Targeted invasive species removal cascades to reduce non-target invasive species through apparent facilitation

Invasion biologists often focus on facilitative interactions between non-native species. These facilitative interactions can result in invasional meltdown, a positive feedback loop where naturalized species facilitate other non-natives to establish to the detriment of native ecosystem structure and function. In order to understand the effects of restoration efforts via the removal of non-native species it is important to quantify the beneficial impacts to the ecosystem when feedback loops are broken by removing key linkages between invasive species. To address this, I tracked the responses of benthic stream invertebrates to invasive fish removal in Hawaiʻi. Invasive fishes were removed in April of 2016 from 12 freshwater streams on the island of Oʻahu, Hawaiʻi, USA. Following fish removal, I collected 96 macroinvertebrate samples (4 replicates from each treatment [Experimental + Control] at 12 sites) using a 30.48 x 30.48 cm Surber sampler. The invertebrates were sorted, identified to the lowest taxonomic resolution and enumerated. Visual surveys of fish communities were performed monthly at each site and invertebrates were collected and processed as before in monthly cycles from November 2016 through August 2017. I observed that the removal of poeciliids, a numerically dominant family of non-native fishes in Hawaiʻi, led to reduced predation pressure on native midge larvae (Chironomidae). As the relative abundance of chironomids increased, there was a decrease in abundance of the non-native caddisfly Cheumatopsyche analis, possibly due to compitition for resources. These results demonstrated that targeted invasive species removal can benefit native species through cascading interactions. In this case the results showed reducing predation pressure on native invertebrates and reversing the effects of invasional meltdown. By understanding the relationships between multiple native and non-native organisms can lead to effective and cost-efficient management in areas that have multiple invasive species.