Implications of high species turnover on the south-western Australian sandplains

Abstract

Species turnover and its components related to replacement and nestedness form a significant element of diversity that is historically poorly accounted for in conservation planning. To inform biodiversity conservation and contribute to a broader understanding of patterns in species turnover, we undertook a floristic survey of 160 plots along an 870 km transect across oligotrophic sandplains, extending from the mesic south coast to the arid interior of south-western Australia. A nested survey design was employed to sample distances along the transect as evenly as possible. Species turnover was correlated with geographic distance at both regional and local scales, consistent with dispersal limitation being a significant driver of species turnover. When controlled for species richness, species replacement was found to be the dominant component of species turnover and was uniformly high across the transect, uncorrelated with either climatic or edaphic factors. This high replacement rate, well documented in the mega-diverse south-west, appears to also be a consistent feature of arid zone vegetation systems despite a decrease in overall species richness. Species turnover increased rapidly with increasing extent along the transect reaching an asymptote at ca. 50 km. These findings are consistent with earlier work in sandplain and mallee vegetation in the south-west and suggests reserve based conservation strategies are unlikely to be practicable in the south-western Australia sandplains when communities are defined by species incidence rather than dominance.

High species diversity and turnover in granite inselberg floras highlight the need for a conservation strategy protecting many outcrops

“…While not being directly comparable with our multiple site measure of beta diversity, it is worth noting that Hunter (, ) measured both high levels of spatial structure in species richness, and low levels of nestedness in the composition of granite inselberg floras on the New England Batholith in temperate eastern Australia. Similar patterns in multiple site measures of beta diversity have also been measured for other OCBIL landscapes in the SWAFR, including BIF inselberg and lateritic sandplain floras (Gibson et al, , ). In the latter, spatial species turnover increased rapidly to 10 km, leveled off at about 50 km, and then increased slowly until maximum extent of ca .…”

“…For all three habitats, species replacement and not nestedness (species loss) is responsible for variation in species composition. The high species replacement on granite inselbergs in the SWAFR mirror patterns found on other OCBIL landscapes in the SWAFR flora (Gibson, Meissner, Markey, & Thompson, ; Gibson et al, ). These patterns indicate that effective conservation strategies are best focused on protecting multiple inselbergs across the entire climate gradient of the region to protect the high level of biodiversity in the region brought about by spatial turnover in species composition.…”

“…Our results concur with those of Porembski and Brown () for granite inselbergs in tropical western central Africa where 75% of all species occurred on fewer than 5 (out of 25) inselbergs, with 37% of species restricted to a single inselberg. High numbers of rare species have also been recognized on Banded Iron Formation (BIF) inselbergs (Gibson et al, ) and in other vegetation types in the SWAFR (e.g., Gibson et al, ; Keighery, Gibson, van Leeuwen, Lyons, & Patrick, ; Wardell‐Johnson & Williams, ). Analysis of evolutionary patterns in floras of granite and BIF inselbergs in the SWAFR shows that these landscape features are areas where species can persist through harsh climatic conditions.…”

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

“…By specifically choosing to develop the edaphic-SDM based on the geomorphological and soil features that inform the microclim data set (Kearney, Isaac, et al, 2014), we were able to calculate microclim estimates across the projection area, including below-ground microclimate. One of the challenges facing studies of SRE flora, especially in highly biodiverse landscapes such as the BIF outcrops of south-western Western Australia (Gibson, Prober, Meissner, & Leeuwen, 2017;Gibson et al, 2010), Table Mountain National Park in South Africa (Helme & Trinder-Smith, 2006), or archipelagos such as New Caledonia (Gâteblé et al, 2019;Kier et al, 2009) is that there may be a large number of SRE species, but they are usually either entirely unique, or a unique clade of closely related species within a taxon. One of the challenges facing studies of SRE flora, especially in highly biodiverse landscapes such as the BIF outcrops of south-western Western Australia (Gibson, Prober, Meissner, & Leeuwen, 2017;Gibson et al, 2010), Table Mountain National Park in South Africa (Helme & Trinder-Smith, 2006), or archipelagos such as New Caledonia (Gâteblé et al, 2019;Kier et al, 2009) is that there may be a large number of SRE species, but they are usually either entirely unique, or a unique clade of closely related species within a taxon.…”

Bioclimatic transect networks: Powerful observatories of ecological change

“…Systematic plant community turnover has been observed along the TREND (Figure ), with families characteristic of mesic ecosystems (e.g., Cyperaceae and Xanthorrhoeaceae) dominating at the temperate end, giving way to a greater prevalence of arid‐adapted families (e.g., Amaranthaceae and Solanaceae) at the drier end (Guerin, Biffin, & Lowe, ). Plant community turnover on the SWATT was high and occurred through species replacement (rather than nestedness) across the transect at a local scale, irrespective of environmental factors (Gibson et al., ).…”