Fighting their last stand? A global analysis of the distribution and conservation status of gymnosperms

Abstract

Aim Gymnosperms are often described as a marginal and threatened group, members of which tend to be out-competed by angiosperms and which therefore preferentially persist at higher latitudes and elevations. The aim of our synthesis was to test these statements by investigating the global latitudinal and elevational distribution of gymnosperms, as well as their conservation status, using all extant gymnosperm groups (cycads, gnetophytes, ginkgophytes and conifers).Location Worldwide.Methods We developed a database of 1014 species of gymnosperms containing latitudinal and elevational distribution data, as well as their global conservation status, as described in the literature. The 1014 species comprised 305 cycads, 101 gnetophytes, the only living representative of ginkgophytes, and 607 conifers. Generalized additive models, frequency histograms, kernel density estimations and distribution maps based on Takhtajan's floristic regions were used.Results Although the diversity of gymnosperms decreases at equatorial latitudes, approximately 50% of the extant species occur primarily between the tropics. More than 43% of gymnosperms can occur at very low elevations (≤ 200 m a.s.l.). Gymnosperms, considering all species together as well as their main taxonomic groups separately, do not exhibit a latitudinal diversity gradient as commonly observed for many other taxa. Gymnosperms, and especially conifers, are on average less threatened at higher and equatorial latitudes.Main conclusions Gymnosperms display an unusual latitudinal diversity gradient, which we suggest cannot fully be accounted for by angiosperm dominance and competitive superiority. We hypothesize that other factors explain their present distribution, such as the development of centres of endemism in several regions and the adaptation of certain taxa to cold and arid climates.

Spatial and evolutionary parallelism between shade and drought tolerance explains the distributions of conifers in the conterminous United States

“…To conclude, in contrast to the angiosperms, many aspects of gymnosperm evolution, ecology and biogeography remain poorly studied (but see Leslie et al ., ; Fragnière et al ., ). Here, we have shown that the strong trade‐off between drought and shade tolerance, which is summarized in wood density as a key functional trait, is the simplest explanation for understanding the current distribution of conifers across southern North America.…”

Key environmental determinants of global and regional richness and endemism patterns for a wild bee subfamily

“…Patterns of bee species richness and endemism A general pattern of declining species diversity from the equator towards the poles holds on the global scale across multiple groups of organisms (Allen et al 2002;Hillebrand (Grenyer et al 2006), gymnosperms (Fragnière et al 2015), as well as some insect groups like aphids (Dixon et al 1987) and sawflies (Kouki et al 1994). Solitary bees appear to provide yet another example of such a reversed latitudinal gradient in species richness and endemism.…”

<b>Adventitious rooting of mature <I>Cycas micronesica</I> K.D. Hill (Cycadales: Cycadaceae) tree stems reveals moderate success for salvage of an endangered cycad</b>

“…Cycads are the most threatened group of plants, with more than 63% of described taxa listed as threatened (Brummitt et al 2015;Fragniere et al 2015). Published research on cycad horticulture and physiology has been inadequate (Cascasan & Marler 2016) even though past reports have illuminated that efforts to cultivate cycads to advance conservation efforts are hindered by the lack of research (Norstog & Nicholls 1997;Donaldson 2003).…”