Diversification is decoupled from biome fidelity: Acacia – a case study

Abstract

Aim To investigate species and clade biome occupancy patterns of Australian Acacia to test for within‐biome diversification, which indicate biome conservatism. Location Australia. Taxon Acacia (Fabaceae). Methods Species distributions were predicted for 481 Australian Acacia using the Thornley Transport Resistance Species Distribution Model and mapped across four biome typologies. Within Acacia 19 clades were identified. The number of biomes occupied and niche size was quantified for every species and clade using the range area projected by the distribution model. Relationships between clade species richness, niche size and biomes occupied were tested using phylogenetic least squares regression models. Results Only 9% of the Acacia 481 species and no clades were biome specialists. There were most specialist taxa in the Crisp Biome classification (8.7%), followed by WWF Biomes (6.2%), González–Orozco Biomes (5.0%) then Functional Biomes (1.2%). On average Acacia species occupied four WWF Biomes, seven Functional Biomes, three Crisp Biomes and three González–Orozco Biomes (out of 7, 13, 5 or 6 biomes respectively). Clades were also distributed across multiple biomes (2–13) with a significant positive relationship between clade species richness and the number of biomes occupied for all biome typologies. Species richness had positive linear relationships with biome area for all biome concepts except the González–Orozco Biomes. Larger clades had larger niche sizes. Main conclusions Acacia diversification occurred across biome boundaries and was not associated with biome specialization. Species and clades mainly occurred in multiple biomes, and there were typically few biome specialists. Diversification in Acacia appears to be decoupled from biome conservatism, associated with expanding niche size across biome boundaries. Major ecological–environmental units such as biomes may constrain adaptive radiation processes via biome conservatism in many groups, but this study leads us to hypothesize that for some lineages biome boundaries are permeable.

The effect of single biome occupancy on the estimation of biome shifts and the detection of biome conservatism

“…This lack of consensus may in part reflect the changing view of the relative frequency of biome shifts as this field has developed. Any biome shifts might have been considered significant when the consensus was that they occurred rarely, but now that more examples are emerging of clades with high biome shift rates and low biome specialisation [ 16 ], a more conservative language may be evolving. It may also reflect the context-dependence of assessing biome shift rates, because there are many factors which influence rates including lineage size, number of biomes present, length of biome boundaries, biome age, environmental similarity of biomes, and methodological approaches [ 1 , 3 ].…”

“…There are many lineages with species that occur in multiple biomes with typical values of between 10–25% of species [ 4 – 6 , 9 , 10 ], that can range as high as 91% [ 16 ]. Biome shift estimates inferred with a single biome occupancy approach may not detect some types of biome shift, for example when species expand into another biome while retaining occupancy in the ancestral biome.…”

Evolution of crassulacean acid metabolism (CAM) as an escape from ecological niche conservatism in MalagasyBulbophyllum(Orchidaceae)

“…The retention of niche‐related ancestral ecological traits over time has been termed niche conservatism (Wiens et al ., 2010), whereas evolutionary change that allows lineages to transverse niche boundaries is known as niche shift (Donoghue & Edwards, 2014). Niche conservatism has long been viewed as the dominant process in ecology across many angiosperm lineages (Crisp et al ., 2009; Donoghue & Edwards, 2014), but there is growing evidence that niche shifts are more common than previously thought (Holstein & Renner, 2011; Evans et al ., 2014; Gamisch et al ., 2016; Cardillo et al ., 2017; Dale et al ., 2020; Herrera, 2020). However, still little is known about the key structural and physiological traits underlying such niche shifts, and their consequences for species diversification at broad phylogenetic and spatial scales (reviewed in Soltis et al ., 2019).…”

Pioneering polyploids: the impact of whole-genome duplication on biome shifting in New Zealand Coprosma (Rubiaceae) and Veronica (Plantaginaceae)

“…Lineage biome occupancy has previously been thought to be generally conserved, with rare biome shifts, reflecting phylogenetic niche conservatism [42][43][44]. However, recent studies suggest that biomes are relatively permeable, with lineages crossing biome boundaries frequently and many species occupying multiple biomes [45][46][47][48]. When WGD promotes niche shifts, it may also foster lineage expansion into new biomes.…”