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811.
Iriartea deltoidea (Arecaceae) is an abundant canopy palm with a wide geographic distribution in Neotropical wet forests. We analyzed the genetic profile across three generations of Iriartea within a 43-ha area encompassing two areas of second-growth and adjoining old-growth forest at La Selva Biological Field Station in northeastern Costa Rica. A total of 311 reproductively mature trees, 99 large saplings, 207 small saplings, and 601 seedlings were genotyped using 141 AFLP loci. Parentage analysis revealed high dispersal distances, both for seed (over 2.3 km) and pollen (over 3.8 km), indicating a large genetic neighborhood within La Selva Biological Station. In a 20-ha area of second growth, the founding palm population was dominated by a small number of parental trees located in the adjacent old-growth forest; two old-growth trees contributed 48% of the second-growth genes. The genetic diversity of reproductively mature trees in this second-growth forest was significantly reduced compared to adjacent old-growth forest. Within 400 m of the border with old-growth forest, we observed a similar reduction of genetic diversity in saplings, and an even greater loss of genetic diversity in the second generation of seedlings. Nearly half of these seedlings were offspring of local parents. In contrast, in the distant portion of second-growth forest (400-800 m from the old-growth border), parentage analysis showed that 40% of seedlings originated from outside the study area and only 10% were offspring of local parents. These high levels of gene flow maintained genetic diversity in saplings and seedlings similar to levels observed in old-growth forest. Our findings highlight the importance of gene flow from diverse seed and pollen sources for sustaining levels of genetic diversity of tree populations in second-growth forests. 相似文献
812.
Response of complex food webs to realistic extinction sequences 总被引:4,自引:0,他引:4
Although an ecosystem's response to biodiversity loss depends on the order in which species are lost, the extinction sequences generally used to explore such responses in food webs have been ecologically unrealistic. We investigate how several extinction orders affect the minimum number of secondary extinctions expected within pelagic food webs from 34 temperate freshwater lakes. An ecologically plausible extinction order is derived from the geographically nested pattern of species composition among the lakes and is corroborated by species' pH tolerances. Simulations suggest that lake communities are remarkably robust to this realistic extinction order and highly sensitive to the reverse sequence of species loss. This sensitivity is not well explained by the known sensitivity of networks to the loss of highly connected species but appears to be better explained by our observation that trophic specialists preferentially consume widely distributed species at low risk of extinction. Our results highlight an important aspect of community organization that may help to maintain biodiversity amidst changing environments. 相似文献
813.
Giuseppe Donati An Bollen Silvana M. Borgognini-Tarli Joerg U. Ganzhorn 《Behavioral ecology and sociobiology》2007,61(8):1237-1251
Animals show specific morphological, physiological and behavioural adaptations to diurnal or nocturnal activity. Cathemeral
species, i.e. animals with activities distributed over the 24-h period, have to compromise between these specific adaptations.
The driving evolutionary forces and the proximate costs and benefits of cathemerality are still poorly understood. Our goal
was to evaluate the role of predator avoidance, food availability and diet quality in shaping cathemeral activity of arboreal
mammals using a lemur species as an example. For this, two groups of collared lemurs, Eulemur collaris, were studied for 14 months in the littoral forest of southeastern Madagascar. Data on feeding behaviour were collected during
all-day and all-night follows by direct observation. A phenological transect containing 78 plant species was established and
monitored every 2 weeks to evaluate food availability during the study period. Characteristics of food items and animal nutritional
intake were determined via biochemical analyses. The ratio of diurnal to nocturnal feeding was used as response variable in
the analyses. The effects of abiotic environmental variables were removed statistically before the analyses of the biotic
variables. We found that diurnal feeding lasted longer during the hot–wet season (December–February), whereas nocturnal feeding
peaked during the hot–dry and cool–wet seasons (March–August). Although the lemurs foraged mostly in lower forest strata during
daylight and used emergent trees preferably at night, the variables which measured animal exposure to birds of prey failed
to predict the variation of the ratio of diurnal/nocturnal feeding. Ripe fruit availability and fiber intake are the two variables
which best predicted the annual variation of the lemur diurnality. The data indicate that feeding over the whole 24-h cycle
is advantageous during lean periods when animals have a fibre-rich, low-quality diet. 相似文献
814.
Sheng Fulai Gary Flomenhoft Timothy J. Downs MaÁngeles Grande‐Ortiz Dana Graef Bert Scholtens Arthur P.J. Mol David A. Sonnenfeld Gert Spaargaren Rajeev K. Goel Edward W.T. Hsieh Serban Scrieciu Reinhard Steurer Christine Polzin Genia Kostka Tiho Ancev Elke Pirgmaier Frank Boons Karl‐Henrik Robèrt Christopher Bryant Ke Zhou Surya Raj Acharya David Huberman Denis J. Sonwa Michelle Mycoo Dabo Guan Klaus Hubacek U. Rashid Sumaila Hector G. Lopez‐Ruiz G. Jason Jolley Michael L. Dougherty André Francisco Pilon Ravi Prakash Tulus Tambunan Sebastian Hermann 《Natural resources forum》2011,35(1):63-72
815.
Reductive Dechlorination of Tetrachloroethylene by Soil Sulfate-Reducing Microbes under Various Electron Donor Conditions 总被引:7,自引:0,他引:7
Biotransformation of tetrachloroethylene (PCE) by soil sulfate-reducing bacteria was investigated using acetate, lactate and methanol as electron donors. Results show that the effectiveness of biotransformation of PCE by soil sulfate-reducing bacterial is dependent upon the type of electron donor used. 相似文献
816.
Haitzer M Löhmannsröben HG Steinberg CE Zimmermann U 《Journal of environmental monitoring : JEM》2000,2(2):145-149
The bioconcentration of pyrene by bacterivorous thread worms (nematodes) of the species Caenorhabditis elegans was studied with laser-induced fluorescence (LIF) spectroscopy, fluorescence imaging and a radiotracer method. The vibronic band intensities of the LIF spectra indicated that the microenvironment of pyrene in the nematodes was similar to a low-polarity solvent, and thus provided direct evidence that pyrene was accumulated in lipid-rich areas inside the nematodes. The concentration of pyrene in the nematodes was estimated from the monomer/excimer fluorescence intensity ratio. Results from this method were in fair agreement with results using 14C labeled pyrene for measuring pyrene bioconcentration. Preliminary results indicated that LIF measurements of pyrene may be possible even in single nematodes. Fluorescence microscopic observations revealed that pyrene was not adsorbed on the outside of the organisms, but was strongly concentrated in restricted areas inside the worms. In the second part of the study, the effects of six different humic substances (HS) on the bioconcentration of pyrene were investigated and sorption coefficients (KDOC) calculated from reductions in bioconcentration (KDOC(biol)) were compared with sorption coefficients measured with a fluorescence quenching technique (KDOC(flu)). The results of these two different experimental methods agreed well (with KDOC(biol) being slightly lower than KDOC(flu), indicating that the fraction of pyrene that was determined as freely dissolved by the fluorescence quenching method was comparable to the bioavailable fraction. 相似文献
817.
Smyth PP Burns R Huang RJ Hoffman T Mullan K Graham U Seitz K Platt U O'Dowd C 《Environmental geochemistry and health》2011,33(4):389-397
Thyroid hormone levels sufficient for brain development and normal metabolism require a minimal supply of iodine, mainly dietary.
Living near the sea may confer advantages for iodine intake. Iodine (I2) gas released from seaweeds may, through respiration, supply a significant fraction of daily iodine requirements. Gaseous
iodine released over seaweed beds was measured by a new gas chromatography–mass spectrometry (GC–MS)-based method and iodine
intake assessed by measuring urinary iodine (UI) excretion. Urine samples were obtained from female schoolchildren living
in coastal seaweed rich and low seaweed abundance and inland areas of Ireland. Median I2 ranged 154–905 pg/L (daytime downwind), with higher values (~1,287 pg/L) on still nights, 1,145–3,132 pg/L (over seaweed).
A rough estimate of daily gaseous iodine intake in coastal areas, based upon an arbitrary respiration of 10,000L, ranged from
1 to 20 μg/day. Despite this relatively low potential I2 intake, UI in populations living near a seaweed hotspot were much higher than in lower abundance seaweed coastal or inland
areas (158, 71 and 58 μg/L, respectively). Higher values >150 μg/L were observed in 45.6% of (seaweed rich), 3.6% (lower seaweed),
2.3% (inland)) supporting the hypothesis that iodine intake in coastal regions may be dependent on seaweed abundance rather
than proximity to the sea. The findings do not exclude the possibility of a significant role for iodine inhalation in influencing
iodine status. Despite lacking iodized salt, coastal communities in seaweed-rich areas can maintain an adequate iodine supply.
This observation brings new meaning to the expression “Sea air is good for you!” 相似文献
818.
Spatial patterns reveal negative density dependence and habitat associations in tropical trees 总被引:1,自引:0,他引:1
Bagchi R Henrys PA Brown PE Burslem DF Diggle PJ Gunatilleke CV Gunatilleke IA Kassim AR Law R Noor S Valencia RL 《Ecology》2011,92(9):1723-1729
Understanding how plant species coexist in tropical rainforests is one of the biggest challenges in community ecology. One prominent hypothesis suggests that rare species are at an advantage because trees have lower survival in areas of high conspecific density due to increased attack by natural enemies, a process known as negative density dependence (NDD). A consensus is emerging that NDD is important for plant-species coexistence in tropical forests. Most evidence comes from short-term studies, but testing the prediction that NDD decreases the spatial aggregation of tree populations provides a long-term perspective. While spatial distributions have provided only weak evidence for NDD so far, the opposing effects of environmental heterogeneity might have confounded previous analyses. Here we use a novel statistical technique to control for environmental heterogeneity while testing whether spatial aggregation decreases with tree size in four tropical forests. We provide evidence for NDD in 22% of the 139 tree species analyzed and show that environmental heterogeneity can obscure the spatial signal of NDD. Environmental heterogeneity contributed to aggregation in 84% of species. We conclude that both biotic interactions and environmental heterogeneity play crucial roles in shaping tree dynamics in tropical forests. 相似文献
819.
Medhi UJ Talukdar AK Deka S 《Journal of environmental biology / Academy of Environmental Biology, India》2011,32(2):185-188
The physico-chemical characteristics of paper mill industry effluent were measured and some were found to be above the permissible limits prescribed by Indian irrigation water standard. A study was conducted in pots to investigate the effects of different concentrations (10, 20, 30, 40, 50, 60, 70, 80 and 100%) of paper mill effluent on growth and production of rice, mustard and peafor three years. The study reveals that the paper mill effluent has deleterious effect on the growth of crop at higher concentrations. However, at lower concentration (viz. 10 to 40% in rice, 10 to 50% in mustard and 10 to 60% in pea) of effluent, beneficial impact on general welfare of the crops was noticed. Growth and development was increased with increasing the concentration of the effluent up to 30% in rice, 40% in mustard and 50% in pea. Investigation showed that the growth and production of rice, mustard and pea was found maximum at a concentration of 30, 40 and 50% effluent respectively. 相似文献
820.
Kumari V Rathore G Chauhan UK Pandey AK Lakra WS 《Journal of environmental biology / Academy of Environmental Biology, India》2011,32(2):153-159
Seasonal changes in abundance of nitrifiers (ammonia-oxidizing and nitrite-oxidizing bacteria) in surface and bottom water of freshwater ponds were examined with respect to temperature, DO, pH as well as concentration of ammonia and nitrite. The most probable number (MPN) of ammonia-oxidizers in different ponds varied from 1297 +/- 3.6 to 1673.23 +/- 0.36 ml(-1) in bottom and 720.5 +/- 8.1 to 955.3 +/- 10.8 ml(-1) in surface water during the rainy season while the MPN ranged from 1074 +/- 1.07 to 1372.17 +/- 4.6 ml(-1) in bottom and 515 +/- 10.1 to 678 +/- 11.8 ml(-1) in surface water in winter. However, the MPN were greatly reduced in summer and ranged from 435.05 +/- 15.7 to 547.54 +/- 2.12 ml(-1) in bottom and 218.7 +/- 7.3 to 368.4 +/- 9.32 ml(-1) in surface water. Similar seasonal trends were also observed in MPN of nitrite-oxidizers. Among all the physico-chemical parameters, abundance of nitrifiers was more positively correlated with ammonia and nitrite concentration in all the seasons. The abundance of nitrifiers in surface and bottom water was highest in rainy season followed by winter and modest in summer. The potential nitrification activities and oxidation rates were shown to be linear and activity of ammonia-oxidizing and nitrite-oxidizing bacteria was highest during rainy season. 相似文献