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991.
The influence of wave exposure and of tidal height on mussel (Perna perna Linnaeus) population structure (size, density, biomass and adult/juvenile correlations) was examined at 18 sites along the
south coast of South Africa. Sites were classified as exposed or sheltered prior to sampling, without reference to the biota,
on the basis of aspect, topography and wave regime. A single set of samples was collected from each site during three spring
tide cycles. Adult mussels on these shores almost always attach directly to the rocks, and layering of mussels is virtually
absent. Shore height always had a strong influence on population structure, but exposure had significant effects only lower
on the shore, and almost exclusively on mussel sizes. Principal component analysis (PCA), based on size distribution data
for each population, revealed a general upshore decrease in the modal size of the adult cohort. The effects of exposure on
size distribution, however, varied with tidal height. PCA separated exposed zones, with larger mussels, from sheltered zones
on the low-shore. Farther upshore the two shore types were increasingly confounded. The maximum size of mussels showed a similar
pattern, with significant differences (ANOVA, p < 0.05) between exposed and sheltered sites only on the low- and mid-shores. Density was calculated from randomly placed
quadrats (i.e. not necessarily from areas of 100% cover) and showed a different pattern. Adult (>15 mm) densities decreased
up the shore, with low-, mid- and high-shore zones being significantly different from one another (ANOVA, p < 0.0001; followed by multiple range tests). However, exposure had no significant effect on density, nor was there a significant
interaction with zone. Recruit (<15 mm) densities were positively correlated with adult (>15 mm) densities in all zones and
for both exposure regimes ( p < 0.05 in all cases), but there was considerable variability and extremely low predictability in these relationships (r
2 generally <0.2). Predictability tended to be greater towards the high-shore, where adults were more clumped. As with density,
biomass was not affected by exposure, but decreased upshore as mean size and density decreased. A reduction in the influence
of exposure farther upshore may be caused by greater emersion overriding the effects of exposure. The presence of free space
within mussel beds and significant correlations between recruit and adult densities suggest that these mussel populations
are recruit limited.
Received: 7 January 2000 / Accepted: 6 July 2000 相似文献
992.
Y. Nassiri P. S. Rainbow C. Amiard-Triquet F. Rainglet B. D. Smith 《Marine Biology》2000,136(3):477-484
The talitrid amphipod crustacean Orchestia gammarellus (Pallas) was collected from metal-contaminated (Dulas Bay, Gironde) and control (Millport) sites in the UK and France. Irrespective
of site of origin, the amphipods showed the same physiological mechanism of trace-metal detoxification, involving the ventral
caeca. Copper was always present in lysosomal residual bodies in the ventral caeca. Following laboratory exposure to zinc
and cadmium, the lysosomes usually contained both copper and zinc but cadmium was not detectable. The lysosomal copper concentration
is positively correlated to that of sulphur, while the concentration of lysosomal zinc is related to that of phosphorus. Results
are interpreted in terms of the differential rates of turnover of metallothioneins chelating copper, zinc or cadmium.
Received: 9 February 1999 / Accepted: 2 December 1999 相似文献
993.
Koala Conservation Policy Process: Appraisal and Recommendations 总被引:1,自引:0,他引:1
Tim W. Clark Nicole Mazur † Steven J. Cork ‡ Steve Dovers § and Ronnie Harding 《Conservation biology》2000,14(3):681-690
994.
995.
996.
Effects of Land-Cover Changes on Mammals in a Neotropical Region: a Modeling Approach 总被引:3,自引:0,他引:3
Alfredo D. Cuarón 《Conservation biology》2000,14(6):1676-1692
997.
The Channel of Santa Cruz is a mangrove area in northeastern Brasil 40 km north of Recife. Until 1991 a chlor-alkali factory
discharged large amounts of mercury into the main tributary of the channel, the Rio Botafogo. The objective of this study
was to assess the potential of the mangrove oyster Crassostrea rhizophorae as a bioindicator for mercury in this area and to examine the influence of condition on mercury concentrations in the oysters.
The investigation was carried out in the late rainy season (July to September) 1993, in the rainy season (April to June) 1994
and in the dry season (November/December) 1994. At 11 stations in the channel, mangrove oysters, surface sediments and suspended
matter were sampled, representing different compartments of the system. The distribution of mercury in the Channel of Santa
Cruz exhibited for all compartments the same distinct spatial pattern with maxima in the Rio Botafogo. Seasonal variations
were small and revealed no clear tendencies. In addition, mangrove oysters were transplanted from more contaminated stations
to less contaminated stations and vice versa. These experiments were designed to study the oysters' capability to adjust their
mercury concentrations to a changing bioavailability of mercury. The transplantation experiments suggest that the oysters
are capable to adjust to changing ambient mercury availability within a few months. The transplantation experiments also revealed
the importance of condition changes on the mercury concentration of the oysters. This factor should not be ignored during
pollution studies. However, condition had apparently no strong influence on the spatial or seasonal mercury variations of
the oysters. The mangrove oyster is a suitable bioindicator for long-term changes in mercury availability.
Received: 20 August 1997 / Accepted: 15 January 1998 相似文献
998.
We investigated mycosporine amino acid (MAA) involvement as protective sunscreens in spawn of the sea hare Aplysia dactylomela to determine if adult diet and ultraviolet (UV) exposure affected the UV sensitivity of developing embryos. Adults were fed
a red alga rich in MAAs (Acanthophora spicifera) or a green alga poor in MAAs (Ulva lactuca). Adults on each diet were exposed for 2 wk to ambient solar irradiance with two types of acrylic filters; one allowed exposure
to wavelengths >275 nm (designated UV) and one to wavelengths only >410 nm (designated NOUV). Spawn from each adult group
was likewise treated with UV or NOUV and monitored during development for differences in mortality and metabolic rate (measured
as oxygen consumption: V˙
O2). Also recorded were number of eggs or embryos per capsule, times to hatching, hatching success, size at hatching, and V˙
O2 of adults. Spawn from adults eating red algae was almost twice as rich in MAAs as spawn from adults eating green algae, suggesting
that MAA content is diet-related. Although overall quantities of MAAs in the spawn reflected MAA contents of the adult diet,
specific MAAs were differentially sequestered in the spawn. Thus, porphyra-334, found in high concentration in Aplysia dactylomela's preferred red algal food, was present in only low concentration in the spawn. Conversely, mycosporine-glycine, in low concentration
in red algal food, was the most abundant MAA in the spawn. UV treatment of adults had no effect on quantities of MAAs in the
spawn. Adults exposed to UV had significantly higher V˙
O2s and spawned twice as often. The UV-treated adults produced spawn with significantly higher V˙
O2s and their embryos developed to hatching sooner. The only significant effect of UV exposure of the spawn was to reduce the
percentage of veligers hatching from 71 to 50%. There was no significant effect on hatching time or size of the veligers at
hatching, nor on number of eggs per capsule.
Received: 13 May 1997 / Accepted: 27 June 1997 相似文献
999.
Testes mass in megachiropteran bats varies in accordance with sperm competition theory 总被引:4,自引:0,他引:4
D. J. Hosken 《Behavioral ecology and sociobiology》1998,44(3):169-177
Sperm competition is a widespread phenomenon influencing a range of characters, including investment in gonadal tissue. Conspecific
proximity is one factor which can influence the risk of sperm competition and hence testicular investment, and decreased confidence
of paternity may be one cost of group living. Aspects of female biology may also influence spermatogenic investment and sperm
morphology. This study examines the associations between relative testes mass and roost-group size across 17 species of Megachiroptera.
Associations between breeding season duration and investment in spermatogenesis are also examined, as are associations between
female reproductive tract dimensions and testes mass and dimensions of spermatozoa across all bats. Relative testes mass was
significantly positively associated with roost-group size at a species level and after appropriate phylogenetic control (pairwise
comparisons and comparison of independent contrasts). There were no significant relationships between breeding season duration
and relative testes mass. Across all bats, neither testes mass nor sperm length were significantly related to dimensions of
the female tract. The results are discussed in the context of sperm competition.
Received: 7 January 1998 / Accepted after revision: 8 August 1998 相似文献
1000.
Genetic divergence and phylogenetic inferences in five species of Mugilidae (Pisces: Perciformes) 总被引:4,自引:0,他引:4
Allozyme electrophoresis was used to compare the genetic divergence of global populations of Mugil cephalus Linnaeus, 1758 and two congeneric [M.␣curema Cuvier & Valenciennes, 1836; M. gyrans (Jordan & Gilbert, 1885)] and two more distantly related [Liza ramada (Risso, 1826); Xenomugil thoburni (Jordan & Starks, 1896)] species on the basis of 18 enzyme loci. The amount of genetic divergence among the species examined
is in agreement with their present systematic status, the differences being larger among non-congeneric species than among
species of the same genus. Intraspecific genetic distances in M. cephalus (average Nei's D= 0.154), although higher than those reported for conspecific populations of fish, appear to be small when compared to the
interspecific values among mugilid species (0.821 ≤ Nei's D ≤ 1.744). Phylogenetic trees obtained by genetic distance methods and discrete character parsimony analysis were of similar
topology, except for the relationships within the genus Mugil and for the arrangement of M. cephalus populations.
Received: 7 April 1997 / Accepted: 4 February 1998 相似文献