Resilience or catastrophe?
From a conservation perspective, the change in western monarch butterflies presents a conundrum. Even knowing how to implement the precautionary principle of “Do no harm” is not obvious. On one hand, the benefits of milkweed in urban gardens – to public outreach and potentially to the monarch population – are large. On the other hand – if diseased monarchs from urban gardens significantly reduce the likelihood of a robust migration – then there might be real harm.
On the positive side, the appearance of this urban population is a promising sign of how resilient the species might be. In northern California, monarch butterflies have reinvented themselves. To residents of coastal California cities, it must seem like a success to be seeing monarch butterflies in their gardens on a regular basis. It is likely – though not guaranteed – that western monarchs will persist in a small portion of their historic range, even if they are lost from most of it. And yet even this positive note is tinged by the knowledge that we are losing something incredible. The overwintering clusters that used to occur in California are a spectacular phenomenon, and we may completely lose monarch butterflies from the interior West.
Perhaps the most striking feature of these changes is how quickly they happened. It has only been about five years since we (Schultz et al. 2017) published our first analyses of declines in overwintering populations of migratory monarch butterflies in the West. The subsequent drops by two more orders or magnitude happened in less than three years. By the time we resolve enough uncertainty to provide clear management guidelines, the system may have shifted again. When Doak et al. (2008) concluded that surprises are common in ecology, most of the examples they pointed to were small-scale surprises in experiments, and often on time scales that aligned much more with the time scales of research or management. One lesson from western monarchs is that, in this rapidly changing world, we should expect some species to change quickly and in completely unexpected ways.