Do lichens show latitudinal patterns of diversity?

Biodiversity gradients in obligate symbiotic organisms: exploring the diversity and traits of lichen propagules across the United States

“…A much smaller number of taxa including aquatic macrophytes and ichneumonid flies demonstrate exceptions to this pattern, having instead a ‘reverse’ latitudinal gradient (Hillebrand, ). Some microbial and fungal groups similarly do not follow a traditional latitudinal gradient: no correlations were found between soil bacterial diversity and latitude in North and South America (Fierer & Jackson, ), a reverse gradient was documented for ectomycorrhizal fungi (Tedersoo et al ., ), and a recent study in western North America demonstrated no clear relationship between latitude and lichen diversity (Holt et al ., ). We found evidence for a reverse gradient in this group of obligate symbiotic organisms as there was a significant, albeit weak, trend towards higher lichen richness based on reproductive propagules at higher latitudes (Fig.…”

“…Species inventories in North America suggest that lichen biodiversity hotspots are associated with areas of intact native habitat, especially those that contain a diversity of lichen substrates such as hardwoods, conifers and exposed rock (Spribille et al ., ; Lücking et al ., ; Tripp & Lendemer, ; Lendemer et al ., ; Lendemer & Allen, ). Yet, the more general biogeography and diversity gradients of North American lichens have been the focus of little empirical investigation (but see McCune et al ., ; Werth, ; Holt et al ., ). On a regional scale, recent study has found no significant link between latitude and lichen diversity, with the latter better explained by other factors linked to longitude such as precipitation and topography (Holt et al ., ).…”

“…Yet, the more general biogeography and diversity gradients of North American lichens have been the focus of little empirical investigation (but see McCune et al ., ; Werth, ; Holt et al ., ). On a regional scale, recent study has found no significant link between latitude and lichen diversity, with the latter better explained by other factors linked to longitude such as precipitation and topography (Holt et al ., ). However, a lack of study on continental or subcontinental scales precludes knowledge of whether lichen biodiversity across larger geographical scales follows the commonly observed latitudinal gradient, with species diversity increasing towards lower latitudes, or which biotic and abiotic factors most strongly impact lichen biogeography at larger scales of enquiry.…”

“…Empirical research on biodiversity gradients has focused almost exclusively on individual lineages (Hillebrand, ), such as birds, rather than on the varied obligate symbioses that abound in nature (e.g. Fabricius & De'ath, ; but see Holt et al ., ). Because the lichen symbiosis (i.e.…”

“…These patterns have been documented in just a few studies (e.g. Lücking, ; Werth, ; Leavitt et al ., ; Lendemer et al ., ; Holt et al ., ) and never in the context of the broader literature on the causes and origins of diversity gradients. In contrast, large‐scale distributions of many plant and animal taxa have been studied for decades (Pianka, ; Tiffney & Niklas, ; McCain, ), so much so that it is now just the causes of these diversity gradients (e.g.…”