Dry Forest Sites Research Articles

Different model assumptions about plant hydraulics and photosynthetic temperature acclimation yield diverging implications for tropical forest gross primary production under warming

AbstractTropical forest photosynthesis can decline at high temperatures due to (1) biochemical responses to increasing temperature and (2) stomatal responses to increasing vapor pressure deficit (VPD), which is associated with increasing temperature. It is challenging to disentangle the influence of these two mechanisms on photosynthesis in observations, because temperature and VPD are tightly correlated in tropical forests. Nonetheless, quantifying the relative strength of these two mechanisms is essential for understanding how tropical gross primary production (GPP) will respond to climate change, because increasing atmospheric CO2 concentration may partially offset VPD‐driven stomatal responses, but is not expected to mitigate the effects of temperature‐driven biochemical responses. We used two terrestrial biosphere models to quantify how physiological process assumptions (photosynthetic temperature acclimation and plant hydraulic stress) and functional traits (e.g., maximum xylem conductivity) influence the relative strength of modeled temperature versus VPD effects on light‐saturated GPP at an Amazonian forest site, a seasonally dry tropical forest site, and an experimental tropical forest mesocosm. By simulating idealized climate change scenarios, we quantified the divergence in GPP predictions under model configurations with stronger VPD effects compared with stronger direct temperature effects. Assumptions consistent with stronger direct temperature effects resulted in larger GPP declines under warming, while assumptions consistent with stronger VPD effects resulted in more resilient GPP under warming. Our findings underscore the importance of quantifying the role of direct temperature and indirect VPD effects for projecting the resilience of tropical forests in the future, and demonstrate that the relative strength of temperature versus VPD effects in models is highly sensitive to plant functional parameters and structural assumptions about photosynthetic temperature acclimation and plant hydraulics.

Environmental controls on seedling establishment in a boreal forest: implications for Scots pine regeneration in continuous cover forestry

In nutrient poor and dry forest sites common to northern Scandinavia, Scots pine (Pinus sylvestris L.) is the most common species both in managed and natural forests. However, Scots pine is sensitive to competition during establishment. Harvesting of all trees within a given area, i.e., clear-cutting, liberates regenerating seedlings from competition with mature trees. However, recently, clear-cut-free or continuous cover forestry has been the subject of substantial debate. When choosing a management method, it is important to recognize how competitive interactions direct the success of Scots pine regeneration. We studied Scots pine regeneration at three environments: beneath the canopy of mature trees, at the canopy edge in full sunlight, and distant from the canopy with no influence of mature trees. We imposed three treatments in each of these environments: root isolation (i.e., trenching), nitrogen (N) fertilization, and control plots. Root isolation enhanced seedling performance under the canopy of mature trees. Nitrogen fertilization enhanced seedling performance to a greater extent in the clear-cut than at the forest edge. However, N fertilization had no effect under the canopy. In the N-fertilized plots, we measured higher N content in the soil under the canopy than in the open environments, indicating that not all excess N was obtained by the mature trees. N-uptake might have been limited by competition for water in the N-fertilized plots. Our results suggest that belowground competition limits the success of regeneration of Scots pine. However, N fertilization presents a tool to compensate for underground competition along canopy edges.

Sharp decline in future productivity of tropical reforestation above 29°C mean annual temperature.

Tropical reforestation is among the most powerful tools for carbon sequestration. Yet, climate change impacts on productivity are often not accounted for when estimating its mitigation potential. Using the process-based forest growth model 3-PGmix, we analyzed future productivity of tropical reforestation in Central America. Around 29°C mean annual temperature, productivity sharply and consistently declined (-11% per 1°C of warming) across all tropical lowland climate zones and five tree species spanning a wide range of ecological characteristics. Under a high-emission scenario (SSP3-7.0), productivity of dry tropical reforestation nearly halved and tropical moist and rain forest sites showed moderate losses around 10% by the end of the century. Under SSP2-4.5, tropical moist and rain forest sites were resilient and tropical dry forest sites showed moderate losses (-17%). Increased vapor pressure deficit, caused by increasing temperatures, was the main driver of growth decline. Thus, to continue following high-emission pathways could reduce the effectiveness of reforestation as climate action tool.

Canopy structure and understorey light availability in Nothofagus and podocarp-broadleaf stands in a New Zealand forest

ABSTRACT The ability of some ectomycorrhizal fungi to access organic sources of nitrogen is known to influence decomposition, nitrogen mineralisation and soil carbon storage. The consequences for aboveground ecosystem structure and processes are less well-documented. We used the LAI-2200C Plant Canopy Analyzer to compare leaf area index and understorey light availability of ectomycorrhizal Nothofagus stands and arbuscular mycorrhizal podocarp-broadleaf stands growing on similar soils at a dry forest site in the Wairarapa district of New Zealand’s North Island. N. solandri was the sole overstorey tree in the three Nothofagus stands, and the ericaceous shrub Leucopogon fasciculatus was prominent in the understorey. The three podocarp-broadleaf stands were more diverse and more varied, the major contributors to basal area being Elaeocarpus dentatus, Hedycarya arborea, Cyathea dealbata, Carpodetus serratus and Dacrydium cupressinum. Leaf area index of Nothofagus stands averaged one unit lower (4.04) than that of neighbouring podocarp-broadleaf stands (5.11). Average light availability under Nothofagus stands (3.6–4.9%) was twice that beneath podocarp-broadleaf stands (1.6–2.1%). The lower leaf area index, greater light transmittance, and monodominance of Nothofagus stands probably reflects suppression of arbuscular mycorrhizal species by ectomycorrhizal short-circuiting of the nitrogen cycle. This study expands the evidence of positive feedback mechanisms stabilising ectomycorrhizal dominance in some forests.

Avifaunas of two dry forest sites in northern Oaxaca, Mexico

Avifaunas de dos bosques secos del norte de Oaxaca, MéxicoSe realizaron inventarios avifaunísticos en el norte de Oaxaca, en dos sitios de la región de la Cañada del Valle de Tehuacán. Se observaron 142 especies de aves, encontrándose cerca de 100 especies en cada sitio. Se encontró un número sorprendente de especies (37) que representan poblaciones aisladas del interior restringidas por una u otra vertiente costera. Además, proporciones similares de especies fueron exclusivamente de una vertiente costera o la otra, creando una extraña mezcla en la avifauna de estos sitios que incluye aves del interior, de la vertiente costera del Pacífico y de la vertiente costera del Atlántico.

Increasing liana biomass and carbon stocks in tropical dry evergreen forests of southern India

Tropical forests act as a great carbon reservoir covering about 30% of the global carbon content, however, structural alteration of these forests caused by forest disturbances adversely affects the carbon cycle. One such structural change happening in these tropical forests is the increasing dominance of lianas (woody climbers). Among various tropical forest types, lianas are an integral constituent of the tropical dry evergreen forests (TDEFs) found in peninsular India. A re-inventory of lianas was carried out to observe temporal changes in basal area and carbon stock in two 1-ha permanent plots of two disturbed tropical dry evergreen forest sites (TDEF; Oorani -OR and Puthupet - PP) over a 19-year interval (2001-2020). The total basal area in OR and PP increased respectively by 2.26 m2 ha-1 and 0.93 m2 ha-1. The total biomass and the carbon stock in OR and PP increased by 82% and 51% respectively. The dominant species Strychnos lenticellata showed an increase in its basal area by three-fold in OR, whereas, in PP, a marginal increase of 4% was observed. The lower diameter class (1-6 cm) showed an increase in basal area in OR and PP by 101% and 16% respectively. The mid-diameter class (6-11 cm) was the top contributor of the total biomass/carbon in both OR and PP in the latest re-inventory (2020). The present results show that lianas, although known to negatively affect the forest biomass/carbon stock, play an important role in carbon sequestration, thus providing insights into their ecological importance which will certainly be useful in proposing strategies for the conservation of this forest type dominated by lianas.

Belowground structure and determinants of woody plant height at a tropical dry forest site in Zambia, southern Africa

AbstractRoot metrics and plant height for 256 excavated saplings and small trees of 27 species, including sown plants, were used to describe belowground structure and assess factors that influence shoot growth in a tropical dry forest (TDF) in Zambia. Models were developed to (i) estimate taproot depth from incomplete excavations and (ii) coarse lateral root biomass from proximal diameter data. The majority of the species studied are slow-growing and had a median height of <200 cm at the age of 16 years. Root development advanced sequentially from taproot elongation to thickening to coarse lateral root development. Shrubs in shallow soil had short taproots with a lower wood density. Plant age explained <10% of the variance in shoot height. Root variables explained the majority of the variance in shoot height. More research is needed to improve our knowledge about how belowground structures influence shoot growth and tree recruitment in TDFs of southern Africa.

Continuous monitoring of forest change dynamics with satellite time series

Several forest change detection algorithms are available for tracking and quantifying deforestation based on dense Landsat and Sentinel time series satellite data. Only few also capture regrowth after clearing in an accurate and continuous way across a diversity of forest types (including dry and seasonal forests) and are thus suitable to address the need for better information on secondary forest succession and for assessing forest restoration activities. We present a new change detection algorithm that makes use of the flexibility of kernel density estimations to create a forest reference phenology, taking into account all historical phenological variations of the forest rather than smoothing these out by curve fitting. The AVOCADO (Anomaly Vegetation Change Detection) algorithm allows detection of anomalies with a spatially explicit likelihood measure. We demonstrate the flexibility of the algorithm for three contrasting sites using all available Landsat time series data; ranging from tropical rainforest to dry miombo forest ecosystems, with different time series data densities, and characterized by different forest change types (e.g. selective logging, shifting cultivation). We found that the approach produced in general high overall accuracies (> 90%) across these varying conditions, but had lower accuracies in the dry forest site with a slight overestimation of disturbances and regrowth. The latter was due to the similarity of crops in the time series NDMI signal, causing false regrowth detections. In the moist forest site the low producer accuracies in the intact forest and regrowth class was due to its very small area class (most forest disappeared by the nineties). We showed that the algorithm is capable of capturing small-scale (gradual) changes (e.g. selective logging, forest edge logging) and the multiple changes associated to shifting cultivation. The performance of the algorithm has been shown at regional scale, but if larger scale studies are required a representative selection of reference forest types need to be selected carefully. The outputs of the change maps allow the estimation of the spatio-temporal trends in the proportions of intact forest, secondary forest and non-forest - information that is useful for assessing the areas and potential of secondary forests to accumulate carbon and forest restoration targets. The algorithm can be used for disturbance and regrowth monitoring in different ecozones, is user friendly, and open source.

Climate-growth relations of congeneric tree species vary across a tropical vegetation gradient in Brazil

Seasonally dry tropical forests are an important global climatic regulator, a main driver of the global carbon sink dynamics and are predicted to suffer future reductions in their productivity due to climate change. Yet, little is known about how interannual climate variability affects tree growth and how climate-growth responses vary across rainfall gradients in these forests. Here we evaluate changes in climate sensitivity of tree growth along an environmental gradient of seasonally dry tropical vegetation types (evergreen forest – savannah – dry forest) in Northeastern Brazil, using congeneric species of two common neotropical genera: Aspidosperma and Handroanthus. We built tree-ring width chronologies for each species × forest type combinations and explored how growth variability correlated with local (precipitation, temperature) and global (the El Niño Southern Oscillation - ENSO) climatic factors. We also assessed how growth sensitivity to climate and the presence of growth deviations varied along the gradient. Precipitation stimulates tree growth and was the main growth-influencing factor across vegetation types. Trees in the dry forest site showed highest growth sensitivity to interannual variation in precipitation. Temperature and ENSO phenomena correlated negatively with growth and sensitivity to both climatic factors were similar across sites. Negative growth deviations were present and found mostly in the dry-forest species. Our results reveal a dominant effect of precipitation on tree growth in seasonally dry tropical forests and suggest that along the gradient, dry forests are the most sensitivity to drought. These forests may therefore be the most vulnerable to the deleterious effects of future climatic changes. These results highlight the importance of understanding the climatic sensitivity of different tropical forests. This understanding is key to predict the carbon dynamics in tropical regions, and sensitivity differences should be considered when prioritizing conservation measures of seasonally dry topical forests.

Assessment of tree species diversity and above-ground biomass in two disturbed tropical dry evergreen forests of Coromandel coast of India

The tree diversity and carbon stock of all woody plants were investigated in two-hectare square plots (100 m x 100 m) were established in Suryanpet (SP) and Velleripet (VP) which is tropical dry evergreen forest (TDEF) sites on the Coromandel Coast of peninsular India. All trees ? 10 cm girth at breast height measured at 1.3 m from the rooting point were enumerated. A total of 35 tree species (? 10 cm gbh) belonging to 34 genera and 23 families were recorded in tropical dry evergreen forests. Tree species richness in 27 (dominant species Dimorphocalyx glabellus Thw.) and 18 (dominant species Strychnos nux-vomica L.) in SP and VP respectively. A total density of woody plants 671 and 1154 individuals in SP and VP respectively. The basal area of trees in the two study sites SP (40.70 m2 ha-1) and VP (45.46 m2 ha-1). Most abundant families are Loganiaceae, Euphorbiaceae and Rutaceae and its family index value (FIV) is 56.14, 39.12 and 21.40 respectively. The aboveground biomass (AGB) of trees totaled in site SP (405.3 Mg ha-1) and VP (721.3 Mg ha-1). The extent of tree species diversity and estimated carbon stock of the TDEF sites, which provides the baseline data on the floristic structure and diversity of this forest for better management and conservation.

Multi-year eddy covariance measurements of net ecosystem exchange in tropical dry deciduous forest of India

Tropical deciduous forests are unique in terms of their geographical distribution, strong seasonality and their contribution to global carbon dynamics, but yet their carbon sequestration potential is poorly sampled. In the current study, we report the carbon balance of 65-year-old tropical dry deciduous forest in central India using the multi-year eddy covariance measurements from November 2011 to May 2019. Over the study period, the forest site was observed to be a net sink of atmospheric CO2 with a mean annual net ecosystem productivity (NEP) of 524 (± 40; ±1 SD across different years) g C m−2 yr−1 with a 233 (±15) day growing season. The NEP was partitioned into gross primary productivity (GPP) of 3358 (± 167) g C m−2 yr−1 and annual carbon loss due to respiration and decomposition (Reco) of 2834 (± 157) g C m−2 yr−1. The ecosystem showed a strong seasonality as a source of carbon during the leaf-off season (March to June), and as a carbon sink during the rest of the year with significant sequestration during the winter season (October to December). The intra-annual analysis suggested that CO2 flux is primarily controlled by canopy greenness with mean Reco/GPP ratio varying from 1.90 (± 0.12) to 0.79 (± 0.04) during leaf-off to leaf-on seasons. The monthly C fluxes in the growing season are found to be strongly correlated to the environmental variables rather than in the leaf-off season, while variability in monthly ecosystem respiration was better explained by air temperature during the leaf-off season than the growing season. Further, the inter-annual variability of NEP was mainly dependent on growing season length and mean annual temperature. The variations in annual GPP and Reco were directly dependent on the increase in mean annual temperature. The eddy covariance-based NEP was complemented by close independent biometric estimates, imparting confidence in our measurements. In conclusion, this tropical dry deciduous forest site is a substantial carbon sink and would add crucial information regarding carbon budgeting of tropical forests in global carbon balance models.

From forest to fragment: compositional differences inside coastal forest moth assemblages and their environmental correlates

Patterns of β-diversity can provide insight into forces shaping community assembly. We analyzed species-rich insect assemblages in two reserve fragments that had once been part of one contiguous Mediterranean coastal pine forest. Local environments are still similar across both fragments, but their landscape context differs strongly, with one surrounded by intense agricultural land, while the other neighbors the urbanized area of Ravenna. Using 23,870 light-trap records of 392 moth species, and multiple local and landscape metrics, we compared the relative importance of habitat- versus landscape-scale environmental factors for shaping small-scale variation in differentiation and proportional insect β-diversity across 30 sites per reserve. Moth assemblage composition differed substantially between fragments, most likely due to ecological drift and landscape-scale variation. For proportional β-diversity, especially local forest structure was important. At well-developed forest sites, additive homogenization could be observed, whereas the lack of typical forest species at dry, dense, and younger forest sites increased species turnover (subtractive heterogenization). For differentiation β-diversity, local and landscape-scale factors were equally important in both reserves. At the landscape-scale (500 m radius around light-trapping sites) the proximity to urban areas and the fraction of human-altered land were most important. At the habitat scale, gradients in soil humidity, nutrient levels and forest structure mattered most, whereas plant diversity had very little explanatory power. Overall, landscape-scale anthropogenic alterations had major effects on moth communities inside the two conservation areas. Yet, even for these parts of one formerly contiguous forest trajectories in community change were remarkably idiosyncratic.

Implementation of BFASTmonitor Algorithm on Google Earth Engine to Support Large-Area and Sub-Annual Change Monitoring Using Earth Observation Data

Monitoring of abnormal changes on the earth’s surface (e.g., forest disturbance) has improved greatly in recent years because of satellite remote sensing. However, high computational costs inherently associated with processing and analysis of satellite data often inhibit large-area and sub-annual monitoring. Normal seasonal variations also complicate the detection of abnormal changes at sub-annual scale in the time series of satellite data. Recently, however, computationally powerful platforms, such as the Google Earth Engine (GEE), have been launched to support large-area analysis of satellite data. Change detection methods with the capability to detect abnormal changes in time series data while accounting for normal seasonal variations have also been developed but are computationally intensive. Here, we report an implementation of BFASTmonitor (Breaks For Additive Season and Trend monitor) on GEE to support large-area and sub-annual change monitoring using satellite data available in GEE. BFASTmonitor is a data-driven unsupervised change monitoring approach that detects abnormal changes in time series data, with near real-time monitoring capabilities. Although BFASTmonitor has been widely used in forest cover loss monitoring, it is a generic change monitoring approach that can be used to monitor changes in a various time series data. Using Landsat time series for normalised difference moisture index (NDMI), we evaluated the performance of our GEE BFASTmonitor implementation (GEE BFASTmonitor) by detecting forest disturbance at three forest areas (humid tropical forest, dry tropical forest, and miombo woodland) while comparing it to the original R-based BFASTmonitor implementation (original BFASTmonitor). A map-to-map comparison showed that the spatial and temporal agreements on forest disturbance between the original and our GEE BFASTmonitor implementations were high. At each site, the spatial agreement was more than 97%, whereas the temporal agreement was over 94%. The high spatial and temporal agreement show that we have properly translated and implemented the BFASTmonitor algorithm on GEE. Naturally, due to different numerical solvers being used for regression model fitting in R and GEE, small differences could be observed in the outputs. These differences were most noticeable at the dry tropical forest and miombo woodland sites, where the forest exhibits strong seasonality. To make GEE BFASTmonitor accessible to non-technical users, we developed a web application with simplified user interface. We also created a JavaScript-based GEE BFASTmonitor package that can be imported as a module. Overall, our GEE BFASTmonitor implementation fills an important gap in large-area environmental change monitoring using earth observation data.

Contrasting CO2 and water vapour fluxes in dry forest and pasture sites of central Argentina

AbstractThe dry forests of South America are a key player of the global carbon cycle and the regional water cycle, but they are being intensively deforested. We used eddy covariance measurements to compare the temporal patterns of CO2 and water vapour fluxes and their relationships with environmental variables in dry forest and pastures sites of central Argentina. Ecosystem fluxes showed clear contrasts in magnitude, timing and response to environmental controls between ecosystems. The dry forest displayed higher daily gross primary productivity (GPP, 10.6 vs. 7.8 g CO2 m−2 d−1) and ecosystem respiration (Reco, 9.1 vs. 7.0 g CO2 m−2 d−1) and lower net ecosystem exchange (NEE, −1.5 vs. −0.7 g CO2 m−2 d−1) than the pasture. These differences were explained by a lower tolerance of the pasture to cool temperatures and drought. The lowest NEE rates were observed between 26°C and 34°C in the pasture, but below this range, NEE increased sharply, switching to a carbon source with temperatures <20°C. By contrast, the dry forest remained as a strong carbon sink down to 18°C. The pasture also showed a stronger drop of GPP with drought compared with the dry forest, becoming a carbon source with soil wetness <25% of soil available water. Rainfall was strongly coupled with GPP in both ecosystems, but the dry forest responded to longer rainfall integration periods. This study helps to understand how ecosystems can respond to climate change, improve global scale modelling and increase the productivity and resilience of rangelands.

Patterns and controls on fine-root dynamics along a rainfall gradient in Ghana

Fine-root biomass relates to environmental variables differently along a rainfall gradient in Ghana. Understanding changes in root dynamics in response to environmental factors is crucial for projections of climate change, yet information on controls of root dynamics is limited in the tropics. This study quantified fine-root dynamics along a rainfall gradient in Ghana, ranging from dry to wet evergreen forests. Fine-root biomass and necromass were estimated by the sequential coring method for a year and analyzed in relation to measured environmental factors (rainfall, soil moisture content, air temperature and soil temperature). Overall, fine-root biomass increased along the gradient with the highest estimate found in the wet forest site. Mean annual fine root production ranged from 276.60 to 348.95 gm−2 year−1 across the different forest types. Fine-root turnover rates ranged from 2.3 to 3.1 year−1, and roots tended to turn over faster in the dry than in the moist and wet forest sites. There was a non-linear but significant relationship between fine-root biomass and soil moisture content in the wet forest. None of the environmental factors related to fine-root biomass in the moist forest. However, there was a significant non-linear relationship between rainfall and fine-root biomass in the dry forest site. These results suggest that environmental factors influence fine-root biomass differently across the three forest types. Therefore, future studies should focus on a comprehensive measurement of environmental controls to deepen our understanding of fine root dynamics.

Land-Use Change in a Mexican Dry Forest Promotes Species Turnover and Increases Nestedness in Plant-Hummingbird Networks: Are Exotic Plants Taking Over?

Background Despite the increasing knowledge of plant-pollinator interaction networks, the effects of human-induced disturbances on them have barely been studied. We analyzed whether land-use changes modified the structure and topology of plant-hummingbird interaction networks or promoted the integration of exotic plant species. Methods Fieldwork was carried out in two vegetation areas in Mexico: a protected tropical dry forest and nearby disturbed sites. For two years we registered hummingbird-plant interactions monthly in each area. Then, we constructed interaction matrices from these data and compared their assemblage structure. Results The conversion of original dry forest to disturbed habitats impacted some assemblage attributes of the plant-hummingbird network. In the disturbed sites, there were more plant species, mainly exotics, and one additional hummingbird species. Most network attributes remained the same except niche width and nestedness (pattern of interactions where generalists and specialists tend to interact with generalists whereas specialist-to-specialist interactions are infrequent), which were higher in the disturbed network. The generalist core in the disturbed network contained half of the core species in the conserved network. Implications for conservation Exotic plants that strongly integrated into the disturbed network may exert a large influence on network dynamics in these areas. Identifying the interacting species and their role provides valuable insights for their conservation and protection. Hummingbirds attracting native plant species have a potential for practical or ornamental use, and hummingbirds presence in human-modified landscapes not only provides positive aesthetic value to people but can additionally contribute to conserving native plants and the biodiversity associated with them.

Changes in tree diversity and carbon stock over a decade in two Indian tropical dry evergreen forests

ABSTRACT Repeated and continuous monitoring of changes in a habitat provides a platform to investigate concurrent variation in the structure, species composition, and function of a forest. We assessed tree diversity and carbon stock changes in two Indian tropical dry evergreen forest (TDEF) sites namely Sendhirakillai (SK) and Palvathunnan (PT) after 10-year time scale. Two 1-ha plots were delimited one in each disturbed and undisturbed site in 2007 and re-measurements were undertaken in 2017. Over the sampling period, species richness showed little variation in both the sites. Out of 38 species identified, 26 species decreased in abundance, nine increased, and three remained unchanged. A total of 860 trees were lost from both the sites in 10-year interval. Site PT witnessed maximum loss (44% – 559 stems). Tree species density, basal area, and carbon stocks decreased tremendously in all girth classes at site PT. Total biomass and carbon stocks were decreased by 42% in site PT and conversely, they increased by 9% in site SK. The substantial difference noticed between the two sites highlights the impact of human disturbance and the need for periodical biodiversity assessment through re-census in Indian TDEFs and also in similar global dry tropical forests.

Habitat modification effects on anuran food webs in the Colombian tropical dry forest

Habitat loss and transformation are major threats to biodiversity and ecosystem functioning, but their effects on species interaction are often poorly understood. We evaluated effects of habitat transformation and seasonality on anuran-prey food webs in Colombian dry-forests. We asked whether anthropic transformation (anthropic vs natural) and/or seasonality (dry, minor and major rain seasons) affect predator load on arthropods, the occurrence of energetic bottlenecks, and the diet overlap of anurans. We selected six dry forest sites in the Caribbean of Colombia, sampled anurans, and identified their stomach contents to construct anuran-prey food webs. We show that the global structure of food webs was affected by disturbance and seasonality, but not by their interaction. Prey vulnerability was higher in anthropic habitats. Habitat transformation enhanced diet overlap among predators, but there was not a differential effect of habitat type according to seasonality for network metrics. Our study shows a strong effect of natural vegetation modification in tropical dry forest on anuran-prey food webs, while seasonality did not seem to further mediate these effects.

Endemics and Cosmopolitans: Application of Statistical Mechanics to the Dry Forests of Mexico.

Data on the seasonally dry tropical forests of Mexico have been examined in the light of statistical mechanics. The results suggest a division into two classes of species. There are drifting populations of a cosmopolitan class capable of existing in most dry forest sites; these have a statistical distribution previously only observed (globally) for populations of alien species. We infer that a high proportion of species found only at a single site are specialists, endemics, and that these prefer sites comparatively low in species richness.

Cryptic diversity and ranavirus infection of a critically endangered Neotropical frog before and after population collapse

AbstractMesoamerican amphibian declines in apparently pristine and protected habitats have been severe, especially at elevations above 500 m sea level and have been linked to emerging diseases and a changing climate. The Craugastor punctariolus species series of direct developing frogs is endemic to the region and used to be comprised of 33 species, seven of which have known populations at present. One of these, C. ranoides, endemic to southern Nicaragua and Costa Rica, was historically found in cloud forest sites of Área de Conservación Guanacaste (ACG) in north‐west Costa Rica and extended into dry forest sites 20 km distant. Here, C. ranoides declined and disappeared from high elevation sites between the mid‐1980s and early 1990s, but populations persisted in the lowland dry forest. We compared the genetic richness and ranavirus infection status of C. ranoides from extant dry forest populations to historic museum specimens of now extinct ACG cloud forest populations using DNA sequence diversity at two mitochondrial loci and molecular screening for ranavirus. Extant dry forest populations of C. ranoides formed a monophyletic group which included historic specimens sampled at cloud forest sites. However, the extirpated ACG cloud forest population contained additional diversity: samples formed a divergent clade with unknown spatial distribution. Ranavirus was detected in both current and museum samples of C. ranoides and sequences from a 267‐nucleotide region of the major capsid protein gene shared 100% sequence identity with one another and with Frog virus 3. Our findings document cryptic diversity within an endangered species that has demonstrated no recovery in cloud forests and raises questions about Ranavirus and its potential link to the amphibian declines in this system. The presence of the same C. ranoides clade within present day and historical samples suggests a potential for effective translocation and repopulation of extirpated cloud forest populations.