Tracking wind‐dispersed seeds using 15N‐isotope enrichment

Seed dispersal influences a wide range of ecological processes. However, measuring dispersal patterns, particularly long‐distance dispersal, has been a difficult task. Marking bird‐dispersed seeds with stable ¹⁵N isotopes has been shown to be a user‐friendly method to trace seed dispersal. In this study, we determined whether ¹⁵N urea solution could be used to enrich seeds of two common wind‐dispersed plants, Eupatorium glaucescens (Asteraceae) and Sericocarpus tortifolius (Asteraceae). We further tested if the water type (distilled versus tap) in ¹⁵N urea solutions influences the level and variability of enrichment of plant seeds, and if increasing spraying frequency per se increases enrichment. Because droughts may lower seed set or kill plants, we wanted to investigate if the additional use of an externally applied anti‐transpirant affects the intake of externally applied ¹⁵N into seeds. The results demonstrate that ¹⁵N enrichment of seeds can facilitate dispersal experiments with wind‐dispersed plants. The use of distilled water in ¹⁵N urea solutions did not increase ¹⁵N enrichment compared to tap water. Further, enrichment was more efficient at lower spray frequencies. Both the use of tap water and low frequencies could lower time, effort and project costs. The results suggest that species can be protected from drought using an anti‐transpirant without decreasing the incorporation of ¹⁵N into seeds.     

Climatic sensitivity of species’ vegetative and reproductive phenology in a Hawaiian montane wet forest

Understanding how tropical tree phenology (i.e., the timing and amount of seed and leaf production) responds to climate is vital for predicting how climate change may alter ecological functioning of tropical forests. We examined the effects of temperature, rainfall, and photosynthetically active radiation (PAR) on seed phenology of four dominant species and community-level leaf phenology in a montane wet forest on the island of Hawaiʻi using monthly data collected over ~ 6 years. We expected that species phenologies would be better explained by variation in temperature and PAR than rainfall because rainfall at this site is not limiting. The best-fit model for all four species included temperature, rainfall, and PAR. For three species, including two foundational species of Hawaiian forests (Acacia koa and Metrosideros polymorpha), seed production declined with increasing maximum temperatures and increased with rainfall. Relationships with PAR were the most variable across all four species. Community-level leaf litterfall decreased with minimum temperatures, increased with rainfall, and showed a peak at PAR of ~ 400 μmol/m²s⁻¹. There was considerable variation in monthly seed and leaf production not explained by climatic factors, and there was some evidence for a mediating effect of daylength. Thus, the impact of future climate change on this forest will depend on how climate change interacts with other factors such as daylength, biotic, and/or evolutionary constraints. Our results nonetheless provide insight into how climate change may affect different species in unique ways with potential consequences for shifts in species distributions and community composition.     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.     

Zeitaufwand für das Ernten und Verstecken von Kiefernsamen bei Dünnschn?bligen Tannenh?hern (Nucifraga caryocatactes macrorhynchos) im Fernen Osten Russlands

Zusammenfassung In einem Vorkommen des Dünnschnäbligen Tannenhähers an der Küste des Ochotskischen Meeres im Fernen Osten Sibiriens wurde das Ernten und Verstecken von Samen aus den Zapfen der Zwergzirbelkiefer (Pinus pumila) untersucht. Der Inhalt von durchschnittlich 2,8 Zapfen, das sind etwa 80 Samen, wurde in der gefüllten Kehltasche transportiert und auf eine Anzahl unter niedriger Zwergstrauchvegetation gelegener Bodenverstecke verteilt. Die Verstecke wurden in annähernd linearer Anordnung ohne Bevorzugung einer bestimmten Himmelsrichtung angelegt. Die Versteckserien enthielten im Median 79, maximal mehr als 120 Samen, das Einzelversteck durchschnittlich 19,6 Samen. Das Ernten und Leeren eines Zapfens geschah im Schnitt innerhalb von 47 s. Für das Verstecken einer Füllung des Kehlsacks benötigten die Vögel ca. 170 s. Für das gesamte Beschaffen und Verstecken eines einzelnen Kiefernsamens errechnet sich ein durchschnittlicher Zeitbedarf von 3,26 s. Nach 20 Tagen war der Zapfenvorrat in der lokalen Kiefernpopulation erschöpft. Jeder Häher hat nach den Hochrechnungen bis zu 100.000 Samen vergraben.

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Harvesting and caching capacities of Thin-billed Nutcrackers in the Russian Far East

Summary At the Ochotskian sea coast Thin-billed Eurasian Nutcrackers (Nucifraga caryocatactes macrorhynchos) harvested seeds of ripe cones of the brush pinePinus pumila in late summer. The mean number of seeds carried in their sublingual pouch was 80, which respresents the harvestable contents of 2.8 cones. These were distributed in an average of 5 caches, exclusively in the soil under low tundra vegetation. Caches were organized in nearly straight lines. Series contained a mean of 82.7 seeds, single caches a mean of 19.6 seeds. Plucking one cone and harvesting its seeds took 47 seconds on average. The caching of a complete pouchful took on average 123.4 seconds. The time invested for harvesting and caching one single seed was calculated at 3.26 seconds. Within three weeks in July, an average individual bird was calculated to have cached a total of up to 100,000 seeds.

     

Massive Seed Predation of Pseudobombax grandiflorum (Bombacaceae) by Parakeets Brotogeris versicolurus (Psittacidae) in a Forest Fragment in Brazil1

Here we report massive seed predation of Pseudobombax grandiflorum (Bombacaceae) by Botogeris versicolurus (Psittacidae) in a forest fragment in Brazil. The intensity of seed predation was very high when compared to other studies in continuous forest, perhaps resulting from a scarcity of resources in such areas. This scarcity may limit the range of parrot's diet to a few plant species. It suggests that studies of Psittacidae seed predation may be important for conservation of some plants in fragments.     

Detection of a natural point mutation in Potato virus A that overcomes resistance to vascular movement in Nicandra physaloides., and studies on seed-transmissibility of the mutant virus

Isolate M of Potato virus A (PVA‐M; genus Potyvirus) is avirulent in Nicandra physaloides L. (family Solanaceae). The inoculated leaves are infected but no systemic infection is observed. Forty plants of ‘Black Pod’ (BP) and ‘Black Pod Alba’ (BPA), two variants of N. physaloides described in this study, were inoculated with PVA‐M. Two plants of BP and one plant of BPA were systemically infected. Mosaic, blistering and dark green islands developed on the systemically infected leaves, and flowers showed colour‐break symptoms. PVAprogeny were sequence‐characterised for the 6K2 protein and viral genome‐linked protein (VPg) encoding regions known to control the long distance movement of PVA in N. physaloides. All virus progeny (designated as PVA‐Mm) in the systemically infected leaves of the plants inoculated with PVA‐M contained only a single amino acid substitution (Vail 16Met) in the central part of VPg due to a nucleotide substitution G6033A, as compared to PVA‐M. Other PVA isolates that infected N. physaloides systemically also contained Metll6 in VPg. In a previous study using chimeric viruses, Metl16 in VPg was shown to be a major determinant for vascular movement of PVA in N. physaloides, and this study reveals that the mutation for Metl16 can occur in vivo during replication of the avirulent PVA‐M in infected plants. Immunolocalisation studies on BP and BPA plants showed that the pods (berries) and seed coat contained PVA‐Mm in the developing seeds, but no virus was detected in embryons. Up to 27% of the mature seeds contained PVA‐Mm but no transmission to seedlings was observed in a total of 450 seeds tested, and no test plants were infected following mechanical inoculation with extracts prepared from the seeds.     

THE INFLUENCE OF THE MATING SYSTEM ON SEED SIZE VARIATION IN CRINUM ERUBESCENS (AMARYLLIDACEAE)

We present evidence that extreme seed size variation in fruits of Crinum erubescens (range: 0.1 to 66.5 g per seed) occurs when mating pairs are inbred, either from selfing or biparental inbreeding. Several relatively uniform seeds of intermediate size are produced when pollen from several pollen donors is applied simultaneously to a flower. Selfed fruits and some fruits pollinated with a single pollen donor produce both large and small seeds, although selfed fruits produce fewer seeds than outcrossed fruit. These results are contrary to the hypothesis that variation in seed size is attributable to either pollen competition or differential allocation of maternal resource to seeds of different genotypes.