摘要:

We have developed microsatellite or simple sequence repeat (SSR) genetic markers for the tropical treePithecellobium elegans(Mimosoideae). The frequency of this class of marker is estimated and the level and distribution of variability at these markers is assessed and contrasted to that found at isozyme markers in the same populations. The results indicate that SSR loci are powerful tools for the analysis of population structure and that, in these populations, they provide a means of accurately examining two important parameters in conservation biology, gene flow and paternity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13873.x

出版商:Wiley    

年代:1996

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb15770.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

An allozyme examination was conducted to study the mating systems and genetic differentiation of populations ofEquisetum arvenseandE. hyemale.The study revealed that the rate of intragametophytic selfing in these homosporous pteridophytes is very low, i.e., on average 0.020 and 0.019, respectively, despite the potential hermaproditism and selfing of the gametophytes. Most populations consisted of numerous genotypes, and the average heterozygosities ofE. arvenseandE. hyemaleequalled 0.092 and 0.134, respectively. The commonly observed excess of the heterozygote genotypes indicates that there are interclonal differences in the frequency of vegetative reproduction. The level of genetic divergence among populations was considerable even within a limited geographic area. It is suggested that the life history ofEquisetum, characterized by the inefficiency of spore germination and gametophyte reproduction in noncolonizing situations, limits the level of gene flow and leads to a great genetic divergence between populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13874.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

We evaluated the influence of the reproductive ecology on low recruitment of sexually derived progeny observed inOpuntia rastreraWeber in the Southern Chihuahuan Desert, in two vegetation types. The flowers are diurnal, remaining open 9–10 hr. Pollen is released in the morning and at the same time the stigmas become receptive. Nectar is produced all day, but the production rate is higher at noon. The flowers are visited by insects, mainly solitary bees (Diadasiasp. andLithurgesp.). Floral characteristics and the pollen/ovule ratio suggest thatOpuntia rastrerais a facultative xenogamous species. Controlled pollinations indicate that it is not apomictic and pollinators are required to set fruit; it is also self‐compatible, but there is strong inbreeding depression for fruit set. However, we were unable to demonstrate differences in reproductive characters between the populations in both vegetation types. The average density of adults per hectare was one order of magnitude higher in the nopalera (Opuntia‐dominated scrublands) than in the grassland. However, the average density of plants that originated from seeds was one order of magnitude lower in the nopalera.Opuntia rastreraproduces abundant flowers, fruits, and seeds in both vegetation types in natural conditions. The low success in the recruitment of new genets cannot be ascribed to the reproductive ecology.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13875.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The self‐sterileSenecio jacobaea(Asteraceae) presents its rayed heads in large, compound inflorescences (corymbs). I examined the role of head and corymb size in pollinator attraction, and whether the positive effect of intact rays (if any) depends on the size of the corymb. Using female fertility as a measure of pollination success, I assessed the performance of stems representing four experimentally produced character combinations: (1) few heads without rays, (2) many heads without rays, (3) few heads with rays, and (4) many heads with rays. The proportion of flowers setting fruit was higher for intact stems (treatments 2, 4) than for stems on which the majority of the heads had been removed (treatments 1, 3), suggesting selection for maximum inflorescence production. By contrast, experimental removal of all rays had a relatively weak negative effect on fruit set, with few‐headed stems (treatment 1) experiencing a greater reduction than stems with many heads (treatment 2). These results suggest that clusters of heads produce a synergistic effect on pollinator attraction, allowing plants to maintain high visitation rates even if there are drastic reductions in the basic attraction units. Hence, the number of heads and the attractiveness of the individual heads interacted in their effect on pollination success. Fruit set per flower differed greatly between sites and was positively correlated with plant density.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13876.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Ramets of some clonal plant species alter their internode lengths or their frequency of lateral branching in response to their immediate microenvironment. Such “plant foraging” responses are thought to allow clones to concentrate in favorable portions of their environment. Despite widespread interest among ecologists in plant foraging, few realistic models have been developed to examine conditions under which plant foraging responses are likely to provide clones with ecological benefit. In this paper, we develop spatially explicit, stochastic simulation models to examine consequences of both empirical and hypothetical plant foraging responses. We construct a hierarchical series of models in which we incorporate effects of resource heterogeneity on spacer lengths, angles of growth, and lateral branch production. We also vary the number, size, and arrangement of patches, and the presence or absence of ramet mortality. Simulations based on hypothetical data demonstrated the potential importance of shortening spacer lengths in favorable habitat. In these simulations, ramet crowding increased significantly, implying a potential cost to plant foraging responses whose magnitude is large enough to cause ramets to concentrate in favorable patches. Models calibrated with empirical data suggest that when clonal plants were able to concentrate in favorable habitat, this was usually caused by increased daughter ramet production in the favorable habitat. Variation in clonal growth angles had little impact on the ability of ramets or clones to locate favorable patches, but did increase the ability of clones to remain in favorable patches once found. Alterations in the number and size of patches strongly influenced the effectiveness of the foraging response. The spatial arrangement of patches also was important: clumped distributions of patches decreased the success with which plants located favorable patches, especially at the genet level and when the number of patches was low. Finally, when ramet mortality varied with patch quality, there was an increase in the percentage of ramets located in favorable patches; differential ramet mortality also lessened the impact of other effects, such as the decreased success of clones when patches are clumped. Overall, our models indicate that the effectiveness of plant foraging responses is variable and is likely to depend on a suite of environmental conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13877.x

出版商:Wiley    

年代:1996

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb15772.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The effects of substrate salinity and salt spray upon seedlings ofScaevola sericeawere examined in this study. Three levels of substrate salinity: 0.0 ppt, 3.0 ppt, and 10.0 ppt were examined in conjunction with three levels of salt spray: zero, medium (200 mg m‐2mdd‐1), and high (1200–1500 mg‐m‐2mdd‐1). Leaf surface area, root to shoot ratio, as well as leaf, stem, and root mass decreased significantly (P0.05) with increasing substrate salinity. Biomass accumulation was very low at 10.0 ppt substrate salinity, suggesting that higher levels of substrate salinity cannot be tolerated by the seedlings. Salt spray had a substantial effect on several of these variables, however its effects were less pronounced than those of substrate salinity. Cell sap osmolarity, leaf thickness, and leaf specific mass increased significantly (P0.05) with both increasing substrate salinity and salt spray levels. Leaf carbon isotope ratios (δl3C) became more positive with increasing salinity, indicating an enhancement of the intrinsic water use efficiency of the seedlings at higher salinities.Scaevola sericeais one of the dominant plants found at the leading edge of strand communities in the Hawaiian archipelago and throughout much of the tropical Pacific. Since substrate salinity and salt spray increase with proximity to the ocean, the two factors may act together to limit the seaward expansion ofS. sericeain coastal habitats.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13878.x

出版商:Wiley    

年代:1996

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb15773.x

出版商:Wiley    

年代:1996

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb15774.x

出版商:Wiley    

年代:1996

数据来源: WILEY