Precipitation and landscape configuration effects on plant-herbivore-parasitoid interactions: a multi-scale approach

MONMANY, A. CAROLINA; AIDE, T. MITCHELL

Miami

Congreso; ATBC Annual Meeting; 2004

ATBC

Studies of plants, herbivores and parasitoids interactions have shown that patterns in this system are scale dependent. But, most studies only considered one or two spatial scales, and to better explain patterns in this system studies should include variables operating at large (e.g. climate), intermediate (e.g. landscape), and small scales (e.g. biotic processes). Moreover, the components of the plant-herbivore-parasitoid community are linked by trophic relations, suggesting that the community and the mechanisms that structure it may be hierarchically organized. We used a hierarchical approach to answer the question: how do precipitation, landscape and biotic variables affect species richness, abundance and composition of a plant-herbivore-parasitoid community? To answer this question we collected and identified plants, herbivores and parasitoids in twelve forest fragments and two reference sites along a precipitation gradient between a subtropical moist forest (Yungas) and a semiarid dry forest (Chaco), in Northwest Argentina. Best subset regression analyses were used to examine plant, herbivore, and parasitoid richness and abundance, and non-metric multidimensional scaling (NMS) was used to examine species composition. Plant richness, and composition, and part of plant density were best explained by precipitation. Plant density, herbivore richness, and parasitoid richness were partially explained by landscape characteristics (i.e. fragment size and matrix). Herbivore abundance and composition, parasitoid abundance, and part of herbivore and parasitoid richness were explained by biotic processes. Herbivore and parasitoid composition did not completely correspond with plant composition, because herbivore and parasitoid populations are smaller and more variable than plants. The plant-herbivore-parasitoid community in the Yungas-Chaco transition in Northwestern Argentina appears to be hierarchically structured. We demonstrated how the hierarchical approach can be applied in a multi-scale, plant-herbivore-parasitoid community study. This approach can determine the relative importance of different constraints on biotic communities, which will help to identify the most important mechanisms and scales for future researches.