Seed Removal Rates Research Articles

Dispersal in a Neotropical tree, Virola flexuosa (Myristicaceae): Does hunting of large vertebrates limit seed removal?

To understand how different frugivores impact dispersal, we studied the assemblage that feed on Virola flexuosa over a two-year period at two sites differing in hunting pressure in Ecuador. We focus on disperser effectiveness and test the hypothesis that seed removal, influenced by differential visits of large-bodied frugivores, will differ between hunted and non-hunted sites. All visiting frugivores were identified, and fruit handling behavior and seed removal rates quantified. Seed traps were placed under fruiting trees to estimate crop size and fruit removal. Seventeen bird and three primate species were recorded foraging in V. flexuosa trees. Toucans and primates were the most important dispersers comprising nearly 85% of visits with six toucan species recorded in 74% of visits. A proportionately larger number of seeds were removed from fruiting trees at a non-hunted site (89.4%) than a hunted site (66.8%). In addition, there were significantly more frugivore visits at the non-hunted than the hunted site. The differences in the frugivore assemblage and the number of seeds dispersed from individual trees between two structurally similar forest sites suggest dispersal limitation resulting from a decline in frugivores.

Combining distances of ballistic and myrmecochorous seed dispersal in Adriana quadripartita (Euphorbiaceae)

The separate contributions of different vectors to net seed dispersal curves of diplochorous systems have rarely been characterised. In Australia, myrmecochory is a common seed dispersal syndrome and in the majority of such systems, seeds are initially dispersed ballistically. We measured ballistic and myrmecochorous seed dispersal distances in relation to canopies of Adriana quadripartita (Euphorbiaceae) and used a simulation model to estimate the net dispersal curve. We also compared seed removal rates and ant abundances under, and outside, plant canopies to examine how foraging patterns by ants may affect net dispersal. Overall ant abundance did not show a significant numerical response to seedfall; however, the abundance of the main seed dispersing ant, Rhytidoponera ‘metallica’ did. Despite this, seed removal rates did not differ significantly between canopy and open locations. Rhytidoponera ‘metallica’ account for 93% of observed seed dispersal events. On average, the ants dispersed seeds 1.54 m and in doing so, moved seed a mean radial distance of 0.76 m away from canopy edges. This contribution to net dispersal distance by ants is considerable since ballistic dispersal moved seeds a median distance of 7.5 cm. Our simulation model indicated that the combination of ballistic and ant seed dispersal is expected to result in seeds being transported a median net radial dispersal distance of 1.05 m from the canopy edge. Thus in this system, an important function of diplochory may simply be to move a higher proportion of seeds from under the canopy of parent plants than is possible by ballistic dispersal alone. This ‘dispersal-for-distance’ may result in reduced parent–offspring competition or may increase the probability that seeds reach rare safe sites for germination and recruitment.

Species-Specific Seed Dispersal in an Obligate Ant-Plant Mutualism

Throughout lowland Amazonia, arboreal ants collect seeds of specific plants and cultivate them in nutrient-rich nests, forming diverse yet obligate and species-specific symbioses called Neotropical ant-gardens (AGs). The ants depend on their symbiotic plants for nest stability, and the plants depend on AGs for substrate and nutrients. Although the AGs are limited to specific participants, it is unknown at what stage specificity arises, and seed fate pathways in AG epiphytes are undocumented. Here we examine the specificity of the ant-seed interaction by comparing the ant community observed at general food baits to ants attracted to and removing seeds of the AG plant Peperomia macrostachya. We also compare seed removal rates under treatments that excluded vertebrates, arthropods, or both. In the bait study, only three of 70 ant species collected P. macrostachya seeds, and 84% of observed seed removal by ants was attributed to the AG ant Camponotus femoratus. In the exclusion experiment, arthropod exclusion significantly reduced seed removal rates, but vertebrate exclusion did not. We provide the most extensive empirical evidence of species specificity in the AG mutualism and begin to quantify factors that affect seed fate in order to understand conditions that favor its departure from the typical diffuse model of plant-animal mutualism.

Weed seed predation in organic and conventional fields

Enhanced biological control of weed seeds may improve sustainability of agricultural production. Biological control due to seed predation may be higher in organic fields because organic production generally supports more seed predators. To investigate such a difference, weed seed predation was studied in autumn in eight organic and eight conventional mixed cropping fields in New Zealand. Predation rates were estimated by observing removal rates of seeds of the annual weeds fathen or common lambsquarter ( Chenopodium album) and Persian speedwell ( Veronica persica). The seed losses were recorded at distances of 0, 3, 9 and 50 m from the field edge. The weed seeds were placed at the above distances on small dishes of finely sieved soil and sunk into the ground. Removal rates were recorded after 48 h. Seed predators were identified using video recording at an organically grown husbandry unit at Lincoln University and in two of the fields used for estimating seed predation. Recording of predators had therefore limited overlap with seed predation assays but was expected to give important information on key seed predators in the region. The mean seed removal rate was 17% in organic fields compared with 10% in conventional fields although variation was high. Significantly different removal rates between the two field types were found only 9 m from the field edge with approximately four times higher losses of fathen seeds in organic fields. There was also a strong tendency towards higher seed losses at organic field edges. Overall, there was no consistent effect of distance from the field edge. Vegetation had a significant influence on the predation rates, with maximum rates at a medium-dense plant cover. Based on the video images, birds were the most important seed predators. The higher weed seed predation rate in the organic fields indicates that there may be an economic advantage associated with the well-established trend that bird populations are generally higher in organic agricultural situations.

The interaction between Cistaceae and a highly specific seed‐harvester ant in a Mediterranean scrubland

We studied the interaction between the ant Goniomma kugleri and Cistaceae in a Cistus ladanifer-dominated scrubland, in southwestern Spain. We monitored seed harvesting, and studied ant preferences among Cistaceae seeds and their capture efficiencies for preferred seeds. For the stand of C. ladanifer, we estimated seed losses due to the ants. Harvesting was restricted to two seasons: mid-autumn to late winter, and late spring. Ant diet relied on Cistaceae seeds: during autumn and winter 90% of seeds returned to nests were of C. ladanifer, and the remaining fraction also comprised Cistaceae seeds. At this time, the ants harvested seeds directly from the plants. In late spring, the ant diet consisted of Tuberaria guttata s.l. seeds. Goniomma kugleri selectively collected Cistaceae seeds. For preferred species, seed removal rates at the colony level and seed capture times invested by individual workers were correlated with seed size. Because of shorter capture time and higher success frequency, capture efficiency in terms of number of seeds captured per unit time was higher for small-seeded species. Although each ant colony collected large numbers (up to 10(5)) of C. ladanifer seeds over the autumn-winter season, the impact of ant removal on the annual seed output was moderate, at around 20%. It is likely that, in C. ladanifer, the staggered seed release period, and the pulsed exposure of seed clumps in capsules through progressive locule dehiscence, effectively minimise seed losses to the ants.

Effects of frugivore impoverishment and seed predators on the recruitment of a keystone palm

Many plant species are threatened as a result of extinction of their large-bodied frugivores all over the world. Additionally, introduced herbivores and seed predators may cause severe pressure on early stages of plant recruitment. We studied the seed dispersal and seed predation of the keystone palm Euterpe edulis on a land-bridge island with a highly impoverished frugivore fauna and overabundant seed predators, and in a continuous Atlantic forest in Brazil. While the diversity of avian seed dispersers and predators was higher on the mainland, the abundance of seed dispersers was 4-fold higher on the island. Turdus flavipes was responsible for 72% and 96% of seeds removed in the island and mainland, respectively. However, the higher density of T. flaviceps on the island did not result in higher seed removal. In fact, seed removal rate was 1.7 times lower there than on the mainland, probably due to the aggressive behavior of the major seed disperser who defend palm fruits. Seed predation, on the other hand, was markedly higher on the island, where nearly 100% of seeds were preyed upon, but only 0.3% on the mainland. As a consequence of higher seed predation the population of E. edulis has few numbers of seedlings and saplings on the island. Therefore, management of the seed predator populations on the island is a key priority for recovering the natural population of this keystone palm and the frugivores that depend on its fruits.

Geographic variation in seed removal of a myrmecochorous herb: influence of variation in functional guild and species composition of the disperser assemblage through spatial and temporal scales

The ecological influence of changes in the functional guild and species composition of ant assemblages on ant‐dispersal mutualisms is still poorly known. Using a multi‐scale approach over an 800 km range within the Iberian Peninsula, we tested the hypothesis that variation in seed removal rate was related to functional guild rather than to species composition variations of disperser assemblages in the myrmecochore herb Helleborus foetidus. At least two premises must be confirmed to validate this hypothesis: 1) ant assemblages that are dissimilar in species composition but with similar functional guild composition will not differ significantly in seed removal, and 2) assemblages with different functional guild composition will render different seed removal services. We conducted 3328 ant‐visitor censuses on 462 individual plants to identify both the species composition and functional guild variation of the ant‐disperser assemblage, and the plant seed removal rate. Functional guild composition of the ant assemblage was determined by the proportion of visits of ants acting as legitimate dispersers, facultative dispersers or elaiosome predators. Results showed that ant‐seed dispersal success seemed to be more sensitive to species composition changes of the ant assemblage than to functional guild shifts. However, this sensitivity was scale‐dependent. Thus, at the fine, inter‐individual scale, seed removal covaried with the species and functional guild composition of the ant assemblages; at the inter‐populational scale, differences in seed removal tended to be related to the dissimilarity of the assemblage species composition rather than the assemblage functional guild; finally, inter‐regional differences in seed removal were unrelated to dissimilarities of the ant assemblage composition or functional guild. Though differences in seed removal and the relative frequency of the legitimate dispersers tended to be positively correlated, none of the above premises were fully confirmed in this study. Therefore, our results did not support in full the hypothesis that the variation in seed removal was explained by shifts in functional guild composition, rather than shifts in species composition.

Factors affecting the relationship between seed removal and seed mortality

S.B. Vander Wall et al. (Ecology, 86: 801–806 (2005)) criticized seed dispersal studies that use seed removal as a proxy for seed predation, because secondary dispersal processes following removal are important to seed fates for many plants. We compared seed removal rates with direct estimates of seed mortality and another mortality index, based on a 3-year experiment that included five temperate deciduous tree species and four exclosure treatments designed to identify effects of different seed consumer groups. Patterns of seed removal rates generally did not match patterns of mortality. Removal and mortality rates were both highest in seed-poor years, indicative of response to food limitation, but annual food abundance interacted with seed type differently for removal rates than for mortality rates. The effect of exclosure type (access by different consumers) on removal rates was opposite its effect on mortality rates; seeds were removed fastest from exclosures that allowed access to tree squirrels (genus Sciurus L., 1758), but these seeds had the lowest mortality because Sciurus is an important seed disperser. We discuss types of studies in which seed removal may be a reasonable index of seed mortality, and we stress the importance of justifying assumptions concerning links between removal and predation.

Effects of Local Disturbance of Tropical Forests on Frugivores and Seed Removal of a Small‐Seeded Afrotropical Tree

Small-scale, local disturbance of tropical forests, for example from selective logging, is widespread, but its effects on biodiversity and ecosystem function have rarely been studied. In 3 East African tropical rainforests, we investigated the effect of different levels of local forest disturbance on the frugivore community and on tree visitation and fruit removal rates of the small-seeded tree Celtis durandii. We quantified birds and primates in little and heavily disturbed sites, distinguishing between forest specialists, forest generalists, and forest visitors. We quantified frugivorous tree visitors and seed removal rates of C. durandii trees in the same sites. Forest disturbance reduced the species richness and density of the frugivore community and of forest specialists. Frugivorous species and individuals visiting the study trees were reduced significantly, which led to a marginally significant decline in fruit removal by all frugivores and a significant reduction in removal by forest specialists. Reduction in fruit removal by forest specialists was not compensated for by increases in removal by forest generalists or visitors. Results did not differ among the 3 rainforests, which suggests they were consistent at a regional scale. So local forest disturbance led to a loss of frugivores and their seed removal services. This suggests that large-seeded tree species and trees with small fruits are losing seed dispersers. Thus, local forest disturbance appears to have a more general negative impact on frugivores and their seed dispersal services than anticipated previously.

Seed predation of Araucaria angustifolia (Araucariaceae) in the Brazilian Araucaria Forest: influence of deposition site and comparative role of small and ‘large’ mammals

Seed predation and seed dispersal are key factors that determine plant recruitment. In this study, we compared the role of small (<200 g) and ‘large’ mammals as predators of Araucaria angustifolia (Araucariaceae) seeds in the Brazilian Araucaria Forest. We also investigated the effect of deposition site, namely open grassland, forest edge or forest interior (>50 m from the edge) on seed-removal rates. We conducted field experiments on seed removal in July 2003 and 2004. We compared the habitat types using two exclusion treatments: semi-permeable exclosure (exclusive access of small rodents) and an open control (access of all mammal groups). We considered proportion of seeds removed after 15 days to investigate the effect of year, habitat type, and exclusion treatment on seed removal by using three-factor permutational ANOVA. We also evaluated seed fate and seed consumers by using spool-and-line devices attached to seeds and camera trapping. The results showed that seed removal differed significantly between years and among habitat types, but not between exclusion treatments. Removal rates were higher in 2004 than in 2003 and also were significantly lower in the open field when compared with both forested types (edge or interior) in both years. There was also a significant interaction between ‘year’ and ‘habitat’ which was driven by an increase in 2004 removal rates in the open field compared to the previous year. Our combination of manipulative experiments, camera-trapping survey, and spool-and-line seed tracking demonstrated that small rodents are responsible for the majority of seed removal of A. angustifolia in the study area. The low removal rates in open habitats indicate that they could serve as safe sites for A. angustifolia seeds. The results also suggested a potential role of small rodents as seed dispersers (about 4% of removed seeds were not consumed). The knowledge of how fragmentation affects pattern of seed predation and establishment of A. angustifolia through changes in abundance of different-sized mammals is essential for the conservation of the Brazilian Araucaria Forest and its most characteristic species.

Geographical variation in the determinants of seed dispersal success of a myrmecochorous herb

1 This paper draws together geographical variation and various correlates of individual seed dispersal success to evaluate spatial variation in major determinants of seed removal rates of the myrmecochore Helleborus foetidus, whose ant assemblages and diaspores vary geographically. 2 We censused seed removal by ants directly from individual plants in 12 populations and four regions across the Iberian Peninsula, and measured the elaiosomed seed, plant fecundity, and the biotic and abiotic environment in the close vicinity of each plant. The relative effect of these three groups of variables on seed removal was then modelled at each region using structural equation models and path analyses. 3 We found a pervasive effect of the close surroundings of each plant on dispersal. We also found a geographically variable influence of diaspore traits on dispersal. Such variable influence of the diaspore was closely related to the compositional and functional variation in ant guilds. 4 Synthesis: The appearance of an effect of diaspore and plant traits on dispersal depended on the surroundings of the plant, the identity of the ant visitors and ant abundance. This dependence itself might lead to different directions of selection among populations, a conclusion that has not emerged from seed offerings to ants, which is the usual protocol in myrmecochory research.

Seed predation and dispersal of glabrous filbert (Corylus Heterophylla) and pilose filbert (Corylus Mandshurica) by small mammals in a temperate forest, northeast China

We investigated the seed dispersal of glabrous filbert (Corylus heterophylla) and pilose filbert (Corylus mandshurica), two large-seeded shrub species in a temperate forest, northeast China, September 2006. Small mammals such as Apodemus speciosus, Clethrlonomys rufocanus, and Eutamias sibiricus, were regarded as the main dispersal agents. More seeds were harvested by small mammals in pilose filbert (98%) than in glabrous filbert (87.5%) till our last survey. Seed removal rates differed between the two species. Fewer seeds of glabrous filbert (17.5%) were eaten in situ than pilose filbert (57.5%). More seeds of glabrous filbert were removed (70%), stay intact after removal (25.5%), eaten after removal (16%) than pilose filbert. However, more seeds were cached after removal in pilose filbert than in glabrous filbert (10.5 and 4%, respectively). Fewer tagged seeds of pilose filberts (14%) were missed than glabrous filberts (24.5%). About 8 and 12 primary caches were found in glabrous filbert and pilose filbert seeds respectively, indicating scatter hoarding. All of the removed seeds were distributed within 10 m of seed stations for both filberts. The average dispersal distances for glabrous filbert did not differ from pilose filbert. Only a small proportion of the caches remained till our last survey (2 and 1%, respectively). Based on the results, we found a difference in dispersal patterns of glabrous filbert and pilose filbert seeds. Evidences showed that glabrous filberts might be a less preferred seed species for small seed-eating mammals compared with pilose filbert, probably due to its harder and thicker husk and low seed profitability.

A keystone ant species promotes seed dispersal in a “diffuse” mutualism

In order to understand the dynamics of co-evolution it is important to consider spatial variation in interaction dynamics. We examined the relative importance of ant activity, diversity and species identity in an ant seed dispersal mutualism at local, regional and continental scales. We also studied the determinants of seed dispersal rates and dispersal distances at eight sites in the Eneabba sandplain (29.63 S, 115.22 E), western Australia to understand local variation in seed dispersal rate and distance. To test the generality of the conclusions derived from the eight local sites, we established 16 sites along a 1650-km transect in western Australia, covering 11 degrees of latitude and a six-fold increase in rainfall, at which we sampled the ant assemblage, estimated ant species richness and ant activity and observed the removal rate of myrmecochorous seeds. We also assessed the importance of ant species identity at a continental scale via a review of studies carried out throughout Australia which examined ant seed dispersal. Among the eight sandplain shrubland sites, ant species identity, in particular the presence of one genus, Rhytidoponera, was associated with the most dispersal and above average dispersal distances. At the landscape scale, Rhytidoponera presence was the most important determinant of seed removal rate, while seed removal rate was negatively correlated with ant species richness and latitude. Most ant seed removal studies carried out throughout Australia reinforce our observations that Rhytidoponera species were particularly important seed dispersers. It is suggested that superficially diffuse mutualisms may depend greatly on the identity of particular partners. Even at large biogeographic scales, temporal and spatial variation in what are considered to be diffuse mutualisms may often be linked to variation in the abundance of particular partners, and be only weakly - or negatively - associated with the diversity of partners.

Diversity of regenerating plants and seed dispersal in two canopy trees from Colombian Amazon forests with different hunting pressure

Hunting may have drastic effects on some populations of frugivores and seed dispersal agents, which in turn may affect patterns of forest regeneration and plant diversity. However, when a species disappears, it is possible that the population of other species increases due to competition release, compensating or not, their ecological roles. The main aim of this study was to measure density compensation in primate communities, their possible effects on seedling and sapling diversity, and compensation of seed removal rates in two canopy trees (Apeiba aspera and Hymenaea oblongifolia). The study site was Amacayacu National Park (Colombian Amazon), where we carried out a census of mammal species using line transect methods in two forests with different levels of hunting pressure. Vegetation plots were used to quantify plant diversity for seedlings and saplings (4 m2 and 25 m2 respectively), and fruit traps were set up to estimate seed removal of A. aspera and H. oblongifolia. Large primates were less frequently encountered near human settlements, while small primates exhibited the opposite pattern, suggesting a density compensation effect. The diversity of regenerating plants was higher in the forest where large primates occur. Seed removal was higher in forests with large primates for A. aspera, but not for H. oblongifolia. Overall, the results support the hypothesis of density compensation on the primate community; however, there is no strong evidence of ecological compensation in terms of seed dispersal and regeneration in the species studied. Finally, the presence of large seed dispersers (e.g. Lagothrix lagothricha) was associated with higher plant diversity.

Effects of mast seeding and rodent abundance on seed predation and dispersal by rodents in Prunus armeniaca (Rosaceae)

Mast seeding is a very common phenomenon in plants that are dispersed by seed scatter-hoarding animals. This reproductive strategy has been explained as adaptation to satiate predators, and predator abundance affect the seed availability and the extent of satiation. We studied how mast seeding and rodent abundance co-influenced seed predation and dispersal by rodents in Prunus armeniaca (Rosaceae) in the Dongling mountain of Beijing, China. We tracked the individual seeds marked with coded tin tags. The effects of seed crop size and rodent density were examined in May, August and October of a mast year (2000) and a non-mast year (2001). The seed removal rate was slower in mast seeding year than that in non-mast seeding year. There were more scatter hoarding and less larder hoarding with farther seed dispersal distance in the mast seeding year than that in the non-mast seeding year. The seed removal rates were positively correlated to the rodent abundance when data of six seasons of 2 years were pooled. There was high proportion of buried seeds in spring for both years. These results indicate that mast seeding and/or low rodent density increases scatter hoarding and dispersal distance, and then benefit seeding regeneration under effect of predator satiation; photoperiod seems not be very important in determining scatter hoarding activities of rodent in spring in the study region.

Savanna fires increase rates and distances of seed dispersal by ants

Myrmecochory (seed dispersal by ants) is a prominent dispersal mechanism in many environments, and can play a key role in local vegetation dynamics. Here we investigate its interaction with another key process in vegetation dynamics-fire. We examine ant dispersal of seeds immediately before and after experimental burning in an Australian tropical savanna, one of the world's most fire-prone ecosystems. Specifically, our study addressed the effects of burning on: (1) the composition of ants removing seeds, (2) number of seed removals, and (3) distance of seed dispersal. Fire led to higher rates of seed removal post-fire when compared with unburnt habitat, and markedly altered dispersal distance, with mean dispersal distance increasing more than twofold (from 1.6 to 3.8 m), and many distance dispersal events greater than the pre-fire maximum (7.55 m) being recorded. These changes were due primarily to longer foraging ranges of species of Iridomyrmex, most likely in response to the simplification of their foraging landscape. The significance of enhanced seed-removal rates and distance dispersal for seedling establishment is unclear because the benefits to plants in having their seeds dispersed by ants in northern Australia are poorly known. However, an enhanced removal rate would enhance any benefit of reduced predation by rodents. Similarly, the broader range of dispersal distances would appear to benefit plants in terms of reduced parent-offspring conflict and sibling competition, and the location of favourable seedling microsites. Given the high frequency of fire in Australian tropical savannas, enhanced benefits of seed dispersal by ants would apply for much of the year.

Impact of agricultural management on carabid communities and weed seed predation

This study evaluated the relationship between diversity and activity-density of carabid beetles and invertebrate weed seed predation in conventional, no-till, and organic management systems in the Midwest USA. Carabid beetles were sampled with pitfall traps and invertebrate seed predation rates of fall panicum and common lambsquarters were assayed with exclosure cages. Total carabid activity-density was over two times higher in the conventional systems compared to the no-till and organic management systems. In contrast, activity-densities of seed-predating carabid species were over three times higher in the no-till compared to the conventional and organic systems. Carabid diversity was higher in the no-till and organic systems compared to the conventional system, and a multivariate analysis showed that carabid community structure was distinct among the three systems. Predation of fall panicum and common lambsquarters seeds was often over two times higher in the no-till compared to the conventional and organic systems, and there was a strong correlation (r > 0.94) between seed removal rates and the total number of carabid seed predators captured in each system.

Trophic and non‐trophic pathways mediate apparent competition through post‐dispersal seed predation in a Patagonian mixed forest

Post‐dispersal predation can be a major source of seed loss in temperate forests. Little is known, however, about how predator‐mediated indirect interactions such as apparent competition alter survival patterns of canopy tree seeds. Understorey plants may enhance tree seed predation by providing sheltered habitat to granivores (non‐trophic pathway). In addition, occurrence of different tree seeds in mixed patches may lead to short‐term apparent competition between seed types, because of the granivores’ foraging response to changes in food patch quality (trophic pathway). We hypothesised that understorey bamboo cover and mixing of seed species in food patches would both increase tree seed predation in aNothofagus dombeyi−Austrocedrus chilensisforest in northern Patagonia, Argentina. Seed removal experiments were conducted for three consecutive years (2000–2002) differing in overall granivory rates. Seed patch encounter and seed removal rates were consistently higher for the larger and more nutritiousAustrocedrusseeds than for the smallerNothofagusseeds. Seed removal was greater beneath bamboo than in open areas. This apparent competition pathway was stronger in a low‐predation year (2000) than in high‐predation years (2001–2002), suggesting a shift in microhabitat use by rodents. Patch composition had a significant, though weaker, impact on seed survival across study years, whereas seed density per patch enhanced encounter rates but did not influence seed removal. Removal of the less‐preferredNothofagusseeds increased in the presence ofAustrocedrusseeds, but the reciprocal indirect effect was not observed. However, this non‐reciprocal apparent competition between seed species was only significant in the high‐predation years. Our study shows that granivore‐mediated indirect effects can arise through different interaction pathways, affecting seed survival patterns according to the predator's preference for alternative seed types. Moreover, results indicate that the occurrence and relative strength of trophic vs non‐trophic pathways of apparent competition may change under contrasting predation scenarios.

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

Abstract 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.

Granivory, seed dynamics and suitability of the seed-dish technique for granivory estimations in a neotropical savanna

Spatial and seasonal patterns of seed removal by rodents, ants and birds were evaluated using seed-dish experiments in a Trachypogon savanna in Venezuela. Four-day experiments were conducted on three dates and at four different sites. Seeds from 10 native plant species representing a broad mass range were offered at densities equivalent to 3145 seeds m−2. We found that total seed removal and relative importance of granivorous groups varied widely among sites and dates. Rodents were the major seed predators in all the habitats, except for the savanna/forest border where birds dominated. Ants removed more seeds than birds, but since they preferred the smallest seeds, ants ranked last in mass removed. We found a temporally variable relationship between seed removal rates and seed rain or seed bank. We inferred monthly seed predation from seed-dish experiments as well as through the decline of the seed bank in the environment during the dry season, and compared both estimations to evaluate the suitability of the seed-dish technique for estimating granivory. We initially hypothesized that seed-dish experiments that emulate seed availability more closely may yield a better estimate of seed predation, but in fact, they may still overestimate granivory intensity.