Recruitment Processes and Species Coexistence in a Sub-boreal Forest in Northern Japan

We investigated the recruitment of saplings (across the 2 m-heightthreshold) of six species,Picea jezoensis, Abies sachalinensis,Betula ermanii, Picea glehnii, Acer ukurunduense andSorbus commixta,in a sub-boreal forest, northern Japan. Data were collectedin a 2.48-ha plot over six growing seasons (1989–1994).We used path analysis to analyse the relationships between therecruitment rates of saplings and the stand structural attributessuch as mother tree abundance, stand crowdedness, stand stratification,Sasabamboo density on the forest floor, and fallen log abundance.The combination of stand structural attributes affecting recruitmentrates of the six sub-boreal forest tree species differed markedlyamong the species and corresponded to species composition. Itis suggested that the size-structure dynamics of adult treesof the sub-boreal forest are regulated largely by differentregeneration processes among the species and only slightly byinterspecific competition between adult trees because interspecificcompetition between adult trees was not evident. The dynamicsof species coexistence of the sub-boreal forest should be describedas a process combining the diversity of recruitment processesof saplings of the component species and the diversity of interspecificcompetition between adult trees. We propose the boundary conditionhypothesis for species coexistence in the sub-boreal forest,that the persistence of each component species is ascribed largelyto the different recruitment processes of saplings (boundaryconditions for adult tree growth dynamics) and only a littleto interspecific adult tree competition. Climax forest; safe site; regeneration niche; mode of competition; species diversity     

Characterization of six microsatellite markers in Trillium camschatcense using a dual‐suppression‐polymerase chain reaction technique

Trillium camschatcense is a herbaceous perennial plant distributed in Hokkaido and northern Honshu, Japan. Geographical variations in the breeding system (partial selfing or obligate outcrossing) are reported in the populations of Hokkaido. We isolated six polymorphic microsatellite loci from this species. The number of allele per locus ranged from four to 12, whereas the expected heterozygosities ranged from 0.69 to 0.83. These markers may allow further investigations to reveal the evolutionary and ecological processes of mating system in T. camschatcense.     

Testing the quick meal hypothesis: The effect of pulp on hoarding and seed predation of Hymenaea courbaril by red‐rumped agoutis (Dasyprocta leporina)

Abstract: Red‐rumped agoutis (Dasyprocta leporina) are important seed dispersers/predators of Neotropical large‐seeded plants. Several species of seeds cached by agoutis have an edible reward, in contrast to temperate rodent‐dispersed diaspores. The quick meal hypothesis states that the presence of a reward such as edible pulp will enhance the efficiency of rodents as seed disperses by satiating the animal and, consequently, reducing seed predation and enhancing hoarding. In this study, this hypothesis was tested using as the reference system the pulp and seeds of Hymenaea courbaril. Seeds with and without pulp were offered to agoutis and the behaviour of each individual was recorded. Since the probability of predation and hoarding were complementary, we used the probability of predation. The proportion of agoutis that preyed on at least one seed was similar for seeds with (42.8% of individuals) and without (40.0% of individuals) pulp. In agoutis that preyed upon at least one seed, the probability that they killed a seed did not differ between seeds with (0.17 ± 0.03) and without (0.20 ± 0.08) pulp. Hence, these results do not support the ‘quick meal hypothesis’.     

Changes in Endogenous Growth Regulators in the Gladiolus Corm during Dormancy

Changes in endogenous growth regulators in gladiolus corms during dormancy were studied using paper and column chromatography followed by a bioassay with the test for straight growth of Avena coleoptile. Corms were grown in the field or in a glass room of a phytotron at 20°C in the light. Another lot was grown in a dark room at 20°C in the dark. Half of the daughter corms in each lot were cold-treated for about one month and the other half were stored at room temperature after harvest. The earliest sprouting was seen in dark grown corms with cold treatment, and the latest sprouting in light grown corms without cold. This pattern was similar in each cultivar over a period of three years. Corms from both lots contained considerable amounts of inhibiting substance just after harvest. However, dark grown corms treated with cold showed a rapid decrease in inhibitor activity and an increase in promoter activity. On the other hand, in light grown corms without cold treatment there was inhibitor activity found consistently even after two months. —There appear to be two inhibiting zones in the chromato-grams. One of these contains two inhibitory substances, one of which was assumed to be abscisic acid.     

Genital lock-and-key system and premating isolation by mate preference in carabid beetles (Carabus subgenus Ohomopterus)

The shapes and lengths of copulatory pieces and vaginal appendices of the carabid beetle subgenus Ohomopterus (genus Carabus) vary among species. In Japan, the species in the group with a medium body size (C. yaconinus, C. iwawakianus, C. maiyasanus, C. uenoi, C. arrowianus, C. esakii, and C. insulicola) are usually allopatric or parapatric, except at Mt Kongosan, where C. uenoi, C. iwawakianus, and C. yaconinus are sympatrically distributed. The degree of premating isolation by mate preference was high between sympatric populations, irrespective of the genetic distance between them. However, premating isolation was absent between parapatric populations. The degree of premating isolation for allopatric populations spanned a wide range of isolation values. Thus, mate discrimination by males seems to have evolved mostly between sympatric pairs. These results suggest two hypotheses. First, premating isolation has evolved through reinforcement or through reproductive character displacement after sympatric contact. Second, premating isolation has evolved in allopatry, and as a result of premating isolation, the species can coexist in sympatry. We also examined the degree of mechanical isolation between C. uenoi and C. iwawakianus (a sympatric pair), which have a very large difference in the length of the copulatory piece. The insertion success was low and only one female produced viable offspring among 15 crosses; however, death in females due to copulation was rare. For sympatric matings between C. uenoi and C. iwawakianus, a large difference in the genital size might reduce the gene flow with small mating costs. Gene flow that was significantly reduced by genital difference might cause either the evolution of premating isolation through reinforcement/reproductive character displacement or through the maintenance of a high degree of premating isolation following sympatric contact. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 145–154.     

Parallel formation of hybrid swarms of ground beetles in the genus Carabus (Coleoptera: Carabidae) in adjacent river basins

Populations of forms intermediate between Carabus (Ohomopterus) insulicola and Carabus (Ohomopterus) arrowianus occur at the boundaries between the two species in the Kiso Valley, Nagano Prefecture, central Honshu, Japan. Morphological and mitochondrial DNA analyses revealed that these populations are derived from a hybrid swarm established as a result of secondary contact between the two species. A similar hybrid swarm has been reported in the Ina Valley, an adjacent river basin separated by the Kiso Mountain Range, where the two species are distributed parapatrically. The hybrid swarm individuals in the two valleys show parallelism in the morphological evolution of the male genitalia upon secondary contact and subsequent formation of hybrid swarms between the two Carabus species.