Edaphic Specialization Research Articles

Reforestation of high elevation pines: Direct seeding success depends on seed source and sowing environment.

Forest persistence in regions impacted by increasing water and temperature stress will depend upon species' ability to either rapidly adjust to novel conditions or migrate to track ecological niches. Predicted, rapid climate change is likely to outpace the adaptive and migratory capacity of long-lived isolated tree species, and reforestation may be critical to species' persistence. Facilitating persistence both within and beyond a species' range requires identification of seed lots best adapted to the current and future conditions predicted with rapid climate change. We evaluate variation in emergent seedling performance that leads to differential survival among species and populations for three high elevation five-needle pines. We paired a fully reciprocal field common garden experiment with a greenhouse common garden study to (1) quantify variation in seedling emergence and functional traits, (2) ask how functional traits affect performance under different establishment conditions, and (3) evaluate whether trait and performance variation demonstrates local adaptation and plasticity. Among study species-limber, Great Basin bristlecone, and whitebark pines-we found divergence in emergence and functional traits, though soil moisture was the strongest driver of seedling emergence and abundance across all species. Generalist limber pine had a clear emergence advantage as well as traits associated with drought adaptation, while edaphic specialist bristlecone pine was characterized by low emergence yet high early survival once established. Despite evidence for edaphic specialization, soil characteristics alone did not explain bristlecone success. Across species, trait-environment relationships provided some evidence for local adaptation in drought-adapted traits, but we found no evidence of local adaptation in emergence or survival at this early life stage. For managers looking to promote persistence, sourcing seed from drier environments is likely to impart greater drought resistance into reforestation efforts through strategies such as greater root investment, increasing the probability of early seedling survival. This research demonstrates, through a rigorous reciprocal transplant experimental design, that it may be possible to select climate- and soil-appropriate seed sources for reforestation. However, planting success will ultimately rely on a suitable establishment environment, requiring careful consideration of interannual climate variability for management interventions in these climate and disturbance-impacted tree species.

Contrasting adaptive trait variation in response to drought in two Mediterranean shrubs

Adaptive evolution and phenotypic plasticity are key mechanisms of climate change responses. However, we still lack a detailed understanding of the strategies different species use to cope with climatic changes such as increased droughts, particularly for species with special edaphic requirements and limited dispersal such as gypsum endemics. In this study, we assessed phenotypic and genotypic selection, phenotypic plasticity and genetic variation in traits potentially related to drought response in two dominant gypsum Mediterranean species, Helianthemum squamatum and Centaurea hyssopifolia. We established a common garden in which 524 plants from 79 maternal families from both species were grown under two contrasting watering treatments. Our results revealed that selection was stronger under drought than well-watered conditions for both species, but we found contrasting adaptive strategies and genetic variation. In H. squamatum, a drought-escape strategy with advanced reproductive phenology and faster growth rates was positively associated with fitness under dry conditions, and most adaptive traits exhibited quantitative genetic variation. In contrast, in C. hyssopifolia, selection under dry conditions favored a drought-tolerance strategy with thicker leaves and longer phenologies, but all traits lacked quantitative genetic variation, indicating that their evolutionary potential may be limited. Most traits exhibited significant plasticity in response to drought and genetic variation for trait plasticity in both species, indicating that trait plasticity can evolve independently of the evolution of trait means in these gypsophiles. Our results show that these gypsum endemic species vary in strategies and adaptive potential in response to drought, which contributes to our understanding of potential adaptive responses to climate change in such edaphic specialists.

Edaphic specialization onto bare, rocky outcrops as a factor in the evolution of desert angiosperms

Understanding the processes that enable organisms to shift into more arid environments as they emerge is critical for gauging resilience to climate change, yet these forces remain poorly known. In a comprehensive clade-based study, we investigate recent shifts into North American deserts in the rock daisies (tribe Perityleae), a diverse tribe of desert sunflowers (Compositae). We sample rock daisies across two separate contact zones between tropical deciduous forest and desert biomes in western North America and infer a time-calibrated phylogeny based on target capture sequence data. We infer biome shifts using Bayesian inference with paleobiome-informed models and find evidence for seven independent shifts into desert habitats since the onset of aridification in the late Miocene. The earliest shift occurred out of tropical deciduous forests and led to an extensive radiation throughout North American deserts that accounts for the majority of extant desert rock daisies. Estimates of life history and micro-habitat in the rock daisies reveal a correlation between a suffrutescent perennial life history and edaphic endemism onto rocky outcrops, an ecological specialization that evolved prior to establishment and diversification in deserts. That the insular radiation of desert rock daisies stemmed from ancestors preadapted for dry conditions as edaphic endemics in otherwise densely vegetated tropical deciduous forests in northwest Mexico underscores the crucial role of exaptation and dispersal for shifts into arid environments.

Limited seed dispersal distance in endemic species from tropical mountaintop grasslands may restrict upward migration in response to climate change

Understanding dispersal systems is a key step towards improving our ability to predict species migration trajectories in response to climate change. However, the abiotic seed dispersal systems of tropical plants remain largely overlooked, with studies inferring seed dispersal from fruit morphology than conducting empirical tests. Here, we determined seed dispersal season experimentally tested the seed dispersal mode, and estimated dispersal distance kernels for five edaphic specialists, mountaintop endemics from campo rupestre, a tropical, megadiverse and nutrient-impoverished grassland. We monitored fruiting phenology for 12 months and established field and laboratory experiments to assess the role of abiotic factors in releasing seeds from dry capsules and to measure seed dispersal distance. Contrary to previous studies that suggested abiotic dispersal, we found no evidence of water- or wind-operated primary seed dispersal mechanisms for all species. We show that fruiting peaks coincided with optimum conditions for seedling establishment, and that short seed dispersal distances are consistent with the idea of reduced dispersibility in edaphic specialists. Seed buoyancy experiments show a large potential for secondary seed dispersal by water run-off. Our data suggest that abiotic dispersal in the study species plays a limited role in displacing seeds away from parental plants, a pattern that markedly contrasts with that found in other vegetation types. Short-distance dispersal in campo rupestre is consistent with theory explaining the evolution of phylomatry, but it also represents reason for concern of species migration in face of global climate changes. The combination of edaphic endemism and limited dispersal in mountaintops species provides limited opportunity for migration and poses a significant threat to their long-term survival.

Pronounced Genetic Separation Among Varieties of the Primula cusickiana Species Complex, a Great Basin Endemic

Abstract— Distinguishing between populations with strong genetic structure and unique species is a common challenge in systematics, especially for taxa occurring in fragmented habitats where allopatric speciation may be widespread and distinct groups may be morphologically similar. Such is often the case with species complexes across sky island environments. In these scenarios, biogeography may help to explain the taxonomic relations between species complex members, and restriction site-associated DNA (RAD) sequencing methods are commonly used to compare closely related taxa across thousands of loci. Here we use RADseq to clarify the boundaries separating the geographically distinct but morphologically similar varieties of the Primula cusickiana species complex, and to contextualize past findings of strong genetic structure among populations within varieties. Our genetic analyses demonstrate pronounced separation between isolated populations of this Great Basin endemic, indicating that the current varietal classification of complex members is inaccurate, and emphasizing their conservation importance. We discuss how these results correspond to recent biogeographical models used to describe the distribution of other sky island taxa in western North America. Our findings also fit into a wider trend observed for alpine Primula species complexes, and we consider how edaphic specialization and heterostylous breeding systems may be contributing to frequent diversification via allopatric speciation in this genus.

Target Enrichment and Extensive Population Sampling Help Untangle the Recent, Rapid Radiation of Oenothera Sect. Calylophus.

Oenothera sect. Calylophus is a North American group of 13 recognized taxa in the evening primrose family (Onagraceae) with an evolutionary history that may include independent origins of bee pollination, edaphic endemism, and permanent translocation heterozygosity. Like other groups that radiated relatively recently and rapidly, taxon boundaries within Oenothera sect. Calylophus have remained challenging to circumscribe. In this study, we used target enrichment, flanking noncoding regions, gene tree/species tree methods, tests for gene flow modified for target-enrichment data, and morphometric analysis to reconstruct phylogenetic hypotheses, evaluate current taxon circumscriptions, and examine character evolution in Oenothera sect. Calylophus. Because sect. Calylophus comprises a clade with a relatively restricted geographic range, we were able to extensively sample across the range of geographic, edaphic, and morphological diversity in the group. We found that the combination of exons and flanking noncoding regions led to improved support for species relationships. We reconstructed potential hybrid origins of some accessions and note that if processes such as hybridization are not taken into account, the number of inferred evolutionary transitions may be artificially inflated. We recovered strong evidence for multiple evolutionary origins of bee pollination from ancestral hawkmoth pollination, edaphic specialization on gypsum, and permanent translocation heterozygosity. This study applies newly emerging techniques alongside dense infraspecific sampling and morphological analyses to effectively reconstruct the recalcitrant history of a rapid radiation. [Gypsum endemism; Oenothera sect. Calylophus; Onagraceae; phylogenomics; pollinator shift; recent radiation; target enrichment.].

Cacti in the Mazapil Region, Chihuahuan Desert, Mexico: Diversity, Geographical Patterns and Conservation

The Chihuahuan Desert Region (CDR) is the largest desert area in North America, and the southeastern portions contain the richest areas in Cactaceae in the continent. This research was advocated to understand the diversity of cacti in northern Zacatecas and southern Coahuila, as well as to explore species rarity, environmental relations and conservation alternatives. A geographical square measuring a quarter degree was intensively surveyed through 50, 3-km long transects, distributed in 25, 6-minute sub-squares. The geographical square was selected because of its altitudinal and environmental heterogeneity. Cacti were identified and local rareness observed, 764 specimens were deposited at the National Herbarium of Mexico (MEXU). Specimen and locality information were captured in the Database for Cacti of Central and North America. A general evaluation of the cactus diversity (species richness), levels of endemism and rarity were performed. A total of 45 species were found, just below El Huizache, Tolimán and Mier y Noriega, with 7 new records for Zacatecas, 2 for Coahuila and 3 for both Mexican states. We found 26 endemic species from the CDR, five endemic to the Main and Meridional subregions and 21 endemic to the Main subregion, sensu Hernández. Two species are endemic to the state of Zacatecas and three species are endemic to both states. A new index for rarity (Average rarity, Ar) is presented, obtained as the mean of five variables: level of endemism, species relative frequencies, local rareness, and climatic and edaphic (soil) specialization. Rabinowitz rarity (1981) was calculated for all species and transformed into numerical values to compare it with the obtained Ar values. There are 26 rare species following Rabinowitz and 16 rare species following Ar (≥0.5). Ar values resulted smooth and with a higher explanation power (r2). Just five species resulted with a Rabinowitz rarity of 7 (transformed R of 1) and Ar (≥0.82). A general complementarity analysis was used to address conservation in the studied area, which was enhanced with other four complementarity analyses, including our Ar. Nine sub-squares were found relevant for cacti protection. Soil types and a complete climatic analysis from original data were used to search for environmental relations through Principal Component Analyses. The main preferences for climatic variables and anomalies are highlighted. The Ar index is an adequate tool for measuring species rarity and presents it in a balanced and smooth way, not just fixed Rabinowitz categories, allowing the understanding that some species might be rare in different ways in different areas and environmental conditions, something that seems to occur in cacti. Further research is encouraged on Ar for comparisons and even mapping, as well as for Natural Protected Areas (NPA) design.

Plant mortality on ultramafic soils after an extreme heat and drought event in the Mediterranean area

AimsPlant mortality associated with the growing frequency and intensity of heatwaves and dry spells is increasingly occurring in various ecosystems worldwide. However, the impacts of extreme events on plant communities of ultramafic soils are still unknown. Here, we describe a first case of plant mortality on serpentine outcrops in Italy following a heat and drought event that occurred between autumn 2016 and summer 2017.MethodsMortality of perennial plants was assessed in thirty plots representing ten major serpentine areas along a SW-NE gradient, with the sparse vegetation of ultramafic soils. Statistical modelling was based on temperature and precipitation data and local site conditions.ResultsResponses of single species were largely different and not related to their taxonomic position, growth form or level of edaphic specialization for serpentine soils. Notably, obligate serpentine endemics were not less impacted than non-endemics. As expected, species mortality decreased with increasing chromosome number, suggesting higher tolerance and adaptive capacity in taxa of likely polyploid origin. Mortality increased with decreasing number of rainy days and duration of the heatwave and decreased with increasing distance from the Tyrrhenian coastline, reaching 60% in the southern and western areas with a Mediterranean climate. Local site conditions such as increasing soil depth and north-facing aspect significantly increased plant survivorship.ConclusionsOur findings show that extreme drought and heat can have a previously unrealized impact on ultramafic plant communities in the short term. Further studies should examine the recovery capacity and resilience of serpentine plants, together with the long term effects.

Gene flow, linked selection, and divergent sorting of ancient polymorphism shape genomic divergence landscape in a group of edaphic specialists.

Interpreting the formation of genomic variation landscape, especially genomic regions with elevated differentiation (i.e. islands), is fundamental to a better understanding of the genomic consequences of adaptation and speciation. Edaphic islands provide excellent systems for understanding the interplay of gene flow and selection in driving population divergence and speciation. However, discerning the relative contribution of these factors that modify patterns of genomic variation remains difficult. We analysed 132genomes from five recently divergent species in Primulina genus, with four species distributed in Karst limestone habitats and the fifth one growing in Danxia habitats. We demonstrated that both gene flow and linked selection have contributed to genome-wide variation landscape, where genomic regions with elevated differentiation (i.e., islands) were largely derived by divergent sorting of ancient polymorphism. Specifically, we identified several lineage-specific genomic islands that might have facilitated adaptation of P. suichuanensis to Danxia habitats. Our study is amongst the first cases disentangling evolutionary processes that shape genomic variation of plant specialists, and demonstrates the important role of ancient polymorphism in the formation of genomic islands that potentially mediate adaptation and speciation of endemic plants in special soil habitats.

Elucidating the Evolutionary History ofOenotheraSect.Pachylophus(Onagraceae): A Phylogenomic Approach

Abstract—Oenotherasect.Pachylophushas proven to be a valuable system in which to study plant-insect coevolution and the drivers of variation in floral morphology and scent. Current species circumscriptions based on morphological characteristics suggest that the section consists of five species, one of which is subdivided into five subspecies. Previous attempts to understand species (and subspecies) relationships at a molecular level have been largely unsuccessful due to high levels of incomplete lineage sorting and limited phylogenetic signal from slowly evolving gene regions. In the present study, target enrichment was used to sequence 322 conserved protein-coding nuclear genes from 50 individuals spanning the geographic range ofOenotherasect.Pachylophus, with species trees inferred using concatenation and coalescent-based methods. Our findings concur with previous research in suggesting thatO. psammophilaandO. harringtoniiare nested within a paraphyleticOenothera cespitosa. By contrast, our results show clearly that the two annual species (O. cavernaeandO. brandegeei) did not arise from theO. cespitosalineage, but rather from a common ancestor ofOenotherasect.Pachylophus. Budding speciation as a result of edaphic specialization appears to best explain the evolution of the narrow endemic speciesO. harringtoniiandO. psammophila. Complete understanding of possible introgression among subspecies ofO. cespitosawill require broader sampling across the full geographical and ecological ranges of these taxa.

Population biology and ecology of the endangered Euphorbia susannae Marloth, an endemic to the Little Karoo, South Africa

Abstract. Jabar L, Siebert SJ, Pfab MF, Cilliers DP. 2021. Population biology and ecology of the endangered Euphorbia susannae Marloth, an endemic to the Little Karoo, South Africa. Biodiversitas 22: 4583-4596. Many euphorbias in the semi-arid parts of South Africa are restricted edaphic specialists with small populations at risk of extinction. Euphorbia susannae is one such species, which grows on the edges of quartz patches along a section of the northern foot slopes of the Langeberg Mountains. This study set out to acquire data on the biology and ecology of the species during a first-ever comprehensive field survey. The resultant dataset allowed for the determination of the geographic distribution of the species, as well as the size and number of populations. Biotic and abiotic environmental variables were employed to generate a habitat profile and a species distribution model. The population structure, regeneration potential, and stability of each subpopulation and the population were also assessed. Euphorbia susannae is a range-restricted species (EOO 170 km2 and AOO 36 km2) confined to eight subpopulations that vary considerably in size. According to this study, 1845 individuals remain in the wild. Habitat preferences of the species were considered in detail and linked to a species distribution model for conservation purposes. It was shown that the species preferred nurse plants. The smallest adults size class was the largest cohort in all the sub-populations and was ascribed to pulse recruitments after an unknown favorable event. Although individuals were not evenly distributed among the size classes, annual recruitments levels were healthy, suggesting good pollination, seed set, and germination conditions.

Edaphic specialization and vegetation zones define elevational range‐sizes for Mt Kinabalu regional flora

Identifying physical and ecological boundaries that limit where species can occur is important for predicting how those species will respond to global change. The island of Borneo encompasses a wide range of habitats that support some of the highest richness on Earth, making it an ideal location for investigating ecological mechanisms underlying broad patterns of species distribution. We tested variation in richness and range‐size in relation to edaphic specialization and vegetation zone boundaries using 3060 plant species from 193 families centered around the elevational gradient of Mt Kinabalu, Borneo. Across species, average range‐size increased with elevation, consistent with Rapoport's rule. However, plants associated with ultramafic soil, which is low in nutrient and water availability and often has high concentrations of heavy metals, had larger range‐sizes and greater richness than expected along the elevational gradient, as compared to a null model with randomization of edaphic association. In contrast, non‐ultramafic species had smaller range‐sizes and lower richness than expected. These results suggest that tolerance of resource limitation may be associated with wider range‐sizes, whereas species intolerant of edaphic stress may have narrower range‐sizes, possibly owing to more intense competition in favorable soil types. Using elevation as a predictor of average range‐sizes, we found that piece‐wise models with breakpoints at vegetation zone transitions explained species distributions better than models that did not incorporate ecological boundaries. The greatest relative increases in range‐size with respect to elevation occurred mid‐elevation, within the montane cloud forest vegetation zone. Expansion of average range‐size across an area without physical boundaries may indicate a shift in ecological strategy and importance of biotic versus abiotic stressors. Our results indicate that elevational range‐size patterns are structured by ecological constraints such as species' edaphic association, which may limit the ability of species to migrate up or down mountains in response to climate change.

Phylogeography of a gypsum endemic plant across its entire distribution range in the western Mediterranean.

Gypsum soils in the Mediterranean Basin house large numbers of edaphic specialists that are adapted to stressful environments. The evolutionary history and standing genetic variation of these taxa have been influenced by the geological and paleoclimatic complexity of this area and the long-standing effect of human activities. However, little is known about the origin of Mediterranean gypsophiles and the factors affecting their genetic diversity and population structure. Using phylogenetic and phylogeographic approaches based on microsatellites and sequence data from nuclear and chloroplast regions, we evaluated the divergence time, genetic diversity, and population structure of 27 different populations of the widespread Iberian gypsophile Lepidium subulatum throughout its entire geographic range. Lepidium subulatum diverged from its nearest relatives ~3 million years ago, and ITS and psbA/matK trees supported the monophyly of the species. These results suggest that both geological and climatic changes in the region around the Plio-Pleistocene promoted its origin, compared to other evolutionary processes. We found high genetic diversity in both nuclear and chloroplast markers, but a greater population structure in the chloroplast data. These results suggest that while seed dispersal is limited, pollen flow may be favored by the presence of numerous habitat patches that enhance the movement of pollinators. Despite being an edaphic endemic, L. subulatum possesses high genetic diversity probably related to its relatively old age and high population sizes across its range. Our study highlights the value of using different markers to fully understand the phylogeographic history of plant species.

Morphological and molecular data support recognition of Spergularia quartzicola (Caryophyllaceae) as a new species endemic to South Africa

A new species, Spergularia quartzicola, is described from the quartz outcrops of Knersvlakte (Namaqualand, South Africa). It was sometimes confused with S. media because of perennial habit and white flowers, but the new species differs by the subshrubby, strongly woody at base, habit (vs. herbaceous, suffruticose at the base); the leaves with a long mucro and stipules narrowly triangular and acuminate (vs. leaves with minute or absent mucro, and stipules broadly triangular and not acuminate); the flowers with styles fused in a long column (vs. styles entirely free), and the seeds with deeply and irregularly lacerate wing (vs. wing entire or slightly eroded). This combination of characters is unique among the known South African relatives. Our trnL-trnF and 5.8-ITS2 phylogenetic trees place S. quartzicola together with the South African S. glandulosa and S. namaquensis in an unresolved clade, which is far from the group of S. media. Furthermore, the outstanding morphological, ecological and chorological divergence exhibited by S. quartzicola support its recognition at species rank. According to the data presented here, S. quartzicola should be considered an edaphic specialist, which might have arisen following ecological diversification on Knersvlakte quartz outcrops, as it occurred in other taxa endemic to that territory.

How specialized is a soil specialist? Early life history responses of a rare Eriogonum to site-level variation in volcanic soils.

Understanding edaphic specialization is crucial for conserving rare plants that may need relocation due to habitat loss. Focusing on Eriogonum crosbyae, a rare soil specialist in the Great Basin of the United States, we asked how site-level variation among volcanic soil outcrops affected plant growth and population distribution. We measured emergence, survival, size, and biomass allocation of E. crosbyae seedlings planted in soils collected from 42 outcrops of actual and potential habitat. We also measured phenotypic variation in the wild, documented abiotic and biotic components of E. crosbyae habitat, re-surveyed Nevada populations, and evaluated occupancy changes over time. Plants responded plastically to edaphic variation, growing larger and allocating relatively more to aboveground tissues in soils with greater nutrient availability and growing smaller in soils higher in copper in the field and the greenhouse. However, the chemical and physical soil properties we measured did not predict site occupancy, nor was plant phenotype in the greenhouse different when plants were grown in soils from sites with different occupation status. We observed occupation status reversals at five locations. Eriogonum crosbyae performed well in soils formed on hydrothermally altered rocks that are inhospitable to many other plants. Extirpation/colonization events observed were consistent with metapopulation dynamics, which may partially explain the patchy distribution of E. crosbyae among outcrops of potential habitat. While soil properties did not predict site occupancy, early life stages showed sensitivity to soil variation, indicating that seedling dynamics may be important to consider for the conservation of this soil specialist.

Floristics of forests across low nutrient soils in Sulawesi, Indonesia

AbstractThe island of Sulawesi formed from the joining of proto‐islands roughly three million years ago. Regions of zoological endemism, corresponding to the proto‐islands, have been reported. Sulawesi's tree communities, however, remain poorly documented. In better‐studied tropical regions, soil types similar to those found in Sulawesi often have distinctive tree communities. To gather data on Sulawesi's tree communities, we established ten (0.25 ha) plots on four soil types across three regions. We documented diversity, endemism, dominance, and species composition. Linear models of species composition showed greater influence of geographic distance rather than soil, and no relationship with climate. This suggests that the legacy of Sulawesi's formation may have influenced tree communities more so than the soil types we sampled. Most of our plots were on stressful soil types making it difficult to conclude on the importance of edaphic specialization in the Sulawesi tree flora. The lack of climatic effects reflects Sulawesi's position within the wet tropics where the small climatic differences are unlikely to have large influence on tree communities.Abstract in Indonesian is available with online material.

Genetic consequences of plant edaphic specialization to solfatara fields: Phylogenetic and population genetic analysis of Carex angustisquama (Cyperaceae).

Edaphic specialization is one of the main drivers of plant diversification and has multifaceted effects on population dynamics. Carex angustisquama is a sedge plant growing only on heavily acidified soil in solfatara fields, where only extremophytes can survive. Because of the lack of closely related species in similar habitats and its disjunct distribution, the species offers ideal settings to investigate the effects of adaptation to solfatara fields and of historical biogeography on the genetic consequences of plant edaphic specialization to solfatara fields. Here, genome-wide single nucleotide polymorphisms were used to reveal the phylogenetic origin of C.angustisquama, and 16 expressed sequence tag-simple sequence repeat markers were employed to infer population demography of Cangustisquama. Molecular phylogenetic analysis strongly indicated that C.angustisquama formed a monophyletic clade with Carex doenitzii, a species growing on nonacidified soil in the sympatric subalpine zone. The result of population genetic analysis showed that C.angustisquama has much lower genetic diversity than the sister species, and notably, all 16 loci were completely homozygous in most individuals of C.angustisquama. Approximate Bayesian computation analysis supported the model that assumed hierarchical declines of population size through its evolutionary sequence. We propose that the edaphic specialist in solfatara fields has newly attained the adaptation to solfatara fields in the process of speciation. Furthermore, we found evidence of a drastic reduction in genetic diversity in C.angustisquama, suggesting that the repeated founder effects associated with edaphic specialization and subsequent population demography lead to the loss of genetic diversity of this extremophyte in solfatara fields.

Reciprocal extrapolation of species distribution models between two islands – Specialists perform better than generalists and geological data reduces prediction accuracy

Abstract This study aims to test the extrapolation effects of species distribution models (SDM) using three groups of predictor variables: climate, relief and geology (bedrock type). We highlight potential ecological differences for selected taxa, regarding both generalists and specialists in terms of edaphic conditions. We used distributional data of 12 woody species shared by two large Mediterranean islands (Crete and Sicily) to calibrate Maxent models of their potential distribution. We trained models with data from Crete and extrapolated to Sicily and vice versa. We tested ten proxies for the three variable groups and compared AUC values as a measure of model performance. Extrapolation of SDMs worked fairly well across species and islands for those models including climatic and relief data, while those including geological information performed worse for the tested species. Edaphic generalists performed less well compared to edaphic specialists. The latter performed best with climate data included in models and more poorly with only geological data. This may be due to differences in bedrock type affinities of species between the two islands.

Adaptation and divergence in edaphic specialists and generalists: serpentine soil endemics in the California flora occur in barer serpentine habitats with lower soil calcium levels than serpentine tolerators.

Adaptation to harsh edaphic substrates has repeatedly led to the evolution of edaphic specialists and generalists. Yet, it is unclear what factors promote specialization versus generalization. Here, we search for habitat use patterns associated with serpentine endemics (specialists) and serpentine tolerators (generalists) to indirectly test the hypothesis that trade-offs associated with serpentine adaptation promote specialization. We predict that (1) endemics have adapted to chemically harsher and more bare serpentine habitats than tolerators, and (2) edaphic endemics show more habitat divergence from their sister species than tolerators do among on- and off-serpentine populations. We selected 8 serpentine endemic and 9 serpentine tolerator species representing independent adaptation to serpentine. We characterized soil chemistry and microhabitat bareness from one serpentine taxon of each species and from a paired nonserpentine sister taxon, resulting in 8 endemic and 9 tolerator sister-taxa pairs. We find endemic serpentine taxa occur in serpentine habitats averaging twice as much bare ground as tolerator serpentine taxa and 25% less soil calcium, a limiting macronutrient in serpentine soils. We do not find strong evidence that habitat divergence between sister taxa of endemic pairs is greater than between sister taxa of tolerator pairs. These results suggest serpentine endemism is associated with adaptation to chemically harsher and more bare serpentine habitats. It may be that this adaptation trades off with competitive ability, which would support the longstanding, but rarely tested, competitive trade-off hypothesis.

Edaphic specialization in relation to termite mounds in Katanga (DR Congo): A reciprocal transplant experiment with congeneric tree species

AbstractQuestionDo termitophilous and non‐termitophilous trees of dry tropical woodlands show local adaptation?LocationRegion of Lubumbashi, Upper Katanga, DR Congo.MethodsThree pairs of congeneric tree species showing strict edaphic specialization with respect to termite mounds, Combretum molle (termitophilous, T)/C. collinum (non‐termitophilous, NT); Strychnos potatorum (T)/S. spinosa (NT), Ziziphus mucronata (T)/Z. abyssinica (NT), were used in a reciprocal transplant experiment in situ. Seedlings were reciprocally transplanted on termite mounds and in the surrounding matrix in a miombo woodland. Growth (height and number of leaves) and survival were monitored for 30 months. Soil physical and chemical properties, and available water, were assessed on and off mounds.ResultsGrowth was little affected by habitat; only one species showed better growth in its home habitat (S. spinosa in the matrix). Survival was strongly affected by habitat, in opposite directions consistent with species’ habitat specialization. Termitophilous species experienced a very high mortality rate in the matrix, especially during the dry season. Available water content was higher in termite mound soil than in the matrix soil.ConclusionsTermitophilous and non‐termitophilous tree species show local adaptation at the seedling stage, expressed mostly as different patterns of mortality in the dry season. The results point to water supply as a critical factor in the edaphic specialization of termitophilous species. In contrast, the higher mortality of non‐termitophilous species on termite mounds is not explained by water stress.