共查询到20条相似文献,搜索用时 31 毫秒
1.
Fellfield is an important habitat in both the Antarctic and sub-Antarctic. However, few studies have examined the abundance
and seasonality of arthropods in sub-Antarctic fellfield habitats. Here, soil arthropod communities were sampled for over
a full year in two distinct habitat components (rocky areas and Azorella selago cushions) in a mid-altitude fellfield on Marion Island. Species richness was relatively high (42 spp.) and consisted almost
exclusively of indigenous species. Maximum mean annual density in the A. selago cushions was 16,000 individuals m−2 for Eupodes minutus. In contrast, the highest density of any species in the rocky, inter-cushion areas was 700 individuals m−2 for Halozetes fulvus. Quantitative analyses highlighted prominent differences in arthropod community structure between the two habitat components,
despite the fact that most species were common to both of them. In general, arthropod abundances were lower in the fellfield
compared with less extreme vegetation types in the sub-Antarctic, but were not dissimilar to those found in fellfield in the
maritime Antarctic. In the Marion Island fellfield, arthropods either showed no pronounced seasonal peak in abundance, or
a summer peak, although these patterns differed between habitat components within species, and between species. These data
provide a firm quantitative foundation for further investigations of community patterns and seasonality in sub-Antarctic fellfield
arthropods.
Accepted: 10 June 2000 相似文献
2.
Summary TheDusmoecetes species complex on sub-Antarctic Marion Island comprises two species. The larger species,D. similis (C.O. Waterhouse), feeds on angiosperms as adults and detritus as larvae, whereas the smaller species,D. marioni Jeannel feeds on bryophytes in all stages.D. similis has seven larval instars and a generation time of one year or longer.D. marioni has between five and seven larval instars, depending on the plant community it inhabits, and a generation time of one year or less. Immatures ofD. similis have a theoretical null point of development of -0.62°C and aQ
10 of 3.57. In both species there are overlapping generations in the field, although in the case ofD. similis there is a distinct seasonal emergence of adults starting in September. Mean standing crop of larvae on the coastal plain is approximately 5.5 kg (dry mass)·ha-1, but can be as high as 11.85 kg (dry mass)·ha-1 inAzorella selago dominated communities. This study indicates that both species are important herbivores and/or detritivores on Marion Island. 相似文献
3.
Bothrometopus elongatus is one of four Ectemnorhinus-group species restricted to the epilithic biotope on the Prince Edward Islands. Here we examine the biology of this species
over a full year at Kerguelen Rise, a mid-altitude fellfield site on Marion Island. B. elongatus adults eclose from April onwards, reaching maximum densities (ca. 17 individuals m−2) in September. Females mature approximately three eggs at a time and these commence hatching in July. Larval eclosion reaches
a peak in November, during which time larval densities are also highest (ca. 153 individuals m−2). The larvae develop through six instars, which is within the range found for other Ectemnorhinus-group species. The high densities of B. elongatus in fellfield habitats, and its single, virtually discrete annual generation, make this species unusual among insects indigenous
to the sub-Antarctic. The latter generally have low densities compared to other micro-arthropods, prolonged life-cycles, and
flexible life-histories. We suggest that the diversity of life-histories found amongst the indigenous insects at Marion Island
presents considerable potential for testing environmental effects on insect life-histories. An overview of sub-Antarctic insect
life-history data suggests that the indigenous species, with generally prolonged life-cycles, are at a disadvantage relative
to introduced species that have more rapid cycles and often complete several generations per year. This is reason for concern
given rapid climate change at these islands.
Accepted: 14 November 1999 相似文献
4.
L. Guglielmo G. C. Carrada G. Catalano A. Dell'Anno M. Fabiano L. Lazzara O. Mangoni A. Pusceddu V. Saggiomo 《Polar Biology》2000,23(2):137-146
Studies on the chemical and biological properties of annual pack ice at a coastal station in Terra Nova Bay (74°41.72′S,
164°11.63′E) were carried out during austral spring at 3-day intervals from 5 November to 1 December 1997. Temporal changes
of nutrient concentrations, algal biomasses, taxonomic composition, photosynthetic pigment spectra and P–E relationships were
studied. Quantity, composition and degradation rates of organic matter in the intact sea ice were also investigated. In addition,
microcosm experiments were carried out to evaluate photosynthetic and photo-acclimation processes of the sympagic flora in
relation to different light regimes. High concentrations of ammonia were measured in four ice-cores (weighted mean values
of the cores ranged from 4.3 ± 1.9 μM to 7.2 ± 3.4 μM), whereas nitrate and phosphate displayed high concentrations (up to
35.9 μM and 7.6 μM, respectively) only in the bottom layer (135–145 cm depth). Particulate carbohydrate and protein concentrations
in the intact sea ice ranged from 0.5 to 2.3 mg l−1 and 0.2 to 2.0 mg l−1, respectively, displaying a notable accumulation of organic matter in the bottom colored layer, where bacterial enzymatic
activities also reached the highest values. Aminopeptidase activity was extremely high (up to 19.7 μM l−1 h−1 ± 0.05 in the bottom layer), suggesting a rapid turnover rate of nitrogen–enriched organic compounds (e.g. proteins). By
contrast, bacterial secondary production was low, suggesting that only a very small fraction of mobilized organic matter was
converted into bacterial biomass (<0.01‰). The sympagic autotrophic biomass (in terms of chlorophaeopigments) of the bottom
layer was high, increasing during the sampling period from 680 to 2480 μg l−1. Analyses of pigments performed by HPLC, as well as microscope observations, indicated that diatoms dominated bottom communities.
The most important species were Amphiprora sp. and Nitschia cfr. stellata. Bottom sympagic communities showed an average P
B
max
of 0.12 mgC mg Chl−1 and low photoadaptation index (E
k=18 μE m−2 s−1, E
m=65 μE m−2 s−1). Results of the microcosm experiment also indicated that communities were photo-oxidized when irradiance exceeded 100 μE m−2 s−1. This result suggests that micro- autotrophs inhabiting sea ice might have a minor role in the pelagic algal blooms.
Accepted: 4 August 1999 相似文献
5.
A macrozoobenthic community study was conducted in an East Greenlandic fjord (Young Sound, 74°18′N; 20°15′W) during the ice-free
period from July to August in 1996. Grab samples as well as underwater photography were used for quantifying the macrozoobenthos
at water depths between 20 and 85 m. Abundance decreased with depth from 2700 ind. · m−2 at 20 m to 900 ind. · m−2 at 85 m. At a time series station at 35 m, abundance increased from 700 ind. · m−2 in mid-July to 1400 ind. · m−2 in mid-August. Polychaetes dominated in grab samples but bivalves constituted an important part of the benthic fauna, especially
at the shallow part of the depth gradient. Photographs revealed high abundances of large epifaunal species, especially brittle
stars. Diversity was generally high, with around 45 species per 201 individuals, as calculated by Hurlbert's rarefaction term.
A gradual change in community structure with depth was observed, which could be related to variation in sediment composition
and disturbance intensity.
Accepted: 20 May 2000 相似文献
6.
7.
The seasonal variations in biomass, abundance and species composition of zooplankton in relation to hydrography and chlorophyll
a were studied in the subarctic waters north of Iceland. The sampling was carried out at approximately monthly intervals from
February 1993 to February 1994 at eight stations arranged along a transect extending from 66°16′N–18°50′W to 68°00′N–18°50′W.
The mean temperature at 50 m depth showed a clear seasonal pattern, with lowest water temperatures in February (∼1.1°C) and
the highest in July (∼5.4°C). The spring growth of the phytoplankton began in late March and culminated during mid-April (∼7.0 mg
Chl a m−3). Both the biomass and the abundance of total zooplankton were low during the winter and peaked once during the summer in
late May (∼4 g m−2 and ∼38,000 individuals m−2). A total of 42 species and taxonomic groups were identified in the samples. Eight taxa contributed ∼90% of the total zooplankton
number. Of these Calanus finmarchicus was by far the most abundant species (∼60% of the total zooplankton). Less important groups were ophiuroid larvae (∼9%),
Pseudocalanus spp. (∼8%), Metridia longa (∼4%), C. hyperboreus (∼3%), Acartia longiremis (∼2%), chaetognaths (∼2%) and euphausiid larvae (∼2%). The dominant copepods showed two main patterns in seasonal abundance:
C. finmarchicus, C. hyperboreus and C. glacialis had one annual peak in numbers in late May, while Pseudocalanus spp., M. longa and A. longiremis showed two maxima during the summer (July) and autumn (October/November). Ophiuroid larvae and chaetognaths (mainly Sagitta elegans) peaked during the middle of July, while the number of euphausiid eggs and larvae was greatest from May to July. The succession
in population structure of C. finmarchicus indicated its main spawning to be in April and May, coincident with the phytoplankton spring bloom. A minor spawning was
also observed sometime between August and October. However, the offspring from this second spawning contributed only insignificantly
to the overwintering stock of C. finmarchicus.
Received: 12 September 1997 / Accepted: 1 March 1998 相似文献
8.
The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the
spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific
flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the
coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E)
coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria
Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 106 trichomes L−1 was recorded. Total bacterial counts (TBC) varied between 94.09 × 108 cells L−1 in the bloom to 1.34 × 108 cells L−1 in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m−1 (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m−1 in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the
bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship
of TBC with Chlorophyll a (R
2 = 0.65, p < 0.01) and CDOM concentrations (R
2 = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid
palythene (λ
max = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM
nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea. 相似文献
9.
L. E. M. Nery M. A. da Silva A. M. Lauro Castrucci 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):624-630
The participation of cyclic nucleotide-dependent intracellular signalling pathways in the pigment translocation induced by
pigment-dispersing hormone (α -PDH) or pigment-concentrating hormone (PCH) was investigated in the erythrophores of the freshwater
shrimp, Macrobrachium potiuna. Cholera toxin, forskolin and dibutyryl cyclic adenosine 3′5′ monophosphate (dbcAMP) were able to induce pigment dispersion
with effective agonist concentrations for half maximal response (EC50 s) of 2.8 · 10−11 mol · l−1, 7.0 · 10−7 mol · l−1 and 3.3 · 10−7 mol · l−1, respectively. KT5720 (10−7 mol · l−1 and 10−6 mol · l−1) significantly shifted the dose response curve to α -PDH to the right. Dibutyryl cyclic guanosine 3′5′ monophosphate (dbcGMP)
was ineffective in inducing either pigment aggregation or dispersion. 2′5′ dideoxyadenosine (DDA) and SQ22,536 essentially
elicit a pigment-aggregating response in a dose-dependent manner. These effects were not due to the activation of purinergic
receptors, since concentrations up to 10−4 mol · l−1 of adenosine and adenosine triphosphate (ATP), and up to 10−3 mol · l−1 of uracil triphosphate (UTP) did not elicit pigment aggregation. In order to verify if PCH decreased cyclic adenosine 3′5′
monophosphate (cAMP) levels, cumulative dose-response curves to PCH in the absence and presence of pertussis toxin and 8-MOM-IBMX
were determined. However, neither drug significantly affected PCH activity. The levels of cAMP in the integument cells of
M. potiuna were significantly increased (P < 0.05) by α -PDH (10−7 mol · l−1) and forskolin (10−6 mol · l−1), but were not affected by PCH (10−7 or 10−10 mol · l−1). In conclusion, α -PDH seems to elicit pigment dispersion through the activation of a Gs-protein coupled receptor resulting
in cAMP increase and cAMP-dependent protein kinase (PKA) activation. Furthermore, although a decrease in cAMP was assumed
to be responsible in turn for the action of PCH, such a decrease could not be directly demonstrated.
Accepted: 11 August 1998 相似文献
10.
Nitrogen uptake in the infiltration community, an ice algal community in Antarctic pack-ice 总被引:1,自引:0,他引:1
S. Kristiansen T. Farbrot H. Kuosa S. M. Myklestad C. H. von Quillfeldt 《Polar Biology》1998,19(5):307-315
An infiltration community was the dominating ice algal community in pack-ice off Queen Maud Land, Southern Ocean, in January
1993. The community was dominated by autotrophic processes, and the most common species were the prymnesiophyte Phaeocystis antarctica and the diatoms Chaetoceros neglectus and Fragilariopsis cylindrus. The concentration of chlorophyll a was 1.3–47.9 μg l−1, and the inner part of the community was nitrate depleted. Uptake rates of nitrate, nitrite, ammonium, urea and amino acids
were measured using 15N. Nitrate was the major nitrogen source for ice algal growth (67 ± 6% nitrate uptake). It is suggested that % nitrate uptake
in the infiltration community decreases during the growth season, from 92% during spring (literature data) to 67% during summer.
Scalar irradiance in the infiltration community was high and variable. It reached ca. 2000 μmol m−2 s−1 at some locations, and nitrate uptake rate was potentially photoinhibited at irradiances >500 μmol m−2 s−1. Nitrate uptake rate in an average infiltration community (0.6 m of snow cover) was lowered by 13% over a 2-week period due
to photoinhibition.
Received: 16 December 1996 / Accepted: 5 January 1998 相似文献
11.
Production of sophorolipids from whey 总被引:5,自引:0,他引:5
Otto RT Daniel HJ Pekin G Müller-Decker K Fürstenberger G Reuss M Syldatk C 《Applied microbiology and biotechnology》1999,52(4):495-501
Sophorolipids, obtained by a two-stage process starting from deproteinized whey concentrate using Cryptococcus curvatus ATCC 20509 and Candida bombicola ATCC 22214, were compared to products from one-stage processes, using different lipidic compounds as substrates. Results
showed that above all carbon source and not cultivation conditions had a distinct influence on the composition of the crude
product mixture and therefore on the physicochemical and biological properties of the sophorolipids, such as, for example,
surface activity, cytotoxicity and stability against hydrolases. The results were completed by corresponding data for purified
mono- and diacetylated (17-hydroxyoctadecenoic)-1′,4′′-lactonized sophorolipids. Crude sophorolipid mixtures showed moderate
to good surface active properties (SFTmin 39 mN m−1, CMC 130 mg l−1), water solubilities (2–3 g l−1) and low cytotoxicities (LC50 300–700 mg l−1). In contrast, purified sophorolipids were more surface active (SFTmin 36 mN m−1, CMC 10 mg l−1), less water soluble (max. 70 mg l−1) and showed stronger cytotoxic effects (LC50 15 mg l−1). Incubation of crude sophorolipid mixtures with different hydrolases demonstrated that treatment with commercially available
lipases such as from Candida rugosa and Mucor miehei distinctly reduced the surface active properties of the sophorolipids, while treatment with porcine liver esterase and glycosidases
had no effect.
Received: 23 February 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999 相似文献
12.
Supercooling points, lower lethal temperatures, and the effect of short-term exposures to low temperatures were examined
during both winter and summer in the adults of six weevil species from three different habitats on Marion Island. Upper lethal
limits and the effects of short-term exposure to high temperatures were also examined in summer-acclimatized adult individuals
of these species. Bothrometopus elongatus, B. parvulus, B. randi, Ectemnorhinus marioni, and E. similis were freeze tolerant, but had high lower lethal temperatures (−7 to −10°C). Seasonal variation in these parameters was not
pronounced. Physical conditions of the habitat appeared to have little effect on cold hardiness parameters because the Ectemnorhinus species occur in very wet habitats, whereas the Bothrometopus species inhabit drier areas. The adults of these weevil species are similar to other high southern latitude insects in that
they are freeze tolerant, but with high lower lethal temperatures. In contrast, Palirhoeus eatoni, a supra-littoral species, avoided freezing and had a mean supercooling point of −15.5 ± 0.94°C (SE) in winter and −11.8 ± 0.98°C
in summer. Survival of a constant low temperature of −8°C also increased in this species from 6 h in summer to 27 h in winter.
It is suggested that this strategy may be a consequence of the osmoregulatory requirements imposed on this species by its
supra-littoral habitat. Upper lethal temperatures (31–34°C) corresponded closely with maximum microclimate temperatures in
all of the species. This indicates that the pronounced warming, accompanied by the increased insolation that has been recorded
at Marion Island, may reduce survival of these species. These effects may be compounded as a consequence of predation by feral
house mice on the weevils.
Received: 4 February 1997 / Accepted: 3 May 1997 相似文献
13.
Estimated Impact of feral house mice on sub-Antarctic invertebrates at Marion Island 总被引:1,自引:0,他引:1
Summary The energy metabolism of feral house mice Mus musculus was established on sub-Antarctic Marion Island, using the doubly-labelled water turnover technique. Mean water influx was 565 ml kg-1 day-1 and mean CO2 production was 5.41 ml g-1 h-1, i.e. 3375 kJ kg-1 day-1. From the energy content of the main items (Lepidoptera larvae, Curculionidae) in the diet of the mice it was estimated that the dry mass of food consumed was 3.5 g mouse-1 day-1. The overall impact of mice on invertebrates, based on mean mouse density and the mean percentage invertebrates in the diet, was estimated at 108 g ha-1 day-1 or 39.4 kg ha-1 y-1 (dry mass). Greatest predation pressure was on larvae of the flightless moth Pringleophaga marioni: 65 g ha-1 day-1 or 23.7 kg ha-1 y-1. Insect biomass is lower on Marion Island than on nearby Prince Edward Island, which is mouse-free. It is suggested that populations of certain insects on Marion Island are depressed by the alien mice. 相似文献
14.
Invasion by a Perennial Herb Increases Decomposition Rate and Alters Nutrient Availability in Warm Temperate Lowland Forest Remnants 总被引:3,自引:0,他引:3
Rachel J. Standish Peter A. Williams Alastair W. Robertson Neal A. Scott Duncan I. Hedderley 《Biological invasions》2004,6(1):71-81
We determined the impact of the invasive herb, Tradescantia fluminensis Vell., on litter decomposition and nutrient availability in a remnant of New Zealand lowland podocarp–broadleaf forest. Using
litter bags, we found that litter beneath mats of Tradescantia decomposed at almost twice the rate of litter placed outside the mat. Values of k (decomposition quotient) were 9.44±0.42 yrs for litter placed beneath Tradescantia and 5.42±0.42 yrs for litter placed in native, non-Tradescantia plots. The impact of Tradescantia on decomposition was evident through the smaller forest floor mass in Tradescantia plots (2.65±1.05 t ha−1) compared with non-Tradescantia plots (5.05±1.05 t ha−1), despite similar quantities of annual leaf litterfall into Tradescantia plots (6.85±0.85 t ha−1 yr−1) and non-Tradescantia plots (7.45±1.05 t ha−1 yr−1). Moreover, there was increased plant nitrate available, as captured on resin bags, in Tradescantia plots (25.77 ± 8.32 cmol(−)/kg resin) compared with non-Tradescantia plots (9.55±3.72 cmol(−)/kg resin). Finally, the annual nutrient uptake by Tradescantia represented a large proportion of nutrients in litterfall (41% N, 61% P, 23% Ca, 46% Mg and 83% K), exceeded the nutrient
content of the forest floor (except Ca), but was a small proportion of the topsoil nutrient pools. Taken together, our results
show that Tradescantia increases litter decomposition and alters nutrient availability, effects that could influence the long-term viability of
the majority of podocarp–broadleaf forest remnants affected with Tradescantia in New Zealand. These impacts are likely mostly due to Tradescantia's vegetation structure (i.e., tall, dense mats) and associated microclimate, compared with native ground covers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean 总被引:4,自引:4,他引:0
From November 1992 to February 1995 a quantitative and qualitative phytoplankton study was conducted at a permanent station
(Kerfix) southwest off the Kerguelen Islands, in the vicinity of the Polar Front (50°40′S–68°25′E). Phytoplankton populations
are low in this area both during summers and winters. They consist, in order of decreasing cell abundance, of pico- and nanoflagellates
(1.5–20 μm), coccolithophorids (<10 μm), diatoms (5–80 μm) and dinoflagellates (6–60 μm). Flagellates form the dominant group
throughout the year and attain the highest summer average of 3.0 × 105 cells l−1. Next in abundance year-round are coccolithophorids with the dominant Emiliania huxleyi (highest summer 1992 average 1.9 × 105 cells l−1), diatoms (summer 1992 average 1.0 × 105 cells l−1) and dinoflagellates (average 3.8 × 104 cells l−1). Winter mean numbers of flagellates and picoplankton do not exceed 8.4 × 104 cells l−1; those of the three remaining algal groups together attain 2 × 104 cells l−1. Summer peaks of diatoms and dinoflagellates are mainly due to the larger size species (>20 μm). The latter group contributes
most to the total cell carbon biomass throughout the year. Dominant diatoms during summer seasons include: Fragilariopsis kerguelensis, Thalassionema nitzschioides, Chaetoceros dichaeta, C. atlanticus, Pseudonitzschia heimii, and P. barkleyi/lineola. This diatom dominance structure changes from summer to summer with only F. kerguelensis and T. nitzschioides retaining their first and second positions. Any one of the co-dominant species might be absent during some summer period.
The variable diatom community structure may be due to southward meandering of the Polar Front bringing “warmer” species from
the north, and to the mixing of the water masses in this area. The entire community structure characterized both during summer
and winters by the dominance of flagellates can be related to deep mixing (ca. 40–200 m) of the water column as the probable
controlling factor.
Received: 13 November 1997 / Accepted: 11 May 1998 相似文献
16.
Hans Mose Jensen Lorna Pedersen AnnDorte Burmeister Benni Winding Hansen 《Polar Biology》1999,21(5):269-278
The distribution of phytoplankton biomass and primary production were studied during summer 1993 at 16 stations from 65 to
72°N off West Greenland, ranging more than 900 km. Hydrography, nutrients and chlorophyll a profiles revealed a significant change in structure from south to north. Nitrate was depleted in the euphotic zone at most
stations except close to the ice edge (West Ice) or close to outflow from large glaciers. The vertical distribution of phosphate
followed that of nitrate, but was never depleted. Despite two stations with relatively high surface concentrations, silica
showed the same distribution as the other two nutrients. In the south, chlorophyll a concentration and primary production were lower than north of Disko Bay (69°N), associated with a well-mixed versus a salinity-generated
stratification, respectively. In Vaigat, a high-production station was identified, (st. 910, 69°52′69N–51°30′61W) with a chlorophyll a concentration in the euphotic zone of >13 μg l−1 and an area primary production of 3.2 g C m−2 day−1. This is seldom encountered in arctic waters and was presumably due to nutrient-rich melt-water originating from the Iluliíssat
Glacier. The overall primary production for the studied area was 67–3207 mg C m−2 day−1 (mean ± SD=341± 743 mg C m−2 day−1), which is within the range of the few results published for West Greenland and eastern Canadian Arctic waters.
Accepted: 24 October 1998 相似文献
17.
W. Bartels B. S. Law F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(3):233-239
Little is known about torpor in the tropics or torpor in megachiropteran species. We investigated thermoregulation, energetics
and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to test whether physiological variables may explain why its range is limited to tropical regions. Normothermic bats
showed a large variation in body temperature (T
b) (33 to 37 °C) over a wide range of ambient temperatures (T
as) and a relatively low basal metabolic rate (1.29 ml O2 g−1 h−1). Bats entered torpor frequently in the laboratory at T
as between 14 and 25 °C. Entry into torpor always occurred when lights were switched on in the morning, independent of T
a. MRs during torpor were reduced to about 20–40% of normothermic bats and T
bs were regulated at a minimum of 23.1 ± 1.4 °C. The duration of torpor bouts increased with decreasing T
a in non-thermoregulating bats, but generally terminated after 8 h in thermoregulating torpid bats. Both the mean minimum T
b and MR of torpid M. minimus were higher than that predicted for a 16-g daily heterotherm and the T
b was also about 5 °C higher than that of the common blossom-bat Syconycteris australis, which has a more subtropical distribution. These observations suggest that variables associated with torpor are affected
by T
a and that the restriction to tropical areas in M. minimus to some extent may be due to their ability to enter only very shallow daily torpor.
Accepted: 22 September 1997 相似文献
18.
A survey was made of the distribution of introduced vascular plants on Marion and Prince Edward Islands. The results of this
survey were compared to results of previous surveys (1965/66, 1975, 1981, 1989). Four new introductions to Marion Island have
taken place, three of which involved species that had been introduced in the past, but had disappeared or were eradicated.
Eighteen species of alien vascular plants are now known from Marion Island. Of these, three were not observed during the present
survey, and another three have been eradicated. Many of the naturalised aliens are still increasing markedly in area and/or
in numbers. Rates of spread of up to 300 m year−1 occur. Three alien vascular species occur on Prince Edward Island. Two are recent introductions, presumably transported to
this island from neighbouring Marion Island by wind or birds.
Accepted: 22 November 1998 相似文献
19.
Semeneh Mengesha Frank Dehairs Michel Fiala Marc Elskens Leo Goeyens 《Polar Biology》1998,20(4):259-272
This study investigates the dynamics of phytoplankton communities and nitrogen uptake in the Indian sector of the Southern
Ocean during spring and summer. The study area is oligotrophic (Chl a stocks <50 mg m−2); nevertheless, a large spatial variation of phytoplankton biomass and community structure was observed. During both seasons
the phytoplankton community in the seasonal ice zone showed higher biomasses and was mainly composed of large diatom cells.
However, in the permanently open ocean zone the community had low biomass and was chiefly composed of nano- and picoflagellates.
In the polar front zone, although biomass was higher, the community structure was similar to the open ocean zone. The results
suggest that the variation in phytoplankton community structure on a larger scale resonates with gradients in water column
stability and nutrient distribution. However, significant changes in biomass and nutrient stocks but little change in community
structure were observed. Absolute nitrogen uptake rates were generally low, but their seasonal variations were highly significant.
During spring the communities displayed high specific nitrate uptake (mean rate = 0.0048 h−1), and diatoms (in the seasonal ice zone) as well as nano- and picoflagellates (in the permanently open ocean zone and polar
front zone) were mainly based on new production (mean ƒ-ratio = 0.69). The transition to summer was accompanied by a significant
reduction in nitrate uptake rate (0.0048 h−1 → 0.0011 h−1) and a shift from predominantly new to regenerated production (ƒ-ratio 0.69 → 0.39). Ammonium played a major role in the
seasonal dynamics of phytoplankton nutrition. The results emphasize that, despite a large contrast in community structure,
the seasonal dynamics of the nitrogen uptake regime and phytoplankton community structure in all three subsystems were similar.
Additionally, this study supports our previous conclusion that the seasonal shift in nitrogen uptake regime can occur with,
as well as without, marked changes in community structure.
Received: 2 December 1997 / Accepted: 20 April 1998 相似文献