Effects of bark damage by feral herbivores on columnar cactus Echinopsis (=Trichocereus) terscheckii reproductive output

Columnar cacti are an important feature of the arid “cardonal” landscape in South America. The predominant columnar cactus in the southern zone is Echinopsis (=Trichocereus) terscheckii. At some sites, the species suffers considerable trunk damage, attributed in previous studies to feral livestock grazing (donkey and cattle). In order to understand the potential impact of this damage on columnar cactus populations, we investigated whether reproductive output (flower, fruit and seed production) of Echinopsis terscheckii individuals was related to damage, controlling for the effect of individual plant size and habitat characteristics measured at meso and micro-scale. Cactus trunk damage negatively correlated with the number of flowers and fruits, but not with fruit size. We also found significant effects of meso and micro-habitat conditions on all the analyzed reproductive parameters while plant size was positively related to flower and fruit production. These results show that bark damage reduces the reproductive potential of cacti, and therefore that large feral herbivores could have negative effects on reproduction of columnar cacti. Such findings highlight the need for management programs to monitor population trends of these plants and also exotic herbivores.     

Removal of Pilosocereus leucocephalus (Cactaceae,tribe Cereeae) seeds by ants and their potential role as primary seed dispersers

Myrmecochory sensu stricto is uncommon in Neotropical forests. In these ecosystems the role of ants as secondary dispersers of non-myrmecochorous seeds is well known, however, the primary dispersal of this type of seed by ants has been poorly documented. Only a few anecdotal observations scattered throughout the literature report the removal of these seeds from fruit on the plant by ants. We show experimentally that ants are able to remove more pulp and seeds from fruit on the branches than do flying vertebrates in Pilosocereus leucocephalus, a columnar cactus bearing typically ornithochorous fruit. In addition, experiments emulating seed cleaning revealed that cleaned seeds germinate earlier. These results suggest a possible role of ants as primary cactus dispersers; one that requires more extensive research on seed fate and seedling establishment success.     

Pre- and post-dispersal seed loss and soil seed dynamics of the dominant Bulnesia retama (Zygophyllaceae) shrub in a sandy Monte desert of western Argentina

In deserts and semi-deserts dominant plants seldom rely on a persistent seed bank to ensure their recruitment from sexual reproduction, which is generally based on the seeds produced in the last reproductive event. We studied pre- and post-dispersal seed loss of Bulnesia retama, a dominant shrub of the sandy Monte deserts (western Argentina). We hypothesised that pre- and post-dispersal seed depletion in B. retama regulate soil seed density and in turn decrease soil seed reserves. We also hypothesised that spatial patches induced by standing vegetation and other microsites additionally affect post-dispersal seed loss and soil seed density.We observed that as much as half the total seed production was lost due to pre-dispersal seed predation. Seed dispersal plus predation showed a negative exponential function with 61% of seeds falling during the first 28 days, and 99% after 90 days, when 34% of the seeds remained inside excluded branches. A significant patch effect was observed on soil seed density and seed dynamics, with a greater number of seeds and increased seed depletion rates below B. retama shrubs. However, spatial patches did not affect seed germination although they increased with burial time, from 22% to 70% after 75 and 276 days, respectively. Likewise, a similar trend was found in potential seed germination; seeds collected directly from mother plants had a low germination rate (less than 25%), which increased to 75% after 276 days of soil burial. About 15% of the dispersed seeds should persist to the next rainy season, thus contributing to a low-density but persistent seed bank.The delay in seed germination and temporal decrease in soil seed density that we observed for B. retama suggest that a set of mechanisms have been developed promoting germination events whenever soil water is available, at any moment of the year.     

大赖草(Leymus racemosus)结实格局

连续2年对新疆阿勒泰地区荒漠植物大赖草(Leymus racemosus)居群(公路附近沙丘平坦处,P1;农田周围沙丘平坦处,P2;周围积水沙丘中下部,P3;多个沙丘中间平坦处,P4;多个沙丘中间隆起处,P5)、小穗间和小穗内的结实格局进行了比较研究。结果表明:(1)2011年大赖草的穗长、穗宽、总花数、结实率和大种子比率都高于2012年,小种子数低于2012年;2年的结实率在5个居群间均表现为P2P3P1P5P4。(2)每花序内不同小穗的穗宽、总花数和结实率表现为中部下部上部。(3)每小穗均有3.7±0.56朵花、0.6±0.09粒种子,小穗基部的结实率较高。大赖草结实率在年际和不同环境下波动较大,水分和温度是影响其结实格局的主要因素;小穗间及小穗内的资源分配符合资源竞争假说。大赖草花多果少的结实格局是适应荒漠资源贫瘠、干旱少雨气候条件的一种生殖保障。     

Seed dispersal and seed fate in Joshua tree (Yucca brevifolia)

Joshua tree (Yucca brevifolia) is a charismatic symbol of the Mojave Desert. Despite its familiarity, we know little about the reproduction of this species, including mechanisms of seed dispersal. Here we examine mechanisms of seed dispersal and resulting seed fate. We experimentally tracked fruit and seed removal and followed the fates of Joshua tree seeds using radioactive tracers. The majority of Joshua tree fruits monitored were taken directly from the tree canopy by white-tailed antelope squirrels, and seeds and fruits on the soil surface were quickly removed by animals. Rodents given seeds labeled with scandium-46 cached them between 0.1 cm and 4.1 cm deep. Seedling emergence was most common for seeds planted 1 cm deep, whereas seeds placed on the soil surface seldom germinated. Wind dispersal is unlikely because fruits and seeds lack adaptations for wind dispersal; wind speeds required to move Joshua tree seeds and fruits across the soil surface were higher than those typically found in the Mojave Desert. Further, rodents removed most seeds before abiotic burial was possible. We conclude that most Joshua tree seeds are dispersed by scatter hoarding by rodents, and that caches made by rodents are suitable sites for seedling emergence.     

Reproductive biology of Spondias tuberosa Arruda (Anacardiaceae), an endemic fructiferous species of the caatinga (dry forest), under different management conditions in northeastern Brazil

In areas under different management conditions (management units, MUs) located either on a slope or at the base of a slope and either in a plantation or in a pasture, we compared the flower and fruit production, floral visitors, visitation rates and pre-emergent reproductive success (PERS) of Spondias tuberosa (Anacardiaceae) in an area of dry forest in NE Brazil. Individuals in the plantation MU produced more flowers per inflorescence than those in other MUs, but there were no statistical differences in mean fruit set among MUs. The only difference in mean visitation rates was between the plantation (65.83 ± 38.49) and the slope sites (11.5 ± 12.8). We observed visits by 19 insect species, including bees (31.6%), butterflies (31.6%), wasps (26.3%) and flies (10.5%). A clustering analysis based on the number of visits showed that a) the plantation site is most different from the other MUs, b) the pasture and the site at the base of the slope are similar to the slope site, and c) the higher frequency of visits of pollinators in the plantation MU was responsible for these differences. Of the 19 species of insects visiting the flowers, 12 were considered pollinators. The pollinator similarity analysis indicated a clear separation between areas and suggested that human activity has resulted in the replacement of native pollinators by exotic species. However, these changes apparently have not affected the pre-emergent reproductive success of S. tuberosa. Our results show that plant reproductive biology in semi-arid ecosystems may be modified by human action and that changes in floral production and pollinator guilds are the most conspicuous effects. However, the traditional management performed by local people may not affect the reproductive success of plant species.     

Vivipary in the cactus family: A reply to Ortega-Baes’ et al. evaluation of 25 species from northwestern Argentina

This is a reply to Ortega-Baes’ et al. (2010) survey of 25 Argentinean species of cacti evaluated for vivipary. We argue that the sample size and geographic area of the species investigated is insufficient to totally exclude the putative commonness of this condition in the Cactaceae. We indicate possible reasons why they did not find viviparous fruits in their survey. Failure to detect vivipary in cacti of NW Argentina may be correlated with limited taxonomic sampling and geographic region in addition to intrinsic and extrinsic plant factors, including different stages of fruit and seed development and genetic, ecological, and edaphic aspects, which, individually or in concert, control precocious germination. We uphold that viviparity is putatively frequent in this family and list 16 new cases for a total of 53 viviparous cacti, which make up ca. 4% incidence of viviparism in the Cactaceae, a substantially higher percentage than most angiosperm families exhibiting this condition. The Cactaceae ranks fourth in frequency of viviparity after the aquatic families of mangroves and seagrasses. We suggest the re-evaluation of cactus vivipary, primarily as a reproductive adaptation to changing environments and physiological stress with a secondary role as a reproductive strategy with limited offspring dispersal/survival and fitness advantages.     

Patterns of seed occurrence in corsac and red fox diets in Mongolia

Corsac fox (Vulpes corsac) and red fox (Vulpes vulpes) diets often consist of small quantities of vegetation, including fruit and seeds that may represent important sources of energy and nutrition. However, details of the species consumed are few, but may provide insight into the role of foxes as seed dispersers. We analyzed scats of corsac (n = 408) and red foxes (n = 533) collected in an arid region of Mongolia from June 2006 to June 2007. We found 13 seed species in corsac scats, the most common being Allium polyrhizum, Asparagus gobicus, and Tribulus terrestris, and 12 species in red fox scats, the most common being Amygdalus pedunculata, Corispermum mongolicum, and T. terrestris. The proportion of scats with seeds varied significantly by season for both foxes. Seeds occurred most frequently during the breeding period, which corresponded with winter, and least frequently during the dispersal period in autumn for both species. We detected no differences in the proportion of scats with seeds between species seasonally. Our results suggest that fruit represents an important component of diet, especially during winter when availability of other prey items is low, and that both foxes may facilitate seed dispersal of some plant species.     

Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.     

Seed predation and moisture limit germination of recalcitrant Dobera glabra (Salvadoraceae) seeds in the Afar rangelands, Ethiopia

We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.     

Woodrat herbivory influences saguaro (Carnegiea gigantea) reproductive output

The saguaro (Carnegiea gigantea) is a keystone resource for Sonoran desert consumers of nectar, pollen, fruit, and cactus tissues. Saguaro tissue contains oxalic acid and is unavailable to most consumers. The white-throated woodrat (Neotoma albigula) is, however, able to consume foods with high oxalate content, and is strongly associated with desert succulents, primarily cacti of the genus Opuntia. N. albigula forages secondarily on saguaro tissues, reducing photosynthetic surface area and eliciting an energetically-demanding wound response that reduces energy stores available to fuel reproduction. We observed and quantified Neotoma herbivory on saguaros in a low desert environment. Evidence of Neotoma grazing was found on 44% of all saguaros surveyed, and 13% of all saguaros had >20% of their surface area affected by Neotoma grazing. Neotoma herbivory on saguaros was predicted by the number of nearby succulents, presence of Neotoma middens, and saguaro age. When comparing similarly sized plants, saguaros with high levels (>20% of surface) of herbivory produced fewer flowers and fruits than plants with no Neotoma herbivory. These findings suggest that periodic use of saguaros by N. albigula, such as during extended droughts with conditions unfavorable for Opuntia growth and establishment, may reduce long-term reproductive capacities in low-density saguaro populations.     

Effects of seed beetles on the performance of desert legumes depend on host species,plant stage,and beetle density

Seeds of many arid habitat plants have a water-impermeable coat and can germinate only after being scarified. Bruchine seed beetles are important parasites of legume seeds in these environments, but their effect on germination can be unpredictable. Beetles deplete seed resources and can kill the embryo but also scarify seeds. We investigated the effects of a generalist parasite, Stator limbatus, on the germination and growth of two common legumes in the Sonoran desert, catclaw acacia (Acacia greggii) and blue paloverde (Parkinsonia florida). Feeding damage from a single larva greatly increased germination of paloverde but not acacia. This benefit was reduced if seeds were attacked by multiple larvae. Beetle-damaged seeds of both hosts germinated more quickly than did control seeds. Infestation by beetles reduced seedling size, though effects were greater for paloverde than for acacia. Our results demonstrate that the effect of S. limbatus can be highly host-specific. In addition, beetle infestation may enhance or reduce seedling recruitment, depending on the availability of other scarifying agents and the number of larvae per seed. Such contingencies make it difficult to predict the net effect of seed beetles on efforts to control invasive legume hosts or establish native hosts during aridland restoration.     

Predispersal reproductive ecology of an arid land crucifer,Moricandia moricandioides: effect of mammal herbivory on seed production

In this paper the effect of herbivory on the seed production ofMoricandia moricandioides(Cruciferae), an annual species living in arid habitats of south-eastern Spain, is analysed. Firstly, the flowering and fruiting phenology and the composition and structure of the pollinator guild is described, in order to compare the overall effect of mutualistic speciesvs. that of antagonistic species onM. moricandioidesseed production. The loss of female reproductive success due to each herbivore species attacking the plant is then quantified, in an attempt to differentiate the effects on plant seed production of each herbivorous species. The results indicate that only antagonistic organisms interacting withM. moricandioidesinfluenced the female fitness of this plant species. In fact, pollinator abundance or activity did not correlate with the number of seeds dispersed by the plants. In addition, of all the herbivore species, only sheep activity significantly influenced seed production ofM. moricandioidesindividuals, the effect of the remaining crucivorous herbivores being cancelled by the stronger herbivory of sheep. The results of this study suggest that herbivory by sheep, in addition to decreasing the seed production ofM. moricandioides, could be an important determinant of the current distribution pattern of this crucifer species on the ramblas of the Baza basin.     

Parthenocarpy, attractiveness and seed predation by birds in Bursera morelensis

Parthenocarpy (production of seedless fruits) is a characteristic associated with a strategy to reduce seed predation by birds and to increase the attractiveness to frugivorous birds. Red cuajiote (Bursera morelensis) is an endemic tree species of Mexico that produces seeded and parthenocarpic fruits. The purpose of this work was to examine whether parthenocarpy is a factor that increases the number of bird visits to trees and if it is a strategy to diminish seeds predation by granivorous birds. We made field observations to determine the relation between the number of bird visits and fruit removal rate, to the total number of parthenocarpic fruits produced, and the number of birdpredated fruits to the number and proportion of parthenocarpic fruits in the trees. We found that in trees with a bigger amount of parthenocarpic fruits, both frugivoruos and granivorous birds made more visits; we then suggested that parthenocarpic fruits can act like a signal of attraction by means of a density and coloration effect. Also, we found that in trees with bigger proportions of parthenocarpic fruit, predation by granivorous birds is smaller. Parthenocarpy has an adaptative value for B.morelensis increasing bird visitation and reducing seed predation in the Tehuacan Valley.     

Reproductive phenology of Isolatocereus dumortieri (Cactaceae) in semiarid scrub in central Mexico: Effect of rain during the dry season

The giant cactus Isolatocereus dumortieri is a dominant species of the semiarid scrub of central Mexico. Its reproductive period is during the dry season, and it produces essential resources (pollen, nectar and fruits) for a great variety of animal species. We related the production of reproductive structures with water variables in the soil–plant system. The main goal of the present study was to evaluate the consequences of a change in rainfall pattern on the phenology of I. dumortieri. We watered some plants in the dry season to simulate heavy rain events, and to test the hypothesis that water availability during the reproductive season has a negative effect on fruiting and a positive effect on vegetative growth. The seasonality of rain events caused variations in soil water potential and plant osmotic potential, and we found that both variables influenced fruit production. The regression models relating the number of fruits with soil water potential, rainfall and osmotic potential were significant for all three study periods. The highest production of reproductive structures occurred in the driest year (2009), during which there was an ENSO event. Watering did not have a significant effect on osmotic potential or growth in the cacti. However, the watering × time interaction had a negative effect on the number of immature fruits. That is, at the end of the experiment, the plants that received the most water showed a decrease in the number of fruits. Plant growth during the rainy period was significantly greater than during the dry period. The results support the hypothesis that a change in rainfall pattern during the dry season has an effect on fruit production. Vegetative growth, however, occurred only during the wet season.     

Recruiting mechanisms of Cylindropuntia leptocaulis (Cactaceae) in the Southern Chihuahuan Desert

Sexual reproduction and vegetative propagation require the establishment of morphologically diverse reproductive structures (seedlings and stem segments). This study assesses both types of Cylindropuntia leptocaulis recruitment in two microenvironments protected from herbivory (in open space and under the canopy of Larrea tridentata) and with two soil types (collected below L. tridentata canopy and from open space).An observational study revealed that sexual establishment was very limited (only 8 juveniles/ha were found), while clonal establishment was more frequent (59 juveniles/ha); both types of propagule were found only under shrub canopy.Field experiments showed that, as in other Cylindropuntia species but contrasting with findings for Opuntia species, seeds germinated and seedlings survived under nurse plants as well as in open space, but they grew faster in the former environment. Faster growth under canopy shade provides better chances of successful recruitment to later life-cycle stages. Stem segments never established in open space, requiring the shade of nurse plants. This may be due to physiological constraints imposed by their small volume. In synthesis, the results indicate that clonal propagation is the most important recruitment mechanism in C. leptocaulis populations, and that it takes places under shrub canopy.     

长汀水土流失区生长季马尾松树干液流密度特征

应用热扩散探针测定福建长汀水土流失区生长季马尾松东南西北4个方位的树干液流密度,并比较不同人工治理措施下马尾松树干液流密度的特征,利用自动气象站同步记录环境因子变化,以探讨先锋树种的水分生理生态特征及其对环境变化的响应.研究表明,马尾松4个方位的树干液流密度日变化均呈现单峰型变化规律;南向树干液流密度峰值最高,日变化幅度也最大;东、西、南、北4个方位的液流密度差异显著(P<0.01),但各方位液流间呈现显著的线性关系;树干4个方位液流的启动时间与太阳辐射之间存在约3个小时的时滞;4个方位液流与环境因子相关性均极显著(P<0.01),其中与液流密度相关性最强的是空气温度,其次为土壤温度和太阳辐射,4个方位液流受环境因子的影响程度存在差异;不同治理措施下的马尾松液流密度日变化规律相似,但数值差异显著(P<0.01),经过人工施肥的样地马尾松树干液流密度峰值明显高于未施肥的样地.     

Soil seed bank longevity of the exotic annual grass Bromus rubens in the Mojave Desert,USA

Although arid environments are often considered among the least invaded terrestrial biomes, the impacts of exotic plant species can be severe and long lasting. Bromus rubens (red brome) is an exotic annual grass species in the Mojave Desert known to outcompete native plant species, alter habitat, and promote accumulation of fuel that contributes to increasing fire frequency and severity. We assessed longevity of the exotic B. rubens seeds in the soil by burying seeds at four depths (0, 2, 5, and 10 cm) and recovering seeds 6, 12, 18, and 24 months after burial. Seed viability was reduced with greater burial depth and greater time since burial. A relatively small proportion of seeds retained viability for two years, suggesting that while the B. rubens seed bank can be large, it is relatively short-lived. Although B. rubens apparently relies more on the annual production, dispersal, and germination of seeds than on a long-lived seed bank for its annual recruitment, the numerous seeds produced by individual plants indicate that even a small proportion of seeds remaining viable for more than a year can aid recruitment from the seed bank and is an important factor in understanding population dynamics.     

Patterns of frugivory,seed dispersal and predation of blue fan palms (Brahea armata) in oases of northern Baja California

Variations in spatial and temporal availability of fruits and seeds in oases are important not only for animal seeking resources, but also for palm population dynamics. We explored spatial association patterns between avian frugivores and blue fan palms in two natural palm patches of Baja California. Spatial patterns were analyzed at the individual tree and at 2 ha patches. We evaluated seed predation by vertebrates and invertebrates, and vertebrate seed dispersal around palms. Birds responded to fruit aggregation at the individual tree and the patch scales, but responses varied between patches. Palm fruit variables—the quantity and the phenological phase—and avian visits showed strong spatial aggregation and association at both scales in one patch, but not in the other. The intensities of seed predation and seed dispersal were significantly higher directly below palms than at >3 m away from them. Patches differed in the intensity of seed predation around palms and in the diversity of mammalian dispersers, but not in the intensity of seed dispersal. Blue fan palms function as important resources' focuses for a great number of animals that use palm oases as corridors, bringing seeds as they move and connecting isolated populations of palms.     

Factors affecting the seed-setting success of Dryas octopetala in front of Brøggerbreen (Brøgger Glacier) in the high Arctic, Ny-Ålesund, Svalbard

To determine the factors restricting plant reproduction in front of a glacier, the gender expression and seed production of Dryas octopetala L. (Rosaceae) were observed, as well as the grazing pattern of reindeer on flowers, near Brøggerbreen (Brøgger Glacier), which is near Ny-Ålesund (78° 55'N, 11° 56'E), Svalbard. Three hundred shoots with flowers and flower buds were randomly tagged in early July 1996. Between then and the end of flowering in late July, 100 (33%) flowers and buds were grazed by reindeer. Out of the surviving flowers, 145 (76%) shoots had hermaphrodite flowers, while 45 (24%) shoots had male flowers without a developed gynocium. Male flowers, which appeared later than hermaphrodite flowers in the population, were significantly smaller than hermaphrodite flowers in dry weight. In the hermaphrodite flowers, moreover, smaller flowers showed lower dry-weight allocation to the gynoecium as compared to larger flowers. During the observation, hermaphrodite flowers did not produce any developed seeds under a natural condition (0% seed-set). Cross-pollinated flowers showed 8% seed-set. On the other hand, flowers which were artificially warmed in small greenhouses during the flowering period showed 60% seed-set, regardless of cross-pollination or autodeposition of pollen from anthers to stigma (self-pollination). Thus, it was found that grazing, gender variation in relation to the length of the growing season and the flower size, and - in the floweriing period - low temperature rather than pollinator limitation strongly affected the seed production of D. octopetala in the population studied.