Abstract: Genebank collection databases can be used for ecogeographical studies under the assumption that the accessions are a geographically unbiased sample. We evaluated the representativeness of a collection of wild potatoes from Bolivia and defined and assessed four types of bias: species, species-area, hotspot, and infrastructure. Species bias is the sampling of some species more often than others. Species-area bias is a sampling that is disproportionate to the total area in which a species is found. Hotspot bias is the disproportionate sampling of areas with high levels of diversity. Infrastructure bias is the disproportionate sampling of areas near roads and towns. Each of these biases is present in the Bolivian wild potato collection. The infrastructure bias was strong: 60% of all wild potato accessions were collected within 2 km of a road, as opposed to 22%, if collections had been made randomly. This analysis can serve as a guide for future collecting trips. It can also provide baseline information for the application of genebank data in studies based on geographic information systems. 相似文献
Population structure and reproductive ecology of the burrowing ghost shrimp Callianassa filholi Milne-Edwards, 1878 were studied in populations along a latitudinal gradient throughout New Zealand during the breeding season.
Size-frequency distributions revealed unimodal populations, with predominantly sexually mature shrimp. All populations showed
an unbiased sex-ratio, and there appeared to be no significant difference in size (carapace length, CL) between sexes. At
the same time, CL and size at maturity differed significantly between populations; however, a general increase in sizes from
north to south was not consistent throughout the latitudinal range studied. The timing of the breeding cycle differed significantly
between populations, and breeding started earlier in southern populations. Number of embryos (fecundity) increased linearly
with female CL at each location, but rates differed significantly between populations. Embryo size was not related to number
of embryos, and the former increased significantly with latitude. With the exception of embryo size, observed differences
in body size/size at maturity and reproductive timing between C. filholi populations are thought to be determined by food availability rather than temperature. Thus, further study is suggested on
these aspects of thalassinid reproductive biology.
Received: 17 June 1999 / Accepted: 8 January 2000 相似文献
Acoustic telemetry was used to examine patterns of activity and space utilisation of coelacanths, nocturnal predators which
spend the day in submarine caves. Nine coelacanths (Latimeria chalumnae) were tracked, each for a period of 1 to 16 nights at Grande Comore, West Indian Ocean. Activities lasted on average 9 h,
usually starting shortly after sunset and ending before sunrise. Vertically, coelacanths moved up and down at and below cave
level by following the bottom contour, mainly between 180 and 400 m depth. The deepest record was 698 m, the shallowest 133 m.
Most time was spent between 200 and 300 m depth. Large individuals performed deep excursions to depths below 400 m, usually
once per night. The fish spent most time in water temperatures of 15 to 19 °C; they rarely ventured into waters warmer than
22 °C measured at depths shallower than 160 m depth. Horizontally, coelacanths stayed in narrow areas ranging from <1 to 10 km
of coastline. Coelacanths are extremely slow drift-hunters with an estimated average swimming speed of 3.2 m min−1, often travelling not more than 3 km per night. They probably take advantage of local upwelling and downwelling and slow
currents occurring parallel to the steep slopes. This study shows that coelacanths are inhabitants of the subphotic zone,
where they are active mainly below the depth of their daytime refuges.
Received: 7 July 1999 / Accepted: 11 February 2000 相似文献
Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage
has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible
prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living
seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification
of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants,
gannets and penguins.
Received: 15 July 1997 / Accepted: 31 October 1997 相似文献
High-resolution videos, scanning electron microscopy and histology were used to study the feeding mechanism of myodocopid
ostracods from the Pacific Coast of Japan, as exemplified by Vargula hilgendorfii (Müller, 1890) and a few other cypridinid species. Ostracods observed in the laboratory were attracted to a wide spectrum
of natural food sources, behaving as predators of living prey (e.g. polychaete annelids), as opportunistic scavengers on dead
animals (e.g. annelids, fishes, squid), and also consuming artificial food. Food sources may be detected by chemoreception.
The fourth limb (endopodites with strong sclerotized setae) and the furcal lamellae (claws with teeth) act in coordination
to abrade and eventually tear open the protective integument of living/dead prey such as annelids. The mandibular palps are
used mainly to hold the food. Food sections and soft-body contents are transferred to the mouth by the fourth limb (endopodial
“rake”) and fifth limb (exopodite with pectinate setae) and are passed to the oesophagus by the endites (mandibles, fourth
and fifth limbs). Food is subsequently pumped up to the stomach by peristaltic contractions of the oesophagus (ring muscles)
and stored in the stomach pouch. The upper lip of bioluminescent (V. hilgendorfii) and non-bioluminescent species of Cypridinidae often contact food, suggesting that some of the glands housed in this organ
may emit digestive enzymes prior to ingestion. Ostracods are able to ingest massive quantities of food within a few minutes
and to survive starvation for several weeks. In V. hilgendorfii, the midgut is a huge sac-like organ with no partition and is lined with a single layer of columnar epithelial cells. No
differentiated hepatopancreas is present. The cypridinid produces a single faecal pellet wrapped in a thin reticulated, peritrophic
membrane. Myodocopid ostracods exhibit a wide range of feeding strategies (detritus-feeding, comb-feeding, scavenging, predation,
ectoparasitism) in both benthic and pelagic niches, and constitute a substantial source of food for many zooplankters. Adaptation
of cypridinids to scavenging/predation is reflected in the morphology of their furcae, mandibles, fourth and fifth limbs,
and their digestive system. Palaeontological data suggest that early Triassic cypridinids and possible late Ordovician myodocopids
may have been carnivorous scavengers feeding on carcasses of cephalopods (ammonoids or orthoconic nautiloids), thus playing
the same role of “recyclers” as modern representatives of the group.
Received: 2 January 1998 / Accepted: 23 July 1998 相似文献
Previously published mtDNA cytochrome b sequences for Xyrichtys novacula (Linnaeus) and two morphologically distinct types of Xyrichtys larvae (Pisces: Labridae) included human cytochrome b sequence, presumably due to sample contamination and/or poor preservation of sample DNA. Those sequences had been used to
identify the two types of Xyrichtys larvae as X. novacula, but owing to the contamination, the identifications are invalid. Fresh specimens were collected: X.␣martinicensis (Cuvier and Valenciennes), X. novacula, X. splendens (Castelnau), and Xyrichtys sp. larvae of each of the two morphotypes (dorsal-forward eye and ventral-forward eye). The cytochrome b fragment was amplified from each specimen using the polymerase chain reaction. Comparison of the sequences with human cytochrome b sequence confirmed that the new sequences were not contaminated. The interspecific differences in Xyrichtys sequences were less than previously reported, but still greater than observed in many fish genera. Distance and parsimony
analyses indicated that X. novacula and X. martinicensis were more closely related to each other than to X. splendens. This conclusion differs from our previous conclusion that X. martinicensis and X. splendens were more closely related to each other than to X. novacula. Distance and parsimony analyses also demonstrated that both larval morphotypes were X. novacula and, thus, our previous conclusions regarding larval ecology and oceanographic transport remain unchanged.
Received: 12 March 1997 / Accepted: 24 October 1997 相似文献
Summary. In the present experiment the behaviour and endocrine status of males of the brown trout, Salmo trutta L., (Salmoniformes: Salmonidae) were studied when males were kept in a stream tank with a nest digging female. Groups of
mature adult males and precocious intact or anosmic male parr were placed with the nesting female so that the group resembled
a natural spawning situation with big anadromous fish acting as dominant males and precocious parr acting as “sneakers”. A
control experiment was also run with only males without a female present. In intact parr there were significant positive correlations
between the per cent of the total observation time spent with a female, milt volume, and plasma concentration of 17α, 20β-dihydroxy-4-pregnen-3-one.
Anosmic parr had significantly lower volumes of strippable milt and gonadal steroid hormone levels compared with intact parr.
However, no differences were found in the control experiment. Significantly fewer anosmic parr attended and courted the nesting
female and those anosmic fish that attended the female had significantly lower plasma levels of gonadal hormones. Intact parr
also displayed a greater number of agonistic acts against other parr without any difference in fighting ability. No differences
in aggression occured in the control experiment. In adult males together with a female, post-experimental gonadal steroid
hormone levels were higher than pre-experimental levels. Positive correlations between aggression and androgen hormone levels
were observed in adult males. No differences in plasma hormone levels were observed between adult males and intact precocious
males. The results show that olfactory occlusion results in low steroid hormone levels and milt volumes in precocious males
placed in a spawning situation. The courting behaviour was also affected by anosmia. Odours from the nesting female may have
caused the enhanced plasma hormone levels and stimulated the males to attend the female.
Received 15 May 1997; accepted 29 June 1997. 相似文献
NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P < 0.05) and negatively with soil moisture content (P < 0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N fromthe grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m3). 相似文献
Understanding how cities can transform organic waste into a valuable resource is critical to urban sustainability. The capture and recycling of phosphorus (P), and other essential nutrients, from human excreta is particularly important as an alternative organic fertilizer source for agriculture. However, the complex set of socio-environmental factors influencing urban human excreta management is not yet sufficiently integrated into sustainable P research. Here, we synthesize information about the pathways P can take through urban sanitation systems along with barriers and facilitators to P recycling across cities. We examine five case study cities by using a sanitation chains approach: Accra, Ghana; Buenos Aires, Argentina; Beijing, China; Baltimore, USA; and London, England. Our cross-city comparison shows that London and Baltimore recycle a larger percentage of P from human excreta back to agricultural lands than other cities, and that there is a large diversity in socio-environmental factors that affect the patterns of recycling observed across cities. Our research highlights conditions that may be “necessary but not sufficient” for P recycling, including access to capital resources. Path dependencies of large sanitation infrastructure investments in the Global North contrast with rapidly urbanizing cities in the Global South, which present opportunities for alternative sanitation development pathways. Understanding such city-specific social and environmental barriers to P recycling options could help address multiple interacting societal objectives related to sanitation and provide options for satisfying global agricultural nutrient demand.