Predation by vertebrates and invertebrates on the seeds of five canopy tree species of an Amazonian forest

We studied the pre-germination loss of seeds to invertebrate and vertebrate seed predators of 5 species of Amazonian trees (Astrocaryum macrocalyx—Palmae; Bertholletia excelsa—Lecithydaceae; Calatola venezuelana—Icacinaceae; Dipteryx micrantha—Leguminosae (Papilionoidae); Hymenaea courbaril-Leguminosae (Caesalpinoidae)). These five species were selected from a large tree flora on several criteria. All possess large (3–10 cm) well-protected seeds that might plausibly be attractive to mammalian seed predators. The reproductive biology of three of the species, or close congeners, had been studied elsewhere in the Neotropics (Astrocaryum, Dipteryx, Hymenaea); one is important to the economy of southeastern Peru (Bertholletia); and one, despite large and apparently edible seeds, appeared to suffer no pre-germination loss to predators (Calatola). We conducted the research in mature forests in the Manu National Park of southeastern Peru where mammal densities are unperturbed by human activities. Densities of adult trees of the five species in our area range from very high (>30 per ha: Astrocaryum) to very low (1 per ha: Hymenaea).Loss of seeds to all causes, and to mammalian seed predators in particular, was determined for seeds placed in 2-square meter mammal exclosures and in open controls located at 10 m (near) and 50 m (far) from a large mature individual of the target species (with minor variations in the design for Astrocaryum and Calatola). The exclosures were of two types: impermeable—designed to exclude all mammals, but not invertebrate seed predators, and semipermeable—designed to admit small (<500 g), but not large mammals. Experimental and control plots were stocked with apparently viable seeds during the dry-wet transition period (October–November) and scored one year later.A significant distance effect (higher predation near vs far from a large conspecific adult) was found in only one of the species (Astrocaryum), the only one to be attacked with high frequency by invertebrate seed predators. The absence of any detectable distance effect attributable to mammals suggests that mammals, over the course of a year, thoroughly search the forest floor for seeds. Invertebrates may thus be responsible for most pre-germination distance (density) effects. With respect to the treatments, we found three qualitatively distinct results: seeds of three species (Astrocaryum, Bertholletia, Dipteryx) were significantly protected by the impermeable, but not semipermeable exclosures, implicating small mammals in seed loss; the seeds of one species (Hymenaea) were significantly protected by exclosures of both types, implicating large mammals; and the seeds of one species (Calatola) exhibited 100% survival, whether or not protected by exclosures.The importance of large mammals as seed predators is generally underestimated in these experiments because semipermeable exclosures may serve as foraging reserves for small mammals. Finally, we noted no relationship between the intensity of mammalian seed predation (as suggested by the survival of unprotected seeds) and the abundance of adults of the five species in the environment. The diversity of results obtained for the five species reveals that large-seeded tropical trees may display a wide range of demographic patterns, and points to the likely importance of post-germination bottlenecks in the population biology of many species, even those that may experience severe pre-germination seed loss.     

Determinants of seed production in Geranium maculatum

Summary We experimentally examined factors limiting seed production in two populations of the perennial woodland herb Geranium maculatum in central Illinois, USA. To test the pollinator-limitation hypothesis, we compared the seed production of plants whose flowers were supplementarily pollinated with outcross pollen to that of control plants receiving natural pollination only. To test if fruit production by early flowers suppresses fruit and seed formation by late flowers, a third group of plants was prevented from producing seed from the first 50% of the flowers to open (stigmas were excised at flower opening). Finally, to test if seed maturation and flower initiation are correlated with photosynthetic capacity, we performed a defoliation experiment in which either the stem leaves within the inflorescence, the stem leaves below the inflorescence, or the rosette leaves were removed during late flowering. Plants that reccived supplemental pollination produced 1.5–1.6 times more seeds than control plants. We found no difference between hand-pollinated plants and controls in mortality, flowering frequency or number of flowers produced in the year following the experiment. In both control and hand-pollinated plants, the fruit set and total seed production of early flowers were more than twice as high as those of late flowers. In one of the two populations, plants whose early flowers were prevented from setting seed produced significantly more seeds from their late flowers than did control plants. Seed predation was low and did not differ between early and late flowers. Leaf removal did not affect seed number or size in the year of defoliation, nor did it reduce survival or flower production in the subsequent year. This suggests that the plants were able to compensate for a partial defoliation by using stored resources or by increasing photosynthetic rates in the remaining leaves. Taken together, the results demonstrate that both pollinator activity and resource levels influence patterns of seed production in G. maculatum. While seed production was pollinatorlimited in both populations, a seasonal decline in resource availability was apparently responsible for the low seed production by late flowers.     

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.     

Pollen limitation in three sympatric species ofVaccinium (Ericaceae) in the Upper Ardennes, Belgium

The reproductive success of three co-flowering species ofVaccinium (V. myrtillus, V. vitis-idaea andV. uliginosum) was studied in one heathland of the Upper Ardennes, Belgium, during three years (1988–1990). The purpose was to examine whether pollen limitation, flower position and flowering phenology may influence patterns of fruit set in these three sympatric species. I quantified fruit and seed set following supplementary hand-pollinations and compared this to natural fruit set. On the same plants, I also quantified fruit and seed set in relation to the spatial position of the flowers on the ramet and their temporal sequence of blooming. Hand-pollination had no significant effect on fruit set inV. vitis-idaea andV. uliginosum, but significantly increased seed number per fruit in 1989. InV. myrtillus both fruit and seed set were increased by supplementary pollination, but significantly in only one year. Analyses of position effects revealed that the fruits in the lower positions in the ramet did not mature preferentially and did not contain more seeds inV. uliginosum and inV. vitis-idaea. Flowering phenology also had no significant effect for these species. InV. myrtillus hand-pollinated flowers showed a seasonal decline in seed number, and control (naturally pollinated) flowers showed a seasonal increase in fruit set. Fruit and seed set appear to be pollen-limited rather than resource-limited inV. uliginosum. In the two other species, unfavorable weather (frosts) could be a more important cause of low fruit and seed set.     

Effect of distance,aggregation, and habitat on levels of seed predation for two mammal — dispersed neotropical rain forest tree species

The effect of seed aggregation and distance from conspecific trees on seed predation was experimentally examined for two neotropical tree species, Macoubea guianensis (Apocynaceae) and Pouteria sp. (Sapotaceae) in a lowland tropical rain forest in northeastern Peru. Results of these experiments are discussed in the context of the Janzen-Connell model (Janzen 1970; Connell 1971), which predicts decreased seed survival near parent trees due to either density-or distance-responsive mortality, and Howe's model (Howe 1989) which predicts that trees with seeds dispersed in clumps (aggregated) will not suffer density-dependent predation, and will have higher survival of seeds near the parent tree than other trees. We also examined whether predation on seeds of these species was affected by seed placement in or near 30-m-wide strips regenerating after clear-cutting. Both species appeared to be mammal-dispersed but differed in how frugivores handled seeds, seed size, overall fruit crop size, and gemination time. Neither of the two species studied appeared to suffer seed predation in a manner predicted by the Janzen-Connell model, and patterns of seed predation for only one of the species was similar to predictions of Howe's model. For neither species did seed predation along the edge of, or in the center of, regenerating clear cuts differ from predation 15 m into the primary forest. For Pouteria, seed predation in and near regnerating strips was significantly greater than around forest trees, but the opposite pattern held for Macoubea. Overall, seed predation was much greater on Macoubea. The difference in seed predation for these two species was most likely a result of differences in the types of seed predators that attacked these two species.     

Effect of ovular receptivity on seed set and fruit development in cucumber (Cucumis sativus L.)

Summary Seed set and fruit development in cucumber (Cucumis sativus L.) were studied in relation to female flower receptivity from day — 2 before anthesis to day + 2 after anthesis. The female cucumber flower is protogynous. The pistil was receptive 2 days before anthesis. The iso-electric focusing (IEF) patterns of the stigma/style proteins, were identical from day -5 to day +2. In pollinated flowers in vivo germination and pollen-tube growth in the ovary were affected by pistil age from day -2 to day +2. In addition, differences in sectorial filling in full seeds were observed within the fruits. A negative correlation was observed between the frequency of fertilized ovules in the pedoncular part of the fruit and ovary length at the time of pollination. In the whole fruit, significant differences in the number of full seeds and fruit size at maturity were found, and these were observed to be correlated with the various stages of female flower maturation at pollination. The day -2 and day +2 stages yielded the smallest fruits with few full seeds compared to the day -1, day 0 and day +1 stages, which had the biggest fruits and a large number of full seeds. A strong positive correlation was found between total seed number (including full and empty seeds), fruit length and weight at maturity. All these results suggest that both seed set in the different parts of the fruit and fruit development are controlled by ovular receptivity rather than by stigma/style receptivity.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

A repellent to reduce mouse damage to longleaf pine seed

Direct seeding is a potential method for reforestation of pines on many southern sites. The success of direct seeding, however, depends, at least in part, in reducing seed predation by birds and rodents. We conducted a series of tests to assess the efficacy of capsicum and thiram in reducing mouse damage to longleaf pine (Pinus palustris) seeds. House mice (Mus musculus) predation was reduced (P<0.05) by treating seeds with either capsicum or thiram or a mixture of the two ingredients. Deer mice (Peromyscus maniculatus) avoided seeds treated with a mixture of capsicum and thiram. We conclude that the capsicum and thiram mixture should be pursued as a potential repellent to protect longleaf pine seeds from animal predation when these seeds are used in direct seeding efforts to establish southern pine forests.     

Seed dispersal, plant recruitment and spatial distribution of Bactris acanthocarpa Martius (Arecaceae) in a remnant of Atlantic forest in northeast Brazil

Seed dispersal ecology of Bactris acanthocarpa Mart. (Arecaceae), an Atlantic forest understory palm, was investigated during two years as an attempt to test the following predictions: (i) seeds of Bactris are dispersed by mammals and large-gaped birds; (ii) Bactris benefits from seed dispersal in terms of seed predation avoidance, improvement of seed germination and seedling survival; and (iii) spatial distribution of adults is related to patterns of seed dispersal. The study was conducted at Dois Irmãos Reserve, a 387.4-ha reserve of Atlantic forest in northeastern Brazil (8º S–35º W). Black–rumped agoutis (Dasyprocta prymnolopha) and Guianan squirrels (Sciurus aestuans) were identified as the seed dispersers/predators, moving seeds short distances (< 4 m from parents) and at low rates (0.04-0.05 diaspore/palm/day). Pyrene burial prevented seed predation by vertebrates and reduced by half seed infestation by Scolytidae beetles. Only buried pyrenes germinated. Pyrene predation was not correlated with distance from conspecific adults. In contrast, early seedling mortality was higher near conspecific adults. Most adults (64%) had their nearest conspecific adult neighbour > 4 m away in contrast to 96% of seedlings that occurred concentrated within 4 m from adults (77% under the palm crowns). Here, we present evidence that spatial distribution of B. acanthocarpa is partly due to low rates of seed removal, short-distance seed dispersal by agoutis and squirrels, and early seedling mortality associated with presence of seedlings under palm crowns.     

Reproductive biology ofCistus ladanifer (Cistaceae)

The phenology, major floral characteristics, fruiting levels, and breeding system ofCistus ladanifer L. (Cistaceae), a common western Mediterranean shrub species, were studied in a southern Spanish population. The white, large (64 mm in diameter) flowers of this shrub appear during spring (March–May) and produce abundant pollen and nectar. In the year of study, flowers lasted up to three days, during which they were visited by a diverse array of insects including beetles, flies, and bees. Hand-pollinations revealed that flowers do not set any seed unless cross pollen is applied to the stigma. Microscopical observations indicate that self pollen tubes grow down the stigma but invariably fail to induce fruit maturation. At the plant level, all estimates of fecundity investigated (number of seeds per capsule, proportion of ovules developing into seed, and proportion of flowers setting fruit) were highly dependent on nearest neighbour distance, with isolated plants setting as little as 0% fruit. In contrast, plants within a clump often transformed into fruit as much as 90% of the flowers. At the population level, seed output was estimated to range between 3,000 and 270,000 seeds per plant during 1991.     

Mast-seeding in the cycad genus Encephalartos: a test of the predator satiation hypothesis

Mast-seeding behaviour was monitored in 18 populations of eight species of the African cycad genus Encephalartos between 1988 and 1991. The coefficient of variation (V) in annual cone production for each population ranged between 88 and 200, indicating large fluctuations in reproductive effort between years. Data were collected to determine whether mast-seeding reduced levels of predispersal seed predation by satiating seed predators in mast years and whether it resulted in a reproductive advantage over plants which reproduced more frequently. Masting intensity was greatest in those populations in which individual plants suffered the highest levels of predispersal seed predation in years when only a few plants produced seeds. The principal seed predators were two congeneric weevil species, Antliarhinus zamiae and A. signatus, which develop exclusively on cycad seeds. The lowest intensity of mast-seeding was recorded for cycad populations with low levels of seed predation and in which A. zamiae and A. signatus occurred only in low numbers or were entirely absent. Larger seed crops appeared to result in lower levels of seed predation by A. zamiae and A. signatus in four populations of E. altensteinii, and differences in seed crop size accounted for 48–66% of variation in levels of seed predation in populations of five cycad species. In one population of E. altensteinii, lower levels of seed predation in plants reproducing periodically resulted in a reproductive advantage over plants reproducing more frequently. These results are consistent with the predator satiation hypothesis. However, in most cycad populations, numbers of seed predators did not appear to decrease significantly after a period of 2–8 years between reproductive episodes and, in two of three populations examined, periodic reproduction did not increase the number of seeds surviving to dispersal over a 4-year period. These results are interpreted to mean that periodic reproduction has not evolved in response to selection imposed by seed predators, but that selection may favour those plants which experience lower levels of seed predation by coning in synchrony with the majority of plants in the population.     

Reproductive biology ofFrangula alnus (Rhamnaceae) in southern Spain

Various aspects of the reproductive biology of the perennial hermaphroditeFrangula alnus Mill. were studied in two populations located in the province of Cádiz, southern Spain. Flowering extends from the second week of May to early July. The small, whitegreenish, entomophilous flowers are incompletely protandrous and last 8–10 days, but pollen transfer takes place only on days 1–3. A very weak, pleasant odour along with nectar and pollen attract over 45 insect species, of which 21 are probable pollinators. These are mainlyDiptera but also includeHymenoptera and the unusual (as flower visitors)Mecoptera. Reproduction is exclusively sexual and strictly xenogamous, with pollen transfer depending solely on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination, and geitonogamy can easily take place, the level of autogamy was negligible. Therefore, some self-incompatibility mechanism is operative in this species. Only 2.8% of open-pollinated flowers set fruit. At the flower level, fruit initiation was apparently limited by availability of cross-pollen, which in turn seemed influenced by the structure of the population. The seed/ovule ratio in ripe fruits was ca. 50%. Predispersal (maternal) reproductive success (percent ovules becoming filled seeds) was 1.42%. For mature individuals this corresponded to ca. 430 to 1560 potential offspring per year.     

Effects of cleistogamy and pollen source on seed production and offspring performance in three endangered violets

In rare plants that often occur in small or isolated populations the probability of selfing between close relatives is increased as a consequence of demographic stochasticity. The mode of pollination (selfing, outcrossing) may have considerable effects on seed traits and offspring performance and hence potential viability. Since current efforts aiming at the restoration of floodplain grasslands through the transfer of plant material from species-rich source stands may lead to the establishment of initially small populations consisting of founders from different populations, the present paper experimentally investigated the effects of pollen source and floral types (i.e. chasmogamous (CH) and cleistogamous (CL) flowers) on seed traits and offspring performance in three highly endangered violet species (Viola elatior, V. pumila, V. stagnina) of these grasslands. We estimated inbreeding depression and tested the performance of selfed and outcrossed offspring in two microbial environments, i.e. in soil inoculated with (i) non-sterile substrate from the same species (‘home’-conditions) and (ii) sterilised substrate.Plants produced more CL capsules than CH flowers. Pollinator exclusion had only small effects on CH seed production. CL seeds had a significantly lower mass per seed than CH seeds. This may be related to constraints in allocation or environmental conditions. Seedling growth was reduced in plants grown under ‘home’-conditions as compared to control soils. Under ‘home’-conditions, relative fitness of selfed seedlings of V. stagnina was significantly higher than that of crossed progeny. Our results suggest that high genetic differentiation among populations as a consequence of isolation may result in outbreeding depression, e.g., through biochemical or physiological incompatibilities between genes or the breaking of coadapted gene complexes. In V. stagnina, offspring fitness differed considerably between environments, but in general we found no indications for inbreeding depression in these rare species.     

Beetle pollination of peacock moraeas (Iridaceae) in South Africa

The peacock moraeas are South African geophytes withIris-like flowers that are characterized by broad outer tepals with iridescent spots. Three of the seven species were studied and found to be exclusively visited and pollinated by beetles. The primary pollinators were hopliine (Scarabaeidae) beetles in the generaPeritrichia, Monochelus, Anisonyx andAnisochelus. These beetles visit flowers for nectar, pollen and mating.Peritrichia rufotibialis was the primary pollinator ofMoraea villosa, P. abdominalis was the primary pollinator ofM. tulbaghensis, whileMonochelus sp. nov. was the primary pollinator of the third species,M. neopavonia. High levels of fruit set attest to the effectiveness of these beetles as pollinators. Average fruit set ranged from 83.5 ± 34.8% (M. villosa) to 97.2 ± 11.6% (M. tulbaghensis). Average seed set in the various populations was more variable, but was also quite high, ranging from 77.3 ± 40.8 (M. villosa) to 342.2 ± 115.0 (M. neopavonia) seeds per capsule. Although hopliine beetles are abundant and diverse in southern Africa and commonly visit flowers, this is the first well-documented report of pollination by these beetles.     

Origins of variance in seed number and mass: interaction of sex expression and herbivory in Lomatium salmoniflorum

Summary As in many plant species, Lomatium salmoniflorum (Umbelliferae) individuals produce many flowers, only a subset of which produce mature seeds that escape seed parasitism and enter the seed bank. The interrelationships between the timing and number of flowers produced, sex expression, seed set, and seed parasitism were studied for their direct and indirect effects on the numbers and masses of viable seeds produced by individual plants. In a sample population of 369 plants that produced 161 386 flowers, 76% of the plants produced some hermaphroditic flowers. The percentage of hermaphroditic flowers increased significantly with the total number of flowers produced by a plant. Seed set was 65–90% in plants producing >600 flowers, but was highly variable in plants producing fewer flowers. Hand-pollinated plants showed the same pattern of seed set, suggesting that variable seed set in small plants may result from insufficient resources for seed development. The majority of schizocarps was produced by only 12% of the plants. Parasites killed 24.5% of the seeds prior to dispersal. Another 14.5% of the seeds lacked endosperm. Hence, the initial 161 386 flowers, which included 25874 hermaphroditic flowers each capable of producing two seeds, produced 42 468 seeds of which an estimated 25906 entered the seed bank as undamaged seeds with fully developed endosperm. Path analysis indicated that the number of hermaphroditic flowers on a plant and the percentage of seeds attacked by seed parasites had the greatest direct effects on the number of viable seeds entering the seed bank. The date at which a plant began flowering and the percentage of flowers setting seed had smaller or only indirect effects on viable seed production. Mean seed mass for plants was not significantly related to any of the factors that affected seed number, but little of the variance in seed mass occurred among plants. Masses of intact seeds in the population ranged 9-fold in both 1987 and 1988. Thirty-five percent of the variance was among seeds within umbels, 46% was among umbels within plants, and only 19% was among plants. The large variation among umbels within plants resulted from a seasonal pattern in which seeds from umbels produced late in the spring had lower mean seed masses than seeds from umbels produced early in the spring. Overall, the results indicate that both direct and indirect interactions between number of flowers, the date of initiation of flowering, seed set, and seed parasitism affect the number of viable seeds entering the seed bank. These interactions strongly bias viable seed output to a small minority of plants that produce many seeds with a wide range of masses over the growing season.     

Interaction between juniper Juniperus communis L. and its fruit pest insects: Pest abundance, fruit characteristics and seed viability

The relationships between the fruit features of Juniperus communis and the presence of fruit pests were studied in Sierra Nevada, SE Spain. The abundance of two insect species — a pulp-sucking scale and a seed-predator wasp — was surveyed with respect both to fruit characteristics and to viability of seeds contained therein. Seed-predator pressure was not significantly related to any fruit characteristics; however, pulp suckers tended to be more abundant in plants with low pulp: seed ratios and high fruit-water content. In addition, fruits with high levels of pulp-sucker attack tended to have higher water content. A multi-factor ANOVA, considering the identity of the plant and the attack of the different pests as factors, showed that plant identity accounts for most of the variation in fruit characteristics. The viability of seeds tended to be lower in plants strongly attacked by both pests. Fruits attacked by seed predators showed significantly lower proportions of viable and unviable seeds than did unattacked fruits. Seed viability was also lower in those fruits heavily attacked by pulp suckers, but this pattern is strongly mediated by plant identity. Pest activity proved to be clearly associated with a direct decrease in juniper reproductive capacity. This loss involved a reduction of the viable-seed number, mainly related to the seed predator, as well as a reduction of fruit attractiveness to frugivorous dispersers, related to the pulp sucker.     

Predispersal seed predation in Bartsia alpina

Summary A northern Swedish population of Bartsia alpina, an arctic-alpine perennial herb, was found to suffer high levels of predispersal seed predation by larvae of two insect species, both specialists on rhinanthoid Scrophulariaceae hosts. The primary predator is Aethes deutschiana (Lepidoptera-Tortricidae), the host of which was previously unknown. The other predator is Gimnomera dorsata (Diptera-Scatophagidae), which is basically a Pedicularis specialist. Both predators are attacked by larvae of Scambus brevicorais (Hymenoptera-Parasitica-Ichneumonidae). Total predation pressure was more or less constant during 1985–1987, but in 1988 the level was doubled, the possible reasons of which are discussed. Large inflorescences of B. alpina suffer significantly higher predation pressures than small ones. It is shown that predation is most intense in the middle of the inflorescences. The same floral nodes are known to produce more selfed seeds than distal and basal nodes. Seed predation in B. alpina thus results in an increased proportion of outcrossed seeds entering the seed pool. Selection pressures on host plant and predator fauna are discussed.     

Assessment of the Biological Control Impact of Seed Predators on the Invasive Shrub Acacia nilotica (Prickly Acacia) in Australia

An impact assessment study was undertaken to determine seed predation rates by two bruchid beetles, Bruchidus sahlbergi Schilsky and Caryedon serratus Olivier, on the invasive shrub Acacia nilotica (L.) Willd. ex Del. The former bruchid was released as a biological control agent for A. nilotica, whereas the latter is naturalized in Australia. We attempted to determine the dynamics and magnitude of bruchid predation, following a number of differing reports of their effectiveness. To investigate the importance of seed availability on bruchid numbers, we compared seed death in high- and low-seed-density habitats, both before and after pods had dropped from tree branches. Bruchid predation was initially low (<2%) in pods on tree branches in both habitats, but increased abruptly to 12% in riparian and 32% in nonriparian exclosures by the third collection date. Bruchid numbers then crashed to below 2% in both habitats, when pods dropped to the ground. B. sahlbergi predation later increased markedly (up to 65%) again at high-pod-density sites. No further increase in predation took place beyond this level. Seed predation by C. serratus was found to be minimal (<5% of seeds infested) throughout the monitoring period. We suggest that seed predation by the bruchids, prior to pod drop and removal by cattle, is insufficient to cause major impacts on A. nilotica populations. Bruchid seed damage is likely to be significant only in situations with low cattle numbers, where cattle cannot remove the majority of fallen seed pods or where cattle are excluded. Exclusion of cattle from some areas within A. nilotica-invaded landscapes to potentially increase bruchid effectiveness is proposed. The demographic impact of optimal A. nilotica seed losses is discussed.     

The reproductive biology ofJaborosa integrifolia (Solanaceae): Why its fruits are so rare?

Jaborosa integrifolia exhibits stigma-height polymorphism. There are individuals with flowers where anthers and stigma are at the same height but the rule is variable herkogamy, the most common type (75%) being that with an exerted stigma. Self- and cross-tubes did not differ in their capability to reach the ovary (t = –0.67,P < 0.53); they had a high growth rate (6.95 ± 2.28 mm h^–1). There is not autogamy but mostly self-incompatibility. Fruits from controlled cross-pollination showed the highest seed set and seed viability. The nectar sugar is characterized by a similar amount of glucose and fructose, and by the absence of sucrose. Although nectar secretion was continuous throughout the life of the flower, most nectar was secreted during the first 24 h after flower opening. Nectar production costs appear to be lower than in other species since nectar secretion is neither inhibited after a removal (i.e. a pollinator visit) nor reabsorbed as the flower ages. Sphingids visit the flowers mainly after midnight. They insert their proboscis down to the base of the corolla tube to reach the nectar. The upper limit to fruit production is set by pollinator visits. Fruits produced from open-pollinated flowers are often predated by numerous larvae (mainly lepidopteran ones). Considering that this species is mostly self-incompatible and pollination is limited, that each plant displays only a low number of flowers throughout the flowering season, and that there is a high rate of fruit predation, it is not surprising that fruits ofJ. integrifolia are so rare.     

Morphology and phenology of seeds and whole fruit eaten by Milne-Edwards’ sifaka,Propithecus diadema edwardsi,in Ranomafana National Park,Madagascar

Although it is an anatomical folivore, the diet of the Milne-Edwards’ sifaka (Propithecus diadema edwardsiA. Grandidier, 1871) in Ranomafana National Park contained 35% seeds, 30% whole fruit, and 28% leaves. Plant species used as seed sources differed from those used as whole fruit sources in terms of temporal variation in consumption, taxonomic affiliation, morphology, and phenology. Although seeds were destroyed in both exploitation styles used by the sifakas—seed and whole fruit-eating—the gross morphology of species used as seed sources conformed to the complex of traits typical for fruits experiencing seed predation, while species used as whole fruit sources conformed to traits typical for fruits that do not experience predispersal predation. Many of the 19 plant species from which the seed was extracted and eaten contained a single seed with moderate testa thickness, and fruits containing this type of seed were medium-sized with dry or fibrous flesh, moderate skin thickness, and a dull color. In contrast, brightly colored, juicy fruits with minimally protected seeds were characteristic of the 38 plant species from which both pericarp and seed were eaten. Compared to transectwide measures of fruit availability or patterns restricted to whole fruit sources, fewer species of seed sources produced fruit per month and fruiting activity was more seasonal.