Résumé
Most organisms in ephemeral habitat patches have resting stages which form
a local species pool in response to temporal variations in the patch’s
availability and suitability. Temporal dispersal from the local species
pool may, therefore, be an important process shaping the community
assembly, particularly soon after patch creation, and possibly interacting
with environmental filtering. As the temporal variation of the
environmental conditions has a major effect on the composition of the
local species pool, we investigated how well contemporary conditions (both
patch availability and patch suitability) and temporal dispersal
(approximated by environmental temporal variation and temporal distance)
explain the changes in community composition in a given locality through
successive ephemeral habitat cycles. We used arable weeds in annual crops
as models. We calculated temporal weed community dissimilarity indices
between weed communities surveyed in cropping seasons at intervals of two
to eight years within a given field. The weeds were surveyed twice each
cropping season to account for any changes in the relative contributions
of temporal dispersal and contemporary conditions during the season. Patch
availability explained most of the temporal weed dissimilarity, suggesting
that patch dynamics have the greatest effect on weed community assembly.
Temporal distance and temporal variation of the environmental conditions
had more effect at the start of the cropping season than later, while
patch suitability had more effect in the middle of the season. These
results suggest that temporal dispersal drives the weed community assembly
when ephemeral habitat patches are created. These assemblies are further
shaped by environmental filtering. This is consistent with a temporal
source-sink dynamic mechanism where the seed bank acts as the main weed
source. However, a large part of temporal weed dissimilarity remains
unexplained, suggesting that other ecological processes such as spatial
dispersal and founder effect may also shape the weed community.