Check out our newly published article in the open access journal PeerJ: A systematic review of the direct and indirect effects of herbivory on plant reproduction mediated by pollination.
Any gardener knows the havoc that herbivores can have on their plants; whether it’s the rabbits eating their cabbage or beetles damaging their prized roses. Herbivores can devastate a floral display or chew away at the leaves until a plant is too sickly to produce flowers or fruit. However, a discerning gardener will know that not all insects are bad for their vegetable garden; rather they should hope for some bees if they expect to see a good yield of tomatoes or strawberries. Both herbivores and pollinators can influence the yield of fruits and seeds for many plants worldwide and therefore impact both crop yields and plant reproduction. The effects of both types of interactions have been repeatedly tested by the scientific community; however, by their nature, these types of studies must simplify things in order to isolate the specific effect of one species on another and therefore neglect the multitude of other species present that might change this interaction. A caterpillar may chew the petal of a flower that a bee then passes over because the flower is no longer perfect or a rabbit may eat the leaves of a plant that, in consequence, only produces one small flower that is easily overlooked. Bees and other pollinators make choices when they choose flowers to visit, and damage to the plant (whether the flower or not) can result in flowers that are less attractive to pollinators. Similarly, the part of the plant attacked (i.e. leaves, roots, stem, or flowers) should certainly impact this choice differently. Damaging flowers directly reduces the appeal of the flower, and removing it entirely certainly eliminates the possibility of pollination; but how does damage to the leaves, roots and stem change the flowers? Damage to these parts can reduce the overall quality of a flower, whether the flower is smaller or produces less nectar, or if there are simply fewer flowers overall.
This dance between herbivores and pollinators is the subject of the review we recently published in the journal PeerJ: “A systematic review of the direct and indirect effects of herbivory on plant reproduction mediated by pollination.” We collected peer-reviewed studies that examined the effects of herbivores and pollinators on plant reproduction. One of our conclusions is evident simply by the number of studies we found; out of a total of 4,304 studies that turned up in a search on the search engine Web of Science, only 59 studies fit our criteria. That is, not many studies look at both herbivores and pollination. Half of these studies looked at damage to flowers and only about a third looked at damage to any of leaves, roots, and stems (the remainder looked at general damage to any tissue). When tightening our criteria to studies that compare damage to flowers and other parts of the plant, we only found three studies. In our paper we discuss in depth the ways herbivores and pollinators interact can call for more studies to compare damage to both flowers (direct damage) and other parts of plants (indirect damage).
While Chris (my co-author) has completed and published many systematic reviews, this was my first. Gathering and sifting through this much data was certainly an experience and quite the grind. However, I have learned many lessons from this process, both about systematic reviews in general and about handling data. One lesson is to make sure to well-document everything in your process, because you will end up going back to look, months or even years later. So, document it, organize it, and if you can, automate it! However, the most important lesson I learned was the importance of a clear question and idea in advance. By the time I had collected all my data and knew the studies well, I felt as though I had lost the entire point of the review. I didn’t have a clue what to do next. It took going back to my original notes and having a discussion with Chris to remember why we had started off on this journey to begin with and to identify what questions we were trying to answer.
Overall, this systematic review gave me an excellent insight into the review process, both what to do and what not to do. However, the content itself provided a firm basis for my own practical field research. I have been in the process of implementing some of my own experiments contrasting the effects of damage to different plant tissues both in the field and in the greenhouse.