Taxonomic distinctness and diversity of a hyperseasonal savanna in central Brazil

ABSTRACTSavannas are characterized by a sharp seasonality, in which the water shortage defines the community functioning. Hyperseasonal savannas, however, experience additionally waterlogging in the rainy season. Since waterlogging may cause local extinctions of intolerant species, we asked whether waterlogging constricts the phylogenetic structure of a hyperseasonal savanna. We studied a hyperseasonal cerrado, comparing it with a nearby seasonal cerrado, never waterlogged, in Emas National Park, central Brazil. In each vegetation form, we sampled all vascular plants by placing fifty 1‐m2quadrats in five surveys. We compared the phylogenetic structure of both vegetation forms, calculating their taxonomic distinctness, taxonomic diversity, expected taxonomic distinctness, and species, genus, and family similarities. The taxonomic distinctness of both cerrados was similar and the values of similarities were high, but taxonomic diversity and expected taxonomic distinctness were lower in the hyperseasonal cerrado than in the seasonal one. Assuming that phenotypic attraction is the major process organizing local communities, the waterlogging in hyperseasonal cerrado assembles phylogenetically unrelated species that have converged on similar habitat use. As a consequence, the habitat use of hyperseasonal cerrado species is a trait widespread in the phylogeny of seasonal cerrado. Waterlogging constrains the phylogenetic structure of the hyperseasonal cerrado, especially by reducing species diversity. In more ecological terms, we can only fully assess the phylogenetic structure of a community if we consider the species abundance.

Summary1. A variety of species richness measures have been used to assess the effects of environmental degradation on biodiversity. Such measures can be highly influenced by sample size, sampling effort, habitat type or complexity, however, and typically do not show monotonic responses to human impact. In addition to being independent of the degree of sampling effort involved in data acquisition, effective measures of biodiversity should reflect the degree of taxonomical relatedness among species within ecological assemblages and provide a basis for understanding observed diversity for a particular habitat type. Taxonomic diversity or distinctness indices emphasize the average taxonomic relatedness (i.e. degree of taxonomical closeness) between species in a community.2. Eutrophication of freshwater ecosystems, mainly due to the increased availability of nutrients, notably phosphorus, has become a major environmental problem. Two measures of taxonomic distinctness (Average Taxonomic Distinctness and Variation in Taxonomic Distinctness) were applied to surface sediment diatoms from 45 lakes across the island of Ireland to examine whether taxonomic distinctness and nutrient enrichment were significantly related at a regional scale. The lakes span a range of concentrations of epilimnic total phosphorus (TP) and were grouped into six different types, based on depth and alkalinity levels, and three different categories according to trophic state (ultra‐oligotrophic and oligotrophic; mesotrophic; and eutrophic and hyper‐eutrophic).3. The taxonomic distinctness measures revealed significant differences among lakes in the three different classes of trophic state, with nutrient‐rich lakes generally more taxonomically diverse than nutrient‐poor lakes. This implies that enrichment of oligotrophic lakes does not necessarily lead to a reduction in taxonomic diversity, at least as expressed by the indices used here. Furthermore, taxonomic distinctness was highly variable across the six different lake types regardless of nutrient level.4. Results indicate that habitat availability and physical structure within the study lakes also exert a strong influence on the pattern of taxonomic diversity. Overall the results highlight problems with the use of taxonomic diversity measures for detecting impacts of freshwater eutrophication based on diatom assemblages.

Background and aims: Due to the high spatial and temporal variation in soil CO₂ efflux, terrestrial carbon budgets rely on a detailed understanding of the drivers of soil respiration from a diverse range of ecosystems and climate zones. In this study we aim to evaluate the independent influence of vegetation structure and climate on soil CO₂ efflux within cerrado ecosystems. Methods: We examine the seasonal and diel variation of soil CO₂ efflux, including its autotrophic and heterotrophic components, within two adjacent and structurally contrasting woody savannas in central Brazil. Principle results: We found no significant difference in the annual soil CO₂ efflux between the two stands (p=0.53) despite a clear disparity in both LAI (p<0.01) and leaf litterfall (p<0.01). The mean annual loss of carbon from the soil was 17.32(± 1.48) Mg Cha⁻¹ of which approximately 63% was accounted for by autotrophic respiration. The relative contribution of autotrophic respiration varied seasonally between 55% in the wet season to 79% of the total soil CO₂ efflux in the dry season. Furthermore, seasonal fluctuations of all the soil respiration components were strongly correlated with soil moisture (R²=0.79-0.90, p<0.01). Conclusions: Across these two structurally distinct cerrado stands, seasonal variations in rainfall, was the main driver of soil CO₂ efflux and its components. Consequently, soil respiration within these ecosystems is likely to be highly sensitive to any changes in seasonal precipitation patterns.

Many crustacean species are obligate associates of pocilloporid corals, where they feed, reproduce, and find shelter. However, these coral-associated crustaceans have been poorly studied in the eastern tropical Pacific. Determining the crustacean richness and taxonomic distinctness could help in comparing different coral reefs and the potential effects of degradation. This study evaluated the spatio–temporal variation of the taxonomic diversity and distinctness of coral-associated crustaceans in four ecosystems of the Central Mexican Pacific (CMP) with different conditions and coral cover. In all ecosystems, 48 quadrants were sampled during the summer and winter for two years. A total of 12,647 individuals belonging to 88 species, 43 genera, and 21 families were recorded. The sampling effort yielded 79.6% of the expected species richness in the study area. Species rarity had 19% singletons, 4% doubletons, 22% unique, and 9% duplicate species; two species represented new records for the Mexican Pacific, and six were new to the CMP. This study recorded most of the symbiotic crustacean species in pocilloporid corals previously reported in the CMP. The taxonomic diversity and distinctness differed significantly between coral ecosystems and seasons, which was also visualized by nMDS ordination, showing an evident spatio–temporal variation in the taxonomic beta diversity.

The Cerrado biome comprises a mosaic of different vegetation types such as grasslands, savannas and forests. We studied soil properties and the herbaceous-shrub layer vegetation in moist grassland, shrub grassland and savanna. We assume that the moist grassland will present a distinct species composition from the other vegetation types, as waterlogging leads to changes in soil features that act as a filter of species that are adapted to this condition. The results showed that the soil in the moist grassland was distinct from the ones in savanna and shrub grassland. We found that the soil organic matter and the proportion of clay particles determined the variation in composition/cover and richness in the herbaceous-shrub layer in the three vegetation types. Higher organic matter content and smaller proportion of clay particles explained the larger distinction in richness and cover in moist grassland (lowest one) compared to shrub grassland and savanna sites. A total of 228 species in 47 families were sampled in the three vegetation types, and only five species were common to all three. The results revealed that, on a local scale, adjacent vegetation types of Cerrado with differences in soil organic matter and clay vary greatly in terms of growth forms, species composition and cover in the herbaceous-shrub layer. Understanding how herbaceous-shrub species richness and cover is related to soil nutrients, and texture heterogeneity in the mosaic of the vegetation types of the Cerrado may be useful in maintaining plant species structure and diversity.

Biotic interactions and limitations to explain their effects on a neotropical savanna plant community

Summary Tower‐based eddy covariance measurements were used to quantify the effect of fire on subsequent carbon dioxide fluxes and water and surface energy balance characteristics for campo sujo savanna located near Brasília in Central Brazil (15°56′ S, 47°51′ W). Campo sujo is a xeromorphic, open shrub savanna with very scattered but definitely visible shrubs and tree‐like shrub elements. We studied two areas, one exposed to a prescribed fire late in the dry season, and a second that had not been burned for the previous 4 years. The fire on 22 September 1998 consumed an estimated 26 mol C m−2. Immediately after the fire, evapotranspiration rates decreased and the savanna became a stronger net source of CO2 to the atmosphere. This was attributed to the removal of the still slightly physiologically active grass layer and higher soil CO2 efflux rates as a consequence of elevated surface soil temperatures post‐burning. On the commencement of the first rains in early October 1998, this situation was reversed, with the burned area rapidly becoming a stronger sink for CO2 and with higher evapotranspiration rates than a nearby unburned (control) area. This difference persisted throughout the wet season (until at least June 1999) and was attributable to greater physiological activity of the regrowing vegetation in the burned area. Early in the growing season, higher soil evaporation rates may also have contributed to faster water use by the previously burned area. Overall, we estimate an annual gross primary productivity for the burned area of 135 mol C m−2 year−1, with that for the unburned area being 106 mol C m−2 year−1. Estimated ecosystem respiration rates were more similar on an annual basis (96 and 82 mol C m−2 year−1 for the burned and unburned areas, respectively), giving rise to a substantially higher net ecosystem productivity for the previously burned area (38 vs 24 mol C m−2 year−1). Stimulation of photosynthetic activity in the rapid post‐fire growth phase means that the negative effects of fire on the ecosystem carbon balance were more or less neutralized after only 12 months.

The seed-bank dynamics of cerrado, a savanna-like vegetation type in central Brazil, was monitored for a year after a fire event in the mid-dry season. Fifty paired soil and litter samples were collected 1 day before and 1 day after the fire to record the immediate effects on the seed bank, and thereafter at monthly intervals to investigate the post-fire seed bank dynamics. The samples were hand-sorted and the intact seeds were classified as monocot or dicot and counted. All seeds underwent germination trials in a germination chamber for 1 month. Seeds that did not germinate were checked for the presence and viability of the embryo. The sorted soil samples were placed in a greenhouse for 6 months, and the count of emerging seedlings was added to the number of germinated and dormant seeds from the germination trials to estimate the total number of viable seeds per sample. The fire did not affect the total seed-bank density: 63 ± 8 seeds m−2 before the fire, and 83 ± 20 seeds m−2 (mean ± se) immediately after it. Although monocots represented 65 % of the pre-fire seed bank, 1 year after the fire, the monocot seed density did not reach the pre-fire value, whereas the density of dicot seeds increased threefold. After the fire, the viable seed density and species richness, decreased with the onset of the rainy season coinciding with germination in the field. Therefore, post-fire recruitment increases genetic variability and contributes to the persistence of plant populations in cerrado communities.

In Central Brazil, plateaus, the most common geomorphologic form, have been undergoing intense conversion from native vegetation to pasture and agriculture in recent decades. We used carbon stable isotope ratios (δ13C) and nitrogen stable isotope ratios (δ15N) to assess possible changes in soil organic matter dynamics under such land use modifications. This study aimed to evaluate the differences in soil δ13C and δ15N and C and N stocks between native vegetation and agricultural or pasture areas in different locations of a plateau in the savannas of Central Brazil. We sampled soil up to 100 cm depth in pasture areas in the summit of the plateau and no-tillage and conventional tillage on the border of a plateau, as well as soils under native vegetation in both landscape locations. Both soil δ13C and δ15N, and C and N stocks showed no differences between land uses. The different relationships between δ15N and C/N ratio at different locations indicated distinct behavior of the soil organic matter between the summit and border of the plateau. Therefore, in addition to land-use, landscape location contributes to both δ13C and δ15N, and C and N stocks in the soil of the plateau.

The current study investigates whether a simple measure of taxonomic diversity (Taxonomic Distinctiveness (TD)) can be used as a proxy for different measures of phylogenetic diversity (Phylogenetic Distinctiveness (PD)) in determining species of regional conservation priority, and uses extant South African Chiroptera and Carnivora as a case study. Published phylogenies for the two mammalian Orders allowed the quantification of a node-based measure that was considered to represent phylogenetic diversity (PD NODE ), as well as a branch length-based measure that was considered to represent the amount of evolutionary change over time (PD BRANCH ). Both the PD NODE and PD BRANCH , together with TD were included in our regional conservation priority assessment. Although no statistically significant differences were detected between the PD NODE , PD BRANCH and the TD for both the Chiroptera and Carnivora, these measures were also shown to be correlated with each other. More importantly, inclusion of either the PD NODE , PD BRANCH , or TD in our analysis did not significantly alter the species that were identified as being of regional conservation priority. Both regional priority scores for the South African Chiroptera and Carnivora and their respective rankings were broadly consistent across the three potential indicators of conservation status utilised. These results suggest that the inclusion of either the PD NODE and/or PD BRANCH in conservation prioritisation exercises may not add value to that currently provided by the TD. Consequently, this implies that in the absence of relevant PD data, the utilisation of the TD in regional conservation priority settings may provide the appropriate information on evolutionary diversity.

Natural fire does not affect the structure and beta diversity of plant-pollinator networks, but diminishes floral-visitor specialization in Cerrado

Bothrops moojeni is a member of the atrox group that occurs in central and southeastern Brazil and adjacent Paraguay and Argentina. We describe habitat use, diel and seasonal activity, biometry, feeding habits, and reproduction of B. moojeni, based on field studies and analysis of 207 preserved specimens. Bothrops moojeni predominantly uses riparian vegetation in the Cerrado (central Brazilian savannas), such as gallery forests and adjacent wet grasslands, although they occasionally use drier interfluvial areas. Sexes are dimorphic in snout–vent length, relative tail length, relative mass, and relative head length. Main prey types were mammals, frogs, and lizards. There is an ontogenetic dietary shift from ectotherms to endotherms. Prey-predator mass ratio ranged from 0.008–1.079, and prey mass was positively correlated with predator mass. Although prey absolute mass was positively correlated with snake mass, large snakes did not eliminate small prey from their diets. There was an ontogenetic decrease in prey relative mass. Females consumed more endothermic prey than males, and this difference probably reflects size differences. The reproductive cycle is lengthy and seasonal, with recruitment restricted to the rainy season. Fecundity is positively correlated with female body size. Life-history characters of B. moojeni are similar to those of other members of the atrox group, even though B. moojeni occurs in the Cerrado, a drier and more seasonal biome.

The Neotropical Savanna in Central Brazil (Cerrado) is characterized by periodic fires and soils with extremely low nutrient levels. We used long-term field experiments to investigate how frequent fires and long-term changes in soil nutrient availability would affect leaf structure and leaf nutrient status of Cerrado trees. We measured specific leaf area (SLA, the ratio of leaf area per leaf dry mass) and leaf nutrient concentrations in 15 tree species of distinct leaf phenologies subjected to eight treatments, including control. Treatments comprised various conditions of nutrient availability (fertilization, addition and removal of litter) and fire regime (controlled biennial fires). The control consisted of undisturbed natural vegetation. Leaf traits generally varied among species. Species responded to fertilization, exhibiting higher Ca and Mg leaf concentrations, while SLA, and leaf N, P and K concentrations did not differ across treatments. We found significant differences reflecting contrasting ecological strategies among phenological groups: deciduous species had higher nutrient leaf concentrations and SLA, while evergreen species showed the lowest values and briefly deciduous species showed intermediate values. We found low leaf-level responses to nutrient manipulations, probably reflecting the conservative resource-use strategy typical of nutrient-poor environments.

Night and day service: Distyly and mixed pollination system in Faramea cyanea (Rubiaceae)

We characterized 22 polymorphic microsatellite markers for the Brazilian treefrog Bokermannohyla ibitiguara and tested their cross-amplification in B. alvarengai, B. circumdata and B. hylax. Our focal species occurs in protected and disturbed Brazilian Cerrado landscapes, a highly threatened savanna in central Brazil. Fourteen markers successfully cross-amplified for at least one congener. These microsatellites will be useful for studies of mating systems, relatedness and landscape genetics of Cerrado populations under various deforestation levels. Moreover, variable markers for B. circumdata and B. hylax will also be useful for landscape genetic studies of taxa typical of the threatened Atlantic Forest domain.