Differentiation of perennial and annual types due to habitat conditions in the wild riceOryza perennis

Populations of the common wild rice of AsiaO. rufipogon Griff. (=Oryza perennis Moench) were studied with regard to interrelations between life-history traits and habitat conditions. They showed a perennial-annual continuum and differed in reproductive allocation and many other traits. Perennial populations were found in deep swamps, while annual populations were in shallower, temporary swamps which were parched in the dry season. The perennial and annual types tended to be in association with other perennial and annual plants, respectively, suggesting their niche differentiation. Intermediate perennial-annual populations were in communities with a high species diversity. In one population, plants growing on the periphery of the swamp were of annual and those in deeper center were of perennial type. Another population seemed to be differentiated into an annual and an intermediate type in accordance with different degrees of habitat disturbance. The small genetic distances found between the sub-populations suggested their differentiation within a gene pool.Contribution from National Institute of Genetics, Japan, No. 1415.     

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.     

Population Genetic structure ofPotentilla fragariodes var.major (Rosaceae) in Korea

The genetic diversity and population structure of eighteenPotentilla fragariodes var.major (Rosaceae) populations in Korea were determined using genetic variations at 22 allozyme loci. The percent of polymorphic loci within the enzymes was 66.7%. Genetic diversity at the species level and at the population level was high (Hes = 0.203; Hep = 0.185, respectively), whereas the extent of the population divergence was relatively low (G_ST = 0.069). F_IS, a measure of the deviation from random mating within the 18 populations, was 0.075. An indirect estimate of the number of migrants per generation (Nm = 3.36) indicated that gene flow was high among Korean populations of the species. In addition, analysis of fixation indices revealed a slight heterozygote deficiency in some populations and at some loci. Wide geographic ranges, perennial herbaceous nature and the persistence of multiple generations are associated with the high level of genetic variation. AlthoughP. fragariodes var.major usually propagated by asexually-produced ramets, we could not rule out the possibility that sexual reproduction occurred at a low rate because each ramet may produce terminal flowers. Mean genetic identity between populations was 0.983. It is highly probable that directional movement toward genetic uniformity in a relatively homogeneous habitat operates among Korean populations ofP. fragariodes var.major.     

Comparative studies on the population dynamics ofMazus japonicus andM. Miquelii,scrophulariaceae

The population dynamics ofMazus japonicus andM. Miquelii was compared. In contrast with the summer annual growth habit (Vandellia crustacea) and the winter one(Veronica persica), M. japonicus had a “year-long annual growth habit” as the population of this species existed all year-round, notwithstanding that each individual of the population germinated and died within a year. TwoMazus species were sympatric on the levee of a rice paddy field where many other species were thickly grown. Those two species were difficult to propagate there, because their seeds, which were light germinators, could hardly germinate in the shade of other plants, or even if germination was possible, their seedlings may have soon died. However, asM. Miquelii, a perennial species, was able to reproduce by stolon vegetatively, it was a dominant species on the levee. On the contrary, the population density ofM. japonicus was thicker in the abandoned paddy field and an upland field than that ofM. Miquelii, because seeds of the former germinated under a greater variety of temperatures and under conditions of less soil moisture than those of the latter. These observations present an example of the fact that the difference of the reproductive strategy in annual and perennial plants has a striking effect on the population dynamics in the sympatric habitat.     

Ribosomal DNA variation and its phylogenetic implication in the genusBrachypodium (Poaceae)

The structure of ribosomal DNA ofBrachypodium and several other grass species was investigated using a heterologous rDNA probe from wheat. Several different rDNA families were present among perennial and annual species within the genus. In contrast to the annual species the perennial species exhibited a very low degree of repeat length variation. An extra Eco RI site and a Hin dIII site were observed in the IGS, which distinguishedBrachypodium from other grass genera. The restriction fragment length polymorphism and length variation of the repeat units have taxonomic value withinBrachypodium and are correlated with the classification ofBrachypodium derived from other data.     

Cytotaxonomy and breeding system of the genusBiscutella (Cruciferae)

Chromosome counts were determined for 46 populations ofBiscutella representing 28 taxa. The genus was found to contain diploid taxa with 2n = 12, 16 and 18, tetraploid taxa with 2n = 36 and hexaploid taxa having 2n = 54.B. laevigata L. s. l. consists of diploid and tetraploid populations which are poorly differentiated morphologically. TetraploidB. laevigata s. l. and hexaploidB. variegata Boiss. & Reuter (s. l.) are characterized by chromosomal instability. The variation in chromosome numbers and the occurrence of polyploidy is discussed in relation to the taxonomy of the genus. An investigation of the breeding system showed that most of the annual species were self-compatible and partly inbreeding and most of the perennial species self-incompatible and, therefore, outbreeding, while one annual species,B. cichoriifolia Loisel., showed both systems.     

Geographic differentiation among populations ofArabis serrata Fr. & Sav. (Brassicaceae)

Geographic variation in morphological traits of thirteen populations ofArabis serrata was analyzed to characterize the life history of each particular population in the field. These localities varied in altitude, topography, soil type, humidity, vegetation structure and degree of disturbance. Twelve morphological characters were measured in each plant, and populations were compared using both univariate and multivariate analyses. Populations showed significant differences for most of the traits measured. Principal component analyses revealed a significant differentiation among populations although a continuous variation for some traits was noted. Length of capsules and leaf length of inflorescence's stalks were correlated with the number of frost free days and with temperature, precipitation and number of days of the growing season. The number of rosettes was also correlated with the same variables but negatively. Seed weight was correlated positively with altitude but negatively with temperature and length of the growing season. Populations were also differentiated according to soil conditions and disturbance regimes distinguishing different types of populations: I) populations with many small rosettes, and few heavy seeds per capsule in volcanic soils with low disturbance; ii) plants with many small seeds and few rosettes in very disturbed localities along asphalt roadways and mountain trails; and iii) large plants with intermediate seed size and intermediate number of seeds per plant in limestone and serpentine soils under different conditions of disturbance. Populations ofA. serrata displayed a complex pattern of differentiation in morphological and life history traits in relation to several biotic and abiotic factors. The quantitative nature of the differences among populations ofA. serrata observed in the field deserves further studies (e.g., quantitative genetics and phenotypic plasticity) under controlled conditions in order to assess the extent of differentiation within this species complex.     

Production,population biology and diet ofNeomysis integer (Leach) in a shallow Frisian lake (The Netherlands)

TheNeomysis integer population of a shallow Frisian freshwater lake, situated in the north of the Netherlands, was studied from May until October 1980. The results were compared with observations on populations in other Frisian lakes, and with the results reported by other authors on brackish-water and marine populations of this species.Three generations were observed: one overwintering generation and two summer generations. Reproduction stopped completely during winter. During 1980 population densities ofN. integer were relatively low in all Frisian lakes. In Slotermeer the maximum population density was only 6 individuals m^–2, production amounted to 10 mg dry wt m^–2 yr^–1. The annual P/B ratio was 4.0. The diet ofN. integer consisted, in terms of biomass, of more than 95% detritus and animal food, the latter mainly consisting ofBosmina and cyclopoid copepods. Feeding intensity reached a maximum at sunset. It was still high during first part of the night and was low in the morning just after sunrise.     

Modelling the recovery of an annual savanna grass following a fire-induced crash

Abstract The native annual Sorghum populations of the Australian wet-dry tropics are highly resilient to dry season fires. During the early wet season, however, fires that occur after the new grass population has emerged can cause catastrophic population crashes. We examined savanna plots that had been burnt in this way, and compared them with adjacent unburnt plots. We found that Sorghum densities in the burnt plots were lower on average by a factor of 10, but that some fires had reduced the density only to one-third of the unburnt plots. It is not clear whether these differences relate directly to site or seasonal factors, or to differences in the way the burning was carried out. Other vegetation components responded to the fires differently: forbs (dicotyledonous herbs) increased in cover, while perennial grasses, woody plants, and overall species richness, were not significantly affected. The amount of leaf litter declined. A population model for Sorghum based on the demography of unburnt populations predicted that they should recover from a wet season burn, taking 7–16 years to return to normal densities. However, the actual field populations did not seem to be recovering, suggesting that wet season fires not only lower densities, but may also fundamentally change population processes in these annual grasses.     

Genetic diversity of SIRE-1 retroelements in annual and perennial glycine species revealed using SSAP

Sequence Specific Amplification Polymorphisms (SSAP) were used to measure the distribution and structure of SIRE-1 retroelement populations in annual and perennial Glycine species. For SSAP analysis, primers corresponding to a region immediately upstream of the 3’LTR of the soybean retroelement SIRE-1 were chosen. Analysis reveals that SIRE-1 is present throughout the Glycine genus and shows that the annual species have similar SIRE-1 populations whilst the perennial species have much more distinct and diverse populations. The high number of species-specific subgroups suggest that SIRE-1 has been active and evolving independently in each species during the course of Glycine evolution.     

Habitat selection and coexistence of invasive cockroach species (Dictyoptera) in sugar-cane fields on Réunion island

Selection of habitat has a profound influence on interactions among species and the assembly of ecological communities. We investigated habitat preferences to understand how different cockroach species coexist in sugar-cane fields on Réunion island.Cockroach populations belonging to a guild of seven species were surveyed during one annual cycle in eight sugar-cane fields that differed by several environmental factors, in order to investigate ecological features of cockroach species and their patterns of coexistence.Structure variations of the cockroach communities were analyzed at the field scale, at the sample unit scale, and according to variations of environmental conditions related to the annual sugar-cane growth cycle. A canonical correspondence analysis (CCA) was used to elucidate relationships between species diversity, population abundance and environmental characteristics.The examination of partitioning at different spatial and temporal scales evidenced that each species occupied a particular type of habitat. The main factors influencing spatial habitat selection were at the sample unit scale: presence of ants, edge effect, soil moisture and granulometry, at the field scale: irrigation, annual rainfall, altitude and age of the field. Although a pair of species shared the same type of habitat, annual population peaks of each species did not coincide in time. This suggests that resource partitioning is based both on ecological factors and interspecific competition.Factors enhancing cockroach coexistence and factors favoring population outbursts are discussed as well as specific invasive capacities of these cockroaches and the role of the cockroach community in the sugar-cane trophic web.     

Ecological evaluation of local extinction: the case of two genera of endemic Mexican fish, Zoogoneticus and Skiffia

The Goodeidae is a family of endemic fish from central Mexico. Populations of several species are declining in the wild and two have been reported extinct; Skiffia francesae and Zoogoneticus tequila. Both species were native to just one locality in the Ameca basin. It is difficult to infer the causes of extinction, since limnological data from Teuchitlán prior to the extinction events are not available, and there are no replicate populations. As an alternative approach, we explored the potential links between key environmental variables and events of local extinction of any species in the two genera (four Skiffia spp. and two Zoogoneticus spp.). In 14 localities known to harbour populations of fish of at least one of the six focal species, we conducted limnological surveys in the rainy and in the dry season, and quantified population densities of endemic and introduced fish. In addition, we quantified the concentration of agricultural pollutants in water and mud samples taken from every locality in the dry season. We found that all the focal species face some conservation threat, but we also discovered an extremely small population of the reputedly extinct Zoogoneticus tequila; in contrast, Skiffia francesae was not found. Eutrophication and habitat fragmentation appear to be the main threats to the focal species, with habitat fragmentation exponentially reducing population size and driving populations into refuges where they face stochastic extinction.     

Farmland habitat selection of wintering lesser kestrels in a Spanish pseudosteppe: implications for conservation strategies

The lesser kestrel Falco naumanni is a globally threatened species, whose breeding populations seem to have declined due to recent agricultural changes. However, nothing is known about habitat requirements during winter, despite the fact that several populations are overwintering in areas affected by agricultural transformations. We studied population size and habitat selection by wintering lesser kestrels in a Spanish pseudosteppe (Los Monegros), where traditional fallow systems for cereals are rapidly being replaced by intensive and/or irrigated crops. About 15% of the adult population wintered in the study area, as determined by systematic roadside counts compared with accurate censuses made during the breeding season. Wintering lesser kestrels preferred to forage on field margins and stubble, while avoiding abandoned fields, ploughs, scrubland, growing cereals and, mainly, the expanding irrigated crops. This work confirms the need to incorporate the habitat requirements of threatened species over their complete annual cycles; while breeding lesser kestrels scarcely use fallow (ploughed at that time), during the winter, fallow (stubble at that time) is their main foraging habitat. Both fallow land and the present agricultural calendar should be maintained to assure the conservation of wintering lesser kestrel populations.     

不同干扰程度下沙生植物异翅独尾草的种群结构与动态特征

不断加剧的人类活动导致古尔班通古特沙漠南缘异翅独尾草(Eremurus anisopterus(Kar.et Kir.)Regel)生存生境片段化,形成许多大小不一的斑块种群。为深刻理解在不同程度破碎化斑块中异翅独尾草种群的生存现状,共选取19个样点,分析其龄级结构,编制静态生命表,绘制存活曲线和死亡曲线,并引入4个生存分析函数。结果表明:古尔班通古特沙漠南缘不同样地中异翅独尾草种群动态因人类干扰与生境破碎化程度的差异,呈现为不同的结构特征及变化趋势,各样地异翅独尾草种群龄级完整性均不同,破碎化程度高的样地中种群的龄级有残缺或断代现象;人类干扰程度中、弱的b类型、c类型斑块的种群年龄结构分别属于稳定至衰退型和增长型,而受干扰最强的a类型斑块中的种群结构表现出较强的波动性,种群趋于衰退的风险较高;存活曲线与4个生存函数曲线表明,a类型种群前、中期稳定,后期衰退;b类型种群前期衰退,中、后期稳定;c类型种群稳定增长。说明异翅独尾草种群的衰退可能是其生境破碎化引起的,因此,对于人类干扰程度强的衰退型种群应亟需减少人为干扰,依据不同生境中的干扰因素及种群生存现状,制定科学与切实可行的保护、恢复策略。     

Genetic diversity and population structure of<Emphasis Type="Italic">Kalopanax pictus</Emphasis> (Araliaceae)

Kalopanax pictus (Araliaceae) is a long-lived woody species primarily distributed throughout East Asia. This species is regarded as medically and ecologically important in Korea. We used starch gel electrophoresis to investigate its allozyme variation and genetic structure in samples from Korean populations (both natural and cultivated). Our analysis of 10 enzymes revealed 18 loci, of which 10 were polymorphic (35.6%). Genetic diversity at the species and population levels were 0.200 and 0.149, respectively, with the mean for cultivated populations (0.124) being lower than for natural (wild) populations (0.181). Asexual and sexual reproduction modes, perennial habitat, and longevity all were possible factors contributing to such high diversity. An indirect estimate of the number of migrants per generation (N _m = 1.08) indicated that gene flow was not extensive among these Korean populations. Therefore, we suggest that geographical distance as well as reproductive isolation between wild and cultivated plants may play roles in shaping the population structure of this species.     

A long-term study of winter and early spring tree pollen in the Tulsa, Oklahoma atmosphere

Since 1986 the atmosphere in Tulsa, Oklahoma has been monitored for airborne pollen and spores with a Burkard 7-day spore trap situated on the roof of a building at The University of Tulsa. The present study specifically examined the early spring tree pollen season for several local taxa and the occurrence of pre-season pollen during December and January. Knowledge of the local pollen season will help identify the presence of out-of-season pollen and possible long distance transport (LDT) events. Average daily concentrations of airborne pollen for species ofBetula, Quercus, Ulmus, and Cupressaceae were determined for each year from 1987 to 1996. The data showed that during the early spring the precise pollination periods for these allergenic tree species are highly variable. There were considerable variations in start date, season length, peak concentration, date of peak, and cumulative season total. The start dates forUlmus, Betula, andQuercus varied by 30 days or more, while the early spring Cupressaceae pollen showed the least variation in start date (only 23 days). More research is needed to understand the mechanisms which govern the onset and magnitude of pollen release. Although several reports have documented episodes of long distance transport (LDT) of pollen, the actual contribution of out-of-season or out-of-region pollen to local air spora is poorly known. The current study also re-examined the LDT ofJuniperus ashei pollen in Oklahoma.Juniperus pollen appeared in the Tulsa atmosphere on 40% of the days in December and January with concentrations as high as 2400 pollen grains/m³ of air; however, no local populations ofJuniperus pollinate at this time of the year. High concentrations occurred on days with southerly winds suggesting thatJuniperus ashei populations in southern Oklahoma and Texas were the pollen source. Since no local pollen is present in the Tulsa atmosphere in December and January, this example of LDT has been easy to document.     

Growth and competition in annual legume—perennial grass pasture in a dry monsoonal climate

The seasonal growth characteristics of a perennial (sabi grass (Urochloa mosambicensis))-annual (Townsville stylo (Stylosanthes humilis)) pasture ecosystem in the dry monsoonal region of norther Australia are described. The phases during which the botanical composition of the ecosystem may change are dry season plant survival, germination, establishment, growth and propagation. A conceptual model with general applicability for a pasture of perennial and annual species is presented and the inter-relationships between the identified phases are indicated. For the example studied, there was a large decline in the proportion of the annual legume in the establishment phase, due to competition for restricted soil moisture. This explains the trend to grass dominance observed in sabi grass-Townsville stylo swards, and is considered to apply generally in a perennial-annual pasture in a dry monsoonal environment. Two distinct environmental periods occurred during the season and were reflected in the observed growth characteristics. During the first, the growth rate of Townsville stylo was slow and plant density fluctuated sharply. The growth rate of sabi grass also fluctuated sharply due to high temperature and radiation, and variable but limiting soil moisture. In the second period temperatures were lower and soil moisture was higher. During this period growth rate of sabi grass and tiller production declined but both the plant density of sabi grass and the growth rate of Townsville stylo increased. As sabi grass has a high initial growth rate and nitrogen and phosphorus contents which are nutritionally acceptable during the transition between the dry and wet seasons, monospecific sabi grass swards are suggested for grazing during this period.     

Reproductive seasonality and nest-site differentiation in three closely related armoured catfishes (Siluriformes: Callichthyidae)

Synopsis Three sympatric, closely related armoured catfishes showed a similar, bimodal breeding season in coastal plain swamps in Suriname (South America). The bimodal pattern of reproduction inCallichthys callichthys,Hoplosternum littorale andHoplosternum thoracatum was correlated to the annual distribution of rainfall. Floating bubble nests were constructed throughout the period of swamp inundation (rainy season). Close inspection of the timing of reproduction ofH. littorale in northern South America revealed the relationship between reproduction and rainfall, but also unexpected differences in the length of the breeding season. Strong interspecific competition among the three species was probably avoided through differentiation of nest sites with respect to water depth, distance to the nearest tree, distance to the edge of the swamp, and cover above the nest. Nests ofH. littorale were built in herbaceous swamps, whileC. callichthys andH. thoracatum build their nests in swamp-forest. Nests ofC. callichthys were observed in extremely shallow water or in holes. Few nests of the three species were observed in canals. Over large parts of their geographical rangeC. callichthys andH. thoracatum are found in small rainforest streams. Several aspects of the reproductive ecology and behaviour of both species are probably related to the unpredictability of the stream habitat.     

Dryinid (Hym.: Dryinidae) parasitoids ofDalbulus leafhopper (Hom.: Cicadellidae) in Mexico

Little is known about the natural enemies of the leafhopperDalbulus spp. (Homoptera: Cicadellidae). Searches for its dryinid (wasps) parasitoids were made in Jalisco, Mexico. Jalisco contains the greatest number ofDalbulus species, and is considered to be near to the center of origin of this leafhopper genus and its host plants: maize, teosintes (Zea spp.) and gamagrasses (Tripsacum spp.). The dryinidGonatopus bartletti was found parasitizingD. maidis on maize and on annual teosinteZea mays spp.parviglumis. G. flavipes was found parasitizingD. elimatus on perennial teosinteZ. perennis; and a new speciesG. moyaraygozai andAnteon ciudadi parasitizingD. quinquenotatus onTripsacum pilosum andT. dactyloides. Parasitism by dryinids was found at altitudes of 680–2,000 m.Dalbulus maidis, the leafhopper species which causes the greatest losses in maize in Latin America, was found to be parasitized from 680–1,760 m. TheDalbulus species associated with annual host plants (maize andZ. mays spp.parviglumis) were parasitized by dryinids during the rainy season, while theDalbulus species associated with perennial host plants (Z. perennis andTripsacum) were parasitized by dryinids during both the rainy and dry season. The greatest diversity of dryinid parasitoids ofDalbulus spp. and the highest levels of parasitism were recorded from perennial plants, indicating that such species are reservoirs of natural enemies ofDalbulus spp.