Résumé
Identifying the drivers of population fluctuations in spatially distinct
populations remains a significant challenge for ecologists. Whereas
regional climatic factors may generate population synchrony (i.e., the
Moran effect), local factors including the level of density-dependence may
reduce the level of synchrony. Although divergences in the scaling of
population synchrony and spatial environmental variation have been
observed, the regulatory factors that underlie such mismatches are poorly
understood. Few previous studies have investigated how density-dependent
processes and population-specific responses to weather variation influence
spatial synchrony at both local and regional scales. We addressed this
issue in a pond-breeding amphibian, the great crested newt (Triturus
cristatus). We used capture-recapture data collected through long-term
surveys in five T. cristatus populations in Western Europe. In all
populations – and subpopulations within metapopulations – population size,
annual survival and recruitment fluctuated over time. Likewise, there was
considerable variation in these demographic rates between populations and
within metapopulations. These fluctuations and variations appear to be
context-dependent and more related to site-specific characteristics than
local or regional climatic drivers. We found a low level of demographic
synchrony at both local and regional levels. Weather has weak and
spatially variable effects on survival, recruitment and population growth
rate. In contrast, density-dependence was a common phenomenon (at least
for population growth) in almost all populations and subpopulations. Our
findings support the idea that the Moran effect is low in species where
the population dynamics more closely depends on local factors (e.g.
population density and habitat characteristics) than on large-scale
environmental fluctuation (e.g. regional climatic variation). Such
responses may have far-reaching consequences for the long-term viability
of spatially structured populations and their ability to response to
large-scale climatic anomalies.