High‐resolution distribution modeling of a threatened short‐range endemic plant informed by edaphic factors

Abstract

Short‐range endemic plants often have edaphic specializations that, with their restricted distributions, expose them to increased risk of anthropogenic extinction. Here, we present a modeling approach to understand habitat suitability for Ricinocarpos brevis R.J.F.Hend. & Mollemans (Euphorbiaceae), a threatened shrub confined to three isolated populations in the semi‐arid south‐west of Western Australia. The model is a maximum entropy species distribution projection constructed on the basis of physical soil characteristics and geomorphology data at approximately 25 m2 (1 arc‐second) resolution. The model predicts the species to occur on shallow, low bulk density soils that are located high in the landscape. The model shows high affinity (72.1% average likelihood of occurrence) for the known populations of R. brevis, as well as identifying likely locations that are not currently known to support the species. There was a strong relationship between the likelihood of R. brevis occurrence and soil moisture content that the model estimated at a depth of 20 cm. We advocate that our approach should be standardized using publicly available data to generate testable hypotheses for the distribution and conservation management of short‐range endemic plant species for all of continental Australia.

The challenge of novel abiotic conditions for species undergoing climate‐induced range shifts

“…By including soil, light availability and topography, plant biologists are able to better capture the full suite of conditions plants are experiencing (Austin 2007). This holistic approach has shaped plant research, including physiology (Bjorkman et al 2017), community ecology (Dearborn and Danby 2017) and distribution modeling (Tomlinson et al 2019, Clason et al 2020), to be more ecologically relevant (Austin and Niel 2011), and this framework also has improved researchers' approaches to understanding how plants will be impacted by climate change and their ability to shift their geographic ranges (Beauregard and Blois 2014). Some plants, such as trees, can tolerate a broad variety of soil conditions as adults, yet soil variation can impact dispersal success and seedling establishment, reducing their ability to track their thermal niche (Lafleur et al 2010).…”

Calcicole–calcifuge plant strategies limit restoration potential in a regional semi‐arid flora

“…Although elevation was among the significant predictors of species richness, species composition, and the proportion of calcifuge plant strategies and nutrient-acquisition strategies in both univariate and multivariate analyses, we assume elevation is likely a proxy for BIF in the Mid-West as previously proposed by Tomlinson et al (2020). The crests and ridges of BIF in the study site are <200 m higher in the landscape than surrounding topography, and elevational gradients in edaphic and vegetative parameters probably reflect the increasing incidence of the shallow, well-drained soil characteristic of BIF (Gibson et al, 2010), rather than altitudinal climatic shifts (Tomlinson et al, 2020).…”

“…Although elevation was among the significant predictors of species richness, species composition, and the proportion of calcifuge plant strategies and nutrient-acquisition strategies in both univariate and multivariate analyses, we assume elevation is likely a proxy for BIF in the Mid-West as previously proposed by Tomlinson et al (2020). The crests and ridges of BIF in the study site are <200 m higher in the landscape than surrounding topography, and elevational gradients in edaphic and vegetative parameters probably reflect the increasing incidence of the shallow, well-drained soil characteristic of BIF (Gibson et al, 2010), rather than altitudinal climatic shifts (Tomlinson et al, 2020). The availability of soil moisture in the upper soil profile (200-1,000 mm) has been identified as a critical factor governing the occurrence of edaphic endemics on BIF (Tomlinson et al, 2020), and at least some BIF species likely rely upon water stored in cracks and fissures in bedrock, particularly during early seedling establishment (e.g., Poot & Lambers, 2003;Robinson et al, 2019;Tomlinson et al, 2020).…”

“…The crests and ridges of BIF in the study site are <200 m higher in the landscape than surrounding topography, and elevational gradients in edaphic and vegetative parameters probably reflect the increasing incidence of the shallow, well-drained soil characteristic of BIF (Gibson et al, 2010), rather than altitudinal climatic shifts (Tomlinson et al, 2020). The availability of soil moisture in the upper soil profile (200-1,000 mm) has been identified as a critical factor governing the occurrence of edaphic endemics on BIF (Tomlinson et al, 2020), and at least some BIF species likely rely upon water stored in cracks and fissures in bedrock, particularly during early seedling establishment (e.g., Poot & Lambers, 2003;Robinson et al, 2019;Tomlinson et al, 2020). BIF are likely water-gaining landforms (Payne et al, 1998), and as topographically complex features in an otherwise relatively uniform arid environment landscape matrix, they likely represented comparatively mesic refugia during periods of increased aridity (Byrne et al, 2017).…”

“…Edaphic endemics on BIF are range-restricted species exhibiting traits associated with specific nutritional, recruitment, or physiological requirements, commonly including specialized drought-avoidance or drought-tolerance strategies (Poot & Lambers, 2003;Nunes et al, 2015;Tomlinson et al, 2020;Elliott et al, 2019;Rajapakshe et al, 2020). These traits may be genetically fixed and may be selected against or place species at a competitive disadvantage on the deeper soils typical of areas lower in the landscape (Poot & Lambers, 2003).…”