To improve management of Department of Defense (DoD) lands, SERDP researchers are examining the effects of species loss on ecosystem resilience. For example, Dr. Jinelle Sperry from the U.S. Army Engineer Research and Development Center is the principal investigator of a SERDP project team whose findings were recently published in Proceedings of the National Academy of Sciences. Specifically, they recently discovered that nonnative bird species dominate plant seed dispersal networks in Oahu, Hawaii. Since Oahu has experienced significant extinction and species invasion, their discovery provides important insight for predicting ecological response to ecological disturbance.

On DoD training lands, species loss holds the potential to lead to land use restrictions that may limit military training activities.  As a result, DoD works hard to counter threats to the ecosystems they manage. Forecasting how species respond to disturbances, however, is a difficult task. Dr. Sperry and her team relied on network science to develop a theoretical and predictive framework that used data describing seed dispersal network interactions in Oahu, Hawaii.

Seed dispersal plays a vital role in ecosystem resilience, affecting “plant population dynamics, community structure, maintenance of biodiversity, and regeneration of degraded ecosystems,” the authors of the paper wrote. Although Oahu was home to a richly diverse set of species, 77 native Hawaiian bird species and subspecies are now extinct. The project team found that these extinctions resulted in nonnative birds dispersing seeds belonging to nonnative plants. 

The study also revealed information about nonnative species functions within seed dispersal networks. This information can help land managers make better decisions about which species and plants to target to maintain ecosystem health.  Although researchers hypothesized that neutral-based traits (e.g., abundance, range) would be important in nonnative-dominated communities, they found that niche-based traits (e.g., degree of frugivory, seed size) were even more critical to network connectivity and stability. With this knowledge, managers can better predict how native and nonnative species will respond to disturbance. These findings will assist managers to determine the focus of their ecosystem management.

Dr. Sperry and her team’s findings provide important information for understanding and predicting ecological responses to threats. Before this study, researchers had not tested the impacts of species loss on seed dispersal networks. The project provides not only a novel focus, but also a framework for improving ecosystem resilience.