Modeling Hawaiian Ecosystem Degradation due to Invasive Plants under Current and Future Climates

Abstract

Occupation of native ecosystems by invasive plant species alters their structure and/or function. In Hawaii, a subset of introduced plants is regarded as extremely harmful due to competitive ability, ecosystem modification, and biogeochemical habitat degradation. By controlling this subset of highly invasive ecosystem modifiers, conservation managers could significantly reduce native ecosystem degradation. To assess the invasibility of vulnerable native ecosystems, we selected a proxy subset of these invasive plants and developed robust ensemble species distribution models to define their respective potential distributions. The combinations of all species models using both binary and continuous habitat suitability projections resulted in estimates of species richness and diversity that were subsequently used to define an invasibility metric. The invasibility metric was defined from species distribution models with <0.7 niche overlap (Warrens I) and relatively discriminative distributions (Area Under the Curve >0.8; True Skill Statistic >0.75) as evaluated per species. Invasibility was further projected onto a 2100 Hawaii regional climate change scenario to assess the change in potential habitat degradation. The distribution defined by the invasibility metric delineates areas of known and potential invasibility under current climate conditions and, when projected into the future, estimates potential reductions in native ecosystem extent due to climate-driven invasive incursion. We have provided the code used to develop these metrics to facilitate their wider use (Code S1). This work will help determine the vulnerability of native-dominated ecosystems to the combined threats of climate change and invasive species, and thus help prioritize ecosystem and species management actions.

Insights from modeling studies on how climate change affects invasive alien species geography

“…Yet in Hawaii, we observed a clear increase of SRC (Vorsino et al., 2014). The authors of this study argued that given its limited latitudinal distribution, plant species need to migrate to upper elevation habitats to find temperature equivalent zones, which is the case for almost two‐thirds of the studied plants, except for plants that already occupied upper elevation wet forest habitats, which explain their predicted decrease in range sizes.…”

Exotic flower visitors exploit large floral trait spaces resulting in asymmetric resource partitioning with native visitors

“…Compared to previous assessments, abundances of native flower visitors in Hawaii are particularly low at lower elevations (Banko et al., ; Magnacca, ; Magnacca & King, ), where exotic plant species are most abundant and only small patches of native habitats are present (Alexander et al., ). Furthermore, it is predicted that exotic species will spread to higher elevations (Vorsino et al., ) potentially diminishing suitable habitats for native flower visitors and thus, accelerating the ongoing decline of native flower visitors.…”

Assessing the potential of translocating vulnerable forest birds by searching for novel and enduring climatic ranges

“…ʻAkekeʻe and ʻakikiki were compared to six endemic forest bird species on Maui and nine species endemic to Hawaiʻi. To assess niche overlap between the native forest birds of Kaua'i and resident destination island species, we calculated the comparative pairwise niche overlap metric, I (Vorsino et al, 2014;Warren et al, 2008), among species SDM projections. This metric compares both baseline and future potential climate-based distributions of 'akeke'e and 'akikiki to all resident destination island species, yielding values ranging from 0 (no overlap) to 1 (complete overlap).…”