Invasive species and natural hazards lead the list of compounding threats to ecological communities on military lands. In these rapidly changing environments, management of invasive species and restoration of native communities has been a difficult problem due to the complexity of interactions among species in novel conditions. Understanding the factors that enable ecosystem stability in the face of change is critical for effective management and restoration. The overall objective of this study is to understand and predict the impacts of multiple, compounding threats on communities and ecosystem stability. This project will examine seed dispersal networks (SDN) using a network analytic approach to empirically test the previously developed theoretical framework. The work uses natural variation and experiments in the wild to understand and predict how disturbances caused by abiotic factors and invasive species influence ecosystem stability and species’ roles. The specific technical objectives are to: 1) Examine temporal variation in ecosystem stability and species’ roles, and determine the impacts of short- and long-term disturbances on these metrics. 2) Experimentally test removal of invasive plant species on ecosystem stability and species’ roles over time and the underlying mechanisms affecting these metrics. 3) Build upon an analytical framework to assess the impact and sensitivity of restoration or loss of plant species on the dispersal of native plants and ecosystem stability. 4) Transition the framework developed in objective 3 into a user-friendly application to be used by managers to identify strategies for increasing ecosystem stability to threats.

This project will examine the effects of invasive species and abiotic factors on ecosystem stability (robustness, resilience, and net change) and species’ roles. For objective 1, the project team will collect field data to examine temporal variation in SDN and species’ roles and examine the indirect and direct effects of species-level traits, community-level traits, and abiotic metrics on stability. The project team will use network analyses and dynamic Bayesian networks to address these questions. For objective 2, the project team will experimentally test how the removal of fruit from invasive species alters ecosystem stability and species’ roles. The project team will accomplish this by comparing treatment subplots where invasive fruit is made inaccessible to dispersers, and unmanipulated control plots, and evaluating how changes in the amount of invasive fruit alters stability and species’ roles, using the same analytical framework in objective 1. For objective 3, the project team will build upon an analytical framework to assess how gain or loss of species with differing traits important for frugivory alter both seed dispersal of native plants and ecosystem stability. The project team will use empirically informed simulations, based on objectives 1 and 2. Lastly, in objective 4, the project team will take the framework developed in objective 3 and make it accessible for land managers to use to increase robustness and resilience in the face of the compounding threats of invasive species and natural hazards on military lands and beyond.

Department of Defense (DoD) installations manage 27 million acres of land that provide refuge to hundreds of threatened and endangered species (TES). Although the DoD is committed to ensuring the long-term viability of TES populations, proactive approaches that limit or even reverse the loss of native communities are paramount. Identifying the sources of robustness and resilience to perturbations in these communities will enable managers to optimally restore their function, particularly in the face of environmental changes. Here the project team will develop a realistic framework to be used by land managers for managing invasive species, and maintaining or restoring native communities. Functioning seed-dispersal mutualisms are essential components of ecosystem stability in the face of these escalating disturbance regimes. Nevertheless, studies empirically assessing ecosystem stability of SDN are rare, and those that do, often do not evaluate stability, temporal variability, how species’ roles may be changing concurrently, or how invasive species and abiotic factors, which are predicted to change, may jointly alter these ecosystems. Here, the project team will not only build realistic frameworks for assessing changes in SDN under varying conditions, but they will greatly contribute to the field of network science by providing a new, highly flexible framework that can be used to evaluate interacting species and the potential fate of these communities in a changing world. (Anticipated Project Completion - 2028)