Tropical Rain Forest Landscape Research Articles

Regional differences of functional and taxonomic bird diversity in tropical agroforests of Peru

AbstractDiversity and functionality of bird communities in tropical agroforests are shaped by their surrounding landscape, particularly the extent and type of natural forest. However, most evidence comes from tropical rainforest landscapes, whereas the bearing of such trends in other forest types remains understudied. We compared functional and beta diversity of bird communities in 23 cacao agroforests embedded in landscapes of two contrasting Peruvian regions: seasonally‐dry tropical forests and subtropical rainforests from the Andean foothills. Strong climatic seasonality affects both landscapes, but forest vegetation structure and complexity differ. We found higher bird species richness (n = 179 spp) and higher species turnover in the subtropical forest than in the dry forest landscape (n = 64 spp). Only in the dry forest landscape, distance from forest increased dissimilarity driven by species loss, that is, the nestedness component of beta diversity. This points to the importance of conserving dry tropical forests within the broader landscape matrix, with known benefits for pest control and cacao yield. Functional diversity indices were not influenced by forest distance in either landscape, but the proportion of insects in birds' diet decreased by 27% along a 1 km distance gradient from forest in the subtropical forest landscape. In the dry forest landscape, however, it decreased by only 3% across the same distance gradient. Far from forest (≥1 km), forest specialization decreased by ~33% and 20% in the subtropical and dry forest landscapes, respectively. These differences indicate that regionally‐adapted agroforest management is paramount for conserving bird diversity and ecosystem services as pest control. Procuring high‐canopy shade trees and adequate microhabitats for insectivorous species is essential to maintain biocontrol services in the subtropical forest. Conversely, in the dry forest enhancing low‐canopy vegetation with a focus on frugivores and ensuring forest closeness to agroforests may maximize bird diversity and their ecosystem services. A complete version of this article is translated to Spanish in the supplements.

Assessing the functional vulnerability of woody plant communities within a large scale tropical rainforest dynamics plot.

Tropical forests are characterized by intricate mosaics of species-rich and structurally complex forest communities. Evaluating the functional vulnerability of distinct community patches is of significant importance in establishing conservation priorities within tropical forests. However, previous assessments of functional vulnerability in tropical forests have often focused solely on isolated factors or individual disturbance events, with limited consideration for a broad spectrum of disturbances and the responses of diverse species. We assessed the functional vulnerability of woody plant communities in a 60-ha dynamic plot within a tropical montane rainforest by conducting in silico simulations of a wide range disturbances. These simulations combined plant functional traits and community properties, including the distribution of functional redundancy across the entire trait space, the distribution of abundance across species, and the relationship between species trait distinctiveness and species abundance. We also investigated the spatial distribution patterns of functional vulnerability and their scale effects, and employed a spatial autoregressive model to examine the relationships between both biotic and abiotic factors and functional vulnerability at different scales. The functional vulnerability of tropical montane rainforest woody plant communities was generally high (the functional vulnerability of observed communities was very close to that of the most vulnerable virtual community, with a value of 72.41% on average at the 20m×20m quadrat scale), and they exhibited significant spatial heterogeneity. Functional vulnerability decreased with increasing spatial scale and the influence of both biotic and abiotic factors on functional vulnerability was regulated by spatial scale, with soil properties playing a dominant role. Our study provides new specific insights into the comprehensive assessment of functional vulnerability in the tropical rainforest. We highlighted that functional vulnerabilities of woody plant communities and their sensitivity to environmental factors varied significantly within and across spatial scales in the tropical rainforest landscape. Preserving and maintaining the functionality of tropical ecosystems should take into consideration the variations in functional vulnerability among different plant communities and their sensitivity to environmental factors.

Ecology and Determinants of a Tropical Rainforest Landscape

Tropical ecosystems are bio-diverse ecosystems that differ according to varied environmental features. This work assessed the tree diversity and environmental variables that define a rainforest ecosystem in southeast Nigeria. 30 forest plots were used to identify trees ≥ 10 cm (DBH measured at 130 cm). Soil samples were collected up to 30 cm deep at four edges and middle of each plot, and bulked for analysis. The survey recorded a total of 2414 trees that belonged to 102 species and 32 families. Shannon-Wiener’s diversity index (H’) of 3.67, Inverse Simpson’s index (C) of 1.06, species evenness of 0.79 and Margalef’s index of species richness (M) of 12.97 were recorded. Fabaceae family recorded the highest number (1037) of individual tree (being 43% of total) observations, while Burseraceae had the least number (1). Species abundance status showed 2.9% of species as “Abundant”, 73.5% as “Endangered”, 2.9% as “Frequent” and 20.6% of species as “Rare”. Soil variables namely phosphorus, magnesium, potassium, particle sizes (sand, silt and clay), CEC, calcium, pH, and aluminium, influenced the distribution of the vegetation in decreasing order. Edaphic factors (soil) determined the distribution of tree stems, growth and abundance of the species within the region. Efforts on conserving the ecosystem along environmental gradients and according to species status and indices are advocated.

Carbon Storage and Environmental Determinants in a Tropical Rainforest Landscape

Tropical ecosystems sequester vast amounts of carbon but remain much varied across different landscapes. In order to provide estimates on carbon storage for the ecosystem and show the role of forest structure and environmental factors in determining aboveground and soil carbon of a rainforest landscape, forest inventory was conducted across 30 forest plots. Each of the plots measured 50 m × 50 m and was used to identify and measure tree species ≥ 10 cm diameter at breast height (DBH measured at 130cm). Soil samples were collected for up to 30 cm deep at the four edges and then the middle of each plot, bulked for analysis and tested in the laboratory. Aboveground carbon estimates ranged from 8.18 - 91.29 t/ha across the ecosystem and were similar with carbon storage in tropical landscapes. With variations in stem density, basal area and structure across the region, much of the carbon capacity across the ecosystem was much varied (F (29, 2127) = 3.794, p = 0.000). Environmental variables (mainly edaphic variables) were not positively correlated with soil carbon and did not largely determine its storage and variation. The need to reduce disturbances (which are a main driver of disparity in biomass carbon storage) across the region and across tropical ecosystems was advocated as a pathway to enhancing higher carbon sequestration.

Spatial and temporal scales of canopy disturbance and recovery across an old‐growth tropical rain forest landscape

AbstractThe distribution of canopy heights in tropical rain forests directly affects carbon storage and the maintenance of biodiversity. We report results from a unique 20‐yr record of annual monitoring of canopy‐height distributions across an old‐growth tropical rain forest landscape at the La Selva Biological Station in Costa Rica. Canopy heights to 15 m were measured annually in 18 0.50‐ha plots at 231 points on a 5 × 5 m grid from 1999–2018 (nine plots in 1999), and heights >15 m were classified as “high canopy.” During the study two major disturbance events (one immediately prior to the study) dominated the landscape‐scale distribution of canopy heights. Height recovery from the 1997–1998 strong El Niño disturbance took approximately 15 yr. Frequency of canopy gaps varied an order of magnitude among years and 96% disappeared in ≤2 yr. High‐canopy coverage and gap frequency varied substantially across the local gradients of soil nutrients and topography, and plot‐level conditions and trends frequently differed from the landscape‐level patterns. In contrast to the two major landscape‐level disturbances, significant plot‐level disturbances were common throughout two decades. Including a similar data set taken in 1992, canopy‐height distributions for the last three decades over this old‐growth tropical rain forest landscape are most parsimoniously interpreted as showing local disturbance and recovery and no unidirectional trends over time. Together these results suggest that understanding the landscape‐ and plot‐level dynamics of tropical rain forest canopy‐height distributions will require repeat sampling for multiple decades, while accurately measuring gap frequency and recovery will require sample intervals of ≤2 yr.

Active restoration fosters better recovery of tropical rainforest birds than natural regeneration in degraded forest fragments

Abstract Ecological restoration has emerged as a key strategy for conserving tropical forests and habitat specialists, and monitoring faunal recovery using indicator taxa like birds can help assess restoration success. Few studies have examined, however, whether active restoration (AR) achieves better recovery of bird communities than natural regeneration, or how bird recovery relates to habitat affiliations of species in the community. In rainforests restored over the past two decades in a fragmented landscape (Western Ghats, India), we examined whether bird species richness and community composition recovery in 23 actively restored (AR) sites were significantly better than recovery in paired naturally regenerating (NR) sites, relative to 23 undisturbed benchmark (BM) rainforests. We measured eight habitat variables and tested whether bird recovery tracked habitat recovery, whether rainforest and open‐country birds showed contrasting patterns, and assessed species‐level responses to restoration. We recorded 92 bird species in 460 point‐count surveys. Rainforest bird species richness was highest in BM, intermediate in AR and lowest in NR. Contrastingly, open‐country bird species richness was least in BM, intermediate in AR and highest in NR. Bird community composition varied significantly across treatment types with composition in AR in transition from NR to BM. Bird community dissimilarity between sites was positively related to dissimilarity in habitat structure and floristics, and geographical distance between sites. Variance partitioning indicated that structural and floristic dissimilarity explained 90% of the variation in community composition. Indicator species analysis revealed significant associations of 34 species with one or more treatment types. Species associated with BM and AR treatment types were all rainforest species, while only 38% of species associated with AR and NR treatment types were rainforest species. Synthesis and applications. We show that active restoration (AR) of degraded fragments benefits rainforest birds and reduces the infiltration of open‐country birds, and highlight the importance of considering rainforest and open‐country species separately. In human‐modified tropical rainforest landscapes, AR of degraded fragments fosters partial recovery and complements protection of mature forests for bird conservation.

What evidence exists on the relationship between agricultural production and biodiversity in tropical rainforest areas? A systematic map protocol

BackgroundAgriculture produces food for billions of humans and creates livelihoods for farmers. However, the current food production systems, driven by the increasing food demand and the ever-growing human population, are undermining ecological resources, primarily those related to biodiversity. Accordingly, agricultural production in tropical rainforest countries has been a trade-off, as regions harbor high biodiversity while also being pressured by agricultural land expansion. Consequently, threats to biodiversity are inevitable and will likely affect the ecosystem service provisions necessary for the agricultural process. Presently, no study reviews and maps the evidence of relationships between biodiversity and agriculture in the tropical rainforest landscape. Therefore, such a study is necessary to identify the knowledge gaps and provide scientific evidence to the relevant policymakers for safeguarding biodiversity within agricultural policies. This study aims to collect available published literature that evaluates the relations of agricultural production and biodiversity. We will focus on the agriculture and priority crops in the countries producing the commodities situated in the tropical rainforest landscape.MethodsGeneric search terms derived from research question elements will be used to search relevant articles. These terms are in English, and the searches will encompass global tropical rainforest countries. Peer-reviewed and gray literature articles retrieved from search engines and databases will be screened first using the title and abstract and second at the full-text level. The latter screening process will involve data coding to retrieve relevant characteristics from each eligible study and finally collate these characteristics into an evidence map, which will provide a current state of knowledge and further support evidence-informed policy formulation. The map presentation in the final report will also be complemented by a narrative synthesis explaining the trends, pinpointing the knowledge gluts and gaps, serving relevant information, and searchable databases for associated stakeholders.

Population dynamics of threatened felids in response to forest cover change in Sumatra.

Habitat loss caused by deforestation is a global driver of predator population declines. However, few studies have focussed on these effects for mesopredator populations, particularly the cryptic and elusive species inhabiting tropical rainforests. We conducted camera trapping from 2009–11 and 2014–16, and used occupancy modelling to understand trends of Sumatran mesopredator occupancy in response to forest loss and in the absence of threats from poaching. By comparing the two survey periods we quantify the trend of occupancy for three sympatric felid species in the tropical rainforest landscape of Kerinci Seblat National Park. Between 2000 and 2014, forest loss across four study sites ranged from 2.6% to 8.4%. Of three threatened felid species, overall occupancy by Sunda clouded leopard (Neofelis diardi) and Asiatic golden cat (Catopuma temminckii) remained stable across all four areas between the two survey periods, whilst marbled cat (Pardofelis marmorata) occupancy increased. In general occupancy estimates for the three species were: lower in lowland forest and increased to attain their highest values in hill forest, where they declined thereafter; increased further from the forest edge; positively correlated with distance to river, except for golden cat in the second survey where the relationship was negative; and, increased further from active deforestation, especially for clouded leopard in the second survey, but this was some 10-15km away. Our study offers fresh insights into these little known mesopredators in Sumatra and raises the practically important question of how far-reaching is the shadow of the encroachment and road development that typified this deforestation.

Keanekaragaman dan komposisi kumbang elaterid (Coleoptera: Elateridae) di kawasan hutan hujan tropis Taman Nasional Bukit Duabelas dan Hutan Harapan, Jambi

Provinsi Jambi merupakan salah satu daerah di Indonesia yang memiliki hutan hujan tropis dengan karakteristik lanskap berbeda di setiap wilayah. Beragam jenis flora dan fauna dapat ditemukan di kawasan hutan hujan tropis ini, di antaranya kumbang elaterid. Kumbang elaterid diketahui berperan penting sebagai bioindikator dalam penelitian ekologi. Penelitian ini bertujuan untuk memelajari pengaruh perbedaan lanskap terhadap keanekaragaman dan komposisi kumbang elaterid. Pengambilan sampel dilakukan di daerah Jambi pada dua lanskap hutan hujan tropis, yaitu lanskap Taman Nasional Bukit Duabelas (TNBD) dan Hutan Harapan. Kumbang elaterid dikumpulkan melalui metode pengasapan (fogging) yang dilakukan pada pagi hari. Pada setiap lanskap ditentukan 4 plot dan pada masing-masing plot terdiri atas 3 subplot sehingga total subplot yang diamati di kedua lanskap sebanyak 24 subplot. Total kumbang elaterid yang terkoleksi sebanyak 2.069 individu, terdiri atas 6 subfamili, 23 genus, dan 59 morfospesies. Jumlah individu tertinggi ditemukan pada lanskap Hutan Harapan, sedangkan jumlah morfospesies tertinggi ditemukan pada lanskap TNBD. Kumbang elaterid yang mendominasi kedua lanskap terdiri atas Subfamili Agrypninae dengan Genus Adelocera dan morfospesies Adelocera sp.01. Hasil analisis menunjukkan bahwa perbedaan lanskap memengaruhi komposisi dan kelimpahan individu kumbang elaterid, akan tetapi tidak memengaruhi kekayaan spesies kumbang elaterid.

Changes in the Abundance and Composition of a Microbial Community Associated with Land Use Change in a Mexican Tropical Rain Forest

Land use change (LUC) has important effects on the aboveground biota, mainly by altering richness and diversity, as well as ecosystem functioning. However, the effects of LUC on abiotic and biotic soil properties need to be assessed to determine recovery potential when the original vegetation is restored. The Los Tuxtlas tropical rain forest landscape in Veracruz, Mexico, offers a suitable framework for testing this. To assess the effect of LUC on the microbial community of this tropical rain forest landscape, we analyzed the whole-cell fatty acid profile of the microbial community and physicochemical properties of soils from four types of land use: crops, pastures, secondary forest, and primary tropical rain forest for the dry and rainy seasons. Regardless of season, the microbial data grouped according to land use. The composition of the microbial community was correlated with soil pH in the dry season, and with nitrate, soil organic matter, and available phosphorus concentration in the rainy season. Land use affects the abundance of the microbial community as a function of seasonal variation. In comparison with the microbial community in primary and secondary forest, that of crops and pastures was more greatly affected by seasonal variation. In fact, there were no significant differences between the primary forests or among secondary forests of different ages. These results may indicate a capacity for fast recovery (5 years or less) by the microbial community upon forest regeneration.

Diversity, distribution and dynamics of large trees across an old-growth lowland tropical rain forest landscape

Large trees, here defined as ≥60 cm trunk diameter, are the most massive organisms in tropical rain forest, and are important in forest structure, dynamics and carbon cycling. The status of large trees in tropical forest is unclear, with both increasing and decreasing trends reported. We sampled across an old-growth tropical rain forest landscape at the La Selva Biological Station in Costa Rica to study the distribution and performance of large trees and their contribution to forest structure and dynamics. We censused all large trees in 238 0.50 ha plots, and also identified and measured all stems ≥10 cm diameter in 18 0.50 ha plots annually for 20 years (1997-2017). We assessed abundance, species diversity, and crown conditions of large trees in relation to soil type and topography, measured the contribution of large trees to stand structure, productivity, and dynamics, and analyzed the decadal population trends of large trees. Large trees accounted for 2.5% of stems and ~25% of mean basal area and Estimated Above-Ground Biomass, and produced ~10% of the estimated wood production. Crown exposure increased with stem diameter but predictability was low. Large tree density was about twice as high on more-fertile flat sites compared to less fertile sites on slopes and plateaus. Density of large trees increased 27% over the study interval, but the increase was restricted to the flat more-fertile sites. Mortality and recruitment differed between large trees and smaller stems, and strongly suggested that large tree density was affected by past climatic disturbances such as large El Niño events. Our results generally do not support the hypothesis of increasing biomass and turnover rates in tropical forest. We suggest that additional landscape-scale studies of large trees are needed to determine the generality of disturbance legacies in tropical forest study sites.

Global restoration opportunities in tropical rainforest landscapes.

Over 140 Mha of restoration commitments have been pledged across the global tropics, yet guidance is needed to identify those landscapes where implementation is likely to provide the greatest potential benefits and cost-effective outcomes. By overlaying seven recent, peer-reviewed spatial datasets as proxies for socioenvironmental benefits and feasibility of restoration, we identified restoration opportunities (areas with higher potential return of benefits and feasibility) in lowland tropical rainforest landscapes. We found restoration opportunities throughout the tropics. Areas scoring in the top 10% (i.e., restoration hotspots) are located largely within conservation hotspots (88%) and in countries committed to the Bonn Challenge (73%), a global effort to restore 350 Mha by 2030. However, restoration hotspots represented only a small portion (19.1%) of the Key Biodiversity Area network. Concentrating restoration investments in landscapes with high benefits and feasibility would maximize the potential to mitigate anthropogenic impacts and improve human well-being.

Forest cover drives leaf litter ant diversity in primary rainforest remnants within human-modified tropical landscapes

The main effects of habitat loss and fragmentation have been addressed through changes in diversity patterns at different spatial levels. Species richness and diversity are the most used descriptors to assess the effect of changes in land use on tropical communities. However, other biological responses such as richness and diversity of trophic guilds may also provide a better understanding about the robustness and resilience of tropical environments to disturbance. In this study, we evaluated how changes in local and landscape characteristics associated to habitat loss and fragmentation affect: (i) species richness and Shannon diversity as well as (ii) trophic guild richness and diversity of leaf litter ants in human-modified tropical rainforest landscapes in Mexico. For this, we sampled ants in 16 sampling sites and recorded a series of descriptors at both local (i.e. elevation, temperature, relative humidity, soil pH, canopy cover, litter volume and vegetation structure) and landscape level (i.e. landscape heterogeneity, forest cover and connectivity). Overall, we observed that increasing primary forest cover within the sampling sites positively influenced richness and diversity of species and trophic guilds. In addition, at the local level, we found that only richness and diversity of ant species were negatively associated with tree density (i.e. number of trees, litter volume and canopy cover). These findings suggest that opportunistic species can be favored in environments with low tree density. In short, our complementary approach highlights the importance of environmental variability and primary forest cover in the maintenance of ant biodiversity in primary rainforest remnants.

Success or failure: the role of ecological restoration on the recovery of dung beetle diversity and function in a tropical rainforest

Recent studies have shown that ecological restoration hardly recovers diversity and ecosystem function of important bioindicator groups such as dung beetles, which have key functional roles in natural and managed ecosystems. Here, we evaluated dung beetle diversity and ecological function in a restored area in a tropical rainforest landscape that comprises 10-year old cattle exclusions that include plantings of local trees and unplanted exclusions that resemble natural succession. As control habitats, we used neighbor pastures and sites in the nearest conserved forest. We found that the restored area did not improve dung beetle abundance and diversity compared to the forest, and did not differ from pastures. On the other hand, dung removal, a key ecosystem function, was similar in the forest and the restored area, but was not carried out by dung beetles in the restored area. Our study supports previous evidence showing that restoration efforts are hardly helping to recover dung beetle diversity despite they can eventually favor the recovery of function. Our results highlight the importance of considering landscape context in restoration programs, including alternative conservation strategies, such as maintenance of forest patches and restoration of connectivity between fragments to maintain dung beetle diversity and function.

Multidecadal stability in tropical rain forest structure and dynamics across an old-growth landscape.

Have tropical rain forest landscapes changed directionally through recent decades? To answer this question requires tracking forest structure and dynamics through time and across within-forest environmental heterogeneity. While the impacts of major environmental gradients in soil nutrients, climate and topography on lowland tropical rain forest (TRF) structure and function have been extensively analyzed, the effects of the shorter environmental gradients typical of mesoscale TRF landscapes remain poorly understood. To evaluate multi-decadal performance of an old-growth TRF at the La Selva Biological Station, Costa Rica, we established 18 0.5-ha annually-censused forest inventory plots in a stratified-random design across major landscape edaphic gradients. Over the 17-year study period, there were moderate differences in stand dynamics and structure across these gradients but no detectable difference in woody productivity. We found large effects on forest structure and dynamics from the mega-Niño event at the outset of the study, with subdecadal recovery and subsequent stabilization. To extend the timeline to >40 years, we combined our findings with those from earlier studies at this site. While there were annual to multiannual variations in the structure and dynamics, particularly in relation to local disturbances and the mega-Niño event, at the longer temporal scale and broader spatial scale this landscape was remarkably stable. This stability contrasts notably with a current hypothesis of increasing biomass and dynamics of TRF, which we term the Bigger and Faster Hypothesis (B&FHo). We consider possible reasons for the contradiction and conclude that it is currently not possible to independently assess the vast majority of previously published B&FHo evidence due to restricted data access.

Partial recovery of a tropical rain forest a half‐century after clear‐cut and selective logging

Summary The extent to which tropical rain forests recover tree species richness, composition and community structure after clear‐cutting or selective harvest is controversial. Thus, the conservation value of forests regenerated after harvest remains unclear, but critically important for biodiversity. We sampled trees from 164 25 × 25 m quadrats across a 160‐km2 tropical rain forest landscape on Hainan Island, China, which had been clear‐cut or selectively harvested and left to recover without management for up to 50 years. Species richness and species abundance distributions were compared among five successional categories to investigate changes in species richness and species abundance over time. Basal areas and three different species similarity indices were compared to reveal temporal changes in species composition and community structure. Species richness recovered faster than species composition and structure in both selectively logged and clear‐cut forests. Both total number of species and number of rare species tended to increase from younger harvested forests through older harvested forests to old‐growth intact forests. Within 20–40 years after harvest species composition of harvested forests tended towards that of old‐growth forests, community similarity between harvested and old‐growth forests decreased subsequently and basal area did not recover, given even a half‐century of succession undisturbed by anthropogenic forces. Shortly after harvest, pioneer species increased rapidly, but shade‐tolerant species required much more time to recover to former abundances. The shift from pioneer species to shade‐tolerant species indicates significant recovery of logged forests. Selectively logged forests recovered more quickly and had higher conservation values than clear‐cut forests. Synthesis and applications. Our findings indicate that logged tropical forests only partially recovered the characteristics of pre‐harvest, primary forest after a half‐century of succession. Recovery of the original tree biodiversity on such post‐harvest landscapes will be slow at best, if measured by species composition or stand structure. Our study amplifies the importance of conserving tropical forest integrity and developing harvest and management approaches that facilitate full recovery of logged tropical forests.

Tropical Forest Fragmentation Affects Floral Visitors but Not the Structure of Individual-Based Palm-Pollinator Networks

Despite increasing knowledge about the effects of habitat loss on pollinators in natural landscapes, information is very limited regarding the underlying mechanisms of forest fragmentation affecting plant-pollinator interactions in such landscapes. Here, we used a network approach to describe the effects of forest fragmentation on the patterns of interactions involving the understory dominant palm Astrocaryum mexicanum (Arecaceae) and its floral visitors (including both effective and non-effective pollinators) at the individual level in a Mexican tropical rainforest landscape. Specifically, we asked: (i) Does fragment size affect the structure of individual-based plant-pollinator networks? (ii) Does the core of highly interacting visitor species change along the fragmentation size gradient? (iii) Does forest fragment size influence the abundance of effective pollinators of A. mexicanum? We found that fragment size did not affect the topological structure of the individual-based palm-pollinator network. Furthermore, while the composition of peripheral non-effective pollinators changed depending on fragment size, effective core generalist species of pollinators remained stable. We also observed that both abundance and variance of effective pollinators of male and female flowers of A. mexicanum increased with forest fragment size. These findings indicate that the presence of effective pollinators in the core of all forest fragments could keep the network structure stable along the gradient of forest fragmentation. In addition, pollination of A. mexicanum could be more effective in larger fragments, since the greater abundance of pollinators in these fragments may increase the amount of pollen and diversity of pollen donors between flowers of individual plants. Given the prevalence of fragmentation in tropical ecosystems, our results indicate that the current patterns of land use will have consequences on the underlying mechanisms of pollination in remnant forests.

Linking functional trade-offs, population limitation and size structure: Termites under soil heterogeneity

Organismal fitness is fuelled by resources. However, resource acquisition often involves conflicting functional demands that may ultimately shape broader ecological patterns. For instance, termites play major roles in ecosystem functioning through their foraging and building activities. Yet, while experiments suggest improved foraging in sand, nest construction depends on clay. Hence, these functions may trade off, with species optima reflecting interspecific variation in building requirements. We investigated whether a foraging–building trade-off could affect termite populations by using three species differing in building requirements, namely Neocapritermes braziliensis, Anoplotermes banksi and Labiotermes labralis. We characterized their populations in relation to soil texture and food amount across a tropical rain forest landscape, and then compared the observed patterns. Colony density was unrelated to food amount in the three species. However, A. banksi was denser at balanced mixtures of sand and clay, consistent with a compromise between foraging and building demands. Further, the species building more mineralized nests (L. labralis) was more abundant on clayish soils, whereas the species relying less on soil for nest construction (N. braziliensis) was more abundant on sandy soils. Changes in colony density correlated with changes in size structure: in N. braziliensis and A. banksi, colony mass variability increased with density due to a sharp decrease in minimum colony mass, consistent with higher productivity and/or size-asymmetric competition. This study suggests a novel functional trade-off that may help drive population density and size structure both within and across termite species.

Increased abundance, but reduced nest predation in the chestnut-backed antbird in costa rican rainforest fragments: surprising impacts of a pervasive snake species

Understory insectivorous birds often disappear from fragmented tropical rainforest landscapes before mechanisms such as increased rate of nest depredation can be evaluated. Here, we took advantage of chestnut-backed antbird (Myrmeciza exsul), a representative rainforest understory insectivore that persists in fragments (unlike many other understory species), to identify variables influencing nest predation rate and to test the hypothesis that nest predation underlies avian extirpation in tropical fragments. We compared nest predation rates, bird density, and predator identities in three habitats of lowland Caribbean Costa Rica: two fragments, a peninsular reserve (La Selva Biological Station), and unfragmented rainforest. Our results suggest an inversely density-dependent nest predation pattern: In fragments, chestnut-backed antbirds reached their highest density and—contrary to predictions—experienced their lowest nest predation rates; La Selva on the other hand experienced the lowest density and highest predation rate. Because nest predation decreased with fragmentation, it appears not to explain declines of understory insectivores from forest fragments generally. Nest survival models indicated that habitat best explained nest predation likelihood, whereas edge, annual, and nest age effects were unimportant. Video surveillance documented both bird-eating snake (Pseustes poecilonotus) causing 80% of nest loss overall (37 of 46 nests) and a larger variety of predators in fragments; thus, landscape factors influenced an understory bird’s nest predation. Given the large effect on our focal species, Pseustes likely affects other understory nesters, a topic warranting further study. Tropical reserve conservation plans should consider potential impacts of specialized nest predators on vulnerable understory birds.

Comparison of direct and indirect methods for assessing leaf area index across a tropical rain forest landscape

Many functional properties of forests depend on the leaf area; however, measuring leaf area is not trivial in tall evergreen vegetation. As a result, leaf area is generally estimated indirectly by light absorption methods. These indirect methods are widely used, but have never been calibrated against direct measurements in tropical rain forests, either at point or landscape scales. Here, we compare direct harvest leaf area index (LAI) measurements taken across an old-growth tropical rain forest landscape with data from two indirect methods, digital hemispherical photography and the LI-COR LAI-2000 Plant Canopy Analyzer. Direct measurements of leaf area were done by collecting all leaf material within an area of 4.6m2, extending from the forest floor to the top of the canopy using a portable aluminum scaffolding tower. The tower was erected at 45 locations following a stratified random design.Mean direct-harvest LAI above 1m was 5.5±0.3 SE. Plant area index (PAI, leaves+wood) was 5.1±0.2 for the LAI-2000, and for the hemispherical photographs was 3.9±0.2, analyzed using Gap Light Analyzer (GLA), and 4.9–6.0±0.2 using WinSCANOPY software. Correction for leaf clumping (non-random distribution of leaves) generally improved LAI estimates of the hemispherical photographs. At the local scale, direct-harvest LAI was not significantly correlated with LAI estimates for either indirect method. However, correlations between direct-harvest LAI and both indirect methods along vertical canopy transects from forest floor to the canopy top were significant. Relationships between harvest LAI and canopy closure (from which indirect LAI values are derived) showed very small changes in closure with large changes in LAI at LAI values>6, indicating that the estimations of LAI using canopy closure values were reaching an asymptote. As a result, at high canopy closure indirect LAI is underestimated. Overall, the LAI-2000 performed better than hemispherical photography for estimating direct-harvest LAI at landscapes scales. However, with corrections for leaf clumping, hemispherical photography can be effective for estimating and characterizing landscape level LAI of tropical rain forest.