Ignorant seed predators and factors affecting the seed survival of a tropical palm

In addition to acting as seed predators, some terrestrial mammals bury seeds via scatter hoarding. This study system used two permanent plots in examining the interaction between small rodents and the seeds of the palm Astrocaryum mexicanum. We tested how experimental burial, and fruiting status of the parent, distance to the parent, seed size, and microsite characteristics affect the survival of these seeds. Up to 34% of the buried seeds that were exposed only to ignorant rodent foragers (individuals not responsible for burial) survived. In comparison, less than 1% of seeds buried by scatter hoarding rodents survived in previous studies, a percentage that is comparable to the low survival of unburied seeds in this study (<2%). Although unburied seeds had very low survival, increasing distance and/or seed density positively affected survival of unburied seeds. Distance to parent had no effect on buried seed survival.
Buried seed survival was most strongly and significantly determined by the fruiting status of the trees under which they occurred. Seeds experienced significantly greater predation if buried under “parent” trees that fruited during the experiment. Buried seed survival was also negatively affected by germination, as germination may signal the presence of a seed to foraging rodents. There was some indication of a positive effect of tree density on seed survival between the two plots, whereas differences in rodent abundance appear to have no effect on seed survival. Seed size and microsite characteristics had no significant effect on buried seed survival, likely due to the greater proportional effects of other factors and the longevity of A. mexicanum seeds. The results of this study were used to generate a hypothetical causal network showing how comparatively low recovery of buried seeds by ignorant foragers – combined with processes determining the removal of scatter hoarding foragers from their scattered seed caches – may affect seedling recruitment in A. mexicanum.     

Effects of frugivore preferences and habitat heterogeneity on seed rain: a multi-scale analysis

Seed rain mediated by frugivores is influenced by (1) the seed-deposition distances following fruit ingestion, (2) the disperser activity, as determined by its behaviour and habitat preferences, and (3) the structure of the habitat within the landscape. Here, we evaluated such components using the fleshy-fruited shrub Ephedra fragilis and the frugivorous Balearic lizard Podarcis lilfordi. We estimated seed-deposition patterns based on the displacements and habitat preferences of lizards, derived from visual surveys and telemetry data. The influence of variables potentially determining lizard habitat preference (i.e., height, slope, four measures of habitat abundance and four measures of habitat fragmentation) was evaluated at three spatial scales: 'home-range' (c. 2.5-10*10(3) m(2); telemetry data), 'within home-range' (c. 100 m(2); telemetry data) and 'microhabitat' (<100 m(2); visual survey). Cumulative lizard displacement (from each telemetric location to the initial capture point) saturated before the peak of seed defecation (seed-retention time), indicating that lizard home-range size and habitat preferences were the main determinants of the spread and shape of seed shadows. Shrub cover was positively correlated with habitat preference at the three scales of analysis, whereas slope was negatively correlated at the home-range scale. Model scenarios indicated that spatially-aggregated seed rain emerged when we incorporated the joint effect of habitat preference at the two largest (home-range and within home-range) scales. We conclude that, in order to predict seed rain in animal dispersed plants, it is important to consider the multi-scale effects of habitat preference by frugivores.     

Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm

Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a wide range of population density on Barro Colorado Island in Panama and assessed its consequences for seed distributions. We found that frugivore visitation, seed removal and dispersal distance all declined with population density of A. butyracea, demonstrating NDD of seed dispersal due to competition for dispersers. Furthermore, as population density increased, the distances of seeds from the nearest adult decreased, conspecific seed crowding increased and seedling recruitment success decreased, all patterns expected under poorer dispersal. Unexpectedly, however, our analyses showed that NDD of dispersal did not contribute substantially to these changes in the quality of the seed distribution; patterns with population density were dominated by effects due solely to increasing adult and seed density.     

Movement strategies of seed predators as determinants of plant recruitment patterns

Plant recruitment in nature exhibits several distinctive patterns ranging from hump shaped to monotonically decreasing with distance from the seed source. We investigate the role of postdispersal seed predation in shaping these patterns, introducing a new mechanistic model that explicitly accounts for the movement strategy used by seed eaters. The model consists of two partial differential equations describing the spatiotemporal dynamics of both seed and predator densities. The movement strategy is defined by how predators move in response to the different cues they can use to search for seeds. These cues may be seed density, seed intake, distance from the plant, density of conspecific foragers, or a mixture of these four. The model is able to reproduce all the basic plant recruitment patterns found in the field. We compare the results to those of the ideal free distribution (IFD) theory and show that hump-shaped plant recruitment patterns cannot be generated by IFD predators and, in general, by foragers that respond exclusively to seed density. These foragers can produce only nonincreasing patterns, the shapes of which are determined by the foragers' navigation capacities. In contrast, hump-shaped patterns can be produced by distance-responsive predators or by foragers that use conspecifics as a cue for seed abundance.     

Effects of neighborhood on pollination and seed dispersal of a threatened palm

Changes in the spatial density and availability of resources offered by plants due to habitat fragmentation and overexploitation of the natural environment are likely to affect mutualistic interactions. We tested whether changes in the density of neighborhood conspecific and heterospecific plants and in the availability of resources influence the frequency and composition of floral and frugivorous visitors of eleven individuals of the same population of the threatened palm Euterpe edulis in Brazil. The frequency of floral visitors was positively associated with conspecific density and availability of resources. Species composition was affected by the availability of resources since some bee species were associated with palms that offered more flowers, whereas others were associated with palms that offered less. Two bee species may be able to mediate long-distance pollen-flow for E. edulis: an undetermined species of Euglossini and Apis mellifera. Frugivorous birds were not influenced by any of the factors investigated. Birds of the genus Turdus predominated in the assemblage and were responsible for most of the interactions. This is probably due to the fact that, unlike larger birds, species of Turdus are considered resilient to environmental disturbances. Due to the continuous defaunation and fragmentation of the Atlantic Forest, the number of large birds that can promote long-distance seed dispersal is declining, with implications for the genetic diversity of E. edulis. Measures to restore the population density of E. edulis will likely favor the recovery of its genetic diversity due to its high capacity for distant pollen dispersal. Recovering and protecting large frugivorous birds may also contribute to the maintenance of the population density and genetic diversity of E. edulis.     

Survival strategies of a frugivore,the sun bear,in a forest-oil palm landscape

As large areas of forest are lost throughout the tropics, prime habitat of many species decline and become fragmented. The island of Borneo is a prime example, with accelerated clearing of forests primarily for oil palm expansion. Borneo is recognized as an important stronghold for the conservation of the sun bear (Helarctos malayanus), but it is unclear how habitat reduction and fragmentation is affecting this frugivore. We used camera traps and sign surveys to understand patterns of sun bear habitat use in a matrix of fragmented forests and extensive oil palm development, which has existed as such for?>?15 years: the Lower Kinabatangan floodplain in Sabah, Malaysian Borneo. Within these small forest fragments, squeezed between a major river and oil palm plantations, bears exhibited selection for areas farther from human activity (plantations, river boat traffic, and buildings), and were rarely active during the day, demonstrating both spatial and temporal avoidance of potential human-related threats. They selected large trees to feed and rest, and also exploited adjacent plantations to feed on oil palm fruits. We conclude that even relatively small forest fragments (~?2000 ha) within large agricultural landscapes can be important for sun bears. Our research highlights the remarkable adaptations this species has employed to persist in a drastically modified landscape.     

Effects of seed dispersal on Juniperus communis recruitment on a Mediterranean mountain

Abstract. The recruitment of the relict shrub Juniperus communis on a mountain in SE Spain was studied during the period 1994–1998. The main objective was to determine both the quantitative and qualitative effects of bird dispersal on seedling establishment. Seed removal by birds, seed rain, post‐dispersal seed predation, germination, and seedling emergence and survival were analysed in different microhabitats. Birds removed 53 ‐ 89% of the seeds produced by plants. Seed rain was spatially irregular as most seeds accumulated near stones used by birds as perches and below mother plants while a few seeds were dropped in wet meadows and open ground areas. Post‐dispersal seed predation by rodents affected < 10% of dispersed seeds but varied significantly among microhabitats. Only 3.6 ‐ 5.5% of dispersed seeds appeared viable, as many seeds had aborted or showed wasp damage. Seeds germinated in the second and third springs after sowing, reaching a germination percentage of 36%. Seedling emergence was concentrated in wet meadows. Seedling mortality was high (75–80%), but significantly lower in wet meadows, the only microhabitat where seedlings could escape from summer drought, the main mortality cause. Seed abortion, germination and seedling mortality proved to be the main regeneration constraints of J. communis on Mediterranean mountains. Birds exerted a strong demographic effect, although their qualitative effect was limited by abiotic factors which caused the pattern of seed rain to differ from the final pattern of recruitment between microhabitats.     

Daphnia as keystone predators: effects on phytoplankton diversity and grazing resistance

Theory predicts that a predator can promote coexistence amongcompeting prey, and so enhance prey diversity (the keystonepredation effect), by fostering dominance of slow-growing, consumption-resistantprey. In contrast, if the predator promotes dominance by fast-growingvulnerable prey, theory predicts that the predator is unlikelyto promote prey diversity. Theory is silent about keystone predationeffects when the predator does not cause a net change in thevulnerability of the prey assemblage. I present experimentalevidence that Daphnia can act as a keystone predator withoutcausing a net change in the grazing resistance of the phytoplanktonassemblage. No change in resistance was observed, despite strongDaphnia effects on the species composition of the phytoplankton.     

Post-dispersal seed mortality of exotic and native species: Effects of fungal pathogens and seed predators

The invasive behaviour of exotic species is assumed to be due to the reduced impact of enemies on their performance, along with other possible mechanisms. I studied whether the seeds of exotics (6 species) are less impacted by seed predators and seed fungal pathogens than the seeds of their related natives (5 species). I also explored whether the co-occurrence of related natives and the time since introduction increased the percentage of lost seeds in exotics. Seeds were either left unprotected during a period of seven months or treated with fungicide, protected by seed predator exclosures or subjected to both treatments. Both treatments improved seed survival rate. Fungicide treatment had more positive effect on seeds of native than of exotic species but the fungicide-by-origin interaction was insignificant. When exotic species only were considered, fungicide had neutral effect on survival of their seeds, irrespective of the co-occurrence of related natives in the vegetation. Time since introduction was shown not to influence the proportion of seeds lost due to fungi or seed predators. Though the results of this study did not support enemy release as a possible mechanism causing the invasiveness of exotic species, it identified fungal pathogens as an enemy group with possibly differential impacts on native and exotic seeds, which thus deserves attention in future studies.     

基于改进的SURF指数甄选海州湾鱼类群落的关键捕食者

关键捕食者在生态系统中对饵料生物的数量波动、丰富度和空间分布等都起到重要的调控作用。本研究基于在海州湾进行的5个航次的渔业资源底拖网调查资料及胃含物分析数据,通过对传统SURF指数进行改进,甄选海州湾鱼类群落中的关键捕食者。结果表明: 星康吉鳗、长蛇鲻、大泷六线鱼、小眼绿鳍鱼和小黄鱼为海州湾鱼类群落中的关键捕食者,这5种鱼类不但具有较高的连接数,还是多种生物的主要捕食者,在物种连接中具有较强的聚集效应,它们的数量波动会对生态系统能量流动和食物网结构产生较大的影响。通过本方法对关键捕食者进行甄选,不仅考虑了物种间的摄食比例,还将捕捞量及物种的资源量作为重要影响因素,与传统方法相比,具有较大的改进,为关键捕食者的甄选提供了一种新的方法。本研究还发现,物种之间的强相互作用在维护食物网的结构与功能中起着重要作用,加强对关键捕食者的保护,有利于维持生物群落的稳定性和物种多样性,在实施基于生态系统的管理时,要优先保护这些关键物种。星康吉鳗和小黄鱼作为重要的经济鱼种,承受的捕捞压力较高,尤其需要加强保护和管理。     

Effects of mute swan grazing on a keystone macrophyte

1. This study describes the early summer foraging behaviour of mute swans (Cygnus olor) on the River Frome, a highly productive chalk stream in southern England in which Ranunculus penicillatus pseudofluitans is the dominant macrophyte. 2. A daily maximum of 41 ± 2.5 swans were present along the 1.1 km study reach during the study period (late May to the end of June). The river was the primary feeding habitat. Feeding activity on the river at dawn and dusk was much lower than during daylight, but we cannot rule out the possibility that swans fed during the hours of darkness. 3. The effects of herbivory on R. pseudofluitans biomass and morphology were quantified. Biomass was lower in grazed areas and swans grazed selectively on leaves in preference to stems. A lower proportion of stems from grazed areas possessed intact stem apices and flowering of the plant was reduced in grazed areas. 4. A model, based on the swans’ daily consumption, was used to predict the grazing pressure of swans on R. pseudofluitans. The model accurately predicted the number of bird days supported by the study site, only if grazing was assumed to severely reduce R. pseudofluitans growth. The proportion of the initial R. pseudofluitans biomass consumed by a fixed number of swans was predicted to be greater when the habitat area was smaller, initial R. pseudofluitans biomass was lower and R. pseudofluitans was of lower food value. 5. We concluded that the flux of N and P through the study reach was largely unaffected by swan activity. The quality of R. pseudofluitans mesohabitat (the plant as habitat for invertebrates and fish) was significantly reduced by grazing which also indirectly contributed to reduced roughness (Manning's n) and by inference water depth. Wetted habitat area for fish and invertebrates would also be lowered over the summer period as a consequence of the reduction in water depth. It was estimated that, while grazing, an individual swan may eat the same mass of invertebrates per day as a 300‐g trout. 6. There is a need to manage the conflict between mute swans and the keystone macrophyte, R. pseudofluitans, in chalk streams, and the modelling approach used here offers a potentially useful tool for this purpose.     

Large herbivores regulate the spatial recruitment of a hyperdominant Neotropical palm

Large mammalian herbivores play an important role in shaping the diversity of tropical forests by affecting the survival of seedlings and saplings beneath parent plants. The white‐lipped peccary (Tayassu pecari) accounts for the largest herbivore biomass that controls seed and seedling survival in Neotropical ecosystems. However, hunting and habitat loss has driven peccaries to local extinction for most of their original distribution, so it is likely that their absence will affect plant recruitment dynamics. We tested the effects of peccary local extinction on the density and spatial distribution of the hyperdominant palm Euterpe edulis by performing a fine‐scale characterization of its spatial recruitment in six forest sites in the Brazilian Atlantic forest. We compared the age structure and the spatial patterns of seedlings, saplings, and adults as well as the relationship between them. We found that while under the presence of peccaries there was a decrease in recruitment rates under adults, the local extinction of these large mammals led to a more clumped process of spatial recruitment. Despite such contrasting spatial patterns of recruitment dynamics, neither age structure nor the random spatial distribution of adults was affected by the presence or absence of peccaries, indicating that their early effects on these palm populations are mitigated as recruitment advances. Our findings highlight the role of large‐bodied forest‐dwelling herbivores in regulating the fine‐scale spatial recruitment of plants and advance our understanding on the effects of defaunation in tropical forests. Abstract in Portuguese is available with online material.     

Indirect interactions between browsers and seed predators affect the seed bank dynamics of a chaparral shrub

Interactions between herbivores and seed predators may have long-term consequences for plant populations that rely on persistent seed banks for recovery after unpredictable fires. We assessed the effects of browsing by deer and seed predation by rodents, ants and birds on the densities of seeds entering the seed bank of Ceanothus cuneatus var. rigidus, a maritime chaparral shrub in coastal California. Ceanothus produced many more seeds when protected from browsers in long-term experimental exclosures than did browsed plants, but the seed densities in the soil beneath browsed and unbrowsed Ceanothus were the same at the start of an intensive one-year study. The density of seeds in the soil initially increased in both treatments following summer seed drop: while densities returned to pre-drop levels within a few weeks under browsed plants, soil seed densities remained high for 5–8 months beneath unbrowsed plants. Rodent abundance (especially deer mice) was higher near unbrowsed plants than >30 m away, and rodents removed Ceanothus seeds from dishes in the experimental plots. At least in the short term, rodent density and rates of seed removal were inversely related to the intensity of browsing. Our data have management implications for maintaining viable Ceanothus populations by regulating the intensity of browsing and the timing, intensity and frequency of fires.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Effects of flower and seed predators and pollinators on fruit production in two sequentially flowering congeners

We examined spatial and temporal variability of understory herbaceousvegetation on opposing north- and south-facing slopes in an eastern deciduousold-growth forest in southeastern Ohio, USA. Secondly, we explored theinfluenceof sampling scale and analytical technique on our assessment of diversitypatterns. The influence of aspect and seasonality were examined at varyingsampling scales using observed richness, evenness, andH diversity measures, non-parametric richnessestimators, species-area curves, and SHE analysis. Herb layer composition,abundance, and diversity were strongly influenced by location (north slope vs.south slope), seasonal sampling period (April, June, August), and plot size(micro (2 m²)- vs. meso (70m²)-scale samples). Although north and south plots werecompositionally distinct, they followed similar courses of change through thegrowing season. Richness, evenness, and H diversitywere generally greater on the south plot whereas herbaceous abundance wasgreater on the north plot. Species composition and diversity showed markedphenological (temporal) changes, and comparison of diversity measures at micro-and meso-scales produced markedly different results. Minimum sample areas of150–200 m² were needed to evaluate micro-scalerichness in these species rich communities, suggesting that forest understoriesmay be frequently undersampled in ecological studies. Comparison of observedandestimated meso-scale richness also suggested underestimation of richness in thenorth plot, particularly earlier in the growing season. Thus, sample size,area,and time of sampling appear critical to assessment of diversity in spatiallyandtemporally variable communities such as herbaceous forest understories.     

Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

Fruit tracking,frugivore satiation,and their consequences for seed dispersal

Vertebrate frugivore communities are easily satiated by abundant fruit supplies and, contrary to abiotic dispersal agents, typically disperse only part of the available seed pool. This frugivore satiation is likely to be a widespread phenomenon and should be an influential predictor of plants’ ability to disperse their offspring to suitable establishment sites; yet it has never been systematically quantified. Here I investigate patterns of fruit abundance, frugivore activity and frugivore satiation, and their consequences for seed dispersal in the fleshy-fruited tree Frangula alnus. Based on constant-effort seed trapping conducted over 3 years, I assess densities of total and frugivore-consumed seedfall across two spatial (within/between populations) and two temporal (within/between ripening seasons) scales. Furthermore, I examine relationships between fruit abundance and the amount of seeds that are actually dispersed away from fruiting trees. Frugivore activity tightly matched fruit abundance, although some differences existed between scales. This marked fruit tracking did not prevent a significant frugivore satiation, however, and only 53% of the available fruit crops were actually consumed. The extent of satiation varied most at the within-population level, likely due to the territorial behaviour of important frugivore species. In contrast, levels of satiation remained remarkably invariable through time, suggesting that frugivores behave as opportunists and closely adjust the composition of their diet to the available food supply. Overall, greater fruit abundance resulted in a higher proportion of seeds falling beneath fruiting trees, but it also helped increase the (absolute) number of seeds dispersed. This study shows that frugivore satiation can be an important phenomenon even when frugivores tightly track fruit abundance. Its negative effects on recruitment may be attenuated, however, if greater fruit crops help increase population-wide frugivore activity and the amount of seeds being dispersed to suitable establishment sites.     

Seed predators exert selection on the subindividual variation of seed size

Subindividual variation among repeated organs in plants constitutes an overlooked level of variation in phenotypic selection studies, despite being a major component of phenotypic variation. Animals that interact with plants could be selective agents on subindividual variation. This study examines selective pressures exerted during post‐dispersal seed predation and germination on the subindividual variation of seed size in hawthorn (Crataegus monogyna). With a seed offering experiment and a germination test, we estimated phenotypic selection differentials for average and subindividual variation of seed size due to seed predation and germination. Seed size affects germination, growth rate and the probability of an individual seed of escaping predation. Longer seeds showed higher germination rates, but this did not result in significant selection on phenotypes of the maternal trees. On the other hand, seed predators avoided wider seeds, and by doing so exerted phenotypic selection on adult average and subindividual variation of seed size. The detected selection on subindividual variation suggests that the levels of phenotypic variation within individual plants may be, at least partly, the adaptive consequence of animal‐mediated selection.