Microevolution of migratory behaviour illustrated by the BlackcapSylvia atricapilla:1993 Witherby Lecture

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Abstract
The view on how rapidly morphological, physiological, and behavioural traits may change as a result of microevolutionary processes (i.e. genetic variation and directional selection) has changed considerably in the recent past. Observations on selection of morphological traits in Darwin's Finches on the Galapagos Islands and results of a 2-way selection experiment on migratory behaviour of Blackcaps Sylvia atricapilla¸ have indicated that substantial changes can occur within short periods. A striking case is represented by Blackcaps breeding in continental Europe. Within the past 30 years, a subpopulation has developed a 'new' migratory direction to the WNW to novel wintering areas on the British Isles. Experimental analysis of migratory orientation behaviour has demonstrated that behavioural changes can result from microevolutionary processes. Similar microevolutionary processes are likely to occur commonly, as both recent field observations and experimental results suggest. One outcome of this, which is of particular interest, involves the effects of continued global warming. Global warming is likely to favour obligate partial and short-distance migrants at higher latitudes and to be disadvantageous to long-distance migrants, and may lead to further reduction of species diversity.