排序方式: 共有36条查询结果,搜索用时 15 毫秒
21.
The relatively low population size and long adult lifespan of dragonflies (Odonata, Anisoptera) makes them one of the few non-vertebrate groups likely to be impacted by direct roadway mortality. We studied adult dragonfly mortality and behavior associated with roadways for a number of species. Daily mortality rates for dragonflies were estimated from standardized surveys along predetermined lengths of roads. Relative abundance and flight behavior around and across roadways, a potentially important mortality factor, was determined from timed roadside observations. Observed flight behavior provided no evidence that roads act as significant barriers to dispersal for adult dragonflies. Estimated mean number killed ranged from 2 to 35 dragonflies/km/day. Species varied greatly in their susceptibility to motor vehicles. Two species (Plathemis lydia and Libellula luctuosa) made up more than 70% of the dead dragonflies collected, but only represented 14% and 31% of live dragonflies observed, respectively. The relatively low flight heights of these two species over roads (typically under 2 m) may explain their susceptibility; however, another common species (Tramea lacerata) also exhibited low flight height but did not experience high mortality, possibly because of its increased flight agility. Large numbers of adult dragonflies were killed over the entire flight season by motor vehicle collisions, exhibiting the need for assessing the long-term impact of roadway mortality on dragonfly population dynamics. 相似文献
22.
对吉林省西部地区蜻蜓目( Odonata)昆虫资源进行了连续调查。调查发现,吉林省西部地区蜻蜓目昆虫共有47种,隶属于9科28属。其中,差翅亚目( Anisoptera)的各级别水平明显高于束翅亚目( Zygoptera);属数和物种数最多的是蜻科(Libellulidae);春蜓科(Gomphidae)、蜻科、蟌科(Coenagrionidae)和丝蟌科(Lestidae)是该地区的优势类群。吉林省西部地区蜻蜓目昆虫成虫群落的演变随着季节的变化而变化。5月份,蜻蜓种群数量缓慢抬升,6至7月份,种群数量显著增加,8至9月份,物种数和个体数量都呈现出下降趋势;不同月份优势种不同。 相似文献
23.
The damselfly Coenagrion mercuriale (Charpentier) (Odonata: Coenagrionidae) is threatened throughout Europe. It is listed on the EC Habitats and Species Directive and is the only odonate currently given priority status in the UK Biodiversity Action Plan. Information about the habitat preferences of this species is required to guide conservation and management programmes. We obtained estimates of density of mature adult C. mercuriale during an intensive mark-release-recapture study over 7.65 km of a water meadow ditch network in the Itchen Valley, Hampshire. Detailed habitat information was also collected, including a variety of physical variables, and data about the in-channel and bankside vegetation. C. mercuriale density and movement were analysed in relation to habitat variables and local population size using Generalized Linear Models. Mean adjacent population density was the single most important factor determining density. However the species was also associated with a number of habitat features, the most important of which were: a channel substrate consisting primarily of silt, wide underwater ledges (berms), in-channel emergent dicots, and bankside monocots. The presence of trees was negatively associated with damselfly density. Mean net lifetime movement was greatest from sections with low density, with smaller than average berms, and with deeper water. The causes and consequences of these findings are discussed in relation to the conservation and management of this rare species. 相似文献
24.
Many Japanese dragonfly species depend on habitat complexes maintained in rice paddy systems. We postulated that recent alterations to habitat complexes in paddy systems have had adverse effects on dragonfly populations, especially those ‘once common species’ that have come to depend primarily on paddy systems following losses of natural floodplain habitats. A high proportion of Japanese lentic dragonfly species depends on paddy fields or agricultural ponds that have been extensively degraded, while lotic species can often use both paddies and natural river systems. Thus we also postulated that lentic species are more susceptible to changes in agricultural habitats and are subject to higher extinction risks than lotic species. We aimed to extend previous work on estimating dragonfly extinction risk by developing mechanistic insights into the processes involved. Postulates were tested by analyzing relationships between (1) previous quantitative extinction risk assessments for dragonfly species and (2) species’ ecological characteristics (i.e., distribution range and habitat type [lentic or lotic]). Lentic species were disproportionately represented among those with elevated extinction risk. Species with large distribution ranges were also subject to higher extinction risks than those with narrower ranges, reflecting a driving force acting at a national scale (i.e., intensive degradation of paddy systems). 相似文献
25.
Contrasting life-history strategies of long versus short pre-reproductive phases are known in adult dragonflies (Odonata)
of temperate regions. Because the long-phase species spend a longer time in terrestrial habitats such as grasslands or woodlands
during their pre-reproductive phase, we hypothesized that long-phase species would be more sensitive to landscape structure
than short-phase species. To test this hypothesis, we conducted periodic censuses of adult dragonflies at small man-made ponds.
We compared the two above functional groups in terms of the degree to which species occurrence depended on landscape structure.
The difference among the two groups was not significant, but occurrence of long-phase species tended to depend on landscape
structure. Long-phase species responded to landscape structure at larger spatial scales and showed stronger spatial autocorrelation
in their occurrence among sampling ponds than short-phase species. 相似文献
26.
The IUCN/SSC Status Survey and Conservation Action Plan: Dragonflies calls for an increase in educating the public and increasing awareness of dragonflies (Odonata). Dragonflies are conspicuous and attractive, and can ‘stand in’ for other invertebrates in raising awareness of the necessity to conserve invertebrates. While reserves have been set aside for dragonfly awareness and conservation in the northern hemisphere, no such dragonfly reserves appear to exist in the southern hemisphere, despite its rich dragonfly fauna. This paper describes the development of a dragonfly-awareness trail in an established and well-visited botanical garden (The National Botanical Gardens, Pietermaritzburg, South Africa). Correlations between species and environmental variables were significantly high for six measured environmental variables: pH, percentage shade, vegetation (structural and compositional), ambient and water temperature, and water depth. Multivariate analyses of data, classified 20 a priori selected sampling units into four ecologically meaningful biotope types, each with a characteristic dragonfly assemblage. The four biotopes provided potential viewing points. To these were added a further three duplicate biotopes so as to link the trail into a circuit. Questionnaires assessed public awareness of dragonflies, and helped design a preliminary leaflet. A final trail design was drawn up along with an expanded booklet. The trail has now been implemented. Recommendations are made on the minimal scientific underpinning required for future trail design. 相似文献
27.
对采集的蜻蜓标本进行鉴定,确定了4个东北地区新记录种和6个吉林省新记录种.其中东北地区新记录种为双横赤蜻Sympetrum rupturm Needham,高斑蜻Libellula basilinea McLachlan,绿金光伪蜻 Somatochlora dido Needham和长叶异痣蟌Ischnura.ele... 相似文献
28.
We compared populations of a forest damselfly —Calopteryx maculata — in two kinds of landscapes. In fragmented landscapes, forested foraging patches were separated from streams (where oviposition
and mating occur) by up to 500 m of pasture. In non-fragmented landscapes, there was continuous forest cover adjacent to streams.
The prevalence and intensity of midgut infections of a gregarine parasite were significantly lower in the fragmented landscapes
than in the non-fragmented landscapes. We have shown elsewhere that in the fragmented landscapes, damselflies move over greater
areas to forage than in the non-fragmented landscapes. We postulate that these movements lower the rate of encounter between
damselflies and oocysts, thus lowering the prevalence and intensity of infection. The differences suggest that actual habitat
fragmentation events would alter the relationship between host and parasite, but that populations of both species would persist
after fragmentation. Prevalence of parasitism is related to age but we found no residual effects of size on parasitism. 相似文献
29.
Beat Oertli Dominique Auderset JoyeEmmanuel Castella Raphaëlle JugeDiana Cambin Jean-Bernard Lachavanne 《Biological conservation》2002,104(1):59-70
Larger areas support more species. To test the application of this biogeographic principle to ponds, we consider the relationship between size and diversity for 80 ponds in Switzerland, using richness (number of species) and conservation value (score for all species present, according to their degree of rarity) of aquatic plants, molluscs (Gastropoda, Sphaeriidae), Coleoptera, Odonata (adults) and Amphibia. Pond size was found to be important only for Odonata and explained 31% of the variability of their species richness. Pond size showed only a feeble relationship with the species richness of all other groups, particularly the Coleoptera and Amphibia. The weakness of this relationship was also indicated by the low z-values obtained (< 0.13). The SLOSS analyses showed that a set of ponds of small size has more species and has a higher conservation value than a single large pond of the same total area. But we also show that large ponds harbour species missing in the smaller ponds. Finally, we conclude that in a global conservation policy (protection, restoration, management), all size ranges of ponds should be promoted. 相似文献
30.