Phylogenetic relatedness of native and exotic plants along climate gradients in California, USA

Abstract

Aim:One hypothesis of Darwin's naturalization conundrum, the pre-adaptation hypothesis, proposed that exotics that are more closely related to species in native communities might be more successful invaders because close relatives share similar traits and might be favoured in similar environments. We test this prediction using regional angiosperm assemblages that have been heavily invaded by exotic species and relating patterns of phylogenetic relatedness to potential environmental drivers-temperature and precipitation.Location: California, USA.Methods: Using a massive, dated phylogeny of angiosperm plants, we assessed differences in phylogenetic structure between native, naturalized exotic and full floras of 35 bioregions in California. We quantified phylogenetic relatedness using the net relatedness index (NRI) and the nearest taxon index (NTI) at varying phylogenetic extent. We measured changes in phylogenetic structure using a metric (phylogenetic relatedness anomaly), which is calculated as the phylogenetic relatedness of the full flora of a bioregion minus that of the native flora of the bioregion. We assessed correlations between phylogenetic structure measures and temperature or precipitation. Results:In general, introduction of exotic species decreased phylogenetic clustering when considering NRI but increased phylogenetic clustering when considering NTI.However, patterns of phylogenetic relatedness for some families were opposite to those for other families (e.g., NRI anomalies for Amaranthaceae, Caryophyllaceae, Fabaceae and Poaceae were opposite to those for Brassicaceae, Asteraceae and all angiosperms combined). Native communities were more phylogenetically clustered in dry regions, while exotic phylogenetic structure was less clearly related to climate. Main conclusions:Exotic species tend to come from clades that are poorly represented but not completely absent from the native flora. Within families, NTI patterns tended to be fairly similar between native and exotic species, suggesting shared responses to the environment, particularly temperature and precipitation, in these two groups. K E Y W O R D Sangiosperms, community assembly, Darwin's naturalization conundrum, niche conservatism, niche convergence, phylogenetic structure

Testing Darwin's Naturalization Conundrum using phylogenetic relationships: Generalizable patterns across disparate communities?

“…Therefore, overall, our study shows that while patterns of phylogenetic relatedness among non-native and native species within a community can offer insight into a community's susceptibility to invasion, phylogenetic relatedness alone may be an insufficient predictive tool for understanding the rules of community assembly. Rather, future efforts integrating phylogenetic diversity with other measures, such as phenotypic traits (e.g., Gaynor, Ng, & Laport, 2018;Marx et al, 2016;Schaefer et al, 2011), and abiotic factors (e.g., Lim, Crawley, De Vere, Rich, & Savolainen, 2014;Qian & Sandel, 2017), will help elucidate whether phylogenetic relatedness together with other factors can be used to predict a community's susceptibility to the establishment of new species.…”

“…For example, a number of prior tests of DNC have focused on a single taxonomic group or clade (e.g., Park & Potter, 2015;Sandel & Tsirogiannis, 2016;Strauss et al, 2006). Although this approach illuminates how phylogenetic relatedness influences invasion success among close relatives, it has limited utility for understanding the invasion dynamics and assembly process of a community comprising species from a wider diversity of evolutionary lineages (e.g., see Cadotte, Hamilton, & Murray, 2009;Lososová et al, 2015;Ordonez, 2014;Qian & Sandel, 2017;Schaefer et al, 2011).…”

“…The susceptibility of a community to invasion has also been hypothesized to vary with environmental differences (reviewed in Gallien & Carboni, 2017), further explaining a lack of consistent patterns in prior investigations of DNC. For example, species in colder climates are thought to be more closely related to each other than those in warmer climates due to historical processes (Latham & Ricklefs, 1993;Qian & Sandel, 2017;Wiens & Donoghue, 2004). This may have downstream effects on the phylogenetic patterns observed between successful invaders and resident species.…”

Reconciling Darwin’s naturalization and pre‐adaptation hypotheses: An inference from phylogenetic fields of exotic plants in Japan

“…Co‐occurrence between exotics and native recipients is commonly evaluated by site‐based analysis using quadrats, islands, grid cells, or geo‐political regions as observational units (e.g. Lososová et al, ; Qian & Sandel, ), thus focusing on site‐specific invasibility of a recipient assemblage. However, site‐based approaches are affected by the spatial grain used for capturing species co‐occurrence patterns (Bar‐Massada, Yang, Shen, & Wang, ).…”

“…The so-called 'Darwin's naturalization hypothesis' asserts that exotics, which are ecologically distinctive from native recipients, are likely to naturalize within the recipient assemblage (Darwin, 1859) because of interspecific niche differentiation (Davies, Cavender-Bares, & Deacon, 2011). Conversely, the 'pre-adaptation hypothesis' (Duncan & Williams, 2002;Qian & Sandel, 2017) posits that exotics that are ecologically similar to natives would be able to invade assemblages with congeneric native species (Darwin, 1859). Previous studies have provided empirical evidence for both naturalization of taxonomically/phylogenetically dissimilar exotics and pre-adaptation of similar exotics (Davies et al, 2011;Lambdon & Hulme, 2006;Ma et al, 2016;Marx, Giblin, Dunwiddie, & Tank, 2016;Ricotta, Godefroid, & Rocchini, 2010;Schaefer, Hardy, Silva, Barraclough, & Savolainen, 2011;Thuiller et al, 2010).…”