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1.
The temporal and spatial patterns of protozooplankton abundance in a eutrophic temperate lake 总被引:6,自引:3,他引:3
The temporal and spatial distribution of planktonic protozoa of Esthwaite, a eutrophic lake, was investigated at 7–10 day intervals between February to October 1988. Sarcodine protozoa were of little significance, the plankton was dominated by ciliates and flagellates. Ciliate density peaked in late May to early June with densities reaching 9.2 × 103 1-1. There was considerable variation in spatial distribution and greatest species diversity occurred in March/April. After the establishment of summer stratification the planktonic ciliates were confined to water of >25% oxygen saturation in the water column. Oligotrichs, particularly the genus Strombidium and tintinnids, and peritrichs dominated the ciliate assemblages. There was no correlation between chlorophyll a concentrations and ciliate numbers, but a correlation was apparent between ciliate numbers and flagellate density. There were significant differences between the protozooplankton communities at the different sampling sites in the lake. 相似文献
2.
R. Galzin S. Planes M. Adjeroud C. Chauvet P. J. Doherty J. Poupin 《Coral reefs (Online)》1998,17(1):15-21
The 9 km2 uplifted lagoon of Taiaro Atoll (15°45′S, 144°38′W) is hypersaline due to its isolation from the ocean, yet it contains a
high diversity of fish. The question unifying our expedition was to discover whether these assemblages could be self-sustaining
despite very limited contact with the ocean. Although we were constrained by time, collections of fish larvae showed that
some species can complete their life-cycle within the lagoon, while others differed genetically between the lagoon and the
ocean, consistent with restricted gene flow. The lagoon contained few oceanic species of zooplankton, confirming its general
isolation, but nevertheless some fish species may depend upon infrequent colonisation from the ocean (when large waves drive
water over the normally dry reef crest). Isotopic signatures in fish otoliths suggest the basis for a more definitive and
inclusive test of the sources of the lagoonal assemblage.
Accepted: 28 August 1997 相似文献
3.
Habitat fragmentation is a process involving splitting of continuous habitats into smaller, and more isolated habitat patches.
To assess the effects of small-scale habitat patchiness and isolation without the confounding effect of habitat loss on benthic
macrofauna, two field experiments were conducted in the Archipelago Sea, SW Finland. Using artificial seagrass units (ASUs)
we contrasted continuous patches (“C”) with fragmented patches (“F”) of the same combined area as the continuous patches.
The fragmentation treatment involved two isolation distances (0.5 and 3.0 m) between the ASUs (“F 0.5”) and (“F 3.0”). This
design was repeated in two consecutive experiments where the patch area was 0.25 and 0.0625 m2, respectively. Mobile epifauna were allowed to colonize patches for 12 days in both experiments. In both experiments, the
total epifaunal density was significantly higher in the “F 0.5” treatment than in the “C” treatment, and the three dominant
taxa showed positive or neutral responses to the habitat configuration. No fragmentation effect on the number of species was
detected in either of the experiments, but fragmentation had a negative effect on the epifaunal diversity (Shannon’s H′) in the experiment with the largest patch area. Epifaunal diversity was significantly lower in “F 3.0” treatment than in
“C” or “F 0.5” treatments in the first experiment, indicating stronger effect of isolation instead of fragmentation per se.
Edge effects were indirectly tested by comparing epifaunal densities with patch edge:area ratios. The results suggest that
edge effects may have a more important role than patch size for the total densities of epifaunal taxa, and that small, isolated
patches have equal or higher habitat value compared to larger fragments. 相似文献
4.
Tropical zooplankton in the highly-enclosed lagoon of Taiaro Atoll (Tuamotu Archipelago, French Polynesia) 总被引:1,自引:0,他引:1
Nocturnal zooplankton assemblages around Taiaro Atoll were sampled over six nights during February 1994. Replicate zooplankton
samples were collected at windward and leeward locations in the enclosed lagoon and adjacent ocean with a metered net (85 cm
diameter, 500 μm mesh) towed for 15 min at 5 m depth. The zooplankton community in the lagoon was very different from that
in the ocean. Oceanic samples contained 50 mostly holoplanktonic taxa (diversity index, H′=2.62; evenness index, J′=0.67).
Lagoonal samples contained 19 mostly meroplanktonic taxa (H′=1.54, J′=0.52) with three taxa (decapod larvae; an ostracod,
Cypridina sp.; a copepod, Acartia fossae) contributing >90% of the individuals. Unlike the ocean, zooplankton distributions in the lagoon were not homogenous; instead
spatial patterns were apparently formed by the interaction between hydrodynamic processes and species-specific behaviour.
Accepted: 28 August 1997 相似文献
5.
Since 1985, China has established three breeding herds of Père David’s deer: the Beijing Père David’s Deer Park (39°07′N,
116°03′E), the Dafeng Père David’s Deer Nature Reserve (33°05′N, 120°49′E) and Shishou (Tianezhou) Père David’s Deer Nature
Reserve (29°49′N, 112°33′E), through reintroductions of about 30–40 founders. Since establishment, all three populations have
grown steadily. However, genetic backgrounds in those populations are still unknown. We studied the genetic diversity in Père
David’s deer and genetic consequences of population relocations in China. We revealed that genetic diversity was extremely
low in Père David’s deer populations in China. Only a single mtDNA D-loop haplotype was found in the deer, furthermore, only
five polymorphic microsatellite loci were screened out from 84 pairs of species-transferred primers. Genetic makeup in the
three Père David’s deer populations were significantly different (P < 0.01). H
E and allelic richness in the Tianezhou population were the highest (0.54, 2.60, n = 31), Beijing population (0.52, 2.4, n = 125) showed the second highest measures, while the Dafeng population (0.46, 2.39, n = 39) measured lowest. Our results suggest that effective management of a species of low genetic diversity like the Père
David’s deer should consider the genetic background of each founder to make sure genetic variations are preserved in both
source population and relocated population. Now, the Tianezhou population is the most appropriate source population in China
when establishing new Père David deer populations in the wild.
相似文献
Zhigang JiangEmail: |
6.
Forty-five sorghum germplasm growing in the Eastern Highlands of Ethiopia were evaluated for 10 qualitative traits. Phenotypic
frequencies between the accessions from each of the nine Aanaas and Alemaya University, grouped in 10 localities were tabulated.
Phenotypic diversity index, H′, was analysed and the result indicated the between localities component of diversity to be relatively smaller than the variation
in H′ among characters within localities. The value of H′ for all sample germplasm ranged from 0.36 to 0.95 with a mean of 0.71. The results showed that there is a wide morpho-agronomical
diversity among the sample germplasm studied. This information can be used for the conservation of these germplasm resources
and future improvement work of the sorghum crop. 相似文献
7.
Curcuma zedoaria (Christm.) Roscoe, a member of the family Zingiberaceae, is one of the most widely distributed Curcuma species in Bangladesh. It is a well-known and important species because of its medicinal and horticultural values. However,
some plant populations are predicted to be depleted due to habitat destruction and due to extensive collection by local inhabitants.
In order to estimate the level of genetic diversity within and between natural populations, RAPD analyses were performed using
individual plants from different populations. We used Shannon’s index to partition genetic diversity which clearly demonstrated
that hilly populations of Srimangal, Chittagong and Sitakundu maintain rather higher genetic diversity than that of plain
land and plateau land populations of Savar and Birganj, respectively. We found a high intrapopulational (H′pop/H′sp) genetic diversity of 0.717 that was higher than the interpopulation diversity G
ST[(H′sp−H′pop)/H′sp] value of 0.283. Principal Coordinates Analysis (PCoA) showed that individuals of the hilly populations were combined in
one group, separated from the plain land and plateau land populations. From a conservation point of view, our results suggest
that special attention should be kept on the small populations of plain and plateau lands that are critically threatened due
to high anthropogenic activities. 相似文献
8.
Eleanor B. Mackay Ian D. Jones Andrew M. Folkard Stephen J. Thackeray 《Hydrobiologia》2011,666(1):85-97
Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes
of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from
eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types,
meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate
analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of
36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida.
Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into
three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow
and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal
areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was
comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were
closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according
to the level of isolation and the local environmental conditions for each marine lake. 相似文献
9.
Martin Günther Joachim L?der Alexandra Claudia Kraberg Nicole Aberle Silvia Peters Karen Helen Wiltshire 《Helgoland Marine Research》2012,66(1):11-23
A monitoring programme for microzooplankton was started at the long-term sampling station “Kabeltonne” at Helgoland Roads
(54°11.3′N; 7°54.0′E) in January 2007 in order to provide more detailed knowledge on microzooplankton occurrence, composition
and seasonality patterns at this site and to complement the existing plankton data series. Ciliate and dinoflagellate cell
concentration and carbon biomass were recorded on a weekly basis. Heterotrophic dinoflagellates were considerably more important
in terms of biomass than ciliates, especially during the summer months. However, in early spring, ciliates were the major
group of microzooplankton grazers as they responded more quickly to phytoplankton food availability. Mixotrophic dinoflagellates
played a secondary role in terms of biomass when compared to heterotrophic species; nevertheless, they made up an intense
late summer bloom in 2007. The photosynthetic ciliate Myrionecta rubra bloomed at the end of the sampling period. Due to its high biomass when compared to crustacean plankton especially during
the spring bloom, microzooplankton should be regarded as the more important phytoplankton grazer group at Helgoland Roads.
Based on these results, analyses of biotic and abiotic factors driving microzooplankton composition and abundance are necessary
for a full understanding of this important component of the plankton. 相似文献
10.
We consider the spatio-temporal dynamics of a spatially-structured generalization of the phytoplankton-zooplankton-fish larvae
model system proposed earlier (Biktashev et al., 2003, J. Plankton Res. 5, 21–33; James et al., 2003, Ecol. Model. 160, 77–90). In contrast to Pitchford and Brindley (2001, Bull. Math. Biol. 63, 527–546), who were concerned with small scale patchiness (i.e., 1–10m), on which the (stochastic) raptorial behaviour of
individual larvae is important, we address here the much larger scale ‘patchy’ problems (i.e., 10–100 km), on which both larvae
and plankton may be regarded as passive tracers of the fluid motion, dispersed and mixed by the turbulent diffusion processes.
In particular, we study the dependence of the fish recruitment on carrying capacities of the plankton subsystem and on spatio-temporal
evolution of that subsystem with respect to the larvae hatching site(s). It is shown that the main features found both in
the nonstructured and age-structured spatially uniform models are observed in the spatially structured case, but that spatial
effects can significantly modify the overall quantitative outcome.
Spatial patterns in the metamorphosed fish distribution are a consequence of quasi-local interaction of larvae with plankton,
in which the dispersion of larvae by large scale turbulent eddies plays little part due to the relatively short timescale
of the larvae development. As a result, in a strong phyto/zooplankton subsystem, with fast reproduction rate and large carrying
capacity of phytoplankton and high conversion ratio of zooplankton, recruitment success depends only on the localization and
timing of the hatching with respect to the plankton patches. In a weak phyto/zooplankton system, with slow reproduction rate
and small carrying capacity of phytoplankton and low conversion ratio of zooplankton, the larvae may significantly influence
the evolution of the plankton patches, which may lead to nontrivial cooperative effects between different patches of larvae.
However, in this case, recruitment is very low. 相似文献
11.
Paul Blanchon 《Coral reefs (Online)》2010,29(2):481-498
The elevation of reefs and coastal deposits during the last Interglaciation (MIS-5e) indicates that sea level reached a highstand
of as much as 6 m above the present, but it is uncertain how rapidly this level was attained and how it impacted reef development.
To investigate this problem, I made a detailed sedimentological analysis of a well-dated reef from the northeast coast of
the stable Yucatan Peninsula. Two linear reef tracts were delineated which are offset and at different elevations. The lower
reef tract crops out along northern shore for 575 m and extends from below present mean sea level to +3 m. The reef crest
facies consists of large Acropora palmata colonies dispersed within a coral boulder-gravel and is flanked by an A. cervicornis-dominated reef-front and a large area of lagoonal framework formed by coalesced patches of A. cervicornis and Montastraea spp. Constituents in the upper centimetre of the lower tract are heavily encrusted by a cap of crustose corallines and, in
places, are levelled by a discontinuous marine-erosion surface. The upper reef tract crops out ~150 m inland up to an elevation
of +5.8 m and parallels the southern section of shore for ~400 m. It also consist of an A. palmata-dominated crest facies flanked by reef-front, back-reef and lagoonal frameworks. In this case, however, lagoonal frameworks
are dominated by a sediment-tolerant assemblage of branching coralline algae. Also different is the lack of encrustation by
corallines, and the infiltration of upper tract facies by beach-derived shell-gravels from regressive shoreface deposits above.
These results indicate that the lower reef tract and lagoonal patch-reefs formed at a sea level of +3 m. Final capping by
crustose corallines and discontinuous marine erosion indicates that the lower tract was terminated by the complete demise
of corals on the crest but only patchy demise in the lagoon. Areas of continuous framework accretion between the lagoonal
patch reefs and the upper reef-tract, however, require that the demise of this reef was ecologically synchronous with initiation
of the upper reef-tract, which had back-stepped 100 m into the lagoon. In this new position, the upper tract developed a reef
crest that corresponded to a final sea-level position of +6 m. Reef flat development at +5 m and large in-place colonies of
A. palmata at the base of the crest unit indicate, however, that sea level must have risen rapidly from +3 to more than +5 m to accommodate
back-stepping. This sea-level jump created a higher energy wave field that mobilized back-reef and lagoonal sediments, and
the resulting high sediment flux eroded lagoonal framework and prevented the recovery of the submerged lower reef crest. So
this single jump in sea level was responsible not only for reef demise and back-stepping but also for marine erosion and suppression
of subsequent reef development—features that elsewhere have been used to support multiple sea-level excursions during the
last interglacial. 相似文献
12.
Based on the maritime data collected from 23°30′–33°00′ N and 118°30′–128°00′ E of the East China Sea (ECS) in four seasons
during 1997–2000, the dynamics of medusae diversity and their causes were analyzed. A total of 103 medusae species were identified,
and these species mainly distributed in the southern and northern offshore areas of the ECS. Species diversity index (H′) of medusae was higher in the south than those in the north, higher in summer and winter than in spring and autumn, and
higher in offshore than in the nearshore areas. The species number was closely correlated with H′ value, whereas the abundance of species had no significant relationship with the diversity index. The lower H′ value of the nearshore in spring and autumn resulted from the aggregation of Muggiaea atlantica in the south nearshore and Diphyes chamissonis in the north nearshore. In addition, water temperature, followed by salinity, is the main environmental factor influencing
the distribution of species diversity. The H′ value was related to the water temperature at the 10 m layer in winter and spring, and it was associated with the surface
water temperature in summer and with the 10 m-salinity-layer in autumn. In spring and summer, the isoline distribution of
H′ value reflected the direction of the Taiwan Warm Current and the variation of the water masses in the ECS. In winter, the
isoline of the H′ value indicated the incursion of Kuroshio current. In conclusion, the H′ isoline is an good indicator for water masses in ECS.
__________
Translated from Biodiversity Science, 2006, 14(6): 508–516 [译自:生物多样性] 相似文献
13.
Despite increasing recognition of the role spatial pattern can play in ecosystem function, few studies have quantified spatial heterogeneity in savanna ecosystems. The spatial distribution of herbaceous biomass and species composition was measured across three scales in a semi-arid savanna in central Kenya, and patterns were related to environmental variables at different scales. Herbaceous biomass declined across a rainfall gradient and from upper to lower topographic positions, but variation within a site (across 5–50 m) was similar in magnitude to among-site variation associated with rainfall and topography. Geostatistical analyses showed that patchiness at scales of 5–25 m explained 20% of total variation in herbaceous biomass. This pattern arose from the presence of both 5–10-m diameter patches containing high herbaceous biomass (> 170 g m–2) and 5–10-m diameter patches characterized by nearly bare soil surfaces (< 40 g m–2). Patch structure was contingent on topography, with larger bare patches at ridgeline and upper hillslope positions. Grass species distributions showed the greatest degree of patch structure and species turnover across distances of 5–45 m. Additional community variation was associated with topography, with minimal variation in species composition across the rainfall gradient. Pattern diversity significantly exceeded levels reported for four other grassland ecosystems, suggesting fundamental differences in local processes generating spatial pattern. It is hypothesized that heterogeneously distributed grazing pressure, interacting with the distribution of shrub canopies, is an important factor generating such high levels of small-scale patch structure in this savanna. 相似文献
14.
The community structure of the macrobenthic fauna was studied in the overall area of Laki Lagoon in September 1997 (salinity 32–35 psu) and monthly from February 1998 to February 1999 in the innermost part of the lagoon (salinity 0.1–6.8 psu). Community structure was analyzed by means of uni- and multivariate methods. In September 1997, the macrofauna in the outer part of the lagoon was characterized by a higher diversity and the occurrence of both lagoonal and marine species, and in the innermost part by a higher total abundance and the occurrence of a few lagoonal species. The combination of distance from the sea, depth, salinity and sediment organic matter correlated best with the spatial distribution pattern of the macrobenthic fauna. Community structure in the innermost part of the lagoon showed a seasonal periodicity. Species composition during spring 1998, at 0.1–2.0 psu, was similar to that in September 1997. During summer the macrobenthic fauna became impoverished, but recovered from late summer onwards. The salinity increase during summer (up to 5–7 psu) was followed by the appearance of marine species in the innermost part of the lagoon. Total abundance displayed a peak in late spring and a lower one in mid-autumn. The seasonal dynamics of the faunal assemblage was mainly governed by water temperature. Predation pressure by Atherina boyeri may have contributed to quantitative community changes during autumn. 相似文献
15.
A 122 cm-long core was taken in the El-Guettiate Sebkha of Skhira (southeastern part of Tunisia) in order to investigate the recent palaeoenvironmental evolution of this region. The quantitative and qualitative analysis of ostracod and benthic foraminifera assemblages coupled with a correspondence analysis allows the reconstruction of palaeoenvironmental changes during the Holocene in this area. Four typical associations of ostracods (open marine, coastal marine, lagoonal and estuarine brackish) and two associations of benthic foraminifera (coastal and lagoonal) were distinguished. The onset of restricted lagoonal environments linked to the building-up of sand spit led to the onset of restricted lagoon and brackish environment at cal. 5408 years BP. The Shannon and equitability index of diversity were used to decipher the structural variations of the populations of ostracods and benthic foraminifera along the sampled core. We note a reduction in the Shannon index from the bottom to the top, which indicates a progressive isolation of the biotope. The open lagoonal episode is characterized by high values of diversity. During restricted lagoonal episodes the Shannon and equitability index are reduced. The correspondence analysis reveals an environmental gradient related to the marine influence. It shows an antagonism between the widely opened estuarian lagoonal species and those of restricted lagoon. The less opened estuarian lagoonal taxa occupy an intermediate position. Based on these evidences, microfauna carried out in the El-Guettiate Sebkha allows us to recognize four phases beginning with a widely opened estuarian lagoon (ca. cal. 7460 years PB), followed by a restricted lagoon (ca. cal. 5408 years BP) and finally a brackish lagoon evolving towards the present-day sebkha environment. The opened estuarine lagoon is characterized by high values of species richness and diversity indices. 相似文献
16.
We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared
macroinvertebrate densities among patches (0.25 m2) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem
conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading
from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and
invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ
among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides
a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these
plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between
natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone
has little effect on the H′-diversity–reed dominance relationship. 相似文献
17.
Luz Allende 《Polar Biology》2009,32(3):493-501
The goal of this study was to address the top-down and bottom-up controls on different microbial web components (bacterioplankton,
picophytoplankton, and >3 μm phytoplankton) in an Antarctic lake. Two experiments using a size fractionation approach and
nutrient addition were conducted at microcosm scale (2.5 l). The variation in net growth rates (k′) of bacterioplankton and phytoplankton size fractions was analyzed after 5 days. The results determined significant differences;
whereas bacterioplankton and large phytoplankton showed an increase in their k′ when their predators were removed, the picophytoplankton showed a decrease. All the studied plankton components presented
the highest k′ when nutrients were added. It is suggested that, in this lake, both the top-down and bottom-up regulations account for the
regulation of bacterioplankton and large phytoplankton. As for picophytoplankton, the bottom-up control was evident and grazing
did not pose a negative impact and rather, had a positive effect probably due to liberation of nutrients. 相似文献
18.
Cinnamate 4-hydroxylase (C4H, EC 1.14.13.11) plays an important role in the phenylpropanoid pathway, which produces many economically important secondary
metabolites. A gene coding for C4H, designated as PhC4H (GenBank accession no. DQ211885) was isolated from Parthenocissus henryana. The full-length PhC4H cDNA is 1,747 bp long with a 1,518-bp open reading frame encoding a protein of 505 amino acids, a 40-bp 5′ non-coding region
and a 189-bp 3′-untranslated region. Secondary structure of the deduced PhC4H protein consists of 41.78% alpha helix, 15.64%
extended strand and 42.57% random coil. The genomic DNA of PhC4H is 2,895 bp long and contains two introns; intron I is 205-bp and intron II is 1,172-bp (GenBank accession no. EU440734).
DNA gel blot analysis revealed that there might be a single copy of PhC4H in Parthenocissus henryana genome. By using anchored PCR, a 963-bp promoter sequence was isolated and it contains many responsive elements conserved
in the upstream region of PAL, C4H and 4CL including the P-, A-, L- and H-boxes. 相似文献
19.
Edwin D. Grosholz 《Oecologia》1993,96(3):347-353
The influence of spatial heterogeneity on the population dynamics of a naturally occurring invertebrate host-pathogen system
was experimentally investigated. At ten week intervals over a two year period, I quantified the spatial distribution of natural
populations of the terrestrial isopod crustacean Porcellio scaber infected with the isopod iridescent virus (IIV). During the seasonally dry periods of summer and early fall in central California,
isopod populations were highly aggregated and the degree of patchiness and distance between inhabited patches was greatest.
Coincident with increased patchiness and patch spacing was an increase in isopod density within patches. During the wet seasons
of winter and spring, isopod population patchiness, inter-patch spacing, and within-patch density was low. Seasonal changes
in virus prevalence were negatively correlated with within-patch density, patchiness, and inter-patch spacing. The influence
of the spatial distribution of isopods on virus prevalence was also tested in field experiments. The virus was introduced
into arrays of artificial habitat patches colonized by isopods in which interpatch distance was varied. The prevalence of
resulting infections was monitored at weekly intervals. In addition, dispersal rates between artificial patches and natural
patches were quantified and compared. The results showed that isopods in treatments with the smallest inter-patch spacing
had the highest virus prevalence, with generally lower prevalence among isopods in more widely spaced patches. The spacing
of experimental patches significantly affected virus prevalence, although the experiments did not resolve a clear relationship
between patch spacing and virus prevalence. Rates of dispersal between patches decreased with increased patch spacing, and
these rates did not differ significantly from dispersal between natural patches. The results suggest that rates of dispersal
between isopod subpopulations may be an important component of the infection dynamics in this system. I discuss the consequences
of these findings for host-pathogen dynamics in fragmented habitats, and for other ecological interactions in spatially heterogeneous
habitats. 相似文献
20.
The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated
at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha−1 at 245 m to 8,895 ha−1 at 510 m. While diversity was variable, with H′ ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages;
a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were
not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable
effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of
past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse
sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas)
but diversity was highest in intermediate areas (H′ = 2.35). 相似文献