Classifying Hawaiian plant species along a habitat generalist-specialist continuum: Implications for species conservation under climate change

Abstract

Plant communities on tropical high islands, such as the Hawaiian Islands, are predicted to experience rapid climate change, resulting in novel climates. If increased temperature and/ or drought exceed plant species' current tolerances, species that are unable to adapt or shift ranges risk extinction. By definition, habitat generalists have a wide niche breadth and thrive in a variety of habitats, whereas habitat specialists have a narrow niche breadth, and typically thrive under more specific climatic characteristics (e.g., cold). The objectives of this study were to: (1) classify plant species in the Hawaiian Islands along a habitat generalistspecialist continuum;(2) independently test the validity of species rankings, using environmental and biogeographic ranges; and (3) identify species' life-history traits that predict species location along the continuum. We quantified specialization for 170 plant species using species co-occurrence data from over one thousand plots to rank species' realized habitat niche breadth using the Jaccard index. The distribution of species along this continuum differed by species biogeographic origin, with endemic plant species ranked on the specialist end and non-native plant species ranked on the generalist end. Habitat specialization rankings also differed for four of nine tested variables (while controlling for biogeographic origin): number of habitat moisture types, minimum elevation, number of Hawaiian Islands, and life form. Life form was the only trait tested that differed across the continuum, with woody species ranked as stronger generalists than herbaceous species; this pattern was particularly evident for non-native species. This indirect method of estimating species' potential climatic flexibility uses increasingly available large plant community data sets with output rankings which represent species' realized habitat niches. Identifying species and plant communities that are on the habitat specialist end of the continuum allows for their prioritization in conservation planning, as globally the loss of specialists is an indication of degradation.

Niche properties constrain occupancy but not abundance patterns of native and alien woody species across Hawaiian forests

“…These findings suggest that the impacts of species’ niche properties on occupancy may percolate across ecological scales to the community level, where spatial variation in species composition of Hawaiian forests has been linked with abiotic factors (Craven et al, 2019). The niche properties of widespread alien species are consistent with previous studies on the Hawaiian Islands showing that alien plant species are habitat generalists (Ainsworth & Drake, 2020) capable of colonizing empty niche space in marginal environmental contexts (Henn et al, 2019). While there are hundreds of non‐native woody species present on the Hawaiian Islands, our results indicate that there is only a small number of widespread species that are invading and restructuring the species composition of the islands forests (Craven et al, 2018).…”

“…These findings suggest that the impacts of species' niche properties on occupancy may percolate across ecological scales to the community level, where spatial variation in species composition of Hawaiian forests has been linked with abiotic factors (Craven et al, 2019). The niche properties of widespread alien species are consistent with previous studies on the Hawaiian Islands showing that alien plant species are habitat generalists (Ainsworth & Drake, 2020) capable of colonizing empty niche space in marginal environmental contexts (Henn et al, 2019).…”

The evolution of thermal performance in native and invasive populations ofMimulus guttatus

“…Alternatively, changes in thermal optima may accompany divergence in average local thermal regimes between the native and invasive range (Angilletta 2009 ), consistent with niche shifts. If source populations already possess plastic genotypes, they may be predisposed toward having a broad thermal niche (Ainsworth and Drake 2020 ), leading to similar thermal performance breadths in native and invasive populations. Alternatively, if the degree of thermal variation (e.g., temperature seasonality) differs in the native and introduced ranges, then thermal breadth could differ between invasive and native populations (Zerebecki and Sorte 2011 ; Bates et al.…”

Composition and structure of woody plant communities as a function of altitude and human degradation in Afromontane moist evergreen forests SW Ethiopia

“…As described by Goodale et al (2012), those habitat generalist species are better suited to connect fragmented forest by enrichment planting so as to protect the watershed from erosion, flood and sediment load in the water body. Meanwhile, tropical tree distribution is strongly influenced by disturbance generated by humans and climate (Silvestrini & Santos, 2015) particularly extreme precipitation and temperature events (Schmitt et al, 2013), and further studies needed to measure their effectiveness and resilience in a context of climate change are required (Ainsworth & Drake, 2020; Meli et al, 2014).…”