As we head into summer, we’ll inevitably start to see more and more movie trailers in which monsters, robots, and aliens overrun a variety of landscapes, prompting inhabitants (and generally a superhero or two) to fight back to reclaim their territory. If you’re in Indiana, you’ll also likely start to seeing common invasive plants, like Japanese Honeysuckle or Garlic Mustard, appearing in your yard and garden.
Invasive species generally have the ability to adapt to new surroundings easily, grow quickly, and reproduce rapidly, all unchecked in the absence of natural predators and other things that keep their populations under control. These qualities allow invasive species to take over an area formerly populated by a whole range of diverse species; thus, such invasions are responsible for roughly 42% of all species listed as threatened or endangered. Studying biodiversity can illuminate how some groups of species can coexist within environments, while others destroy everything in their paths.
Ecologists study the relationships between living things and their environments; one of the field’s foundational questions asks, “why are there so many species?” Current estimates quantify the number of species on earth at 8.7 million; while many theoretical answers to this question exist, a clear explanation remains elusive. Ranjan Muthukrishnan, an Invasive Species Ecology Fellow at the Environmental Resilience Institute, who arrived at IU in the fall of 2018, runs simulations to test theories about the relationship between invasive species and phenotypic plasticity.
Phenotypic plasticity - the ability of a genotype (an organism’s genetic makeup) to produce more than one phenotype (a set of observable traits) when it is exposed to different environments - might, according to Muthukrishnan, account for some organisms’ ability to adapt quickly to new environments. To his thinking, it’s not that a particular invasive species will always outperform another; rather, if they’re constantly moving to new habitats, what is it that makes them able to change quickly?To answer this question, Muthukrishnan uses IU’s supercomputers to run simulations with remote sensing data from real landscapes to gain a sense of how colonizing organisms might move through space, and their rates of speed. He begins by creating a gridded landscape, and in each square, Muthukrishnan places a certain number of species. He then writes code to establish rules about growth and interaction between species, which mimics how it would occur in a real-life landscape. He plays this game out in several locations on the board, and also varies the rules to query what might happen if every point on the landscape were nutrient-rich, or if a new plot opens up only once every ten years instead of offering 50% more new locations each year, or if species growth were to increase in one area. How do these variables influence species movement, competition, and advantage?
If one were to consider only one set of conditions, this type of simulation would not be overly complex; to play it out in lots of different circumstances, high performance computing resources, like those IU provides through Big Red II and Carbonate, are essential. Playing out these games in ways that explicitly includes a landscape of possible locations requires a large amount of computer memory, but remains important to measure the pressure invasive species exert on native species. IU’s supercomputers give the large-scale simulation ample time to run through different scenarios and show results even when they depend on important rare events.
In an age of ever-changing challenges to the earth’s ecosystems, work like Muthukrishnan’s offers valuable understanding of what’s at stake in species competition and coexistence. Interaction is inevitable, and even important, within biodiverse ecosystems. Understanding how these interactions can occur could help alleviate some of the stressors invasive species place on their environments.