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81.
Comparative evaluations of population dynamics in species with temporal and spatial variation in life-history traits are rare because they require long-term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978-1996 for six populations of western terrestrial garter snakes (Thamnophis elegans) from two evolutionarily divergent ecotypes. Three replicate populations from a slow-living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast-living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8-13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (lambda(s)) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M-slow) and lakeshore (L-fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on lambda(s). The magnitude of variation in the proportion of gravid females and its effect on lambda(s) was greater in M-slow than L-fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on lambda(s) was 4 23 times greater in M-slow than L-fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L-fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life-history traits in the two ecotypes, which, in turn, affect population dynamics. M-slow populations have evolved life-history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long-term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life-history evolution. 相似文献
82.
Rita Hargitai Kathryn E. Arnold Márton Herényi József Prechl János Török 《Behavioral ecology and sociobiology》2009,63(6):869-882
Offspring survival can be influenced by resources allocated to eggs, which in turn may be affected by the environmental factors
the mother experiences during egg formation. In this study, we investigated whether experimentally elevated social interactions
and number of neighbouring pairs influence yolk composition of collared flycatchers (Ficedula albicollis). Social challenge was simulated by presentation of a conspecific female. Experimental females spent more time near the cage
and produced eggs with higher androgen concentration, but local breeding density did not affect yolk androgen level. Moreover,
we found that females exposed to more intra-specific interactions and those that bred at higher density produced eggs with
smaller yolk. These females may be more constrained in foraging time due to more frequent social encounters, and there might
be increased competition for food at areas of higher density. In contrast, the present study did not reveal any evidence for
the effect of social environment on yolk antioxidant and immunoglobulin levels. However, we found that yolk lutein and immunoglobulin
concentrations were related to the female’s H/L ratio. Also, yolk lutein and α-tocopherol levels showed a seasonal increase
and were positively related to the female’s plasma carotenoid level. Mothers may incur significant costs by transferring these
compounds into the eggs, thus only females in good physiological condition and those that lay eggs later, when food is probably
more abundant, could allocate higher amounts to the eggs without compromising their defence mechanisms. Our results suggest
that environmental circumstances during egg formation can influence conditions for embryonic development. 相似文献
83.
Bielmyer GK Arnold WR Tomasso JR Isely JJ Klaine SJ 《Environmental monitoring and assessment》2012,184(5):2797-2804
Copper sheeting is a common roofing material used in many parts of the world. However, copper dissolved from roof sheeting
represents a source of copper ions to watersheds. Researchers have studied and recently developed a simple and efficient model
to predict copper runoff rates. Important input parameters include precipitation amount, rain pH, and roof angle. We hypothesized
that the length of a roof also positively correlates with copper concentration (thus, runoff rates) on the basis that runoff
concentrations should positively correlate with contact time between acidic rain and the copper sheet. In this study, a novel
system was designed to test and model the effects of roof length (length of roof from crown to the drip edge) on runoff copper
concentrations relative to rain pH and roof angle. The system consisted of a flat-bottom copper trough mounted on an apparatus
that allowed run length and slope to be varied. Water of known chemistry was trickled down the trough at a constant rate and
sampled at the bottom. Consistent with other studies, as pH of the synthetic rainwater decreased, runoff copper concentrations
increased. At all pH values tested, these results indicated that run length was more important in explaining variability in
copper concentrations than was the roof slope. The regression equation with log-transformed data (R
2 = 0.873) accounted for slightly more variability than the equation with untransformed data (R
2 = 0.834). In log-transformed data, roof angle was not significant in predicting copper concentrations. 相似文献
84.
Diversity and host range of foliar fungal endophytes: are tropical leaves biodiversity hotspots? 总被引:2,自引:0,他引:2
Fungal endophytes are found in asymptomatic photosynthetic tissues of all major lineages of land plants. The ubiquity of these cryptic symbionts is clear, but the scale of their diversity, host range, and geographic distributions are unknown. To explore the putative hyperdiversity of tropical leaf endophytes, we compared endophyte communities along a broad latitudinal gradient from the Canadian arctic to the lowland tropical forest of central Panama. Here, we use molecular sequence data from 1403 endophyte strains to show that endophytes increase in incidence, diversity, and host breadth from arctic to tropical sites. Endophyte communities from higher latitudes are characterized by relatively few species from many different classes of Ascomycota, whereas tropical endophyte assemblages are dominated by a small number of classes with a very large number of endophytic species. The most easily cultivated endophytes from tropical plants have wide host ranges, but communities are dominated by a large number of rare species whose host range is unclear. Even when only the most easily cultured species are considered, leaves of tropical trees represent hotspots of fungal species diversity, containing numerous species not yet recovered from other biomes. The challenge remains to recover and identify those elusive and rarely cultured taxa with narrower host ranges, and to elucidate the ecological roles of these little-known symbionts in tropical forests. 相似文献
85.
It has become relatively common to estimate human dioxin body burden and to document dioxin exposures by measuring dioxin and dibenzofuran congeners in adipose tissue, whole blood or blood plasma, and reporting these values on a lipid basis. It has not been determined whether these three types of specimens contain identical dioxin and dibenzofuran levels. This paper compares paired plasma and adipose tissue and paired whole blood and adipose tissue in analyses from two groups of patients. The first group consists of twenty U.S. veterans with paired plasma and adipose specimens. The second group consists of four German adults with whole blood compared to adipose tissue. Forty-eight analyses were performed. The results suggest that for some higher chlorinated compounds, such as OCDD, plasma lipid values may be higher than adipose lipid values, but whole blood lipid values for the higher as well as lower chlorinated PCDD/Fs may be relatively similar. On the other hand, the values for the lower chlorinated PCDD/Fs, such as TCDD, are similar in blood plasma, adipose tissue and whole blood. Total PCDD/F dioxin “toxic equivalents” are similar within each of the two series reported here, using the current “International Dioxin Toxic Equivalent” system. 相似文献
86.
87.
88.
J. G. Arnold R. Srinivasan R. S. Muttiah J. R. Williams 《Journal of the American Water Resources Association》1998,34(1):73-89
ABSTRACT: A conceptual, continuous time model called SWAT (Soil and Water Assessment Tool) was developed to assist water resource managers in assessing the impact of management on water supplies and nonpoint source pollution in watersheds and large river basins. The model is currently being utilized in several large area projects by EPA, NOAA, NRCS and others to estimate the off-site impacts of climate and management on water use, non-point source loadings, and pesticide contamination. Model development, operation, limitations, and assumptions are discussed and components of the model are described. In Part II, a GIS input/output interface is presented along with model validation on three basins within the Upper Trinity basin in Texas. 相似文献
89.
Abstract A series of mesocosms was exposed to a suite of light treatments and nutrient enrichment in order to generate algal communities of varying biomass. the influence of this biomass on the speciation of copper (II) was studied. Distribution coefficients ( Kd,Lkg?1) were relatively high (log Kd = 5 to 7), indicative of robust trace metal sequestration, and were likely controlled by the particulate organic carbon content (foc). Differences in Kd over time and among treatments were significant, as was the relationship between Kd and foc. Fluorescence quenching was used to determine binding capacities ( Lt , M) and their associated binding constants ( Kcond ,M?1) in order to model the solid phase copper speciation. the Kcond ranged between 2.1 and 5.2 × 1012M?1, indicating a very strong copper-ligand complex, and was higher in mesocosms that received more light. the light Lt increased over time, dramatically after the nutrient enrichment, but did not vary systematically among light treatments. Lt ranged from 7.2 × 10? 7 to 4.9 × 10? 5 M. the large magnitudes of Kd , Kcond and Lt ensured that greater than 97% of total copper in the mesocosms was complexed by organic matter. the total copper concentration ([Cu]T, M) needed to reach a target dissolved copper concentration of 10?12.5 M (pCu = 12.5) was determined for each mesocosm over time. [Cu]T was between 8.02 × 10?5 and 3.41 × 10?2 M, and increased over time. the [Cu]T normalized to the target pCu (Effective Dose Ratio, EDR) increased directly with increases in algal biomass, indicating a direct link between system productivity and copper exposure. Approximately 45% of the variance in EDR was explained by variance in total biomass, while the residual variance in EDR was due likely to differences in the strengths of particle associations and magnitude of binding capacities. 相似文献
90.
Arnold Schecter Justin A. Colacino Nirav Shah Olaf Päpke Mathias Opel Keyur Patel 《毒物与环境化学》2013,95(6):1053-1063
Levels of polybrominated diphenyl ether (PBDE) flame retardants have been increasing in humans and the environment for the past few decades. Human levels are markedly higher in the US than Europe. Although food appears to be a significant route of intake, food PBDE levels are not substantially higher in the US than Europe. House and office dust appear to be major routes of exposure with air believed to usually provide a lesser route of intake. Because there are very few measurements of airborne PBDE that have been performed in relevant microenvironments in the US, increased efforts to assess airborne PBDE in the US as sources of exposure are needed. This study reports, for the first time from a Southwestern US city in Texas, the results of measurements of airborne PBDE in multiple locations, two outdoor and six indoor (residential and office) from active air sampling with collection of a combination of both vapor- and particulate-phase PBDE. Higher PBDE levels were measured in indoor than outdoor air, which confirms previous findings. Of 11 measured congeners including BDE 209, total PBDE levels in two outdoor air samples were 112 and 125 pg m?3 and the indoor air levels ranged from 175 to 1232 pg m?3 with a median of 572 pg m?3. These findings suggest that sources of air contamination with PBDE may be similar in Texas as elsewhere in North America. However, more sampling is required to (1) better determine if this is the case and (2) attempt to characterize potential sources of PBDE contamination in both indoor and outdoor air by analysis of congener patterns. 相似文献