Ecological networks

Species do not live in isolation – they depend on ecological interactions with other species. Butterflies, for example, are prey for birds and bats, pollinators for flowers, hosts for parasitoids and viruses, parasites on host plants, co-mimics of other butterflies, etc. We describe ecological interactions as networks, with species as nodes and interactions as links between them. Much of the research in our unit is related to different types of ecological networks. Here are some examples.

Müllerian mimicry in butterflies

Müllerian mimicry in Lepidoptera means that chemically defended species advertise their bad taste via wing color patterns. Species which share the same color pattern benefit from the presence of each other (mutualistic interaction). Through evolution, this leads to the convergence of color patterns between coexisting species. We study how these networks of mimetic interactions have emerged and how the process of selection for mimetic species affects the evolution of microhabitat, host-plant or climatic preferences.

Butterfly-plant networks

Although butterflies are free-living as adults, their caterpillars act as parasites for the host plants. During the larval stage, caterpillars feed on their host plants to grow. This damages the plant and can weaken it. The interaction affects the life-history traits of both the caterpillars and the plants and drives the co-evolution between the two. As a result, many butterfly species have become very specific about which plants they choose as food sources for their caterpillars.  While insect-plant relationships have been relatively well studied in temperate regions, they remain largely unknown for most tropical species. We are only beginning to uncover the complexity of these interactions in regions of high diversity. 

Arctic networks

One of the key challenges in characterising networks is their diversity. If you have a hundred species, they can, in principle, interact in 100x100, i.e., 10,000 different ways. We, however, overcome this diversity “issue” in the Arctic. Here, species richness is relatively low – and at the same time, climate change is particularly fast. We have used these presumptively simple networks as model systems. In terms of structure, we have found that even the simplest arctic networks are highly complex. With climate change, we have detected increasing variation year-to-year. For any two species interacting with each other (like pollinators and plants), this means longer periods of hunger for pollinators and less pollinators for plants. It is like we are putting interacting species into a tumble-dryer and saying “well now try to interact”.

Modeling and predicting species interactions

Rapid environmental change is a major challenge for most species on Earth. Climate change affects species distribution across large geographical regions, and patterns of co-occurrence between interacting species. Thus, understanding the ecological and evolutionary dynamics of species interactions in the face of change is a major challenge. For a host-parasite interaction to happen, the parasite needs to be able to use that host, and the host and the parasite need to occur in the same place at the same time. Recent methodological developments allow us to investigate how parasites might lose and gain the ability to use different hosts over evolutionary time. We can also model the occurrence of hosts and parasites in different parts of the world, and then calculate the probability that a given parasite will encounter a given host. We can then unravel what host-parasite interactions are likely, even if we have not observed them yet. We can also predict how current interactions will be affected by future changes in climate and land use.