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941.
942.
We compared the effects of natural and anthropogenic watershed disturbances on methyl mercury (MeHg) concentration in bulk
zooplankton from boreal Shield lakes. MeHg in zooplankton was monitored for three years in nine lakes impacted by deforestation,
in nine lakes impacted by wildfire, and in twenty lakes with undisturbed catchments. Lakes were sampled during spring, mid-
and late summer. MeHg in zooplankton showed a seasonal trend: concentrations were the lowest in spring, then peaked in mid-summer
and decreased in late summer. Over the three study years, MeHg concentrations observed in mid-summer in zooplankton from forest
harvested lakes were significantly higher than in reference and fire-impacted lakes, whereas differences between these two
groups of lakes were not significant. The pattern of distribution of MeHg in zooplankton during the different seasons paralleled
that of dissolved organic carbon (DOC), which is known as a vector of Hg from watershed soils to lake water. Besides DOC,
MeHg in zooplankton also showed a positive significant correlation with epilimnetic temperature and sulfate concentrations.
An inter-annual decreasing trend in MeHg was observed in zooplankton from reference and fire-impacted lakes. In forest harvested
lakes, however, MeHg concentrations remained higher and nearly constant over three years following the impact. Overall these
results indicate that the MeHg pulse observed in zooplankton following deforestation by harvesting is relatively long-lived,
and may have repercussions to the accumulation of MeHg along the food chain. Therefore, potential effects of deforestation
on the Hg contamination of fish should be taken into account in forest management practices. 相似文献
943.
Stages in the life cycle of the rhizostome jellyfish Rhizostoma octopus (L.) were reared in the laboratory from planula to young medusa and are described here. Fertilization of eggs was external,
and planulae, 110–150 μm in length, appeared after 2 days. These settled and developed into the scyphistoma stage. Scyphistomae
reached a maximum size of 2.3 mm, bore up to 24 tentacles, and had a large manubrium. Polyps reproduced asexually mainly by
podocysts. Strobilation was induced by temperature change. Each strobila released up to five ephyrae that measured 2.7–5.8 mm
in diameter at liberation. During transformation from newly released ephyra to young medusa, velar lappets appeared and increased
in number, the manubrium developed eight branched oral arms with epaulettes, and a marginal gastric network arose. Only one
cnidocyst type, the “a”-atrichous haploneme, was present in the planula. In addition to these haplonemes, heterotrichous microbasic
euryteles were observed in polyps, ephyrae, and medusae. Statoliths, located in the rhopalia, had a characteristic compact
shape. These sensory structures increased in number and size with the growth of ephyrae and medusae. 相似文献
944.
Catch and acoustic telemetry data were used to test three predictions of lekking behaviour in Atlantic cod (Gadus morhua L.) at a small-scale spawning ground (∼25 km2) in Placentia Bay, Newfoundland: (1) that cod form male-skewed aggregations during spawning; (2) spawning arenas occur at consistent sites; and (3) on the arenas, there will be higher proportions of spawning fish. Forty-two fishing sets from 1998 to 2003 indicated male-skewed sets early in the spawning season (April) in 5 of 6 survey years. Male-skewed sets were consistently distributed at depths < 50 m and mostly in one part of the ground. The proportions of spawning females and spent males were significantly higher in male-skewed sets, whereas sets with equal sex ratios had significantly higher proportions of immature males and spent females. In addition, cod of both sexes were significantly larger in male-skewed sets. Telemetric tracking of 25 cod in 2002 and 2003 (12 males, 13 females) indicated that both males and females were highly mobile while present on the spawning ground. Overall, our results add support to the hypothesis that cod employ a lekking mating system. 相似文献
945.
Low temperature limits the rate of biochemical reactions and aerobic scopes of cold water ectotherms. To compensate for this
limiting effect, animals living in cold environments often possess physiological or morphological adaptations to maintain
vital functions. Cross-latitudinal comparison of aerobic capacities is one method to test which factors constrain activity
in thermally distinct environments particularly when congeneric studies are carried out on related species with conservative
ecology and habitat. Burrowing is a major aerobic activity of bivalve molluscs that is described here for the first time for
the tropical mangrove species Laternula truncata and Laternula boschasina and then compared with their Antarctic congener Laternula elliptica. About 80% of L. truncata (16.3–46.1 mm shell length) and 63% of L. boschasina (11.3–27.7 mm shell length) buried within 24 h at 28°C. The burrowing rate index (BRI = [3√wet weight/time to bury]×104) ranged between 1.1 and 20.2 for L. boschasina and 1.1–32.9 for L. truncata. These values are 2–3 orders of magnitude less than other tropical bivalve molluscs and are amongst the lowest recorded for
any bivalve. Comparisons with the Antarctic L. elliptica showed little or no differences in BRI (Q
10 of 1.0–1.2 for specimens of the same size). This is contrary to the general pattern over a wide range of bivalves, where
BRI increases with a Q
10 of between 2.9 and 6.4 between high latitudes and the equator. L. elliptica has 25–30% longer relative foot length than tropical congeners of the same size, which could be a morphological adaptation
compensating for reduced burrowing speeds in a colder environment. Burrowing rates within the genus Laternula could, however, also be maintained by differing habitat, ecological and physiological constraints on burrowing capability. 相似文献
946.
F. Bentivegna F. Valentino P. Falco E. Zambianchi S. Hochscheid 《Marine Biology》2007,151(5):1605-1614
Previous studies have shown that loggerhead sea turtles (Caretta caretta), monitored by satellite telemetry, complete long-distance migration between the western and eastern Mediterranean basins
following a seasonal pattern. This study investigated if these migration routes may be influenced by surface currents by superimposing
the tracks of three loggerhead turtles (curved carapace length >55 cm), migrating from the western to the eastern Mediterranean
basin, on Lagrangian data of current developed into pseudo-eulerian speed fields. The average travel speed of the turtles
was 1.6 km h−1 and did not depend on the current speed or direction. We observed a connection between surface currents and the turtles’
migration routes, although not a conclusive one. These observations show that neritic stage loggerhead turtles conduct migration
in two distinct alternate phases: the first characterized by high and constant speed of travel both when swimming with or
against currents and the second typified by low travel speeds and a good concurrence between the trailed routes and the course
of the currents. These two phases corresponded to two types of movements, one where the turtle migrates actively to reach
a specific destination (either neritic foraging, wintering or nesting ground) and the other, where the turtle drifts with
the mesoscale current and forages pelagically. It seemed thus, that the influence of currents on a turtle’s movements depends
on the turtle’s momentary behaviour and location of residence. 相似文献
947.
Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology.
Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show
here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence
dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish,
Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and
leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined.
Critical speed was 27.5 ± 1.0 cm s−1 (30.9 BL s−1), and in situ speed was 13.6 ± 0.6 cm s−1. Fastest individuals were 44.6 and 25.0 cm s−1, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed.
Unfed larvae swam 172 ± 29 h at 8–10 cm s−1 (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was
2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional
swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction
to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming
SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left
(more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates
the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction.
Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours,
and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to
behaviour of other settlement-stage pomacentrid larvae that are older and larger. 相似文献
948.
Gnathiid isopods are one of the most abundant groups of ectoparasites on coral reef fishes. They, and other isopods, have
been shown to significantly affect the health and behaviour of many reef fish. Whether isopod emergence differs among habitats
on coral reefs is not known. In this study, we measured emergence rates of parasitic isopods (Gnathiidea and Flabellifera)
in six habitats at two sites at Lizard Island during new moon periods in March and December 2004. Isopods were collected from
the periphery and centres of micro-reefs, patch reefs, continuous reefs, and from inter-reefal habitats (sand or rubble) with
1 m2 emergence traps. Sites (Casuarina and Coconut Beach) were located on opposite sides of Lizard Island. Live gnathiids were
collected with light traps in November 2005 to investigate species differences between sites. At both sites, the most abundant
gnathiid species was exclusive to that site. More gnathiid larvae emerged at night, and emergence of fed gnathiids (pranizae)
and flabelliferan isopods was almost exclusively nocturnal. Diurnal emergence was greater at Coconut Beach than Casuarina
Beach. Although emergence counts were not consistently affected by parameters such as habitat, site, or sampling period, gnathiid
size and feeding state were. Where significant differences existed, gnathiids were larger and more often fed over reef borders
than centrally. We suggest first stage larvae (Z1) have the largest influence on total abundance and are patchily distributed
in accordance with adults from which they have recently hatched. As later stage larvae depend on fish, more successful (fed)
and older larvae are found on the edges of reefs where appropriate hosts may be more abundant, or predation is lower. Gnathiids
were over-dispersed in all habitats investigated, including apparently homogeneous beds of coral rubble and sand. This indicates
that their distributions may be better predicted by very fine scale differences in substrate or that aggregations are the
result of gregariousness and may be difficult to predict on the basis of substrate. Emergence traps collected comparatively
few parasitic flabelliferan isopods. This community differed greatly from the previously described community of scavenging
isopods at Lizard Island. These differences are probably the result of differences in trapping methodology. 相似文献
949.
Gail L. Patricelli Marc S. Dantzker Jack W. Bradbury 《Behavioral ecology and sociobiology》2007,61(7):1099-1110
Studies of animal acoustic communication have found that the frequency and temporal structure of acoustic signals can be shaped
by selection for efficient communication. The directionality of acoustic radiation may also be adapted for communication,
but we know relatively little about how directionality varies with signal function, sender morphology, and the environment
in which the sound is transmitted. We tested the hypothesis that the directionality of a vocalization is adapted to its function
in communication. This hypothesis predicts that vocalizations that are directed to multiple conspecifics (e.g., advertisements
and alarms) will be relatively omnidirectional because this will maximize the number of neighbors and mates that receive the
signal, and that vocalizations directed to particular individuals will be relatively directional because this will maximize
detection of the signal by the targeted receiver and minimize eavesdropping. To test these predictions, we measured the directionality
and amplitude of red-winged blackbird (Agelaius pheoniceus) vocalizations in the field by recording vocalizations simultaneously on eight calibrated microphones encircling the bird.
We found significant variation in directionality among vocalizations. Supporting our predictions, we found that the most omnidirectional
vocalizations were those used to alert conspecifics to danger, and the most directional vocalizations are those used during
courtship and solicitation of copulation, when the costs of eavesdropping are likely to be high. These results suggest that
the directionality of red-winged blackbird vocalizations is shaped by selection for effective communication. This study is
the first to provide statistical support for the hypothesis that directionality is related to the function of a signal in
communication. 相似文献
950.
Net emissions of CH4 and CO2 in Alaska: implications for the region's greenhouse gas budget. 总被引:1,自引:0,他引:1
Q Zhuang J M Melillo A D McGuire D W Kicklighter R G Prinn P A Steudler B S Felzer S Hu 《Ecological applications》2007,17(1):203-212
We used a biogeochemistry model, the Terrestrial Ecosystem Model (TEM), to study the net methane (CH4) fluxes between Alaskan ecosystems and the atmosphere. We estimated that the current net emissions of CH4 (emissions minus consumption) from Alaskan soils are approximately 3 Tg CH4/yr. Wet tundra ecosystems are responsible for 75% of the region's net emissions, while dry tundra and upland boreal forests are responsible for 50% and 45% of total consumption over the region, respectively. In response to climate change over the 21st century, our simulations indicated that CH4 emissions from wet soils would be enhanced more than consumption by dry soils of tundra and boreal forests. As a consequence, we projected that net CH4 emissions will almost double by the end of the century in response to high-latitude warming and associated climate changes. When we placed these CH4 emissions in the context of the projected carbon budget (carbon dioxide [CO2] and CH4) for Alaska at the end of the 21st century, we estimated that Alaska will be a net source of greenhouse gases to the atmosphere of 69 Tg CO2 equivalents/yr, that is, a balance between net methane emissions of 131 Tg CO2 equivalents/yr and carbon sequestration of 17 Tg C/yr (62 Tg CO2 equivalents/yr). 相似文献