Ectomycorrhizal fungal richness declines towards the host species’ range edge

Lankau, Richard A.; Keymer, Daniel P.

doi:10.1111/mec.13628

Cited by 41 publications

(35 citation statements)

References 67 publications

(162 reference statements)

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“…Taxa identified as “other” ( N = 6 OTUs) and “undetermined” ( N = 27 OTUs) were excluded from further guild‐based analyses. We considered only FUNGuild assignments with a confidence score of “probable” or “highly probable” and classified taxa with assignment scores below these as undetermined (Lankau & Keymer, ). FUNGuild did not identify any arbuscular mycorrhizal fungi in the dataset, and we therefore exclude this guild from further analyses.…”

Section: Methodsmentioning

confidence: 99%

Plant–soil feedbacks mediate shrub expansion in declining forests, but only in the right light

et al. 2017

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Abstract1. Contemporary global change, including the widespread mortality of foundation tree species, is altering ecosystems and plant communities at unprecedented rates.Plant-soil interactions drive myriad community dynamics, and we hypothesized that such interactions may be an important driver of succession following the loss of foundation tree species.2. We examined whether plant-soil biota interactions, in the context of a putatively important light gradient associated with foundation tree decline, mediate the expansion of Rhododendron maximum in southeastern US forests where Tsuga canadensis (eastern hemlock), a dominant foundation tree species, is in decline.Using an 11-month, controlled inoculation experiment paired with Illumina sequencing, we tested the following hypotheses: (1) Relative to conspecific (R. maximum-conditioned) soils, R. maximum seedlings have higher performance in soils conditioned by T. canadensis and lower performance in interspace soils (conditioned by neither T. canadensis nor R. maximum) due to variation in soil fungal biota, and (2) seedling performance is greater in high-light vs. low-light environments (matching environments under infested vs. uninfested T. canadensis crowns, respectively).3. In partial support of the first hypothesis, we found that R. maximum seedling performance was highest in T. canadensis-conditioned and R. maximum-conditioned soils and lowest in interspace soils. Mechanistically, soils conditioned by T. canadensis and R. maximum had more ericoid and ectomycorrhizal fungi, less saprotrophic fungi, and were less species-rich than interspace soils, and variation in these community traits predicted substantial variation in R. maximum seedling biomass.However, in support of our second hypothesis, soil effects on plant performance were evident in high light only; in low light, soil inoculation did not affect plant performance and plants performed worse on average.4. Synthesis. Our findings suggest that interactions with soil biota act synergistically with altered abiotic environments to mediate species responses to widespread foundation tree mortality, providing evidence for a novel mechanism of plant response to large-scale disturbance. Examining plant-soil interactions in the context of relevant abiotic gradients can, therefore, enhance our understanding, predictions and management of community development processes following forest disturbance.Paper previously published as Standard Paper

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Section: Methodsmentioning

confidence: 99%

Plant–soil feedbacks mediate shrub expansion in declining forests, but only in the right light

et al. 2017

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“…Rare species may, however, experience costs that outweigh the fitness gains of competitive release through a variety of mechanisms involving positive density-or frequency-dependence. Costs due to positive density-or Manuscript received 30 June 2018; revised 29 November frequency-dependence (PDD or PFD, respectively) include a range of Allee effects (reviewed in Taylor andHastings 2005, Berec et al 2007) including reproduction (e.g., a lack of mates when rare [Courchamp et al, 1999, Schreiber, 2003, Zhou and Zhang, 2006), survival (e.g., a loss of required mutualists [Nuñez et al, 2009, Chung and Rudgers, 2016, Lankau and Keymer, 2016 or a reduction in predator saturation [Schreiber, 2003, Gascoigne andLipcius, 2004]), and reduced vigor owing to inbreeding and genetic drift (Fischer et al, 2000, Willi et al, 2005. Thus, rarity may have costs that outweigh benefits.…”

Section: Introductionmentioning

confidence: 99%

When rarity has costs: coexistence under positive frequency‐dependence and environmental stochasticity

Schreiber

Yamamichi

Strauss

2019

Ecology

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Stable coexistence relies on negative frequency‐dependence, in which rarer species invading a patch benefit from a lack of conspecific competition experienced by residents. In nature, however, rarity can have costs, resulting in positive frequency‐dependence (PFD) particularly when species are rare. Many processes can cause positive frequency‐dependence, including a lack of mates, mutualist interactions, and reproductive interference from heterospecifics. When species become rare in the community, positive frequency‐dependence creates vulnerability to extinction, if frequencies drop below certain thresholds. For example, environmental fluctuations can drive species to low frequencies where they are then vulnerable to PFD. Here, we analyze deterministic and stochastic mathematical models of two species interacting through both PFD and resource competition in a Chessonian framework. Reproductive success of individuals in these models is reduced by a product of two terms: the reduction in fecundity due to PFD, and the reduction in fecundity due to competition. Consistent with classical coexistence theory, the effect of competition on individual reproductive success exhibits negative frequency‐dependence when individuals experience greater intraspecific competition than interspecific competition, i.e., niche overlap is less than one. In the absence of environmental fluctuations, our analysis reveals that (1) a synergistic effect of PFD and niche overlap that hastens exclusion, (2) trade‐offs between susceptibility to PFD and maximal fecundity can mediate coexistence, and (3) coexistence, when it occurs, requires that neither species is initially rare. Analysis of the stochastic model highlights that environmental fluctuations, unless perfectly correlated, coupled with PFD ultimately drive one species extinct. Over any given time frame, this extinction risk decreases with the correlation of the demographic responses of the two species to the environmental fluctuations, and increases with the temporal autocorrelation of these fluctuations. For species with overlapping generations, these trends in extinction risk persist despite the strength of the storage effect decreasing with correlated demographic responses and increasing with temporal autocorrelations. These results highlight how the presence of PFD may alter the outcomes predicted by modern coexistence mechanisms.

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“…As a general rule, however, widely dispersing symbionts are thought to be associated with a greater diversity of hosts than symbionts with limited dispersal (Herre et al, 1999;Roy et al, 2008). Biogeographic analyses of such microbial symbionts are often complicated by insufficient knowledge of species boundaries of microbial symbionts, requiring high-resolution genetic analyses to differentiate species and population boundaries (e.g., Douhan, Vincenot, Gryta, & Selosse, 2011;Gazis, Rehner, & Chaverri, 2011;Lankau & Keymer, 2016).…”

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confidence: 99%

Biogeography of mutualistic fungi cultivated by leafcutter ants

et al. 2017

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Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov-Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.

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Ectomycorrhizal fungal richness declines towards the host species’ range edge

Cited by 41 publications

References 67 publications

Plant–soil feedbacks mediate shrub expansion in declining forests, but only in the right light

Plant–soil feedbacks mediate shrub expansion in declining forests, but only in the right light

When rarity has costs: coexistence under positive frequency‐dependence and environmental stochasticity

Biogeography of mutualistic fungi cultivated by leafcutter ants

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