Human-modified Tropical Landscapes Research Articles

Linking changes in landscape structure to insect herbivory in forest edges and interiors of Atlantic Forest remnants.

Human activities have triggered profound changes in natural landscapes, resulting in species loss and disruption of pivotal ecological interactions such as insect herbivory. This antagonistic interaction is affected by complex pathways (e.g., abundance of herbivores and predators, plant chemical defenses, and resource availability), but the knowledge regarding how forest loss and fragmentation affect insect herbivory in human-modified tropical landscapes still remains poorly understood. In this context, we assessed multi-pathways by which changes in landscape structure likely influence insect herbivory in 20 Atlantic forest fragments in Brazil. Using path analysis, we estimated the direct effects of forest cover and forest edge density, and the indirect effect via canopy openness, number of understory plants and phenolic compounds, on leaf damage in understory plants located in the edge and interior of forest fragments. In particular, plants located in forest edges experienced greater leaf damage than interior ones. We observed that landscape edge density exerted a positive and direct effect on leaf damage in plants sampled at the edge of forest fragments. Our findings also indicated that forest loss and increase of edge density led to an increase in the canopy opening in the forest interior, which causes a reduction in the number of understory plants and, consequently, an increase in leaf damage. In addition, we detected that phenolic compounds negatively influence leaf damage in forest interior plants. Given the increasing forest loss in tropical regions, in which forest fragments become stranded in highly deforested, edge-dominated and degraded landscapes, our study highlights the pervasive enhancement in insect herbivory in remaining forest fragments-especially along forest edges and canopy gaps in the forest interior. As a result, increased herbivory is likely to affect forest regeneration and accelerate the ecological meltdown processes in these highly deforested and disturbed anthropogenic landscapes.

Elevated litterfall phosphorus reduces litter and soil organic matter pools in exotic-dominated novel forests in Singapore

Abstract The estimation of leaf litter turnover is often limited to early-stage decomposition using unrepresentative models and litter types. In tropical secondary forests, particularly exotic-dominated novel forests, the characterisation of litter turnover remains poor. This study estimated the annual turnover of in-situ leaf litter across four forest successional types in Singapore using a Weibull residence time model. Litter turnover and nutrient dynamics diverged between young secondary and old-growth forests. In particular, within novel forests, annual phosphorus return via leaf litterfall was three times that of primary forests, while the mass loss of in-situ leaf litter was highest among all forest successional types, estimated at 92.8% annually with a mean residence time of 176 days, resulting in a litter pool size a third that of primary forests. Our findings suggest that tree species composition and species-specific effects shaped the observed variations in litter turnover and nutrient dynamics across forest successional types and forest stands, whereas tree species richness, canopy structure, soil nutrient levels, and microclimate were found to be non-predictors. Taken together, our study provides an insight into litter turnover in human-modified tropical landscapes increasingly characterised by novel forests, potentially leading to a reduction in surface litter and soil organic carbon pools.

Producing context specific land cover and land use maps of human-modified tropical forest landscapes for infectious disease applications

Satellite-based land cover mapping plays an important role in understanding changes in ecosystems and biodiversity. There are global land cover products available, however for region specific studies of drivers of infectious disease patterns, these can lack the spatial and thematic detail or accuracy required to capture key ecological processes. To overcome this, we produced our own Landsat derived 30 m maps for three districts in India's Western Ghats (Wayanad, Shivamogga and Sindhudurg). The maps locate natural vegetation types, plantation types, agricultural areas, water bodies and settlements in the landscape, all relevant to functional resource use of species involved in infectious disease dynamics. The maps represent the mode of 50 classification iterations and include a spatial measure of class stability derived from these iterations. Overall accuracies for Wayanad, Shivamogga and Sindhudurg are 94.7 % (SE 1.2 %), 88.9 % (SE 1.2 %) and 88.8 % (SE 2 %) respectively. Class classification stability was high across all three districts and the individual classes that matter for defining key interfaces between human habitation, forests, crop, and plantation cultivation, were generally well separated. A comparison with the 300 m global ESA CCI land cover map highlights lower ESA CCI class accuracies and the importance of increased spatial resolution when dealing with complex landscape mosaics. A comparison with the 30 m Global Forest Change product reveals an accurate mapping of forest loss and different dynamics between districts (i.e., Forests lost to Built-up versus Forests lost to Plantations), demonstrating an interesting complementarity between our maps and the % tree cover Global Forest Change product. When studying infectious disease responses to land use change in tropical forest ecosystems, we recommend using bespoke land cover/use classifications reflecting functional resource use by relevant vectors, reservoirs, and people. Alternatively, global products should be carefully validated with ground reference points representing locally relevant habitats.

In highly-biodiverse tropical landscapes, multiple-objective optimization reveals opportunities for increasing both conservation and agricultural production

In humid tropics, small and medium farming systems are important for producing food but also because they retain rainforest patches with high conservation value. Forest conservation and agricultural production strongly compete for land in Tropical Farming Systems (TFS). Finding solutions that synergize increasing conservation areas and agricultural production is an issue that has yet to be resolved in human-modified tropical landscapes. Achieving this objective requires analyzing how farms could be reorganized to relieve the pressure for production on the land. Pareto-based genetic algorithms that produce a set of solutions that satisfy apparently opposed objectives may tackle multi-objective problems. We explored trade-offs and synergies to increase the profits by sustainable intensification and maintain or increase rainforest areas in five TFS. There was a strong trade-off between conservation and economic profits in all TFS. However, depending on the total farming area, initial configurations and the amount of external inputs used, TFS showed low (two out of five) or high (three out of five) potential to increase forest conservation and profits. In low potential areas, the expansion of conservation areas and profits was only possible by increasing external inputs, primarily due to the limiting farming area and intensification status in those areas. In contrast, in high potential areas it was possible to increase conservation areas and profits through sustainable intensification practices, such as increasing maize silage, changing high for low use-pesticides crops but also reducing variable costs by minimizing cost-supply uses or external feeds. Alternative management and resource allocation options were specific for each TFS. The multi-objective simulation yielded novel results showing that it is possible to overcome the conservation-production antagonism (a regional-global scale issue) by adjusting management at farm (local) scale.

Plant Diversity in the Diet of Costa Rican Primates in Contrasting Habitats: A Meta-Analysis

In human-modified tropical landscapes, the survival of arboreal vertebrates, particularly primates, depends on their plant dietary diversity. Here, we assess the diversity of plants included in the diet of Costa Rican non-human primates, CR-NHP (i.e., Alouatta palliata palliata, Ateles geoffroyi, Cebus imitator, and Saimiri oerstedii) inhabiting different habitat types across the country. Specifically, we analyzed 37 published and unpublished datasets to assess: (i) richness and dietary α-plant diversity, (ii) the β-diversity of dietary plant species and the relative importance of plant species turnover and nestedness contributing to these patterns, and (iii) the main ecological drivers of the observed patterns in dietary plants. Dietary data were available for 34 Alouatta, 16 Cebus, eight Ateles, and five Saimiri groups. Overall dietary plant species richness was higher in Alouatta (476 spp.), followed by Ateles (329 spp.), Cebus (236 spp.), and Saimiri (183 spp.). However, rarefaction curves showed that α-diversity of plant species was higher in Ateles than in the other three primate species. The γ-diversity of plants was 868 species (95% C.I. = 829–907 species). The three most frequently reported food species for all CR-NHP were Spondias mombin, Bursera simaruba, and Samanea saman, and the most consumed plant parts were leaves, fruits, and flowers. In general, plant species turnover, rather than nestedness, explained the dissimilarity in plant diet diversity (βsim > 0.60) of CR-NHP. Finally, primate species, habitat type (life zone and disturbance level) and, to a lesser degree, study province, were the best predictors of the dietary plant assemblages. Our findings suggest that CR-NHP diets are diverse, even in severely disturbed habitats.

Chronic anthropogenic disturbances and aridity negatively affect specialized reproductive traits and strategies of edible fruit plant assemblages in a Caatinga dry forest

Chronic anthropogenic disturbances and climate change are the main threats to biodiversity, acting as potential drivers of assembly reorganization in human-modified tropical landscapes. We aimed to understand how the reproductive traits of edible fruit plant assemblages respond to chronic disturbances and aridity in the Caatinga, a dry forest in northeastern Brazil housing a human population that greatly depends on natural resources for subsistence and is threatened by increasing aridity. The study was carried out across 20 permanent plots of Caatinga, covering gradients of chronic disturbances (livestock grazing, wood extraction and non-timber product exploitation) and aridity (1051 mm to 664 mm). We registered 24 native plant species with fruits that are edible for humans, which were classified according to their flowering/fruiting pattern, floral size and reward, sexual and reproductive systems, pollination systems, and fruit types. They were also grouped into two categories of reproductive strategies (generalists and specialists). We documented that chronic disturbances and aridity pose more negative than positive effects on the reproductive traits of edible fruit plants in terms of trait richness (negative: 29% of the traits; positive: 3.2%) and abundance (negative: 19.3%; positive: 3.2%). In general, we observed that 79.2% of the studied species had at least one reproductive trait that was negatively reduced by increased chronic disturbance and/or aridity in terms of trait richness and abundance. Overall, 75% of the edible fruit species have specialized reproductive strategies that were negatively affected by chronic disturbances and/or aridity. Specifically, individual or combined effects of chronic anthropogenic disturbances or aridity negatively impacted the richness and abundance of specialized reproductive traits such as supra-annual flowering and fruiting patterns and obligatory cross-pollinated edible fruit species. Also, in terms of richness, the reproductive functional diversity of specialized reproductive strategies was negatively affected by increasing aridity. Our findings indicate that in the expected future scenarios of increased land-use and climate change, the Caatinga could face a collapse in the offer of edible fruits to local human communities by impacting the provision of this ecosystem service.

Diet Composition of Bats in a Human-Modified Tropical Landscape

Human-modified landscapes are often composed of small and isolated natural habitat fragments immersed in agricultural and urban matrices. Within them, ecosystem services provided by wildlife, such as pest insect suppression, may decrease or even be lost leading to a substantial increase in agricultural production costs. Pest insect suppression by bats has been identified as an essential ecosystem service but remains poorly investigated. For example, we still lack a basic understanding of the proportion of pest insects that comprises the diet of many bat species. Here, we explored the diet composition of eight Brazilian bat species (78 individuals) in a human-modified landscape through the analysis of stable carbon (13C) and nitrogen (15N) isotopes. Bats were categorised into guilds: open-space aerial insectivores, narrow-space gleaning frugivores, or narrow-space gleaning nectarivores. We divided the insects collected into three groups depending on their δ13C values: forest, mixed, and pest insects. We found that open-space insectivorous bats had the highest proportion of insects in total in their diet — consuming primarily from the forest group (56%) and the pest group (34%). Interestingly, narrow-space gleaning frugivores also consumed pest insects (almost 20%). The narrow-space gleaning nectarivores had traces of insects in their diet, yet the actual proportion was inconclusive. Even though bats were from different guilds, with diets consisting mainly of plants and insects, the δ15N indicated that they fitted to similar trophic levels, as secondary consumers. Therefore, the trophic level of nectarivorous and frugivorous bats showed a more generalist diet than previously assumed. The proportion of forest insects in the diet of open-space aerial insectivores may indicate the importance of small forest patches as food resources for wildlife such as the ones included in human-modified landscapes. The bats' contribution to this ecosystem service could improve the economic conservation value of Neotropical bats in human-modified landscapes.

Tropical land use drives endemic versus exotic ant communities in a global biodiversity hotspot

Understanding how land-use change affects biodiversity is a fundamental step to develop effective conservation strategies in human-modified tropical landscapes. Here, we analyzed how land-use change through tropical small-scale agriculture affects endemic, exotic, and non-endemic native ant communities, focusing on vanilla landscapes in north-eastern Madagascar, a global biodiversity hotspot. First, we compared ant species richness and species composition across seven land-use types: old-growth forest, forest fragment, forest-derived vanilla agroforest, fallow-derived vanilla agroforest, woody fallow, herbaceous fallow, and rice paddy. Second, we assessed how environmental factors drive ant species richness in the agricultural matrix to identify management options that promote endemic and non-endemic native while controlling exotic ant species. We found that old-growth forest, forest fragment, and forest-derived vanilla agroforest supported the highest endemic ant species richness. Exotic ant species richness, by contrast, was lowest in old-growth forest but highest in herbaceous fallows, woody fallows, and rice paddy. Rice paddy had the lowest non-endemic native ant species richness. Ant species composition differed among land-use types, highlighting the uniqueness of old-growth forest in harboring endemic ant species which are more sensitive to disturbance. In the agricultural matrix, higher canopy closure and landscape forest cover were associated with an increase of endemic ant species richness but a decrease of exotic ant species richness. We conclude that preserving remnant forest fragments and promoting vanilla agroforests with a greater canopy closure in the agricultural matrix are important management strategies to complement the role of old-growth forests for endemic ant conservation in north-eastern Madagascar.

Landscape structure shapes the diversity of tree seedlings at multiple spatial scales in a fragmented tropical rainforest.

The maintenance of seedling diversity of animal-dispersed tree species is fundamental for the structure and function of forest patches in fragmented tropical rainforests. Nonetheless, the effects of landscape structure at different spatial scales on α- and β-diversity of tree seedling communities are recently explored. Using a multi-scale approach, we assessed the relative effect of landscape composition and configuration on α- and β-diversity of animal-dispersed seedlings within 16 forest patches in the Lacandona rainforest, Mexico. We assessed these effects at 13 spatial scales (from 300 to 1500 m radius, at 100 m intervals) for three metrics of effective number of species considering α- and β-diversity. We found that α-diversity was largely affected by landscape composition and β-diversity by landscape configuration. On the one hand, the amount of secondary forest influenced α-diversity. Additionally, species richness increased in landscapes with highly aggregated forest patches. On the other hand, β-diversity was affected positively by forest fragmentation and negatively by the edge contrast of forest patches with the surrounding matrix. Our findings indicate that landscape configuration is a strong driver of seedling diversity in highly deforested rainforests. Promoting forest patches and secondary forests through payment for ecosystem services' programs, favoring matrix quality within land-sharing schemes of smallholder agriculture and secondary forest management, and identifying restoration opportunities for assisted or unassisted natural regeneration are urgently needed for conservation of seedling diversity in human-modified tropical landscapes.

Orangutan movement and population dynamics across human-modified landscapes: implications of policy and management

ContextAgricultural expansion is a leading cause of deforestation and habitat fragmentation globally. Policies that support biodiversity and facilitate species movement across farmland are therefore central to sustainability efforts and wildlife conservation in these human-modified landscapes.ObjectivesWe investigated the conservation impact of several potential management scenarios on animal populations and movement in a human-modified tropical landscape, focusing on the critically endangered Bornean orangutan, Pongo pygmaeus.MethodsWe used an individual-based modelling platform to simulate population dynamics and movements across four possible landscape management scenarios for a highly modified oil palm-dominated landscape in Sabah, Malaysian Borneo.ResultsScenarios that maximised the retention of natural forest remnants in agricultural areas through sustainability certification standards supported stable orangutan populations. These populations were up to 45% larger than those supported under development-focused scenarios, where forest retention was not prioritised. The forest remnants served as corridors or stepping-stones, increasing annual emigration rates across the landscape, and reducing orangutan mortality by up to 11%. Sensitivity analyses demonstrated that this outcome was highly contingent on minimising mortality during dispersal.ConclusionsManagement that promotes maximising natural forest cover through certification, such as that promoted by the Roundtable on Sustainable Palm Oil, can maintain viable orangutan populations over the lifespan of an oil palm plantation and facilitate movement among otherwise isolated populations. However, minimising hunting and negative human–orangutan interactions, while promoting peaceful co-existence between apes and people, will be imperative to insure positive conservation outcomes.

Recovery of logged forest fragments in a human-modified tropical landscape during the 2015-16 El Ni\xf1o

The past 40 years in Southeast Asia have seen about 50% of lowland rainforests converted to oil palm and other plantations, and much of the remaining forest heavily logged. Little is known about how fragmentation influences recovery and whether climate change will hamper restoration. Here, we use repeat airborne LiDAR surveys spanning the hot and dry 2015-16 El Niño Southern Oscillation event to measure canopy height growth across 3,300 ha of regenerating tropical forests spanning a logging intensity gradient in Malaysian Borneo. We show that the drought led to increased leaf shedding and branch fall. Short forest, regenerating after heavy logging, continued to grow despite higher evaporative demand, except when it was located close to oil palm plantations. Edge effects from the plantations extended over 300 metres into the forests. Forest growth on hilltops and slopes was particularly impacted by the combination of fragmentation and drought, but even riparian forests located within 40 m of oil palm plantations lost canopy height during the drought. Our results suggest that small patches of logged forest within plantation landscapes will be slow to recover, particularly as ENSO events are becoming more frequent.

Effects of thinning on the demography and functional community structure of a secondary tropical lowland rain forest

Tropical secondary forests play a prominent role in conserving biodiversity and providing ecosystem services, but their recovery can be slow and their succession trajectory is distinct from old-growth forests. Thinning is an essential silvicultural approach to enhance the recovery rate and timber production of forests. However, the selection of trees to thin has been mainly based on size class rather than on species identity. There is little empirical or experimental evidence of species-focused thinning with the goal of altering species composition. We examined the effects of thinning on community structure, demographic rates, species richness and functional diversity of woody plants in a detailed investigation of 60-year-old secondary tropical lowland rain forest on Hainan Island, South China. The density and basal area of trees ≥5 cm DBH (diameter at breast height) increased significantly after five years' recovery with no significant change for saplings (DBH < 5 cm). Species composition after thinning changed significantly and mid-to late-successional species of both saplings and trees were more abundant after five years’ recovery. The relative growth rates (RGR) and recruitment rates were significantly higher in thinning plots for both saplings and trees, and RGRs increased by 127% and 48%, respectively. The mortality rate decreased by 13% for trees and increased by 47% for saplings in thinning plots compared to the control. The community weighted mean (CWM) of the specific leaf area (SLA) of saplings showed a significantly decreasing trend while CWMs of wood density (WD) and mean maximum height (Hmax) of saplings increased after thinning. By contrast, CWMs of SLA and Hmax of trees were significantly higher, but WD was significantly lower- in thinning plots than the control. RGR and recruitment rate of saplings and trees increased significantly as thinning intensity increased. However, the thinning intensity had a weak or nil effect on the mortality rate. Our results support the selective removal and girdling of pioneer and mid-successional species in a way that could accelerate recovery and improve the growth and recruitment of late-successional species in tropical secondary forests. Thinning at a relatively low intensity can maintain species diversity and alter species functional composition. This outcome shows promise for improved future management of tropical forests in human-modified tropical forest landscapes.

Effects of landscape composition and site land-use intensity on secondary succession in a tropical dry forest

Regenerating forests after agricultural land abandonment are increasingly common in human-modified tropical landscapes. These secondary forests preserve biodiversity and provide multiple ecosystem services, but such important roles depend on their recovery rates, which can be difficult to predict. Recovery is expected to occur faster when landscape composition favors seed dispersal to the regenerating site, and when previous land-use does not significantly reduce propagule bank or future plant growth. Here, we test such expectations for the recovery of a Mexican tropical dry forest during secondary succession. For this purpose, we measured several indicators of landscape composition and site land-use intensity in 30 regenerating sites located along gradients of age of abandonment and amount of surrounding forest. Generalized linear models and redundancy analysis were fitted to test if values of four vegetation properties (aboveground biomass, total and dominant species diversity, and species composition) were indicative of such effects. We found evidence that, as expected, species richness recovers faster in sites surrounded by higher forest cover, while aboveground biomass recovers slower as surrounding pasture cover increases. Species composition was also significantly but poorly explained by the interaction between age of abandonment and the amount of forest cover. Contrary to our expectations, we found weak evidence on the impact of site land-use intensity on all vegetation properties, except on the number of dominant species, which showed higher values in sites with higher land-use intensity. Our findings show that landscape context plays a major role in structuring successional plant communities in this tropical dry region, even stronger than site land-use intensity. This seems to be related to the influence of landscape patterns on dispersal and recruitment limitation, but also on the likelihood of further human disturbances. Therefore, conserving landscape quality is paramount to enhance forest recovery and its contribution to the preservation of biodiversity and ecosystem services.

The relative influence of different landscape attributes on dung beetle communities in the Brazilian Atlantic forest

Abstract Land-use change is considered the greatest threat to biodiversity worldwide. As such, identifying the drivers that shape biological communities is crucial for enhancing conservation strategies in human-modified tropical landscapes. We used a hybrid patch-landscape design and a multi model inference approach to assess the relative impacts of forest loss, increased edge density and increased pasture cover on dung beetle functional groups in the Brazilian Atlantic Forest – a biodiversity hotspot. Our findings provide novel empirical evidence showing that edge density can be a major driver for dung beetles when compared to forest and pasture cover at the landscape scale. However, forest and pasture cover also influenced some dung beetle responses, supporting the idea that biological communities are negatively affected by habitat loss and changes in land cover. We found that dung beetle body size, protibia area and metatibia length were all larger in landscapes with increased edge density, reinforcing the need for further studies exploring which mechanisms could favour the presence of larger dung beetles in fragmented tropical landscapes. Taken together, these results suggest the need of conservation and management strategies focused on the protection of the remaining Atlantic Forest fragments, and the promotion of forest recovery and reduction in the pasture cover and edge density at the landscape-level.

Intensive silviculture enhances biomass accumulation and tree diversity recovery in tropical forest restoration.

Maximizing initial aboveground woody biomass (AGB) accumulation in order to obtain early payments for carbon stocking is essential for the financial viability of reforestation programs fostered by climate mitigation efforts. Intensive silviculture, i.e., silviculture traditionally used in commercial forestry to maximize productivity and gains, has recently been advocated as a promising approach to enhance AGB accumulation in restoration plantations. However, this approach may hamper natural forest regeneration and ecological succession due to high competition between colonizing plants and planted trees. We investigated the impacts of different silvicultural treatments applied to restoration plantations with 20 native tree species on AGB accumulation and spontaneous regeneration of native woody species in an experiment set up in the Atlantic Forest of Brazil. Intensive silviculture demonstrated a remarkable potential to enhance AGB accumulation in restoration plantations by increasing up to three times the AGB of tree stands (from ~25 to 75Mg/ha in the 12th year). Intensive fertilization/weed control enhanced AGB accumulation, while higher tree density and the proportion of pioneers did not have a significant effect on AGB over the time. In spite of higher costs (cost increase of 13-19%), the cost-effectiveness for AGB accumulation of intensive silviculture was comparable to that of traditional silviculture applied to restoration (US$50-100/Mg AGB for 3×2m spacing). Contrary to our expectations, we did not find a trade-off between AGB accumulation by planted trees and the spontaneous regeneration of tree species, since intensive silviculture enhanced the regeneration of both planted (total of 12 species) and colonizing woody species (total of 30 species) in the plantation understory. Specifically, a strong association was found between AGB stocks and the abundance and richness of colonizing species, a vast majority of which (90% of species and 95% of individuals) were dispersed by animals. We report a case of positive correlation between AGB stocking and woody species regeneration in the restoration of the Atlantic Forest. Fostering the establishment and maintenance of restoration tree plantations can, in some cases, be a win-win strategy for climate mitigation and biodiversity conservation in human-modified tropical landscapes.

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.

Direct and Cascading Effects of Landscape Structure on Tropical Forest and Non-forest Frugivorous Birds

Global biodiversity is increasingly threatened by land-use change, but the direct and indirect drivers of species diversity in human-modified tropical landscapes are poorly known. Forest-dependent species are expected to be particularly sensitive to changes in landscape composition (e.g., forest loss) and configuration (e.g., increase of forest edges), both directly and indirectly through cascading landscape effects on local patterns of forest structure and resource availability. In contrast, non-forest-dependent species are probably more strongly related to landscape changes than to local forest patterns, as these species are able to use resources not only from the forest, but also from other landscape elements over larger spatial scales. We tested these hypotheses using structural equation modeling. In particular, we sampled 20 landscapes (115 ha each) from the Brazilian Atlantic rainforest to assess the effect of landscape-scale forest cover and amount of forest edges on the diversity of frugivorous birds, both directly and indirectly through the effect that these landscape variables may have on vegetation complexity and fruit biomass. We separately assessed the response of forest-dependent and non-forest-dependent frugivores to infer potential mechanisms underlying bird assemblages in fragmented landscapes. The diversity of forest-dependent birds mainly decreased with the simplification of vegetation complexity in more deforested landscapes, but increased with increasing fruit biomass in more forested landscapes (indirect effects). Both patterns were significant, thus supporting a strong bottom-up control, i.e., local habitat simplification and resource scarcity in highly deforested landscapes limits the maintenance of forest-dependent birds. Conversely, but as expected, non-forest-dependent birds were more strongly and directly related to landscape-scale patterns. In particular, landscapes with higher forest edge amount showed higher bird species diversity, probably because the increasing length of ecotones and interspersion/juxtaposition of different habitat types in landscapes with more forest edges can increase resource availability and foraging efficiency of non-forest-dependent birds. As the seed dispersal services offered by forest-dependent species cannot be ecologically compensated for by the proliferation of non-forest-dependent species, preventing forest loss is imperative to maintain forest-dependent birds and forest regeneration in this vanishing biodiversity hotspot.

Weaker plant-enemy interactions decrease tree seedling diversity with edge-effects in a fragmented tropical forest

In fragmented forests, tree diversity declines near edges but the ecological processes underlying this loss of diversity remain poorly understood. Theory predicts that top-down regulation of seedling recruitment by insect herbivores and fungal pathogens contributes to maintaining tree diversity in forests, but it is unknown whether proximity to forest edges compromises these diversity-enhancing biotic interactions. Here we experimentally demonstrate that weakened activity of fungal pathogens and insect herbivores reduced seedling diversity, despite similar diversity of seed rain, during recruitment near forest edges in a human-modified tropical landscape. Only at sites farthest from forest edges (90–100 m) did the application of pesticides lower seedling diversity relative to control plots. Notably, lower seedling diversity corresponded with weaker density-dependent mortality attributable to insects and fungi during the seed-to-seedling transition. We provide mechanistic evidence that edge-effects can manifest as cryptic losses of crucial biotic interactions that maintain diversity.

Direct and cascading effects of landscape structure on tropical forest and non-forest frugivorous birds.

Global biodiversity is increasingly threatened by land-use change, but the direct and indirect drivers of species diversity in human-modified tropical landscapes are poorly known. Forest-dependent species are expected to be particularly sensitive to changes in landscape composition (e.g., forest loss) and configuration (e.g., increase of forest edges), both directly and indirectly through cascading landscape effects on local patterns of forest structure and resource availability. In contrast, non-forest-dependent species are probably more strongly related to landscape changes than to local forest patterns, as these species are able to use resources not only from the forest, but also from other landscape elements over larger spatial scales. We tested these hypotheses using structural equationmodeling. In particular, we sampled 20 landscapes (115ha each) from the Brazilian Atlantic rainforest to assess the effect of landscape-scale forest cover and amount of forest edges on the diversity of frugivorous birds, both directly and indirectly through the effect that these landscape variables may have on vegetation complexity and fruit biomass. We separately assessed the response of forest-dependent and non-forest-dependent frugivores to infer potential mechanisms underlying bird assemblages in fragmented landscapes. The diversity of forest-dependent birds mainly decreased with the simplification of vegetation complexity in more deforested landscapes, but increased with increasing fruit biomass in more forested landscapes (indirect effects). Both patterns were significant, thus supporting a strong bottom-up control, i.e., local habitat simplification and resource scarcity in highly deforested landscapes limits the maintenance of forest-dependent birds. Conversely, but as expected, non-forest-dependent birds were more strongly and directly related to landscape-scale patterns. In particular, landscapes with higher forest edge amount showed higher bird species diversity, probably because the increasing length of ecotones and interspersion/juxtaposition of different habitat types in landscapes with more forest edges can increase resource availability and foraging efficiency of non-forest-dependent birds. As the seed dispersal services offered by forest-dependent species cannot be ecologically compensated for by the proliferation of non-forest-dependent species, preventing forest loss is imperative to maintain forest-dependent birds and forest regeneration in this vanishing biodiversity hotspot.

Spatial and temporal shifts in functional and taxonomic diversity of dung beetles in a human-modified tropical forest landscape

Functional diversity is commonly used to assess the conservation value of ecosystems, but we have not yet established whether functional and taxonomic approaches are interchangeable or complementary to evaluate community dynamics over time and in response to disturbances. We used a five-year dataset of dung beetles from undisturbed forest, primary forest corridors, and Eucalyptus plantations to compare the sensitivity of conceptually equivalent metrics to temporal variation in different anthropogenic disturbances. We compared species richness with functional richness, Pielou’s evenness with functional evenness, and Simpson’s diversity with Rao’s quadratic entropy. We assessed the sensitivity of the metrics to anthropogenic changes. The indices showed complex patterns among habitat types, with with similar responses in some cases and not in other, and little incongruence between the pairs within the same year. The influence of disturbance on longer-term temporal variation over the five-year period revealed lower temporal variation in functional than taxonomic metrics. Both approaches showed greater variation in plantations compared to native forests. We evaluated the variation in taxonomic and functional metrics between consecutive years and among habitats. Most metrics showed similar shifts between years in all habitats, except for species and functional richness. We demonstrate that even conceptually similar indices may not provide similar information on dung beetles responses to disturbance. However, the differences between the indices can yield key insights about the drivers of change, especially over the long-term. It is important to use taxonomic and functional diversity in tandem to better understand community responses to environmental and anthropogenic changes.