J. Lindstrom et al., LARGE-SCALE SYNCHRONY IN THE DYNAMICS OF CAPERCAILLIE, BLACK GROUSE AND HAZEL GROUSE POPULATIONS IN FINLAND, Oikos, 76(2), 1996, pp. 221-227
We analysed 1964-1983 data on population numbers of capercaillie, blac
k grouse and hazel grouse in 11 provinces in Finland. The three specie
s are known to display cyclic dynamics with a periodicity of approxima
tely six yr. Synchrony in species-specific population fluctuations was
scored by calculating cross correlations with zero lag among all the
provinces. Provincial data were also used to assess the relation betwe
en climatic factors and synchrony in the population fluctuations. To e
nable the statistical analysis, the number of the 12 climate variables
was reduced to three non-correlating principal components. A bootstra
p method was used both for parameter estimation and for assessing stat
istical significance level when comparing the tetraonid synchrony with
the climate data. For all three species we found large-scale synchron
y in population fluctuations. The level of synchrony decreased, howeve
r, with geographical distance among the provinces. When a partial corr
elation analysis is done correcting for the weather derived principal
components, correlations with synchrony and distance remained with two
of the three principal components. When corrected for distance, there
is correlation between synchrony and climate for capercaillie and bla
ck grouse. We conclude that spatial phenomena, such as climatic homoge
neity within closely located areas and dispersal of individuals are re
sponsible for maintaining large-scale synchrony.