Living with locusts: Connecting soil nitrogen, locust outbreaks, livelihoods, and livestock markets using empirical and modeling approaches
Coupled human and natural systems (CHANS) are systems of feedbacks linking people and ecosystems. A feature of CHANS is that these ecological feedbacks connect people across time and space. Failing to account for these dynamic linkages results in intertemporal and spatial externalities, reaping benefits in the present but imposing costs on future and distant people, such as occurs with overgrazing. Recent findings about locust-nutrient dynamics create new opportunities to address spatio-dynamic ecosystem externalities and develop new, sustainable strategies to understand and manage locust outbreaks. These findings in northeast China demonstrate that excessive livestock grazing promotes locust outbreaks in an unexpected way - by lowering plant nitrogen content due to soil degradation. We tested these human-locust-livestock-nutrient interactions using a combination of lab and field studies and mathematical models.
This talk will give an overview of our CHANS project, results from subprojects from the first phase, and directions for the future. Our earlier work demonstrated that Mongolian locusts preferred and survived best on low nitrogen grasses collected from overgrazed, degraded landscapes. We compared nutritional preferences of closely related locusts in China and Australia and found they all preferred low protein diets. This matched field observations of Australian locust outbreaks occurring on overgrazed, degraded pastures, similar to the Mongolian locust. Furthermore, we found that this low protein diet optimal for growth was also optimal for promoting development of migratory swarms. Using a modeling approach, we found multiple equilibria by exploring the interactions between land management, soil and plant N, and locust outbreaks and migration. In the future, this ecological model will be linked to an economic model investigating linkages between livestock markets, policies, and livelihoods. Such empirical discoveries provide opportunities to address externalities such as locust outbreaks, but society’s ability to act may be limited by pre-existing institutional arrangements.