Recently, I switched on my computer, ready to analyse my data, when I learned that my work was obsolete. I work on invasive species, that is species introduced in areas outside their native range, and invasion science seems to be a rather elusive discipline. Invasion science is now about 30 years old (the Scientific Committee on Problems of the Environment put biological invasions on top of its research agenda in 1983) but already, its obituaries are being written.
Publications like “Another call for the end of invasion biology” by Loïc Valéry et al. or “Don’t judge species on their origins” by Mark Davis et al. and the latest “The Anthropocene could raise biological diversity” by Chris D. Thomas, are calling for an end of the native vs. non-native dichotomy. While I agree that it is important to challenge and philosophically discuss a young growing discipline, I find that current discussions are excessive and keep us from getting the job done: That is, to understand the mechanisms behind biological invasions and translate these into useable, useful management schemes. My fist reflex when hearing the call to put an end to the native vs. non-native dichotomy was: “This is the easy way out!”. We, as global citizens, have promoted the spread of non-native species across the globe. Surely we can’t now sit back and rest the case on catchphrases like “ecosystem services” and “biological diversity in the Anthropocene”.
Luckily, I could turn to a really helpful field guide from David M. Richardson and Anthony Ricciardi, which underpins my reflex with real facts. It is a field guide for invasion science, just published in Diversity and Distributions. There, they summarize and invalidate the criticisms of invasion science in one table. Yes, non-native species drive species extinction. Yes, non-native invaders are ecologically more disruptive than native invaders (species that vigorously spread). No, increase of species introduction does not raise biodiversity. Focusing on species counts is a misleading approach. It neglects genetic swamping (hybridizations), reproductive interference and that species extinction due to invasive species takes time.
I agree with the critics that it is sometimes difficult to determine if a species is in fact non-native, or that we should prioritize management efforts on species that are most harmful, and that we should keep in mind climate change when we discuss range expanding species. However, these range expanding species can only expand their range with our help. We assist them to overcome natural borders, which they could have never crossed with their own dispersal mechanisms. In this light I also think we need to focus more on culture and not only on ecology. About five years ago, I listened to a talk from Prof. John Maron, University of Montana. He emphasized that by biotic exchange we lose uniqueness. We lose uniqueness of landscapes across the globe. I don’t want to travel to Africa, South-America, North-America, and Europe just to see the same flora and the same fauna. I want to see unique biomes, with all that is attached to it.
Below you see a post-card from one of my study areas. I studied the sweetbriar rose during my PhD in its native range in Europe and in parts of its invasive range in Argentina. This post-card is from Argentina. You can see six species on this post card with the title “forest flowers of Patagonia, Argentina”. Who can spot the non-native plants? I tell you this much: half of them are not native to South America. Two plants on this card are from Europe (and I already gave away one of them, the sweetbriar rose) and one is from North-America. People from Patagonia do believe that these plants are native to their area and that they are typical Patagonian plants. Losing uniqueness.