Timescales of indirect effects in ecological communities

Pulsed inputs of resource subsidies can fundamentally influence food-web dynamics, generating diverse, seemingly unpredictable, indirect effects. We showed that timescale hierarchy of food-web processes can successfully predict/explain such variable influences of resource pulses within a single theoretical framework (Takimoto et al. 2009). In a collaborative field experiment, we used stable isotope technique to test a part of the theoretical predictions (Spiller et al. 2010). Also, we showed by modeling that seasonal resource pulses can stabilize food-web dynamics (Takimoto et al. 2002).

Environmental determinants of food-chain length

What determines food-chain length? This is a long-standing fundamental question in ecology since Elton. Empirical evidence has shown that ecosystem size (e.g., lake volume) is a strong determinant of food-chain length, but previously only in aquatic ecosystems. I used stable isotope technique to quantify food-chain length on islands, and showed, for the first time in a terrestrial ecosystem, that food-chain length increases with ecosystem size (Takimoto et al. 2008). This field pattern was well congruent with the theoretical prediction from a model that I developed (Takimoto et al. submitted). To facilitate applications of stable isotope techniques, we have also developed a formal definition of food-chain length (Post and Takimoto 2007) and a technique for lipid extraction (Post et al. 2007).

Speciation reversal and hybrid speciation

Niche divergence may promote speciation, but recent human activities tend to homogenize environmental heterogeneity and deprive opportunities for niche differentiation. Increasing empirical examples suggest that ecologically-isolated close species collapse into hybrid swarms in homogenized environments. At the same time, other empirical evidence shows that hybridization can introduce additional genetic diversity, potentially generating a third hybrid species when an ecological niche for the hybrid is available. By combining literature survey and mathematical modeling, we explored the roles of hybridization in changing biodiversity in human-altered environments (Seehausen et al. 2008).

Sympatric speciation by sexual selection

The likelihood of sympatric speciation has been a major subject of debate in evolutionary biology. In a series of our theory papers, we have shown that sympatric speciation by sexual selection is plausible (Higashi et al. 1999, Takimoto et al. 2000, Takimoto 2002). These studies have contributed for broader appreciation of ecological speciation without geographical isolation.