摘要:

The breeding bird communities present in 33 isolated wetlands in the Po plain (northern Italy), ranging in size from 0.3 to 63 ha, were investigated in order to evaluate the effects of area, isolation and habitat diversity on community structure. In simple and multiple regressions, the effect of area was always preponderant (r2= 64–83%). No other variables affected the number of species nesting exclusively within the wetlands while habitat structural diversity and isolation significantly increased the explained variance of the total number of species and of other community variables. The S.L.O.S.S. (Single Large or Several Small) debate is criticized where species level studies are not carried out.

ISSN:0373-4137    

DOI:10.1080/11250009309355794

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Twelve heronries were investigated in the Po plain (northwestern Italy) from 1974 to 1984. A total of 219 blood films was obtained from chicks and young of the night heronNycticorax nycticoraxand the little egretEgretta garzetta,24.6% of which harbouredLeucocytozoonparasites. Infection prevalence varied between heronries, mainly due to variation in simulid abundance. The abundance of vectors was affected by the agricultural practices for rice cultivation: irrigation canals and ditches were periodically drained and cleaned out with the consequent destruction of the aquatic vegetation in which simulid larvae and pupae settle. Discrimination of heron colonies (number of cases) where infection was detected from those where infection was not detected was mainly by simulid abundance, and secondly by colony population size. From 1974–1979 to 1980–1984 the increase in infection prevalence seems to be associated either with the increase in the number of breeding herons or the decrease in the number and surface area of heronries.Leucocytozoonparasites hardly seem to be pathogenic because they did not affect breeding success and did not reduce the fitness of the hosts.

ISSN:0373-4137    

DOI:10.1080/11250009309355795

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Clone pool diversity was studied in two parthenogeneticOctolasionspecies in South Finland belonging to the region of Fennoscandia where the species occur at the northern margin of their European range. In spontaneously dispersingO. tyrtaeumwe recorded 24 clones (238 individuals/8 localities), but in anthropochorously dispersingO. cyaneumonly two clones (134 ind./4 locs.) were found. InO. tyrtaeumthe clone pools of the East ( = sample region) and the North were more similar to each other than to that in the West. Clone groups showed a clinal distribution pattern, which suggests that they may be adapted to regional environments. The low clonal heterogeneity ofO. cyaneumis attributed to a small founder population and clonal drift. Morphological variability showed that characters related to reproductive organs vary extremely little in the two species. Considering somatic characters, segment number seemed to be mostly controlled by the genotype, whereas body size varied mostly according to the locality and region implying the role of environmental variables. In the North,O. tyrtaeumadults were larger than their counterparts in the East and the West.

ISSN:0373-4137    

DOI:10.1080/11250009309355796

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The authors describe two new animals from the Middle‐Cambrian Burgess shale. One is formally described asMetaspriggina walcottiand is probably related to the sprigginids, and the other has probable Chordate affinities. Both share an imperfect bilateral symmetry, with alternating left and right segments, an arrangement found both in the Precambrian vendozoans and in the living Acrania and Cyclostomata. The authors discuss their possible evolutionary significance and the persistence of Precambrian‐like animals well into the Middle Cambrian.

ISSN:0373-4137    

DOI:10.1080/11250009309355797

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new genus,Dendropodola,and species,D. transitionalis,are described in the family Dactylopodolidae. Three new species,Cephalodasys hadrosomus, Mesodasys adenotubulatus,andMesodasys ischiensis,are described in the family Lepidodasyidae. And, six new species,Pseudostomella etrusca, Ptychostomella tyrrhenica, Tetranchyroderma heterotubulatum, Tetranchyroderma hypopsilancrum, Tetranchyroderma pachysomum,andTetranchyroderma thysanophorum, aredescribed in the family Thaumastodermatidae. All were collected in littoral and shallow sublittoral sediments along the Italian coastline of the Mediterranean Sea and its adjacent waters.

ISSN:0373-4137    

DOI:10.1080/11250009309355798

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Dugesia (Girardia) tigrina,a freshwater planarian native to America and able to reproduce either sexually or by fission, has been casually introduced into Europe and various other areas of the world. In most cases, the immigrant specimens are fissiparous and, exceptionally, sexual. One sexual population, collected from the Lake of Monticchio in Southern Italy, is here described together with biogeographycal and karyological data.

ISSN:0373-4137    

DOI:10.1080/11250009309355799

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

From 1986 to 1989 a series of cruises were conducted in the central Mediterranean Sea, to determine distribution and relative abundance of cetaceans. Observation sessions lasted for a total of 2433 h. The presence of animals was assessed visually. Relative sighting frequencies among species and among subdivisions of the study area were calculated, based on observation time. Seven species were observed, including, in order of decreasing frequency: bottlenose dolphins(Tursiops truncatus),striped dolphins(Stenella coeruleoalba),fin whales(Balaenoptera physalus),sperm whales(Physeter catodon),Risso's dolphins (Grampus griseus), common dolphins(Delphinus delphis)and long‐finned pilot whales(Globicephala melas).The highest sighting frequencies occurred in the Ligurian‐Corsican Sea; cetaceans were scarcest in the Tyrrhenian Sea and in the northern Adriatic Sea. Bottlenose dolphins were found throughout the study area in neritic waters. Fin whales, sperm whales, Risso's dolphins, and striped dolphins were sighted in the offshore waters of the Ligurian‐Corsican, Tyrrhenian, and Ionian Seas. The now rare common dolphin was mostly seen in the Sardinian Sea, in the Sicily Channel, and in the Ionian Sea. Pilot whales were observed, occasionally, in the Ligurian‐Corsican and Tyrrhenian Seas.

ISSN:0373-4137    

DOI:10.1080/11250009309355800

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250009309355801

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250009309355783

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor