Predispersal Seed Predation Research Articles

Pre-dispersal seed-predation affects fruit crop and seed fitness in a highly fragmented savanna tree

Context Silver banksia (Banksia marginata) savannas of south-eastern Australia were formerly widespread but are now largely cleared and fragmented, with small populations often showing recruitment limitation. Which may, in part, be due to seed predation by yellow-tailed black cockatoos (Zanda funerea), which have been observed foraging for seed. Aims The study aimed to investigate the impact of pre-dispersal seed predation by yellow-tailed black cockatoos on fruit crop between early development and seed release. Additionally, we wanted to assess seed fitness from partially damaged and discarded cones. Methods The study quantified silver banksia infructescence removal at four populations between early December and seed release in March. We also quantified seed mass and germinability of seeds from cones removed in December, February and March. Key results All populations experienced significant seed predation (>50%), with almost complete removal of cones from some populations. Early removal limits seed release from cones (only 18% of early removed follicles released seed). Further, early removal also significantly reduced seed mass and germination. Conclusions Pre-dispersal seed predation by cockatoos is likely to act as a strong filter for recruitment limitation in silver banksia, by negatively affecting annual seed crop size, seed fitness and germinability. Implications Our study showed the potential impact fragmentation can have on antagonistic plant–animal interactions. Small, isolated B. marginata populations are likely to continue to decline without active strategies to remedy seed predation such as large-scale restoration.

Are the Interactions between Oaks and Pre-Dispersal Seed Predators Retained in Urban Environments? An Analysis of Two Quercus Species in Southern Mexico City

As urbanization proceeds, natural ecosystems surrounding cities are transformed, but usually some elements persist, notably trees from forest ecosystems. However, it is still unknown the extent to which isolated trees, immersed in an urban matrix, maintain their interactions with insects that feed on their seeds. In this work we analyzed pre-dispersal seed predation by the two main groups of insects, weevils (Coleoptera; Curculionidae) and moths (Lepidoptera: Tortricidae), whose larvae feed on the acorns of two oak species (Quercus rugosa and Q. castanea). We compared these interactions between trees located in a protected forested area and trees isolated in an urban matrix. Our hypothesis was that, since pre-dispersal seed predation depends on insect dispersal, acorns from isolated trees would have lower predation levels than acorns from trees in the forest. A second hypothesis, based on reports that moths exhibit larger dispersal distances than weevils, was that isolated trees would have higher predation levels from moths than from weevils compared to their respective proportions in forest trees. Finally, we expected that moth predation would increase with seed size, as it does in weevils. We collected 1200 acorns of the two oak species (ten trees per species) in a protected oak forest and a nearby highway in southern Mexico City. From the whole sample, 17.3% of the acorns were predated by weevils and 3.8% by moths. The probability of predation was larger in acorns from trees in the forest (0.30) than in those from isolated trees (0.07), which confirmed the first hypothesis; tree species identity did not have a significant effect on the proportion of predated acorns. When only predated acorns were analyzed, predation by weevil larvae was larger than predation by moths in both oak species, although the probability of predation by weevils was higher in the oak species having large acorns (Q. rugosa, 0.93), than in the species with small acorns (Q. castanea, 0.63). Inversely, predation by moths was higher in Q. castanea (0.37) than in Q. rugosa (0.07). Seed predation decreased similarly for weevils and moths in isolated trees, so we failed to find support for our second hypothesis. A positive relationship between seed predation by weevils and seed size was found in Q. rugosa but not in Q. castanea; seed size did not affect predation by moth larvae. Therefore, although isolated trees in the urban matrix harbor smaller populations of pre-dispersal seed predators than forest trees, their interactions with the two main groups of insects feeding on acorns are maintained, which points to their importance for the conservation of urban biodiversity.

Pre-dispersal seed predators boost seed production in a short-lived plant.

Pre-dispersal seed predation diminishes fitness and population growth rate of many plant species. Therefore, plants have developed multiple strategies to reduce the harmful effects of this type of herbivory. The present study aims to determine the effect of pre-dispersal seed predators (PSPs) on the fitness of a short-lived herb, and to discern the mechanisms allowing the plants to reduce the impact of pre-dispersal seed predation. Knowing that the interplay between pre-dispersal seed predators and plants is strongly shaped by the presence of other co-occurring organisms, we tested whether detritivores modulate plant responses towards pre-dispersal seed predators. To do so, we experimentally manipulated in the field pre-dispersal seed predators and detritivores interacting with the short-lived herb Moricandia moricandioides. We found that detritivores did not alter the response of plants to PSPs. Strikingly, the plant overcompensated for pre-dispersal seed predation, almost doubling the number of seeds produced. Plant response to PSPs led to substantial changes in shoot architecture, reproductive traits, chemical defences in leaves and seeds and in seed nutrient content. The overcompensating mechanism seems to be meristem activation, which allowed plants to produce more reproductive tissue, and increasing the proportion of ovules that became seeds, a response which specifically compensates for pre-dispersal seed predation. As far as we know, this is the first experimental evidence of a positive effect of PSPs on plant lifetime fitness as a consequence of plant overcompensation.

Pre-Dispersal Seed Predation in a Species-Rich Forest Community: Patterns and the Interplay with Determinants.

Pre-dispersal seed predation (PDSP) is commonly observed in woody plants, and recognized as a driver of seed production variability that is critical for successful regeneration. Earlier studies on PDSP and its determinants were mostly species specific, with community-level PDSP rarely estimated; and the interactions between the temporal variability of seed production and PDSP remain elusive. In this study, the community seed rain of woody plants in a mixed evergreen-deciduous broadleaf forest was monitored for seven years. We examined predation on collected seeds and analyzed the determinants of PDSP. PDSP was recorded in 17 out of 44 woody plant species, and three-quarters of PDSP was due to insect predators. Annual seed production varied substantially at community level, reversely linked with the temporal variation of PDSP rate. The PDSP rate was biased regarding fruit types, and being significantly correlated with seed mass when using phylogenetic independent contrasts (PICs) or without taking into account phylogenetic relations, especially for nuts. PDSP rate was also negatively correlated with seed density, showing a threshold-related predator satiation effect. The community-level PDSP rate was primarily determined by tree height, fruit type, and interannual variation of seed production and seed mass. Our analysis revealed a causal link between seed production and the dynamics of PDSP rate at the community level. The predator satiation effect was primarily contributed by the dominant species, whereas the rare species seemed to apply a distinct “hide-and-seek” strategy to control the risk of PDSP. The mechanistic difference of seed production between the common and rare species can shed new light on species coexistence and community assembly. Long-term monitoring of both seed rain and seed predation is required for understanding the ecological and evolutionary implications of species regeneration strategies in a species-rich forest community.

Presence and Intensity of Predispersal Seed Predation in a Rare Plant in Response to Habitat Quality and Population Metrics

ABSTRACT: Predispersal seed predation can be detrimental for any plant, but especially for rare plants. In this study, we examined the relationship of predispersal seed predation to different habitat types (i.e. open, semi shaded, and shaded), population size, and population density for Synthyris bullii, a rare Midwestern US endemic plant. In 2009, 2010, and 2011, a total of 18 populations were sampled across the range of Synthyris bullii. Fruit damage and predispersal seed predation were determined from up to 20 randomly collected infrutescences from each population. Predispersal seed predation had an impact on reproductive output and varied by habitat type. In addition, predispersal seed predation varied by population size and population density. Understanding the effects of predispersal seed predation on rare plants can be crucial for maintaining stable populations and developing better conservation and management strategies.

Variation in Pre-Dispersal Seed Predation and Seed Traits among Provenances of Dalbergia Melanoxylon (Guill.& Perr.)

Variation in Pre-Dispersal Seed Predation and Seed Traits among Provenances of Dalbergia Melanoxylon (Guill.& Perr.) Dalbergia melanoxylon is an important timber species used for the manufacturing of musical instruments and decorative objects such as carvings. The extent of pre-dispersal seed predation variation among D. melanoxylon provenances for seed harvested after maturity at different collection dates was investigated. Provenance variation in seed morphological traits in terms of seed length, width, number of seeds/pod and 100 seed weight were also examined.

Effects of pollen load, parasitoids and the environment on pre-dispersal seed predation in the cleistogamous Ruellia nudiflora

Few studies have simultaneously addressed the effects of biotic and abiotic factors on pre-dispersal seed predation (PSP). Plant-seed predator interactions may be influenced by natural enemies and pollinators (the latter through changes in fruit or seed traits), and the activity of pre-dispersal seed predators and their natural enemies may both be affected by the abiotic environment. Additionally, in the case of cleistogamous plants with fruit dimorphism, PSP may be biased towards larger and more seeded chasmogamous (CH) fruits [relative to the smaller cleistogamous (CL) fruits], and the effects of biotic and abiotic factors may be contingent upon this fruit dimorphism. We studied PSP in the cleistogamous Ruellia nudiflora using a split-plot experimental design and asked the following: (1) is PSP biased towards CH fruits and is there an effect of pollen load on PSP? (2) Do parasitoids influence PSP and is their effect influenced by pollen load or fruit type? And (3) do light and water availability modify PSP and parasitoid effects? PSP was higher for CH relative to CL fruits, and under low water availability it was lower for pollen-supplemented CH fruits relative to open-pollinated CH fruits. Parasitoids were not influenced by abiotic conditions, but their negative effect on PSP was stronger for pollen-supplemented CH fruits. Overall, we show that fruit dimorphism, abiotic factors and natural enemies affect PSP, and that these effects can be non-additive.

Predispersal seed-predation by insects in the Venezuelan Central Plain: Overall patterns and traits that influence its biology and taxonomic groups

Predispersal seed predation (PSP) by insects was studied in a plant community of the Venezuelan Central Plain (VCP). The main goal was to examine to what extent vegetation structure and fruit–seed attributes determined the incidence of PSP by insects at the community level. We studied a total of 187 species from 59 families, in five habitat types. The proportion of seed-predated plant species (N=89; 47.6% of the total) was explained by different factors such as the abundance of legume families, plant species richness, fruit dehiscence, seed biomass, and starch content. Coleoptera was the most diverse taxonomic order of insect seed predators, with Bruchidae and Curculionidae showing the largest number of genera and species, followed by Lepidoptera (Pyralidae). Bruchidae and Pyralidae, but not Curculionidae, tended to be separated according to vegetation attributes, such as vegetation structure and flowering and fruiting phenology. In addition, Bruchidae was associated with dehiscent fruits, legumes, epizoochory, and granivory, whereas Curculionidae was more related with indehiscent fruits and endozoochory, and Pyralidae with abiotic seed dispersal. Bruchid larvae tended to prey upon single seeds, whereas larvae of Lycaenidae usually preyed upon more than one seed per fruit; Curculionidae did not show any clear pattern on this. One larva developing in a single seed (Type I) was the most common type of PSP, closely followed by one or more larvae developing outside seeds within the fruit (Type II). Type III (seed predation by adult insects inside the fruit) was the least common. Type I appears to occur most frequently in climbers, in the forest–savanna transition habitat, and in those cases in which insect adults emerged during the rainy season. By contrast, Types II and III tended to be associated with annual herbs, the lowest stratum (0.05–0.6 m), and disturbed areas. Moreover, Type I was usually found in samaras, drupes, and indehiscent fruits, whereas Type II and Type III were more commonly observed in capsules. Type I and Type II seeds differed in their nutritional composition, which in turn appears to affect seed predation specialization. The number of insect seed predator species and plant richness per habitat were positively correlated. The number of seed predator species was associated with the abundance of trees and climbers because more complex plant life forms offer a large variety of resources, woody species frequently had fruits and seeds larger than herbaceous species, and trees and climbers showed the lowest values of host specificity. To our knowledge, this study is the first one that characterizes the community of predispersal seed predators and simultaneously evaluates ecological, morphological, and nutritional factors determining the groups of seed predators and how PSP occurred.

Pre‐dispersal acorn predation in mixed oak forests: interspecific differences are driven by the interplay among seed phenology, seed size and predator size

Summary1. Pre‐dispersal seed predation (PSP) often occurs in multi‐host–predator systems (e.g. several plant species exposed to a common array of granivorous insects). However, whether the interaction among seed phenology, seed size and predator size accounts for interspecific differences in PSP remains elusive.2. We studied PSP in a mixed‐oak forest with two oaks (the larger‐seeded Quercus humilis and the smaller‐seeded Q. ilex), both depredated by two acorn weevils (the smaller Curculio glandium and the larger C. elephas). We intensively monitored acorn production and infestation phenology and we identified the weevil species depredating acorns by means of DNA taxonomy.3. The minimum acorn size required for infestation was lower for C. glandium than for C. elephas, in accordance with their different body sizes. This resulted in an earlier infestation phenology in C. glandium and the ability of this species to infest both smaller and larger acorns. Above a minimum acorn size threshold, no selection for larger acorns by weevils was observed.4. Initial acorn crop size was similar in the two oaks. Nonetheless, the earlier acorn phenology and the production of larger acorns in Q. humilis favoured the earlier infestation by C. glandium and the predation by both small and large weevils. Smaller acorns of Q. ilex almost excluded infestation by the larger C. elephas.5. Although larger acorns of Q. humilis could better survive infestation (preserve the embryo), higher PSP in this species finally resulted in a lower mature acorn crop size than in Q. ilex.6. Synthesis. In a multi‐host–predator system, smaller‐seeded species may benefit from a reduced PSP because they exclude larger granivorous insects, but also by means of a ‘free‐rider effect’, if larger‐seeded heterospecifics earlier reach a critical size to be depredated. These results also highlight the benefits of a small body size in granivorous insects to depredate seeds earlier and to forage on a wider range of seed sizes. Whether the advantage of ‘being small’ in this antagonistic plant–animal interaction is offset by other processes, or whether it results in a pressure towards seed and insect size reduction, deserves further attention.

Predispersal Seed Predation by Insects vs. Vertebrates in Six Dipterocarp Species in Sarawak, Malaysia1

ABSTRACTWe investigated the predispersal survivorship of seeds of six dipterocarp species (Dipterocarpus globosus, D. tempehes, Dryobalanops aromatica, D. lanceolata, Shorea beccariana, and S. pilosa) during 2001–2002, when a general flowering occurred in Lambir Hills National Park, Sarawak, Malaysia. More immature seeds dropped during the first month in Dryobalanops and Shorea spp. than in Dipterocarpus spp. Insects attacked the seeds of all species during all developmental stages through to maturity, although temporal patterns varied among the dipterocarps. In contrast, arboreal vertebrates only occasionally ate seeds, and produced less damage than insects. In four species, insects damaged a significantly higher percentage of seeds than did vertebrates. Direct observations of seed survival patterns and bagging experiments using two sizes of mesh (cloth and wire) in the canopy of Dryobalanops aromatica identified insects as the principal seed predators during both the last phase, and overall. These results document the relative importance of insects as predispersal seed predators in these dipterocarp species.

Masting behavior of Fagus crenata in northern Japan: spatial synchrony and pre-dispersal seed predation

An 11-year study of total seed and seed production in five natural Japanese beech ( Fagus crenata) forests in Hokkaido, northern Japan, estimated the spatial synchrony of masting and examined whether variation in annual total seed production resulted in fluctuations in pre-dispersal seed-predator populations. We found less synchrony in total seed production than in sound seed production among sites. The coefficients of variation of sound seeds (1.3–2.1) were greater than those of total seeds (0.8–1.3) in each site. Pre-dispersal seed predation by moth larvae has a major influence on sound seed production in F. crenata. To test whether variation in annual total seed production resulted in fluctuations in predator populations, we examined the relationship between the ratio of current year total seed production to previous year total seed production, and the percentage of pre-dispersal seed predation in the current year. We found a negative correlation between insect predation and the ratio of current to previous year total seed production, suggesting that poor total seed years resulted in a decrease in predator populations. The pre-dispersal seed predators of F. crenata appeared to cope well with up to 10-fold variation in total seed production between years, but when the total seed production exceeded 20 times that of the prior year, the predators were satiated.

Relationship between capitulum size and pre-dispersal seed predation by insect larvae in common Asteraceae.

The evolution of a showy floral display as an advertisement to pollinators could simultaneously advertise the availability of resources to pre-dispersal seed-predators. The hypotheses tested here are that the incidence of seed predation by bud-infesting insect larvae in capitula of Asteraceae is positively related to (1) capitulum size among species, (2) capitulum size within species, (3) capitulum lifespan, and (4) the degree of flowering asynchrony on individual plants. Three populations of each of 20 common herbaceous species of Asteraceae from disturbed ground and grassland habitats were monitored for the presence of pre-dispersal, seed-eating insect larvae. Mean capitulum size (receptacle width) of each species was measured. In a sub-set of eight species, individual capitula were tagged to determine their flowering phenology and lifespan (from anthesis to seed shedding). From these data an index of flowering synchrony on individual plants was derived. Among species, the incidence of larval infestation increased with capitulum size. Small-flowered species such as Achillea millefolium were largely free of bud-infesting larvae, whilst large-flowered species such as Arctium minus were heavily infested. In three cases investigated in greater detail, bud infestation was found to increase with capitulum size within species, suggesting a potential for natural selection to favour smaller capitula. No relationship was found between infestation levels and either capitulum lifespan or degree of flowering synchrony, and there was no evidence that the relationship between capitulum size and infestation was confounded by correlations with these other features. The results support hypotheses 1 and 2, but not 3 and 4. It is suggested that the characteristic capitulum size of each species may represent a trade-off between the opposing selection pressures of pollinators and pre-dispersal seed predators.

Patterns of Predispersal Seed Predators in the Fabaceae of the Sydney Region, South-Eastern Australia

Predispersal seed predators are widespread throughout the legume flora of south-eastern Australia. Within the Coleoptera, weevils, anthribids and bruchids are important seed predators. Some weevils are restricted to certain host plant genera and are found on many species of these genera, e.g. Melanterius on Acacia; Plaesiorhinus on Bossiaea. Anthribids and bruchids are found in a range of plant genera. Host-specific relationships in these latter two groups must await further insect collections and subsequent taxonomic treatments of the insects involved. More generalist seed feeders are some Hymenoptera, including Eurytoma (Eurytomidae) and probably Megastigmus (Torymidae). Other hymenopterans associated with seeds are mostly parasitic on coleopteran larvae, e.g. Diospilus spp. (Brachonidae) on Plaesiorhinus (Curculionidae). Lepidopterans are also widespread seed feeders; however, detailed relationships between lepidoptera and host plants requires successful rearing of adult moths. Hemipterans are probably relatively unimportant as destructive seed feeders in south-eastern Australian legumes.

Predispersal Seed Predation, Postdispersal Seed Predation and Competition in the Recruitment of Seedlings of a Native Thistle in Sandhills Prairie

-Platte thistle (Cirsium canescens Nutt.) is a native monocarpic plant species of Sandhills prairie. We concurrently tested three biological interactions that could influence its recruitment and population density: (1) predispersal flower and seed consumption by insects; (2) postdispersal loss of seeds to vertebrates, and (3) seedling competition with established plants. Few previous experimental studies have analyzed more than one of these processes at a time. Each interaction had a significant negative impact on seedling establishment. Insect seed predation caused major losses that were magnified in each succeeding life history stage. A 3-fold reduction in viable seeds by insects led to a 6-fold decrease in seedling establishment and a 6to 37-fold reduction in the eventual number of new adults. Germination was low (1.7%) and 80% of the seedlings were in exclosure cages, particularly in those cages placed in an open disturbed area instead of in the grassland. Competition between seedlings and established grasses led to a 9.5-fold decrease in seedling survival. Platte thistle populations were thus limited successively, first by seed predation and then by competition with established grasses. Both processes therefore reinforce selection for the fugitive life history observed in this species.

Changes in Predispersal Seed Predation Levels after Fire for Two Australian Legumes, Acacia Elongata and Sphaerolobium Vimineum

Predispersal seed predation was estimated before and for 2-3 yr after a single fire for two legume species. The relationship between this seed predation and the build-up of a buried seedbank for future seedling recruitment was assessed. For Acacia elongata Sieb. ex DC, loss of seed was mainly due to a weevil, Melanterius acaciae Lea (Coleoptera: Curculionidae). There was no evidence of decline in the intensity of this predation following the fire. However, the large initial seed-crop after the fire may have satiated the available seed predators. Predispersal seed predators destroyed some 97% of the second fruit-crop produced after the fire, limiting the build-up of a buried seed bank. For Sphaerolobium vimineum Sm., loss of seed was due to two species of Eurytoma (Hymenoptera: Eurytomidae). There was no seed predation in the first seed-crop after the fire, perhaps because the seed predators were unable to locate the host population. However, in the second seed-crop after fire, the intensity of seed predation returned to the pre-burn level. In this species, seed production was high in all sampled years and the build-up of the buried seed bank after the fire was ensured, even in the presence of Eurytoma.

Variation in Predispersal Seed Predation in Several Australian Acacia spp.

Predispersal seed predation was examined in seven Acacia spp. over both time and space. Each species was associated with a particular major seed predator. Two species, A. elongata and A. myrtifolia, each had a host-specific seed predator: Melanterius acaciae (Coleoptera: Curculionidae) on A. elongata and Diethusa sp. (Coleoptera: Curculionidae) on A. myrtifolia. Three other species were preyed on by Melanterius corosus, whilst the remaining two species were preyed on by M. maculatus. Variation in the degree of predispersal seed predation was apparent both between populations of any particular Acacia sp. and within species over consecutive fruiting seasons. Some of this variation is in response to varying seed-crop sizes and associated predator satiation. However, since the dynamics of the weevil populations are unknown, much of the variation remains unexplained. Where Acacia spp. occupied the same habitat and were both attacked by one species of predispersal seed predator, differences in seed predator attack were apparent. A. linifolia was more susceptible to M. maculatus attack than was A. terminalis, and A. suaveolens was more readily attacked by M. corosus than was A. longifolia. No differences in seed predator attack were found between A. suaveolens and A. ulicifolia. The importance of this seed predation on the dynamics of the host species is briefly discussed.

The evolutionary ecology of mast seeding in trees

The hypothesis that masting by trees is a defensive strategy which satiates seed predators in mast years and starves them in the intervening periods is tested in 59 sets of data on the seed production and pre-dispersal seed-predation of 25 tree species. Twenty-lour of the 59 data-sets support the hypothesis and show a statistically significant positive relationship between the proportion of seeds surviving the pre-dispersal stage and the log10 of the crop size for the same year. Evidence that pre-dispersal seed survival increases with the length of the mast interval is poor. A positive relationship between the strength of the masting habit and the maxintum observed pre-dispersal seed mortality in a sample of 15 tree species suggests that the masting habit is best developed in predator-prone species. A survey of seed crop frequencies in the woody plant flora of Nortli America shows masting species to be under-represented amongst shrubs and amongst trees which disperse their seeds in fleshy dispersal units. The selection pressures and evolutionary constraints which operate on the evolution of masting plants and their seed predators are discussed.