Post‐fire seed predation: Does distance to unburnt vegetation matter?

Human‐induced changes to fire regimes result in smaller, more patchy fires in many peri‐urban areas, with a concomitant increase in potential edge effects. In sclerophyll vegetation, many structurally dominant serotinous plants rely on the immediate post‐fire environment for recruitment. However, there is little information about how fire attributes affect seed predation or recruitment for these species. We examined the influence of distance to unburnt vegetation on post‐dispersal seed predation for five serotinous species from sclerophyll vegetation in the Sydney region, south‐eastern Australia; Banksia serrata L.f., Banksia spinulosa Sm. var. spinulosa, Hakea gibbosa (Sm.) Cav., Hakea teretifolia (Salisb.) Britten (all Proteaceae) and Allocasuarina distyla (Vent.) L. Johnson (Casuarinaceae). We used cafeteria trials and differential exclusion of vertebrates and invertebrates to test whether rates of seed removal for these five species differed among (i) unburnt, (ii) burnt‐edge (approx. 10 m from unburnt vegetation) and (iii) burnt‐interior (approx. 100 m from unburnt vegetation) locations. When all animals had access to seeds, seeds were removed at lower rates from burnt‐interior areas than from other locations. Vertebrates (small mammals) showed this pattern markedly the first time the experiment was run, but in a repeat trial this effect disappeared. Rate of seed removal by invertebrates differed among plant species but we did not detect any such differences for removal by vertebrates. Overall rates of seed removal also differed significantly between the two fires studied. Our results indicate that small mammal seed predation can be substantial for large‐seeded serotinous shrubs, and that differences in the perimeter: area ratio, severity or size of a fire are likely to affect seed predation.     

The effect of frugivory on postdispersal seed removal and germination in the pantropical forest tree Antiaris toxicaria Leschenault

The quality of seed treatment by frugivores has an effect on seed removal after dispersal, seed germination and tree recruitment. We provide information on postdispersal seed removal, germination and subsequent recruitment in tropical forest tree species Antiaris toxicaria in Ghana. We tested whether postdispersal seed removal and germination rates were differentially affected by the following seed treatments: seeds that were spat out by monkeys with all fruit pulp removed and spitting seeds with fruit pulp partially removed as observed in some birds and bats. We used seeds of intact ripened fruits as control. Frugivore seed treatment and distance from bole affected seed removal patterns, whereas intact seeds were significantly removed from all seed stations. The germination success was greater for seeds that were spat out by monkeys and poor for seeds with fruit pulp partially removed and intact fruits. More recruits were recorded at the edge of the adult A. toxicaria canopy radius. There was weak relationship (r² = 0.042) between the number of recruits and distance away from the adult tree. Results suggest that the subsequent recruitment in tropical forest tree species may be enhanced by some frugivore fruit‐handling behaviour where fruit pulp is removed from the seeds without destroying the seeds.     

片段化景观中壳斗科植物种子捕食和扩散模式

生境片段化伴随的面积效应和边缘效应, 可改变分散贮食动物的竞争强度、觅食行为以及隐蔽条件, 影响种子捕食和扩散模式。阐明生境片段化对多物种种子捕食和扩散的影响, 对理解片段化生境中的植物更新和生物多样性维持十分重要。该研究在浙江省千岛湖地区的岛屿和大陆上开展了针对6种壳斗科植物的种子捕食和扩散实验, 分析了物种、分散贮食动物相对多度、种子产量、岛屿大小和边缘效应如何共同影响种子命运和种子扩散距离。主要结果: (1)种子命运和扩散距离在物种间存在显著差异; (2)大陆比岛屿有更长的种子留存时间, 小岛种子留存时间最短, 岛屿内部比岛屿边缘有更长的种子留存时间; (3)物种和岛屿大小对种子原地取食率存在交互作用, 白栎(Quercus fabri)种子在大岛上有更高的原地取食率; (4)种子在小岛上有最高的扩散率, 分散贮食动物相对多度对种子扩散后贮藏率有负效应。表明在千岛湖地区, 生境片段化改变了种子捕食和扩散模式, 且面积效应对不同物种的种子捕食和扩散模式产生了不同作用, 从而影响森林群落更新和生物多样性维持。     

Petals may act as a reward: myrmecochory in shrubby Darwinia species of south‐eastern Australia

The removal rates of fruits (the diaspore) were assessed in exclusion experiments in three shrubby species of Darwinia, endemic to the Sydney Basin of south‐eastern Australia. There was a clear pattern of fruit removal in just a few days by small species of ants from the genera Iridomyrmex, Crematogaster and Pheidole. When only ants had access to fruits an average of 41% of fruits were removed, whereas when only vertebrates had access an average of 13% of fruits were removed. There was some variation in the number of fruits removed both between species and within species across study sites or annual seed crops. When ants had access to seeds this variation in removal amounted to 10–80% over 1–4 days. Uniquely in Darwinia, it is the old petals (which remain attached to the fruit) that are attractive to the ants, rather than a specific lipid body. This likely represents a case of successful ecological fitting by Darwinia to take advantage of the widespread presence of myrmecochory in the Australian flora.     

Differential Effects of Hunting on Pre-Dispersal Seed Predation and Primary and Secondary Seed Removal of Two Neotropical Tree Species

Many of the mammals undergoing drastic declines in tropical forests worldwide are important seed dispersers and seed predators, and thus changes in mammal communities due to hunting will affect plant recruitment. It has been hypothesized that larger-seeded species will suffer greater reductions in seed removal and thus greater increases in predispersal seed predation than smaller-seeded species. We compared primary and secondary seed removal and predispersal seed predation of two tree species between hunted and nonhunted sites in Central Panama. Seeds of Oenocarpus mapora (Arecaceae) are 16-times greater in size than those of Cordia bicolor (Boraginaceae). We quantified primary seed removal and predispersal seed predation using seed traps, and we assessed secondary seed removal using seed removal plots. Primary removal of C. bicolor was 43 percent lower in the hunted sites, while primary removal of O. mapora was not significantly different. Secondary removal of unprotected O. mapora seeds on the ground was 59 percent lower in hunted sites, while secondary removal of C. bicolor was not significantly different. Predispersal seed predation of O. mapora by mammals was significantly lower in hunted sites, while predispersal seed predation by insects was not significantly different in either species. In combination with other studies, our results suggest that seed size is not a reliable predictor of the impacts of hunting. Mammal defaunation differentially affects stages and modes of seed dispersal and seed predation of different plant species, suggesting that these influences are complex and related to multiple plant traits.     

Insects remove more seeds than mammals in first‐year prairie restorations

Seed sowing is a common early step in restoration, but seed consumers can impede plant establishment and alter community structure. Moreover, seed consumers vary in feeding behaviors and the relative importance of different seed consumer groups during restoration are not well understood. At 12 first‐year prairie restorations in Michigan, we studied seed predation using seed removal trays to ask: What is the relative magnitude of seed removal by insects and mammals? Do seed removal rates change over the growing season? Do habitat edges influence seed removal? At what rates are 10 prairie plant species' seeds removed by mammals and insects? Seed removal depended on consumer type, time of year, and seed species. Insects accounted for the majority of seed removal, contrary to previous research in similar systems. In May, insects removed 1.8 times more seeds than mammals, while in August, they removed 5.1 times more. There was greater seed removal in August. During May 28% of seeds were removed, compared to 54% of seeds removed during August, an increase driven by insects. Edge proximity did not influence seed removal. Certain seed species were removed more than others. For example, Lespedeza capitata (round‐headed bush clover) was always removed at high rates, whereas Coreopsis lanceolata (lance‐leaved coreopsis) and Andropogon gerardii (big bluestem) were always removed at low rates. Mammals and insects showed different preferences for several species. This research suggests a prominent role of seed predation, particularly by insects, for early prairie restoration dynamics, with influences varying temporally and among species.     

The biology and ecology of narrow endemic and widespread plants: a comparative study of trait variation in 20 congeneric pairs

The objective of this study is to examine whether habitat, herbivory and traits related to resource acquisition, resource conservation, reproduction and dispersal differ between narrow endemic plant species and their widespread congeners. We undertook pairwise contrasts of 25 ecological characteristics and biological traits in 20 congeneric pairs of narrow endemic and widespread plant species in the French Mediterranean region. Within each pair, the two species had the same life-form, pollination mode and dispersal mode. Endemic species differed significantly from widespread congeners for a number of attributes. Endemic species occur in habitats on steeper slopes, with higher rock cover and in lower and more open vegetation than their widespread congeners. Endemic species are significantly smaller than widespread species, but show no differences in traits related to resource acquisition (specific leaf area, leaf nitrogen content, maximum photosynthetic rate) or resource conservation (leaf dry matter content). After accounting for their smaller stature, endemic species produce fewer and smaller flowers with less stigma-anther separation and lower pollen/ovule ratios and produce fewer seeds per plant than their widespread congeners. No consistent variation in seed mass and propagule structure was found between congeneric species. Herbivory levels did not differ between congeneric species. Ecological characteristics, notably the occupation of rocky habitats with low aboveground competition, may thus have played an important role in the differentiation of narrow endemic species in the Western Mediterranean. Morphological and ecophysiological traits of narrow endemic species indicate that they are not more stress-tolerant than their widespread congeners. Lower investment in pollen transfer and seed production suggest that local persistence is a key feature of the population ecology of narrow endemic species.     

Seed removal in two coexisting oak species: ecological consequences of seed size, plant cover and seed-drop timing

Seed predation and dispersal can critically influence plant community structure and dynamics. Inter‐specific differences arising at these early stages play a crucial role on tree recruitment patterns, which in turn could influence forest dynamics and species segregation in heterogeneous environments such as Mediterranean forests. We investigated removal rates from acorns set onto the ground in two coexisting Mediterranean oak species –Quercus canariensis and Q. suber– in southern Spain. We developed maximum likelihood estimators to investigate the main factors controlling probabilities of seed removal and to describe species‐specific functional responses. To account for inter‐specific differences in seed‐drop timing, two experiments were established: a simultaneous exposure of acorns of the two species (synchronous experiments) and a seed exposure following their natural seed‐drop phenology (diachronic experiments). A total of 1536 acorns were experimentally distributed along a wide and natural gradient of plant cover, and removal was periodically monitored for three months at two consecutive years (with contrasting differences in seed production and thus seed availability on the ground). The probability of seed removal increased with plant cover (leaf area index, LAI) for the two oak species. Inter‐specific differences in acorn removal were higher in open areas and disappeared in closed microhabitats, especially during a non‐mast year. Despite later seed‐drop, Q. suber acorns were removed faster and at a higher proportion than those of Q. canariensis. The higher probability of seed removal for this species could be attributed to its larger seed size compared to Q. canariensis, as inter‐specific differences were less pronounced when similar sized acorns were exposed. Inter‐specific differences in seed removal, arising from seed size variability and microsite heterogeneity, could be of paramount importance in oak species niche separation, driving stand dynamics and composition along environmental gradients.     

A multi-species assessment of post-dispersal seed predation in the central Chilean Andes

BACKGROUND AND AIMS: Post-dispersal seed predation in alpine communities has received little attention despite evidence that seeds removed by granivores can decrease plant recruitment into ecosystems. Moreover, few studies have assessed the effects of removal of seeds of a range of species after dispersal on the seeds remaining in ecosystems. A comparison was made of the magnitude of seed removal by ants and birds of nine different shrubby-, herbaceous- and cushion-plant species in the central Chilean Andes in order to assess the interactions between birds, ants and wind, and the types of seeds. METHODS: A total of 324 soil-covered plates, each containing 50 seeds of one species, were placed in the field at an altitude of 2700 m and assigned to one of four treatments: control, exclusion of ants, birds, and both. The design also allowed the effects of wind to be assessed. Seed removal from plates was monitored over 20 d. KEY RESULTS: Mean accumulative seed removal by granivores averaged over all nine species combined was 25%. However, large differences between species were evident, with limited seed removal (3-11%) in three herbaceous species (Alstroemeria pallida, Sisyrinchium arenarium, Pozoa coriacea), moderate (18-33%) in five species, including a shrub (Chuquiraga oppositifolia), two herbs (Taraxacum officinale, Rhodophiala rhodolirion), and two cushion-plants (Laretia acaulis, Azorella monantha), and substantial (78%) in the shrub Anarthrophyllum cumingii. The magnitudes of losses caused by birds compared with ants did not differ for the majority of species, although removal by birds was greater than by ants in A. cumingii, and smaller for C. oppositifolia. CONCLUSIONS: Post-dispersal seed removal is shown to be an important cause of decreased potential plant species recruitment into alpine ecosystems. The substantial differences in the magnitude of seed losses to ants and birds demonstrate the need for evaluation of seed removal on a wide range of species in any given ecosystem.     

Mutualism vs. antagonism in introduced and native ranges: Can seed dispersal and predation determine Acacia invasion success?

Plant species introduced to new regions can escape their natural enemies but may also lose important mutualists. While mutualistic interactions are often considered too diffuse to limit plant invasion, few studies have quantified the strength of interactions in both the native and introduced ranges, and assessed whether any differences are linked to invasion outcomes. For three Acacia species adapted for ant dispersal (myrmecochory), we quantified seed removal probabilities associated with dispersal and predation in both the native (Australian) and introduced (New Zealand) ranges, predicting lower removal attributable to dispersal in New Zealand due to a relatively depauperate ant fauna. We used the role of the elaiosome to infer myrmecochory, and included treatments to measure vertebrate seed removal, since this may become an important determinant of seed fate in the face of reduced dispersal. We then tested whether differences in seed removal patterns could explain differences in the invasion success of the three Acacia species in New Zealand.Overall seed removal by invertebrates was lower in New Zealand relative to Australia, but the difference in removal between seeds with an elaiosome compared to those without was similar in both countries. This implies that the probability of a removed seed being dispersed by invertebrates was comparable in New Zealand to Australia. The probability of seed removal by vertebrates was similar and low in both countries. Differences in the invasive success of the three Acacia species in New Zealand were not explained by differences in levels of seed predation or the strength of myrmecochorous interactions. These findings suggest that interactions with ground foraging seed predators and dispersers are unlikely to limit the ability of Acacia species to spread in New Zealand, and could not explain their variable invasion success.     

Barriers to Forest Regeneration in an Abandoned Pasture in Puerto Rico

Sources of forest regeneration (soil seed bank, seed rain) and barriers to seedling establishment were examined in a recently abandoned pasture in eastern Puerto Rico. Few woody species were found in the soil seed bank or in the seed rain. The number of seeds and species in the seed rain and soil seed bank declined with distance from the adjacent secondary forest. Nine species naturally dispersed and colonized plots during the study, with the wind‐dispersed tree Tabebuia heterophylla being the predominant colonizer (91% of all seedlings). Barriers to seedling establishment were determined using a blocked field experiment with eleven woody species representative of a variety of life histories. Each species was planted under the pasture vegetation (control) or in areas where all vegetation was removed (removal). Germination was enhanced for four species in the control treatment, five species were not affected, and two species did not germinate under either treatment. Survival to 6 months was higher in the removal treatment for two species. Seedling biomass was greater in the removal treatment at 12 months for one species. Seed mass was a good predictor of germination success and final shoot biomass, but not survival. This study demonstrates that seeding recently abandoned pastures with a mix of known pioneer species may accelerate the rate of secondary succession, but some species will have to be planted in later successional stages in order to overcome strong barriers to establishment.     

Unusual abundance–range size relationship in an Afromontane bird community: the effect of geographical isolation?

Aim To show that the frequently reported positive trend in the abundance–range‐size relationship does not hold true within a montane bird community of Afrotropical highlands; to test possible explanations of the extraordinary shape of this relationship; and to discuss the influence of island effects on patterns of bird abundance in the Cameroon Mountains. Location Bamenda Highlands, Cameroon, Western Africa. Methods We censused birds during the breeding season in November and December 2003 using a point‐count method and mapped habitat structure at these census points. Local habitat requirements of each species detected by point counts were quantified using canonical correspondence analysis, and the size of geographical ranges of species was measured from their distribution maps for sub‐Saharan Africa. We tested differences in abundance, niche breadth and niche position between three species groups: endemic bird species of the Cameroon Mountains, non‐endemic Afromontane species, and widespread species. Results We detected neither a positive nor negative abundance–range‐size relationship in the bird community studied. This pattern was caused by the similar abundance of widespread, endemic and non‐endemic montane bird species. Moreover, endemic and non‐endemic montane species had broader local niches than widespread species. The widespread species also used more atypical habitats, as indicated by the slightly larger values of their niche positions. Main conclusions The relationship detected between abundance and range size does not correspond with that inferred from contemporary macroecological theory. We suggest that island effects are responsible for the observed pattern. Relatively high abundances of montane species are probably caused by their adaptation to local environmental conditions, which was enabled by climatic stability and the isolation of montane forest in the Cameroon Mountains. Such a unique environment provides a less suitable habitat for widespread species. Montane species, which are abundant at present, may also have had large ranges in glacial periods, but their post‐glacial distribution may have become restricted after the retreat of the montane forest. On the basis of comparison of our results with studies describing the abundance structure of bird communities in other montane areas in the Afrotropics, we suggest that the detected patterns may be universal throughout Afromontane forests.     

Tree Seed Fate in a Logged and Fragmented Forest Landscape, Northeastern Costa Rica1

We compared the seed fate of two animal‐dispersed, large‐seeded timber species (Dipteryx panamensis [Fabaceae] and Carapa guianensis [Meliaceae]) in logged and fragmented forests with that for continuous forest in northeastern Costa Rica. For both species, we quantified rates of seed removal (an index of vertebrate predation) and the fate of dispersed seeds (those carried away from their original location that either germinated or were not subsequently removed within three months). We predicted that (1) fewer seeds would be dispersed by vertebrates in fragmented forest than in continuous forest due to low population abundances after hunting and/or loss of suitable habitat, and (2) seed predation rates would be higher in forest fragments than in continuous forest due to high abundance of small‐bodied seed consumers. We compared three forest fragments currently managed for timber (140–350 ha) and a large reserve of continuous forest (La Selva, 1500 ha and connected to a national park). An exclusion experiment was performed (seeds placed in the open vs. seeds within semipermeable wire cages; 5 cm mesh size) to evaluate the relative roles of large and small animals on seed removal. Seed germination capacity did not differ among all four sites for both species. Removal of Dipteryx seeds was higher in forest fragments (50% removal within 10 days and related to the activity of small rodents) compared to La Selva (50% removal after 50 days). Also, more Dipteryx seeds were dispersed at La Selva than in fragmented forests. Contrary to our predictions, removal of Carapa seeds was equally high among all four sites, and there was a trend for more seeds of Carapa to be dispersed in fragments than in La Selva. Our results suggest that fragmentation effects on tree seed fate may be specific to species in question and contingent on the animal biota involved, and that management strategies for timber production based on regeneration from seed may differ between forest patches and extensive forests.     

Reproductive ecology of Thymelaea velutina (Thymelaeaceae)- Factors contributing to the maintenance of heterocarpy

Thymelaea velutina (Thymelaeaceae) is a dioecious shrub that presents a unique type of heterocarpy which consists of the simultaneous production of dry and fleshy fruits. It is endemic to the Balearic Islands (Western Mediterranean) and is found both in dunes and mountain areas. The goal of this study was to identify which factors influence the production of both fruit types, examining the variation of their effects at a spatio-temporal scale (comparing two localities in different years). Specifically, we investigated (1) whether pollen limitation influences the type of fruit produced, and (2) the possible differences in seed size, mass, dispersal capacity, seed predation, germination patterns and seedling survival between fruit types. We also examined if the production of fleshy fruits was modified with the application of gibberellins to reproductive branches. Although fleshy fruits were consistently more abundant than dry ones at both populations, their proportion was significantly higher at the site with greater precipitation. The addition of either pollen or gibberellins did not affect the proportion of each fruit type. Seeds in fleshy fruits are consistently larger, heavier and more likely to be dispersed than seeds in dry fruits, but germinability, germination rate and seedling survival was similar among fruit types. Heterocarpy in this species is currently maintained as there is no apparent factor that exerts any strong selective pressure on either fruit type. The two fruit types might even have different `functions', one serving especially for dispersal and population expansion and the other for producing a seed bank that ensures an eventual germination.     

Comparing seed removal rates in actively and passively restored tropical moist forests

High rates of seed removal can impede forest recovery, but tropical seed removal studies are few and mainly from the neotropics. Little is known about the comparative influences of active restoration (i.e. planting) and passive restoration (i.e. protection of natural regrowth) on seed removal. We conducted an evaluation of seed removal in grasslands, natural forests (tropical moist semideciduous forest), and actively (21‐, 17‐, 16‐, 11‐, 8‐, and 6‐year‐old) and passively (21‐year‐old) restored forests in Kibale National Park, Uganda. We wanted to compare the effect of vegetation type, time since restoration and restoration actions (i.e. active vs. passive) on removal of seeds of five animal‐dispersed tree species during wet and dry seasons. Seeds were either fully exposed or placed in closed mesh cages or under a mesh roof. We used differential removal rates between these treatments to attribute seed removal to different animal taxa. Seed removal rate (percentage of seed removed over a 4‐day period) was highest in passively restored forests, compared with actively restored forests, grasslands, and natural forests. We detected no significant relationship between time since restoration and seed removal rates within actively restored sites. Seed removal rate from roofed treatments was not significantly different from removal from open treatments but was significantly higher than removal from closed treatments, which we interpret as reflecting the greater effect of small mammals versus insects. Smaller seeds tended to be removed at a greater rate than larger seeds. We discuss the implications of these findings for forest regeneration.     

Seed Removal Rates Under Isolated Trees and Continuous Vegetation in Semiarid Thornscrub

Clearing native vegetation to increase the amount of land available for agriculture in northeastern Mexico has left remnants ranging in size from fragments of continuous vegetation to isolated individual trees. These provide valuable opportunities for restoring larger areas of native vegetation. We explored whether fragmentation of Tamaulipan thornscrub affects the removal of seeds from 12 woody species that encompass a range of sizes and dispersal mechanisms. We tested whether (1) seed removal rates under isolated trees were higher than under continuous vegetation; (2) dispersal structures, such as fleshy pericarps, made some seeds more attractive to seed removers; and (3) microenvironmental variation affected seed removal rates. Seeds were placed under canopies of Texas ebony (Ebenopsis ebano) and Mesquite trees (Prosopis laevigata). Seed removal trials were conducted three times, each trial lasting 30 days. Most seeds were removed in all trials by the end of one month. Seed removal rate was slower under isolated trees. In general, fleshy fruits were removed faster than other fruits; whole fruits and fleshy tissue were removed faster than depulped seeds. In species with fleshy pericarps, acid washing of seeds, to simulate seeds processed in the digestive tract of dispersers, reduced the seed removal rates, suggesting that it would be a good pre‐treatment for restoration efforts.     

Do rock endemic and widespread plant species differ under the Leaf–Height–Seed plant ecology strategy scheme?

Westoby (1998) proposed the Leaf–Height–Seed (L–H–S) scheme, i.e. the use of three functional traits, specific leaf area (SLA), plant canopy height and seed mass, to describe plant ecological strategies. In this study, we examine whether endemic species from cliffs and rocky outcrops can be discriminated in a regional Mediterranean flora according to these three traits. First, we conducted a comparison across 13 pairs of rock endemic species and widespread congeners. Second, we performed a canonical discriminant analysis to compare the position in the L–H–S volume of these 13 pairs of endemic and widespread congeners with that of 35 phylogenetically unrelated widespread species taken from the same regional flora. Our results show that rock endemic species only differ from their widespread congeners in their smaller stature. However, when compared with the 35 unrelated widespread species, endemic species are discriminated by higher SLA and taller stature, and thus are not close to the stress‐tolerant pole of ecological strategies (small stature, low SLA), as hypothesized in the literature.     

Variation in seed packaging of a fleshy‐fruited conifer provides insights into the ecology and evolution of multi‐seeded fruits

• The study of intraspecific seed packaging (i.e. seed size/number strategy) variation across different populations may allow better understanding of the ecological forces that drive seed evolution in plants. Juniperus thurifera (Cupressaceae) provides a good model to study this due to the existence of two subspecies differentiated by phenotypic traits, such as seed size and cone seediness (number of seeds inside a cone), across its range.
• The aim of this study was to analyse seed packaging (seed mass and cone seediness) variation at different scales (subspecies, populations and individuals) and the relationship between cone and seed traits in European and African J. thurifera populations.
• After opening more than 5300 cones and measuring 3600 seeds, we found that seed packaging traits followed different patterns of variation. Large‐scale effects (region and population) significantly contributed to cone seediness variance, while most of the seed mass variance occurred within individuals. Seed packaging differed between the two sides of the Mediterranean Sea, with African cones bearing fewer but larger seeds than the European ones. However, no differences in seed mass were found between populations when taking into account cone seediness. Larger cones contained more pulp and seeds and displayed a larger variation in individual seed mass.
• We validated previous reports on the intraspecific differences in J. thurifera seed packaging, although both subspecies followed the same seed size/number trade‐off. The higher seediness and variation in seed mass found in larger cones reveals that the positive relationship between seed and cone sizes may not be straightforward.We hypothesise that the large variation of seed size found within cones and individuals in J. thurifera, but also in other fleshy‐fruited species, could represent a bet‐hedging strategy for dispersal.

     

Frugivory and Seed Fate in Bursera inversa (Burseraceae) at Tinigua Park,Colombia: Implications for Primate Conservation1

The large ateline primates are efficient seed dispersers in Neotropical forests and hunting is driving their populations to extinction, but we do not know whether other frugivores could substitute primates in their ecological role as seed dispersers. In this study we test this possibility using a potential keystone species (Bursera inversa) at Tinigua Park, Colombia. This plant species allows us to compare seed removal rates between emergent, isolated trees, without primate visitors and trees with connected crowns. We used traps to estimate fruit production and seed removal rates in six different trees, and fruiting trees were observed during 2 yr to quantify the number of seeds manipulated by different animal species. We carried out seed predation experiments to test if seed removal by predators was affected by distance or density effects. We found that the most productive trees attracted more visiting species and seed removal rates differed among trees, the lowest corresponding to trees without primate access. Seed removal rates from the ground by predators were not higher below parental trees than away from them, but the distribution of saplings in the forest suggests that seed dispersal is advantageous. Although it is likely that the effect of primate extinctions will vary depending on tree species traits, conserving the populations of primate seed dispersers is critical to maintain the ecological processes in this forest.     

Seed removal,seed dispersers,and the allocation of tissues in Myrtaceae seeds

To avoid seed predation, plants may invest in protective seed tissues. Often related to seed size, allocation in seeds' physical defenses can also be influenced by dispersers. We explore the relationships between seed traits (seed mass and hardness) and seed removal in 22 Myrtaceae species of the Brazilian Atlantic Forest, a dominant and diverse fleshy-fruited taxon dispersed by birds, rodents, and other mammals. Our goal is to understand how seed traits influence seed removal rates, and whether dispersers can affect tissue allocation in the seed coat. Seeds were exposed to field removal experiments. In the laboratory, total seed mass and seed coat mass were obtained. To evaluate the influence of seed traits on removal, we performed Kruskal–Wallis and Simple Linear Regression tests. We assessed seed coat and seed mass covariation through standardized major-axis allometric regressions. Harder seeds were larger than softer ones. Seed traits affect removal rates, as tougher and heavier seeds had lower removal. Seed mass significantly predicts seed coat proportion in seven of the 14 species tested. Bird-dispersed species tend to exhibit lower proportions of seed coat as seed mass increases, whereas rodent-dispersed species apparently present the opposite trend, with seed coat proportion increasing with seed mass. Such difference may be caused by the contrasting seed predation pressure represented by birds and rodents. Energy allocation for defense, expressed in seed coat proportion, is greater in large seeds, as these are mostly dispersed by rodents whose propensity to cache and disperse seeds is greater for large and well-protected seeds.