摘要:

AbstractAll the known Badger setts in Essex were resurveyed in the mid‐1980s to record any changes in Badger distribution and status, and any associated changes in habitat and land use, during the preceding 20 years. New setts were also located. Being on the edge of London, Essex has undergone many recent changes that might be disadvantageous to Badgers. It is subjected to a high demand for land to meet increasing housing needs, intensive arable farming is widespread and few undisturbed habitats remain. These are typical of the pressures facing the Badger population in many areas of north‐west Europe, and so Essex was an ideal area in which to look at the status of the Badger, and in particular the impact of human activities on a Badger population. Much of the county is unsuitable for sett construction, since it consists of London Clay and glacial tills, and the highest concentration of setts was found in the Bagshot Beds. Woodland is rare in Essex, but it was still the favoured site for sett construction. Although over half the county is devoted to arable farming, Badgers tended to avoid such areas, and also avoided close proximity to roads, particularly busy roads, for sett sites. Since much of the county is low‐lying, man‐made embankments were particularly important sett sites, and land‐reclamation activities have probably provided additional sites for Badger setts. The effects of human activities on Badger distribution and numbers in Essex are

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1991.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1991.tb00288.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe past history of the Badger in Essex is reviewed. It is shown that the population has fluctuated in the past, and that heavy gamekeeping pressure probably reduced numbers at the turn of the century, although Badgers were probably never as rare as early recorders believed. In recent years Badgers have been rare or absent in many areas of the county because they did not afford suitable sett sites, and the county as a whole is not particularly good for Badgers. Against this already low‐density Badger population, in the 20 years up to the mid‐1980s, 36 % of known setts had disappeared, with agricultural activities being the major cause of sett losses, and of the remaining setts there was a 14 % reduction in the number occupied by Badgers. Also, the modal sett size was reduced from six holes to three. Direct disturbance affected nearly a quarter of all viable setts in Essex. The significance of these findings is evaluated, and the effects of changing land use, sett disturbance, Badger digging, road deaths and sub‐lethal levels of agricultural chemicals on Badger numbers are discussed and quantified where possible. The possible effects of a continued fragmentation of the Badger population in Essex is reviewed. The need for further research on particular aspects of the problem, and the value of such data in understanding the population pressures facing the Badger elsewhere in Europe, are highli

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1991.tb00289.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBecause the mammary gland has no known homologue among the extant reptiles, attempts to reconstruct its evolution must focus on evidence from living mammals. Of the numerous structures that have been hypothesized to have given rise to the mammary gland, only three remain as plausible progenitors: sebaceous glands, eccrine glands and apocrine glands. Ancestral mammary glands are usually assumed to have produced a copious watery secretion like that of human eccrine sweat glands. However, in terms of anatomy, physiology, development and topographical distribution, mammary glands are more similar to apocrine and sebaceous glands than to typical eccrine glands. Nevertheless, each of the three populations of cutaneous glands exhibit specializations unlikely to be primitive for the mammary gland. The mammary gland either predated full differentiation of mammalian cutaneous glands or, more probably, evolved as a neomorphic mosaic that combined the properties of apocrine and sebaceous glands. Consequently, ancestral, prototypic lacteal glands may have had the capacity to synthesize and secrete small amounts of organic substances, as do sebaceous and apocrine glands of living mammals.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1991.tb00290.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY