When I talk to researchers about my studies of the attraction of insectivorous birds to herbivore-damaged trees, they, even ecologists, often comment that it’s so difficult to control several trophic levels at the same time. I agree, it can be difficult, but not impossible. With good planning you can get amazing results.
In this blog I will give you practical tips how to successfully study a system with several trophic levels. As you can guess from the title, this will be a series of blog posts. The emphasis will be on experiments with (insectivorous) birds, but I’m sure you can use the tips also for experiments including e.g. only plants and insects. The first few posts will be rather self-evident, but the tips will get more technical/detailed later. To learn more about what I have studied related to this topic, check the About link of this blog.
Let’s begin from the bottom of this trophic interaction, plants. I have used in my own experiments trees. Mainly deciduous but also coniferous trees. You can also use smaller plants, such as some bushy species or even blueberries, if you think those are a suitable study set-up.
Nature vs. lab: There are several choices you need to make. First: will you do the experiments in nature or cut branches from the trees to do experiments in a lab or in an aviary. For both of these you usually need some kind of licence or permission from the land-owner. I have done my experiments in both ways. If you don’t need to cut branches, the study set-up could be more natural (e.g. Mäntylä et al. 2008a, 2014 and photo on the left) but for some experiments you will need to use cut branches (e.g. Mäntylä et al. 2004, 2008b and photo on the right).
Location: Related to the above is of course where you do the study. If you want to do some lab/aviary experiments, it is really good to have the study trees near, especially if you need to cut branches for your experiment.
Species: Then of course it is important to choose a species that is common and you can get enough individuals to get a reliable study. In northern Finland I used mountain birches (Betula pubescens ssp. czerepanovii) because that is the only common tree species there (easy choice 😉 ). In southern Finland I used silver birches (B. pendula) and downy birches (B. pubescens) because they are common species there. In Germany I used branches cut from Scots pines (Pinus sylvestris) because the research group had permission and facilities for that.
Planted vs. wild: Another thing to consider is whether to use planted or wild trees. With wild trees the study could be a bit more natural (and possibly more complicated). With planted trees, you usually know the history, or even genotype, of the individuals. And with planted trees you have even an option to use small trees growing in pots (as in Amo et al. 2013 and Koski et al. 2015). But then you should keep in mind that sometimes the chemistry of small trees (especially saplings) differs from bigger trees (e.g. Boege & Marquis 2005). And also the growth in a pot can cause some unwanted effects. If possible, do some comparisons with trees of the same species growing in nature.
Natural herbivory: When choosing individual trees, check at least the level of natural herbivory. If possible, pick trees that have no or very little herbivory. Or if there are more insects around, count and monitor those. And even then it’s not possible to say what will happen later in the growing season. A few times I’ve had experiments not going as planned because of outbreak of geometrid moths [the photo on top is from autumnal moth (Epirrita autumnata) outbreak area].
Sunlight: One other thing to check is the amount of sunshine. All the experimental trees should be in more or less similar light conditions. To get the best results I recommend using trees that get plenty of sunshine or at least cut branches from the side that gets the most sunshine. I learned this during my PhD (Mäntylä et al. 2008b).
This is not a comprehensive list what to remember when choosing your plant species. Please, feel free to comment if you have ideas of some things I should add.
© Elina Mäntylä (firstname.lastname@example.org), 8 June 2016