Investigations of density interactions among breeding birds in ponderosa pine forests: correlative and experimental evidence

Summary We assessed the importance of interspecific competition among insectivorous birds breeding in northcentral Arizona's ponderosa pine forests. We examined density interactions among species using two analytic approaches; correlative and experimental. The correlative approach examined patterns of change in breeding densities over four years at the community level and within two foraging guilds; picker-gleaners and aerial feeders. The relationships between morphological and behavioral similarity with pairwise density interactions were also assessed. Our experimental approach involved placement of nest boxes on two treatment plots to increase breeding densities of secondary cavity nesting birds that were in foraging guilds with open nesting insectivores.We found little evidence of interspecific competition. Patterns of density fluctuations indicated large positive covariances among species at both the community level and within guilds. Pairwise density interactions were independent of morphological or behavioral similarity. Nest boxes significantly increased breeding densities of the secondary cavity nesters. However, these increases did not induce reprocal density changes in the open nesting species. Interspecific competition for food during the breeding season appears to be unimportant in ponderosa pine bird communities.     

曲霉属种间原生质体融合后病毒传递及遗传重组——Ⅱ.黑曲霉与米曲霉种间杂交

感染直径28-33纳米球形病毒的葡糖淀粉酶生产菌黑曲霉与无病毒生长较快的米曲霉通过原生质体融合杂交,获得两种形态不同的种间杂种。杂种Ⅰ经遗传及生化分析推测是二倍体,杂种Ⅱ不产孢子并生长较慢。两个杂种均感染了病毒,病毒形态、血清反应、衣壳多肽及核酸组份均与亲本黑曲霉的病毒相同。杂种诱发分离的后代中,多数包括亲代型黑曲霉分离子及其它分离子均感染了病毒,只有一个分离子和来自异核体的一个分离物例外,二者均产生亲代型米曲霉类型的孢子。这种亲代型分离表明病毒种间传递并非胞质遗传。 黑曲霉与米曲霉分属黑曲霉群及黄曲霉群,是曲霉属内亲缘关系远的种间杂交,迄今并无报道。杂种Ⅰ具有接近原始亲本的葡糖淀粉酶的产量及米曲毒的生长速度。     

Dihaploids of Elymus from the interspecific crosses E. dolichatherus x E. tibeticus and E. brevipes x E. panormitanus

Summary Dihaploids (n=2x=14, SY) of two Elymus species, i.e., E. dolichatherus (Keng) Löve (2n=4x=28, SSYY) and E. brevipes (Keng) Löve (2n=4x=28, SSYY), were obtained from the interspecific hybrid combinations E. dolichatherus () x E. tibeticus (Meld.) G. Singh () and E. brevipes () x E. panormitanus (Parl.) Tzvelev (). The dihaploids were probably formed through selective elimination of male parental chromosomes in early embryo development. Meiotic chromosome behavior was studied in E. dolichatherus, E. brevipes, and their dihaploids. The two parental Elymus species had regular meioses with predominantly ring bivalent formation. A low frequency of homoeologous chromosome pairing was observed, with an average of 0.81 bivalents and 0.03 trivalents in the dihaploid of E. dolichatherus, and 0.26 bivalents in the dihaploid of E. brevipes. Up to two chromatid bridges accompanied by small fragments were present at anaphase I of the E. dolichatherus dihaploid. It is concluded from this study that: (i) both E. dolichatherus and E. brevipes are allotetraploid species; (ii) a low affinity exists between the S and Y genomes of the two Elymus species.     

Isozyme analysis as a tool for introgression of Sinapis alba germ plasm into Brassica napus

Summary Isozyme analysis of Brassica napus cv Topas and CGRC5006 as well as of Sinapis alba cv Emergo revealed significant polymorphism between the two species for the isozymes, aconitate hydratase, glucose phosphate isomerase, and diaphorase. F₁ hybrids between B. napus 5006 and S. alba cv Emergo were backcrossed to B. napus cv Topas, and the S₁ progeny of the first two backcrosses were studied isozymically. At the backcross one level the frequency of S. alba or S. alba plus B. napus patterns observed ranged from 18% to 87% across the four lines studied. There were differences between lines for the frequency of S. alba patterns, which could have an impact on the efficiency of selection for subsequent backcrossing. By the backcross two generation in one of the two lines studied, GR86-24, the S. alba patterns for GPI and DIA had been lost, while in the other line, GR86-28, the S. alba pattern for ACO had been lost, resulting in lost opportunity for S. alba gene transfer. In a wide cross such as S. alba x B. napus, which requires an intensive effort to accomplish, the isozymes ACO, GPI, and DIA may serve as useful markers to ensure gene transfer between the two species has occurred. In addition, the identification of lines with divergent isozyme patterns from B. napus will provide the basis for establishing linkages between S. alba traits of interest and isozyme markers.     

庐山常绿阔叶,落叶阔叶混交林乔木种群种间联结性研究

本文通过２×２联列表以多种指标分别测定了庐山常绿阔叶、落叶阔叶混交林３６个乔木种群在抽样面积分别为１００ｍ２和４００ｍ２时的种间联结性。结果表明：在中亚热带山地森林植被研究中,以Ｘ２检验为基础,结合联结系数ＡＣ和共同出现百分率ＰＣ来测定植物种群的联结性,效果较好。一方面,不同大小的样方能反映物种种间联结性的空间变化;另一方面,抽样面积为１００ｍ２,更能准确全面地表现优势种群种间联结性的特征。种间正联结性越强,其生态位重叠值越大,反之,种间负联结性越强,其生态位重叠值越小。最后,还将这３６个种群按其联结性划分为４个生态种组。     

马尾松红锥混交林现状分析与评价

本文根据广西六万林场马尾松、红锥混交林的调查结果,分析了松、锥混交林各树种的胸径、树高和材积的生长现状;土壤的理化特性;松锥混交林营造技术措施。并对该场松锥混交林存在的问题,初步探讨了松锥混交林合理的种间关系和营林的主要技术措施。     

Predicting extinctions: interspecific competition,predation and population variability in experimental Daphnia populations

We examine how interspecific competition and two types of size-selective predation affect population density, variability and persistence in laboratory cultures of two species of Daphnia, D. magna and D. longispina. When both species were analysed together, and for D. longispina alone, there were weak negative relationships between mean population density and population variability. Interspecific competition resulted in lower population densities and higher population variability. Extinct populations had lower densities and were also more variable than persisting ones. There was still an effect of population variability on extinction probability after the effect of density on population variability had been accounted for. Hence, the effects of population density and variability on population persistence were partly independent of each other. The effects of size-selective predation on population persistence were more species-specific and not directly related to density or variability. Since the effects of species interactions on persistence were large, we suggest that it is likely that population vulnerability analyses not incorporating effects of interspecific interactions are often misleading.     

Chloroplast DNA variation in Populus. II. Interspecific restriction fragment polymorphisms and genetic relationships among Populus deltoides,P. nigra,P. maximowiczii,and P. x canadensis

Restriction fragment analysis was conducted to determine interspecific chloroplast DNA (cpDNA) variation and genetic relationships among Populus deltoides, P. nigra, P. x canadensis (P. deltoides x P. nigra), and P. maximowiczii. Total cellular DNAs of these poplars were digested with 16 restriction endonucleases, and Southern blots of the restriction digests were probed with six different cloned cpDNA fragments from Petunia. P. deltoides, P. nigra, and P. maximowiczii each had a distinct chloroplast genome, separated by many restriction-site and restriction-fragment-length mutations, predominantly in the large single-copy region of the genome. P. x canadensis shared the same cpDNA restriction fragment patterns as P. deltoides var. deltoides. P. nigra was most diverged from P. deltoides, and P. deltoides showed close cpDNA relationships to P. maximowiczii. Nucleotide substitutions per site in cpDNA were 0.0036 between P. deltoides and P. maximowiczii, 0.0071 between P. nigra and P. maximowiczii, and 0.0077 between P. deltoides and P. nigra. We suggest that P. nigra should be classified in a new separate section, the Nigrae.     

Inheritance of resistance to podfly and podborer in the interspecific cross of pigeonpea

 Pigeonpea, Cajanus cajan, is an important grain legume of Asia and Africa. The podfly, Melanagromyza obtusa, and the podborer, Helicoverpa armigera, are the major insect pests of this crop. An accession (JM 4147) of the wild species Cajanus scarabaeoides appears to possess resistance to these insect pests. For investigating the inheritance of resistance a cross was made between the susceptible cultivar Pant A-3 as female and the wild species. The parental lines and their F₁, F₂ and backcross generations were studied. For podfly, the per cent pod damage was recorded on individual plants. The results suggested that resistance to podfly is governed by the two recessive genes. In the podborer screening for antixenosis was carried out through the dual-choice arena test. The results indicated that a single dominant gene is involved in the antixenosis. Received : 11 March 1997 / Accepted : 4 April 1997