) metapopulation

 Habitat fragmentation is becoming increasingly common, yet, the effect of habitat spatial structure on population dynamics remains undetermined for most species. Populations of a single species found in fragmented and nonfragmented habitat present a rare opportunity to examine the effect of habitat spatial structure on population dynamics. This study investigates the impact of highly fragmented habitat on dispersal patterns, mating behavior, and genetic variation in a pika (Ochotona princeps) population with a mainland-island spatial structure. Juvenile dispersal patterns in fragmented habitat revealed that individuals tended to disperse to neighboring habitat patches. However, within-patch band-sharing scores from multilocus DNA fingerprints did not differ from what would be expected if individuals were assorting randomly among habitat patches each year. Multiple, short-distance dispersal targets for juveniles and occasional long-distance dispersal events suggest that habitat fragmentation on this scale has not resulted in restricted dispersal and a genetically subdivided population. Although pikas tended to mate with the closest available partner, DNA fingerprinting band-sharing scores between mated pairs were consistent with a random mating hypothesis. Random mating in this population appears to be an incidental effect of dispersal in a fragmented habitat. This pattern is distinct from that found in nonfragmented habitat (large talus patches) where mating was non-random and consistent with mating between individuals of intermediate relatedness. DNA fingerprinting data revealed within-species variation in the mating habits of the pika directly attributable to habitat spatial structure. Received: 4 November 1996 / Accepted: 30 June 1997     

Competitive ability is linked to rates of water extraction

Summary The relative competitive abilities of Agropyron desertorum and Agropyron spicatum under rangeland conditions were compared using Artemisia tridentata ssp. wyomingensis transplants as indicator plants. We found A. desertorum to have substantially greater competitive ability than A. spicatum as manifested by the responses of Artemisia shrubs that were transplanted into nearly monospecific stands of these grass species. The Artemisia indicator plants had lower survival, growth, reproduction, and late-season water potential in the neighborhoods dominated by A. desertorum than in those dominated by A. spicatum. In similar, essentially monospecific grass stands, neutron probe soil moisture measurements showed that stands of A. desertorum extracted water more rapidly from the soil profile than did those of A. spicatum. These differences in extraction rates correlate clearly with the differences in indicator plant success in the respective grass stands. Nitrogen and phosphorus concentrations in Artemisia tissues suggested these nutrients were not limiting indicator plant growth and survival in the A. desertorum plots.     

Competitive ability and the potential for lotteries among territorial reef fishes

Stegastes diencaeus and S. dorsopunicans are mutually territorial Caribbean damselfishes. S. diencaeus is larger, grows faster and lives longer than S. dorsopunicans. S. diencaeus is a habitat specialist that shares its primary habitat mainly with S. dorsopunicans. Field manipulations show that both S. diencaeus and S. dorsopunicans readily take over living space from smaller, but not larger, heterospecific neighbors. Natural changes in the use of living space by both species occur frequently and adult S. diencaeus often aggressively usurp the living areas of smaller S. dorsopunicans. Lunar and seasonal patterns of juvenile recruitment by S. diencaeus and S. dorsopunicans are similar. Large size bestows competitive superiority on S. diencaeus by giving its adults a superior ability to aggressively acquire living space, and by enabling its juveniles to quickly escape the period when they lack a size advantage. Hence they spend much of their lives as competitive dominants. There is no evidence that competitive advantages arising from large size are offset either by other adult attributes or by differences in temporal patterns of recruitment that affect priority of access to space. The lottery hypothesis for species coexistence relies on patterns of abundance being determined by patterns of recruitment to vacant space because different species have equal space-holding abilities. These data show that the existence of such a mechanism is doubtful.     

Experimental translocation of juvenile water voles in a Scottish lowland metapopulation

Population density affects dispersal success because residents can hinder or facilitate immigration into a new site, via a “social fence effect” or “social attraction” (or “conspecific attraction”), respectively. These mechanisms can affect the dynamics of fragmented populations and the success of translocations. However, information on the settlement behaviour of dispersers is rare. We conducted a manipulative field experiment using wild water voles, which exist in metapopulations along waterways in Scotland. We translocated 17 young of dispersal age into either an occupied site or a vacant site containing good habitat, which had recently become extinct due to a feral predator (American mink) moving through. We monitored the movements of translocated voles using radio telemetry. Translocated voles were less likely to settle in occupied sites with higher densities of residents, suggesting a possible social fence effect at high density. There was evidence of a social attraction mechanism, because voles never remained at new sites unless another individual arrived soon after translocation, and they were more likely to settle in occupied or colonised sites than vacant ones. Voles remained in the transient phase of dispersal for many days, and often followed a “stepping stone” trajectory, stopping for several days at successive sites. We suggest that trajectories followed by dispersing water voles, the time scale and long dispersal distances found in this species are conducive to locating conspecifics at low density and colonising vacant habitat. These results are encouraging for prospects of metapopulation persistence and future translocation success.     

Local dynamics and dispersal in a structured population of the whirligig beetle Deneutus assimilis

The study illustrates the ecological determinants and evolutionary consequences of dispersal in the pond-living water beetle Dineutus assimilis (Coleoptera: Gyrinidae). Over 2 years, local populatiopn dynamics were studied in 51 ponds within a 60-km² study area. In most of the 31 occupied ponds, and even in large populations, abundances changed dramatically from one year to the next. Nine extinction and nine colonisation events were observed. These temporal patterns show no sign of spatial autocorrelation. Such a habitat distribution should favour high dispersal rates. Indeed, D. assimilis was found to be a very effective coloniser of newly available sites (mean propagule size: 23). A mark-recapture study showed that most dispersal occurred after diapause and over distances ranging from 100 m to at least 20 km. Yet despite frequent movement, the local variability in environmental conditions maintiins a large variance in average reproductive success per pond. Furthermore, immigration rates vary widely within a season. The apparent lack of correlation between these two sources of variation should greatly strengthen the role of drift in this system. A companion paper (Nürnberger and Harrison 1995) documents a non-random distribution of mitochondrial haplotypes due to recent population bottlenecks.     

The effects of between-habitat dispersal rate on protist communities and metacommunities in microcosms at two spatial scales

The effect of manipulation of between-habitat dispersal rates in multiple patch systems was examined experimentally using protist communities in laboratory microcosms. Replicate landscapes of eight microcosms (patches) at two spatial scales (patch sizes) were inoculated with 13 species of protists. Dispersal was carried out by transferring a small random sample of medium and protists from one randomly selected microcosm to another within a landscape. Four dispersal rates (24, 6, 2 and 0 transfers very 3 days) were used, and the microcosms were sampled after 6 and 12 weeks. Patch size had a consistent effect on within-path (community) and within-landscape (metacommunity) diversity, both being lower in small patch systems. Higher dispersal rates had a slight effect on community and metacommunity diversity after 12 weeks, with a tendency for higher dispersal to slightly offset the rate of loss of species. Both dispersal and patch size had effects on the abundance of many individual species, though in a variety of ways. The individual species results suggest that extinction is selective with respect to both patch size and dispersal rate treatments, and may be influenced by species interactions. It seems likely that in metacommunity systems of this sort, rather than mainland-island systems, the potential effect of between-patch dispersal rate in rescuing and recolonizing where local extinctions occur may be much reduced by the effect of selective extinction, relative to that expected under the assumption of random extinction.     

Postmetamorphic dispersal and recruitment of first breeders in a Bufo calamita metapopulation

The migratory capacity of metamorphs and their later integration into local breeding populations was studied in a Bufo calamita metapopulation inhabiting the northern Rhineland, Germany (1991–1994). A new tagging method allowed unequivocal distinction among metamorphs (n = 1,709), which originated either from the spring-breeding cohort in 1991 and 1992 or from the summer-breeding cohort in 1991. The life history of batch-marked individuals was followed until adulthood, focusing on postmetamorphic dispersal, choice of breeding locality and timing of adult reproduction. Almost all metamorphs left the patches used for breeding within a few weeks after emergence. They were found at about the same density in all favourable microhabitats in a radius of up to 2 km around their native patch. This demonstrates that even small toadlets (6–11 mm snout-to-vent length) migrate distances of several hundred metres within a short time and that they significantly help prevent local extinction in sink populations (rescue effect). Recaptures of reproductive adults originating from tagged metamorphs were limited to males belonging to the 1997 spring and summer cohorts. The absence of recaptured females was probably due to their greater vagility and later sexual maturation. First-breeding males (2 years old) without exception joined the breeding cohort from which they originated: early breeders originated from spawn of the spring cohort, mid-summer breeders from spawn of the summer cohort. This result is in accordance with the hypothesis that the integration of first breeders to a specific breeding cohort is genetically controlled in central European natterjacks. The exchange of individuals between different cohorts in the same patch is considerably less than the migratory exchange between the same breeding cohorts among local populations, as predicted from the allozyme data. Received: 28 October1996 / Accepted: 4 June 1997