Edaphic specialization and vegetation zones define elevational range‐sizes for Mt Kinabalu regional flora

Abstract

Identifying physical and ecological boundaries that limit where species can occur is important for predicting how those species will respond to global change. The island of Borneo encompasses a wide range of habitats that support some of the highest richness on Earth, making it an ideal location for investigating ecological mechanisms underlying broad patterns of species distribution. We tested variation in richness and range-size in relation to edaphic specialization and vegetation zone boundaries using 3060 plant species from 193 families centered around the elevational gradient of Mt Kinabalu, Borneo. Across species, average range-size increased with elevation, consistent with Rapoport's rule. However, plants associated with ultramafic soil, which is low in nutrient and water availability and often has high concentrations of heavy metals, had larger range-sizes and greater richness than expected along the elevational gradient, as compared to a null model with randomization of edaphic association. In contrast, non-ultramafic species had smaller range-sizes and lower richness than expected. These results suggest that tolerance of resource limitation may be associated with wider range-sizes, whereas species intolerant of edaphic stress may have narrower range-sizes, possibly owing to more intense competition in favorable soil types. Using elevation as a predictor of average range-sizes, we found that piece-wise models with breakpoints at vegetation zone transitions explained species distributions better than models that did not incorporate ecological boundaries. The greatest relative increases in range-size with respect to elevation occurred mid-elevation, within the montane cloud forest vegetation zone. Expansion of average range-size across an area without physical boundaries may indicate a shift in ecological strategy and importance of biotic versus abiotic stressors. Our results indicate that elevational range-size patterns are structured by ecological constraints such as species' edaphic association, which may limit the ability of species to migrate up or down mountains in response to climate change.

Further food for thought: higher tropical mountains revisited once again

“…There are no altitudinal range peaks at 1900 2200 m, reflecting the variable altitude of the lower to upper montane forest ecotone according to topography. Our data also support Whitman et al (2021) in that range altitudinal amplitudes increase with elevation in keeping with Rapaport's Rule (originally proposed for latitude; Stevens 1989), although the wide lowland-lower montane transition presents an exception. There are a surprising 44 species at Kinabalu which have been recorded from the lowlands (＜1300 m) to upper montane-subalpine woodlands (＞2800 m) greatest species' altitudinal amplitudes.…”

“…1a and 1b). On Kinabalu, our data support the conclusion of Whitman et al (2021) that forest zone boundaries are more closely correlated with species' altitudinal range limits than when such boundaries are ignored, although limits assumed to be correlated with temperature alone also decline. Total species presences reach a peak (1000 1300 m) at the lowland-lower montane forest transition, along with a slight peak in minimum species' altitudes.…”

“…-What forest elevational change occurs at higher latitudes, and in the transition between tropical and warm temperate climates. The first of these questions has been ably answered in a recent paper by Whitman et al (2021), in an exhaustive analysis of altitudinal ranges among the 3060 vascular plant species recorded from the equatorial Mount Kinabalu, 4095 m; but no comparisons were made with tropical mountains at higher latitudes, nor with similarly forested temperate mountains, necessary to test Janzen's hypothesis.…”

“…They therefore serve for an abbreviated gradient analysis, albeit strengthened by field observations on the many other mountains in tropical and temperate East Asia (see references in Ashton 2003;2017;Ashton & Zhu 2020). We have selected tree or woody species for comparison: 1124 tree species on Mount Kinabalu, northern Malaysian Borneo, 4095 m, 6°10′ N, 116°32′ E in the equatorial tropics, thanks to John Beaman's floristic monograph (Beaman and Beaman 1998;Beaman et al 2001;Beaman and Anderson 2004); 487 tree species in the Bhutan and Sikkim Himalaya at 27°N, 88 92°E, from the Gangetic Plain at 100 m to maximum elevations at 7561 m and 8586 m, respectively, located at the tropicalwarm temperate forest margin at c.2000 m and therefore including both tropical and temperate altitudinal sequences, where Rebecca Pradhan has culled tree species altitudinal ranges on 300 m intervals from the Flora (Grierson andLong 1983 2001); 252 woody plant species (including shrubs and liana) on the subtropical island mountain of Yakushima, 1936 m, 30°20′ N, 130°30′ E (mostly from Tashiro 1926); and 213 woody species on the isolated Mount Fuji, 3776 m, 35°20′ N, 138°40′ E (mostly from Miyawaki 1971), towards the northeast margin of the east Asian warm-temperate forest zone, where indigenous forest no longer remains below c.900 m. For Mount Kinabalu, we extrapolated the minimum elevation of species occurrence outside the Kinabalu Park by incorporating species occurrence data in lowland (Dryad dataset of Whitman et al 2021). Similarly, we extended the minimum elevation of species occurrence for Mount Fuji to lower altitudes by examining the local flora of the nearby lowlands (Shizuoka, Kanagawa, Tokyo and Chiba Prefectures).…”

“…There are a surprising 44 species at Kinabalu which have been recorded from the lowlands (＜1300 m) to upper montane-subalpine woodlands (＞2800 m) greatest species' altitudinal amplitudes. This is primarily due to the wide altitudinal range of ultramafic exposures, many of whose characteristic flora have a wider altitudinal range than species on other soils (Whitman et al 2021). The narrowest ranges are mostly in the lowland and lower montane forests (400 1900 m), but only one third are associated with ultramafic extrusions (ultramafic specialists or tolerants).…”