The Ohgushi Laboratory at Center for Ecological Research, Kyoto University

Research

My main research interest is on animal-plant interactions including following major research areas.

Key words:

Animal-plant interactions, Population biology, Herbivorous insects, Indirect iteraction web, Multi-trophic interactions, Biodiversity, Field experiments, Life history evolution, Insect herbivores, Ecosystem engineer, Species invasion, Willow, Goldenrod, Mycorrhiza, Aphid-ant mutualisms

Indirect interaction web: biodiversity and species interactions

Biodiversity comes from species diversification and interactions among them. Insect-plant interactions, involving more than 75% of all species in the world, have an important role in maintaining high species diversity in the terrestrial ecosystem. The traditional food web approach, which has been used for understanding the species network of interactions, has long ignored the important role of non-trophic, indirect interactions on determining species and interaction diversity. Non-trophic interactions are much more common in terrestrial systems, and they provide basis of trait-mediated indirect effects, which have the potential to increase species and interaction diversity. In particular, the interaction web approach, that emphasizes how multiple interactions are connected each other, provide a profound insights to understanding the maintenance of species coexistence and thus biodiversity.

I am focusing on spatio-temporal dynamics of species interactions as a key promoter of species and trait diversity in a terrestrial ecosystem. Without the maintenance of this interaction diversity among species, the maintenance of species and genetic and/or phenotypic biodiversity themselves becomes increasingly threatened. Main aims of our project are to understand the dynamic features of interactions that are created by variability and heterogeneity of woody plants, and ecological and evolutionary implications of mechanisms responsible for maintenance of species and trait biodiversity of herbivorous insects.

Indirect interaction web on the willow, Sailx miyabeana

Plants respond to herbivore damage by changes in allelochemistry, cell structure and growth, physiology, morphology, and phenology. Because herbivory is common and usually nonlethal on terrestrial plants, this ensures that most plants have traits altered by herbivory. The modification of plants in ways other than the simple removal of tissue can have complex impacts on other herbivores, and produce effects that cascade upward to higher trophic levels including predators and parasitoids. Thus, it can be of crucial importance in determining the ecological and evolutionary interactions among community members centred on the plant. The concept of indirect interaction webs integrate direct and indirect effects of plant-mediated traits on the ecology and evolution of plant-herbivore interactions. Indirect Interaction Webs integrate information on how nontrophic, indirect effects structure plant-based communities through changes in plant traits in terrestrial systems. It synthesizes these data to provide a more complete understanding of plant-based ecological community, which will provide a new perspective on the organization of these communities. This subject is of great importance in understanding not only community organization but also in identifying the underlying mechanisms of maintenance of biodiversity.

References on “Indirect Interaction Webs”

Ohgushi, T.(2005) Indirect interaction webs: herbivore-induced indirect effects through trait change in plants. Annual Review of Ecology, Evolution, and Systematics 36, 81-105.

Ohgushi, T., Craig, T. P. & Price, P. W.(2007) Ecological Communities: Plant Mediation in Indirect Interaction Webs, Cambridge University Press, Cambridge, UK.

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Ecology and evolution of animal-plant interactions

There are more than 1.5 million species in the world. Any species are interacted with other species, through prey-predator, competitive, and mutualistic interactions. Thus, community organization is largely dependent on various interactions involved in the system.

My main interests involve variability and flexibility in insect-plant interactions, with focusing on vertical interactions through trophic levels and horizontal interactions within a trophic level. The work is also focusing on how herbivorous insects alter quality and quantity of plant traits as food and habitat resources available to herbivorous and predacious insects in upper trophic levels. Our ongoing project chiefly concerns insect-plant interactions, involving willow, willow insects and their natural enemies. Willow is a very suitable model system for studying direct and indirect insect-plant interactions, because a number of generalist and specialist herbivores attack willows with various defensive chemical substances against herbivorous insects. We are currently investigating the following issues:

1. Oviposition preference-offspring performance linkage
2. Plant responses to insect herbivory
3. Plant-mediated indirect interactions
4. Mutualistic indirect interactions between herbivorous insects
5. Multi-trophic interactions

Rabdophaga rigidae Aphis farinos Furcula furcula sangaica Chrysomela vigintipunctata
Rabdophaga rigidae Aphis farinosa Furcula furcula sangaica Chrysomela vigintipunctata
Endoclyta excrescens Phyllocolpa sp. Aphrophora pectoralis Plagiodera versicolora
Endoclyta excrescens Phyllocolpa sp. Aphrophora pectoralis Plagiodera versicolora

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Population dynamics of herbivorous insects

Populations consist of individuals with a wide variety of life history traits. This suggests that these traits largely affect temporal and spatial dynamics of populations. Nevertheless, traditional population studies long have overlooked the population consequences of adaptive life history traits. On the other hand, behavioral ecology has long neglected population dynamics as selective forces on life history traits. Until last two decades, there is increasing recognition on the need to bridge the gap between population ecology and behavioral ecology.

I have studied population dynamics of herbivorous lady beetle, Epilachna niponica, with emphasis on adaptive oviposition behavior as a mechanism producing high stability of lady beetle populations.

In summary:
(1) Populations of the lady beetle are maintained in a dynamic equilibrium state in terms of resource availability by the strong regulatory mechanisms.
(2) The regulatory mechanism includes egg resorption in response to resource quality and inter-plant movement of ovipositing females to avoid oviposition on plants with high egg density, both of which decrease reproductive rate in a density-dependent manner.
(3) The both of behavioral and physiological oviposition tactics increase lifetime fitness of offspring.
(4) The population introduction experiment altered these oviposition tactics, resulting in reduction of population stability of the introduced population, as we expected.
This population study clearly demonstrated that population regulation is based on life history traits and that adaptive traits determine population dynamics of the lady beetle.

Epilachna niponica Epilachna niponica
Epilachna niponica Epilachna niponica
Epilachna niponica
References on population dynamics of the lady beetle

Ohgushi, T. (1998) Bottom-up population regulation of an herbivorous lady beetle: an evolutionary perspective. pp. 367-389. In Dempster, J.P. & McLean, I.F.G. (eds.), Insect Populations: in Theory and in Practice, Kluwer, London.

Ohgushi, T. (1995) Adaptive behavior produces stability in herbivorous lady beetle populations. pp. 303-319. In Cappuccino, N. & Price, P.W. (eds.), Population Dynamics: New Approaches and Synthesis, Academic Press, San Diego, USA.

Ohgushi, T. (1992) Resource limitation on insect herbivore populations. pp. 199-241. In M.D. Hunter, T. Ohgushi & P.W. Price (eds.), Effects of Resource Distribution on Animal-Plant Interactions, Academic Press, San Diego, USA.

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