Disturbance may be beneficial for the maintenance of biological diversity owing to the heterogenous landscape it can produce. Yet, when disturbance intensity or magnitude is elevated beyond what may be considered favourable, due to natural or anthropogenic means, there may be severe consequences for biota. In Long Point, Ontario, Canada, a sandspit in Lake Erie, anuran amphibians have experienced a chance overlap of major disturbance events: the herbicide treatment of the invasive reed, Phragmites australis australis, and an extensive dune washout. Both disturbances had the capacity to destabilize the ecosystem, transform the landscape, and hence, alter the distribution of the resident organisms. In this research, we explored how these habitat modifications affect population- and community-level responses of the resident frog and toad species using minnow traps, acoustic surveys, and visual surveys, before and after the disturbances. Some areas within the study site were directly affected by the dune washouts alone and not the Phragmites treatment, while others were not affected by the washouts and only by the Phragmites treatment. There were also areas affected by both disturbances and some unaffected by either disturbance. Therefore, this study area allowed the application of a 3-replicate 2x2 factorial site design of disturbance regimes.
The washout of dunes and treatment of Phragmites monotypic stands accomplished similar outcomes; both disturbances appeared to reduce accumulated landscape homogeny, and where the dune washout occurred, the formation of open, sand-filled ponds. The sand buried the Phragmites reeds, delaying regrowth in non-sprayed sites, though regrowth was evident by August. In August 2020, 77 Anura, representing 10% of total captures, were trapped in 530 trap-days, compared to August 2021 where 244 Anura, 11% of total captures, in 480 trap-days. Post-disturbance, Ranidae species were significantly less abundant in sites affected by dune washouts and where Phragmites was treated. These species tended to inhabit treated and control sites, where vegetation was more abundant. Notably, the natural washout produced ideal breeding habitat for the federally endangered Fowler’s Toad (Anaxyrus fowleri). Toads successfully bred in washout sites, regardless of herbicide-treatment status. The resulting landscape heterogeneity produced by the natural dune washout disturbance allowed the breeding success of Fowler’s toads to attain levels not seen in the past two decades. It is the hope that insights gleaned from this research will assist in understanding the effects of the disturbances on anuran communities and inform future dune and Phragmites management endeavours.