Increased seed predation in the second fruiting event during an exceptionally long period of community-level masting in Borneo

In Southeast Asian tropical rainforests, community-level masting (CM) occurs at irregular intervals of 2–10 years. During CM periods, many plant species from various families synchronously flower and subsequently undergo community-level fruiting. Seed predation is a key factor in understanding the ecological and evolutionary factors affecting CM. Masting is proposed to decrease seed mortality due to predation in two ways: by depressing predator abundance through extended and unpredictable absences of seeds; and by satiating predators via mass seed production (predator satiation hypothesis). If the hypothesis is valid in these rainforests, the incidence of seed predation will be higher in a fruiting event that occurs soon after a previous fruiting event, because the intervening period of seed absence would be inadequate to starve the predators. In this study, we examined seed predation by insects, focusing on five dipterocarp species that exceptionally reproduced twice during an extended CM period. All of the five species suffered more intense seed predation in the second fruiting event, consistent with the prediction expected from the predator satiation hypothesis. Weevils, bark beetles and mammals were the main cause of increased seed predation in three, one and one plant species, respectively. However, seed predation intensity did not increase during the second fruiting event in a few combinations of predator and plant species. We discuss the possibility that competition for seeds among predators and/or the interspecific differences in life history traits among predators might affect the varying intensities of seed predation among dipterocarp species by different seed predators.     

Responses of pre‐dispersal seed predators to sequential flowering of Dipterocarps in Malaysia

Many species of Dipterocarpaceae and other plant families reproduce synchronously at irregular, multi‐year intervals in Southeast Asian forests. These community‐wide general flowering events are thought to facilitate seed survival through satiation of generalist seed predators. During a general flowering event, closely related Shorea species (Dipterocarpaceae) stagger their flowering times by several weeks, which may minimize cross pollination and interspecific competition for pollinators. Generalist, pre‐dispersal seed predators might also track flowering hosts and influence predator satiation. We addressed the question of whether pre‐dispersal seed predation differed between early and late flowering Shorea species by monitoring flowering, fruiting and seed predation intensity over two general flowering events at the Pasoh Research Forest, Malaysia. Pre‐dispersal insect seed predators killed up to 63 percent of developing seeds, with Nanophyes shoreae, a weevil that feeds on immature seeds being the most important predator for all Shorea species. This weevil caused significantly greater pre‐dispersal seed predation in earlier flowering species. Long larval development time precluded oviposition by adults that emerged from the earliest flowering Shorea on the final flowering Shorea. In contrast, larvae of weevils that feed on mature seeds before seed dispersal (Alcidodes spp.), appeared in seeds of all Shorea species almost simultaneously. We conclude that general flowering events have the potential to satiate post‐dispersal seed predators and pre‐dispersal seed predators of mature fruit, but are less effective at satiating pre‐dispersal predators of immature fruit attacking early flowering species.     

On the density-dependence of seed predation in<Emphasis Type="Italic"> Dipteryx micrantha</Emphasis>, a bat-dispersed rain forest tree

We studied the effect of seed density on seed predation by following the fate of bat-dispersed Dipteryx micrantha (Leguminosae) seeds deposited under bat feeding roosts. The study was conducted in Cocha Cashu biological station, Amazonian Peru, during the fruiting period of Dipteryx. Predation of Dipteryx seeds in the area is mainly by large to medium-sized rodents. Seed deposits beneath bat feeding roosts were monitored for a 13-week period in an 18-ha study area. A total of 210 seed deposits were found, and on average, seed predators encountered 22% of them during any one week. About one-third of the seed deposits escaped predation, and those deposits that had relatively few seeds were more likely to go unnoticed by rodents than were deposits with many seeds. The mean seed destruction rate was 8% per week; deposits with many seeds tended to lose a smaller proportion of their seeds to seed predators than did deposits with few seeds. Regression tests for the weekly data showed that, at the beginning of the observation period, seed predation was not density-dependent. Later, when the total seed crop beneath roosts was high, the number of seeds predated per deposit was positively density-dependent, while the proportion of seeds predated was negatively density-dependent, indicating predator satiation. Seed deposits that had been visited by seed predators once had a higher probability of being revisited the week after, especially if they contained many seeds when first encountered. This indicates that the foraging behavior of rodents may be affected by their remembering the location of seed-rich patches.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Seed production and predispersal seed predation

Seed production and predispersal seed predation in the shrub Acacia suaveolens were examined over 3 consecutive years in eight populations in south-eastern Australia. Seed-crop sizes varied both between and within populations of different ages. Seed production was maximal in the first one to four flowering seasons after establishment, and then declined with plant age. The size of the annual seed-crop was also influenced by rainfall for that year. Predispersal seed predation varies between populations over fruiting seasons with the initial large seed-crops resulting in predator satiation. Within one fruiting season, no significant variation in the extent of predispersal seed predation was found in any of three populations studied. There were two major forms of predispersal seed loss: toss of whole fruits to Melanterius corosus (Coleoptera: Curculionidae) and external insect seed grazers, and loss of individual seeds within fruits to M. corosus. Exclusion experiments showed that seeds lost to these predispersal seed predators would otherwise have been matured by the parent plant. The effects of predispersal seed predation cannot be directly related to seedling recruitment. Indirectly, such predation may influence the dispersion of seeds in the soil profile and hence, subsequent recruitment.     

Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range

Predator satiation and seed abortion have been reported as effective mechanisms reducing pre-dispersal seed predation, however, whether they may act simultaneously and whether their contribution to seed defense may spatially vary has been barely addressed. Across the altitudinal range of the dry tropical tree Acacia pennatula we investigated the importance of seed production and seed abortion as defense mechanisms against its pre-dispersal seed predators (Mimosestes spp.). Additionally, we measured the potential relationship between the number of seeds that escaped predation and plant recruitment. Predator satiation was effective since greater fruit production was associated with a lower proportion of predated seeds, while high seed abortion rates were related to increases in larval mortality. Although both mechanisms were present simultaneously, their relative contribution varied considerably across the altitudinal range: predator satiation was favored in the middle parts of the range, where seed production is much higher, whereas seed abortion was particularly relevant at the peripheral sites and especially high at the upper margin. The number of seeds that escaped predation was related to seedling density at plot level, indicating the demographic significance of these defense mechanisms against pre-dispersal seed predation. Overall, these results highlight the importance of considering spatial variability when analyzing seed defense traits and they also suggest considering predator satiation and seed abortion as two complementary mechanisms to reduce seed loss.     

Fruit production in Sorbus aucuparia L. (Rosaceae) and pre-dispersal seed predation by the apple fruit moth (Argyresthia conjugella Zell.)

Variation in fruit production and pre-dispersal seed predation by Argyresthia conjugella was studied in␣four populations of Sorbus aucuparia in northern Sweden.␣The number of infructescences, fruits per infructescence, consumed seeds and developed unattacked seeds per fruit were scored in marked trees from 1984 to 1990. The results showed that the number of fruits produced in each population determined the number of seed predators occurring in the host population, as the yearly number of seed predators was significantly and positively correlated with yearly number of fruits, in all but one population. The seed predators showed a delay in response to variation in number of fruits produced. This lag in response resulted in a large proportion of fruits being attacked and seeds consumed in a bad fruiting year that followed a good fruiting year, and vice versa. The proportion of fruits attacked and seeds consumed was largest in the population showing the greatest between-year variation in fruit production and lowest in the population showing the lowest between-year variation in fruit production. Furthermore, the individuals within the former population were synchronised, while they were not in the latter population. These results contradict one of the possible explanations of mast-seeding, where large synchronised between-year variation is supposed to reduce pre-dispersal seed predation. Instead, differences in attraction of the seed predator to differences in fruit crop size could explain the observed difference in seed predation between the two populations with opposite fruiting patterns. Within each population, irrespective of year, the proportion of fruits attacked and seeds consumed was independent of a tree's fruiting display. Therefore, trees with high fruit production, despite harbouring the largest number of seed predators, produced the largest number of developed seeds in absolute numbers, compared to trees that produced few fruits. Received: 25 February 1996 / Accepted: 30 November 1996     

Temporal Variation in Seed Predation by Insects in a Population of Syagrus romanzoffiana (Arecaceae) in Santa Catarina Island, SC, Brazil

Insect seed predation may vary depending on seed production. The present study considers the hypothesis that the rates of seed predation tend to be smaller in years of higher fruit production. Thus, we monitored the production of fruits and predation of seeds of the palm Syagrus romanzoffiana over 2?years in the Atlantic Forest (Parque Municipal da Lagoa do Peri, Florianópolis, SC, Brazil), between July 2006 and June 2008. Plots of 0.25?m² were fitted under 20 mother plants and fruits were monthly collected for assessment of abundance and seed predation. There was variation in fruit production between the 2?years and among reproductive plants. Predation rates were high and occurred in the predispersal phase by the Curculionidae Revena rubiginosa Boheman, Anchylorhynchus aegrotus Fahraeus, and Anchylorhynchus variabilis Gyllenhal. Seed predation by these species of Anchylorhynchus is first registered in the present study. In average, about 60% of the seeds monthly produced in the population tend to escape insect predation in year of high or low production, becoming available for recruitment. The predation rate was not related to the amount of fruits produced per reproductive plant. Also, different than expected, there was a positive relation between the rates of seed predation and the total of fruits produced monthly on the plots. Thus, no evidence for the satiation of insect seed predators was found in this study with S. romanzoffiana.     

Masting behaviour in a Mediterranean pine tree alters seed predator selection on reproductive output

• Context‐dependency in species interactions is widespread and can produce concomitant patterns of context‐dependent selection. Masting (synchronous production of large seed crops at irregular intervals by a plant population) has been shown to reduce seed predation through satiation (reduction in rates of seed predation with increasing seed cone output) and thus represents an important source of context‐dependency in plant‐animal interactions. However, the evolutionary consequences of such dynamics are not well understood.
• Here we describe masting behaviour in a Mediterranean model pine species (Pinus pinaster) and present a test of the effects of masting on selection by seed predators on reproductive output. We predicted that masting, by enhancing seed predator satiation, could in turn strengthen positive selection by seed predators for larger cone output. For this we collected six‐year data (spanning one mast year and five non‐mast years) on seed cone production and seed cone predation rates in a forest genetic trial composed by 116 P. pinaster genotypes.
• Following our prediction, we found stronger seed predator satiation during the masting year, which in turn led to stronger seed predator selection for increased cone production relative to non‐masting years.
• These findings provide evidence that masting can alter the evolutionary outcome of plant‐seed predator interactions. More broadly, our findings highlight that changes in consumer responses to resource abundance represent a widespread mechanism for predicting and understanding context dependency in plant‐consumer evolutionary dynamics.

     

Herb endozoochory by cockatoos: Is ‘foliage the fruit’?

Establishing whether herb seed endozoochory is accidental or has evolved independently or in combination with other dispersal mechanisms may be valuable in the study of plant–animal interactions, but it remains unexplored for birds. We tested whether an Australian cockatoo, the galah (Eolophus roseicapilla), swallows entire seeds when feeding on other tissues without subsequent seed digestion, thus enhancing seed dispersal (the ‘foliage is the fruit’ hypothesis). Our preliminary sampling provides strong evidence supporting that this seed predator also acts as a legitimate endozoochorous disperser. A large proportion of droppings contained numerous seeds of six herb species of three plant families, surviving gut passage to be dispersed as viable propagules. The wide range in the number of seeds found in combinations with up to five species in particular droppings suggests both simultaneous and sequential passive ingestion without seed digestion and/or focused seed predation and digestion. As expected for inadvertent ingestion and inefficient digestion, our findings suggest that seed number and richness of dispersed plants are associated traits in this particular mutualistic interaction. This relationship can have important implications in community‐wide processes, favouring herbs whose seeds are disseminated in a viable state over those predated or negatively affected by gut transit.     

The effects of seed abundance on seed predation and dispersal by rodents in <Emphasis Type="Italic">Castanopsis fargesii</Emphasis> (Fagaceae)

Based on the animal dispersal hypothesis and the predator satiation hypothesis, we examined the effects of seed abundance at both population (i.e., mast seeding) and community levels on seed predation and dispersal of Castanopsis fargesii (Fagaceae), a rodent-dispersed mast species in Eastern Asia. In a subtropical evergreen broadleaved forest in the Dujiangyan region of Sichuan Province, China, individual seeds with coded tin tags were tracked in two contrasting stands (seed-poor and seed-rich) over two years (2000, a low-seed year; 2001, a high-seed year). Our results showed that: (1) small rodents did not harvest the tagged seeds of C. fargesii more rapid in the high-seed year than in the low-seed year in either stand. But, seed harvest was significantly faster in the seed-rich stand than in the seed-poor stand. (2) The removal proportion was significantly lower in the high-seed year than in the low-seed year for either stand, but the removal proportion was slightly higher in the seed-poor stand than in the seed-poor stand. This indicates that high seed abundance decreases seed removal (predator satiation hypothesis). (3) There were only small differences about seed caching, seed survival and seedling establishment of C. fargesii between years and stands. During the survey, no cached seeds survived to geminate in the spring for both stands and years. (4) Mean dispersal distances of the cached seeds are much shorter in the high-seed year (3.1 m) than in the low-seed year (8.1 m) in the seed-rich stand, though similar trend is not examined in the seed-poor stand. Our results indicate that seed predation and dispersal of C. fargesii are influenced by both mast seeding and community-level seed abundance, which is not completely consistent with either the animal dispersal hypothesis or the predator satiation hypothesis, but seems more related to the predator satiation hypothesis.     

Oviposition pattern and within-season spatial and temporal variation of pre-dispersal seed predation in a population of Mimosa bimucronata trees

Spatial and temporal variation of pre-dispersal seed predation was investigated in a population of Mimosa bimucronata trees located in the south-east region of Brazil. Three main hypotheses were addressed: (1) that the life stages of the seed predator Acanthoscelides schrankiae are synchronised with the reproductive stages of its host plant; (2) that seed predation levels vary spatially as a result of differences in fruiting phenology synchrony and fruit production among trees; and (3) that predation levels should be affected by the proximity of trees, showing a spatial structure. Also investigated was the oviposition pattern of A. schrankiae among seeds and fruits. Twenty spatially referenced trees were monitored throughout a year to examine tree phenology and egg laying and adult emergence. The bruchine’s life stages were synchronised with the reproductive stages of M. bimucronata trees. Egg distribution among seeds and fruits was aggregated. Infestation rates of adult bruchines were not spatially related to fruiting phenology and there is evidence that seed predation is a spatially density-independent process, because the relationship between infestation rates and fruit production was not significant. Finally, it was observed that the distribution of adult bruchines was spatially structured, because similar levels of infestation were found among nearby trees.     

Seed predation of two alien Opuntia species invading Mediterranean communities

Invasibility depends on the interaction of the introduced species with the abiotic and biotic factors of the recipient community. In particular, the biotic resistance posed by native herbivores has been claimed to be of great importance in controlling plant invasion. We investigated fruit and seed predation of two exotic Opuntia species within and between Mediterranean communities in order to determine how patterns of predation matched patterns of invasion. Predators were small mammals, presumably mice, which could consume more than 50% of the seeds produced. Predators could be equally effective in consuming fruit and single seeds. O. maxima fruits were slightly preferred to O. stricta fruits, but predators did not distinguish between seeds. Seed predation was more intense in invaded than in non-invaded communities. However, there was a high spatial variation in seed predation that did not always match patterns of invasion, suggesting that seed predation alone is not a good predictor of community invasibility to Opuntia. According to these results invasibility to Opuntia is limited in some (but not all) communities by native mice. Seed losses by predation were high for both species. However, we estimated that more than 75% of seeds dispersed by birds to non-invaded areas are not predated.     

A new hypothesis for the importance of seed dispersal in time

Most studies on seed dispersal in time have focused on seed dormancy and the physiological triggers for germination. However, seed dispersed by animals with low metabolic and moving rates, and long gut-passage times such as terrestrial turtles, could be considered another type of dispersal in time. This study tests the hypothesis that seeds dispersed in time may lower predation rates. We predicted that seeds deposited below parent trees after fruiting fall has finished is advantageous to minimize seed predators and should show higher survival rates. Four Amazonian plant species, Dicranostyles ampla, Oenocarpus bataua, Guatteria atabapensis and Ocotea floribunda, were tested for seed survival probabilities in two periods: during fruiting and 10-21 days after fruiting. Experiments were carried out in two biological stations located in the Colombian Amazon (Caparú and Zafire Biological Stations). Seed predation was high and mainly caused by non-vertebrates. Out of the four plant species tested, only Guatteria atabapensis supported the time escape hypothesis. For this species, seed predation by vertebrates after the fruiting period increased (from 4.1% to 9.2%) while seed predation by non-vertebrates decreased (from 54.0% to 40.2%). In contrast, seed predation by vertebrates and by non-vertebrates after the fruiting period in D. ampla increased (from 7.9% to 22.8% and from 40.4% to 50.6%, respectively), suggesting predator satiation. Results suggest that for some species dispersal in time could be advantageous to avoid some type of seed predators. Escape in time could be an additional dimension in which seeds may reach adequate sites for recruitment. Thus, future studies should be address to better understand the survival advantages given by an endozoochory time-dispersal process.     

Reproductive success of individuals with different fruit production patterns. What does it mean for the predator satiation hypothesis?

The predator satiation hypothesis states that synchronous periodic production of seeds is an adaptive strategy evolved to reduce the pressure of seed predators. The seed production pattern is crucial to the predator satiation hypothesis, but there are few studies documenting the success of individuals that are in synchrony and out of synchrony with the whole population. This study is based on long-term data on seed production of Sorbus aucuparia and specialised pre-dispersal seed predation by Argyresthia conjugella, in a subalpine spruce forest in the Western Carpathians (Poland). At the population level, we tested whether functional and numerical responses of predators to the variation of fruit production operate. At the individual level, we tested whether individuals with higher interannual variability in their own seed crops and higher synchrony with the population have higher percentages of uninfested fruits. The intensity of pre-dispersal seed predation was high (average 70 %; range 19–100 %). There were both functional and numerical responses of predators to the variation of fruit production at the population level. We found that individuals that were expected to be preferred under seed predator pressure had higher reproductive success. With increasing synchrony of fruit production between individual trees and the population, the percentage of infested fruits decreased. There was also a negative relationship between the interannual variation in individual fruit production and the percentage of infested fruits. These results confirm selection for individuals with a masting strategy. However, the population does not seem well adapted to strong seed predation pressure and we suggest that this may be a result of prolonged diapause of A. conjugella.     

Allometric allocation in fruit and seed packaging conditions the conflict among selective pressures on seed size

Selective pressures on seed size could vary among the different stages of plant life cycles, so no simple relation could explain a priori its evolution. Here, we determined the relationships between seed size and two fitness components—seed dispersal and survival from predation—in a bird-dispersed tree, Crataegus monogyna. We interpret these relationships in relation to the patterns of mass allocation to fruit and seed components. Selection patterns were assessed at two levels (1) selection pressures on the parent tree; comparing seed dispersal efficiency among individual plants and (2) selection pressures at the individual seed level; comparing seed size variation (i) before and after dispersal, and (ii) before and after postdispersal seed predation. Dispersal efficiency (percentage of seed crop dispersed) was positively correlated with fruit mass and fruit width. Differences in crop size did not offset this effect, and larger seeds were overrepresented in the seed rain relative to the seed pool before dispersal. However, the advantage of larger seeds during the dispersal stage was cancelled later by an opposite selection pressure exerted by seed predators. As a result, smaller seeds had a higher probability of surviving postdispersal seed predation, establishing an evolutionary conflict imposed by the need for dispersal and the danger of being predated. Birds and rodents preferentially selected highly profitable fruits and seeds in terms of the relative proportion of their components. Larger fruits had a higher pulp to seed proportion than smaller ones, and all seeds had the same proportion of coat relative to the embryo-plus-endosperm fraction. Hence, although predator pressures were stronger than disperser ones, larger seeds invested proportionally less in structural defense than in dispersal.     

应用结构方程模型解析影响黄连木果实产量 和种子命运的因素

果实(种子)产量和质量是影响植物种群更新的重要因素。为了探明影响黄连木果实产量和种子命运的因素以及这些影响因素之间的相互作用, 作者于2009年对河南省济源市45株黄连木(Pistacia chinensis)结果样树的植株特征、果实特征、果实产量和种子命运等进行了测定, 并用结构方程模型进行综合分析。结果表明: (1)黄连木果实产量与树高、树冠面积和果序大小等特征成正相关, 但与胸径、果实大小相关性不显著; (2)与捕食者饱和假说的预测不一致, 单株果实产量对黄连木广肩小蜂(Eurytoma plotnikovi)的种子捕食率(即虫蛀率)无显著直接负向效应; (3)树高和果实大小对虫蛀率为显著直接正向效应, 胸径对虫蛀率为显著直接负向效应, 显示黄连木广肩小蜂对植株特征和果实特征有一定的选择能力; (4)空壳率与虫蛀率成显著负相关, 空壳果实越多, 越易逃避黄连木广肩小蜂的寄生, 空壳果实的存在对完好种子起到了一定保护作用, 可能是黄连木防御昆虫寄生的重要机制; (5)空壳率和虫蛀率对种子完好率有显著直接负向效应, 而胸径、果序大小和果实产量对完好率为间接正向效应, 树高和果实大小为间接负向效应。可见, 黄连木植株特征和果实特征均不同程度地影响其果实产量和昆虫寄生, 从而影响黄连木的种子质量和种群更新。     

Intensity of pre‐dispersal seed predation in the invasive legume Leucaena leucocephala is limited by the duration of pod retention

Abstract The intensity of seed predation the invasive tropical legume Leucaena leucocephala by the bruchid Acanthoscelides macropthalmus was investigated in south‐eastern Queensland, Australia. The number of seeds damaged by A. macropthalmus as a proportion of total seeds available was found to increase the longer the pods remained on the tree. Seed predation ranged from a mean of 10.75% of seeds on pods that remained on the plant for 1 month and increased to 53.54% for pods that remained of the plant for 4 months. The low bruchid populations at high pod densities results in ‘predator satiation’. However, pods dehisce over time and the proportion of pods available over time to the bruchid correspondingly declines. By the time bruchid densities build up, most pods have dehisced and the seeds consequently escape predation. As a result the number of seeds lost to bruchid damage increases only marginally over time. Despite the levels of seed predation observed over the course of the study, the number of seeds in the soil seedbank almost doubled over time increasing from 8.5 seeds m^?3 to 15.5 seeds m^?3 over a 4‐month period. Levels of seed predation and addition of seeds to the soil seedbank were not correlated. The taxonomic (subspecies) status and apparency of host plants as measured by plant and patch traits (average plant height, density of podding plants and patch size) did not influence levels of seed predation. Pre‐dispersal seed predation studies need to take into account the pod/seed retention behaviour of the plant. The ability of the bruchid to regulate the invasiveness of Leucaena through influencing its demography is likely to be diminished if the insect populations cannot increase rapidly enough to use the seeds before pod dehiscence.     

BIRD-DISPERSAL OF PHYTOLACCA AMERICANA L. AND THE INFLUENCE OF FRUIT REMOVAL ON SUBSEQUENT FRUIT DEVELOPMENT

Characteristics of fruits, seeds, and ripening of Phytolacca americana were studied in New Jersey, USA to assess their importance in the dispersal strategy of this species. Removal by birds was directly related to the percent of ripe fruits available on a raceme. Fruit removal from a raceme resulted in lower fruit pulp and seed weights for fruits developing on the same raceme, but these differences probably do not influence probability for dispersal by birds. We demonstrate that characteristics of the fruit pulp may decrease seed availability for the primary seed predator, Peromyscus leucopus, and increase the time fruits are available for dispersal. We speculate on the significance of the sequential fruiting in Phytolacca and the relationship to availability of dispersal agents and high-lipid fruits. Sequential ripening and protection from predation result in seed dispersal from late August to early December.     

Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks

The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hierarchical pre-dispersal fitness assessment in a Mediterranean shrub plant

Under the concept of modularity, it is possible to recognise how seed production, as well as any other process affecting it, are hierarchically structured within fruits, within individual plants and within populations. In this work, we analysed the effects of pre-dispersal seed predation by insects upon a set of hierarchical levels in a population of the Mediterranean shrub plant Cistus ladanifer (“rock rose”) throughout a complete fruit-producing season (which takes place during the summer months). Almost all individual plants were predated, which implies that the effects of predation at the population level (regardless of the extent of predation within each individual) were virtually uniform. Within the individuals, however, the predation rate was close to a proportion of 0.5 (half of the fruits of each individual were predated), which indicates that this hierarchical level is likely to be subjected to a differential action of selection. Predation rates within the fruits showed an intermediate value (lower than that observed at the population level but higher than that at the individual level). According to these results, the pressure of phenotypic selection may therefore give rise to greater variation among fruits of the same individual than among seeds of the same fruit. In terms of the temporal patterns observed there was a large variation in the increments of predation along the fruiting season, which implies a high degree of heterogeneity in the temporal distribution of the effects of predation pressure on fitness. Besides its use in the specific example of the plant species studied in this work, the methodological procedure presented in this paper (integration of the temporal changes of different hierarchical levels) might be foreseen, in fact, as a useful tool for analysing the hierarchical structuring of fitness in modular organisms in general. This procedure allows to discriminate and integrate selection pressures and their effects across different phenotypic levels, from the infra-individual ones up to the population level.