Andres Hernandez

Are Lianas Increasing in Importance in Tropical Forests? A 17-Year Record from Panama

The relative importance of large lianas (woody vines) increased by 100% for stem enumerations conducted during the 1980s and 1990s in widely scattered Neotropical forests. We use three independent types of data to evaluate the hypothesis that lianas have increased in importance in old growth forests on Barro Colorado Island, Panama. Liana leaf litter production and the proportion of forest-wide leaf litter composed of lianas increased between 1986 and 2002. In contrast, liana seed production and liana seedling densities were much more variable through time with particularly high levels during and immediately after El Nino years. Longer time series will be required to detect shifts in life-form composition for highly dynamic seed and seedling communities. The Barro Colorado Island leaf production data are, however, consistent with the hypothesis that lianas are increasing in importance in Neotropical forests.

Tropical forest dynamics across a rainfall gradient and the impact of an El Niño dry season

Tropical forest demography and dynamics were examined in three inventory plots across a precipitation gradient in central Panama. The harsh dry season of 1998 that accompanied the 1997-98 El Ni ˜ no was spanned by censuses at all three sites. The wet and intermediate plots were similar in total species richness, the dry site somewhat lower in diversity; all three sites differed substantially from each other in species composition. Forest-wide growth of large trees was higher at the wet and intermediate sites than at the dry site, but sapling growth was highest at the dry site and lowest at the intermediate site. Forest-wide growth differences were reflected by individual species, for example, saplings of species at the dry site grew faster than saplings of the same species at the intermediate site. Forest-wide mortality was lowest at the dry site and highest at the wet, and this difference was also reflected by individual species. We suggest that low mortality and growth in the drier forest was due to the longer annual dry season and higher deciduousness, and that high sapling growth at the dry site was due to greater light penetration to the forest floor. Growth rates were elevated at all three sites during 1998, possibly due to reduced cloud-cover during the El Ni ˜ no. Contrary to expectation, mortality during 1998 was not elevated at wet and intermediate sites during the El Ni ˜ no drought, but was at the dry site. Finally, we found that some species performed poorly at one site and declined in abundance, while having stable or increasing populations at another site, demonstrating that the communities are not at equilibrium.

ANNUAL AND SPATIAL VARIATION IN SEEDFALL AND SEEDLING RECRUITMENT IN A NEOTROPICAL FOREST

2 National Center for Ecological Analysis and Synthesis, Santa Barbara, California 93101-5504 USA Abstract. An economy of scale may lead to selection to increase interannual variation in seed production when the per seed probability of seedling establishment increases with seed production. Variable annual seedfall will, however, reduce this probability when post- dispersal seed fate is negatively density dependent on the local density of seeds, and seed dispersal and density dependence act identically across years. Intuitively, more variable annual seedfall causes the representative seed to experience a greater density of conspecific seeds and suffer greater density-dependent effects. This handicap must be overcome for the per seed probability of recruitment to be greater in years with greater seed production. We quantified spatial and annual variation in seedfall and seedling recruitment, evaluated density dependence and economies of scale during the seed-to-seedling transition, and investigated the synergistic consequences of density dependence and variable annual seed- fall for seedling recruitment on Barro Colorado Island (BCI), Panama. Weekly censuses of 200 0.5-m 2 seed traps documented seedfall for 15 years and 108 plant species. Annual censuses of 600 1-m 2 seedling plots documented recruitment for nine years and 32 species. The density of seedling recruits tended to increase with the density of seeds; however, the per seed probability of recruitment invariably decreased with seedfall density. Negative density dependence characterized the seed-to-seedling transition. Observed levels of spatial and interannual variation in seedfall density would reduce long-term recruitment by up to 28% if negatively density-dependent survival acted identically across years; however, the strength of negative density dependence varied significantly among years for 12 of 32 species. Negative density dependence occurred in all years for these species but was sig- nificantly weaker during the one or two years of greatest seedfall than during the remaining years of lower seedfall. The per seed probability of recruitment increased significantly with annual seedfall for eight of these species. These eight species realized postdispersal econ- omies of scale despite the reduction in long-term recruitment expected from the synergism between variable annual seed production and negatively density-dependent seed fate.

LIFE HISTORY TRADE-OFFS IN TROPICAL TREES AND LIANAS

It has been hypothesized that tropical trees partition forest light environments through a life history trade-off between juvenile growth and survival; however, the generality of this trade-off across life stages and functional groups has been questioned. We quantified trade-offs between growth and survival for trees and lianas on Barro Colorado Island (BCI), Panama using first-year seedlings of 22 liana and 31 tree species and saplings (10 mm < dbh < 39 mm) of 30 tree species. Lianas showed trade-offs similar to those of trees, with both groups exhibiting broadly overlapping ranges in survival and relative growth rates as seedlings. Life history strategies at the seedling stage were highly correlated with those at the sapling stage among tree species, with all species showing an increase in survival with size. Only one of 30 tree species demonstrated a statistically significant ontogenetic shift, having a relatively lower survival rate at the sapling stage than expected. Our results indicate that similar life history trade-offs apply across two functional groups (lianas and trees), and that life history strategies are largely conserved across seedling and sapling life-stages for most tropical tree species.

Liana Abundance, Diversity, and Distribution on Barro Colorado Island, Panama

Lianas are a key component of tropical forests; however, most surveys are too small to accurately quantify liana community composition, diversity, abundance, and spatial distribution – critical components for measuring the contribution of lianas to forest processes. In 2007, we tagged, mapped, measured the diameter, and identified all lianas ≥1 cm rooted in a 50-ha plot on Barro Colorado Island, Panama (BCI). We calculated liana density, basal area, and species richness for both independently rooted lianas and all rooted liana stems (genets plus clones). We compared spatial aggregation patterns of liana and tree species, and among liana species that varied in the amount of clonal reproduction. We also tested whether liana and tree densities have increased on BCI compared to surveys conducted 30-years earlier. This study represents the most comprehensive spatially contiguous sampling of lianas ever conducted and, over the 50 ha area, we found 67,447 rooted liana stems comprising 162 species. Rooted lianas composed nearly 25% of the woody stems (trees and lianas), 35% of woody species richness, and 3% of woody basal area. Lianas were spatially aggregated within the 50-ha plot and the liana species with the highest proportion of clonal stems more spatially aggregated than the least clonal species, possibly indicating clonal stem recruitment following canopy disturbance. Over the past 30 years, liana density increased by 75% for stems ≥1 cm diameter and nearly 140% for stems ≥5 cm diameter, while tree density on BCI decreased 11.5%; a finding consistent with other neotropical forests. Our data confirm that lianas contribute substantially to tropical forest stem density and diversity, they have highly clumped distributions that appear to be driven by clonal stem recruitment into treefall gaps, and they are increasing relative to trees, thus indicating that lianas will play a greater role in the future dynamics of BCI and other neotropical forests.

Does relatedness matter? Phylogenetic density-dependent survival of seedlings in a tropical forest

A complex set of interactions among neighbors influences plant performance and community structure. Understanding their joint operation requires extensive information on species characteristics and individual performance. We evaluated first-year survival of 35719 tropical forest seedlings of 222 species and 15 annual cohorts relative to the density of conspecific and heterospecific neighbors and the phylogenetic similarity of heterospecific neighbors. Neighbors were from two size classes, and size asymmetric interactions provided insight into likely mechanisms. Large heterospecific and conspecific neighbors reduced seedling survival equally, suggesting resource competition rather than host-specific enemies as a mechanism. In contrast, much stronger negative conspecific effects were associated with seedling neighbors capable of limited resource uptake, suggesting shared pests rather than competition as the mechanism. Survival improved, however, near phylogenetically similar heterospecific neighbors, suggesting habitat associations shared among closely related species affect spatial patterns of performance. Improved performance near phylogenetically similar neighbors is an emerging pattern in the handful of similar studies.

Succession of Ephemeral Secondary Forests and Their Limited Role for the Conservation of Floristic Diversity in a Human-Modified Tropical Landscape

Both local- and landscape-scale processes drive succession of secondary forests in human-modified tropical landscapes. Nonetheless, until recently successional changes in composition and diversity have been predominantly studied at the patch level. Here, we used a unique dataset with 45 randomly selected sites across a mixed-use tropical landscape in central Panama to study forest succession simultaneously on local and landscape scales and across both life stages (seedling, sapling, juvenile and adult trees) and life forms (shrubs, trees, lianas, and palms). To understand the potential of these secondary forests to conserve tree species diversity, we also evaluated the diversity of species that can persist as viable metapopulations in a dynamic patchwork of short-lived successional forests, using different assumptions about the average relative size at reproductive maturity. We found a deterministic shift in the diversity and composition of the local plant communities as well as the metacommunity, driven by variation in the rate at which species recruited into and disappeared from the secondary forests across the landscape. Our results indicate that dispersal limitation and the successional niche operate simultaneously and shape successional dynamics of the metacommunity of these early secondary forests. A high diversity of plant species across the metacommunity of early secondary forests shows a potential for restoration of diverse forests through natural succession, when trees and fragments of older forests are maintained in the agricultural matrix and land is abandoned or set aside for a long period of time. On the other hand, during the first 32 years the number of species with mature-sized individuals was a relatively small and strongly biased sub-sample of the total species pool. This implies that ephemeral secondary forests have a limited role in the long-term conservation of tree species diversity in human-modified tropical landscapes.

Species with greater seed mass are more tolerant of conspecific neighbours: a key driver of early survival and future abundances in a tropical forest

Multiple niche-based processes including conspecific negative density dependence (CNDD) determine plant regeneration and community structure. We ask how interspecific and intraspecific density-dependent interactions relate to plant life histories and associated functional traits. Using hierarchical models, we analysed how such interactions affected first-year survival of seedling recruits of 175 species in a tropical forest, and how species abundances and functional traits are related to interspecific variation in density-dependent effects. Conspecific seedling neighbour effects prevailed over the effects of larger conspecific and all heterospecific neighbours. Tolerance of seedling CNDD enhanced recruit survival and subsequent abundance, all of which were greater among larger seeded, slow-growing and well-defended species. Niche differentiation along the growth-survival trade-off and tolerance of seedling CNDD strongly correlated with regeneration success, with manifest consequences for community structure. The ability of larger seeded species to better tolerate CNDD suggests a novel mechanism for CNDD to contribute to seed-size variation and promote species coexistence through a tolerance-fecundity trade-off.

Association of Pulmonary Tuberculosis and Diabetes in Mexico: Analysis of the National Tuberculosis Registry 2000-2012

Background Tuberculosis (TB) remains a public health problem in Mexico while the incidence of diabetes mellitus type 2 (DM) has increased rapidly in recent years. Objective To describe the trends of incidence rates of pulmonary TB associated with DM and not associated with DM and to compare the results of treatment outcomes in patients with and without DM. Materials and Methods We analysed the National Tuberculosis Registry from 2000 to 2012 including patients with pulmonary TB among individuals older than 20 years of age. The association between DM and treatment failure was analysed using logistic regression, accounting for clustering due to regional distribution. Results In Mexico from 2000 to 2012, the incidence rates of pulmonary TB associated to DM increased by 82.64%, (p <0.001) in contrast to rates of pulmonary TB rate without DM, which decreased by 26.77%, (p <0.001). Patients with a prior diagnosis of DM had a greater likelihood of failing treatment (adjusted odds ratio, 1.34 (1.11–1.61) p <0.002) compared with patients who did not have DM. There was statistical evidence of interaction between DM and sex. The odds of treatment failure were increased in both sexes. Conclusion Our data suggest that the growing DM epidemic has an impact on the rates of pulmonary TB. In addition, patients who suffer from both diseases have a greater probability of treatment failure.

Performance of the inFLUenza Patient-Reported Outcome (FLU-PRO) diary in patients with influenza-like illness (ILI)

Background The inFLUenza Patient Reported Outcome (FLU-PRO) measure is a daily diary assessing signs/symptoms of influenza across six body systems: Nose, Throat, Eyes, Chest/Respiratory, Gastrointestinal, Body/Systemic, developed and tested in adults with influenza. Objectives This study tested the reliability, validity, and responsiveness of FLU-PRO scores in adults with influenza-like illness (ILI). Methods Data from the prospective, observational study used to develop and test the FLU-PRO in influenza virus positive patients were analyzed. Adults (≥18 years) presenting with influenza symptoms in outpatient settings in the US, UK, Mexico, and South America were enrolled, tested for influenza virus, and asked to complete the 37-item draft FLU-PRO daily for up to 14-days. Analyses were performed on data from patients testing negative. Reliability of the final, 32-item FLU-PRO was estimated using Cronbach’s alpha (α; Day 1) and intraclass correlation coefficients (ICC; 2-day reproducibility). Convergent and known-groups validity were assessed using patient global assessments of influenza severity (PGA). Patient report of return to usual health was used to assess responsiveness (Day 1–7). Results The analytical sample included 220 ILI patients (mean age = 39.3, 64.1% female, 88.6% white). Sixty-one (28%) were hospitalized at some point in their illness. Internal consistency reliability (α) of FLU-PRO Total score was 0.90 and ranged from 0.72–0.86 for domain scores. Reproducibility (Day 1–2) was 0.64 for Total, ranging from 0.46–0.78 for domain scores. Day 1 FLU-PRO scores correlated (≥0.30) with the PGA (except Gastrointestinal) and were significantly different across PGA severity groups (Total: F = 81.7, p<0.001; subscales: F = 6.9–62.2; p<0.01). Mean score improvements Day 1–7 were significantly greater in patients reporting return to usual health compared with those who did not (p<0.05, Total and subscales, except Gastrointestinal and Eyes). Conclusions Results suggest FLU-PRO scores are reliable, valid, and responsive in adults with influenza-like illness.