Phenological synchrony affects interaction strength of an exotic weevil with Platte thistle,a native host plant

Phenological synchrony of a consumer population with its resource populations is expected to affect interaction intensity. We quantified phenological variation and synchrony of populations of an invasive Eurasian flower head weevil, Rhinocyllus conicus, that consumes florets, ovules, and seeds of developing flower heads of a native North American thistle, Cirsium canescens, in Sand Hills prairie in Nebraska, USA. Variation in timing of adult activity among weevil populations was larger than variation in timing of flower head development among C. canescens populations, and it drove the observed variation in the phenological synchrony between weevil and host plant populations. Furthermore, the degree of phenological synchrony between populations was significant in explaining variation in weevil egg load on the newly acquired host plant. Because population growth of C. canescens is limited by predispersal seed losses to floral herbivores, variation in the synchrony of herbivore and plant flowering will affect the density of the plant population. These results provide strong quantitative support for the hypothesis that the synchrony of insect activity with plant resources can determine the magnitude of impact of floral herbivores on their host plant populations.     

Priority resource access mediates competitive intensity between an invasive weevil and native floral herbivores

Mechanisms underlying invasive species impacts remain incompletely understood. We tested the hypothesis that priority resource access by an invasive biocontrol weevil, Rhinocyllus conicus, intensifies and alters the outcome of competition with native floral herbivores over flower head resources of the non-target, native host plant Cirsium canescens, specifically with the predominant, synchronous tephritid fly Paracantha culta. Four main results emerged. First, we documented strong, asymmetric competition, with R. conicus out-competing P. culta. Second, weevil priority access to floral resources accelerated competitive suppression of P. culta. Evidence for competitive suppression with increased weevil priority included decreases in both the numbers and the total biomass of native flies, plus decreases in individual P. culta fly mass and, so, potential fitness. Third, we found evidence for three concurrent mechanisms underlying the competitive suppression of P. culta by R. conicus. Prior use of a flower head by R. conicus interfered with P. culta pre-oviposition behavior. Once oviposition occurred, the weevil also reduced fly post-oviposition performance. Preemptive resource exploitation occurred, shown by the significant effect of flower head size on the total number of insects developing and in the magnitude of R. conicus effects on P. culta. Interference also occurred, shown by a spatial shift of surviving P. culta individuals away from the preferred receptacle resources as R. conicus priority increased. Finally, fourth, using an individual-based model (IBM), we found that the competitive interactions documented have the potential for imposing demographic consequences, causing a reduction in P. culta population sizes. Thus, priority resource access by an invasive insect increased competitive impact on the predominant native insect in the invaded floral guild. This study also provides the first experimental evidence for non-target effects of a weed biological control agent on an associated native insect herbivore.     

Exotic weevil invasion increases floral herbivore community density,function, and impact on a native plant

Consumer communities are being re‐arranged through unprecedented rates of human‐mediated invasions and extinctions. Such changes in consumer diversity potentially alter community function and impact on resource populations. Although insect herbivore invasions are increasingly common, the influence of such species additions on native resident herbivore guilds, along with their individual and combined effects on native plant resources, are rarely investigated. Here, we used site‐to‐site and plant‐to‐plant variation in herbivore composition to examine how the addition of an invasive exotic weevil, Rhinocyllus conicus, combines with a guild of native floral herbivores (tephritid flies, pyralid moths) to influence two key components of herbivore community function – aggregate herbivore densities and cumulative levels of seed destruction – on a native thistle, Cirsium canescens. Invasion of a site by R. conicus more than doubled aggregate herbivore density, resulting in increased levels of seed destruction and a halving of seed production by the native thistle. Further, herbivore function was significantly higher on individual plants attacked by R. conicus, compared to plants attacked only by native herbivores. Insect densities and levels of seed destruction on plants attacked by multiple herbivore taxa never exceeded those observed for plants attacked by R. conicus alone, suggesting that increases in herbivore community function with invasion resulted from the inclusion of a functionally dominant insect rather than any complementarity effects. Some evidence for interference between insects emerged, with a trend towards reduced moth and weevil densities in two and three taxon mixtures compared with plants attacked by each taxon alone. However, density compensation was limited so that, overall, the addition of a novel herbivore to the floral guild was associated with a significant increase in herbivore community function and impact on seed production. The results suggest that invasion of a functionally dominant herbivore into an unsaturated recipient community can augment function within a resource guild.     

Consequences of variation in flowering phenology for seed head herbivory and reproductive success in Erigeron glaucus (Compositae)

Summary We examined the relationship between flowering phenology, reproductive success (seed production only), and seed head herbivory for 20 similarly sized clones of Erigeron glaucus growing at Bodega Bay Reserve, northern California, USA. Although clones tended to reach peak flowering on the same date, they differed in the proportion of their total flowers produced around that date (flowering synchrony). Clones also differed in the number and density of flower heads presented at any one time to pollinators and herbivores (floral display). Both of these characteristics had consequences for herbivory and plant reproductive success. The proportion of flower heads damaged by insect herbivores was greater for clones that concentrated flowering activity during the main flowering period for the population as a whole (high synchrony) compared to clones that spread flowering out temporally. The primary reason for this result was that clones with low flowering synchrony produced a significant proportion of their flower heads during the fall and therefore, escaped attack by the tephritid fly, Tephritis ovatipennis. Clones with intermediate synchrony had lower seed success (total number of viable seeds produced over the year) than clones with either low or high synchrony. The proportion of flower heads damaged by insect herbivores and number of tephritid flies reared from flower heads were both negatively correlated to floral display while seed head mass and germination rates were positively related to display. Thus, clones which produced dense floral displays were favored both in terms of reduced herbivory and increased successful seed production.     

Host recognition by Rhinocyllus conicus of floral scents from invasive and threatened thistles

One of the main obstacles of classical biological control is that biological control organisms cannot be recalled once they are released in nature. It is particularly true for the flowerhead weevil, Rhinocyllus conicus Frölich, which was released as a biological control organism for the invasive musk thistle, Carduus nutans L. (MT). While weevils successfully suppressed introduced populations of musk thistles and other invasive thistle species, non-target attacks have been reported on multiple native thistles including federally listed threatened and endangered (T&E) thistle species. To investigate the foraging behavior of female weevils on invasive and native thistles, we examined volatile organic compounds (VOCs) emitted from MT and a T&E plant species, Sacramento Mountains thistle, Cirsium vinaceum Wooton & Standley (SMT) in the Lincoln National Forest, New Mexico. We used a dynamic headspace volatile collection system and gas chromatography-mass spectrometry to compare volatile profiles between MT and SMT. Female weevils reacted to 7 electrophysiologically active chemical compounds in the blends based on gas chromatography-electroantennography. The behavioral response of female weevils was indifferent when VOCs from both thistles were offered in y-tube olfactometry experiments. Yet, they preferred VOCs collected from MT to purified air. The searching time of female weevils was longer to VOCs collected from SMT over controls. Investigating signals during the initial host recognition of released biological control organisms may open new opportunities to reduce non-target attacks on T&E plant species.

     

Individually mark–mass release–resight study elucidates effects of patch characteristics and distance on host patch location by an insect herbivore

1. How organisms locate their hosts is of fundamental importance in a variety of basic and applied ecological fields, including population dynamics, invasive species management and biological control. However, tracking movement of small organisms, such as insects, poses significant logistical challenges. 2. Mass‐release and individual–mark–recapture techniques were combined in an individually mark–mass release–resight (IMMRR) approach to track the movement of over 2000 adult insects in an economically important plant–herbivore system. Despite its widespread use for the biological control of the invasive thistle Carduus nutans, the host‐finding behaviour of the thistle head weevil Rhinocyllus conicus has not previously been studied. Insects were released at different distances from a mosaic of artificially created host patches with different areas and number of plants to assess the ecological determinants of patch finding. 3. The study was able to characterize the within‐season dispersal abilities and between‐patch movement patterns of R. conicus. Weevils found host plant patches over 900 m away. Large patches, with tall plants, situated close to the nearest release point had the highest first R. conicus resights. Patch area and plant density had no effect on the number of weevils resighted per plant; however, R. conicus individuals were more likely to disperse out of small patches and into large patches. 4. By understanding how R. conicus locates host patches of C. nutans, management activities for the control of this invasive thistle can be better informed. A deeper mechanistic understanding of host location will also improve prediction of coupled plant–herbivore spatial dynamics in general.     

Classical Biological Control of Nodding and Plumeless Thistles

Nodding (musk) thistle (Carduus thoermeri Weinmann in the Carduus nutans L. group) and plumeless thistle (Carduus acanthoides L.) are introduced noxious weeds of Eurasian origin. Both weeds are problematic in pastures, rangelands, and croplands and along state highways in many parts of the United States. The success of both species of thistles is largely due to their prolific seed production, seed longevity, competitive ability, and lack of natural enemies. Classical biological control of nodding thistle in Virginia has been achieved with three exotic thistle herbivores, Rhinocyllus conicus Froelich (Coleoptera: Curculionidae), Trichosirocalus horridus (Panzer) (Coleoptera: Curculionidae), and Cassida rubiginosa Müller (Coleoptera: Chrysomelidae). T. horridus also effectively controls plumeless thistle. These insect herbivores complement each other. Nodding thistle biological control is achieved in about 5–6 years in Virginia, Missouri, and Montana. In addition, a rust fungus (Puccinia carduorum Jacky) (Uredinales: Pucciniaceae) has been introduced and established for control of nodding thistle in Virginia. Development and reproduction of the three thistle herbivores are not adversely affected by the rust. The rust hastens plant senescence and reduces seed production. Control of plumeless thistle with R. conicus and T. horridus takes approximately twice as long as control of nodding thistle.     

Small‐scale spatial autocorrelation and the interpretation of relationships between phenological parameters

Question: Are flower production and associated phenological variables (onset, end, duration, and three measures of flowering synchrony) randomly distributed in space or, alternatively, is there a neighbourhood structure (spatial autocorrelation) in the values of these variables? To which extent does spatial autocorrelation affect the correlation tests between phenological traits? Location: A tree savanna reserve in Southeastern Brazil (22°15′S,47°08′W). Methods: The flowering season of Chromolaena odorata was followed for all (96) individuals in a completely mapped area of 3000 m². The phenological traits were estimated by counting flower heads in anthesis on individual plants every seven days for 14 weeks. Results: Flowering time was unimodally distributed, but with different peak dates depending on whether individual flower heads or plants were counted. Three phenological traits and canopy closure above the plants showed some degree of spatial autocorrelation, which caused loss of up to 35% of degrees of freedom in nine of 36 correlation tests. Such a decrease in the degrees of freedom resulted in loss of significance for correlations in three pairs of variables. Conclusions: We hypothesize that the spatial autocorrelation in phenological traits between C. odorata neighbours may be driven by genetic similarity among neighbouring plants and/or spatial structuring of environmental factors. Because location and distance between samples may affect their statistical independence, we suggest that spatial autocorrelation should be taken into account in future studies of plant phenology, e.g. by using effective sample size in statistical tests.     

Host utilization of field-caged native and introduced thistle species by Rhinocyllus conicus

Rhinocyllus conicus Fr?elich was introduced from Europe into North America as a biological control agent of the exotic weed Carduus nutans L. Concern exists over the feeding of this weevil on at least 25 species of native Cirsium thistles. Beginning in 2008, cage studies isolating adults of R. conicus on buds and flower heads of all eight thistle species (native and introduced) recorded from Tennessee were conducted to test if R. conicus could use these species for reproduction and what impacts larval feeding of R. conicus may have on seed production. Larvae of R. conicus completed development in heads of the native species C. carolinianum (Walter) Fernald and Schubert. and C. horridulum Michaux, and significant reductions in seed numbers of both species occurred during 2008. Rhinocyllus conicus oviposited on both C. carolinianum and C. horridulum at significantly greater levels than the introduced species C. arvense (L.) Scopoli and C. vulgare (Savi) Tenore. Infested heads of C. carolinianum contained numbers of R. conicus per centimeter of plant head width similar to Ca. nutans in 2008, and both native species contained numbers of R. conicus per centimeter of plant head width similar to C. arvense and C. vulgare in 2009. Body length was similar between R. conicus reared on native thistles and its target host Ca. nutans. This report is the first documentation of R. conicus feeding and reproducing on C. carolinianum and C. horridulum. Although R. conicus has been observed only on introduced thistles in naturally occurring populations in this region, the utilization of C. carolinianum and C. horridulum as host species in controlled conditions warrants continued monitoring of field populations and further investigation into factors that may influence nontarget feeding in the future.     

THE POPULATION ECOLOGY OF A DUNE THISTLE,CIRSIUM RHOTHOPHILUM (ASTERACEAE)

A population study of a thistle, Cirsium rhothophilum, was carried out in the coastal dunes of northern Santa Barbara County, California during 1978 and 1979. Seedling establishment, growth, flowering, and fruiting were observed in permanently marked transects. A total of 1,041 individuals were recorded. Despite 41% mortality during the year of study, the average population features changed remarkably little. Cirsium rhothophilum was found to be monocarpic but relatively long-lived. Extrapolations from rosette size growth and proportions of rosettes in different size classes giving rise to flowering individuals suggest that the average plant may have a vegetative stage of more than 5 years. Growth analysis of c . rhothophilum is complicated by the subsurface branching of stems, presumed to be the result of insect damage and sand burial. Dissection of fruiting heads showed that sound achenes were only about 22% of the total number of potential achenes. Insect damage was evident on about 20% of the unsound achenes. Considering both the loss of achenes within heads and of entire heads which failed to mature, insects are estimated to destroy at least 25% of the achenes. Achenes germinate readily and do not appear to have more than mild dormancy. A burial experiment showed that emergence declined sharply with depth of burial to zero at 8 cm. Despite the dynamic nature of the dune habitat, C. rhothophilum populations appear stable. The relatively large size and ability to grow rapidly and adapt to burial allow C. rhothophilum to average out environmental vicissitudes.     

Mutualistic interaction between a weevil and a rust fungus, two parasites of the weed Cirsium arvense

We present a mutualism between a stem-boring weevil, Apion onopordi Kirby (Coleoptera: Apionidae), and a rust fungus, Puccinia punctiformis (Str.) Röhl. (Uredinales), both parasites of the creeping thistle, Cirsium arvense (L.) Scop. (Asteraceae). Females, but not males, of A. onopordi induced systemic rust infections of thistle shoots in the season after they were attacked by the weevil, indicating that insect oviposition is a crucial stage in pathogen transmission. Adult weevils emerged from systemically infected thistle shoots were heavier than weevils from healthy C. arvense shoots. Heavier females had a higher fecundity and laid larger eggs. The weevil preferred to deposit eggs in systemically rust-infected over healthy thistle shoots, which seemed to be a sub-optimal host. This is to our knowledge the first report of a mutualistic interaction between an herbivorous insect and a biotrophic plant pathogen. The mechanism responsible for the advantage of rust-infected shoots for A. onopordi causes a different outcome in other thistle herbivores, and therefore can not be explained by a general enhancement of nutritional quality in rust-infected tissue. This mutualism likely has evolved from a competitive relationship. Unlike other thistle herbivores A. onopordi seems to be better suited as mutualist for P. punctiformis because of its small impact on the host plant and its feeding niche on plant parts not directly associated with pathogen reproduction.     

Seedlings and ramets recruitment in two rhizomatous species of Rupestrian grasslands: Leiothrix curvifolia var. lanuginosa and Leiothrix crassifolia (Eriocaulaceae)

Leiothrix curvifolia var. lanuginosa and Leiothrix crassifolia are endemic and sympatric species in the Brazilian rupestrian grasslands, a habitat that has a predominance of sandy and shallow soils with low water retention. Based on the premise that soil moisture is one of the abiotic factors that affects most reproduction in plants, we hypothesized that the flowering phenology events and establishment of sexual and vegetative offspring would occur in the periods of higher soil water availability. We marked 478 ramets distributed among 100 genets of L. curvifolia var. lanuginosa and 693 ramets distributed among 100 genets of L. crassifolia, so that they could be observed monthly along the two rainy seasons from December 2003 to 2004. Both species showed phenological synchrony in the flower heads and seedlings production with soil moisture availability. Seedling mortality was intense in the dry period. Unlike the seedlings, the ramets survived was 100%. The greater capacity of ramets to survive can result from a much greater biomass compared with seedlings, and ramets become adult much faster. We conclude that for a successful seedling establishment, the synchronization with the rainy season was required, and moreover, that repeated seedling recruitment can be important for the maintenance of local populations of these species which suffer from high seedling mortality in the drought period. It is likely that the coincidence of the rainy period with seedling establishment is an important factor that determines the flowering phenological pattern of L. curvifolia var. lanuginosa and L. crassifolia in rupestrian grasslands.     

Spatial prediction of habitat overlap of introduced and native thistles to identify potential areas of nontarget activity of biological control agents

Nontarget feeding of Rhinocyllus conicus Fr?elich and Trichosirocalus horridus (Panzer) on native North American thistles in the genus Cirsium has been documented. Some species of these native thistles have shown greater infestation levels of R. conicus in populations that are in close proximity to the target plant species, Carduus nutans L. In 2005 a study was initiated to identify areas of potential nontarget feeding by R. conicus and T. horridus on thistle species by predicting habitats of two known introduced hosts [C. nutans and Cirsium vulgare (Savi) Tenore] and two native species [Cirsium carolinianum (Walter) Fernald and Schubert and C. discolor (Muhlenberg ex Willdenow) Sprengel] using Mahalanobis distance (D(2)). Cumulative frequency graphs showed that the D(2) models for all four plant species effectively identified site conditions that contribute to the presence of the respective species. Poisson regression showed an association between D(2) values and plant counts at field-test sites for C. nutans and C. carolinianum. However, negative binomial regression detected no association between D(2) values and plant counts for C. discolor or C. vulgare. Chi-square analysis indicated associations between both weevil species and sites where C. vulgare and Carduus nutans were found, but not between the weevil and native thistle species. Habitats of C. nutans and Cirsium carolinianum overlapped in ≈12% of the study area. Data-based habitat models may provide a powerful tool for land managers and scientists to monitor native plant populations for nontarget feeding by introduced biological control agents.     

The strength of assortative mating for flowering date and its basis in individual variation in flowering schedule

Although it has been widely asserted that plants mate assortatively by flowering time, there is virtually no published information on the strength or causes of phenological assortment in natural populations. When strong, assortative mating can accelerate the evolution of plant reproductive phenology through its inflationary effect on genetic variance. We estimated potential assortative mating for flowering date in 31 old‐field species in Ontario, Canada. For each species, we constructed a matrix of pairwise mating probabilities from the individual flowering schedules, that is the number of flower deployed on successive dates. The matrix was used to estimate the phenotypic correlation between mates, ρ, for flowering date. We also developed a measure of flowering synchrony within species, S, based upon the eigenstructure of the mating matrix. The mean correlation between pollen recipients and potential donors for flowering date was  = 0.31 (range: 0.05–0.63). A strong potential for assortative mating was found among species with high variance in flowering date, flowering schedules of short duration and skew towards early flower deployment. Flowering synchrony, S, was negatively correlated with potential assortment (r = ?0.49), but we go on to show that although low synchrony is a necessary condition for phenological assortative mating, it may not be sufficient to induce assortment for a given phenological trait. The potential correlation between mates showed no seasonal trend; thus, as climate change imposes selection on phenology through longer growing seasons, spring‐flowering species are no more likely to experience an accelerated evolutionary response than summer species.     

Factors affecting fruit and seed production of Paeonia ostii “Feng Dan”, an economically important oil tree

Many factors may affect reproduction of animal-pollinated species. In this study, the effects of pollen limitation, attractive traits (flower number, plant height and flower width) and flowering phenological traits (flowering onset, duration and synchrony) on female reproduction, as well as the patterns of variation in fruit and seed production within plants, were investigated in Paeonia ostii “Feng Dan” over two flowering seasons (2018 and 2019). Fruit set was very high (90%), and pollen supplementation did not increase fruit and seed production in either year, indicating no pollen limitation. Fruit set, ovule number per fruit and mean individual seed weight per fruit were not affected by any of the six attractive and phenological traits in either year, whereas seed number per fruit was related to the three attractive traits in one or both years. Seed number per plant was positively affected by the three attractive traits and best explained by flower number in both years, but the effect of each of the three phenological traits on seed number per plant differed between years. Within plants, the fruit set, ovule number, seed set and seed number per fruit declined from early- to late-opening flowers, presumably because of resource preemption, but the mean individual seed weight did not vary across the flowering sequence. Our study shows that attractive traits of Paeonia ostii “Feng Dan” are more important than flowering phenological traits in the prediction of total seed production per plant.     

Direct and Indirect Effects of a Shoot-Base Boring Weevil and Plant Competition on the Performance of Creeping Thistle, Cirsium arvense

Creeping thistle or Canada thistle, Cirsium arvense (L.) Scop., is considered one of the world's worst weeds and the third most important weed in Europe. Biological control of this indigenous weed in Europe by use of native agents may provide a low-cost alternative to use of chemical or mechanical control measures and contribute to a more sustainable weed management. We investigated the potential of a shoot-base boring weevil, Apion onopordi Kirby (Coleoptera: Apionidae), for biological weed control, in the presence or absence of plant competition by three grass species. Infestation of thistle shoots by A. onopordi at natural infestation levels reduced above- and belowground plant performance after 2 years. Plant competition at natural levels had an overall greater effect than that of herbivory, significantly reducing both above- and belowground thistle performance in both years, thereby slowing the propagation of the weed. Weevil infestation and grass competition had a synergistic effect on C. arvense growth; the combined effects of the two factors was greater than the sum of both single-factor effects. The experiment revealed that A. onopordi promotes systemic infections of the rust fungus Puccinia punctiformis (Str.) Röhl in the year following weevil infestation. Systemically infected thistle shoots died before the end of the growing season. Although the direct effect of A. onopordi may not be sufficient to control creeping thistle, the synergistic interaction with plant competition and the indirect effect via promotion of systemic rust infections makes A. onopordi a promising agent for the biological control of this weed.     

Intra- and interspecific density dependence mediates weather effects on the population dynamics of a plant–insect herbivore system

Temperature and precipitation are two major factors determining arthropod population densities, but the effects from these climate variables are seldom evaluated in the same study system and in combination with inter- and intraspecific density dependence. In this study, I used a 19 year time series on plant variables (shoot height and flowering incidence) and insect density in order to understand direct and indirect effects of climatic fluctuations on insect population densities. The study system includes two closely related leaf beetle species (Galerucella spp.) and a flower feeding weevil Nanophyes marmoratus attacking the plant purple loosestrife Lythrum salicaria. Results suggest that both intraspecific density dependence and weather variables affected Galerucella population densities, with interactive effects of rain and temperature on insect densities that depended on the timing relative to insect life cycles. In spring, high temperatures increased Galerucella densities only when combined with high rain, as low rain implies a high drought risk. Low temperatures are only beneficial if combined with little rain, as high rain cause chilly and wet conditions that are bad for insects. In summer, interactive effects of rain and temperature are different because high temperatures and little rain cause drought that induce wilting in plants, thus reducing food availability for the leaf feeding larvae. In contrast, the density of the flower feeding weevil was less affected by temperature and precipitation directly, and more indirectly interspecific density dependent effects through reduced resource availability caused by previous Galerucella damage.     

Pollen availability,seed production and seed predator clutch size in a tephritid—thistle system

Summary We develop a simple model explaining clutch size behaviour ofOrellia ruficauda on its principle host in North America,Cirsium arvense. Offspring of flies feed solely on thistle seeds and seed production is pollen-limited. Thus, female flies risk reduced offspring fitness when committing large clutches to hosts (female flower heads) occurring in localities where male plants are locally absent. We therefore predict that attacked hosts will contain fewer eggs in such localities, a prediction that is consistent with data obtained in the field: large clutches are never laid in flower heads in low-pollination localities. However, larvae reared from such low-quality hosts are significantly smaller on average and will therefore carry smaller egg loads as adults. Small clutches in poor-quality hosts may thus be an expression of lower per-adult fecundity. Nevertheless, sufficient numbers of large, fecund flies are produced in low-pollination localities to make this last explanation less convincing.     

Phenological variation in fruit characteristics in vertebrate-dispersed plants

Summary We investigated inter-specific variation in fruit characteristics — fruit size, seed number per fruit, seed weight, nutritional content, fruit persistence, and fruit synchronization — in relation to flowering and fruiting phenology in 34 species of fleshy fruited plants. Except for aspects of fruit synchrony and persistence, the results in general were inconsistent with previous suggestions about adaptive variation in phenologically related fruit traits. The main results were as follows: (1) Late flowering, late fruiting, lengthy development time from flower to fruit, and highly persistent fruits constitute a complex of correlated characteristics among the species. (2) Synchronization of fruiting within individuals increased from early ripening fruits to late ripening fruits. Fruiting synchrony was more pronounced in species with a small crop size than in species with a large fruit crop, whereas synchrony was not significantly related to flowering synchronization, nor to life form. (3) Nitrogen and carbohydrate content of fruit pulp did not vary in relation to phenology, whereas lipid content decreased from early to late ripening fruits. (4) No seasonal trends were found for variation in seed size or seed number per fruit. (5) Interactions with flowering phenology and developmental constraints are important in phenological fruiting patterns. Temporal variation in start of fruiting was partly (36%) explained by variation in flowering time. Seed weight variation explained 17% of variation in development time from flower to fruit. (6) Despite constraints from flowering and seed development, some adaptive adjustment in fruiting phenology is likely to be allowed for among the investigated species. Such an adaptive variation in fruiting phenology was suggested by intra-generic comparisons of Prunus and Vaccinium species.