DOI: 10.5061/dryad.34tmpg4p0
title: Diversity in habit expands the environmental niche of Ziziphus (Rhamnaceae)

description: Aim: Ziziphus (Rhamnaceae) is a widely distributed genus across the
 Australasian and African tropics with unusual diversity in habit, and many
 species of significance to people. Here, we quantify the environmental
 limits of Ziziphus species and examine inter-specific relationships among
 functional traits, environment, biome and range size. Methods: We
 developed a curated geolocation database for Ziziphus and used it to
 examine the environmental limits of the genus relative to temperature,
 rainfall and seasonality. To assess the relationship between biome and
 habit, Permanova were used, while hierarchical clustering was used to
 determine whether habit, leaves and fruit traits were related to biome.
 For 40 species with adequate geolocation data, range size was calculated
 to assess its relationship with habit, biomes, and cultivation. Finally,
 niche identity tests were used to determine niche equivalency among
 cultivated and non-cultivated species. Results: Liana species are
 restricted to closed forest and the geoxylic habit is found only in open
 grasslands. Further, habit is significantly associated with range size,
 with trees having on average larger range sizes than shrubs, lianas and
 geoxyles, but biome was not correlated with range size. Cultivated species
 have ranges ~10 times that of non-cultivated tree species and with
 significantly different and broader environmental niches.
 Conclusion:  The unusually wide distribution of Ziziphus can be
 explained by its diversity of habits associated with different biomes
 spanning continents. This, along with the usage of many Ziziphus species
 by people for their fruits, expands the range and environmental occupation
 of the genus.
description: We curated species occurrence records that resulted in a
 taxonomically verified database of 1847 unique records for 50 species of
 <em>Ziziphus</em>. We primarily used the BIEN package v1.2.4
 (downloaded 9 December 2020) which integrates global botanical observation
 data from sources such as plot data, herbaria, and specimen records and
 where data have undergone additional taxonomic and spatial verification to
 that supplied by GBIF (The Global Biodiversity Information Facility 2021)
 (Maitner et al 2017). Following Meyer, Diniz-Filho and Lohmann (2017),
 where species had &lt;10 geolocations, records were added from a
 combination of georeferenced herbarium specimens and from additional GBIF
 data (Table S1). For three species (<em>Z. apetala, Z.
 hoaensis</em>, and <em>Z. linnae</em>i) no geographic
 information was available, possibly due to a combination of factors; the
 tropics are undercollected (Prance et al 2000), the availability of
 digitized herbarium specimens varies greatly, and digitized resources
 often suffer from a lack of maintenance and updating (Lughadha et al
 2018). Records without latitude and longitude were excluded as were
 specimens for the same occurrences, and the remaining spatially
 georeferenced records were cleaned by removing occurrences outside of the
 known distribution of the genus. Taxonomy was checked using the Taxonomic
 Name Resolution Service, Plants of the World Online, GBIF, and
 floras. Species of <em>Ziziphus </em>were
 assigned to biomes based on data from floras, peer-reviewed articles, grey
 literature such as doctoral dissertations, United Nation Development
 Programme (UNDP) reports, herbarium labels, and expert knowledge from Dr.
 Gopal Rawat (personal correspondence) (Table S4). Biomes were categorised
 as ‘open’, ‘closed’, and ‘desertic’. Following the typology of Earth’s
 ecosystems by Keith et al (2020) that groups ecosystems into biomes for
 the purpose of enabling comparative work, in the analyses here, closed
 biomes are analogous to T1 ‘tropical and subtropical forests’ that include
 lowland rainforests, tropical montane forests, tropical dry forests, and
 tropical heath forests. Desertic biomes are analogous to T5 ‘deserts and
 semi-deserts’, that includes semi-desert steppes, thorny deserts and
 semi-deserts, sclerophyll hot deserts and semi-deserts, cool deserts and
 semi-deserts, and hyper-arid deserts. Open biomes are analogous to T3
 ‘shrublands and shrubby woodlands’ and T4 ‘savannas and grasslands’
 following Bond (2019) as both ecosystems are mediated by similar processes
 (Keith et al 2020). These include seasonally dry tropical shrublands,
 seasonally dry temperate heaths and shrublands, cool temperate heathlands,
 rocky pavements, screes and lava flows, trophic savannas, pyric tussock
 savannas, hummock savannas, temperate woodlands, and temperate subhumid
 grasslands. Cultivated species and primary human uses
 were identified from peer-reviewed articles, floras, and grey literature
 such as a United States Department of Agriculture Handbook (Table S4).
 Following Flower et al (2021), we distinguished between species with no
 use or unknown uses, species which are widely used but not cultivated
 (harvested in situ), and species which are deliberately cultivated. Uses
 for non-cultivated species included spiritual, medicinal, edible, and wood
 for building or forage. Where multiple uses were listed for a species, the
 most common usage was selected.