Trading forage quality for quantity? Plant phenology and patch choice by Svalbard reindeer

Plant phenology of Luzula heathland plots in Spitsbergen (78°N) was manipulated by adding or removing snow, which altered the time for plots (2 m×2 m; n=10) to become snow-free. A 2-week difference in snowmelt, equivalent to approximately one-sixth of the growing season, was achieved between advanced (first to be snow-free) and delayed (last to be snow-free) treatments, which influenced plant biomass and plant quality. Nitrogen content of the forage species decreased with time after snowmelt, whereas C:N ratio increased. Manipulation of snowmelt led to a shift in ”phenological time”, without altering these plant quality parameters as such. Early in the growing season, Svalbard reindeer (Rangifer tarandus platyrhynchus) selected the advanced plots which had been snow-free for longest, presumably because of the greater biomass of both Luzula confusa and Salix polaris, major components of reindeer diet at that time of the year. Moreover, the proportion of live Luzula leaves was highest in advanced plots, relative to both unmanipulated control and delayed plots. In contrast, plant quality, measured as nitrogen content and C:N ratio of leaves, was lowest in the preferred plots. Phenolic content did not differ among treatments, and is therefore unlikely to play a role in reindeer selection for plots with early snowmelt. Unlike in temperate regions, where selection for plant quality seems to be of major importance, selection for plant quantity might be an outcome of generally low levels of plant biomass and high forage quality during the growing season in the high Arctic. Reindeer selection for high plant biomass is likely to lead to a more favourable nitrogen and energy return than selection for high plant quality. Received: 25 May 1999 / Accepted: 15 November 1999     

Warming effects on shoot developmental growth and biomass production in sympatric evergreen alpine dwarf shrubs Empetrum nigrum and Loiseleuria procumbens

Effects of experimental warming on shoot developmental growth and biomass production were preliminarily investigated in two evergreen dwarf shrubs Empetrum nigrum and Loiseleuria procumbens, using the International Tundra Experiments open-top chamber (OTC) method, in the Tateyama Range, central Japan. An OTC was installed over shrub (E. nigrum and L. procumbens) -dominated vegetation and over shrub-forb (such as Anemone narcissiflora var. nipponica and Solidago virga-aurea ssp. leiocarpa) mixed vegetation, and stem samples of the evergreen shrubs were obtained at 26 months after installing the OTC. The OTC increased the daily mean temperature by 0.1°C to 1.8°C, on average, during the growing season. Shoot developmental growth and biomass production were considerably different between species of different vegetation types. The boreal species E. nigrum generally showed better growth inside the OTC than the arctic and subarctic species L. procumbens. Both species showed significantly larger shoot elongation and biomass production inside the OTC over shrub-dominated vegetation, whereas smaller or reduced growth was detected inside the OTC over shrub-forb mixed vegetation. The variations of growth responses to warming between species of different vegetation types are discussed, especially in relation to interspecific competition under a simulated environmental change.     

Sequential flowering of neighboring goldenrods and the movements of the flower predator Epicauta pennsylvanica

Summary As neighboring plants flower sequentially, do flower feeders preferentially remain in the area, rather than move to another area with flowering plants? I examined the movements of the meloid beetle Epicauta pennsylvanica, a flower predator specializing on Solidago, in four types of replicated experimental plots — monocultures of Solidago altissima, or S. altissima interplanted with members of the same genus, same family, or different taxonomic orders. I released marked beetles only in the genus plots, which contained four species of Solidago, two that bloom before S. altissima. The number of beetles in the genus plots declined steadily as S. altissima came into flower in all the plots; the total number of beetles in all the plots remained fairly constant. I found no evidence that plant neighborhoods affected beetle distribution. Beetles foraging on the early blooming Solidago species did not remain in the genus plots as S. altissima came into flower. In addition, beetles that left the genus plots did not differentially accumulate in any of the other plot types, even though one type of plot was a monoculture with four times the density of S. altissima than the other plots.     

Aridity mediates the effect of wood extraction on the reproductive output of an endemic disturbance-adapted woody species (Cenostigma microphyllum,Leguminosae) in the Caatinga dry forest

Chronic anthropogenic disturbances and climate change have been recognized as drivers of biological reorganization across human-modified tropical landscapes, also negatively affecting the reproductive output of some plant species. Here, we investigated to what extent these drivers affect the reproductive output of Cenostigma microphyllum, a disturbance-adapted tree species endemic to the Caatinga dry forest. The production of flowers/inflorescence, fruits and seeds was estimated for 105 plants (≥3 cm diameter at soil height) across 11 forest stands (20 × 50 m each), covering gradients of chronic disturbances (e.g. goat and livestock herbivory; wood extraction; and removal of non-timber forest products) and aridity at the Catimbau National Park. We documented that when the drivers were analysed in isolation, the fruit-set was positively associated with increased wood extraction, and the fruit-set and total number of seeds/plots were reduced under increasing aridity. We also verified a complex interaction between wood extraction and aridity emerged. In forest stands, the combination of high levels of aridity and wood extraction leads to a decrease in the fruit-set and total number of seeds/plots. Conversely, the fruit-set and total number of seeds/plots increased in stands exposed to lower aridity but high levels of wood extraction. Our results suggest that chronic disturbances and aridity affect plant fitness in a complex way including both negative and positive effects on attributes related to plant reproductive performance, which could result in both proliferation and population decline in the same landscape. Although C. microphyllum benefits from anthropogenic disturbances and is considered a disturbance-adapted species, it apparently does not benefit from increases in aridity, which is an expected future scenario for the Caatinga dry forest.     

Plant distribution in relation to the length of the growing season in a snow-bed in the Taisetsu Mountains,northern Japan

The distribution pattern of plants was studied in an alpine snow-bed in six plots along a snow-melting gradient. Each plot consisted of two habitats with respect to the microtopography; the flat habitat and the mound habitat. The number of species per plot decreased with the shortened snow-free period. In the flat habitat, the dominant growth forms changed from the early exposed plots to the late exposed ones as follows; lichens evergreen and deciduous shrubs forbs graminoids bryophytes. In the mound habitat, evergreen and deciduous shrubs prevailed widely along the gradient because of the ability to exploit new habitat by creeping over exposed rocks. For shrubs, the existence of mounds contributed to the expansion of the distribution ranges. Forbs and graminoids shifted their distribution modes to the late exposed plots where shrubs decreased in cover. Deciduous shrubs and forbs completely disappeared in the latest exposed plot.     

Microgametophytes in flowers with and without fruits ofPhlox drummondii (Polemoniaceae)

Relationships between microgametophyte numbers per flower and fruit-set were sought inPhlox drummondii Hook. This was accomplished by counting fluorescentstained pollen tubes in flowers with and without fruits in 21 populations, and in flowers subject to either supplemental or sparse pollination, and then determining whether the flowers initiate fruits. There was a conspicuous variation in mean pollen tubes per flower (3–38) and in percent fruit-set (17%–92%) among populations. Neighboring populations often differed strikingly in these respects. Flowers with fruits had an average of 15.2 pollen tubes per stigma whereas those without had an average of 3 7 tubes. Over all flowers, there was a mean of 3.7 tubes per ovule. There was a strong correlation between mean tube number within populations and their percent fruit-set (r = 0.86). Supplemental pollination significantly enhanced fruit-set, thereby supporting the notion that fruit-set was pollen-limited in most populations. In both natural and artificial pollinations a portion of flowers without fruits still had several pollen tubes. The occurrence of fruitless flowers containing tubes is explained by attrition factors, like late-acting pollen-pistil incompatibility, and resource limitation. Fruit-set could be initiated with one pollen tube, but this rarely occurred in nature. Higher pollen loads were accompanied by higher percents of fruit-set and number of seeds per flower.     

开花期加拿大一枝黄花水浸提液对3种作物种子萌发和幼苗生长的影响

测定了入侵杂草加拿大一枝黄花（Solidago canadensis）开花期的茎、叶和花序水浸提液对辣椒(Capsicum annuum)、番茄(Lycoperiscum esculetum)、长梗白菜(Brassica chinensis var. communis)种子萌发和幼苗生长的影响。结果表明：（1）处于开花期的加拿大一枝黄花存在明显的化感作用,在25 mg·mL^-1时,对3种作物种子苗生长有促进作用,浸提液高于50 mg·mL^-1时,作物种子的萌发率和生长受到抑制,这种抑制作用随处理液浓度的提高而增强,在100 mg·mL^-1浓度处理下,甚至使作物种子失去活力;（2）加拿大一枝黄花叶和花序的水浸提液对种子萌发和生长的影响要大于其茎的浸提液;（3）在3种作物中,长梗白菜种子对加拿大一枝黄花水浸提液的敏感性最高。     

Fruit set,fruit reduction,and fruiting strategy in Cornus sanguinea (Cornaceae)

We studied various aspects of the fruiting biology of Cornus sanguinea (Cornaceae), a fleshy-fruit-producing deciduous shrub, in four populations in northwest Spain. One population was studied over a 5-yr period (1989-1994), and the remaining populations in 1994 only. Fruit-set level varied among years (range 11-18%) and among populations (range 8-22%), but was in all cases low. Within plants, fruit-set level did not vary significantly among inflorescences, indicating that inflorescence fruit set is independent of inflorescence position and inflorescence, phenology. To investigate the function of surplus flowers, we carried out flower removal experiments. Inflorescence fruit-set level was unaffected by removal of up to =75% of flowers. These results suggest that Cornus sanguinea regulates its fruit-set level via plasticity in the number of fruits aborted: if flower mortality has been high, fewer fruits will be aborted. Within the inflorescence, surplus flowers thus act as insurance against flower loss.     

Reductions in grassland species evenness increase dicot seedling invasion and spittle bug infestation

Previous experiments that tested whether diverse plant communities have lower invasibility have all varied species richness. We experimentally varied evenness of four grassland species (three grasses and one forb) by planting a field experiment in Texas, and monitored the number of unplanted dicot and monocot species that invaded plots for two growing seasons. By varying evenness, we eliminated any sampling effect in our diversity treatment, because all plots contained the same plant species. Experimentally reducing evenness led to a greater number of dicot invaders, which emerged in plots throughout the growing season, but had less of an effect on monocot invaders, which emerged in flushes when experimental plants were semi‐dormant. Frequency of Solidago canadensis (altissima) stems with spittle bugs significantly increased with reductions in evenness during the first year, apparently because the greater number of Solidago stems in high evenness plots diluted the spittle‐bug effect. These results support the view that higher diversity plant communities are more resistant to dicot invaders and insect herbivores.     

Changes in flowering and abundance of Delphinium nuttallianum (Ranunculaceae) in response to a subalpine climate warming experiment

High‐altitude and high‐latitude sites are expected to be very sensitive to global warming, because the biological activity of most plants is restricted by the length of the short snow‐free season, which is determined by climate. Long‐term observational studies in subalpine meadows of the Colorado Rocky Mountains have shown a strong positive correlation between snowpack and flower production by the forb Delphinium nuttallianum. If a warmer climate reduces annual snowfall in this region then global warming might reduce fitness in D. nuttallianum. In this article we report effects of experimental warming on the abundance and flower production of D. nuttallianum. Plant abundance (both flowering and vegetative plants) was slightly greater on warmed than control plots prior to initiation of the warming treatment in 1991. Since 1994 experimental warming has had a negative effect on D. nuttallianum flower production, reducing both the abundance of flowering plants and the total number of flowers per plant. Flower bud abortion was higher in the heated plots than the controls only in 1994 and 1999. Results from both the warming experiment and analyses of unmanipulated long‐term plots suggest that global warming may affect the fecundity of D. nuttallianum, which may have cascading effects on the pollinators that depend on it and on the fecundity of plants that share similar pollinators.     

Size-dependent pollination efficiency in Anchusa officinalis (Boraginaceae): causes and consequences

Summary Bumblebees foraging on the self-incompatible Anchusa officinalis fly between near neighbour plants and between near neighbour inflorescences within plants. Although many-flowered plants attracted most bumblebees these plants received fewer visits on a per flower basis than smaller plants, and each bumblebee visited a smaller proportion of the flowers. The calculated effective visitation rate per flower was highest on plants of an intermediate size. If pollen-carryover was assumed to be limited the most efficient plant was predicted to be smaller since the proportion of fertilized flowers per bumblebee visit is expected to decrease further on the largest plants in relation to the total flower number. These predictions were tested by measuring fruit-set in the field. The percentage fruit-set decreased with plant size at all sizes that were investigated. That the most efficient plant was small indicates that pollen-carryover was indeed limited. However, the low percentage fruit-set associated with large size did not present a serious problem since the total estimated seed production per plant still increased with size. Selection favoring smaller plants may be low or absent in Anchusa.     

Functional response and progeny production of the Madeira mealybug parasitoid, Anagyrus sp. nov. nr. sinope: The effects of host and parasitoid densities

We tested the hypothesis that control of an herbivorous pest would be improved by providing floral resources for adult natural enemies. The herbivore was euonymus scale, Unaspis euonymi (Comstock) (Homoptera: Diaspididae), a serious pest of woody ornamental plants. The experimental landscape consisted of 3 × 3 m plots, each containing a central bed of Euonymus fortunei (Turcz.) that was infested with the scale. Floral resource plants were cultivars of four species that overlapped in bloom periods to provide a continuous supply of floral resources during summer: Trifolium repens L., Euphorbia epithymoides L., Coreopsis verticillata L. var. ‘Moonbeam,’ and Solidago canadensis L. var. ‘Golden Baby.’ Plots contained either low or high densities of all four species, or no resource plants. Densities of euonymus scale were typically lower in plots containing resource plants than in plots without them. Parasitism by Encarsia citrina (Craw.) (Hymenoptera: Aphelinidae) was rarely influenced by the experimental treatments, flower biomass, whole-plant biomass, or scale density, but in some cases was inversely correlated with density of scales within a generation and in the subsequent generation. Parasitism occasionally reduced densities of scales in plots containing resource plants, but this effect apparently was related to vegetative, not floral qualities of plants. A steady increase in parasitism rate over the three-year course of the experiment across the entire landscape was associated with decreasing density of scales, suggesting a numerical response by the parasitoid population. These findings suggest that the parasitoid is capable of effectively controlling euonymus scale in ornamental landscapes where environmental conditions are favorable.     

Evolution of flower shape inVeroniceae (Scrophulariaceae)

Floral evolution in the tribeVeroniceae was examined using phylogenetic analysis combining 24 adult morphology and chromosome number characters with 22 qualitative and quantitative floral development characters. Taxa sampled included nine species ofVeroniceae and as an outgroup one species each ofDigitaleae andVerbasceae. Veronica, Besseya, andSynthyris formed one clade, subtended byPseudolysimachion and then by theHebe group;Veronicastrum orWulfenia represent the basal-most branch of the tribe. The ancestral flowers of theVeroniceae may have been small with moderately short corolla tubes and lobes; long corolla tubes arose four times in the tribe and large corolla lobes twice.     

Post-glacial range fragmentation is responsible for the current distribution of Potentilla matsumurae Th. Wolf (Rosaceae) in the Japanese archipelago

Aim We aimed to elucidate how the current geographic distribution of alpine plants in the Japanese archipelago was shaped during Quaternary climatic oscillations, using Potentilla matsumurae as a case study. According to previous phylogeographic studies, post‐glacial range fragmentation (vicariance scenario) and stepwise migration (dispersal scenario) are both possible. We thus aimed to assess which scenario is more probable for the distribution changes of alpine plants in the Japanese archipelago. Location The alpine zone in the Japanese archipelago. Methods Using amplified fragment length polymorphism we determined the genotype of 161 individuals of P. matsumurae from 22 populations. Relationships among individuals and populations were examined using principal coordinates analysis and a neighbour‐joining (NJ) tree, respectively. To examine the genetic population structure, we performed analysis of molecular variance (amova ) and structure analysis. Results Differentiation between central Honshu and northern Japan was not very strong based on the principal coordinates analysis among individuals, the NJ tree of populations (59% bootstrap support), or amova (12% of genetic variation). Moreover, structure analysis did not detect clear geographic differentiation across populations. Although the populations in central Honshu were structured geographically (Mantel test: r = 0.45, P < 0.005; NJ tree), those in northern Japan did not exhibit geographic structure regardless of geographic distance (Mantel test: r = 0.26, P = 0.03; NJ tree). Population relationships in the NJ tree did not always reflect the geographic location. Main conclusions The current geographic structure of P. matsumurae could not be explained by stepwise migration. This suggests that a single continuous distribution during the last glacial period was later fragmented, perhaps by recovering forest, during the post‐glacial period, resulting in the current distribution and phylogeographic structure of P. matsumurae. Our data support the vicariance scenario.     

Competition and facilitation among plants for pollination: can pollinator abundance shift the plant–plant interactions?

We hypothesize interactions among plants for pollination may depend on pollinator abundance, which always varies among years and habitats and has different effects on plant reproductive success. Honeybee-pollinated plants, Lotus corniculatus, and its commonly coflowering neighbor, Potentilla reptans var. sericophylla, were used in a two-year project. We designed six types of plant combinations with different conspecific and interspecific flower densities in 2011 and repeated this in the same site in 2012. Meanwhile, we artificially increased pollinator abundance by hiring beehives only in 2011. Pollinator abundance as well as flower density significantly affected pollination of L. corniculatus plants from both the conspecific and interspecific plots. Total number of bees visiting a plot was enhanced by an increase in both the conspecific and interspecific flower densities regardless of high or low pollinator abundance. However, changes in visitation rates and fruit sets in the focal plants when flower densities were increased depended on pollinator abundance. Under high pollinator abundance, an increase in both the conspecific and interspecific flower densities significantly enhanced pollinator visits to L. corniculatus. However, under low pollinator abundance, the pollinator visitation rate remained unchanged as conspecific flower density increased, but decreased when there was an increase in interspecific flower density. Coflowering plants enhanced fruit sets of L. corniculatus only when the pollinator abundance was high. The findings suggest that the interactions among plants for pollination are influenced not only by a plant density threshold, but also by a pollinator abundance threshold.     

Reproductive biology ofCaesalpinia calycina andC. pluviosa (Leguminosae) of the caatinga of north-eastern Brazil

The pollination biology, breeding system and fruiting success ofCaesalpinia calycina andC. pluviosa var.sanfranciscana were studied in caatinga vegetation in Bahia, NE Brazil. The principal pollinators for both species were carpenter bees.Caesalpinia calycina is andromonoecious but inC. pluviosa all flowers are hermaphrodite. InC. calycina all selfed flowers were abscised within 72 h despite rapid self-pollen tube growth to the ovary and ovule penetration. Prevention of selfing therefore seems to be controlled by a post-zygotic mechanism. Both species had very low fruit-set and it is suggested that this is at least in part due to geitonogamous pollinations with ovule penetration by self pollen tubes.     

The relative importance of architecture and resource competition in allocation to pollen and ovule number within inflorescences of Hosta ventricosa varies with the resource pools

Background and Aims

Allocation of resources to floral traits often declines distally within inflorescences in flowering plants. Architecture and resource competition have been proposed as underlying mechanisms. The aim of the present study is to assess the relative importance of resource competition and architectural effects in pollen and ovule production on racemes of Hosta ventricosa, an apomictic perennial herb.

Methods

Combinations of two defoliation treatments (intact and defoliated) and two fruit-set treatments (no-fruit and fruit) were created, and the roles of architecture and resource competition at each resource level were assessed.

Key Results

Pollen and ovule number per flower increased after defoliation, but pollen to ovule ratio per flower did not change. Pollen, ovules and the pollen to ovule ratio per flower declined distally on racemes at each resource level. In the intact treatment, fruit development of early flowers did not affect either pollen or ovule number of late flowers. In the defoliated treatment, fruit development of early flowers reduced both pollen and ovule numbers of late flowers due to over-compensation caused by defoliation. Late flowers on defoliated fruit racemes produced less pollen than intact fruit racemes but the same number of ovules; therefore, the reduction in pollen number was not caused by over-compensation. In addition, the fruit-set rate of early flowers during flowering was higher in intact racemes than in defoliated racemes.

Conclusions

In flowering plants, the relative importance of architecture and resource competition in allocation to pollen and ovules may vary with the resource pools or the overall resource availability of maternal plants.     

Effect of storage time,site and floral morph on seed germination of the threatened distylous primrose Primula cusickiana var. maguirei

Ex situ conservation of rare plant species requires an understanding of germination requirements. We report the first successful germination trials for Maguire primrose (Primula cusickiana var. maguirei[L.O. Williams] N.H. Holmgren & S. Kelso), a threatened perennial herb narrowly restricted to a 20‐km canyon in northern Utah, USA. Seeds collected from different sites (upper or lower canyon populations) and flower morphs (pin or thrum) that had been stored for either 1 or 2 years were cold, moist stratified in darkness at 1–2°C for 270 days. Independent of treatment, time to first germination was approximately 75 days, time to 50% germination (T₅₀) was approximately 165 days, and total germination was 55.8%. Higher mean germination was observed in seeds stored for 2 years compared with seeds stored for 1 year, as well as in seeds from pin flowers compared with thrum flowers. There was not a significant effect of site on mean germination, but there was a significant storage time × site interaction. Seeds stored for 2 years also had a lower mean T₅₀ versus seeds stored for 1 year. In addition, seeds from upper canyon populations had a higher mean T₅₀ than those from lower canyon populations. Our results suggest that short‐term storage should not significantly decrease seed viability, and that both flower morph and canyon location may influence germination. Evidence suggests that germination patterns are adaptive. Our results contribute to our understanding of the germination biology of P. cusickiana var. maguirei and inform future conservation efforts for this threatened species.     

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.