Hiroshi Tomimatsu

Effects of genotype identity and diversity on the invasiveness and invasibility of plant populations

Genetic diversity within species is a potentially important, but poorly studied, determinant of plant community dynamics. Here we report experiments testing the influence of genotype identity and genotypic diversity both on the invasibility of a foundation, matrix-forming species (Kentucky bluegrass, Poa pratensis), and on the invasiveness of a colonizing species (dandelion, Taraxacum officinale). Genotypes of Kentucky bluegrass in monoculture showed significant variation in productivity and resistance to dandelion invasion, but the productivity and invasion resistance of genotypic mixtures were not significantly different from those of genotypic monocultures. Indirect evidence suggested temporal shifts in the genotypic composition of mixtures. Dandelion genotypes in monoculture showed striking and significant variation in productivity and seed production, but there was no significant tendency for these variables in mixtures to deviate from null expectations based on monocultures. However, productivity and seed production of dandelion mixtures were consistently greater than those of the two least productive genotypes, and statistically indistinguishable from those of the three most productive genotypes, suggesting the possibility of greater invasiveness of genotypically diverse populations in the long run due to dominance by highly productive genotypes. In both experiments, the identity of genotypes was far more important than genetic diversity per se.

Sustaining ecosystem functions in a changing world: a call for an integrated approach

With ever-increasing human pressure on ecosystems, it is critically important to predict how ecosystem functions will respond to such human-induced perturbations. We define perturbations as either changes to abiotic environment (e.g. eutrophication, climate change) that indirectly affects biota, or direct changes to biota (e.g. species introductions). While two lines of research in ecology, biodiversity-ecosystem function (BDEF) and ecological resilience (ER) research, have addressed this issue, both fields of research have nontrivial shortcomings in their abilities to address a wide range of realistic scenarios. We outline how an integrated research framework may foster a deeper understanding of the functional consequences of perturbations via simultaneous application of (i) process-based mechanistic predictions using trait-based approaches and (ii) detection of empirical patterns of functional changes along real perturbation gradients. In this context, the complexities of ecological interactions and evolutionary perspectives should be integrated into future research. Synthesis and applications. Management of human-impacted ecosystems can be guided most directly by understanding the response of ecosystem functions to controllable perturbations. In particular, we need to characterize the form of a wide range of perturbation-function relationships and to draw connections between those patterns and the underlying ecological processes. We anticipate that the integrated perspectives will also be helpful for managers to derive practical implications for management from academic literature. Management of human-impacted ecosystems can be guided most directly by understanding the response of ecosystem functions to controllable perturbations. In particular, we need to characterize the form of a wide range of perturbation-function relationships and to draw connections between those patterns and the underlying ecological processes. We anticipate that the integrated perspectives will also be helpful for managers to derive practical implications for management from academic literature.

Phylogeography of Camassia quamash in western North America: postglacial colonization and transport by indigenous peoples

Recent human activities have spread numerous plant species across the globe, yet it is unclear to what degree historical human activities influenced plant dispersal. In western North America, Camassia quamash was one of the most important food plants for indigenous peoples, who transported its propagules either intentionally or accidentally. We investigated how human and natural dispersal might have contributed to the current pattern of spatial genetic structure in C. quamash by performing phylogeographical surveys at two geographical scales. We sequenced two noncoding regions of chloroplast deoxyribonucleic acid (DNA) in 226 individuals from 53 populations of C. quamash as well as 126 individuals from 21 populations of the non‐food plant Zigadenus venenosus. Contrary to the expectation of anthropogenic transport, C. quamash populations did not exhibit weaker genetic structure than Z. venenosus populations. We also failed to find convincing evidence for signatures of transport. Instead, our data showed strong effects of past glaciation and geographical barriers of the mountains in the Cascade Range, Olympic Peninsula and Vancouver Island. West of the Cascades, the species appears to have largely migrated northward from a southern refugium after deglaciation, whereas few populations having a highly divergent haplotype might have survived in southwestern Washington. Our data suggest that despite substantial ethnobotanical evidence for anthropogenic transport, the current pattern of genetic structure of C. quamash does not show any detectable signatures of transport by indigenous peoples and is better understood as the result of natural dispersal processes.

Effects of genotypic diversity of Phragmites australis on primary productivity and water quality in an experimental wetland

An increasing number of studies have shown that genetic diversity within plant species can influence important ecological processes. Here, we report a two-year wetland mesocosm experiment in which genotypic richness of Phragmites australis was manipulated to examine its effects on primary productivity and nitrogen removal from water. We used six genotypes of P. australis, and compared primary productivity and nitrogen concentration in the outflow water of the mesocosms between monocultures and polycultures of all six genotypes. We also quantified the abundance of denitrifying bacteria, as denitrification is a primary mechanism of nitrogen removal in addition to the biotic uptake by P. australis. Plant productivity was significantly greater in genotypic polycultures compared to what was expected based on monocultures. This richness effect on productivity was driven by both complementary and competitive interactions among genotypes. In addition, nitrogen removal rates of mesocosms were generally greater in genotypic polycultures compared to those expected based on monocultures. This effect, particularly pronounced in autumn, may largely be attributable to the enhanced uptake of nitrogen by P. australis, as the abundance of nitrite reducers did not increase with plant genotypic diversity. Although our effect sizes were relatively small compared to previous experiments, our study emphasizes the effect of genotypic interactions in regulating multiple ecological processes.

Female and male fitness consequences of clonal growth in a dwarf bamboo population with a high degree of clonal intermingling

BACKGROUND AND AIMS Although many studies have reported that clonal growth interferes with sexual reproduction as a result of geitonogamous self-pollination and inbreeding depression, the mating costs of clonal growth are expected to be reduced when genets are spatially intermingled with others. This study examined how clonal growth affects both female and male reproductive success by studying a population of a mass-flowering plant, Sasa veitchii var. hirsuta, with a high degree of clonal intermingling. METHODS In a 10 × 10 m plot, genets were discriminated based on the multilocus genotypes of 11 nuclear microsatellite loci. The relationships between genet size and the components of reproductive success were then investigated. Male siring success and female and male selfing rates were assessed using paternity analysis. KEY RESULTS A total of 111 genets were spatially well intermingled with others. In contrast to previous studies with species forming distinct monoclonal patches, seed production linearly increased with genet size. While male siring success was a decelerating function of genet size, selfing rates were relatively low and not related to genet size. CONCLUSIONS The results, in conjunction with previous studies, emphasize the role of the spatial arrangement of genets on both the quantity and quality of offpsring, and suggest that an intermingled distribution of genets can reduce the mating costs of clonal growth and enhance overall fitness, particularly female fitness.

Genet dynamics of a regenerating dwarf bamboo population across heterogeneous light environments in a temperate forest understorey

Abstract Despite the advantage of plant clonality in patchy environments, studies focusing on genet demography in relation to spatially heterogeneous environments remain scarce. Regeneration of bamboos in forest understoreys after synchronous die‐off provides an opportunity for assessing how they come to proliferate across heterogeneous light environments. In a Japanese forest, we examined genet demography of a population of Sasa kurilensis over a 7‐year period starting 10 years after die‐off, shortly after which some genets began spreading horizontally by rhizomes. The aboveground biomass was estimated, and genets were discriminated in 9‐m2 plots placed under both canopy gaps and closed canopies. Overall, the results suggest that the survival and spread of more productive genets and the spatial expansion of genets into closed canopies underlie the proliferation of S. kurilensis. Compared to canopy gaps, the recovery rate of biomass was much slower under closed canopies for the first 10 years after the die‐off, but became accelerated during the next 7 years. Genet survival was greater for more productive genets (with greater initial number of culms), and the spaces occupied by genets that died were often colonized afterward by clonal growth of surviving genets. The number of genets decreased under canopy gaps due to greater mortality, but increased under closed canopies where greater number of genets colonized clonally from outside the plots than genets died. The colonizing genets were more productive (having larger culms) than those originally germinated within the plots, and the contribution of colonizing genets to the biomass was greater under closed canopies. Our study emphasizes the importance of investigating genet dynamics over relevant spatiotemporal scales to reveal processes underlying the success of clonal plants in heterogeneous habitats.

Ecological properties of shoot- and single seeds in a hardwood, Zelkova serrata

The data presented in this paper is supporting the research article　“Variable seed behavior increases recruitment success of a hardwood tree, Zelkova serrata, in spatially heterogeneous forest environments” (Oyama et al., 2018) [1]. We provided the data of several ecological properties of the two types of the seeds (i.e. shoot seeds vs. single seeds) with distinctly different dispersal behaviors. We provide data of terminal velocity, which was measured by releasing 50 replicates of each seed type from a height of 5.0 m in dead air space in a gymnasium. We also show the data of germination cue [i.e. red:far-red (R:FR) ratios], which was examined in plant growth chambers that received three distinct R:FR ratios (0.1, 0.4, and 1.0; 16 h photoperiod) or no illumination. Further, we show the data of the rates of multi-locus outcrossing rates and biparental inbreeding in each of single- and shoot seeds. The mating system parameters were estimated by assaying a total of 80 shoot seeds and 70 single seeds that were randomly collected from Parent 1 and Parent 2 for five microsatellite loci. Finally, we show the data of hemispherical canopy photographs, which were taken at different distance from the adults using a digital camera equipped with a fisheye lens.