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21.
Responses of sawgrass and spikerush to variation in hydrologic drivers and salinity in Southern Everglades marshes 总被引:3,自引:3,他引:0
Daniel L. Childers David Iwaniec Damon Rondeau Gustavo Rubio Emilie Verdon Christopher J. Madden 《Hydrobiologia》2006,569(1):273-292
Aboveground net primary production (ANPP) by the dominant macrophyte and plant community composition are related to the changing
hydrologic environment and to salinity in the southern Everglades, FL, USA. We present a new non-destructive ANPP technique
that is applicable to any continuously growing herbaceous system. Data from 16 sites, collected from 1998 to 2004, were used
to investigate how hydrology and salinity controlled sawgrass (Cladium jamaicense Crantz.) ANPP. Sawgrass live biomass showed little seasonal variation and annual means ranged from 89 to 639 gdw m−2. Mortality rates were 20–35% of live biomass per 2 month sampling interval, for biomass turnover rates of 1.3–2.5 per year.
Production by C. jamaicense was manifest primarily as biomass turnover, not as biomass accumulation. Rates typically ranged from 300 to 750 gdw m−2 year−1, but exceeded 1000 gdw m−2 year−1 at one site and were as high as 750 gdw m−2 year−1 at estuarine ecotone sites. Production was negatively related to mean annual water depth, hydroperiod, and to a variable
combining the two (depth-days). As water depths and hydroperiods increased in our southern Everglades study area, sawgrass
ANPP declined. Because a primary restoration goal is to increase water depths and hydroperiods for some regions of the Everglades,
we investigated how the plant community responded to this decline in sawgrass ANPP. Spikerush (Eleocharis sp.) was the next most prominent component of this community at our sites, and 39% of the variability in sawgrass ANPP was
explained by a negative relationship with mean annual water depth, hydroperiod, and Eleocharis sp. density the following year. Sawgrass ANPP at estuarine ecotone sites responded negatively to salinity, and rates of production
were slow to recover after high salinity years. Our results suggest that ecologists, managers, and the public should not necessarily
interpret a decline in sawgrass that may result from hydrologic restoration as a negative phenomenon. 相似文献
22.
Sharon M. L. Ewe Evelyn E. Gaiser Daniel L. Childers David Iwaniec Victor H. Rivera-Monroy Robert R. Twilley 《Hydrobiologia》2006,569(1):459-474
We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP)
by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida
Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program
are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins
that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ
significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades
transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but
no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins
ranged from 255 to 606 g m−2 year−1. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m−2 year−1 and 342–10371 g C m−2 year−1, respectively. Mangrove productivity ranged from 340 g m−2 year−1 at Taylor River to 2208 g m−2 year−1 at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m−2 year−1 and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton
productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either
SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing
and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to
the total productivity of this ecosystem. 相似文献
23.
Characteristics of surface-water flows in the ridge and slough landscape of Everglades National Park: implications for particulate transport 总被引:1,自引:1,他引:0
Lynn Leonard Alexander Croft Daniel Childers Sherry Mitchell-Bruker Helena Solo-Gabriele Michael Ross 《Hydrobiologia》2006,569(1):5-22
Over the last one hundred years, compartmentalization and water management activities have reduced water flow to the ridge
and slough landscape of the Everglades. As a result, the once corrugated landscape has become topographically and vegetationally
uniform. The focus of this study was to quantify variation in surface flow in the ridge and slough landscape and to relate
flow conditions to particulate transport and deposition. Over the 2002–2003 and 2003–2004 wet seasons, surface velocities
and particulate accumulation were measured in upper Shark River Slough in Everglades National Park. Landscape characteristics
such as elevation, plant density and biomass also were examined to determine their impact on flow characteristics and material
transport. The results of this study demonstrate that the release of water during the wet season not only increases water
levels, but also increased flow speeds and particulate transport and availability. Further, flow speeds were positively and
significantly correlated with water level thereby enhancing particulate transport in sloughs relative to ridges especially
during peak flow periods. Our results also indicate that the distribution of biomass in the water column, including floating
plants and periphyton, affects velocity magnitude and shape of vertical profiles, especially in the sloughs where Utricularia spp. and periphyton mats are more abundant. Plot clearing experiments suggest that the presence of surface periphyton and
Utricularia exert greater control over flow characteristics than the identity (i.e., sawgrass or spike rush) or density of emergent macrophytes,
two parameters frequently incorporated into models describing flow through vegetated canopies. Based on these results, we
suggest that future modeling efforts must take the presence of floating biomass, such as Utricularia, and presence of periphyton into consideration when describing particulate transport. 相似文献
24.
Colin J. Saunders Min Gao Jason A. Lynch Rudolf Jaffé Daniel L. Childers 《Hydrobiologia》2006,569(1):475-492
We measured the abundance of Cladium jamaicense (Crantz) seeds and three biomarkers in freshwater marsh soils in Shark River Slough (SRS), Everglades National Park (ENP)
to determine the degree to which these paleoecological proxies reflect spatial and temporal variation in vegetation. We found
that C. jamaicense seeds and the biomarkers Paq, total lignin phenols (TLP) and kaurenes analyzed from surface soils were all significantly correlated with extant aboveground
C. jamaicense biomass quantified along a vegetation gradient from a C. jamaicense to a wet prairie/slough (WPS) community. Our results also suggest that these individual proxies may reflect vegetation over
different spatial scales: Paq and kaurenes correlated most strongly (R
2 = 0.88 and 0.99, respectively) with vegetation within 1 m of a soil sample, while seeds and TLP reflected vegetation 0–20 m
upstream of soil samples. These differences in the spatial scale depicted by the different proxies may be complementary in
understanding aspects of historic landscape patterning. Soil profiles of short (25 cm) cores showed that downcore variation
in C. jamaicense seeds was highly correlated with two of the three biomarkers (Paq, R
2 = 0.84, p<0.005; TLP, R
2 = 0.97, p<0.0001), and all four of the proxies indicated a recent increase in C. jamaicense biomass at the site. Using a preliminary depth-to-age relationship based on matching charcoal peaks with available ENP fire
records (1980-present) specific to our coring site, we found that peak-depths in C. jamaicense seed concentration appeared to correspond to recent minimum water levels (e.g., 1989 and 2001), and low seed abundance corresponded
to high water levels (e.g., 1995), consistent with the known autecology of C. jamaicense. In summary, the combination of C. jamaicense seeds and biomarkers may be useful for paleoecological reconstruction of vegetation change and ultimately in guaging the
success of ongoing efforts to restore historic hydrologic conditions in the South Florida Everglades. 相似文献
25.
Background
Long-lasting insecticidal nets (LLINs) reduce malaria transmission by protecting individuals from infectious bites, and by reducing mosquito survival. In recent years, millions of LLINs have been distributed across sub-Saharan Africa (SSA). Over time, LLINs decay physically and chemically and are destroyed, making repeated interventions necessary to prevent a resurgence of malaria. Because its effects on transmission are important (more so than the effects of individual protection), estimates of the lifetime of mass distribution rounds should be based on the effective length of epidemiological protection.Methods
Simulation models, parameterised using available field data, were used to analyse how the distribution's effective lifetime depends on the transmission setting and on LLIN characteristics. Factors considered were the pre-intervention transmission level, initial coverage, net attrition, and both physical and chemical decay. An ensemble of 14 stochastic individual-based model variants for malaria in humans was used, combined with a deterministic model for malaria in mosquitoes.Results
The effective lifetime was most sensitive to the pre-intervention transmission level, with a lifetime of almost 10 years at an entomological inoculation rate of two infectious bites per adult per annum (ibpapa), but of little more than 2 years at 256 ibpapa. The LLIN attrition rate and the insecticide decay rate were the next most important parameters. The lifetime was surprisingly insensitive to physical decay parameters, but this could change as physical integrity gains importance with the emergence and spread of pyrethroid resistance.Conclusions
The strong dependency of the effective lifetime on the pre-intervention transmission level indicated that the required distribution frequency may vary more with the local entomological situation than with LLIN quality or the characteristics of the distribution system. This highlights the need for malaria monitoring both before and during intervention programmes, particularly since there are likely to be strong variations between years and over short distances. The majority of SSA's population falls into exposure categories where the lifetime is relatively long, but because exposure estimates are highly uncertain, it is necessary to consider subsequent interventions before the end of the expected effective lifetime based on an imprecise transmission measure. 相似文献26.
Seasonal occurrence of key arthropod pests and associated natural enemies in Alabama Satsuma citrus 总被引:1,自引:0,他引:1
Fadamiro HY Xiao Y Hargroder T Nesbitt M Umeh V Childers CC 《Environmental entomology》2008,37(2):555-567
Six Alabama Satsuma mandarin orchards (four conventionally sprayed and two unsprayed) were surveyed during 2005 and 2006 to determine the population dynamics of arthropod pests and their natural enemies. Twenty-eight arthropod pest species were encountered; the major foliage pests were citrus whitefly, Dialeurodes citri (Ashmead); purple scale, Lepidosaphes beckii (Newman); Glover scale, L. gloveri (Packard); and citrus red mite, Panonychus citri (McGregor). Two distinct population peaks were recorded for citrus whitefly at most locations. The most important direct sources of citrus whitefly mortality were parasitism by Encarsia lahorensis (Howard) and infection by the pathogenic fungus, Aschersonia aleyrodis Webber. In general, all stages of both scale insects (purple scale and Glover scale) were present in the orchards year-round, indicative of overlapping generations; however, the highest densities were recorded during the early season. Citrus whitefly, purple scale, and Glover scale were more abundant on leaves collected from the interior of the tree canopy than in the exterior canopy. Citrus red mite densities were highest in the spring, with populations declining at the start of the summer, and were more abundant in the exterior canopy than in the interior canopy. The most important natural enemies of citrus red mite were predatory mites belonging to several families, of which Typhlodromalus peregrinus Muma (Phytoseiidae) was the predominant species. Major differences were recorded in the relative abundance of different arthropod pest species in the orchards: citrus whitefly, purple scale, and Glover scale predominated in the unsprayed orchards, whereas citrus red mite infestations were more severe in the sprayed orchards. The results are discussed in relation to the possible effect of orchard management practices on abundance of the major pests. 相似文献
27.
Marcos G Godoy Alejandra Aedo Molly JT Kibenge David B Groman Carmencita V Yason Horts Grothusen Angelica Lisperguer Marlene Calbucura Fernando Avendaño Marcelo Imilán Miguel Jarpa Frederick SB Kibenge 《BMC veterinary research》2008,4(1):1-13
Background
Several forms of progressive retinal atrophy (PRA) segregate in more than 100 breeds of dog with each PRA segregating in one or a few breeds. This breed specificity may be accounted for by founder effects and genetic drift, which have reduced the genetic heterogeneity of each breed, thereby facilitating the identification of causal mutations. We report here a new form of PRA segregating in the Border Collie breed. The clinical signs, including the loss of night vision and a progressive loss of day vision, resulting in complete blindness, occur at the age of three to four years and may be detected earlier through systematic ocular fundus examination and electroretinography (ERG). 相似文献28.
Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique? 总被引:10,自引:0,他引:10
The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment
is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this
review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in
the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment
gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated
microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is
P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced
soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in
the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades
may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree
of limitation.
Received 23 August 2000; Accepted 23 March 2001. 相似文献
29.
Silas A. Buck Thomas Steinkellner Despoina Aslanoglou Michael Villeneuve Sai H. Bhatte Victoria C. Childers Sophie A. Rubin Briana R. De Miranda Emma I. O'Leary Elizabeth G. Neureiter Keri J. Fogle Michael J. Palladino Ryan W. Logan Jill R. Glausier Kenneth N. Fish David A. Lewis J. Timothy Greenamyre Brian D. McCabe Claire E. J. Cheetham Thomas S. Hnasko Zachary Freyberg 《Aging cell》2021,20(5)
Age is the greatest risk factor for Parkinson''s disease (PD) which causes progressive loss of dopamine (DA) neurons, with males at greater risk than females. Intriguingly, some DA neurons are more resilient to degeneration than others. Increasing evidence suggests that vesicular glutamate transporter (VGLUT) expression in DA neurons plays a role in this selective vulnerability. We investigated the role of DA neuron VGLUT in sex‐ and age‐related differences in DA neuron vulnerability using the genetically tractable Drosophila model. We found sex differences in age‐related DA neurodegeneration and its associated locomotor behavior, where males exhibit significantly greater decreases in both DA neuron number and locomotion during aging compared with females. We discovered that dynamic changes in DA neuron VGLUT expression mediate these age‐ and sex‐related differences, as a potential compensatory mechanism for diminished DA neurotransmission during aging. Importantly, female Drosophila possess higher levels of VGLUT expression in DA neurons compared with males, and this finding is conserved across flies, rodents, and humans. Moreover, we showed that diminishing VGLUT expression in DA neurons eliminates females'' greater resilience to DA neuron loss across aging. This offers a new mechanism for sex differences in selective DA neuron vulnerability to age‐related DA neurodegeneration. Finally, in mice, we showed that the ability of DA neurons to achieve optimal control over VGLUT expression is essential for DA neuron survival. These findings lay the groundwork for the manipulation of DA neuron VGLUT expression as a novel therapeutic strategy to boost DA neuron resilience to age‐ and PD‐related neurodegeneration. 相似文献
30.
Inhibition of aromatase cytochrome P-450 by 10-oxirane and 10-thiirane substituted androgens. Implications for the structure of the active site 总被引:1,自引:0,他引:1
J T Kellis W E Childers C H Robinson L E Vickery 《The Journal of biological chemistry》1987,262(9):4421-4426
The mechanism of inhibition of estrogen synthetase (P-450arom) by 19R- and 19S-isomers of 10-oxiranyl-and 10-thiiranyl-4-estrene-3,17-dione was investigated using human placental microsomes and purified enzyme preparations. The 19R-isomers were potent inhibitors and exhibited affinities 36-fold (10-oxirane) and 80-fold (10-thiirane) greater than the respective 19S-isomers. Kinetic experiments showed that inhibition by the 19R-isomers is competitive with respect to substrate; inhibition constants for the (19R)-10-oxirane (Ki = 10 nM) and the 19R-10-thiirane (Ki = 2 nM) indicate that each binds with greater affinity than the androgen substrates androstenedione and testosterone. Inhibition time courses and kinetic data were consistent with high affinity, reversible binding. Spectral titrations of microsomal preparations and purified P-450arom showed that binding of the 19R-isomers shifts the Soret maximum of the ferric enzyme to 411 nm (10-oxirane) or 425 nm (10-thiirane); addition of excess androstenedione reversed the spectral changes, producing the high spin form of the enzyme with a Soret peak at 393 nm. These spectral shifts suggest that the oxygen atom of the 10-oxirane and the sulfur atom of the 10-thiirane are bound to the heme iron in the inhibitor complexes. These results suggest that the high affinities of the inhibitors arise from their dual interaction with the androgen binding site and with the heme. Coordination of the C19 heteroatom to the heme indicates that C19 of androgen substrates may be positioned sufficiently close to the heme to allow direct attack by an iron-bound oxidant. Stereoselective binding of the 19R-isomers by P-450arom further suggests that the heme is likely to be positioned above C1 and C2 of the A ring. 相似文献