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Lab Members |
Ecosystem process is mainly composed of three processes, i.e. production, consumption, and decomposition. Recently, it is revealed that plant genotype had important roles on each ecosystem process. On the other hand, because the three processes are associated with each other, the effects of plant genotype would feedback to plant productivity through each ecosystem process. Although this is predicted by many researchers, experimental test for the prediction has just started.
My research goal is to detect a feedback loop among the ecosystem processes on the basis of plant genotype, and to determine which process is the most important to dominate the feedback loop.
(Key words: ecosystem function, feedback mechanism, willow)
Mutualism is an interaction where the both individuals derive benefits from the others. Mutualism is ubiquitous in any ecosystems. However, the forms of mutualism are diverse, and the relationships are occasionally broken down, depending on the conditions. The study in dynamics and maintenance of mutualism is one of central issues in community and evolutional ecologies because mutualism plays a key factor of which produce the species diversity.
Among homopteran insects, some species build mutualism with ants. Such insects attract ants by giving them sugar-rich waste liquid, which is so called 'honeydew'. In return, the ants protect them from natural enemies. However, some aphid's natural enemies adapt themselves to the ant protection, and the ants cannot exclude them. Considering such interactions, it is expected that the ant-aphid mutualism changes the community structure of aphid's natural enemies, and as a result, the cost/benefit for the mutualism also change. Thus, there is a feedback process in the ant-aphid mutualism. Therefore, I mainly focus on the ant-aphid interaction, and study the dynamics and maintenance of mutualism, considering the mutualism as multi-specific interactions.
(Key words: mutualism, ants, aphid, multi-specific interaction)
Recently, introduced plants are increasingly appreciated as "model organisms", which provide an excellent research opportunity to understand how insect-plant associations structure arthropod communities on novel plants. Introduced plants lack interactions with herbivores, mutualists, and competitors associated with their original ranges, but gain new interactions with native species in new habitats. Studying arthropod communities associated with introduced plants is more likely to answer a question how direct and indirect insect-plant interactions are newly established on novel plants.
Pattern of arthropod communities on introduced plants in new habitats differs from that in original ranges. For example, introduced plants are more likely to be used by generalist herbivores in new habitats, but by specialist herbivores in original ranges. I focus on indirect interaction webs (proposed by Ohgushi 2005) newly organized on an introduced tall goldenrod Solidago altissima which came from North America and examine why pattern of arthropod community on tall goldenrods in Japan differs from that in the original region. Recent studies have shown that the genotypic diversity of a stand of plants can influence the density and diversity of the arthropod communities. I hypothesize that one of the factors creating the differences between the arthropod communities on tall goldenrods in their original and introduced ranges is the genotypic composition of the plants.
(Key words: introduced species, interaction, community structure)
Herbivore-induced plant responses, such as morphological, phenological, and chemical changes in a host plant, are ubiquitous phenomena in terrestrial systems. Interestingly, these responses can link temporally/spatially-separated various species indirectly. For instance, spring herbivory by insects often affects densities, distribution, survival, and reproduction of subsequent insects emerging in autumn and next year due to inducing modification of plant traits.
I have studied that such indirect interactions affect population dynamics and community structures of insects and evolution of insect traits, using a willow-insect system. Willows are common woody deciduous plants in mid-/downstream riparian environments in Japan and I have focused on willows' vigorous regrowth response involving changes in several traits (e.g. nutritional status, shoot size, and leaf morphology) following biotic (e.g. damage by boring of a swift moth larva) and abiotic factors (e.g. river flooding).
An evolutionary consequence of ecological indirect interactions through induced changes of plant traits is a major key concept of my current studies. This may lead to understand evolutionary dynamics of organisms in a context of complex ecological communities.
(Key words: animal-plant interaction, population ecology, community ecology, evolutional ecology)
The enemy release hypothesis predicts that when exotic plants are introduced with loss of the specialist herbivore insects from native range and are not a preferred choice of generalist herbivores in their introduced range they will suffer low rates of attack by herbivores and thereby gain greater abundance over native plants. Based on this hypothesis, many introductions of the specialist herbivore insect from native range to introduced range have been conducted for the reduction in abundance of exotic plant. However, most of them failed. These suggest that the biotic interactions to depress the success in establishment of introduced insect or the reduction in abundance of exotic plants may prevail over introduced range. Whereas predation and parasitism on introduced insects were examined, in particular, the indirect effects of herbivorous insects on survival and reproduction of introduced insects are still unclear although it has become clear that diverse indirect positive or negative interactions among insects on plants emerge.
I use ragweed Ambrosia artemisiifolia, as exotic plant and beetle Ophraella communa as introduced insect to examine the indirect effects of herbivorous insects via predator or this plant on survival and reproduction of this beetle and the negative effect of this beetle on the growth and reproduction of ragweed.
Refer for my past researches to
http://jglobal.jst.go.jp/detail.php?JGLOBAL_ID=200901079209593401&t=1&d=1&q=1000312029
(Key words: Invasive organism, indirect interaction, community structure)
Food webs are composed of multiple interactions among organisms. One of important interactions is predator-prey interactions. It is well known that prey escape from predation changing their morphology or behaviour. However, predators and prey inhabit with other organisms in nature. I am studying effects of biotic factors on predator-prey interactions and decision making in prey for predator avoidance.
(Key words: antipredator response, predator-prey interactions, induced plant response, tritrophic system, herbivory, herbivore-induced volatiles, plant commnucation)
Litter quality affects decomposition process. It is widely recognized the effect of insect herbivory on litter quality, which affects decomposition process. Recently, some studies showed the effects of plant clones(genotype) on litter quality and decomposition process. On the other hand, several studies suggested that there are the variation with the difference of plant clone in innate traits of plant and the way herbivory-induced diffence occured. So there are three effects by which litter quality and decomposition process change. 1)effects of herbivory which doesn't have interaction with plant clone. 2)effects of innate plant traits which differ with plant clone. 3)effects of herbivory-induced diffence which differ with plant clone. These effects should be divided but less studies did.
My materials are goldenrod and lace bug dominant on it and I try to devide those effects.
By last-year experiments, I showed 1)herbivore density differed between clones, 2)concentration of total phenol in litter differed. the results also suggested that concentolation of total phenol and nitrogen in litter affect decomposition rate in early decomposition stage.
(Key words: decomposition process, herbivory-induced defense, indirect effect)
Ecosystem functioning is used to describe a variety of ecological processes, such as productivity and decomposition. The maintenance of such functioning requires aboveground and belowground components. For example, effects of aboveground herbivores on plants can exert important belowground effects, with likely long and short-term aboveground consequences through altered supply rates of plant-available nutrients from the soil and changes in the litter quality. Therefore, we need to incorporate above- and belowground processes to understand ecosystem functions.
Sucking insects such as aphids are likely to affect belowground processes. For example, they often secrete surplus ingested carbohydrates that contain sugars usually extremely labile and easily utilized by belowground microorganisms. In a result, belowground microorganism activity can increase, and available nutrients in soil will decrease due to microbial immobilization. In addition, aphids can affect litter contents (e.g. phenol and nitrogen) directly by sap feeding, and indirectly by changing in association of the plant and belowground symbiotic microbes. These changes will subsequently affect liberation of nutrients in litter.
In my study, I examine aphid effects on decomposition and nitrogen flux in soil using soybean which is associated with rhizobia.
(Key words: Aphid herbivory, Ecosystem function, Litter decomposition, Nitrogen flux)
The gall midge Rhabdophaga salicivora (Diptera) initiates galls on current-year shoots of Salix eriocarpa, which induces lateral shoot elongation. Plagiodera versicolora (Coleoptera), Smaragdina semiaurantiaca (Coleoptera), and Aphis farinosa (Hemiptera) increase on the galled current-year shoots because leaves which newly emerge on the lateral shoots have high quality (Nakamura et al. 2003). The trend means R. salicivora has indirect positive effect on P. versicolora and so on. But P. versicolora and so on have potential to change the trait of S. eriocarpa, too. Therefore, when P. versicolora and so on increase on galled current-year shoots, they could have some sort of effects on R. salicivora. And so, in this research, I will verify chain reaction of indirect effect in a herbivore community through feeding damage-induced responses of plants and feedback by the chain reaction by using materials similar to what Nakamura et al. used.
(Key words: gall, indirect effect, feedback)
Recently parasite manipulation has been very focused on and many studies of it done in macrobiology. Most of the studies are about evolutionary significances of the phenomenon, but there are few researches about ecological consequences. Parasite manipulation generally changes host trait (e.g. prey consumption, behavior, physiology, morphology, and so on), so parasitized host can make novel effects on trophic cascade/interactions.
I will reveal whether parasite manipulation really affects trophic interactions, and if it has an impact on them, examine how essential the effect is. To do this, I use horsehair worms (parasite) and mantis (host).
(Key words: parasite manipulation, trait-mediated indirect effect, trophic cascade)
