Table of Contents

01 March 2024, Volume 62 Issue 2
Cover illustration: Islands and mountains are home to a large proportion of global terrestrial biodiversity. Olivar et al. (this issue, pp. 215-232; upper side half) looked into evolutionary dynamics on islands of the Indo- Australian Archipelago, the most complex tropical region on Earth. Azevedo et al. (this issue, pp. 305- 320; lower side half) investigated rocky ecosystems in eastern Brazil, including campos rupestres, campos de altitude, granitic- gneiss lowland inselbergs and limestone outcrops, [Detail] ...
    Issue Information
  • Editorial
  • Alexandra N. Muellner-Riehl, Fabien Anthelme, and Thomas Ibanez
    J Syst Evol. 2024, 62(2): 195-200.
  • Research Articles
  • Gunnar Keppel, Francis J. Nge, and Thomas Ibanez
    J Syst Evol. 2024, 62(2): 201-214.
    Islands in the tropical Pacific Ocean are renowned for high biodiversity and endemism despite having relatively small landmasses. However, our knowledge of how this biodiversity is formed remains limited. The taxon cycle, where well-dispersed, earlier colonizers become displaced from coastal to inland habitats by new waves of colonizers, producing isolated, range-restricted species, has been proposed to explain current biodiversity patterns. Here, we integrate the outcomes of phylogenetic studies in the region to investigate the sources, age, number of colonizations, and diversification of 16 archipelagos in the tropical and subtropical South Pacific. We then evaluate whether the results support the taxon cycle as a plausible mechanism for these observations. We find that most species in the Pacific arrived less than 5 Mya from geographically close sources, suggesting that colonization by new taxa is a frequent and ongoing process. Therefore, our findings are broadly consistent with the theory of the Taxon Cycle, which posits that ongoing colonization results in the gradual displacement of established lineages. Only the oldest archipelagos, New Caledonia and Fiji, do not conform to this trend, having proportionally less recent colonization events, suggesting that the taxon cycle may slow on older islands. This conclusion is further validated by New Caledonia having lower diversification rate estimates than younger islands. We found that diversification rates across archipelagos are negatively correlated with area and age. Therefore, a taxon cycle that slows with island age appears to be a suitable concept for understanding the dynamic nature and biodiversity patterns of the Pacific Islands.
    Biodiversity on islands in the tropical South Pacific has mostly originated through recent colonization events less than 5 Mya from the closest source areas. Only the oldest archipelagos diverge from that pattern, having an older biota and lower diversification rates. These findings correspond to the processes of the taxon cycle slowing down on older islands.
  • Jay Edneil C. Olivar, Frank Hauenschild, Hannah J. Atkins, Gemma L.C. Bramley, and Alexandra N. Muellner-Riehl
    J Syst Evol. 2024, 62(2): 215-232.
    The general dynamic model (GDM) of oceanic island biogeography views oceanic islands predominantly as sinks rather than sources of dispersing lineages. To test this, we conducted a biogeographic analysis of a highly successful insular plant taxon, Cyrtandra, and inferred the directionality of dispersal and founder events throughout the four biogeographical units of the Indo-Australian Archipelago (IAA), namely Sunda, Wallacea, Philippines, and Sahul. Sunda was recovered as the major source area, followed by Wallacea, a system of oceanic islands. The relatively high number of events originating from Wallacea is attributed to its central location in the IAA and its complex geological history selecting for increased dispersibility. We also tested if diversification dynamics in Cyrtandra follow predictions of adaptive radiation, which is the dominant process as per the GDM. Diversification dynamics of dispersing lineages of Cyrtandra in the Southeast Asian grade showed early bursts followed by a plateau, which is consistent with adaptive radiation. We did not detect signals of diversity-dependent diversification, and this is attributed to Southeast Asian cyrtandras occupying various niche spaces, evident by their wide morphological range in habit and floral characters. The Pacific clade, which arrived at the immaturity phase of the Pacific Islands, showed diversification dynamics predicted by the island immaturity speciation pulse model (IISP), wherein rates increase exponentially, and their morphological range is controlled by the least action effect favoring woodiness and fleshy fruits. Our study provides a first step toward a framework for investigating diversification dynamics as predicted by the GDM in highly successful insular taxa.
    In this study, we showed that dispersing lineages arriving at island maturity have diversification rates following predictions of adaptive radiation and have a wide range of morphological features to occupy remaining niches in an island. On the other hand, dispersing lineages arriving early in the ontogeny of an island have diversification rates following predictions of the island immaturity speciation pulse model and have a limited range of morphological features due to the least action effect.
  • Short Communication
  • Andrea C. Westerband, Tiffany M. Knight, and Kasey E. Barton
    J Syst Evol. 2024, 62(2): 233-241.
    Despite representing a fraction of the global terrestrial surface area, oceanic islands are disproportionately diverse in species, resulting from high rates of endemicity. Island plants are thought to share a unique phenotype—referred to as an island syndrome—which is thought to be driven by convergent evolution in response to selection by shared abiotic and biotic factors. One aspect of the island plant syndrome that has received relatively little research focus is that island plants are expected to have converged on conservative resource use associated with slow growth rates and weak competitive abilities. Here we tested whether native, woody Hawaiian plant species are phenotypically distinct—with more resource-conservative leaf traits—compared to a globally distributed sample of continental species. Using an archipelago-wide trait data set, we detected that on average, native Hawaiian species had lower leaf nutrient concentrations overall, and lower nutrient concentrations at high leaf mass per area, but no other phenotypic differences compared with continental plants. There was also considerable overlap in the trait spaces of native Hawaiian species and continental species. Our findings indicate that an island plant syndrome for leaf traits is not present in the Hawaiian flora, and that island species can demonstrate extensive variation in their resource-use strategies, on a scale that is comparable with that of continental species worldwide.
  • Research Articles
  • Riccardo Testolin, Fabio Attorre, Vanessa Bruzzaniti, Riccardo Guarino, Borja Jiménez-Alfaro, Michele Lussu, Stefano Martellos, Michele Di Musciano, Salvatore Pasta, Francesco Maria Sabatini, Francesco Santi, Piero Zannini, and Alessandro Chiarucci
    J Syst Evol. 2024, 62(2): 242-256.
    Small islands represent a common feature in the Mediterranean and host a significant fraction of its biodiversity. However, the distribution of plant species richness across spatial scales—from local communities (alpha) to whole islands (gamma)—is largely unknown, and so is the influence of environmental, geographical, and topographical factors. By building upon classic biogeographic theory, we used the species–area relationship and about 4500 vegetation plots in 54 Central Mediterranean small islands to identify hotspots of plant species richness and the underlying spatial determinants across scales. To do so, we fitted and averaged eight species–area models on gamma and alpha richness against island area and plot size, respectively. Based on positive deviations from the fitted curves, we identified 12 islands as cross-scale hotspots. These islands encompassed around 70% of species and habitat richness, as well as almost 50% of the rarest species in the data set, while occupying less than 40% of the total island surface. By fitting generalized linear mixed models, we found that gamma richness was mainly explained by island area and was weakly related to mean annual temperature (positively) and annual precipitation (negatively). As for alpha richness, after accounting for the idiosyncratic effect of habitats and islands, plot size and gamma richness remained the only significant predictors, showing a positive relationship. This work contributes to the understanding of the patterns and drivers of plant diversity in Central Mediterranean small islands and outlines a useful methodology for the prioritization of conservation efforts.
    We used the species–area relationship to identify plant richness hotspots and coldspots at the island and vegetation community scales. The 12 selected cross-scale hotspots were mainly located in Southern Italian archipelagos. Species richness patterns were mainly related to area and the idiosyncratic effect of habitats and islands, with climate and other large-scale processes playing a secondary role.
  • Julián Aguirre-Santoro, Alejandro Zuluaga, Emma Stonesmyth, Julio Betancur, and Rachel S. Jabaily
    J Syst Evol. 2024, 62(2): 257-274.
    Phylogenomics enhances our understanding of plant radiations in the biodiverse Andes. Our study focuses on Puya, primarily Andean and a part of the Bromeliaceae family. Using a phylogenomic framework based on the Angiosperms353 probe set for 80 species, we explored Puya′s phenotypic evolution and biogeography. Divergence time analyses and ancestral area estimations suggested that Puya originated in Central Coastal Chile around 9 million years ago (Ma). Subsequently, it dispersed to the dry valleys of the Central Andes and Puna regions between 5–8 Ma, leading to the emergence of major lineages. Key events in the last 2–4 million years include the recolonization of Chilean lowlands and dispersal to the northern Andes via Peru's Jalcas, facilitating passage through the Huancabamba depression. This event gave rise to the high-elevation Northern Andes clade. Using phylogenetic comparative methods, we tested the hypothesis that adaptation to the Andes' island-like high-elevation ecosystems was facilitated by unique leaf and floral traits, life history, and inflorescence morphology. Our findings suggest correlations between inflorescence axis compression, protective bract overlap, and high-elevation living, potentially preventing reproductive structure freezing. Semelparity evolved exclusively at high elevations, although its precise adaptive value remains uncertain. Our framework offers insights into Andean evolution, highlighting that lineages adapted to life in dry ecosystems can easily transition to high-elevation biomes. It also underscores how the island-like nature of high-elevation ecosystems influences phenotypic evolution rates. Moreover, it opens avenues to explore genetic mechanisms underlying adaptation to extreme mountain conditions.
    By employing phylogenomics, we elucidate the evolutionary relationships within Puya (Bromeliaceae), providing valuable insights into its biogeography and trait evolution in the biodiverse Andes. Our study reveals the origin of Puya in Central Coastal Chile approximately 10 Ma, followed by dispersal to the dry valleys of the Central Andes, and subsequent emergence of major lineages. Semelparity and inflorescence traits related to thermoregulation in Puya are associated with life in high-elevation ecosystems, offering new perspectives on adaptation to extreme conditions in mountain systems.
  • Martha Kandziora, Juan M. Gorospe, Luciana Salomon, Diana L. A. Vásquez, Maria Pinilla Vargas, Filip Kolář, Petr Sklenář, and Roswitha Schmickl
    J Syst Evol. 2024, 62(2): 275-290.
    Habitat stability is important for maintaining biodiversity by preventing species extinction, but this stability is being challenged by climate change. The tropical alpine ecosystem is currently one of the ecosystems most threatened by global warming, and the flora close to the permanent snow line is at high risk of extinction. The tropical alpine ecosystem, found in South and Central America, Malesia and Papuasia, Africa, and Hawaii, is of relatively young evolutionary age, and it has been exposed to changing climates since its origin, particularly during the Pleistocene. Estimating habitat loss and gain between the Last Glacial Maximum (LGM) and the present allows us to relate current biodiversity to past changes in climate and habitat stability. In order to do so, (i) we developed a unifying climate-based delimitation of tropical alpine regions across continents, and (ii) we used this delimitation to assess the degree of habitat stability, that is, the overlap of suitable areas between the LGM and the present, in different tropical alpine regions. Finally, we discuss the link between habitat stability and tropical alpine plant diversity. Our climate-based delimitation approach can be easily applied to other ecosystems using our developed code, facilitating macro-comparative studies of habitat dynamics through time.
    Using a climate-based delimitation to compare the extent of tropical alpine areas between the present and during the last glacial maximum permits us to estimate the degree of habitat stability. This new approach facilitates macro-comparative studies of habitat dynamics through time.
  • Luiz Bondi, Camila M. Patreze, Ricardo P. Louro, and Laura Jane M. Santiago
    J Syst Evol. 2024, 62(2): 291-304.
    Climate change is promoting global declines in plant diversity, which are expected to be more critical in islands or island-like ecosystems due to environmental constraints and isolation. The species' vulnerability to climate change (VUL) depends on their ability to cope with changes or mitigate them. Therefore, we investigate the influence of growth and dispersal strategies of species from the Sugarloaf Rock Complex, Brazil, an island-like ecosystem, on their niche breadth (NB), long-dispersal (LD) capacity, and geographical range (GR). Besides, we evaluate the potential use of these strategies as indicators of species' VUL. We found that rock specialists exhibit narrower NB, lower LD capacity, and a more restricted GR when compared to other species. We also found that 63% of rock specialists are found in conservation red-lists and they are more vulnerable to climate change than woody plants. Conversely, self-dispersed plants are expected to be less vulnerable to climate change when compared to species with other dispersal mechanisms. Species vulnerable to climate change are 14 times more likely to be included in conservation red lists, and it might indicate that the species' VUL might also describe the species' vulnerability to other anthropogenic threats. Still, we suggest conservation attention on some species that are expected to be vulnerable to climate change but were not yet included in conservation red lists. We advocate for more efforts to ensure the conservation aspects of different functional groups in which inselbergs might not only offer isolation but also a refuge opportunity.
    Rock specialists exhibit narrower niche breadth, lower long-dispersal capacity, and a more restricted geographical range when compared to other species. Moreover, 63% of them are found in conservation red lists as they are more vulnerable to climate change than woody plants. Therefore, we suggest conservation attention on rock specialists that are not only expected to be more vulnerable to climate change but also to the negative effects of other anthropogenic factors.
  • Luísa Azevedo, Daniela Cristina Zappi, Daniela Melo Garcia de Oliveira, Leila Meyer, Eimear Nic Lughadha, Rosie Clegg, Leonardo Dias Meireles, Pablo Hendrigo Alves de Melo, R. Toby Pennington, and Danilo M. Neves
    J Syst Evol. 2024, 62(2): 305-320.
    The geodiversity of rocky ecosystems includes diverse plant communities with specific names, but their continental-scale floristic identity and the knowledge on the role of macroclimate remain patchy. Here, we assessed the identity of plant communities in eastern Brazil across multiple types of rocky landscapes and evaluated the relative importance of climatic variables in constraining floristic differentiation. We provided lists of diagnostic species and an assessment of the conservation status of the identified floristic groups. We compiled a data set of 151 sites (4498 species) from rocky ecosystems, including campos rupestres, campos de altitude, granitic-gneiss lowland inselbergs, and limestone outcrops. We used unsupervised clustering analysis followed by ANOSIM to assess floristic groups among sites. We performed a random forest variable selection to test whether the identified floristic groups occupy distinct climatic spaces. Six groups (lithobiomes) segregated floristically according to lithology and climate. Alongside campos de altitude and limestone outcrops, inselbergs were divided according to the biome in which they occur (Atlantic Forest or Caatinga), and campos rupestres were largely segregated according to their lithological matrix (ironstone or quartzitic). Plant communities of Caatinga inselbergs were more similar to limestone outcrops, while Atlantic Forest inselbergs communities resembled campos de altitude. The composition of plant communities on outcrops seems to be largely constrained by lithology, but climatic factors are also meaningful for sites with similar lithology. The current network of protected areas does not cover these unique ecosystems and their floristic heterogeneity, with Caatinga inselbergs and limestone outcrops being the least protected.
  • Alba Rodríguez-Pacheco, Victoria Formoso-Freire, M. Olalla Lorenzo-Carballa, Andrés Baselga, and Carola Gómez-Rodríguez
    J Syst Evol. 2024, 62(2): 321-331.
    Given the sensitivity of mountain biodiversity to human pressure, it is essential to quantify changes in montane biological communities and contrast them with expectations based on potential drivers of change. This need is particularly pressing for biological groups representing important but little-studied fractions of biodiversity, such as insects. We analyze the temporal changes (between 1998 and 2015) of leaf beetle communities in an altitudinal gradient in the Sierra de Ancares (NW Spain). Our results show temporal changes in the composition of local communities, with a tendency to assemblage thermophilization, as well as a homogenization of the spatial turnover pattern, mostly driven by an increased similarity between communities at the lower and intermediate altitudes. These temporal changes in community composition and in the spatial structure of biodiversity were associated with upward shifts of the upper altitudinal limit of warm-adapted species and with downward shifts of the lower altitudinal limit of cold-adapted species. While this upward shift is consistent with expectations of climate change effects, the observed downward shift suggests a land-use change effect. Our results point to the joint effect of multiple factors (climate and land-use change) behind temporal changes of these leaf beetle communities, which result in compositional reorganization and biotic homogenization, rather than a mere coherent displacement toward higher altitudes. More generally, we show that understanding temporal change of biodiversity requires assessing multiple community-level metrics (e.g., variation in assemblage composition and/or changes in spatial turnover) for the detection of tendencies among the species-specific signals (e.g., altitudinal range shifts).