In nature different animal species live together in communities. Often these are species that are closely related and ecologically very similar. As such, they usually have very similar needs, and are expected to be competitors, for example with regard to the food they take. So how is it possible that such communities do exist at all, without one successful species outcompeting all the others? To find the answer I studied many complex communities of tens of small land snail species (‘microsnails’) in the tropical lowlands of Malaysian Borneo. I found that the communities are very much closed off, with little exchange of individuals among local communities. Based on a genetic analysis of the plant diet and microbiome from individual snails, I found little correlation between diversity of the diet and the community. However, a more diverse diet is associated with a more diverse microbiome. In addition, I found that, even though most snails have a very diverse plant diet, there’s surprisingly little diet differentiation among species. This suggests that there’s little competition among species within the community. Various theoretical models supported the idea that these complex snail communities are indeed not so much composed based on different species trying to avoid each other (e.g. by choosing a different diet), but instead that the influence of randomness is more important. Therefore, to understand the assembly of complex communities, it is important to first study the influence of stochasticity.