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51.
Sheila K. Schueller 《Evolutionary ecology》2007,21(1):81-98
A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought
to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated
plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist.
I first determined differences in floral morphology and pollinator composition between island and mainland populations of
N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with
on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with
site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites.
I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring
phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated
with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds
did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection
for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite
the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to
other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift. 相似文献
52.
Estimates of biomass are essential for studies modeling the structure, animal growth, production, and energy flow in ecosystems.
The relationships between dry weight and carapace width of two varunid crab species in two different populations were examined.
Distribution of the length-weight plots did not show remarkable differences between species, sexes, and populations. Our results
suggest that length-weight relationships, regardless of sex or population or including multiple species, are valid for estimation
of dry weight. 相似文献
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55.
三种森林生态系统昆虫病原真菌优势种生态位比较 总被引:3,自引:0,他引:3
研究了天然阔叶林、天然阔叶次生林和马尾松人工纯林3种不同森林生态系统中昆虫病原真菌优势种的数量组成及生态位宽度和生态位重叠值.结果表明:球孢白僵菌在这3种森林生态系统中分别为第三、第一和第二优势种.该菌在3种森林生态系统中的营养生态位宽度和时间生态位宽度均最大,远大干环链棒束孢、粉棒束孢和细脚棒束孢等优势种;该菌与其他优势种的时间生态位重叠值较大,而营养生态位重叠值较小.球孢白僵菌在3种森林生态系统中都是发生时间最长、寄主昆虫最丰富、适应环境能力最强的昆虫病原真菌. 相似文献
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Genetic variation among populations in the degree of sexual dimorphism may be a consequence of selection on one or both sexes. We analysed genetic parameters from crosses involving three populations of the dioecious plant Silene latifolia, which exhibits sexual dimorphism in flower size, to determine whether population differentiation was a result of selection on one or both sexes. We took the novel approach of comparing the ratio of population differentiation of a quantitative trait (Q(ST) ) to that of neutral genetic markers (F(ST) ) for males vs. females. We attributed 72.6% of calyx width variation in males to differences among populations vs. only 6.9% in females. The Q(ST) /F(ST) ratio was 4.2 for males vs. 0.4 for females, suggesting that selection on males is responsible for differentiation among populations in calyx width and its degree of sexual dimorphism. This selection may be indirect via genetic correlations with other morphological and physiological traits. 相似文献
58.
We present a new 23‐site network of white spruce ring‐width chronologies near boreal treeline in Old Crow Flats, Yukon Territory, Canada. Most chronologies span the last 300 years and some reach the mid‐16th century. The chronologies exhibit coherent growth patterns before the 1930s. However, since the 1930s, they diverge in trend and exhibit one of two contrasting, but well‐replicated patterns we call Group 1 and Group 2. Over the instrumental period (1930–2007) Group 1 sites were inversely correlated with previous‐year July temperatures while Group 2 sites were positively correlated with growth‐year June temperatures. At the broader northwestern North America (NWNA) scale, we find that the Group 1 and Group 2 patterns are common to a number of white spruce chronologies, which we call NWNA 1 and NWNA 2 chronologies. The NWNA 1 and NWNA 2 chronologies also share a single coherent growth pattern prior to their divergence (ca. 1950s). Comparison of the NWNA 1/NWNA 2 chronologies against gridded 20th‐century temperatures for NWNA and reconstructed northern hemisphere summer temperatures (ad 1300–2000) indicates that all sites responded positively to temperature prior to the mid‐20th century (at least back to ad 1300), but that some changed to a negative response (NWNA 1) while others maintained a positive response (NWNA 2). The spatial extent of divergence implies a large‐scale forcing. As the divergence appears to be restricted to the 20th century, we suggest that the temperature response shift represents a moisture stress caused by an anomalously warm, dry 20th‐century climate in NWNA, as indicated by paleoclimatic records. However, because some sites do not diverge and are located within a few kilometres of divergent sites, we speculate that site‐level factors have been important in determining the susceptibility of sites to the large‐scale drivers of divergence. 相似文献
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