Cecropia Insignis Research Articles

Seed permeability: an essential trait for classifying seed dormancy type

Abstract Seed dormancy in plants can have a significant impact on their ecology. Recent work by Rojas-Villa and Quijano-Abril (2023) classified the seed dormancy class in 14 plant species from the Andean forests of Colombia by using germination trials and several microscopy techniques to describe seed anatomy and morphology. The authors conclude that Cecropia species have both physical and physiological dormancy (of which they call physiophysical dormancy) based on seed morphology and mean germination times of over 30 days. Here, we present seed permeability and germination data from neotropical pioneer tree species: Ochroma pyramidale, Cecropia longipes, and Cecropia insignis, as well as Cecropia peltata (present in Rojas-Villa and Quijano-Abril, 2023), to demonstrate that Cecropia species do not exhibit dormancy and also have high levels of seed permeability. We find that the mean germination time for all three Cecropia species in our study was less than 30 days. This suggests a need for reporting the conditions in which germination trials take place to allow for comparability among studies and using seed permeability tests to accurately identify the physical dormancy class of seeds. Further, we present data from the literature that suggests that dormancy is not a requirement for seed persistence in the seed bank.

Closely related tree species support distinct communities of seed‐associated fungi in a lowland tropical forest

Abstract Previous theoretical work has highlighted the potential for natural enemies to mediate the coexistence of species with similar life histories via density‐dependent effects on survivorship. For plant pathogens to play this role, they must differ in their ability to infect or induce disease in different host plant species. In tropical forests characterized by high diversity, these effects must extend to phylogenetically closely related species pairs. Mortality at the seed and seedling stage strongly influences the abundance and distribution of tropical tree species, but the host preferences and spatial distributions of fungi are rarely determined. We examined how host species identity, relatedness and seed viability influence the composition of fungal communities associated with seeds of four co‐occurring pioneer trees (Cecropia insignis, C. longipes, C. peltata and Jacaranda copaia). Seeds were buried in mesh bags in five common gardens in the understorey of a lowland tropical forest in Panama and retrieved at intervals from 1 to 30 months. A subset of the seeds in each bag was used to determine germination success. One half of each remaining seed was tested for viability; and the other half was used to culture and identify seed‐infecting fungi. Seeds were infected by fungi after burial. Although fungal communities differed in viable versus dead seeds, and across burial locations, community composition primarily varied as a function of plant species identity (30.7% of variation in community composition vs. 4.5% for viability and location together), even for congeneric Cecropia species. Phylogenetic reconstruction showed that relatedness of fungi mostly reflected differences between Jacaranda (Bignoniaceae) and Cecropia (Urticaceae). Although the proportion of germinable seeds decreased gradually over time for all species, intraspecific variation in survival was high at the same location (e.g. ranging from 0% to 100% for C. peltata) suggesting variable exposure or susceptibility to seed pathogens. Synthesis. Our study provides evidence under field conditions that congeneric tree species with similar life history traits differ markedly in seed‐associated fungal communities when exposed to the same soil‐borne fungi. This is a critical first step supporting pathogen‐mediated coexistence of closely related tree species.

Characterization of twenty-six microsatellite markers for the tropical pioneer tree species Cecropia insignis Liebm (Urticaceae)

Cecropia insignis is an ecologically important Neotropical pioneer tree and major vertebrate food source. Although this species is relatively common in faunally intact tropical rainforests, its population dynamics may be negatively impacted by hunting of seed-dispersing animals. To better understand gene flow and regeneration dynamics in C. insignis, we characterized 26 microsatellite markers in a population sampled from Barro Colorado Island, Panama. Eleven loci of ≥3 alleles were tested on 48 individuals, whereas the remaining 15 loci of two alleles were tested on 12 individuals. Allelic richness ranged from 2 to 9 per locus. Observed and expected heterozygosity averaged 0.478 and 0.440 respectively. Polymorphism information content was between 0.141 and 0.757. Only two loci exhibited deviation from Hardy–Weinberg proportions.

Habitat partitioning among neotropical pioneers: a consequence of differential susceptibility to browsing herbivores?

Four species of fast-growing pioneer tree species in the genus Cecropia exist in the forests in central Panama. Cecropia insignis is dominant in old-growth forests but absent from nearby secondary forests; C. obtusifolia, and C. peltata are abundant in secondary forests but rare in old-growth forest, and C. longipes is uncommon in both. To determine whether Cecropia habitat associations are a consequence of local dispersal or differences in recruitment success, we grew seedlings of these species in common gardens in large treefall gaps in secondary and old-growth forest. In contrast to the observed adult distribution, only C. insignis grew significantly over 16 months in secondary forests; remaining species were heavily browsed by herbivores. C. insignis also grew and survived best in old-growth forest. Differences in susceptibility to herbivory did not result from an ant defence mutualism; none of the plants were colonised by ants during the experiment. To test whether C. insignis, the species least susceptible to herbivory, trades off investment in growth in favour of defence, we also grew the four Cecropia species in a screened growing house under light conditions comparable to large forest gaps. Contrary to expectation, species growth rates were similar; only C. peltata grew significantly faster than C. insignis. These results suggest that (1) conditions in ~40-year-old secondary forests no longer support the recruitment of Cecropia species, which are canopy dominants there; and (2) among congeners, differences in plant traits with little apparent cost to growth can have large impacts on recruitment by affecting palatability to herbivores.

Diversity and evolutionary origins of fungi associated with seeds of a neotropical pioneer tree: a case study for analysing fungal environmental samples

Fungi associated with seeds of tropical trees pervasively affect seed survival and germination, and thus are an important, but understudied, component of forest ecology. Here, we examine the diversity and evolutionary origins of fungi isolated from seeds of an important pioneer tree ( Cecropia insignis, Cecropiaceae) following burial in soil for five months in a tropical moist forest in Panama. Our approach, which relied on molecular sequence data because most isolates did not sporulate in culture, provides an opportunity to evaluate several methods currently used to analyse environmental samples of fungi. First, intra- and interspecific divergence were estimated for the nu-rITS and 5.8S gene for four genera of Ascomycota that are commonly recovered from seeds. Using these values we estimated species boundaries for 527 isolates, showing that seed-associated fungi are highly diverse, horizontally transmitted, and genotypically congruent with some foliar endophytes from the same site. We then examined methods for inferring the taxonomic placement and phylogenetic relationships of these fungi, evaluating the effects of manual versus automated alignment, model selection, and inference methods, as well as the quality of BLAST-based identification using GenBank. We found that common methods such as neighbor-joining and Bayesian inference differ in their sensitivity to alignment methods; analyses of particular fungal genera differ in their sensitivity to alignments; and numerous and sometimes intricate disparities exist between BLAST-based versus phylogeny-based identification methods. Lastly, we used our most robust methods to infer phylogenetic relationships of seed-associated fungi in four focal genera, and reconstructed ancestral states to generate preliminary hypotheses regarding the evolutionary origins of this guild. Our results illustrate the dynamic evolutionary relationships among endophytic fungi, pathogens, and seed-associated fungi, and the apparent evolutionary distinctiveness of saprotrophs. Our study also elucidates the diversity, taxonomy, and ecology of an important group of plant-associated fungi and highlights some of the advantages and challenges inherent in the use of ITS data for environmental sampling of fungi.

Burial and secondary dispersal of small seeds in a tropical forest

Abstract:Secondary dispersal is an important stage in the life cycle of tree species, determining the fate of a high proportion of all seeds. For small-seeded species both physical and biological processes may influence the secondary fate of seeds, however the relative importance of these processes is not well known. Seeds of the pioneer tree species Cecropia insignis (seed mass 0.5 mg), Trema micrantha (2.5 mg) and Apeiba aspera (14.2 mg) and five types of artificial seed were sown in understorey, treefall-gap and large-gap sites on Barro Colorado Island, Panama, during the wet season of 2005. Sowing areas were excavated after periods up to 26 d and cores divided into depths of 0–5, 5–10, 10–20 and 20–50 mm to allow high-resolution estimation of the rate and amount of burial and displacement of seeds. Over 26 d, 2.8% of artificial seeds were buried to a mean depth of 10.5 mm below the soil surface and 43.9% of unburied seeds displaced laterally >5 cm. Significantly more (87.9% and 80.9%) seeds of Cecropia insignis and Trema micrantha were displaced than artificial seeds of similar mass, size and density. A generalised linear model suggested that burial mostly occurred within 15 d, while displacement occurred continuously up to 26 d. The dominant cause of displacement and burial was probably rainfall, while seed removal by ants may also have contributed to displacement.

Phenology and Stem Diameter Increment Seasonality in a Costa Rican Wet Tropical Forest

ABSTRACTThe relationship between phenology and tree stem diameter increment is largely unexplored in tropical species, especially in wet tropical forests. To explore links between these phenomena, we measured stem diameter increment and phenology of ten canopy tree species from a range of functional types in the Atlantic lowlands of Costa Rica to test for seasonal and interannual patterns. We measured stem diameter increment using band dendrometers and visually assessed leaf and reproductive phenology monthly from 1997 to 2000. We categorized the species into groups based on patterns of leaf exchange and reproduction. Species were either deciduous with synchronous or asynchronous leaf drop, or evergreen with continuous or seasonal leaf flushing. Flowering occurred supra‐annually, annually, or continuously. Of the ten species studied, four species,Cecropia insignis, Dipteryx panamensis, Lecythis ampla,andSimarouba amara, had consistent seasonal stem diameter increment patterns in both years.Dipteryx panamensisandL. amplawere deciduous with synchronized leaf drop. Cecropia insigniswas evergreen and produced new leaves continuously.Simarouba amara, also evergreen, exchanged leaves over a brief period once a year. We tested whether stem diameter increment was correlated to phenology using logistic regression. Leaflessness significantly explained patterns in stem diameter increment but reproductive phenology did not. Deciduous trees were 2.6–9.3 times more likely to grow less than average the month following leaffall than in months when trees had full crowns.

Effects of litter manipulation on early-stage decomposition and meso-arthropod abundance in a tropical moist forest

Differences in forest productivity due to climate change may result in permanently altered levels of litterfall and litter on the forest floor. Using experimental litter removal and litter addition treatments, we investigated the effects of increased and decreased litterfall on early-stage litter decomposition and the abundance of meso-arthropods in a moist tropical forest. Litterbags containing freshly fallen leaves of Cecropia insignis (above and below the litter on the forest floor, and with and without fungicide) and Simarouba amara, or untreated birch wood ( Betula sp.) were placed in either (1) plots where all litterfall was removed monthly (L−); (2) plots where litterfall was doubled monthly (L+), or (3) control plots (CT). Litter removal significantly slowed decomposition of both species and reduced the abundance of meso-arthropods on Simarouba litter. The fungicide treatment did not reduce apparent mass loss of Cecropia leaves. The litter addition treatment accelerated the decay of birch wood, probably because of increased nutrient availability from the extra litter; but there was no change in leaf-litter decomposition or meso-arthropod abundance in the L+ treatment. After 68 days, the concentrations of nitrogen, phosphorus, potassium, and magnesium in partially decomposed Cecropia litter were higher in the L+ treatment and lower in the L− treatment. The accumulation of phosphorus and nitrogen was greater in the litter in L+ plots and lower in the L− plots while the release of potassium and magnesium from decomposing litter was lower in the L+ treatment and greater in the L− plots. Thus, differences in the quantity of litterfall affect decomposition with consequences for carbon and nutrient storage and cycling.

Post‐Dispersal Seed Removal and Germination Selected Tree Species Dispersed byCebus capucinuson Barro Colorado Island, Panama1

ABSTRACTDispersal quality, an important component of seed disperser effectiveness, may strongly affect the rate of plant recruitment. Here we evaluated the quality ofCebusmonkey dispersal by comparing the secondary removal fate and germination of fresh andCebus‐ingested seeds of nine tree species on Barro Colorado Island, Panama. Overall, rates of secondary seed removal by vertebrates were low, with mostCebusdefecations remaining undisturbed for extended periods on the forest floor. Only four of 30 feces were completely buried by dung beetles, and we found significantly higher vertebrate removal of defecated seeds than control seeds for only one species,Cordia bicolor. Seed germination varied greatly between plant taxa. Seeds of 3 out of 9 species showed significantly higher percent germination after monkey gut passage than control fresh seeds. Germination times tended to be shorter for defecated than for control seeds but were significantly different only for one of nine species,Cecropia insignis. Low rates of seed removal fromCebusfeces, coupled with high germination probabilities, suggest high dispersal effectiveness forCebusand contrasts strongly with patterns of post‐dispersal seed fate recorded for other primate species.

Regeneration niche partitioning in neotropical pioneers: effects of gap size, seasonal drought and herbivory on growth and survival.

Adaptive trade-offs underlie the specialisation that permits habitat partitioning in species rich plant communities. We investigated the influence of the trade-offs that determine differences in growth and survival among six species of neotropical pioneer trees in gaps in semideciduous forest in Panama. Seedlings of Miconia argentea, Cecropia insignis, Luehea seemannii, Trema micrantha, Ochroma pyramidale and Croton bilbergianus were planted into artificial small (25 m(2)), medium (64 m(2)) and large (225 m(2)) gaps in secondary forest in the Barro Colorado Nature Monument. Trema and Ochroma suffered >/=50% mortality across all gap sizes, while Cecropia had high mortality only during the dry season and in the small gaps, and Miconia and Croton suffered low to zero mortality across all environments. The highest growth rates in large gaps were attained by Cecropia seedlings and in the smaller gaps by Miconia seedlings, although there were indications that Trema and Ochroma required gaps that were larger than any used in this study. Variation in growth and mortality could not be attributed to differences in foliar herbivore damage. Instead, there was strong evidence of a trade-off between maximum growth in the wet season and the ability to survive seasonal drought, particularly in small gaps. We conclude that variation in allocation in response to multiple limiting resources may be as important as allocation to growth and defence in determining the habitat preferences of neotropical pioneers.

GETTING TO THE CANOPY: TREE HEIGHT GROWTH IN A NEOTROPICAL RAIN FOREST

There is still limited understanding of the processes underlying forest dy- namics in the world's tropical rain forests, ecosystems of disproportionate importance in terms of global biogeochemistry and biodiversity. Particularly poorly documented are the nature and time scale of upward height growth during regeneration by the tree species in these communities. In this study, we assessed long-term height growth through ontogeny for a diverse group of canopy and emergent tree species in a lowland neotropical rain forest (the La Selva Biological Station, northeastern Costa Rica). Species were evaluated based on annual height measurements of large samples of individuals in all postseedling size classes, over a 16-yr period ( .11 000 increments). The study species were seven nonpi- oneers (Minquartia guianensis, Lecythis ampla, Hymenolobium mesoamericanum, Sima- rouba amara, Dipteryx panamensis, Balizia elegans,and Hyeronima alchorneoides ) and two pioneers (Cecropia obtusifoliaand Cecropia insignis). For each species, inherent height growth capacity was estimated as the mean of the five largest annual height increments (from different individuals) in each juvenile size class (from 50 cm tall to 20 cm in diameter). All species showed marked ontogenetic increases in this measure of height growth potential. At all sizes, there were highly significant differences among species in height growth potential. The two Cecropia species consistently showed the highest observed maximum height increments as smaller juveniles (#4 cm in diameter). Among the nonpioneers, Sim- arouba had the highest growth potential across all juvenile sizes. For all species, mean annual height increments in all juvenile size classes were very much lower than the species' potential growth rates and reflected the impacts of frequent periods of zero growth and major height losses from physical damage. Because of the same factors, maximum net height increments declined over increasing measurement intervals (1-15-yr periods). With only one exception (Simarouba amara saplings #1 cm in diameter that survived 10 yr), the annual height growth increments of these species showed no significant temporal au- tocorrelation. For the seven nonpioneer species, we estimated the minimum time required to grow from 50 cm tall saplings to 10 cm diameter trees, based on their greatest net height increments over increasing intervals. Estimated passage times increased from 7-33 yr, when based on maximum 5-yr height increments, to 37-83 yr, when based on maximum net height growth over 15 yr for the six longest studied (nonpioneer) species. Given the erratic height growth trajectories found for these juvenile trees in this 16-yr study, it is clear that much longer term observation is required. Still unknown are the actual growth trajectories that characterize successful regeneration in each of our focal species, how much time successful trees spend as suppressed juveniles, and the number of times they experience and recover from major physical damage.

DISPERSAL PATTERNS AND SEED BANK DYNAMICS OF PIONEER TREES IN MOIST TROPICAL FOREST

Seed dispersal patterns and seed persistence in the soil should strongly influence the distribution of pioneer tree recruits in gaps. Nonetheless, seed distribution patterns for pioneers are poorly known, and processes controlling the fate of seeds in the soil have been little explored. We examined patterns of seed rain, seed abundance in the soil, and seed mortality of two common pioneer trees, Miconia argentea (Melastomataceae) and Cecropia insignis (Moraceae), on Barro Colorado Island, Panama. For each species, we selected four isolated, reproductive trees within a 50-ha forest dynamics plot. Seed rain and soil seed bank samples were collected, respectively, in mesh traps and from soil cores sampled along transects radiating away from the tree crowns. At below-crown sites, seed rain inputs far exceeded soil seed bank densities measured at the end of the fruiting season. For Miconia, the below-crown seed bank in the surface 3 cm of soil accounted for only 23% of seed rain, and for Cecropia, only 2%. However for Miconia, at distances >5 m from the crown seed bank densities exceeded the annual seed rain input. For both species log seed densities in the seed bank declined linearly with log distance from the crown and also decreased dramatically through the year. The annual loss rate of Miconia seeds was >90% below the crown and declined to 65% at 30 m from the crown. The annual loss rate for Cecropia was >90% at all distances. Seed losses in the seed bank could be largely attributed to mortality from pathogenic fungi. Fungicide treatment significantly increased seed survival in the soil for both species. For these two gap-dependent pioneer species, rapid seed-bank turnover rates and logarithmic declines in soil seed density with distance from adults suggested that both the spatial distribution and timing of gap formation may have influenced their chances of successful gap colonization. Recruitment from distant seed sources, or from seeds surviving in the soil after the death of the parent tree, may be relatively rare for these species.

Changes in the δ 13 C values of trees during a tropical rainy season: some effects in addition to diffusion and carboxylation by rubisco?

The d13C values of deciduous and evergreen tree leaves were compared in open and closed- canopy environments throughout a rainy season in Panamá. Newly emerging leaves had higher d13C values than older leaves of all seedlings and trees at all dates sampled. This was apparently not caused by a decline in water use efficiency as leaves develop because instantaneous ci/ca was significantly higher in newly emerging than in expanded leaves on the same twigs of trees in the field as well as on seedlings growing in a controlled, unchanging environment. Higher d13C values in newly emerging leaves occurred across diverse environmental comparisons. For example, leaves emerging during the rainy season had higher d13C values than corresponding mature leaves that had emerged both during the dry season and when water was abundant. The early enrichment in 13C may thus reflect the translocation of carbon to initiate a new leaf. Furthermore, the lack of sensitivity of this enrichment to a microclimate suggests that it might be the result of processes that occur after carbon fixation by Rubisco. Other changes in d13C values as leaves developed may also have resulted from carbon translocation processes. Foliar d13C decreased significantly after most of the leaf biomass of the deciduous Apeiba membranacea had developed. The d13C values of the evergreen Cecropia insignis were lower in the open canopy than in closed-canopy forests at the end of the rainy season. These findings suggest that the d13C values of leaves can yield ecological information about the allocation of carbon within trees.

Life History Diversity of Canopy and Emergent Trees in a Neotropical Rain Forest

To assess the diversity of tropical tree life histories, a conceptual framework is needed to guide quantitative comparative study of many species. We propose one such framework, which focuses on long—term performance through ontogeny and over the natural range of microsites. For 6 yr we annually evaluated survival, growth, and microsite conditions of six non—pioneer tree species in primary tropical wet forest at the La Selva Biological Station, Costa Rica. The species were: Lecythis ampla, Hymenolobium mesoamericanum, Dipteryx panamensis, Pithecellobium elegans, Hyeronima alchorneoides (all emergents), and Minquartia guianensis (a canopy species). The study was based on long—term measurement of individuals from all post—seedling size classes. Trees were sampled from 150 ha of primary forest spanning several watersheds and soil types. To evaluate individuals' microsites we recorded the number of overtopping crowns, forest phase (gap, building, mature), and crown illumination index (an estimate of the tree's light environment). For comparison, we also evaluated the microsites of three species that have been categorized as pioneers (Cecropia insignis, C. obtusifolia) or high—light demanders (Simarouba amara). For the six species of non—pioneers, mortality rates declined with increasing juvenile size class. As a group, these emergent and canopy trees showed a much lower exponential annual mortality rate (0.44%/yr at >10 cm diameter) than has been found for the La Selva forest as a whole. Growth rates increased with juvenile size class for all six species. As adults (trees >30 cm in diameter), all five emergent species showed substantial annual diameter increments (medians of 5—14 mm/yr). Small saplings and adults of all species had significant year—to—year variation in diameter growth, with much greater growth occurring in the year of lowest rainfall. Passage time analysis suggests that all six species require >150 yr for growth from small saplings to the canopy. Evaluation of all nine species revealed four patterns of microsite occupancy by juveniles. Among the non—pioneers, one species pair (Lecythis and Minquartia: Group A) was associated with low crown illumination and mature—phase forest in all juvenile stages. For two species (Dipteryx and Hymenolobium: Group B) the smallest saplings were in predominantly low—light, mature—forest sites, but crown illumination and association with gap— or building—phase sites increased with juvenile size (Simarouba also showed this pattern). Two species (Pithecellobium and Hyeronima: Group C) were strongly associated with gap or building phase as small juveniles (≤4 cm diameter) and again as subcanopy trees (>10—20 cm diameter), but were predominantly in mature—phase sites at intermediate sizes. Juveniles of the two pioneer species (Cecropia: Group D) showed the highest crown illumination and association with gap or building sites. Among the six non—pioneer species, only one aspect of juvenile performance clearly varied according to microsite group. The smallest saplings (≤1 cm diameter) of Groups B and C showed significant mortality differences across a small gradient in crown illumination; neither of the Group A species showed this pattern. Otherwise, juvenile performance was strikingly similar among the six species. All showed a capacity for growth responses to small increases in light, substantial height and diameter increments at higher light levels, equal ability to survive 4—yr periods of no growth, and very low mortality rates at intermediate—to—large juvenile sizes. Species differed significantly in growth rates, but relative differences shifted with tree size and were unrelated to microsite group. These findings do not support prevailing paradigms concerning trade—offs and correlated suites of traits. For non—pioneer tropical trees, life history classification based on generalized concepts such as gap dependence and shade tolerance is inadequate to describe the complex size—dependent patterns of life history differences and similarities that exist among species.

Leaf Change and Fruit Production in Six Neotropical Moraceae Species

(1) New leaves and fruits of the Moraceae are prominent components in the diets of vertebrate primary consumers on a pantropical basis. In many cases, feeding data suggest that such items from particular genera or species are available in particular habitats for most or all of an annual cycle. (2) To investigate annual production patterns of new leaves and fruits in Moraceae, a 2-year study was carried out in Panama on individuals of six Moraceae species, Ficus insipida and F. yoponensis (subgenus Pharmacosycea), F. obtusifolia and F. costaricana (subgenus Urostigma), Cecropia insignis and Poulsenia armata, using bi-weekly inventories of materials in standardized collection plots and data from canopy scans. (3) Both Urostigma species were deciduous but flushed immediately after leaf drop; other species were evergreen. Dead leaves were shed by all species throughout both years. All species produced large crops of new leaves at intervals shorter than 1 year. Although annual leaf production occasionally showed clustering for a particular species, in general, there was considerable intraspecific variability in the timing of new leaf production. Some individuals of three species (P. armata, C. insignis and F. yoponensis) produced small quantities of new leaves more or less continuously with occasional peaks in new leaf production. Other individuals of these and other species produced large numbers of new leaves more or less episodically. (4) All species initiated fruit crops at intervals averaging < 1 year. In four species, intervals between fruit initiations averaged < 26 weeks. Annual fruit production in five species was intraspecifically asynchronous and, within species, individuals tended to alter the time(s) of year of fruit initiation. C. insignis, the only dioecious species in the sanmple, had a single synchronized period of fruit production each year, lasting approximately 6 months. Trees of F. costaricana showed fruit in the crown for periods lasting 2, 3 or more consecutive months. Inflorescence production in two larger trees of P. armata took place more or less continuously. At the individual level, 87% of the sample trees produced fruit crops at least once per year and many produced more than one. (5) Overall, phenological activities were more pronounced in the drier half of the year. In spite of this trend, at least some leaf shed, leaf flush and fruit production took place throughout the year in most species. A bimodal trend was noted for some phenological events in some species (e.g. leaf shed and leaf flush in F. yoponensis). (6) As a family, as species and, frequently, as individuals, these Moraceae exhibited phenological traits that would tend to make their new leaves and/or fruits available to primary consumers in this forest for much or all of an annual cycle. Similar patterns of frequent and/or intraspecifically asynchronous new leaf and fruit production

Gap-Phase Regeneration of Three Pioneer Tree Species in a Tropical Forest

(1) The gap-phase regeneration behaviour of three pioneer tree species in a Panamanian forest is described. For each species recruitment, mortality and height growth of saplings were recorded during the first 8-9 years of regrowth in thirty natural treefall gaps. The gaps were 20-705 m2 in area. (2) Trema micrantha individuals that survived until years 8-9 were recruited (reached 1 m tall) only in the first year after gap formation. This species grows very fast (up to 7 m year1). After 8-9 years it occurred in only the largest gaps ( > 376 mi2). (3) Cecropia insignis survivors were recruited mostly in the first year after gap formation, but some survived from years 2 and 3. This species did not grow as fast (up to 4 9 m year1) as Trema micrantha. It occurred in the larger gaps (>215 mi2). (4) Miconia argentea survivors were recruited mostly in years 2 and 3, but some survivors were recruited as late as 7 years after gap formation. This species had the slowest growth of the three species studied (up to 2 5 m year-') and colonized gaps from the largest to one of only 102 m2. (5) The gap-phase regeneration behaviour of these species forms a gradient in terms of recruitment, growth, and gap-size requirement. Such dissimilarity could maintain some diversity of gap colonizers, but apparent overlap in regeneration behaviour among these and other pioneer species suggests that chance also promotes their coexistence. Correlates of pioneer species abundance are discussed.

Intraspecific Variation in Herbivory on Two Tropical Tree Species

Levels of herbivory on young and mature leaves were determined for two tree species, Trichilia cipo (Meliaceae) and Cecropia insignis (Moraceae), in a lowland rain forest of Panama. Saplings of both species were studies in light gaps, and in addition, Trichilia was studies in the understory. Rates of leaf damage by insects were measured on marked plants during four 3—wk sample periods conducted at 5—mo intervals. Mature leaves of Cecropia suffered average damage rates that were five times greater than those suffered by Trichilia; the reverse was true for young leaves. Patterns of intraspecific variation in herbivory on mature leaves were similar for the two species, despite differences in life history, habitat, defensive characteristics, and levels of damage. Variation among individuals at any one sample period was high. Damage levels during sequential samples were not significantly correlated within an individual but were highly variable. For each sample period, a different group of individuals (with one exception) comprised the 20% most heavily grazed. These patterns of herbivory are discussed with respect to seasonal effects, possible causal mechanisms, and implications for escape of herbivores and selection of defenses.