Species definitions are discussed, with particular reference
to biological species concepts and the conservation viewpoint.
Techniques available for examining differences between populations
and species of animals are reviewed. The most recent
techniques using nuclear or mitochondrial DNA have been effectively
used in hybridisation studies of mammal species.
The occurrence of hybridisation between four pairs of British
mammals are examined in detail:
Hybridisation between mountain hare and brown hare is very rare
under natural conditions and hybrids in Britain would appear to
present only novelty value.
The genetic mix of red and sika deer in Britain is complex.
Morphometric studies have suggested that hybridisation between
these two species is widespread in some areas. Current
investigations using molecular and genetic techniques hope to
further evaluate the real extent of hybridisation and
introgression. Current evidence suggests that introgression
of sika into the red deer populations will increase rather than
Whether wildcats and domestic cats can be considered to be
subspecies or separate species is unresolved. Past European
studies, mainly skull morphometrics, suggested that hybridisation
between the two types was widespread. The proportion of
hybrids within a population has yet to be objectively
measured. Current research in Scotland is using DNA
techniques, sampling living and historic cats across
British ferrets are probably domesticated directly from European
polecats. The recent spread of polecats from Wales into the
English Midlands may lead to the introgression of domestic genes
into wild polecats. However, it is not known to what extent
feral ferrets survive in mainland Britain, and as yet hybridisation
is not perceived as a substantial threat to the species.
Examples of hybridisation in British Birds and fish are
summarised. Many bird species hybridise and the reasons for
this are discussed. Conservation issues concerning ruddy
ducks, crossbills and goshawks are briefly outlined.
In conclusion, the two mammals at greatest risk from hybridisation
and subsequent loss of native type, are the wildcat and red
deer. The importance of maintaining native habitat for native
species is also stressed. It is recommended that studies
initiated using modern molecular techniques be followed through,
and that hypotheses based on these findings, about the
ecological/behavioural reasons for hybridisation be
investigated. Even though the best methods available are
used, it should be recognised that descriptions of a species for
legal purposes will contain a degree of subjectivity.
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