BIOTROPICA 43(3): 324–334 2011 10.1111/j.1744-7429.2010.00696.x A Dated Phylogeny Complements Macroecological Analysis to Explain the Diversity Patterns in Geonoma (Arecaceae) Julissa Roncal1, Anne Blach-Overgaard, Finn Borchsenius, Henrik Balslev, and Jens-Christian Svenning Ecoinformatics & Biodiversity Group, Department of Biological Sciences, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark ABSTRACT Integrating phylogenetic data into macroecological studies of biodiversity patterns may complement the information provided by present-day spatial patterns. In the present study, we used range map data for all Geonoma (Arecaceae) species to assess whether Geonoma species composition forms spatially coherent floristic clusters. We then evaluated the extent to which the spatial variation in species composition reflects present-day environmental variation vs. nonenvironmental spatial effects, as expected if the pattern reflects historical biogeography. We also examined the degree of geographic structure in the Geonoma phylogeny. Finally, we used a dated phylogeny to assess whether species richness within the floristic clusters was constrained by a specific historical biogeographic driver, namely time-for-diversification. A cluster analysis identified six spatially coherent floristic clusters, four of which were used to reveal a significant geographic phylogenetic structure. Variation partitioning analysis showed that 56 percent of the variation in species composition could be explained by spatial variables alone, consistent with historical factors having played a major role in generating the Geonoma diversity pattern. To test for a time-for-diversification effect, we correlated four different species richness measures with the diversification time of the earliest large lineage that is characteristic of each cluster. In support of this hypothesis, we found that geographic areas with higher richness contained older radiations. We conclude that current geographic diversity patterns in Geonoma reflect the present-day climate, but to a larger extent are related to nonenvironmental spatial constraints linked to colonization time, dispersal limitation, and geological history, followed by within-area evolutionary diversification. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. Key words: Amazonia; cenozoic; historical biogeography; neotropics; palms; phylogenetic structure; time-for-diversification; tropical species richness. EXPLANATIONS FOR THE GEOGRAPHIC PATTERNS in plant species diver- lineages (Ricklefs & Schluter 1993, Ricklefs 2004, Wiens & Don- sity that we observe today have, in recent decades, focused mostly oghue 2004, Svenning & Skov 2005, Hawkins et al. 2006, on environmental correlations (Gentry 1988, Ruokolainen et al. Donoghue 2008, Svenning et al. 2008). Evolutionary and other 1997, Tuomisto et al. 2003, Jones et al. 2006, Donoghue 2008, historical factors are not necessarily proposed to substitute environ- Sesnie et al. 2009). These are based on the premise that spatial mental explanations, but at least to complement them toward turnover in species composition is driven by the interaction of the a more comprehensive interpretation of biodiversity patterns, as environment with the evolved characteristics of lineages (Gould & species diversity is the product of diversification, dispersal, and Lewontin 1979, Gentry 1988, Donoghue 2008). Environmental extinction of its constituent lineages (Ricklefs 2004, Wiens & characteristics and biological interactions are assumed to mediate Donoghue 2004, Donoghue 2008). With the rapid increase in phylo- plant community composition and are usually components in genetic studies, an increasing understanding of evolutionary niche models of floristic (Pitman et al. 2001, Austin 2002) and species dynamics (Prinzing et al. 2001, Desdevises et al. 2003, Wiens & richness patterns (Hawkins et al. 2003, Currie et al. 2004, Kreft & Donoghue 2004, Warren et al. 2008), and the new development of Jetz 2007). However, alternative explanatory models have also been analytical tools to infer historical biogeography and diversification proposed. Notably, species distributions may result from demo- times (Graham 2003, Ree et al. 2005, Rutschmann 2006, Ricklefs graphic stochasticity and the cumulative effect of dispersal limita- 2007), we anticipate a growing number of studies that integrate tion through evolutionary time (Condit 1996, Bell 2001, Hubbell historical factors into explanatory biodiversity distribution models. 2001, Svenning & Skov 2005), and these distributions could gen- The idea that species richness in an area might be limited by erate richness patterns via their interactions with geographic do- the time since the area was colonized has a long history and is main geometry (Colwell & Lees 2000) or biogeographic history referred to in the literature as the ‘evolutionary time hypothesis’ (Bjorholm et al. 2006). In this scenario, dispersal limitation might (Willis 1922, Stebbins 1974) or the ‘time-for-speciation effect’ be expressed as a spatial pattern in which floristic similarity is ex- (Stephens & Wiens 2003). Evidence for such an effect along lati- pected to decrease with increasing geographic distance (Condit tudinal and elevational gradients has only been found in a few stud- et al. 2002). ies involving well-dated molecular phylogenies (Stephens & Wiens Whether the main drivers of species diversity are environmen- 2003; Wiens et al. 2006, 2007), and very few studies have analyzed tal or not, there is increasing awareness that a comprehensive it at different spatial (local and continental) scales (Stephens & understanding of this issue will require an integration of the under- Wiens 2003). Mechanisms controlling species richness have been lying evolutionary and biogeographic history of the constituent associated with small-scale species interactions within communities (local determinism) and large-scale processes acting over long time Received 8 October 2009; revision accepted 30 May 2010. spans, such as species migration and biogeographical history 1Corresponding author; e-mail: [email protected] (reviewed in Ricklefs 2004). Reconciliation of the local/ecological 324 r 2010 The Author(s) Journal compilation r 2010 by The Association for Tropical Biology and Conservation Diversity Patterns in Geonoma 325 and continental/historical perspectives has been proposed by sug- for-diversification in shaping Geonoma diversity by comparing clus- gesting that the interactions among locally coexisting individuals ter diversity with the age of the earliest large clade making up its adjust the geographical and ecological species range (Ricklefs flora. We screened for a time-for-diversification effect not only on 2004). Another approach that connects local and continental rich- cluster diversity, represented by cluster-wide species richness (g di- ness is the species-pool hypothesis, which claims that local species versity) and endemic species richness, but also on local (11 square) richness is determined by the number of species available at a larger species richness (a diversity), as predicted by the species-pool hy- scale (Zobel 1997). In support thereof, case studies across a broad pothesis. By exploring whether time-for-diversification on a cluster range of taxa and continents have indeed shown that there can be area level also constrains the diversity of local (11 square) assem- strong continental effects on local diversity beyond those driven by blages, our study goes beyond all previous studies (but see Stephens the local environment (Ricklefs et al. 2004, Freestone & Harrison & Wiens 2003). 2006, Dickson & Foster 2008, Malard et al. 2009). We therefore hypothesize that if there is a time-for-diversification effect on rich- METHODS ness within large continental areas, then this effect should also ap- pear at smaller local community scales. GEOGRAPHIC, ENVIRONMENTAL, AND FLORISTIC DATASET.—We ob- With its approximately 68 species (Henderson et al. 1995, tained species range maps for Geonoma from Henderson et al. Govaerts & Dransfield 2006), Geonoma is widespread throughout (1995), and nomenclature for the macroecological analyses also the American tropics, and its burst of diversification occurred dur- followed this work. We digitized the range maps at a 11 Â 11 res- ing the Miocene, 11.9–19.5 million years ago (mya; Roncal et al. olution (Bjorholm et al. 2005). The study area thus consisted of 2010). This estimate is broadly contemporaneous with the diversi- 1010 11 Â 11 grid cells where Geonoma was present, after excluding fication timing estimated for other plant lineages in tropical Amer- 53 cells of coastal and small island cells with incomplete environ- ica; e.g., large genera like Ocotea (Lauraceae), Inga (Fabaceae), mental data. We used 12 environmental factors as explanatory vari- Annona and Guateria (Annonaceae), Costus (Costaceae), Renealmia ables. Elevation (ELV), mean annual temperature (MAT), (Zingiberaceae), Chamaedorea (Arecaceae), and the tribes Isertieae temperature of the coldest month (MTCO), mean annual precip- and Cinchoneae (Rubiaceae) all radiated in the late Tertiary itation (MAP), minimum monthly precipitation (MINMPR), (Chanderbali et al. 2001; Richardson et al. 2001, 2004; Kay et al. and water balance (WATBAL) were taken from the high-resolution 2005; Sarkinen et al. 2007; Cuenca et al. 2008; Antonelli et al. climate grid CRU CL 2.0 (New et al. 2002). WATBAL was com- 2009). Hence, an improved understanding of the drivers of the puted