Yanjun Li: Herbivory increases the dominance of invasive alien species

In this post, Ms. Yanjun Li, PhD student at Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, China, presents her latest work: “Herbivory may mediate the effects of nutrients on the dominance of alien plants.” She discusses how the level and fluctuation of nutrient availability interacts with the trophic level to affect plant invasion.

About the paper

It is frequently assumed that increases in nutrient availability may promote alien plant invasion because successful aliens are more likely to be pre-adapted to high-nutrient environments. In addition to this, nutrient fluctuations (i.e. nutrient changes in their variability) may also affect alien plant invasions. This is supported by both theoretical and empirical studies. However, whether changes in nutrient availability could interact with nutrient fluctuations to affect alien plant invasion remains unclear.

Besides abiotic factors (e.g. nutrient changes), biotic factors could also affect alien plant invasion. For example, the enemy release hypothesis points out that the lack of natural enemies in the invaded area is an important factor driving the invasion success of alien plants. However, little is known about the interactive effect of abiotic and biotic factors on alien plant invasion. Particularly, there is a lack of information regarding how nutrient variability affects alien plant invasion via the trophic levels. Therefore, using a multi-trophic, multi-species experiment, we tested how changes in nutrient availability and fluctuations therein affect invasion success of alien plants in resident communities via insect herbivores (i.e. another trophic level).

A grasshopper feeding on a native plant during the experiment (Credit: Yanjun Li)

Our experiment showed that although increases in nutrient availability promoted the absolute biomass of both the alien target species and native communities, it suppressed the dominance of the alien target species in resident communities. Herbivory, on the other hand, increased the dominance of the alien target species. Interestingly, we also found tentative evidence that herbivory may interact with changes in nutrient availability and nutrient fluctuations to affect the dominance of the alien target species. In particular, the dominance of the alien plants decreased in response to a nutrient pulse, but only when the overall nutrient availability was low and when herbivores were present. In other words, our experiment suggests that herbivory might mediate the interactive effect of nutrient enrichment and fluctuations in nutrient supply on alien plant invasion.

About the research

Due to ongoing global environmental changes, understanding the process of alien plant invasion is important for predicting its risk. Our research reveals that the presence of a higher trophic level can mediate the effect of resource fluctuation on alien plant invasion, which challenges the important theory of “resource fluctuation hypothesis” in invasion ecology. We highlighted that future studies should pay more attention to the coupling effect of biotic factors and abiotic factors on alien plant invasion at the same time. It is crucial for the accurate assessment of alien plant invasion under global changes.

Overview of all plants growing for three weeks in herbivory-treatment cage (Credit: Yanjun Li)

Although our study is the first multi-trophic, multi-species experiment that tested how another trophic level influences the effects of nutrient fluctuations on alien plant invasion, our study has several caveats that should be considered in future studies. For example, we did not consider the effects of herbivory intensity and the feeding period in this study. In addition, more insights into how herbivory interacts with nutrient availability and fluctuations therein on belowground biomass of the alien and native species are also needed.

About the author

I became involved in ecology when I was an undergraduate. I was awarded an internship opportunity to learn ecology, and, through working in the field, I became captivated with the subject area. One of my professors, Prof. Yingzhi Gao, told me that ecology is the oldest and youngest science—it is the philosophy of nature. Inspired by his words, I began my journey of scientific research. Currently, I am a PhD student at the Northeast Institute of Geography and Agroecology, Chinese academy of science, China. In 2020, I completed a project in Prof. Yanjie Liu’s lab and began my research into invasion ecology. During that period, I learned a lot from Prof. Liu, such as how to effectively design experiments, analyse data, and write scientific manuscripts. In Prof. Liu’s lab, I also received a lot of support from other partners in the group. Without their help this work would not have been achievable.

The first author Yanjun Li (Credit: Yanjun Li)

Enjoyed the blog? Read the research here

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