Seed dispersal and seed predation in Neotropical palms

Seed dispersal and seed predation in Neotropical palms
Organized by:
 Patrick A. Jansen, Community and Conservation Ecology University of
Groningen, the Netherlands
 Kirsten M. Silvius, Gordon and Betty Moore Foundation, San Francisco
Palms are a dominant life form in many Neotropical forests. Their fruits often represent
an important food resource for frugivores and granivores, which act as dispersers and/or
predators of palm seeds. This symposium aims to present recent work on interactions
between palms, frugivores and granivores. We will invite people studying aspects of
palm seed dispersal, seed predation and seedling recruitment. We aim for a 10-12 talk
state-of-the-art symposium with strong coherence and a logical thread, starting with talks
on specific interactions and finishing with talks on palm-centered food webs. A second
aim is to stimulate co-operation among the participants and their research groups.
Bruchids as predators on palm seeds (Coleoptera: Bruchidae)
Jesús Romero Napoles
Instituto de Fitosanidad, Colegio de Postgraduados
Bruchids comprise approximately 66 genera and 1,700 species worldwide. Of these, more
than half are known from the New World and the remainder spread on the rest of the
world. Actually the family Bruchidae is divided into the subfamilies Amblycerinae,
Bruchinae, Eubaptinae, Kytorhininae, Pachymerinae, and Rhaebinae. About 80% of
bruchid species are in the Bruchinae, 10% in the Amblycerinae, 9% in the Pachymerinae,
with the other 1% assigned to the other three subfamilies. All bruchid larvae feed in seeds
and about 84¬% of bruchid species feed in the seeds of the Fabaceae. The others feed in
the families Arecaceae (4.5), Convolvulaceae (4.5), and Malvaceae (2%). The remaining
5% feed in seeds of 35 other plant families. No all species of Pachymerinae are predators
of seed palms; the tribes Caryopemini and Caryedontini are restricted to the Old World
and feed mainly on seeds of Fabaceae and Combretaceae. All species commonly called
palm bruchids are in the tribe Pachymerini, which is restricted to the New World. Some
species of Pachymerinae are now cosmopolitan in their distribution. The Pachymerini is
formed by the genera Caryoborus (3 species), Caryobruchus (6 species), Pachymerus (7
species), and Speciomerus (4 species). Some studies state that Pachymerini females lay
eggs only in seeds where the exocarp and mesocarp have been removed, and larval
predation may be up to 100%.
Using the BRUCOL data base (Romero & Johnson, 2004) it is known that Pachymerini
may feed on seeds of 32 genera and about 110 species of Arecaceae family, with the
single exception of Pachymerus abruptestriatus, which feeds on Dyospiros sp. seeds
keywords: Palm bruchids, hosts, predation
Phenology and seed predation in three species of palms
Evan Notman 1 and Ana Villegas 2
National Science Foundation
Gordon and Betty Moore Foundation
The timing of fruit and seed production may influence seed survival via differences in
abiotic and biotic conditions. Levels of seed predation may differ with time of dispersal
for various reasons, including seasonal changes in predator abundance, and changes in
the number of conspecific seeds produced. We examined how the timing of seed
production influenced seed survival and germination of three species of lowland
rainforest palms, Welfia regia, Socratea exorrhiza, and Iriartea deltoide in Costa Rica.
We also compared timing of seed production and seed germination and survival of S.
exorrhiza between a site in Panama with highly seasonal rainfall, and a site in Costa Rica
with a relatively weak dry season. We expected that levels of seed predation would be
influenced more strongly by time of seed production for the species that had more
pronounced fruiting peaks (S. exorrhiza, and I. deltoide) than for W. regia which fruits
throughout the year. We also expected larger differences in seed survival for S. exorrhiza
between placement dates in the more seasonal site in Panama than in Costa Rica. Seeds
of each species in Costa Rica were placed in the field during 24 different time periods
that represented a low and high period of conspecific fruit production and survival and
germination was monitored. In Panama seeds of S. exorrhiza were placed in the field
during 2 periods corresponding to the start and the peak of S. exorrhiza fruiting. Although
seed survival rates differed between placement dates, survival patterns were not
consistent between predator type or palm species, and contrary to expectations, the
greatest differences in seed survival time between placement dates were found for W.
regia. Despite the seasonal differences between Costa Rica and Panama the rate of seed
predation between placement dates was fairly similar at both sites.
Keywords: phenology, palms, seed predation, Costa Rica, Panama
Fruit handling by frugivorous vertebrates enables niche partitioning by
granivorous beetles: small scale pattern detected by a landscape scale
Mariana Silvius Kirsten
Gordon and Betty Moore Foundation
Preliminary data from Barro Colorado Island, Panama, suggested that co-occurrence and
relative population abundance of two sympatric bruchid beetles restricted to the same
host palm species is mediated by vertebrate frugivore use of the palm fruits. A large scale
field experiment at Maraca Island Ecological Reserve, Brazil, confirms that the two
bruchid species use the palm resource differently--Speciomerus giganteus is almost
completely restricted to endocarps derived from fruits whose husk has been removed by
vertebrates, while Pachymerus cardo occurs in those derived from both handled and
intact fruits. Early in the fruiting season, paired vertebrate exclosures containing 30 intact
and 30 handled fruits were placed at 4 replicate fruiting trees at each of 6 sites along a 10
kilometer ecosystem-and-palm-density gradient ranging from interior terra firme through
edge forest, savanna forest islands and riverine forest. Endocarps were collected after 1
year and the exit holes left by emerging beetles measured. Speciomerus produces
significantly larger exit holes than Pachymerus; exit hole size is not related to endocarp
size. Exit holes were significantly larger for handled fruits than for intact fruits,
indicating predominant use by the larger Speciomerus. Although there were significant
site effects and site-by-fruit type interactions, niche separation was consistent across all
habitats. Lab based experiments are needed to determine the mechanism for separation. If
Speciomerus cannot use intact fruits in the absence of Pachymerus, then it would be
excluded by Pachymerus at sites of low mammal abundance. Pachymerus is the
dominant competitor, being able to use both forms of fruits. Speciomerus is more
abundant than Pachymerus at BCI, while the opposite is true at Maraca, suggesting an
over-abundance of small frugivorous mammals at BCI relative to Maraca.
Keywords: Bruchid beetle, niche-separation, competition, Attalea, frugivory
Seed density, dispersal and predation in an understory palm
Tarek Milleron
Utah State University
Rodents cache and consume seeds of Astrocaryum gynacanthum, an abundant understory
palm, in lowland rain forests of the Caura River Basin, in southern Venezuela. I did
several experiments with marked and unmarked seeds to examine the effect of seed
density on seed caching and removal. Hunting in the study area may have very slightly
reduced populations of agoutis, but did not impact acouchy, spiny rat or large felid
populations during a period of at least a decade before this study. Seed caching was
intensive toward the tail-end of a fruiting peak and then fell off sharply. Initial seed
density in 1-m x 1-m plots did not affect rates of seed removal, but there was a trend
toward lower proportions being removed from higher density plots. On plots of a range of
sizes, from 0.5-m x 0.5-m to 12-m x 12-m, there was an inverse trend of
disproportionately long caching distance with initial density. More unmarked seeds were
taken from open sites than from paired sites accessible only to small rodents (p = 0.01),
but time to discovery did not differ between access treatments. These results comport
with caching models derived from other field sites. Manipulative experiments of much
greater sophistication will be required in order to elucidate mechanisms behind seed
caching and consumption.
Keywords: rodents,palms, seeds
Differential handling of palm seeds by Central American agoutis
(Dasyprocta punctata; Rodentia) and collared peccaries (Tayassu tajacu;
Artiodactyla) has contrasting effects on seed fates
Erin K. Kuprewicz
University of Miami, Department of Biology
In neotropical forests, terrestrial mammals are important palm seed dispersers and
predators. The positive (dispersal) and negative (predation) effects that mammals have on
seeds influence tree propagation and forest regeneration yet little is known about how
seed dispersers with different seed-handling strategies affect seed fates. Central American
agoutis (Dasyprocta punctata) disperse seeds via scatter-hoarding whereas collared
peccaries (Tayassu tajacu) consume and kill most of the seeds they find. The main goal
of this study was to determine the effects that agoutis and peccaries each have on the
survival of palm seeds at Estacion Biologica La Selva, Costa Rica and how scatterhoarding by agoutis affects seed survival. I tracked individual threadmarked seeds of
Socratea exorrhiza and Astrocaryum alatum over 34-day periods to determine their fates.
Seeds were either exposed to only agoutis and small mammals (excluding peccaries) or to
all terrestrial mammals. I also simulated agouti hoards and exposed seeds to invertebrate
or vertebrate seed predators for 34 days. Seed removal was faster at depots open to all
mammals but most Socratea seeds suffered predation by peccaries, whereas seeds in
semi-permeable mammal exclosures survived longer and were more likely to be hoarded
and dispersed by agoutis. Artificially-hoarded seeds escaped predation by invertebrates
and vertebrates while exposed seeds suffered high beetle infestation or almost complete
removal by mammals. Peccaries consumed most Socratea seeds present on the forest
floor, however hoarding by agoutis may counteract the overall damage that peccaries and
insects have on seed survival to germination.
Keywords: Dasyprocta, Tayassu, seed dispersal, seed predation, scatter-hoarding
Production and fate of Astrocaryum mexicanum seeds before and after
hurricane Iris in southern Belize
Marcel Rejmanek1 and Rob Klinger2
University of California, Davis
US Geological Survey
Astrocaryum mexicanum is an understory dominant palm species that is an important
constant food resource for many mammals of all sizes. Before hurricane Iris (October 8,
2001), mean fruit production was 45.4 fruits per tree per year. After the hurricane, mean
annual production exceeded 130 fruits per tree. This was due to a substantial increase in
mean canopy openness (from <7% to 32% between July 2001 and March 2002) that is
currently only slowly declining. Fruit production approached the pre-hurricane level in
2005. However, in 2007 fruit production appeared to be declining to about 60% of the
pre-hurricane level. As canopy openness is still significantly higher than in the prehurricane years, this decline must be attributed to a physiological exhaustion of the
reproductive trees. In general, while >95% of seeds falling into exclosures below mature
Astrocaryum trees either did not germinate or failed to produce viable seedlings because
of desiccation or decomposition, seeds dispersed and buried under the surface by
mammals, namely by Heteromys desmarestianus, had significantly higher survival rates.
Removal rates and fate of A. mexicanum seeds were strongly related to abundance of H.
desmarestianus. Because all other fruit production ceased for two years after the
hurricane, density of H. desmarestianus decreased from 46 per ha in September 2001 to
23 per ha between January 2002 and January 2004. While this resulted in a 60% decline
in removal rates of A. mexicanum seeds, the proportion that was eaten increased by 50%
because no alternative foods were available. Seed removal rates and the proportion eaten
returned to pre-hurricane levels as density of H. desmarestianus increased after fruiting
non-Astrocaryum woody plants resumed in January 2004.
Keywords: Astrocaryum mexicanum, hurricane, seed production, seed fate, Heteromys
Seed predation and the Arecaceae: a valid model for tropical systems?
Steven Brewer
University of North Carolina Wilmington
What can be learned from single-taxon studies of seed predation, and how suitable is the
Arecaceae as a model for seed predation in general? In order to be an appropriate model
for the effects of seed predation on tropical forest structure and dynamics, the Arecaceae
should be ecologically representative of plant taxa in general. This study examines what
is known about (1) how palm taxa respond to environmental variation compared to
arborescent species in general, using studies from Central and South America and (2)
population dynamics of palms and their associated guilds of seed predators. In the studies
examined, patterns of variation in the composition of palm species is similar to those of
arborescent taxa in general, suggesting that palms and other taxa respond similarly to
community-organizing forces. Physiological and morphological constraints imposed by
Arecaceae phylogeny on palm reproduction offer unique opportunities for detailed
quantification of plant population dynamics, however they impose considerable
limitations to the applicability of long-term studies of palm seed predation and dispersal.
Keywords: seed predation, seed dispersal, palms
Seed dispersal and predation in two Atlantic Forest palms with different
responses to habitat loss
Alexandra dos Santos Pires1, Cecilia Siliansky de Andreazzi2, Clarissa Scofield
Pimenta2, Fernando Antonio dos Santos Fernandez2 and Mauro Galetti 2
Departamento de Ciencias Ambientais, Universidade Federal Rural do Rio de Janeiro
Departamento de Ecologia, Universidade Federal do Rio de Janeiro
Fragmentation impacts biodiversity through several mechanisms, including the disruption
of plant-animal interactions. We investigated the processes of seed dispersal and
predation in two palms dispersed by scatterhoarding rodents but with distinct responses to
fragmentation: Astrocaryum aculeatissimum, which is negatively affected, and Attalea
humilis, which increase their abundance in small remnants. Attalea has more pulp, a
harder endocarp and 1-3 seeds per fruit, while Astrocaryum has thinner endocarp and
only one seed per fruit. We compared seed predation beneath parents and seed dispersal
rates among large (2400 and 3500ha) and small (19, 26 and 57ha) Atlantic Forest
fragments in southeastern Brazil. The number of endocarps remaining beneath palms was
significantly higher in small fragments, both for Astrocaryum (U=98, p<0.01) and Attalea
(U=168, p<0.01), indicating low seed removal in these remnants. For Attalea, this result
was also due to increased fruit production in small areas (U=115.5, p<0.01). Predation
rates by rodents beneath palms were low (below 20%) in most cases for both palms.
Beetle predation seemed to be more important, as rates were high (always above 60%).
For Astrocaryum beetle predation was higher in small remnants (U=512.5, p<0.05)
whereas for Attalea predation rates tended to be higher at the larger ones (U=138,
p=0.08). For both palms, the number of dispersed seeds was lower in smaller fragments
(Astrocaryum: U=1619.5, p<0.01; Attalea: U=1258.5, p<0.01), where viable populations
of dispersers (such as Dasyprocta spp.) probably cannot be maintained in long term. In
synthesis, in small fragments Astrocaryum is strongly affected by the intense predation
pressure from beetles combined with the loss of its dispersers, whereas Attalea, even with
reduced dispersal rates as well, is more resilient because it suffers less predation by
beetles and because its higher productivity allows high local recruitment. Support:
Keywords: fragmentation, palms, seed dispersal, seed predation, Atlantic Forest
Hunting indirectly alters the abundances of insect seed predators
S. Joseph Wright1, Dumas Galvez and Patrick A. Jansen2
Smithsonian Tropical Research Institute
University of Groningen
Hunters are removing game species from most tropical forests, giving rise to the
pantropical bush meat crisis. Game species interact with plants as seed dispersal agents
and seed predators, and through these interactions hunting also affects plants. Game
species also interact with insects, and we will explore how hunter-game species
interactions affect insect seed predators and their palm hosts. Seeds of the palm, Attalea
butyraceae, are eaten and killed by larvae of the bruchid beetle, Speciomerus giganteus.
The female bruchid is only able to lay eggs on the stony endocarp after the tough exocarp
has been removed. The hard, white eggs are nearly 2 mm long and are easily counted. A
single larva develops inside a seed, and the emerging adults leave large circular exit
holes. These traits make it possible to manipulate seed availability to bruchids and to
determine how many eggs are produced and how many adults recruit to the bruchid
population. We compare bruchid population dynamics at protected and hunted sites. The
agouti, Dasyprocta punctata, is both a prized game species and a voracious predator of
Attalea seeds and the bruchid larvae they contain. An order of magnitude more adults
recruit to the bruchid population at hunted sites, where predation by agoutis on bruchid
larvae is greatly reduced. The phenology of oviposition differs with eggs produced yearround at hunted sites and just during the six months of peak seed production at protected
sites. Nonetheless, the number of eggs produced is only twice as large at hunted sites as
at protected sites. This suggests compensatory mortality among adult bruchids at hunted
sites. Bruchids only kill 70% of the available seeds at hunted sites, and many more seeds
survive to produce seedlings at hunted sites than at protected sites. Similar huntergameplant-insect interactions are to be expected elsewhere.
Keywords: bruchid beetle, hunting, seed predation, larval predation, beetle recruitment
Hunting relieves recruitment limitation in a Neotropical palm
Patrick A. Jansen1, Pieter Van Eijk1, S. Joseph Wright 2 and Helene Muller-Landau2
University of Groningen
Smithsonian Tropical Research Institute
University of Minnesota
Recruitment limitation contributes to the coexistence of many tree species in tropical
forest. We studied how various components of recruitment limitation are affected by
hunting, which alters the mammal fauna, changing the abundances of seed dispersers and
natural enemies. We studied the palm Astrocaryum standleyanum, the agoutis that
disperse palm seeds through scatter-hoarding, and various mammals and insects that
depredate the seeds, in Central Panama. We selected 60 individuals across 12 plots with
contrasting levels of hunting and palm abundance, and compared rates of pre- and post
dispersal seed predation, seed removal, seed dispersal, seed survival, seedling
establishment, and seedling survival. We found that two components of recruitment
limitation, source limitation and dispersal limitation, were stronger under hunting. But,
the third component of recruitment limitation, establishment limitation, was dramatically
weaker under hunting. The net effect of hunting was to relieve intense recruitment
limitation. Our results suggest that hunting can indirectly affect mechanisms of species
coexistence. This effect may partially explain why palms attain dominance in disturbed
forests, which usually have high levels of hunting, at the cost of other tree species and
hence biodiversity.
Keywords: Astrocaryum standleyanum, Panama, seed dispersal, seed predation, seedling
Impact of vertebrate defaunation on seed predation and dispersal of
palms: implications for rain forest conservation
Eduardo Mendoza and D Camila onatti
Department of Biological Sciences, Stanford University
Palms are an emblematic component of tropical forests that exemplifies the complex
network of trophic interactions occurring in these ecosystems. A diverse array of
vertebrates preys upon palm seeds, impacting the seed/seedling transition. At the same
time, a large proportion of palm species rely on vertebrates to disperse their seeds and
escape from the attack of other vertebrates and insects. Both ensembles of animals
(predators/dispersers) include a common set of species, predominantly medium and
large-bodied mammals and birds. Defaunation is strongly decimating populations of
medium and large mammals, a situation contrasting with that observed in populations of
small rodents and birds, which seem to be coping better with anthropogenic perturbation.
This situation opens the possibility to find divergent effects of defaunation on palm
recruitment brought about by the simultaneous breakdown of predation and dispersal
interactions. This study is aimed at: i) providing an overview of the levels of palm seed
predation by vertebrates and palm dependence on vertebrate dispersal as inferred from
the literature, ii) presenting case studies from rain forests sites in Brazil and Southeast
Mexico illustrating the mechanisms that may lead to palm decline in the absence of their
dispersers (recruitment limitation) or palm escape in the absence of their seed predators
(differential size related predation), iii) presenting a conceptual framework to guide the
study of the factors that need to be taken into account to evaluate the overall impact of
vertebrate predator/dispersal defaunation on palm performance. Our study indicates that
there is a spectrum of responses to defaunation among palms and that these responses are
scale dependent. However, whether palm populations respond positively or negatively to
defaunation there is a strong potential for rain forest functioning to be affected as a
consequence of the disruption of vertebrate-palm interactions.
Keywords: Defaunation, palms, seed dispersal, seed predation, rain forest conservation
A plague of palms: why large-seeded Attalea form monodominant
stands in anthropogenic landscapes
Jose Manuel Vieira Fragoso 1 and Kirsten M. Silvius2
University of Hawaii
Gordon & Betty Moore Foundation
Researchers have long commented on the predilection of Attalea palms to form large
monodominant stands on pasture and farmland. A number of hypotheses have been
proposed to explain this phenomenon, including fire resistance and removal of potential
competitors. We compared seed mortality around adult trees in pasture and old growth
forest and found significantly higher survivorship in pasture. Bruchid beetles and fungi
were the only mortality agents in pasture, while these plus white-lipped peccaries and
rodents added significantly to mortality in forest. We found no difference in beetle
generated mortality between the two vegetation types. However, in pasture survivorship
was higher due to a lack of seed depredation by white-lipped peccaries and rodents.
Mortality by beetles in forest may be higher than measured, as white-lipped peccaries
open seeds to eat beetle larvae. Early stage seed survivorship patterns sets the
regeneration trajectory and in pasture this contributes to the formation of high-density
monodominant stands of Attalea palms.
Keywords: Attalea, Bruchid beetles, recruitment limitation, Janzen-Connell, pasture