Abstracts of the Annual Meeting of the Ecological Society of Japan

In response of damage by herbivores, plants are known to emit volatiles that enhance the effectiveness of carnivorous natural enemies of herbivores. Studies on plant-carnivore interactions mediated by such infochemicals have focused on tritrophic systems in which plants are infested by a single herbivore species. In natural ecosystems, however, plants are often simultaneously infested by several herbivorous species. Here, we focus on two herbivore species that simultaneously attack crucifer plants, and their respective specialist parasitic wasps. We first show the specific responses of the two specialist parasitic wasps to infochemicals originated from cabbage plants infested by each of their respective host larvae. We then coupled the two tritrophic systems on the same plants. These experiments demonstrated the presence of indirect interactions between the two herbivore species. Overall, the results indicate the presence of infochemical-mediated indirect interaction networks on a single plant, and a filed community of herbivores can be better understood from the perspective of such interaction networks.

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Ecological theory demonstrates how competition can structure communities of plants and animals, and its importance has been demonstrated experimentally, particularly in plant, bird and rocky-shore communities. But equally many communities are unlikely to be structured by competition, for example herbivorous insects which frequently feed on non-overlapping resources, or which are typically too rare to exhaust food supplies. Here, it may be pressures from higher rather than lower trophic levels that structure communities, and indeed the theory of apparent competition shows that the actions of natural enemies can in many ways be homologous to the effects of resource competition. There is, however, relatively little evidence for apparent competition in the field. I will review the role of apparent competition in insect herbivore communities and describe experiments on two systems. The first involves aphids and the parasitoids, pathogens and predators that attack them (in the UK), the second leaf-miners and their parasitoids (in tropical Central America). I will conclude that the evidence to date suggests apparent competition is widespread, and hence may be very significant in insect community structure.

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Recent theoretical and experimental work provides clear evidence that biodiversity loss can have profound impacts on functioning of natural and managed ecosystems and their ability to deliver ecological services to human societies. Work on simplified ecosystems in which the diversity of a single trophic level is manipulated shows that diversity can enhance ecosystem processes such as primary productivity and nutrient retention. Theory also strongly suggests that biodiversity can act as biological insurance against potential disruptions caused by environmental changes.
One of the major current challenges, however, is to extend this knowledge to multitrophic systems that more closely mimic complex natural ecosystems. Our theoretical work shows clearly that trophic interactions have a strong impact on the relationships between diversity and ecosystem functioning, whether the ecosystem property considered be total biomass or temporal variability of biomass at the various trophic levels. In both cases, food-web structure and trade-offs that affect interaction strength have major effects on these relationships. Multitrophic interactions are expected to make biodiversity-ecosystem functioning relationships more complex and nonlinear, in contrast to the monotonic changes predicted for simplified systems with a single trophic level. Merging food-web and biodiversity-ecosystem functioning approaches is an exciting challenge which offers promising perspectives.

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Agroecology is the science of applying ecological concepts and principles to the design and management of sustainable agroecosystems (Gliessman, 1998). The need for developing sustainable agriculture that is built upon local knowledge of ecological, social and economic conditions has increasingly been recognized worldwide. The goals of this paper are to: 1) review development in American agroecology during the last decade, and 2) discuss sustainability indicators as they apply to Japanese and California agriculture.
During the last decade, agroecology has been widely accepted among scientists and practitioners across the Americas and beyond. Recently Francis, et al. (2003) proposed a broader definition of agroecology as the ecology of food systems. A food system is the interconnected meta-system of agroecosystems, their economic, social, cultural, and technological support systems, and systems of food distribution and consumption. Toward holistic understanding of complex food systems, the definition encourages interdisciplinary research across natural and social sciences at multiple scales spatially and temporally.
Whereas California agriculture is dominated by large-scale operations with specialty crops, Japanese agroecosystems are characterized as small-scale paddy-oriented farms that are managed intensively by older part-time farmers. Sustainability of Japanese and California agroecosystems is discussed based on characteristics identified using a broader definition of agroecology.

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