Humans have been domesticating plants for over 10,000 years, and for just as long have impacted the ecology of native plants across the globe.
European explorers, for example, brought new species of plants to North America. This introduction of foreign plants rocked the ecological world of local plant populations, often resulting in declines or even extinctions of indigenous plants.
An example of this phenomenon is the invasion of foreign species in the grasslands of California during the 18th and 19th centuries.
Carol Malmstrom, a plant biologist, noticed she would be covered by small insects called aphids when she walked through grasslands dominated by the non-native, invasive grass. However, in areas still dominated by native grasses she rarely found aphids. This observation spurred her to investigate what caused the differences, and what they meant to the health of the grasslands.
Her work focused on viruses that can be spread by aphids, much the same way mosquitoes spread disease among humans. Using new molecular techniques, Malmstrom’s team was able to collect genes from viruses preserved in very old, dry, pressed specimens of grasses from the early 1900s.
Comparing genetic information of historic and modern viruses provided the team with clues about the role those viruses play in changing plant communities.
Researchers think that viruses introduced with the European plants and transmitted by aphids may have caused native grasses to become sick due to their lack of immunity to these novel pathogens.
Understanding how diseases like viruses change and move over long periods of time and across large areas helps show how human influence may impact Earth’s natural systems.