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.     

Seed Dynamics of Early and Late Successional Tree Species in Tropical Abandoned Pastures: Seed Burial as a Way of Evading Predation

We explored different treatments to enhance the probability of sowed seeds of two early successional (ES, Cecropia obtusifolia and Ochroma pyramidale) and two late successional (LS, Brosimum costaricanum and Dialium guianense) species to escape predation and germinate in abandoned cattle‐raising pasture fields in Southeastern Mexico. ES species were sown in groups of 50 seeds under three treatments: invertebrate exclusion, burial, and exposition to seedeaters. LS species were sown in groups of 10 seeds under three treatments: vertebrate exclusion, burial, and exposition to seedeaters. We registered seed predation and germination 2, 4, 8, 16, 32, and 64 days after the initial sowing. Overall, ES showed higher predation rates (mean ± SE = 0.45 ± 0.07 seed seed^?1 day^?1; n = 3) than LS species (0.09 ± 0.02 seed seed^?1 day^?1). Cecropia obtusifolia was completely predated in all treatments after 8 days. Burial and exclusion treatments reduced final predation in circa 6% for O. pyramidale, relative to that of exposed seeds (85% after 8 days); most germination occurred in buried seeds (3.7%). In B. costaricanum, burial enabled germination by 10%; exposed and excluded seeds were removed 100%. Dialium guianense showed 12% germination in buried seeds and circa 20% of the seeds were not removed after 64 days. Direct sowing would be a recommended rainforest restoration practice for species with relatively large seeds if deposited in groups and buried. Studies which address variation across numerous sites are necessary in order to generate more consistent seed predation patterns and rainforest restoration principles in tropical pastures.     

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     

啮齿类取食的物种偏好与时空格局

通过强烈消耗土壤种子库,动物取食种子对植物种群更新和群落动态产生深远的影响。一般认为种子被食概率的空间格局取决于种子密度和离母树的距离,而环境（如地形）异质性的影响则一直没有得到足够的关注,与此相关的机制及其影响程度亦不清楚。研究设计在野外埋放种子以模拟种子扩散后的情形,监测啮齿类对种子的取食,以检验种子取食受埋藏生境、时间及动物对种子种类的偏好等因素的影响。结果表明,经过1a实验,8种落叶阔叶树种子的累计取食概率为0～48．25％,平均值为20％;山顶部位的取食概率大致是其它部位概率的3倍;埋放在凋落物层中的种子被食概率大约为埋放在土壤层中概率的2倍。利用logistic回归模型进行统计分析表明,种子被食概率变化的45％可以被上述因素解释。其中,物种偏好是影响种子被取食概率的首要因素,其后依次是地形、埋藏时间和深度。啮齿类明显喜好较大的种子;其取食行为在山脊部位明显较其它部位更频繁和剧烈;对埋藏种子的取食从3月份开始加剧,到7月份以后平息下来。种子埋放深度对啮齿类的取食概率有显著影响。     

Effects of ants,ground beetles and the seed-fall patterns on myrmecochory of Erythronium japonicum Decne. (Liliaceae)

Erythronium japonicum (Liliaceae) inhabits deciduous mesic forests of Hokkaido, northern Japan. Myrmecochory of this species was investigated, especially the dispersal frequency, the effect of seed predators and the seed fall pattern. In the quadrat census using marked seeds of E. japonicum, the ant Myrmica kotokui frequently transported the seeds. However, the frequency of seed removal was low and most seeds were dispersed as little as 1 m or less. The spatial distribution of E. japonicum individuals was nearly random and most seedlings were established 5–20 cm away from the fertile plants, indicating that even this small scale of seed dispersal contributes to avoiding crowding of seedlings. Some arthropods, e.g. springtails, spiders and ticks, hindered seed dispersal by devouring elaiosomes and seeds. Although ground beetle species also damaged seeds and elaiosomes, a few of them exhibited seed removal behaviour. E. japonicum dropped their seeds not all at once but bit by bit, taking 3–6 days to drop all seeds. This seed-fall pattern was effective in raising the frequency of seed removal by ants and reducing seed predation by some arthropods.     

Flowering phenology and female fitness: impact of a pre-dispersal seed predator on a sexually polymorphic species

In order to produce seeds, animal-pollinated plants must flower synchronously with and be attractive to their pollinators while avoiding antagonists. Here, we explore temporal and inter-individual patterns in pollination and pre-dispersal seed predation of Dianthus sylvestris by Hadena moths, within and among three sex morphs. We scored plants that started flowering at different periods in 2001 and 2003 and found that fruit set decreased and predation rates increased over one season, and most of the other season, granting a female reproductive advantage to early flowering plants, though, we found no morph-specific temporal patterns. Female plants set more fruits, and more of their fruits escaped predation in one year, but this did not grant them a reproductive advantage since they produce fewer flowers per plant than the other morphs. Instead, mixed plants showed a clear female reproductive advantage. We also examined predation types by Hadena and seed production in attacked and intact fruits of individually marked flowers. Though female Hadena moths laid eggs preferentially into perfect flowers, flower sexes suffered similar predation by itinerant caterpillars. Attacked fruits contained fewer and lighter seeds than un-attacked ones. We conclude that pre-dispersal seed predation by Hadena may select on flowering onset of this sexually polymorphic species.     

Dispersal and predation in alien Acacia

Summary I investigated seed removal in the litter layer of alien Acacia stands at bimonthly intervals throughout one year. Both ants (dispersers) and rodents (predators) removed significant quantities of seeds and may compete for seeds in low density Acacia stands. Seed removal from depots was greatest prior to seed-fall (Sept.–Nov.) and lowest during seed-fall (Jan.–Mar.). As rodents may consume a large proportion of the annual seed production at low Acacia densities, I propose that ants have played a critical role in accumulating Acacia seed banks.     

Effects of dung and seed size on secondary dispersal,seed predation,and seedling establishment of rain forest trees

Seeds dispersed by tropical, arboreal mammals are usually deposited singly and without dung or in clumps of fecal material. After dispersal through defecation by mammals, most seeds are secondarily dispersed by dung beetles or consumed by rodents. These post-dispersal, plant-animal interactions are likely to interact themselves, as seeds buried by dung beetles are less likely to be found by rodents than unburied seeds. In a series of three experiments with seeds of 15 species in central Amazonia (Brazil), we determined (1) how presence and amount of dung associated with seeds influences long-term seed fate and seedling establishment, (2) how deeply dung beetles bury seeds and how burial depth affects seedling establishment, and (3) how seed size affects the interaction between seeds, dung beetles, and rodents. Our overall goal was to understand how post-dispersal plant-animal interactions determine the link between primary seed dispersal and seedling establishment. On average, 43% of seeds surrounded by dung were buried by dung beetles, compared to 0% of seeds not surrounded by dung (n=2,156). Seeds in dung, however, tended to be more prone than bare seeds to predation by rodents. Of seeds in dung, probability of burial was negatively related to seed size and positively related to amount of dung. Burial of seeds decreased the probability of seed predation by rodents three-fold, and increased the probability of seedling establishment two-fold. Mean burial depth was 4 cm (0.5–20 cm) and was not related to seed size, contrary to previous studies. Probability of seedling establishment was negatively correlated with burial depth and not related to seed size at 5 or 10 cm depths. These results illustrate a complex web of interactions among dung beetles, rodents, and dispersed seeds. These interactions affect the probability of seedling establishment and are themselves strongly tied to how seeds are deposited by primary dispersers. More generally, our results emphasize the importance of looking beyond a single type of plant-animal interaction (e.g., seed dispersal or seed predation) to incorporate potential effects of interacting interactions.     

Pre‐dispersal seed predators and fungi differ in their effect on Luehea seemannii capsule development,seed germination,and dormancy across two Panamanian forests

Pre‐dispersal seed predation can greatly reduce crop size affecting recruitment success. In addition, non‐fatal damage by seed predators may allow infection by fungi responsible for post‐dispersal seed losses. The objectives of this study were (1) to quantify pre‐dispersal seed predation and fungal infection in a Neotropical tree species, Luehea seemannii, that produces dehiscent fruits and wind‐dispersed seeds, and (2) to link pre‐dispersal effects on seed quality to seed survival in the soil. To examine how seed predators and fungi influence seed losses, mesh exclosures, fungicide, and the combination of both treatments were applied to separate branches in the canopy of trees in Gamboa and Parque Natural Metropolitano (PNM), Panama. To determine if treatments affect seed viability and survival in the soil, half of the seeds collected from each treatment were buried for 4 weeks in forest soils and subsequently allowed to germinate before and after the breaking of dormancy. Overall, 24 percent of developing fruit were lost to insect attack. In contrast, fungi infected only 3 percent of seeds at the pre‐dispersal stage. For seeds germinated directly after collection, fungicide significantly increased germination in the wetter site (Gamboa) but decreased germination in the drier site (PNM). The pre‐dispersal insect exclosure treatment increased the fraction of seeds that remained dormant after burial in the soil. This result suggests that exposure to insect predators may cause physical damage to seeds that results in the loss of physical dormancy but does not necessarily increase the susceptibility of seeds to pathogen attack in the soil.     

Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests

Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches (‘Church forests’). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety‐two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests.     

The fate of Datura ferox seeds in the soil as affected by cultivation, depth of burial and degree of maturity

Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses. In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.     

Seed and microsite limitations of recruitment and the impacts of post-dispersal seed predation at the within population level

Seed predation may cause important seed losses in plant populations, but its impact on the dynamics of populations will depend on the degree of seed or microsite limitations for recruitment. Seed losses will only affect recruitment if it is seed limited. The nature of recruitment limitation (seeds or microsites) is usually ascribed to whole plant populations but it may vary within populations among microhabitats and habitats. Thus, the potential impact of seed predation will also vary within the population, being highest where recruitment is seed limited. The impact to the whole population will depend on the spatial concordance between the intensity of seed predation and that of seed limitation. Recruitment limitations (with seed addition experiments), seed predation (with seed removal experiments), and the dynamics of seed availability in the soil (with soil samples taken both after seed dispersal and before the following dispersal event) of the shrub Corema album (Empetraceae) were investigated in dunes in NW Spain, at microhabitats ‘open ground’, ‘underneath C. album ♀’, and ‘underneath C. album ♂’ at two habitats, sparse and dense scrub. The nature of recruitment limitation (seeds vs. microsites) varied within the population. It was seed limited in the microhabitat ‘open ground’ and microsite limited under shrub cover. The spatial patterns of seedling recruitment were unrelated to seed availability but strongly affected by germination requirements. The spatial discordance between seed availability and recruitment implies a crucial constraint for processes affecting seed availability (seed predation but also e.g., dispersal) to impact recruitment. They will not affect its spatial pattern but only its quantity as long as they act in those sites selected by seeds to germinate. Seed predation was highest underneath mother plants and lowest in open ground. Thus, its potential impact is low, as it is centred where recruitment is not seed limited. This study shows that the analysis of seed predation in relation to recruitment limitations at smaller spatial scales within the population provides more insight to understand its impact.     

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.     

The role of Rhytidoponera metallica (Hymenoptera,Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

The fire avoidance hypothesis proposes that a benefit of seed dispersal by ants (myrmecochory) is to protect seeds from being killed during fire and to facilitate post‐fire germination of seeds that require heat shock to break their physical dormancy. The aim of this study was to quantify the effect of fire and seed burial by a predominant seed‐dispersing ant, Rhytidoponera metallica (subfamily: Ectatomminae) on germination levels of three ant‐dispersed legume species (Pultenaea daphnoides, Acacia myrtifolia and Acacia pycnantha). Experimental burial of seeds within aluminium cans at a site prior to being burnt and at an adjacent unburnt site showed that fire increased germination levels, particularly for seeds buried at 1‐ and 2‐cm deep and that overall, germination levels differed among the three plant species. To quantify seed burial depths and post‐fire germination levels facilitated by R. metallica ants, seeds were fed to colonies prior to fire at the burnt and unburnt sites. Of the seeds buried within nests that were recovered, between 45% and 75% occurred within the upper 6 cm of the soil profile, although unexpectedly, greater percentages of seeds were recovered from the upper 0–2 cm of nests in the unburnt site compared with nests in the burnt site. Germination levels of buried seeds associated with R. metallica nests ranged from 21.2% to 29.5% in the burnt site compared with 3.1–14.8% in the unburnt site. While increased seed germination levels were associated with R. metallica nests following fire, most seeds were buried at depths below those where optimal temperatures for breaking seed dormancy occurred during the fire. We suggest that R. metallica ants may provide fire avoidance benefits to myrmecochorous seeds by burying them at a range of depths within a potential germination zone defined by intra‐ and inter‐fire variation in levels of soil heating.     

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.     

The relocation of ant nest entrances: Potential consequences for ant-dispersed seeds

The rate at which ant nests relocate may affect the fate of ant-dispersed seeds by influencing nutrient and seed accumulation in localized areas. In this study, the movement of ant nest entrances was monitored in fixed quadrats in dry sclerophyll woodland in Kuringai Chase National Park, NSW. Changes in entrance location were rapid for most species, with few entrances remaining in use for more than 6 months. Approximately 30% of entrances that closed were subsequently re-opened. There was no obvious seasonal pattern in entrance relocation. After 1 year, between 5 and 40% of the ground surface of the quadrats had been within 10 cm of a nest entrance. New nest entrances did not cluster near old entrances, indicating that nest entrance relocation may be accompanied by changes in underlying nest structure. Nutrient levels in soil samples from active nests of Rhytidoponera metallica, Aphaenogaster longiceps, Pheidole sp. 1 and Iridomyrmex sp. 8 did not differ significantly from random locations. The rapid changes in entrance location and the lack of nutrient enrichment may be the result of continual and progressive underground shifts in nest location. Such shifts have three potential consequences for seeds that remain buried within the nests. First, seeds will not benefit following germination by being in a nutrient-rich microsite. Second, a proportion of seeds collected by harvester ant species may escape predation if left in an abandoned section of the nest. Third, concentrations of seeds in localized areas may be reduced, leading to a reduction in competition between establishing seedlings.     

Ecological significance of the aerial seed pool of a desert lignified annual,Blepharis sindica (Acanthaceae)

Reproductive traits of a lignified annual plant, Blepharis sindica were studied in relation to the formation of an 'aerial seed pool' on dead plants in an arid grassland in the Thar Desert of northwestern India. The dead plants remained standing on the soil surface and retained fruits for more than one year. Aerial seed pools developed about 6 cm above the ground. There were no seed pools on or below the ground surface. Only 5.7% of seeds died on dead plants because of insect predation or fungi infection during one year. Seed release was cued by rainfall, and a fraction of seeds on the aerial seed pools was released in each rainfall event. After 13 rainfall events during the monsoon season, 25% of seeds was still retained on the plants. Seed predation on the ground surface was intensive; all cones placed on the soil surface were removed within four days, and 97% of fruits were removed within 10 days. Fifty percent of seeds germinated within 3.5 h, and there were no differences in viability and time required for germination between first year seeds and older seeds. The results indicate that the aerial seed-holding on dead plants is an available way to avoid seed predation in harsh desert environments where seed predation is intense and favorable periods for growth are temporally limited and unpredictable.     

Distribution and characteristics of the soil seed bank of the black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis>) in a headwater basin in northern Japan

Invasive expansion of Robinia pseudoacacia is a worldwide problem. A method to control existing R. pseudoacacia populations is urgently needed. In addition to plants above the ground, seed banks should be targets for the management of R. pseudoacacia. We targeted an old plantation of R. pseudoacacia and its surroundings in a headwater basin to determine the spatial characteristics of the distribution. We established 49 square plots in which the number of buried seeds and seeds dispersed by wind, and several other related environmental factors were surveyed. The relationship between the spatial extent of seeds dispersed by wind and the distribution of the seed bank was analyzed. Environmental factors that potentially influenced the density of buried seeds were also analyzed. We found that barochory and anemochory were the main factors that contributed to R. pseudoacacia forming seed banks. The greatest factor controlling the density of buried seeds was slope angle; thus, transfer of seeds by rolling is important for the formation of seed banks in headwater basins. From these results, some guidelines for the management of seed banks in headwater basin are presented. First, unnecessary soil disturbance within about a 100-m buffer area around seeding trees should be avoided. Second, plantation soil from gentle slopes should not be applied for revegetation of other locations. In situations where R. pseudoacacia populations are planted on steep slopes near streams, there is a chance that seeds will be carried away and form seed banks at lower or downstream sites.     

Litter and seed burying alter food availability and foraging efficiency of granivorous birds in the Monte desert

We assessed experimentally if the main granivorous bird species that feed on the ground in the central Monte desert are able to detect and consume seeds buried in the soil or trapped within litter. Understanding seed vulnerability to birds allows 1) a better understanding of how seed abundance translates into seed availability, a necessary step to assess seed limitation scenarios, and 2) whether birds alter the distribution of soil seeds through their consumption. Rufous‐collared sparrows found and consumed high proportions of buried seeds, though less seeds were eaten at increasing depths. In contrast, many‐colored chaco‐finches, common diuca‐finches and cinnamon warbling‐finches did not find buried seeds. All bird species fed on every substrate offered but, as a whole, birds reduced by 50% their seed consumption in Prosopis litter, and by 30% in Larrea litter, compared to consumption in bare soil. This effect was less notable for rufous‐collared sparrows, whose ‘double scratch’ foraging method would contribute to its great diet breath and abundance in the Monte desert. As birds do not reach a fraction of seeds buried and trapped by litter, seeds readily available for them may be scarcer than previously estimated through soil seed bank studies. Furthermore, since the four bird species detect and consume seeds from littered microhabitats, seed consumption by them surely affects the seasonal dynamics of the soil seed bank in all microhabitat types of the Monte desert.     

The role of pre- and post-dispersal seed predation in determining total seed loss

Most seed predation studies focus on either pre- or post-dispersal predation and may therefore underestimate the role of predation in regulating plant populations. We therefore estimated total seed predation of an invasive tree, mesquite (Leguminoseae: Prosopis spp.), by examining the entire seed pool from tree to seed bank. The spatio-temporal dynamics of total seed predation was examined by sampling across its Australian distribution and through time. The main predator was a host-specialist multivoltine beetle, Algarobius prosopis L. (Bruchidae), previously introduced as a biocontrol agent. Seed predation exceeded 20% in all seed stages (in pods on and off the tree, and seeds within woody endocarps (capsules) and free seeds on and in the ground) but was consistently highest in capsules on the ground (up to 90%). Pre-dispersal predation contributed little. Total seed predation rates were primarily determined by predation rates on the most persistent seed stage, in this case fallen pods if only pods are considered and seeds in capsules for the total seed pool. This pattern was consistent across the surveyed taxa, regions, years and seasonally. Predation rate was relatively unaffected by seed density, potentially because densities were always low (<150 seeds m⁻²). Average total seed predation within a region reached 55%, but we conclude that any population regulation of mesquite by seed predation will principally be through reduced seed bank persistence. Our results highlight the need to consider the entire seed pool, especially the often cryptic and overlooked long-lived stages, when determining seed loss to predation and its likely population consequences.