INVESTIGADORES
KITZBERGER Thomas
artículos
Título:
Interannual changes in folivory and bird insectivory along a natural productivity gradient in northern Patagonian forests
Autor/es:
MAZÍA, C.M; KITZBERGER, T,; CHANETON, E.
Revista:
ECOGRAPHY
Editorial:
BLACKWELL
Referencias:
Año: 2004 vol. 27 p. 29 - 40
ISSN:
0906-7590
Resumen:
Trophic regulation models suggest that the magnitude of herbivory and predation (topdown
forces) should vary predictably with habitat productivity. Theory also indicates
that temporal abiotic variation and within-trophic level heterogeneity both affect
trophic dynamics, but few studies addressed how these factors interact over broad-scale
environmental gradients. Here we document herbivory from leaf-feeding insects along a
natural rainfall/productivity gradient in Nothofagus pumilio forests of northern
Patagonia, Argentina, and evaluate the impact of insectivorous birds on foliar
damage experienced by tree saplings at each end of the gradient. The study ran over
three years (1997_/2000) comprising a severe drought (1998_/1999), which allowed us to
test how climatic events alter top-down forces. Foliar damage tended to increase
towards the xeric, least productive forests. However, we found a predictable change of
insect guild prevalence across the forest gradient. Leaf miners accounted for the greater
damage recorded in xeric sites, whereas leaf chewers dominated in the more humid and
productive forests. Interannual folivory patterns depended strongly on the feeding guild
and forest site. Whereas leaf-miner damage decreased during the drought in xeric sites,
chewer damage increased after the drought in the wettest site. Excluding birds did not
affect leaf damage from miners, but generally increased chewer herbivory on hydric and
xeric forest saplings. Indirect effects elicited by bird exclusion became most significant
after the drought, when total folivory levels were higher. Thus, interannual abiotic
heterogeneity markedly influenced the amount of folivory and strength of top-down
control observed across the forest gradient. Moreover, our results suggest that spatial
turnovers between major feeding guilds may need be considered to predict the
dynamics of insect herbivory along environmental gradients.