Phenological Adaptations in Ficus tikoua Exhibit Convergence with Unrelated Extra-Tropical Fig Trees

Flowering phenology is central to the ecology and evolution of most flowering plants. In highly-specific nursery pollination systems, such as that involving fig trees (Ficus species) and fig wasps (Agaonidae), any mismatch in timing has serious consequences because the plants must balance seed production with maintenance of their pollinator populations. Most fig trees are found in tropical or subtropical habitats, but the dioecious Chinese Ficus tikoua has a more northerly distribution. We monitored how its fruiting phenology has adapted in response to a highly seasonal environment. Male trees (where fig wasps reproduce) had one to three crops annually, whereas many seed-producing female trees produced only one fig crop. The timing of release of Ceratosolen fig wasps from male figs in late May and June was synchronized with the presence of receptive figs on female trees, at a time when there were few receptive figs on male trees, thereby ensuring seed set while allowing remnant pollinator populations to persist. F. tikoua phenology has converged with those of other (unrelated) northern Ficus species, but there are differences. Unlike F. carica in Europe, all F. tikoua male figs contain male flowers, and unlike F. pumila in China, but like F. carica, it is the second annual generation of adult wasps that pollinate female figs. The phenologies of all three temperate fig trees generate annual bottlenecks in the size of pollinator populations and for female F. tikoua also a shortage of fig wasps that results in many figs failing to be pollinated.     

Responses of pigmentation and δ13C in Qilian juniper to cold and drought stresses under natural conditions in the Qilian Mountains,China

The seasonal changes of pigments and stable carbon isotope composition (δ¹³C values) were investigated in needles of Qilian juniper (Sabina przewalskii Kom.) from two typical sites, one drier and the other wetter, in the Qilian Mountains, China. The anthocyanins and rhodoxanthin content from both sites were much higher in winter than in summer. Plant needles contained more carotenoids and xanthophylls in winter at the wetter site, while no seasonal difference appeared at the drier site. However, lower chlorophyll content and higher proline and δ¹³C were observed at the drier site. Average tree height was shorter at the drier site trees than at the wetter site. Our results suggested that under natural conditions, pigmentation in S. przewalskii may serve to improve the energy balance of the photosynthetic apparatus under cold and drought stresses. Proline and δ¹³C could be used as drought indicators for S. przewalskii.     

Few figs for frugivores: Riparian fig trees in Zimbabwe may not be a dry season keystone resource

Most plants flower and fruit at times of year when probabilities of pollination and seedling establishment are high. Fig trees (Ficus spp.) are often considered as keystone resources for vertebrate frugivores, in part because of year-round fig production. This unusual fruiting phenology results in the maintenance of fig wasp populations, but in seasonal environments this means fruiting occurs during periods when the chances of seedling establishment are low. Under these circumstances, selection is expected to favour any individuals that reduce or eliminate fruiting at these times. Here, we describe a large-scale survey of the extent of dry season fruiting by three riparian Ficus species in Gonarezhou National Park, Zimbabwe. Few trees of two monoecious species, F. sycomorus and F. abutilifolia, had figs, and most crops of F. sycomorus were far smaller than the trees were capable of producing. Large stands of the dioecious F. capreifolia were present, but fig densities were low and no mature female (seed containing) figs were recorded. Even though fig trees may have been the only species bearing fruit, the consequences of the low investment in reproduction by the three Ficus species were clear—there were too few figs for a landscape-scale keystone role.     

The reproductive success of Ficus altissima and its pollinator in a strongly seasonal environment: Xishuangbanna, Southwestern China

Fig trees (Ficus spp.) are of great ecological significance, producing fruits that are fed on by more birds and mammals than any other plants in the tropics. They are pollinated by host-specific pollinator fig wasps (Hymenoptera, Agaonidae), and their fruit phenology and reproductive success are, therefore, modulated by symbiotic fig wasps. However, there are few studies focusing on the variation of Ficus reproductive success in strongly seasonal environments. We examined the phenology and reproductive success of Ficus altissima growing in a highly seasonal climate towards the northern limit of the range of fig trees in Xishuangbanna, China. Leaf production occurred at irregular intervals throughout the year, with new leaves and syconia initiated together, producing between three and seven crops over a 3-year period. Syconia were produced in synchronous crops with asynchrony between trees. The syconia produced more seeds than pollinators, and those syconia with more seeds also produced more pollinators. Reproductive success (measured as the number of seeds and pollen-carrying agaonid females produced by each syconium) varied greatly between seasons. It was highest for crops that matured during the cooler, relatively dry periods from February to March and October to November, and was lowest during the summer months from April to August. This variation corresponded to small differences in the number of flowers in the syconia, but was mainly driven by large seasonal differences in the relative abundance of non-pollinating fig wasps.     

Mast fruiting of large ectomycorrhizal African rain forest trees: importance of dry season intensity, and the resource-limitation hypothesis

Mast fruiting is a distinctive reproductive trait in trees. This rain forest study, at a nutrient-poor site with a seasonal climate in tropical Africa, provides new insights into the causes of this mode of phenological patterning. At Korup, Cameroon, 150 trees of the large, ectomycorrhizal caesalp, Microberlinia bisulcata, were recorded almost monthly for leafing, flowering and fruiting during 1995-2000. The series was extended to 1988-2004 with less detailed data. Individual transitions in phenology were analysed. Masting occurred when the dry season before fruiting was drier, and the one before that was wetter, than average. Intervals between events were usually 2 or 3 yr. Masting was associated with early leaf exchange, followed by mass flowering, and was highly synchronous in the population. Trees at higher elevation showed more fruiting. Output declined between 1995 and 2000. Mast fruiting in M. bisulcata appears to be driven by climate variation and is regulated by internal tree processes. The resource-limitation hypothesis was supported. An 'alternative bearing' system seems to underlie masting. That ectomycorrhizal habit facilitates masting in trees is strongly implied.     

REPRODUCTIVE OUTPUT AND BIOMASS ALLOCATION IN SESBANIA EMERUS IN A TROPICAL SWAMP

This study examined the correlation of moisture, reproductive phenology, density of mature plants, and herbivory of apical meristems with the morphology and reproductive output of Sesbania emerus, an annual legume growing along a moisture gradient in a swamp in Guanacaste Province, Costa Rica. It also determined how biomass allocation varied and how it was related to reproductive output of plants growing along the moisture gradient within the swamp. Morphological changes included production of more stems and branches in response to herbivory, more and higher prop roots and more aerenchyma as water depth increased, and greater stem diameter in lower densities. Plant height varied greatly within a site, but not among habitats. Plants began to produce flowers and fruits later in wet sites than in dry sites. Reproductive output was generally more sensitive to environmental variables than was plant size. Fruit number and plant height were positively correlated for almost every treatment. Greater fruit and seed production were correlated with drier sites, earlier phenology, and lower density, but not with herbivory. Total biomass accumulation did not vary among moisture sites, but root production appeared to occur at the expense of reproductive output in the wetter sites. Plants in the wetter sites had both a greater percent and a greater absolute amount of biomass in roots, and a lower percent and a lower absolute amount of biomass in fruits and seeds than plants in drier sites. The root: shoot ratio was nearly five times higher in the wet than the dry site. Seed number per plant ranged from a mean of 6,800 at the wet site to a mean of 16,878 at the dry site. If this striking phenotypic variation in reproductive output and biomass accumulation has a genetic basis, the possibility of ecotypic differentiation exists in S. emerus.     

Seed source environment predicts response to water availability in Plantago patagonica

The intensity, duration, and severity of drought increasing across the American Southwest. Plant restoration efforts are often thwarted by drought-induced effects (i.e. drought-induced mortality or failure to reproduce). Careful selection of plant materials to match future environmental conditions could improve restoration success under climate change. Here, we focus on Plantago patagonica, a priority arid land restoration species in the southwestern US. Using experimental drought in a greenhouse and supplemental watering in a common garden experiment, we quantified how the seed-collection site environment influenced plant growth, performance, phenotypic plasticity, and evidence of local adaptation in 12 populations of P. patagonica. In the greenhouse, we found plants from hotter and drier environments had higher root:shoot ratios, while those from more variable precipitation regimes had greater total biomass in response to drought. Populations sourced from warmer environments exhibited sevenfold greater plasticity in root:shoot ratio compared to those from cooler environments, and there was strong evidence for local adaptation in phenology, as populations sourced from geographic locations nearer the common garden exhibited five times more flowering individuals than those sourced furthest from that garden. In the common garden, we found that plants sourced from wetter locations and those with more consistent precipitation regimes had lower mortality and higher specific leaf area, a proxy for growth, under unwatered ambient conditions. These results suggest plant performance of P. patagonica under reduced water availability is strongly shaped by the seed-collection site environment and may be a useful tool for improving restoration outcomes in a changing world.     

Phenological patterns of <Emphasis Type="Italic">Ficus citrifolia</Emphasis> (Moraceae) in a seasonal humid-subtropical region in Southern Brazil

Year-round flowering is widely reported in fig trees and is necessary for the survival of their short-living, specialized Agaonid pollinators. However, seasonality in both fig and leaf production has been noted in almost all published phenological studies. We have addressed the following questions in the present study: (1) Are reproductive and vegetative phenologies seasonal and, consequently, related to climate? (2) Does Ficus citrifolia produce ripe figs year round? (3) Is the fig development related to climate? And, (4) Are reproductive and vegetative phenologies independent? By investigating these questions with a F. citrifolia population over a two-year period, at the southern edge of the tropical region in Brazil, we detected phenological seasonality that was significantly correlated with climate. Our findings can be summarized as follows: (1) Trees became deciduous during the cold and dry months; (2) The flowering onset was asynchronous among individuals, but with moderate concentration during the hot and rainy months; (3) There was a correlation between the onset of flowering and vegetative phenology, with significantly higher crop initiations in individuals with full-leaf canopy; (4) Fig developmental time was longer in cold months; and (5) Ripe fig production occurred year-round and was not correlated with climate. Our results suggest that there are strong selection pressures that maintain the year-round flowering phenology in figs, for we have observed little seasonality in the phenology of such species despite the strong seasonality in the environment.     

Predicting bird phenology from space: satellite‐derived vegetation green‐up signal uncovers spatial variation in phenological synchrony between birds and their environment

Population‐level studies of how tit species (Parus spp.) track the changing phenology of their caterpillar food source have provided a model system allowing inference into how populations can adjust to changing climates, but are often limited because they implicitly assume all individuals experience similar environments. Ecologists are increasingly using satellite‐derived data to quantify aspects of animals' environments, but so far studies examining phenology have generally done so at large spatial scales. Considering the scale at which individuals experience their environment is likely to be key if we are to understand the ecological and evolutionary processes acting on reproductive phenology within populations. Here, we use time series of satellite images, with a resolution of 240 m, to quantify spatial variation in vegetation green‐up for a 385‐ha mixed‐deciduous woodland. Using data spanning 13 years, we demonstrate that annual population‐level measures of the timing of peak abundance of winter moth larvae (Operophtera brumata) and the timing of egg laying in great tits (Parus major) and blue tits (Cyanistes caeruleus) is related to satellite‐derived spring vegetation phenology. We go on to show that timing of local vegetation green‐up significantly explained individual differences in tit reproductive phenology within the population, and that the degree of synchrony between bird and vegetation phenology showed marked spatial variation across the woodland. Areas of high oak tree (Quercus robur) and hazel (Corylus avellana) density showed the strongest match between remote‐sensed vegetation phenology and reproductive phenology in both species. Marked within‐population variation in the extent to which phenology of different trophic levels match suggests that more attention should be given to small‐scale processes when exploring the causes and consequences of phenological matching. We discuss how use of remotely sensed data to study within‐population variation could broaden the scale and scope of studies exploring phenological synchrony between organisms and their environment.     

Plasticity and diversity of the phenology of dioecious Ficus species in Taiwan

While Ficus present a series of traits often associated with dioecy, the prevalence of dioecy in Ficus is atypical. In Asian floras, dioecious Ficus species generally outnumber monoecious ones. Further this is also true in relatively northerly locations for Ficus such as the island of Taiwan. Ficus are pollinated by species-specific wasps that use fig flowers as breeding sites. In dioecious fig species, pollinators develop only in the inflorescences of male fig trees. In this study, we investigated the reproductive phenology of four dioecious Ficus species with distinct ecologies in several locations in northern and southern Taiwan. The two first species (Ficus erecta and Ficus septica) were investigated in four locations. Reproductive phenology was quite different among sites, even within a single species. For example, F. erecta presented well-defined crops at the population level in its usual high-elevation habitat but continuous fig production at low elevations, especially in South Taiwan. The two other fig species (Ficus pedunculosa var. mearnsii and Ficus tinctoria subsp. swinhoei), are shrubs growing together along seashores in exposed locations on coral reef remnants. These two species presented quite different traits allowing the survival of pollinating wasp populations. Ficus pedunculosa var. mearnsii produced figs continuously so that fresh receptive figs were always available for the pollinating wasps while F. tinctoria subsp. swinhoei extended the period of receptivity of its figs, so that receptive figs that had been waiting for pollinating wasps were almost always available. In summary, dioecious figs in Taiwan showed remarkable variation in their phenology, within species among locations or among species within location. Nevertheless, despite this variation, the phenology of the trees always allowed survival of pollinating wasp populations. Dioecious figs seem to have adopted a differentiated set of strategies which result in high resilience of pollinator populations. This resilience could help explain the atypical prevalence of dioecy in Ficus.     

Scots pine plantations growth adaptation to climate warming in locations at the southernmost distribution limit of the species

Under the current climate change conjuncture, understanding the forest plantations capacity of acclimation to warming and increased drought stress is crucial for forest managers. To get some understanding of their adaptability, plantations of similar provenance but located in climatically contrasting sites can be compared. Here we study the growth dynamics and their relationship with climate and drought in two Scots pine (Pinus sylvestris L.) plantations located in the center (Sierra de Guadarrama, wetter site) and south (Sierra Nevada, drier site) of Spain, the latter situated at the southernmost distribution limit of the species. Our objectives are to quantify the trends in radial growth of these plantations, to quantify the influence of climate on growth, and to project the plantations growth as a function of forecasted climate. Results reveal that the plantations from the drier site show lower, and less responsive to climate, growth and greater resilience than those from the wetter site. Furthermore, if the current climate-growth relationships continue in the future, these plantations would maintain the current limited growth rate during the 21st century. On the contrary, plantations from the wetter site show higher growth rate and more resistance to drought, and they are projected to increase growth under the warmer conditions forecasted for the 21st century. Our study shows that plantations in drier sites may have a great capacity to acclimate to local climate conditions and would not be negatively impacted by the projected climate warming.     

Putative biotic drivers of plant phenology: With special reference to pathogens and deciduousness

Plant phenology is not only manifested in the seasonal timing of vegetative and reproductive processes but also has ontogenetic aspects. The adaptive basis of seasonal phenology has been considered mainly in terms of climatic drivers. However, some biotic factors as likely evolutionary influences on plants’ phenology appear to have been under‐researched. Several specific cases of putative biotic factors driving plant phenology are outlined, involving both herbivores and pathogens. These illustrate the diversity of likely interactions rather than any systematic coverage or review. Emphasis is on woody perennials, in which phenology is often most multifaceted and complicated by the ontogenetic aspect. The complete seasonal leaf fall that characterizes deciduous plants may be a very important defense against some pathogens. Whether biotic influences drive acquisition or long‐term persistence of deciduousness is considered. In one case, of leaf rusts in poplars, countervailing influences of the rusts and climate suggest persistence. Often, however, biotic and environmental influences likely reinforce each other. The timing and duration of shoot flushing may in at least some cases contribute to defenses against herbivores, largely through brief periods of “predator satiation” when plant tissues have highest food value. Wide re‐examination of plant phenology, accommodating the roles of biotic factors and their interplays with environments as additional adaptive drivers, is advocated toward developing and applying hypotheses that are observationally or experimentally testable.     

Among population differentiation at nuclear genes in native Scots pine (Pinus sylvestris L.) in Scotland

In the Scottish Highlands, Scots pine is at the north-western extreme of its wide natural distribution. Here, the remaining native populations are patchily distributed in highly variable environments, from the more continental, drier eastern Highlands to the milder, wetter Atlantic Ocean coast. As these pinewoods are the remnants of a naturally established forest, they form a valuable system for analysis of genetic and adaptive variation in heterogeneous environments. Using samples from across the Scottish population, we analysed data from nuclear and mitochondrial genes to assess patterns of within and between population genetic variation. Within population diversity levels were high, and significant genetic differentiation among pairs of Scottish populations at relatively small spatial scales was present at several nuclear loci. At these loci, no differentiation had been found among continental populations, even those separated by large geographic distances. Overall, no clear clustering of Scottish samples was found in population structure analysis suggesting that geographically distant populations with high intra-population nucleotide diversity are not strongly isolated or diverged from each other. Scottish populations lacked a mitotype that is widespread in eastern and north-eastern Europe, indicating that pines from that area may not have participated in the most recent colonisation of the British Isles.     

Do differences in understory light contribute to species distributions along a tropical rainfall gradient?

In tropical forests, regional differences in annual rainfall correlate with differences in plant species composition. Although water availability is clearly one factor determining species distribution, other environmental variables that covary with rainfall may contribute to distributions. One such variable is light availability in the understory, which decreases towards wetter forests due to differences in canopy density and phenology. We established common garden experiments in three sites along a rainfall gradient across the Isthmus of Panama in order to measure the differences in understory light availability, and to evaluate their influence on the performance of 24 shade-tolerant species with contrasting distributions. Within sites, the effect of understory light availability on species performance depended strongly on water availability. When water was not limiting, either naturally in the wetter site or through water supplementation in drier sites, seedling performance improved at higher light. In contrast, when water was limiting at the drier sites, seedling performance was reduced at higher light, presumably due to an increase in water stress that affected mostly wet-distribution species. Although wetter forest understories were on average darker, wet-distribution species were not more shade-tolerant than dry-distribution species. Instead, wet-distribution species had higher absolute growth rates and, when water was not limiting, were better able to take advantage of small increases in light than dry-distribution species. Our results suggest that in wet forests the ability to grow fast during temporary increases in light may be a key trait for successful recruitment. The slower growth rates of the dry-distribution species, possibly due to trade-offs associated with greater drought tolerance, may exclude these species from wetter forests.     

Sexual specialization in two tropical dioecious figs

Ficus species (figs) and their species-specific pollinator wasps are involved in an intimate mutualism in which wasps lay eggs in some ovaries of the closed inflorescences (syconia), and mature, inseminated offspring carry pollen from mature syconia to fertilize receptive inflorescences. In monoecious species, each syconium produces seeds and wasps. In functionally dioecious fig species, making up approximately half the figs worldwide, male and female functions are separated; hermaphrodite (functionally male) trees produce wasps and pollen only, while female trees produce seeds only. This sexual separation allows selection to act independently on the reproductive biology of each sex. Examining sexual specialization in a tight mutualism allows us to determine aspects of the mutualism that are flexible and those that are canalized. In this study, we quantified the phenology of two species of dioecious figs, F. exasperata and F. hispida, for 2 years by following the fates of several thousand syconia over time. In studying each of these species in a dry and a wet site in south India, we tested specific predictions of how dioecious figs might optimize sexual function. On female trees of both species, more inflorescences matured during the wet (monsoon) season than in any other season; this fruiting period enabled seeds to be produced during the season most suitable for germination. In F. exasperata, functionally male trees released most wasps from mature syconia in the dry season, during peak production of receptive female syconia, and thus maximized successful pollination. In F. hispida, “male” trees produced more syconia in the dry and monsoon seasons than in the post-monsoon season. In both species, male and female trees abscised more unpollinated, young inflorescences than pollinated inflorescences, but abscission appeared to be more likely due to resource- rather than pollinator- limitation. The phenology of F. exasperata requires that male inflorescences wait in receptive phase for scarce pollinators to arrive. As expected, male inflorescences of this species had a longer receptive phase than female inflorescences. In F. hispida, where pollinators are rarely scarce, duration of receptive phase was the same for both sexes. Duration of developing phase was longer in female syconia of both species than in male syconia, most likely because they need a longer period of investment in a fleshy fruit. Variation in developing phase of female syconia in one species (F. exasperata) was also greater than that in male syconia, and enabled female trees to sample a variety of germination environments in time. The strong sexual differences in both fig species support the hypothesis that selection for sexual specialization has strongly influenced the reproductive biology of these species. Received: 28 May 1997 / Accepted: 2 February 1998     

Reproduction of an early-flowering Mediterranean mountain narrow endemic (Armeria caespitosa) in a contracting mountain island

Reproduction at population lower edges is important for plant species persistence, especially in populations on contracting high-mountain islands. In this context, the ability of plants to reproduce in different microhabitats seems to be important to guarantee seed production in stressful environments, such as Mediterranean high mountains. We hypothesised that the warmer and drier conditions at the lower edge would be deleterious for the reproduction of Armeria caespitosa, an early-flowering plant. In addition, reproductive plasticity along this mountain gradient may also be microhabitat-dependent. We studied factors affecting the reproductive success of A. caespitosa , an endemic of the Spanish Sistema Central. We considered a complex set of predictors, including phenology, plant size and environmental factors at different scales using generalised estimating equations and generalised linear models. Microhabitat, together with the position in the altitudinal gradient and inter-annual variability affected the reproduction of A. caespitosa . In addition, individuals with longer flowering periods (duration of flowering) had significantly lower fruit set and a higher number of unviable seeds; delayed flowering peaks favoured the production of both viable and unviable fruits. Microhabitat variability over an altitudinal range is relevant for the reproduction of A. caespitosa, and is more important at the lower edge of the altitudinal range, where the species faces the most adverse conditions. In addition, the ability to reproduce in different microhabitats might increase the chances of the species to cope with environmental uncertainties under on-going climate warming. Finally, reproduction of this early-flowering plant is constrained by summer drought, which might shape its reproductive phenology.     

Seasonality of Leaf and Fig Production in Ficus squamosa,a Fig Tree with Seeds Dispersed by Water

The phenology of plants reflects selection generated by seasonal climatic factors and interactions with other plants and animals, within constraints imposed by their phylogenetic history. Fig trees (Ficus) need to produce figs year-round to support their short-lived fig wasp pollinators, but this requirement is partially de-coupled in dioecious species, where female trees only develop seeds, not pollinator offspring. This allows female trees to concentrate seed production at more favorable times of the year. Ficus squamosa is a riparian species whose dispersal is mainly by water, rather than animals. Seeds can float and travel in long distances. We recorded the leaf and reproductive phenology of 174 individuals for three years in Chiang Mai, Northern Thailand. New leaves were produced throughout the year. Fig production occurred year-round, but with large seasonal variations that correlated with temperature and rainfall. Female and male trees initiated maximal fig crops at different times, with production in female trees confined mainly to the rainy season and male figs concentrating fig production in the preceding months, but also often bearing figs continually. Ficus squamosa concentrates seed production by female plants at times when water levels are high, favouring dispersal by water, and asynchronous flowering within male trees allow fig wasps to cycle there, providing them with potential benefits by maintaining pollinators for times when female figs become available to pollinate.     

Hatching date influences winter habitat occupancy: Examining seasonal interactions across the full annual cycle in a migratory songbird

Birds experience a sequence of critical events during their life cycle, and past events can subsequently determine future performance via carry‐over effects. Events during the non‐breeding season may influence breeding season phenology or productivity. Less is understood about how events during the breeding season affect individuals subsequently in their life cycle. Using stable carbon isotopes, we examined carry‐over effects throughout the annual cycle of prairie warblers (Setophaga discolor), a declining Nearctic–Neotropical migratory passerine bird. In drier winters, juvenile males that hatched earlier at our study site in Massachusetts, USA, occupied wetter, better‐quality winter habitat in the Caribbean, as indicated by depleted carbon isotope signatures. For juveniles that were sampled again as adults, repeatability in isotope signatures indicated similar winter habitat occupancy across years. Thus, hatching date of juvenile males appears to influence lifetime winter habitat occupancy. For adult males, reproductive success did not carry over to influence winter habitat occupancy. We did not find temporally consecutive “domino” effects across the annual cycle (breeding to wintering to breeding) or interseasonal, intergenerational effects. Our finding that a male''s hatching date can have a lasting effect on winter habitat occupancy represents an important contribution to our understanding of seasonal interactions in migratory birds.     

Warming, plant phenology and the spatial dimension of trophic mismatch for large herbivores

Temporal advancement of resource availability by warming in seasonal environments can reduce reproductive success of vertebrates if their own reproductive phenology does not also advance with warming. Indirect evidence from large-scale analyses suggests, however, that migratory vertebrates might compensate for this by tracking phenological variation across landscapes. Results from our two-year warming experiment combined with seven years of observations of plant phenology and offspring production by caribou (Rangifer tarandus) in Greenland, however, contradict evidence from large-scale analyses. At spatial scales relevant to the foraging horizon of individual herbivores, spatial variability in plant phenology was reduced--not increased--by both experimental and observed warming. Concurrently, offspring production by female caribou declined with reductions in spatial variability in plant phenology. By highlighting the spatial dimension of trophic mismatch, these results reveal heretofore unexpected adverse consequences of climatic warming for herbivore population ecology.     

Are tetraploids more successful? Floral signals,reproductive success and floral isolation in mixed-ploidy populations of a terrestrial orchid

Background and Aims Polyploidization, the doubling of chromosome sets, is common in angiosperms and has a range of evolutionary consequences. Newly formed polyploid lineages are reproductively isolated from their diploid progenitors due to triploid sterility, but also prone to extinction because compatible mating partners are rare. Models have suggested that assortative mating and increased reproductive fitness play a key role in the successful establishment and persistence of polyploids. However, little is known about these factors in natural mixed-ploidy populations. This study investigated floral traits that can affect pollinator attraction and efficiency, as well as reproductive success in diploid and tetraploid Gymnadenia conopsea (Orchidaceae) plants in two natural, mixed-ploidy populations.Methods Ploidy levels were determined using flow cytometry, and flowering phenology and herbivory were also assessed. Reproductive success was determined by counting fruits and viable seeds of marked plants. Pollinator-mediated floral isolation was measured using experimental arrays, with pollen flow tracked by means of staining pollinia with histological dye.Key Results Tetraploids had larger floral displays and different floral scent bouquets than diploids, but cytotypes differed only slightly in floral colour. Significant floral isolation was found between the two cytotypes. Flowering phenology of the two cytotypes greatly overlapped, and herbivory did not differ between cytotypes or was lower in tetraploids. In addition, tetraploids had higher reproductive success compared with diploids.Conclusions The results suggest that floral isolation and increased reproductive success of polyploids may help to explain their successful persistence in mixed-ploidy populations. These factors might even initiate transformation of populations from pure diploid to pure tetraploid.