Why are ferns regularly over‐represented on state and provincial rare plant lists?

Several recent studies have suggested that rare species are not randomly distributed throughout plant taxa. This would appear to apply to North American ferns, which are frequently over-represented on local lists of rare plant species. However, such lists often paint a skewed portrait of the true situation because of our tendency to recognize the rarity of well-known and charismatic species while ignoring that of lesser-known or less-appreciated species. In order to verify if this over-representation of ferns is a real and consistent trend throughout local floras in North America, we used data from what we consider to be the most complete and objective available database: NatureServe Explorer ( http://www.natureserve.org/explorer/ ). We compiled data on total vascular plant species, total fern species, as well as rare vascular plant species and rare fern species for each North American subnational (Canadian province or US state) flora. Rare species were defined as those belonging to one of NatureServe's 'at risk' categories. The null hypothesis that the contribution of rare ferns to total rare species did not differ from their contribution to the total vascular flora was assessed using χ². Out of 64 subnational floras, we obtained significantly higher values than expected in 28 cases, and significantly lower in only one case. Similar trends hold true for individual fern families. These tendencies could be related to several factors of anthropogenic, biological, climatological, evolutionary, and geographical origin. However, we believe that the main reason is related to scale, namely the geopolitical units at which rarity is often studied. Our results illustrate one of the problems of a parochial approach to conservation, where the perceived rarity of an entire taxon is exaggerated because of the scale at which rarity is addressed.     

Non-genetic inheritance and the patterns of antagonistic coevolution

ABSTRACT: BACKGROUND: Antagonistic species interactions can lead to coevolutionary genotype or phenotype frequency oscillations, with important implications for ecological and evolutionary processes. However, direct empirical evidence of such oscillations is rare. The rarity of observations is generally attributed to inherent difficulties of ecological and evolutionary long-term studies, to weak or absent interaction between species, or to the absence of negative frequency-dependence. RESULTS: Here, we show that another factor - non-genetic inheritance, mediated for example by epigenetic mechanisms - can completely eliminate oscillations even if only a small fraction of offspring are affected. We analytically derive the threshold value of this fraction at which the dynamics change from oscillatory to stable, and investigate how selection, mutation and generation times differences between the two species affect the threshold value. These results strongly suggest that the lack of phenotype frequency oscillations should not be attributed to the lack of strong interactions between antagonistic species. CONCLUSIONS: Given increasing evidence of non-genetic effects on the outcomes of antagonistic species interactions, we suggest that these effects should be incorporated into ecological and evolutionary models of interacting species.     

Functional rarity of plants in German hay meadows — Patterns on the species level and mismatches with community species richness

Functional rarity (FR) — a feature combining a species'' rarity with the distinctiveness of its traits — is a promising tool to better understand the ecological importance of rare species and consequently to protect functional diversity more efficiently. However, we lack a systematic understanding of FR on both the species level (which species are functionally rare and why) and the community level (how is FR associated with biodiversity and environmental conditions). Here, we quantify FR for 218 plant species from German hay meadows on a local, regional, and national scale by combining data from 6500 vegetation relevés and 15 ecologically relevant traits. We investigate the association between rarity and trait distinctiveness on different spatial scales via correlation measures and show which traits lead to low or high trait distinctiveness via distance‐based redundancy analysis. We test how species richness and FR are correlated, and use boosted regression trees to determine environmental conditions that are driving species richness and FR. On the local scale, only rare species showed high trait distinctiveness while on larger spatial scales rare and common species showed high trait distinctiveness. As infrequent trait attributes (e.g., legumes, low clonality) led to higher trait distinctiveness, we argue that functionally rare species are either specialists or transients. While specialists occupy a particular niche in hay meadows leading to lower rarity on larger spatial scales, transients display distinct but maladaptive traits resulting in high rarity across all spatial scales. More functionally rare species than expected by chance occurred in species‐poor communities indicating that they prefer environmental conditions differing from characteristic conditions of species‐rich hay meadows. Finally, we argue that functionally rare species are not necessarily relevant for nature conservation because many were transients from surrounding habitats. However, FR can facilitate our understanding of why species are rare in a habitat and under which conditions these species occur.     

Eutrophication and fragmentation are related to species’ rate of decline but not to species rarity: results from a functional approach

Due to ubiquitous eutrophication and fragmentation, many plant species are actually threatened in Europe. Most ecosystems face an overall nutrient input leading to changes in species composition. Fragmentation is effectively influencing species survival. We investigate if two different measures of species performance of 91 calcareous grassland species–rate of decline and rarity—are related to comparable traits and hence processes. On the one hand we expected that species rate of decline is mainly determined by the processes of eutrophication and fragmentation. On the other hand we hypothesized that the importance of site characteristics may overwhelm the effect of eutrophication and fragmentation for species rarity. Hence, we compared persistence traits responding to eutrophication, dispersal traits being related to fragmentation and ecological site factors for decreasing and increasing species and for rare and common species. The results suggest that increasing species had better means of long-distance dispersal and were more competitive than decreasing species. In contrast, there were hardly any differences in traits between rare and common species, but site characteristics were related to species rarity. Rare species were in the main those with ecological preferences for warm, dry, light and nutrient poor conditions. This study may represent a basis for the assessment of plant species threat. Applying the deduced knowledge about the life history of decreasing versus increasing species to habitat-scale approaches it is possible to predict which species may become threatened in the future simply from the combination of their trait values. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Book Review

Abstract

Most studies on population ecology of bryophytes have involved common species. However, some studies have compared life history strategies in rare and common species. We review the life history strategies (life expectancy, sexual and asexual reproduction, spore production, spore size and dispersal) for species that are rare in relation to pattern and persistency of suitable habitat patches. In particular, we discuss the dynamics on two levels, within and among localities, for different categories of rare species. We predict that most rare species will be found to have restricted dispersal capacities but higher than average life expectancies of local subpopulations. Natural rarity is distinguished from human-induced rarity and species rare for the latter reason are distinguished as 'threatened'.     

The value of structuring rarity: the seven types and links to reproductive ecology

Since 1981, 365 papers have cited a rarity matrix organized along three axes: geographic range (GR) (large vs. small), habitat specificity (HS) (specialist vs. generalist), and local abundance (LA) (dense vs. sparse). In the wider ecology literature, research on the association between plant species distributions and life history traits has mainly focused on a single axis such as GR. However, the internal structure of species ranges is widely recognized as important. In order to determine if identifying different types of rarity leads to alternative conclusions regarding the causes and consequences of rarity, we created a dataset linking the seven types of rarity matrix and to reproductive ecology traits. We found associations between the axes and these traits in a dataset of 101 rare plant species culled from 27 papers. Significant traits included mating system and seed dispersal mechanism. Species with small GR are more likely to have ballistic or wind dispersal than biotically-mediated dispersal (abiotic:biotic ratio 3:1). Habitat specialist species with small GRs are more likely to have outcrossing mating systems compared to habitat specialists of large GR (16:1). These results show that, within rare species, the structure of rarity is important (e.g. habitat specialization is different from small GR) and should be identified when determining basic mechanisms of plant distribution and abundance.     

Better common than rare? Effects of low reproductive success,scarce pollinator visits and interspecific gene flow in threatened and common species of Tibouchina (Melastomataceae)

The reasons for plant rarity have been the focus of many studies, especially because rare species are more prone to extinction than common species. Under the same habitat conditions, rare plants are expected to attract fewer flower visitors and to show some limitation in their reproductive success. Here, using one of the most emblematic Neotropical plant genus (Tibouchina) we tested whether narrow endemic and threatened species in Ecuador have a lower reproductive success or are visited by fewer pollinators than common species, in 13 populations monitored from 2011 to 2013. We also assessed whether interspecific gene flow could be considered a threat to the rare species. However, contrary to expectations, we found that few pollinators visited the flowers, independently of species rarity. Natural outcross pollinations were always very low in all small‐size populations, leading to high levels of pollen limitation. Interspecific crossing experiments also revealed weak reproductive barriers in some species. This study reveals that both narrow and common species of Tibouchina have similar reproductive and pollinator patterns in Ecuador and, therefore, other causes of the rarity of these species should be considered.     

Categorizing locally rare plant taxa for conservation status

Locally rare taxa are those that are rare or uncommon within a local geographical boundary while more common outside of that boundary. In addition to the rare taxa identified by global, national, and state/provincial levels, locally rare taxa are important for the preservation of species diversity and ecological processes, and therefore require effective and recognizable conservation status. Currently, there are no specific local rarity criteria in use to categorize taxa at regional jurisdictional levels. To address this need, we developed criteria for categorizing locally rare plant taxa by using the framework the Natural Heritage Network’s Element Ranking System combined with attributes of the World Conservation Union’s Red List Criteria. We then tested the efficacy of our classification system (called L-ranks) on the flora of Napa County using a geographic information system and available plant distribution data for the State of California. Results indicated that 89 taxa from 34 families met the area of occupancy criteria for local rarity status. Our findings demonstrated that with available geographic data, the proposed criteria for classifying locally rare plants can be usefully applied at the county level to identify significant peripheral plant populations. The proposed L-rank system was specifically designed to be compatible with existing multi-scale conservation programs and will augment the current systems in use by local organizations. By systematically classifying locally rare plants, current regulations that are applicable to locally rare taxa may be used more effectively in conservation planning and prioritizing at the county scale.     

Predicting loss of evolutionary history: Where are we?

The Earth's evolutionary history is threatened by species loss in the current sixth mass extinction event in Earth's history. Such extinction events not only eliminate species but also their unique evolutionary histories. Here we review the expected loss of Earth's evolutionary history quantified by phylogenetic diversity (PD) and evolutionary distinctiveness (ED) at risk. Due to the general paucity of data, global evolutionary history losses have been predicted for only a few groups, such as mammals, birds, amphibians, plants, corals and fishes. Among these groups, there is now empirical support that extinction threats are clustered on the phylogeny; however this is not always a sufficient condition to cause higher loss of phylogenetic diversity in comparison to a scenario of random extinctions. Extinctions of the most evolutionarily distinct species and the shape of phylogenetic trees are additional factors that can elevate losses of evolutionary history. Consequently, impacts of species extinctions differ among groups and regions, and even if global losses are low within large groups, losses can be high among subgroups or within some regions. Further, we show that PD and ED are poorly protected by current conservation practices. While evolutionary history can be indirectly protected by current conservation schemes, optimizing its preservation requires integrating phylogenetic indices with those that capture rarity and extinction risk. Measures based on PD and ED could bring solutions to conservation issues, however they are still rarely used in practice, probably because the reasons to protect evolutionary history are not clear for practitioners or due to a lack of data. However, important advances have been made in the availability of phylogenetic trees and methods for their construction, as well as assessments of extinction risk. Some challenges remain, and looking forward, research should prioritize the assessment of expected PD and ED loss for more taxonomic groups and test the assumption that preserving ED and PD also protects rare species and ecosystem services. Such research will be useful to inform and guide the conservation of Earth's biodiversity and the services it provides.     

Plant adaptation to climate change—Where are we?

Climate change poses critical challenges for population persistence in natural communities, for agriculture and environmental sustainability, and for food security. In this review, we discuss recent progress in climatic adaptation in plants. We evaluate whether climate change exerts novel selection and disrupts local adaptation, whether gene flow can facilitate adaptive responses to climate change, and whether adaptive phenotypic plasticity could sustain populations in the short term. Furthermore, we discuss how climate change influences species interactions. Through a more in‐depth understanding of these eco‐evolutionary dynamics, we will increase our capacity to predict the adaptive potential of plants under climate change. In addition, we review studies that dissect the genetic basis of plant adaptation to climate change. Finally, we highlight key research gaps, ranging from validating gene function to elucidating molecular mechanisms, expanding research systems from model species to other natural species, testing the fitness consequences of alleles in natural environments, and designing multifactorial studies that more closely reflect the complex and interactive effects of multiple climate change factors. By leveraging interdisciplinary tools (e.g., cutting‐edge omics toolkits, novel ecological strategies, newly developed genome editing technology), researchers can more accurately predict the probability that species can persist through this rapid and intense period of environmental change, as well as cultivate crops to withstand climate change, and conserve biodiversity in natural systems.     

Genetic consequences of habitat fragmentation in plant populations: susceptible signals in plant traits and methodological approaches

Conservation of genetic diversity, one of the three main forms of biodiversity, is a fundamental concern in conservation biology as it provides the raw material for evolutionary change and thus the potential to adapt to changing environments. By means of meta‐analyses, we tested the generality of the hypotheses that habitat fragmentation affects genetic diversity of plant populations and that certain life history and ecological traits of plants can determine differential susceptibility to genetic erosion in fragmented habitats. Additionally, we assessed whether certain methodological approaches used by authors influence the ability to detect fragmentation effects on plant genetic diversity. We found overall large and negative effects of fragmentation on genetic diversity and outcrossing rates but no effects on inbreeding coefficients. Significant increases in inbreeding coefficient in fragmented habitats were only observed in studies analyzing progenies. The mating system and the rarity status of plants explained the highest proportion of variation in the effect sizes among species. The age of the fragment was also decisive in explaining variability among effect sizes: the larger the number of generations elapsed in fragmentation conditions, the larger the negative magnitude of effect sizes on heterozygosity. Our results also suggest that fragmentation is shifting mating patterns towards increased selfing. We conclude that current conservation efforts in fragmented habitats should be focused on common or recently rare species and mainly outcrossing species and outline important issues that need to be addressed in future research on this area.     

Patterns of genetic variation in rare and widespread plant congeners

Rare species are typically considered to maintain low levels of genetic variation, and this view has been supported by several reviews of large numbers of isozyme studies. Although these reviews have provided valuable data on levels of variability in plant species in general, and rare species in particular, these broad overviews involve comparisons that may confound the effects of rarity with a multitude of other factors that affect genetic variability. Additionally, the statistical analyses employed assume the data to be independent, which is not the case for organisms that share a common phylogenetic history. As the role of evolutionary history and historical constraints has become better understood, more researchers have studied widespread congeners when investigating the genetic diversity of rare species in an effort to control for these effects. We summarize the available data from such studies, comparing for rare and widespread congeners (1) the levels of genetic variability at the population and species levels and (2) measures of population substructuring. At the population level, we summarized data for percentage polymorphic loci (%P(pop)), mean number of alleles per locus (A(pop)), and observed heterozygosity (H(o)). Species-level measures used were percentage polymorphic loci (%P(spp)), mean number of alleles per locus (A(spp)), and total genetic diversity (H(T)). Indices of population subdivision (either F(ST) or G(ST)) were also examined. Using Wilcoxon signed rank tests, we found significant, but small, differences between rare and widespread species for all diversity measures except H(T). However, there does not appear to be a difference between rare and widespread congeners in terms of how genetic variation is partitioned within and among populations. Levels of diversity, for all measures examined, between rare and widespread congeners are highly correlated.     

Are there adequate data to assess how well theories of rarity apply to marine invertebrates?

Understanding the biology of rare species is a very important part of conservation biology. Most of our current understanding of rarity has, however, come from studies of terrestrial plants, birds, mammals and some insects. Freshwater and marine habitats are underrepresented in published studies of rare species or conservation biology. We therefore have little knowledge about how well our understanding of what makes particular species rare and how rare species persist applies to marine invertebrates which form a major component of coastal biodiversity. In this review, I examine some theories about rarity with respect to intertidal and shallow subtidal invertebrates to identify whether there are adequate data to apply these theories to marine invertebrates and how well such theories apply. The general conclusions are that the lack of quantitative data on abundances, ranges, habitat-requirements, dispersal and connectedness among populations for marine invertebrates means that their status as rare species cannot really be assessed appropriately. It is also unlikely that, without extensive sampling programmes and considerable expense, adequate data could be obtained for these small, cryptic animals, which typically have very patchy, variable and unpredictable patterns of distribution and abundance. Intertidal and subtidal assemblages are diverse, including species with many different life-histories from many phyla, occupying the same suite of habitats. It is therefore suggested that future research on rare organisms in marine habitats should build upon the long and successful history of experimental marine studies to test specific hypotheses about processes influencing rarity in the field. Such studies would not only add a new dimension to our current understanding of rarity, but would also provide badly-needed data on the status of rare marine invertebrates. abundances, invertebrates, marine, range, rarity     

An evolutionary framework for understanding habitat partitioning in plants

Many plant species with overlapping geographic ranges segregate at smaller spatial scales. This spatial segregation—zonation when it follows an abiotic gradient and habitat partitioning when it does not—has been experimentally investigated for over a century often using distantly related taxa, such as different genera of algae or barnacles. In those foundational studies, trade-offs between stress tolerance and competitive ability were found to be the major driving factors of habitat partitioning for both animals and plants. Yet, the evolutionary relationships among segregating species are usually not taken into account. Since close relatives are hypothesized to compete more intensely and are more likely to interact during mating compared to distant relatives, the mechanisms underlying habitat partitioning may differ depending on the relatedness of the species in question. Here, I propose an integration of ecological and evolutionary factors contributing to habitat partitioning in plants, specifically how the relative contributions of factors predictably change with relatedness of taxa. Interspecific reproductive interactions in particular are understudied, yet important drivers of habitat partitioning. In spatially segregated species, interspecific mating can reduce the fitness of rare immigrants, preventing their establishment and maintaining patterns of spatial segregation. In this synthesis, I review the literature on mechanisms of habitat partitioning in plants within an evolutionary framework, identifying knowledge gaps and detailing future directions for this rapidly growing field of study.     

Future directions in the ontogeny of plant defence: understanding the evolutionary causes and consequences

Plant defence often varies by orders of magnitude as plants develop from the seedling to juvenile to mature and senescent stages. Ontogenetic trajectories can involve switches among defence traits, leading to complex shifting phenotypes across plant lifetimes. While considerable research has characterised ontogenetic trajectories for now hundreds of plant species, we still lack a clear understanding of the molecular, ecological and evolutionary factors driving these patterns. In this study, we identify several non‐mutually exclusive factors that may have led to the evolution of ontogenetic trajectories in plant defence, including developmental constraints, resource allocation costs, multi‐functionality of defence traits, and herbivore selection pressure. Evidence from recent physiological studies is highlighted to shed light on the underlying molecular mechanisms involved in the regulation and activation of these developmental changes. Overall, our goal is to promote new research avenues that would provide evidence for the factors that have promoted the evolution of this complex lifetime phenotype. Future research focusing on the questions and approaches identified here will advance the field and shed light on why defence traits shift so dramatically across plant ontogeny, a widespread but poorly understood ecological pattern.     

植物繁育系统研究的最新进展和评述

 植物繁育系统是当今进化生物学研究中最为活跃的领域。繁育系统是指代表所有影响后代遗传组成的有性特征的总和,主要包括花形态特征、花的开放式样、花各部位的寿命、传粉者种类和频率、自交亲和程度和交配系统,其中交配系统是核心。我们重点综述了植物 有性繁育系统研究中1）传粉模式的多样性,2）从历史发生角度利用系统发育方法检验花性状的演化和繁育系统的生态转变过程,3）近交衰退对植物生殖史的影响及其机制和4）混和交配系统的时空动态、维持机理以及进化趋势的最新研究结果。总结了繁育系统在研究花适应性、物种形成机制和濒危植物     

The contribution of rare species to community phylogenetic diversity across a global network of forest plots

Niche differentiation has been proposed as an explanation for rarity in species assemblages. To test this hypothesis requires quantifying the ecological similarity of species. This similarity can potentially be estimated by using phylogenetic relatedness. In this study, we predicted that if niche differentiation does explain the co-occurrence of rare and common species, then rare species should contribute greatly to the overall community phylogenetic diversity (PD), abundance will have phylogenetic signal, and common and rare species will be phylogenetically dissimilar. We tested these predictions by developing a novel method that integrates species rank abundance distributions with phylogenetic trees and trend analyses, to examine the relative contribution of individual species to the overall community PD. We then supplement this approach with analyses of phylogenetic signal in abundances and measures of phylogenetic similarity within and between rare and common species groups. We applied this analytical approach to 15 long-term temperate and tropical forest dynamics plots from around the world. We show that the niche differentiation hypothesis is supported in six of the nine gap-dominated forests but is rejected in the six disturbance-dominated and three gap-dominated forests. We also show that the three metrics utilized in this study each provide unique but corroborating information regarding the phylogenetic distribution of rarity in communities.     

Sampling Plant Diversity and Rarity at Landscape Scales: Importance of Sampling Time in Species Detectability

Documenting and estimating species richness at regional or landscape scales has been a major emphasis for conservation efforts, as well as for the development and testing of evolutionary and ecological theory. Rarely, however, are sampling efforts assessed on how they affect detection and estimates of species richness and rarity. In this study, vascular plant richness was sampled in 356 quarter hectare time-unlimited survey plots in the boreal region of northeast Alberta. These surveys consisted of 15,856 observations of 499 vascular plant species (97 considered to be regionally rare) collected by 12 observers over a 2 year period. Average survey time for each quarter-hectare plot was 82 minutes, ranging from 20 to 194 minutes, with a positive relationship between total survey time and total plant richness. When survey time was limited to a 20-minute search, as in other Alberta biodiversity methods, 61 species were missed. Extending the survey time to 60 minutes, reduced the number of missed species to 20, while a 90-minute cut-off time resulted in the loss of 8 species. When surveys were separated by habitat type, 60 minutes of search effort sampled nearly 90% of total observed richness for all habitats. Relative to rare species, time-unlimited surveys had ∼65% higher rare plant detections post-20 minutes than during the first 20 minutes of the survey. Although exhaustive sampling was attempted, observer bias was noted among observers when a subsample of plots was re-surveyed by different observers. Our findings suggest that sampling time, combined with sample size and observer effects, should be considered in landscape-scale plant biodiversity surveys.     

Genetic conservation and management of the California endemic,Torrey pine (Pinus torreyana Parry): Implications of genetic rescue in a genetically depauperate species

Rare species present a challenge under changing environmental conditions as the genetic consequences of rarity may limit species ability to adapt to environmental change. To evaluate the evolutionary potential of a rare species, we assessed variation in traits important to plant fitness using multigenerational common garden experiments. Torrey pine, Pinus torreyana Parry, is one of the rarest pines in the world, restricted to one mainland and one island population. Morphological differentiation between island and mainland populations suggests adaptation to local environments may have contributed to trait variation. The distribution of phenotypic variances within the common garden suggests distinct population‐specific growth trajectories underlay genetic differences, with the island population exhibiting substantially reduced genetic variance for growth relative to the mainland population. Furthermore, F1 hybrids, representing a cross between mainland and island trees, exhibit increased height accumulation and fecundity relative to mainland and island parents. This may indicate genetic rescue via intraspecific hybridization could provide the necessary genetic variation to persist in environments modified as a result of climate change. Long‐term common garden experiments, such as these, provide invaluable resources to assess the distribution of genetic variance that may inform conservation strategies to preserve evolutionary potential of rare species, including genetic rescue.