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opencc-zeroMar 2021View details →

More widespread alien tree species do not have larger impacts on regeneration of native tree species in a tropical forest reserve

There is insufficient information regarding the factors affecting the environmental impacts of alien species. In particular, little is known about whether there is any relationship between the invasiveness (establishment and spread) of an introduced species and its per-capita impact. We experimentally assessed the relationship between the extent of spread of up to 29 alien plant species and their impact on recruitment of native tree species in Amani Botanical Garden, Tanzania. We also studied the effects of allelochemicals of selected alien on native plant species to assess potential mechanisms of impact. We found no relationship between the extent of spread of an alien tree species and their impact on seed germination, seedling survival and seedling communities of native trees in their understory, and no indication that allelochemicals consistently explain their effects on recruitment of the studied species. These results suggest that extent of spread cannot be used as a proxy for impact. Hence, managers should continue assessing both the spread and the impact of alien species when prioritising alien species for management.

opencc-zeroMay 2020View details →

Data from: Fire and grazing controlling a tropical tree line: Effects of long‐term grazing exclusion in Bale Mountains, Ethiopia

Aims: Tropical tree lines are often associated with abrupt shifts in vegetation, soils and disturbance regimes, but the underlying mechanisms are poorly understood. We analysed the role of grazing, fuels and fire in maintaining a sharp tree line with flammable heathland above non-flammable forest. Location: Bale Mountains, Ethiopia. Methods: Grazing exclosures, repeated vegetation sampling, soil analyses and burning and sowing experiments along an altitudinal gradient with Hagenia abyssinica forest, Erica trimera forest and Erica heathland; all heavily grazed, the latter burnt on short rotation. Results: Contrary to expectation, livestock exclusion did not increase forest fuel flammability, but instead resulted in a dense carpet of non-flammable herbs. In the heathland, livestock exclusion led to somewhat faster post-fire fuel recovery, but no major vegetation change. Seeding of tree species resulted in some seedling establishment, but notably Hagenia grew poorly in the heathland, even when protected from livestock. A bioassay, as well as observations of outpost trees on atypical soil above the treeline, suggest that this poor growth is caused by the acidic soils, rather than harsh climate. Despite frequent fires, heathland soils had lower pH and higher organic matter content than forest soils. Below the tree line, tree seedling establishment was successful only in forest gaps, and if livestock was excluded. In both forest and heathland rapid vegetative regeneration in the ground flora after disturbance restricted major species shifts. Conclusions: These results suggest that the contrasting fire potential between heathland and forest, and thus the sharp tree line would be maintained, or possibly even accentuated, in the absence of livestock grazing, and that Hagenia colonisation upwards into the heathland is restricted not only by fire and grazing, but also the acidic soils, a legacy of centuries of Erica dominance.

opencc-zeroDec 2018View details →

Data from: Colonial history impacts urban tree species distribution in a tropical city

Urban forests associated with green infrastructure for sustainable outcomes are particularly critical in the Global South, where some of the world's fastest-growing cities are located. However, compared to temperate cities, the drivers of urban tree species distribution in tropical cities remain understudied. In this study, we quantify the spatial distribution and abundance of urban forests in the tropical city of Georgetown, Guyana. British colonialism has shaped this city, including forced movement of peoples under slavery from Africa and indentured servants from the Indian Subcontinent. We studied how this multicultural context has influenced tree species distributions in the capital city of the only Anglophone country in South America. We quantified the abundance of tree species using a stratified sampling design to distribute transects across fifteen neighborhoods that vary in distance to the colonial center of the city and ethnic composition. We recorded a total of 57 unique species, the majority of which (73%) were cultivated for their edible fruits. We identify tree species that likely represent Guyana's unique multicultural heritage by comparing our species list to flora in nine cities in neighboring countries (Venezuela and Brazil) with different colonial histories. This international comparison identified a set of tree species that occurred only in Guyana. Relationships between ethnic composition and colonial history and tree species distribution were weak at the neighborhood scale, where proportion of East Indian residents had little explanatory power and distance to colonial center was correlated with abundance of only some species groups. This apparent discrepancy between neighborhood and national scales may relate to the establishment of Guyanese food as a unifying national identifier across ethnicities. The prominence of edible fruit trees in our study suggests a set of species that could be incorporated into urban planning to strengthen biocultural linkages, foster cultural integration, and promote food security.

opencc-zeroDec 2018View details →

Data from: Differences in carbon stocks along an elevational gradient in tropical mountain forests of Colombia

Tropical mountain forests provide an exceptional opportunity to evaluate the patterns of variation of carbon stocks along elevational gradients that correspond to well-defined temperature gradients. We predicted that carbon stored in live aboveground biomass, aboveground necromass, and soil components of forests on the eastern flank of the Colombian Andes would change with elevation along this gradient extending from 750 to 2800 m above sea level. The rationale was that the corresponding change in temperature (14°C to 26°C) would influence tree growth and decomposition of organic matter. To address this hypothesis, we examined the carbon stored in these three components using data from 20 0.25-ha plots located along this elevational gradient. The mean total carbon stock found in the study region was 241.3±37.5 Mg C/ha. Aboveground carbon stocks decreased with elevation (p =0.001), as did necromass carbon stocks (p =0.016). Although soil organic carbon stocks did not differ significantly along the gradient (p =0.153), they contributed proportionately more at higher than at lower elevations, counterbalancing the opposite trends in aboveground carbon and necromass carbon stocks. As such, total carbon stocks did not vary significantly along the elevational gradient (p =0.576).

opencc-by-4.0May 2020View details →

Data for 'Robust Enhancement of Tropical Convective Activity by the 2019 Antarctic Sudden Stratospheric Warming'

These data were used for making plots in the manuscript entitled 'Robust Enhancement of Tropical Convective Activity by the 2019 Antarctic Sudden Stratospheric Warming'. DOI: 10.1029/2020GL088743. Data format is NetCDF.

opencc-zeroSep 2020View details →

Data from: Soil microbial biomass increases along elevational gradients in the tropics and sub-tropics but not elsewhere

Abstract Aim: Our aim is to use elevational gradients to quantify the relationship between temperature and ecosystem functioning. Ecosystem functions such as decomposition, nutrient cycling and carbon storage are linked with the amount of microbial biomass in the soil. Previous studies have shown variable relationships between elevation and soil microbial biomass (SMB). Understanding the biological mechanisms linking SMB with elevational gradients will shed light on the environmental impacts of global warming. Location: Global. Time period: 2002-2018. Major taxa studied: Soil microbes. Method: We performed a global meta-analysis of the relationships between SMB and elevation. Data were collected from 59 studies of 73 elevational transects from around the world. Results: We found no consistent global relationship between SMB and elevation. SMB increased significantly with elevation in the tropics and sub-tropics, but not in other climate zones. However, we found consistent positive relationships between SMB, soil organic carbon and total nitrogen concentrations. Main conclusions: Our results suggest that global warming will impact tropical and sub-tropical ecosystems more severely than colder regions. Tropical ecosystems, already at risk from species extinctions, will likely experience declines in SMB as the climate warms, resulting in losses of fundamental ecosystem functions such as nutrient cycling and carbon storage.

Allopatric instead of parapatric divergence in an ectomycorrhizal fungus (Laccaria trichodermophora) in tropical sky-islands

In tropical sky-islands, cold-affinity populations tend to become isolated at highlands during the interglacial periods, and to expand into the lowlands where they become more connected during the glacial periods. Although this has been widely studied in trees, it is poorly understood how fungal symbionts can differentiate among mountains (allopatrically), or within a single mountain (parapatrically) due to climate fluctuations. Here, we conducted population genomic analyses on the ectomycorrhizal fungus Laccaria trichodermophora in three tropical sky-islands using Genotyping by Sequencing (GBS) at low DNA concentrations. There were no significant differences between altitudes within a single mountain, but we observed significant genetic differentiation among populations from different mountains, supporting the allopatric differentiation hypothesis. Our results indicate that L. trichodermophora populations are under a sky-island population dynamics that started during the Pleistocene climate fluctuations.

opencc-zeroDec 2019View details →

Data from Beyond MAP: A guide to dimensions of rainfall variability for tropical ecology

Tropical ecologists have long recognized rainfall as the key climate filter shaping tropical ecosystem structure and function across space and time. Still, tropical ecologists have historically had a limited toolkit for characterizing rainfall, largely relying on simple metrics like mean annual precipitation (MAP) and dry season length to characterize rainfall regimes that vary along many more dimensions. Here, we review methods for quantifying dimensions of rainfall variability on multiple time scales, with a focus on ecological applications of these methods. We also discuss key considerations for tropical ecologists looking to use rainfall metrics that better align with hypothesized biological or ecological mechanisms or that more effectively describe rainfall variability in the systems we study, and provide a toolkit (R scripts and gridded datasets) to do so. We argue that incorporating more sophisticated approaches to quantify rainfall variability into study design and statistical analyses will enhance our understanding of past, ongoing, and future changes in tropical ecosystems.

opennotspecifiedMay 2020View details →

FIGURE 1. A in Relict Humid Tropical Forest In Mexico Promotes Differentiation In Barred Woodcreepers (Aves: Furnariidae)

FIGURE 1. A) Phylogenetic reconstruction (in BEAST) of the relationships among Dendrocolaptes haplotypes based on sequences of the mtDNA concatenated ND2 and CytB. Clades with high a posteriori support (>0.9, BI) are depicted at each node. A divergence time scale in years is included. B) Allele networks for three nDNA loci.

opennotspecifiedMay 2020View details →

FIGURE 3. A in Relict Humid Tropical Forest In Mexico Promotes Differentiation In Barred Woodcreepers (Aves: Furnariidae)

FIGURE 3. A) Map of the occurrence records of D. s. sheffleri and the other taxa of D. sanctithomae. The inset details the boundary between both taxa and depicts the random points generated for the Range-breaking (Ribbon) test. B) Geographic projection of the environmental niche model developed with primary occurrence data of D. s. sheffleri. C) Geographic projection of the environmental niche model developed with primary occurrence data of the remaining populations of D. sanctithomae.

opennotspecifiedMay 2020View details →

FIGURE 2 in Relict Humid Tropical Forest In Mexico Promotes Differentiation In Barred Woodcreepers (Aves: Furnariidae)

FIGURE 2. Overall ventral (above), dorsal (middle), and lateral (below) plumage coloration patterns in specimens of Dendrocolaptes from Mexico (MZFC). From left to right: D. s. sheffleri (Guerrero MZFC 19494, 19495); D. s. sanctithomae (Oaxaca [Chimalapas] MZFC 11806; Veracruz [Los Tuxtlas] MZFC 7817; Campeche [Silvituc] MZFC 13702; Quintana Roo [Puerto Morelos] MZFC 13486; and Chiapas [Ocozocuautla] MZFC 11409). Photos by Leopoldo Vázquez.

Data from: Small tropical forest trees have a greater capacity to adjust carbon metabolism to long‐term drought than large canopy trees

The response of small understory trees to long‐term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long‐term drought is, however, also likely to expose understory trees to increased light availability driven by drought‐induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (J max, V cmax), leaf respiration (R leaf), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world's longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased J max, V cmax, R leaf and LMA (71%, 29%, 32%, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.

Functional diversity and redundancy of tropical forest mammals over time

Globally, tropical rain forests comprise some of the most diverse and functionally rich ecosystems but are increasingly degraded by human impacts. Protected areas have been shown to conserve species diversity, but their effectiveness at maintaining functional diversity over time is less well known, despite the fact that functional diversity likely reveals more ecological information than taxonomic diversity. By extension, the degree to which species loss decreases functional diversity within protected areas is also unknown; functional redundancy may buffer communities from loss of functional diversity from some local extinctions. Using eight years of camera trap data, we quantified annual functional dispersion of the large mammal community in the Volcán Barva region of Costa Rica and tested for changes in functional dispersion over time in response to environmental and anthropogenic predictors. We quantified functional redundancy based on modeled declines in functional dispersion with species loss. Functional dispersion did not change significantly over time and was not associated with measured environmental or anthropogenic predictors. Quantitative modeling of change in functional traits over time did not identify significant changes. We did however find qualitative trends in relative trait proportions, which could be indicative of functional change in the future. We found high functional redundancy, with average functional dispersion declining significantly only after 9 out of 21 large mammal species were lost from the community. We cautiously suggest that protected tropical rain forests can conserve functional diversity over the course of a decade even in heavily fragmented landscapes.

Three eco-physiological strategies of response to drought maintain the form and function of a tropical montane grassland

1. Ecologists seek a general scheme to classify the diversity of plant responses to environmental factors into a few strategies (e.g. competitor -C, stress-tolerant -S, ruderal-R), while plant physiologists seek a mechanistic scheme to explain such different responses (e.g. tolerance, escape, avoidance). So far, few attempts have been made to combine both perspectives into plant eco-physiological strategies. Moreover, the relative contribution of different strategies to maintain both community structure and ecosystem functioning during drought has rarely been assessed. This limits our capacity to predict how extreme events caused by climate change will affect plant communities. 2. Here, we present an integrated framework to identify plant eco-physiological strategies and to estimate their contribution to community originality (diversity of trait-combinations), dominance (species relative frequency), and ecosystem functioning (productivity and evapotranspiration). 3. We applied this framework in a tropical montane grassland and found three co-occurring eco-physiological strategies in this community (S-tolerance/avoidance, CS-escape/tolerance and CR-escape/avoidance). While CS-species contributed more to dominance and functionality, CR- and S-species contributed more to originality. Therefore, all three strategies were important to support the grassland form and function. Synthesis: Plants exhibit different strategies, as well as different contributions to community and ecosystem attributes. We developed an integrated approach to both identify strategies and estimate their relative contribution. Thereby, as droughts intensify, we can better predict which plants are more likely to be lost and how their loss will impact the communities and ecosystem where they occur. This knowledge is necessary for specifying conservation priorities and for developing more efficient conservation practices.

Impacts of rodent eradication on seed predation and plant community biomass on a tropical atoll

Invasive rodent eradications are frequently undertaken to curb island biodiversity loss. However, the breadth of rodents' ecological impact, even after eradication, is not always fully recognized. For example, the most widespread invasive rodent, the black rat (Rattus rattus), while omnivorous, eats predominantly seeds and fruit. Yet, the effects of seed predation release after eradication on plant communities and ecological functions are not well understood, posing a gap for island restoration. We examined the role of seed predation release following black rat eradication in changes to tree composition and above-ground biomass across an islet network (Palmyra Atoll) in the Central Pacific. We conducted repeated surveys of seed, juvenile, and adult tree biomass and survival in permanent vegetation plots before and after the eradication of rats. We observed a 95% reduction in seed predation for an introduced, previously cultivated tree population (Cocos nucifera). Juvenile tree biomass of all species increased 14-fold, with C. nucifera increasing the most, suggesting that eradication increased this tree's competitive advantage. Indeed, based on stage-structured demographic models, rat eradication led to a 10% increase in C. nucifera population growth rate. The effect of invasive rodent seed predation varies considerably among the plant species in a community and can shift competitive dynamics, sometimes in favor of invasive plants. These bottom-up effects should be considered in evaluating the costs and benefits of eradication. Documenting the variation in invasive rodent diet items, along with long-term surveys, can help prioritize island eradications where restoration is most likely to be successful.

opencc-by-4.0Aug 2020View details →

Cryptic species and genetic connectivity among populations of the coral Pocillopora damicornis (Scleractinia) in the tropical southwestern Pacific

Studying population genetic connectivity (i.e., identifying gene flow among populations and understanding their impacts on the genetic structure and diversity of populations) is first a matter of knowing what we work on, that is, accurately delimiting evolutionary units. Here, we focused on Pocillopora damicornis sensu stricto (or Pocillopora PSH04 sensu Gélin et al. in Mol Phylogenet Evol 109:430–446. http://dx.doi.org/10.1016/j.ympev.2017.01.018, 2017). From 458 colonies sampled within the tropical southwestern Pacific [Chesterfield Islands and New Caledonia (Grande Terre and Loyalty Islands)], Bayesian assignments and network analyses were conducted with 11-microsatellite loci to first evaluate the genetic partitioning of the colonies in distinct Secondary Species Hypotheses (SSHs), then in distinct clusters. Population genetic connectivity was then assessed for each cluster separately. Pocillopora PSH04 was partitioned into two highly differentiated SSHs (SSH04a and SSH04b), regularly found in sympatry. Furthermore, SSH04a was subdivided into two clusters (SSH04a-1 and SSH04a-2). This pattern of genetic structuring seems not related to clonality, but rather to the establishment of reproductive barriers. Nevertheless, considering each cluster separately, the populations appeared highly differentiated, suggesting relatively weak gene flow. This low connectivity among populations, coupled with the existence of cryptic species, brings new insights to the connectivity pattern of this understudied Pacific region. This dataset contains the microsatellite genotypes analysed (458 Pocillopora PSH04 colonies × 13 loci).

Structure of small tropical islands freshwater fish and crustacean communities: a niche- or dispersal-based process?

Determining the relative importance of niche- and dispersal-based processes in the structuring of animal communities is central in ecology. Freshwater fish and crustacean communities of small tropical islands can bring new insights for understanding these processes as all their species present a pelagic larval stage which gives them important dispersal capacities. Consequently, we hypothesized that dispersal-based process maybe preponderant for structuring these communities from the regional- to the local, i.e. survey site, scales. Gradient forest analyses allowed us to model the effect of 12 environmental variables on freshwater taxa abundances in two southwestern Indian Ocean islands: Mayotte (26 taxa) and Reunion (21). A total of 153 surveys in Mayotte and 266 in Reunion were used for building the models. Despite the strong heterogeneity of environmental conditions between the two islands, the main factors structuring freshwater fish and crustacean communities in both islands were the elevation and the slope of the sites. The observed structure appeared more pronounced for predatory species than for primary consumers and omnivores. As predators generally have limited locomotor capacities, it is concluded that dispersal-based process structures these communities not only at large geographical scales but also at the intra-watershed scale, by limiting the inland penetration (or dispersion) of species in relation to their locomotor capacities. However, more knowledge concerning ecological traits and taxonomic status of many species is needed to confirm this assumption.

opencc-zeroSep 2020View details →

Data from: Linking coordinated hydraulic traits to drought and recovery responses in a tropical montane cloud forest

Understanding plant hydraulic functioning and water balance during drought has become key in predicting species survival and recovery. However, the insightful studies that couple physiological and morphological attributes do not exist in many ecosystems, such as the vulnerable Tropical Montane Cloud Forests (TMCF). In this study, we evaluate drought resistance and recovery for saplings for five tree species spanning deciduous to evergreen habits from a Mexican TMCF. Methods Drought treatments withheld water until plants reached species-specific P50 or P88 values (pressures required to induce a 50 or 88 percent loss in hydraulic conductivity), at which point they were rewatered. Drought resistance were considered within the isohydric-anisohydric framework and compared to leaf gas exchange, water status, pressure-volume curves, specific leaf area, and stomatal density. Results TMCF species closed stomata well before significant losses in hydraulic conductivity (isohydric). Yet, despite the coordination of these traits, they did not predict how long it took species to reach critical hydraulic thresholds. Instead, maximum photosynthesis rates explained these times reinforcing the linkage between hydraulic and carbon dynamics. Despite varying hydraulic conductivities, stomatal responses, and times to hydraulic thresholds, all study plants except for two individuals (out of 60) recovered following rewatering. The recovery of photosynthesis and stomatal conductance was explained by the P50 values and isohydry. Conclusions This study raises new questions surrounding drought management strategies, recovery processes, and how lethal thresholds are defined. Further studies need to consider the role of water and carbon balance in allowing for both survival and recovery to drought.

opencc-zeroSep 2020View details →

Symbiotic efficiency and genetic characterization of bacteria associated with cowpea genotypes grown in semiarid tropics of Kenya

Cowpea (Vigna unguiculata (L.) Walp) is an important multipurpose legume crop grown in arid semiarid areas of sub-Saharan Africa. The crop associates with a wide diversity of high ecological value rhizobia bacteria, improving biological soil fertility and crop production. Here, we evaluated the symbiotic efficiency (SE) and genetic diversity of native rhizobia isolated from root nodules of cowpea genotypes cultivated in semiarid areas of Kenya. Rhizobia trapping and SE experiments were done in the greenhouse while genetic diversity was evaluated based on 16S rRNA gene sequencing. Ninety four bacterial nodule isolates were purified from root nodules and placed into 20 groups based on morphological characteristics. SE of the native isolates varied (p<0.0001) significantly. Remarkably, two isolates, M2 and M3 recorded higher SE of 82.49 % and 72.76 % respectively compared to the commercial strain Bradyrhizobia sp. USDA 3456 (67.68 %). The isolates closely resembled bacteria belonging to the genus Rhizobium and non-rhizobial endophytes Enterobacter, Strenotrophomonas, Pseudomonas, and Paraburkholderia. For the first time, we report the presence of an efficient native nodule isolate Paraburkholderia phenoliruptrix BR3459a in Kenya. Our results form an important step towards the development of efficient microbial inocula which are pertinent for sustainable food production in African agriecosystems.