Japanese insect phenology and phenological changes among trophic levels

Background/Question/Methods

Phenology has proven to be an effective metric for assessing how climate change is impacting organisms around the world. In response to warmer temperatures and altered precipitation, plants and animals have adjusted their phenologies to various degrees. Here, we investigated how a suite of insect species from throughout Japan has responded to changes in climate both spatially and temporally. Forty years of data on emergence dates of 14 insect species from 102 observatories of the Japan Meteorological Agency (JMA) were used for this research along with basic natural history traits. The results of analysis of this insect dataset were then compared to datasets of plant and bird phenology to evaluate how the phenologies of organisms at different trophic levels are changing. If, for example, organisms at each trophic level are responding differently to changes in climate, then there is the potential for ecological mismatches. In such a scenario, the phenologies of associated organisms are no longer synchronous and the success of future populations may be put in danger. Extensive datasets exist on the phenology of plants, insects, and birds in Massachusetts and these were analyzed with additional data from the JMA to address this larger question.

Results/Conclusions

The emergence dates of insects in Japan are closely correlated with temperature, with individuals of most species emerging earlier in warmer years. Surprisingly however, insects are emerging later over time in a country that is growing progressively warmer. This apparent disparity may be due to extreme declines in populations due to factors outside of climate, such as land use change or urbanization. Insects in Massachusetts are also responding to temperature, with some showing a temporal response and others not. Looking across trophic levels, plant flowering and leaf-out have the strongest response to temperature as well as the greatest amount of variation explained by temperature. Bird migration phenology exhibits the weakest pattern of change with temperature, along with the weakest explanatory power. Insects fall in the middle and generally have a strong response to temperature, yet weak explanatory power. Although the animals in these studies are often generalist feeders, the fact that each trophic level is impacted differently by climate change is cause for concern. The finding that organisms at a given trophic level are responding similarly in different parts of the world gives additional weight to this study as altered relationships among species are not geographically confined.