Shrubs versus ‘gullivers’: woody species coping with disturbance in grasslands

Resprouting of trees and shrubs in forest-grassland ecotones is a key process to understand the dynamics of these systems under different disturbance regimes. This study integrates resprouting of grassland shrubs and pioneer forest trees (??gullivers??), burned in subtropical lowland grassland and cut in temperate highland grassland of Rio Grande do Sul, Brazil. Per grassland site, 20 individuals each of 1?C2 grassland shrub species (Asteraceae) and two forest tree species (Myrsinaceae, Myrtaceae) were tagged, and post-disturbance survival and growth monitored for 1?year at 2?C4?month intervals. Differences in resprouting vigour (summed-up basal area of resprouted shoots per pre-disturbance summed-up area of basal stems), and in density and allometry of resprouted shoots (allocation mode) were compared between tree and shrub species by linear mixed effects modelling and multiple comparisons, using the Tukey test. All grassland shrub individuals resprouted and regained 73?C142?% (species average) of pre-disturbance basal area within one year, as opposed to 14?C24?% in trees. All Myrtaceae ??gullivers?? resprouted, but up to two-thirds of Myrsine individuals did not survive disturbance. Tree species tended to produce either many slender or few stout shoots, while shrub species were intermediate between these extremes. Forest trees regained 22?C46?% of pre-disturbance height, independent of allocation mode, and grassland shrubs up to 73?%. This suggests that grassland fires allow grassland shrubs but not forest trees to persist and to grow to reproductive size. Differing sprout allocation modes may reflect allometric constraints rather than strategies to outgrow the fire-prone grass matrix.     

Climatic sensitivity of species’ vegetative and reproductive phenology in a Hawaiian montane wet forest

Understanding how tropical tree phenology (i.e., the timing and amount of seed and leaf production) responds to climate is vital for predicting how climate change may alter ecological functioning of tropical forests. We examined the effects of temperature, rainfall, and photosynthetically active radiation (PAR) on seed phenology of four dominant species and community-level leaf phenology in a montane wet forest on the island of Hawaiʻi using monthly data collected over ~ 6 years. We expected that species phenologies would be better explained by variation in temperature and PAR than rainfall because rainfall at this site is not limiting. The best-fit model for all four species included temperature, rainfall, and PAR. For three species, including two foundational species of Hawaiian forests (Acacia koa and Metrosideros polymorpha), seed production declined with increasing maximum temperatures and increased with rainfall. Relationships with PAR were the most variable across all four species. Community-level leaf litterfall decreased with minimum temperatures, increased with rainfall, and showed a peak at PAR of ~ 400 μmol/m²s⁻¹. There was considerable variation in monthly seed and leaf production not explained by climatic factors, and there was some evidence for a mediating effect of daylength. Thus, the impact of future climate change on this forest will depend on how climate change interacts with other factors such as daylength, biotic, and/or evolutionary constraints. Our results nonetheless provide insight into how climate change may affect different species in unique ways with potential consequences for shifts in species distributions and community composition.     

Colilargo’s occupancy and the role of native and exotic plants in hantavirus expansion and transmission risk

Mammal Research - In this work, we examined the relationship of Oligoryzomys longicaudatus’ (the Andes virus [ANDV] host, commonly known as the colilargo) occupancy and the cover of dominant...     

Dynamics and potential impact of ‘generalist’ phytoseiids in agroecosystems and possibilities for establishment of exotic species

Generalists, i.e. those species which consume a wide variety of foods, including some of plant origin such as pollen, are the dominant members of the phytoseiid mite fauna in some perennial crops. Biological attributes commonly evident in generalist in contrast to specialist phytoseiids include a lower reproductive potential on mite prey, close association with certain plant species, population increases in the absence of mite prey, and intraplant distribution unrelated to that of spider mites. Some studies are reviewed that suggest the ability of certain generalist phytoseiids to maintain tetranychid populations at low densities. Possible biological factors influencing the establishment of exotic generalist phytoseiids are considered. Some of the attributes usually considered important in effective phytoseiid predators may be of minor importance in more stable situations at low population densities.     

Plant species loss from European semi‐natural grasslands following nutrient enrichment – is it nitrogen or is it phosphorus?

Aim Although many studies support the prevailing paradigm of nitrogen (N)‐driven biodiversity loss, some have argued that phosphorus (P) may be the main culprit. This questions the generality of the global threat through N enrichment. The major objective here was to quantify the relative importance of soil N and P in explaining patterns of plant species richness, under different levels of N and P limitation. Location North‐western Europe. Methods We collected soil, productivity and plant species data from 132 semi‐natural grasslands located along a gradient of nutrient availability and atmospheric N deposition. We used linear mixed models to investigate the relation between soil nutrients, acidity, limitation and productivity on one side, and indices for plant species richness on the other. Results Mixed models explained between 38 and 50% of the total variation in species numbers, forbs and endangered species. Soil P was significantly negatively related to total species number, forbs and endangered species. Soil N was only significantly negatively related to number of forbs and endangered species. Compared with soil P, the explained variation attributed to soil N was between five‐ and twenty‐fold lower. P‐limited grasslands exhibited higher species richness, numbers of forbs and endangered species. Species richness and number of forbs decreased with lower soil acidity. N deposition was negatively related to the number of forbs and endangered species, as well as to soil acidity. Productivity was weakly positively related to soil P and negatively to species and forb numbers. We found no interaction factors between the explanatory variables. Main conclusions P enrichment can present a greater threat to biodiversity than N enrichment in at least some terrestrial ecosystems. However, as N‐ and P‐driven species loss appeared independent, our results suggest that simultaneously reducing N and P inputs is a prerequisite for maintaining maximum plant diversity.     

Patterns of native and exotic species richness in the urban flora of Brussels: rejecting the ‘rich get richer’ model

In this study we analyzed patterns of native and exotic species richness in the urban flora of Brussels (Belgium) using a coarse-scale systematic sampling grid of 1 km². The observed correlation between native and exotic richness within the grid cells sampled was then compared to the results of an adequate null model assuming no species interactions. In addition, ordinary least-squares and quantile regressions were used to analyze the relationship between the ratio of exotics to natives and the proportion of densely built up areas in each cell. Though the results obtained conform to the Eltonian expectation that exotic species preferably invade areas of low native species diversity, traditional niche-filling mechanisms seems inadequate to explain the observed pattern. Rather, aliens simply tend to have different environmental requirements than natives.     

Docking of the alkaloid geissospermine into acetylcholinesterase: a natural scaffold targeting the treatment of Alzheimer’s disease

Pharmacological studies from our group [Lima et al. Pharmacol Biochem Behav 92:508, (2009)] revealed that geissospermine (GSP), the major alkaloid of the bark extract of Brazilian Geissospermum vellosii, inhibits acetylcholinesterases (AChEs) in the brains of rats and electric eels (Electrophorus electricus). However, the binding mode (i.e., conformation and orientation) of this indole-indoline alkaloid into the AChE active site is unknown. Therefore, in order to propose a plausible binding mode between GSP and AChE, which might explain the observed experimental inhibitory activity, we performed comparative automatic molecular docking simulations using the AutoDock and Molegro Virtual Docker (MVD) programs. A sample of ten crystal structures of the Pacific electric ray (Torpedo californica) TcAChE, in complex with ten diverse active site ligands, was selected as a robust re-docking validation test, and also for GSP docking. The MVD results indicate a preferential binding mode between GSP and AChE, in which GSP functional groups may perform specific interactions with residues in the enzyme active site, according to the ligand–protein contacts detected by the LPC/CSU server. Four hydrogen bonds were detected between GSP and Tyr121, Ser122, Ser200, and His440, in which the last two residues belong to the catalytic triad (Ser200···His440···Glu327). Hydrophobic and π–π stacking interactions were also detected between GSP and Phe330 and Trp84, respectively; these are involved in substrate stabilization at the active site. This study provides the basis to propose structural changes to the GSP structure, such as molecular simplification and isosteric replacement, in order to aid the design of new potential AChE inhibitors that are relevant to the treatment of Alzheimer’s disease.     

Pollination and floral ecology of Arundina graminifolia (Orchidaceae) at the northern border of the species’ natural distribution

Arundina graminifolia is an early successional plant on Iriomote Island, the Ryukyus, Japan, where it is endangered. Populations flower for more than half a year, and many inflorescences bloom for one to several months. The nectarless gullet flowers, which open for up to six days, are self-compatible but cannot self-pollinate spontaneously; thus they rely on pollinating agents for capsule production. Field observations at two habitats identified at least six species of bees and wasps, primarily mate-seeking males of Megachile yaeyamaensis and Thyreus takaonis, as legitimate pollinators. Thus, this orchid is a pollinator generalist, probably owing to its long blooming period and simple flower morphology. Carpenter bees, which were previously reported to pollinate this orchid, frequently visited flowers but were too large to crawl into the labellum chamber and never pollinated the flowers. Extrafloral nectaries on inflorescences attracted approximately 40 insect taxa but were not involved with pollination. Fruit-set ratios at the population level varied spatiotemporally but were generally low (5.2–12.4 %), presumably owing to infrequent flower visits by mate-seeking pollinators and the lack of food rewards to pollinators.     

Effects of clonal integration in the expansion of two alien <Emphasis Type="Italic">Carpobrotus</Emphasis> species into a coastal dune system – a field experiment

What makes a plant a successful invader is one of the most interesting questions in modern ecology. Comparative studies including congeners differing in invasiveness are a straightforward approach to detect potential traits explaining invasions. In this experiment we studied the importance of clonal integration and the capacity to buffer fragmentation in the expansion of two stoloniferous invaders, Carpobrotus edulis, considered more invasive, and Carpobrotus acinaciformis, considered less invasive. In particular we aim to determine whether differences in these clonal traits may explain differences in invasiveness between both species. We report evidence that clonal integration favour the expansion of the two exotic clonal species into a sand dune system. Benefit derived from clonal integration by itself does not explain differences in invasiveness between theses two exotic species. However, our result indicates that the greater invasiveness of C. edulis could be explained by a higher capacity to buffer the negative effect of fragmentation in comparison with C. acinaciformis. To elucidate the real contribution of clonal traits in plant invasions, new comparative studies should be conducted including more clonal species.