Climatic niche limits and community‐level vulnerability of obligate symbioses

Abstract

Aim Communities with many species at their climatic niche limits may be vulnerable to species losses, suggesting that niche‐based measures can inform vulnerability assessments. We aimed to quantify spatial variation in community‐level vulnerability indices based on niche limits, not just central tendencies, to predict where climate changes will produce rapid, pronounced shifts in ecological communities. Location North America. Taxon Epiphytic lichenized fungi. Methods We integrated broad‐extent herbarium data (46,343 North American sites, for estimation of realized niches) with systematic, whole‐community macrolichen surveys from the U.S. Forest Inventory and Analysis inventory (6,474 U.S. sites, for standardized vulnerability estimation). We introduce three niche‐based vulnerability indices describing (a) percentage of vulnerable species occurring at their upper climatic limits, (b) community‐mean percentile, and (c) deviation of local conditions from community‐mean upper limits. We also performed sensitivity analyses and evaluated vulnerability in future climate change scenarios. Results Sensitivity of indices to uncertainty in climate variables was minor. Present‐day vulnerability was greatest in north‐central California, in the Southwest along the western Colorado Plateau, and on the Southeastern coastal plain—locations where climatically‐induced compositional changes will become most evident. Under future warming scenarios (+0.5 to + 3.6°C increases), the percentage of U.S. epiphytic macrolichen communities exceeding critical values grew from about 2%–20%. Main conclusions In all scenarios the most vulnerable communities were concentrated in low‐elevation and southerly locations, suggesting that many ostensibly “warm‐adapted” communities may be close to exceeding their climatic limits. Findings indicate that warming and moisture changes will modify community compositions through the local loss of intolerant species pushed beyond their niche limits. Assessing vulnerability of bioindicators such as lichens will help prioritize locations where the greatest climate‐induced changes in species distributions and diversity will occur.

Towards understanding diversity, endemicity and global change vulnerability of soil fungi

“…Communities with many species at their environmental niche limits may be particularly vulnerable to local extinctions (Watson et al 2013; Smith et al 2020b). Thus, we evaluated the relative vulnerability of soil fungal functional groups by estimating the percentage of species occurring at their upper niche limits to three major global change drivers – land use (land cover change), heat (maximum monthly temperature), and drought (lowest quarterly precipitation).…”

“…The vulnerability of soil fungal groups was estimated relative to three global change drivers – heat (maximum monthly temperature), drought (negative of inverse hyperbolic sine-transformed precipitation in the driest quarter), and land cover change – for the year 2070 (relative to 2015 baseline) using the community-mean percentile vulnerability index (V 2 ; Smith et al 2020b). This index is based on averaging percentiles of all species at a given global change driver value.…”

Global diversity and ecological drivers of lichenised soil fungi

“…Our results are in accordance with previous studies indicating the relatively high richness of lichenised fungi in Europe and Africa, but relatively low richness in South America (Will‐Wolf et al ., 2004; Bowker et al ., 2016; Rodriguez‐Caballero et al ., 2018). Disjunct global distribution patterns of lichenised soil fungi are likely to be related to distinct climatic characteristics across continents (Will‐Wolf et al ., 2004; Tedersoo et al ., 2014; Alatalo et al ., 2017; Smith et al ., 2020). For example, Africa had relatively high annual mean temperature and aridity (i.e.…”

Resilience of Epiphytic Lichens to Combined Effects of Increasing Nitrogen and Solar Radiation

“…Likewise, the increased temperature has also been highlighted as a major damaging factor for epiphytic lichen vitality. Smith and collaborators [ 55 ] found that warm climate tolerant lichen communities are already close to exceeding their upper climatic limits and are even more vulnerable to increased temperatures than high-elevation lichens. Our experimental design, which accounted for exposing wet lichens to direct solar radiation, does not allow us to discriminate between the effect of increased radiation and temperature.…”