Characterization of 14 microsatellite DNA markers for the tropical forest tree Virola surinamensis (Rol.) Warb. (Myristicaceae)

Fourteen microsatellite DNA markers were developed for studies of gene flow in the Neotropical rain forest tree Virola surinamensis. The loci were unlinked and polymorphic in a sample of 21 individuals, with two to 10 alleles per locus and observed heterozygosity ranging from 0.14 to 0.76. The overall exclusion probability (0.997) indicates high resolution for parentage-based analyses of gene flow.     

Pollen dispersal and representation in a neotropical rain forest

Results of 3 years of pollen trapping on Barro Colorado Island, Panama, are presented. Minimum pollen dispersal distances are estimated for the most abundant pollen taxa. Dispersal distances for some taxa appear to be as low as 5 m, while for other taxa at least 50% of the trapped pollen had travelled more than 40 m. No consistent pattern of spatial variation was reflected in the pollen rain, however, samples close to large canopy gaps had exceptional abundances of 'disturbance' taxa. A preliminary analysis of the representation of canopy components indicates that as much as 19% of pollen caught in the traps was derived from large tree species.     

Reproductive ecology of 21 coexisting Psychotria species (Rubiaceae): when is heterostyly lost?

Heterostyly is a genetic polymorphism in which plant populations are composed of two or more morphs that differ in stigma and anther heights. The polymorphism promotes intermorph pollen transfer, thus outcrossing. Heterostyly has been reported in 28 angiosperm families and is frequently lost in heterostylous lineages. To assess ecological factors related to shifts from heterostyly to monomorphy, we examined the reproductive ecology of heterostylous tropical shrubs of Psychotria . Among 21 species at Barro Colorado Island and the nearby Parque Nacional Soberania, Panama, 14 species were heterostylous while seven were monomorphic. A molecular phylogeny and the existence elsewhere of heterostylous populations indicated that the breakdown of heterostyly had occurred independently. Heterostylous and monomorphic species were visited by the same bee species, although visit frequencies were lower in monomorphic species. Monomorphic species had significantly lower population density and greater fruit set than did heterostylous species. Autonomous autogamy made a large contribution to fruit set in monomorphic species and was only rarely observed in heterostylous species. The results indicate monomorphic and heterostylous species produce more seeds through selfing and outcrossing, respectively. The limitation of outcrossing as a result of low population density may be related to the breakdown of heterostyly and the evolution of selfing.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 125–134.     

Diapause in a large aggregation of a tropical beetle

Abstract. 1_˜ Diapause is described for adults of Stenotarsus rotundus Arrow (Endomychidae, Coleoptera) in the tropical lowland forest on Barro Colorado Island, Panama.
2 . Diapause lasted up to 10 months each year, covering some 6 months of the wet season plus 4 months of the dry season. When in diapause the beetles clustered in an aggregation of up to 70 ,000 individuals on the stem of a palm tree, the same individual palm tree in at least four successive years.
3. The habitat and habits of the beetle when not in diapause are unknown, but one or two generations may be produced during this period. Beetles returned to the diapause site from June until late August.
4. Soon after arrival at the diapause site the flight muscles degenerated and did not develop again until February/March. The ovaries were undeveloped when the beetles arrived at the site and remained in that condition until the onset of yolk deposition in March. At the beginning of the rainy season in April the beetles mated and dispersed.
5. Lean dry weight of the beetles did not decrease noticeably during diapause, but fat content did. It is suggested that the beetles do not feed, or feed very little, while in diapause. During diapause, the metabolic rate is surprisingly low considering a mean ambient temperature of 25° C.
6. Juvenile hormone analogue (ZR515) stimulated flight muscle and ovary development. Daylength, when different from LD 12: 12 , initiated a partial flight muscle development, but there was no effect on the ovaries. Field observations suggest that neither temperature nor humidity had an effect on the termination of diapause.
7. Although the development of both flight muscles and ovaries were stimulated by juvenile hormone analogue and both developed around March of each year, it is suggested that the mechanisms causing this development are different.     

Local neighborhood effects on long-term survival of individual trees in a neotropical forest

The survival of approximately 235 000 individual tropical trees and saplings in the 50 ha permanent plot on Barro Colorado Island (BCI), Panama was analyzed over a 13-year interval (1982–1995) as a function of four biotic neighborhood variables: (i) total stem density; (ii) conspecific density; (iii) relative plant size; and (iv) relative species richness. These neighborhood variables were measured in annular rings of width 2.5 m, extending 30 m from a given focal plant, and in one more distant annulus at 47.5–50 m. Because survival was spatially autocorrelated, a Gibbs sampler and a Monte Carlo Markov chain method were used for fitting an autologistic regression model to obtain unbiased estimates of parameter variances for hypothesis testing. After pooling all species at the community level, results showed that all four variables had significant and often strong effects on focal plant survival. Three of the four variables had negative effects on focal plant survival; relative plant size was the only variable with a positive effect (18% increase in the survival odds ratio). The variables with a negative effect on the survival odds ratio, in order of their effect strength in the nearest annulus, were: stem density (a 70% reduction in the survival odds ratio), conspecific density (50% reduction) and species richness (13% reduction). A guild-level analysis revealed considerable heterogeneity among guilds in their responses to these variables. For example, survival of gap species showed a much larger positive response to relative plant size than did survival of shade-tolerant species. Survival of shrub species was positively affected by conspecific density, but canopy tree survival was negatively affected. Conspecific density negatively affected survival of rare species much more strongly than survival of common species. The neighborhood effects of conspecific density disappear within approximately 12–15 m of the focal plant. Although locally strong, the rapid spatial decay of these effects raises unanswered questions about their quantitative contribution to the maintenance of tree diversity on landscape scales in the BCI forest.     

Spatial scale and sampling resolution affect measures of gap disturbance in a lowland tropical forest: implications for understanding forest regeneration and carbon storage

Treefall gaps play an important role in tropical forest dynamics and in determining above-ground biomass (AGB). However, our understanding of gap disturbance regimes is largely based either on surveys of forest plots that are small relative to spatial variation in gap disturbance, or on satellite imagery, which cannot accurately detect small gaps. We used high-resolution light detection and ranging data from a 1500 ha forest in Panama to: (i) determine how gap disturbance parameters are influenced by study area size, and the criteria used to define gaps; and (ii) to evaluate how accurately previous ground-based canopy height sampling can determine the size and location of gaps. We found that plot-scale disturbance parameters frequently differed significantly from those measured at the landscape-level, and that canopy height thresholds used to define gaps strongly influenced the gap-size distribution, an important metric influencing AGB. Furthermore, simulated ground surveys of canopy height frequently misrepresented the true location of gaps, which may affect conclusions about how relatively small canopy gaps affect successional processes and contribute to the maintenance of diversity. Across site comparisons need to consider how gap definition, scale and spatial resolution affect characterizations of gap disturbance, and its inferred importance for carbon storage and community composition.