Seed Dispersal and Spatial Pattern in Tropical Trees

Theories of tropical tree diversity emphasize dispersal limitation as a potential mechanism for separating species in space and reducing competitive exclusion. We compared the dispersal morphologies, fruit sizes, and spatial distributions of 561 tree species within a fully mapped, 50-hectare plot of primary tropical forest in peninsular Malaysia. We demonstrate here that the extent and scale of conspecific spatial aggregation is correlated with the mode of seed dispersal. This relationship holds for saplings as well as for mature trees. Phylogenetically independent contrasts confirm that the relationship between dispersal and spatial pattern is significant even after controlling for common ancestry among species. We found the same qualitative results for a 50-hectare tropical forest plot in Panama. Our results provide broad empirical evidence for the importance of dispersal mode in establishing the long-term community structure of tropical forests

Interrogating Plant Cell Culture Library for Novel Antimicrobial Agents

The Plant Cell Culture Library (PCCL) at UMass Amherst contains more than 2,200 live plant cell cultures, representing diverse plant species from around the world. The availability of this collection offers a rich resource for us to discover bioactive phytochemicals and uncover their mechanisms of action. Using data-mining surveys of bioactive plant extracts, I have organized subsets of PCCL cell lines that are likely to possess antifungal, antibacterial, antiviral, anthelmintic, anti-trypanosomal, or anticancer properties, which prove to be useful when deciding which species to screen first against a specific pathogen. Another distinct advantage of using the live plant cells in this research is the ability to stimulate the biosynthesis of pathogen-specific phytochemicals upon simulation of an attack (elicitation) by the microorganism in question. This could be accomplished by pathogen homogenates or plant hormones responsible for mounting defenses to infection. Over the past six months, I have been working to optimize elicitation, lysis, and extraction conditions for obtaining high-throughput screening materials to be used against variable pathogens. Equipped with crude extracts from appropriately elicited cells, I am collaborating with a multidisciplinary team of UMass scientists to develop and implement high-throughput screening protocols for profiling a large number of plant-derived materials against various pathogens. Recently, I have screened a small pool (40) of extracts derived from cell lines with predicted anti-fungal properties against the highly resistant strain of fungus Fusarium oxysporum, one of the causal agents of an opportunistic infection often seen in immunocompromised patients known as fusariosis. Gratifyingly, I have found several plant species that produced specialized metabolites with better antifungal activity than the leading antibiotic against F. oxysporum, Amphotericin B, validating this line of antimicrobial research. We are also actively reaching out to other academic labs partners to form partnerships in diverse antimicrobial research venues

Widespread sampling biases in herbaria revealed from large-scale digitization

SUMMARY 1. Non-random collecting practices may bias conclusions drawn from analyses of herbarium records. Recent efforts to fully digitize and mobilize regional floras online offer a timely opportunity to assess commonalities and differences in herbarium sampling biases. 2. We determined spatial, temporal, trait, phylogenetic, and collector biases in ~5 million herbarium records, representing three of the most complete digitized floras of the world: Australia (AU), South Africa (SA), and New England, USA (NE). 3. We identified numerous shared and unique biases among these regions. Shared biases included specimens i) collected close to roads and herbaria; ii) collected more frequently during biological spring and summer; iii) of threatened species collected less frequently; and iv) of close relatives collected in similar numbers. Regional differences included i) over-representation of graminoids in SA and AU and of annuals in AU; and ii) peak collection during the 1910s in NE, 1980s in SA, and 1990s in AU. Finally, in all regions, a disproportionately large percentage of specimens were collected by very few individuals. We hypothesize that these mega-collectors, and along with their associated preferences and idiosyncrasies, shaped patterns of collection bias via ‘founder effects’. 4. Studies using herbarium collections should account for sampling biases, and future collecting efforts should avoid compounding these biases to the extent possible.Organismic and Evolutionary Biolog

The Spatial Aggregation Statistic, <i>K(d),</i> Evaluated at a Range of Distances for Tree Species in Four Dispersal Syndromes

<p>Within each dispersal syndrome, the graph shows the mean <i>K(d)</i> value ± 1 standard error. A species is aggregated at distance <i>d</i> if <i>K(d)</i> exceeds unity. Dotted lines indicate <i>K(d)</i> for a Poisson random spatial distribution. All species are strongly aggregated at small spatial scales and weakly aggregated at large scales. At spatial scales <i>d</i> ≤ 75 m, each of the dispersal types has a significantly different mean <i>K(d)</i> value (Wilcoxon <i>p</i> < 0.008). At larger spatial scales (<i>d</i> > 200m), spatial aggregation is not significantly correlated with dispersal syndrome. (The other three dispersal syndromes are omitted for clarity.)</p

The Relationship Between Dispersal Syndrome and Spatial Aggregation among 425 Tropical Tree Species, Restricted to Mature Trees Only (Stem Diameter > 5 cm)

<p>The figure shows the mean spatial cluster size σ for tree species in each of seven dispersal syndromes. Dispersal syndromes are significantly associated with spatial aggregation among mature trees (Kruskal-Wallis, df = 6, χ² = 46.7, <i>p</i> < 10⁻⁶).</p

The Relationship between Dispersal Syndrome and Spatial Aggregation for 561 Tree Species at Pasoh, Malaysia

<p>The figure shows the mean ± 1 standard error of the spatial cluster size (σ) for tree species in each of seven dispersal syndromes.</p

Examples of Mapped Tree Populations for Four Species in the 50-ha Pasoh Forest Plot

<p>Upper left, Baccaurea racemosa (animal dispersed; <i>n</i> = 1,228, σ = 146.5 m); lower left, Neobalanocarpus heimii (gravity dispersed; <i>n</i> = 3,334, σ = 86.7 m); upper right, Shorea leprosula (gyration dispersed; <i>n</i> = 2,154, σ = 33.1 m); lower right Croton argyratus (ballistically dispersed; <i>n</i> = 1,248, σ = 27.9 m).</p

Functional group dominance and identity effects influence the magnitude of grassland invasion

Variation in functional community composition is expected to influence the extent of exotic species invasions. Yet, whether resident functional groups control invasion through their relative biomass (mass ratio hypothesis) or by traits other than biomass (identity hypothesis) remains poorly understood. We performed a 6-year experiment to determine the effects of removing different functional groups on exotic species biomass in a Flooding Pampa grassland, Argentina. Functional groups were defined by life-form (grasses or forbs), phenology (winter or summer) and origin (native or exotic). Removal of each functional group was compared against the removal of an equivalent amount of random biomass. Exotic group responses were monitored over 4 years of continuous removals, and after 2 years of recovery without manipulations. Removal of dominant native summer grasses caused the greatest impact on exotic species and overall community composition. Native summer-grass removal significantly increased exotic grass (120%) and forb (730%) biomass beyond the level (46% and 180%, respectively) expected from deleting a similar amount of biomass at random. Exotic annual grasses showed only a transient increase, whereas exotic forb invasion persisted even after 2 years without removals. Removing subordinate, native or exotic winter grasses, and rare native forbs significantly promoted exotic forbs, but to the same level (300%) as random biomass removals. Total grass removal increased exotic forbs to half the extent expected from adding the effects of single grass group removals. Dispersal limitation and harsh abiotic conditions may constrain exotic forb spread into such heavily grass-depleted patches. Synthesis. The impact of losing a functional group on the magnitude and persistence of invasion reflected its relative contribution to community biomass. Identity attributes other than biomass (e.g. phenological niche) further enhanced the biotic control that dominant native grasses exerted on established exotic species. Our findings highlight the community legacies of past disturbances to dominant functional groups.Fil: Longo, Maria Grisel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas A la Agricultura; ArgentinaFil: Seidler, Tristram G.. Harvard University; Estados UnidosFil: Garibaldi, Lucas Alejandro. Universidad Nacional de Rio Negro. Sede Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tognetti, Pedro Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Chaneton, Enrique Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas A la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentin