INVASION BIOLOGY DENIALIST TAKE-DOWN #376
With every passing shitty social media post, deniers of invasion biology continue to become the ideological equivalent of creationists, with skulls too thick to be able to make their empathetic and compassionate versions of the world mesh with the reality of both evolution, natural selection, ecology and the native distribution of living things prior to human trans-oceanic travel. I don’t necessarily fault them for it - to understand why some things are invasive and others not requires a much broader perspective on the world that an 80-year human lifespan does not innately afford us.
This topic encompasses the very broad fields of biogeography and speciation itself. There are textbooks on both biogeography and evolution. Carl Zimmer's textbook on evolution is a great place to start. Species evolve as members of ecosystems, each species has its own series of checks and balances. For plant species those checks and balances come in the form of fungi and insects. Millions of years of an evolutionary arms race exist between a plant species and any antagonistic fungal or insect species. If the plant species doesn't go extinct altogether it eventually evolves resistance, as happened with Chinese chestnuts and the chestnut blight. The adaptation of Chinese chestnuts to chestnut blight took millions of years and many intermediate steps of pathogenicity and resistance.
The result of those millions of years of an evolutionary arms race was that Chestnut blight is only a mild pathogen to Chinese chestnuts. When that flight was brought across an ocean that it could never have crossed on its own, and that a spore could never have been blown across because the oceans are fucking 3,000 miles wide, It found a new host that had no resistance because it had not spent millions of years evolving in the same ecosystem. So what happened? American chestnuts became functionally extinct within 50 years.
The same case has repeated itself, although maybe not to the same degree, hundreds of times in the last century or two due to human assisted dispersal across oceans of plant, vertebrate, insect and fungus species
Kudzu is not invasive in Japan because there are numerous insects and fungi that prevent it from becoming so. As a result it is a very important plant species there, and helps keep the biosphere intact. Bring that kudzu to a new continent where the checks and balances don't exist however, and it smothers entire ecosystems. Will something eventually evolve in North America to keep kudzu in check? Absolutely, but in the 5,000 to 50,000 years that might take how many plants species will go extinct and how many habitats will be smothered and at what point will the entire ecosystem collapse, and will that happen before something evolves to control kudzu? Maybe.
The worst invasive species tend to be very important pioneer (the fact that this word is italicized and highlighted in bold should imply to you how important an understanding of it is) on other continents - and indeed some of our most valuable native pioneer species like Verbesina encelioides, Acer negundo, Robinia and Solidago sp. are highly invasive on other continents. The entire process of ecological succession is immensely important towards understanding not only why some plants are invasive but how eosystems on planet Earth heal from disturbance events such as landslides, floods, wildfires, or most commonly - bulldozing and land clearance by humans. Pioneer species are primary successional plants that are the first to move in after disturbance. They re-colonize barren ground very quickly, tend to grow fast, produce a shit-ton of seeds, and are generally short lived. Along the way, they provide cirtical services to the ecosystem, such as shading the ground and creating a microclimate of humidity and cooler temperatures, their roots infiltrating the soil and providing vital scofflding for beneficial microbes. They basically “prep” the land for the slower-growing, longer-lived species that can only get established once conditions on the ground have improved enough after a disturbance event.
Pioneer species are immensely important to ecosystems where they are native - where they spent millions of years evolving relationships with other plant, insect, fungal and vertebrate species that they grow sympatrically with. No species is an autonomous entity, existing by itself in a vacuum, but a critical member of a much larger functioning system full of a multitude of other species with which it has spent exponentially long amounts of time evolving relationships with. Those relationships can be mutualistic or antagonistic. Each species is a “gear in the machine” - the living machine - that is the biosphere. Likewise, humans can be mutualists for many species, rather than antagonists - as we so often are when clear massive swaths of land for agriculture or because we think plants look “messy”, or when unthinkingly establish plant species from other continents without considering the ecological behavior of those species and whether or not they might behave invasively and aggressively in their new habitats.
Why do some people think invasion biology is nonsense? Most likely it is because they have a perspective that has not "zoomed out" far enough, not only spatially but temporally, And also because the field of ecology and evolution are only a century and a half old, and it is something that most of us are not taught nor do we encounter in our very brief and short human lives.
FURTHER READING : Any Biogeography textbook. THE ECOLOGY OF PLANTS (3rd edition) by Gurevitch (it was once available on libgen, which has now shutdown, but might be available on Anna’s Archive. EVOLUTION : MAKING SENSE OF LIFE by Carl Zimmer. RAVEN BIOLOGY OF PLANTS (8th edition).
