Showing papers in "Biotropica in 2021"

Human perturbations reduce dung beetle diversity and dung removal ecosystem function

Abstract: Biodiversity drives ecological functioning, ultimately providing ecosystem services. Ecosystem processes are favored by greater functional diversity, particularly when groups of functionally different species interact synergistically. Many of such functions are performed by insects, among which dung beetles stand out for their important role in dung decomposition. However, anthropogenic disturbances are negatively affecting their ecological dynamics and ecosystem services. We conducted a manipulative field study to evaluate the effect of human disturbance on dung beetle diversity (abundance, species richness, and functional group richness) and dung removal rates, comparing perturbed and conserved forests in three regions of Colombia (Caribbean, Andes, and Amazon). We also assess the relationship between dung beetle diversity and dung removal rates. Dung beetle diversity was assessed using pitfall traps, and specimens were measured and assigned to functional groups according to body size and dung relocation strategy. We used exclusion control units and experimental units to assess dung degradation with and without dung beetle activity and evaluate differences in removal rates between two dung removal strategies: paracoprids and telecoprids. Dung removal rates, abundance, and functional group richness were lower in perturbed forests compared to conserved forests. Dung removal increased with abundance, species richness, and functional group richness. Moreover, dung removal performed by telecoprids increased with species richness of telecoprids and paracoprids. Our results evidence a negative effect of human perturbation on dung beetle richness, abundance, and dung removal rates, and also that dung beetle diversity and functional group richness enhance dung removal rates. Abstract in Portuguese is available with online material.

It is not just about time: Agricultural practices and surrounding forest cover affect secondary forest recovery in agricultural landscapes

Abstract: Natural regeneration of forests has significantly led to increased native forest cover in some regions. Several studies have explored the spatial drivers of forest cover increase, yet little is known about their effects on forest structure and species richness and diversity. We quantified the effects of local (forest age, remnant Eucalyptus basal area, slope, soil fertility, and clay content) and landscape drivers (surrounding land use, distance from streams, and surrounding forest cover and its change over time) on the aboveground biomass, species density, and phylogenetic diversity of native trees in second-growth forests. We sampled 44 naturally regenerating forests established on former pastures and abandoned Eucalyptus plantations for 11–46 years in agricultural landscapes of the southeastern Atlantic Forest, Brazil. We used generalized linear mixed effect models to quantify the effect drivers on forest attributes. While only Eucalyptus basal area and proximity to sugarcane plantations had a consistent negative effect on forest biomass, other drivers were among the best models to explain forest attributes, but their effect was variable. Age increased tree biomass but the effect was not consistent. Similarly, species richness and phylogenetic diversity were mainly affected by landscape drivers such as surrounding forest cover. In tropical agricultural landscapes, effective forest recovery requires more than just time, as forest age can be less important in determining forest attributes than human land uses and surrounding native forest cover. Crucially, forest recovery can be improved through interventions and policies that promote less impactful human activities and enhance existing forest cover. Abstract in Portuguese is available with online material.

On the floristic identity of Amazonian vegetation types

Abstract: The Amazon forest is far from uniform, containing different forest types and even savannas, but quantitative analyses of this variation are lacking. Here, we applied ordination analyses to test the floristic differentiation among Amazonian vegetation types using data for virtually all known tree species occurring in the Amazon (8224), distributed across 1584 sites. We also performed multiple regressions to assess the role of climate and substrate in shaping continental‐scale patterns of community composition across Amazonia. We find that the traditional classification of Amazonian vegetation types is consistent with quantitative patterns of tree species composition. High elevation and the extremes of substrate‐related factors underpin the floristic segregation of environmentally “marginal” vegetation types and terra firme forests with climatic factors being relatively unimportant. These patterns hold at continental scales, with sites of similar vegetation types showing higher similarity between them regardless of geographic distance, which contrasts with the idea of large‐scale variation among geographic regions (e.g., between the Guiana Shield and southwestern Amazon) representing the dominant floristic pattern in the Amazon. In contrast to other tropical biomes in South America, including the Mata Atlântica (second largest rain forest biome in the neotropics), the main floristic units in the Amazon are not geographically separated, but are edaphically driven and spatially interdigitated across Amazonia. Two thirds of terra firme tree species are restricted to this vegetation type, while among marginal vegetation types, only white‐sand forests (campinaranas) have a substantial proportion of restricted species, with other vegetation types sharing large numbers of species.

The mechanical stability of the world’s tallest broadleaf trees

Abstract: The factors that limit the maximum height of trees, whether ecophysiological or mechanical, are the subject of longstanding debate. Here, we examine the role of mechanical stability in limiting tree height and focus on trees from the tallest tropical forests on Earth, in Sabah, Malaysian Borneo, including the recently discovered tallest tropical tree, a 100.8 m Shorea faguetiana named Menara. We use terrestrial laser scans, in situ strain gauge data and finite element simulations, to map the architecture of tall tropical trees and monitor their response to wind loading. We demonstrate that a tree's risk of breaking due to gravity or self‐weight decreases with tree height and is much more strongly affected by tree architecture than by material properties. In contrast, wind damage risk increases with tree height despite the larger diameters of tall trees, resulting in a U‐shaped curve of mechanical risk with tree height. Our results suggest that the relative rarity of extreme wind speeds in north Borneo may be the reason it is home to the tallest trees in the tropics. Abstract in MALAY is available with online material.

Shade tree traits and microclimate modifications: Implications for pathogen management in biodiverse coffee agroforests

Abstract: Diversified coffee agroforests modify microclimate conditions in comparison with monocultures, impacting the success of significant plant pathogens, such as Hemileia vastatrix, which causes coffee leaf rust (CLR). However, research is often limited to the dichotomous analysis of shaded agroforestry systems or unshaded monocultures, often overlooking the nuanced effect of shade tree trait diversity. Our study aims to determine the cumulative effects of shade tree canopy architectural characteristics and leaf functional traits in biodiverse agroforests on microclimate modifications and CLR incidence. We measured plot-level microclimate conditions (air temperature, relative humidity, leaf wetness duration, throughfall kinetic energy) in three single-stratum and two double-strata shade tree canopy treatments, including Erythrina poeppigiana, Terminalia amazonia, and Chloroleucon eurycyclum. Commonly reported canopy characteristics and leaf traits were compared to average microclimate conditions and CLR incidence levels. We found that shade tree trait expression significantly explained most microclimate conditions, and that two key shade tree traits (canopy openness, leaf area) significantly explain CLR incidence levels (R2 = 0.211, p = 0.036). Our results highlight the differences in microclimate conditions and CLR incidence among biodiverse agroforests, as well as the important explanatory power of shade tree traits. Specific effects of shade tree traits on pathogen dynamics can directly inform agroforestry system design (i.e., shade tree species selection) and sustainable coffee farm management practices (i.e., pruning practices).

A meta‐analysis of tropical land‐use change effects on the soil microbiome: Emerging patterns and knowledge gaps

Abstract: Modifications to vegetation and soil due to changes in land use have the potential to alter the soil microbiome, with consequences for carbon and nutrient cycling. Despite the important function of soil microorganisms, little is known about their response to land‐use change, especially in tropical regions where current rates of land conversion are greatest. The aim of this meta‐analysis was to examine how land‐use change influences soil microbial properties in tropical ecosystems and to identify current trends and knowledge gaps in the literature. We identified 83 published paired studies that reported data on microbial biomass, abundance, composition, and enzyme activity under representative land‐use changes in the tropics. We calculated response ratios for studies that compared the following: reference forests to (a) agriculture, (b) pastures, (c) plantations, and (d) secondary forests. Soil microbial biomass decreased with forest conversion to agriculture and plantations. Microbial biomass response to land‐use change depended on rainfall classes, although this was the only microbial variable which had sufficient data to test for a rainfall effect. Microbial abundance and enzyme activity showed variable results depending on the type of forest conversion. Microbial diversity and richness did not show any pattern with forest conversion or recovery to secondary forests. Published studies were not representative of the range of biophysical conditions observed in the tropics. Sites in moist regions in the American tropics were overrepresented. To better predict how land‐use change affects the soil microbiome and its contribution to nutrient cycling, research should reflect observed environmental variation in the tropics. Abstract in Spanish is available with online material.

Habitat structure mediates vulnerability to climate change through its effects on thermoregulatory behavior

Abstract: Tropical ectotherms are thought to be especially vulnerable to climate change because they are thermal specialists, having evolved in aseasonal thermal environments. However, even within the tropics, habitat structure can influence opportunities for behavioral thermoregulation. Open (and edge) habitats likely promote more effective thermoregulation due to the high spatial heterogeneity of the thermal landscape, while forests are thermally homogenous and may constrain opportunities for behavioral buffering of environmental temperatures. Nevertheless, the ways in which behavior and physiology interact at local scales to influence the response to climate change are rarely investigated. We examined the thermal ecology and physiology of two lizard species that occupy distinct environments in the tropics. The brown anole lizard (Anolis sagrei) lives along forest edges in The Bahamas, whereas the Panamanian slender anole (Anolis apletophallus) lives under the canopy of mature forests in Panama. We combined detailed estimates of environmental variation, thermoregulatory behavior, and physiology to model the vulnerability of each of these species. Our projections suggest that forest-dwelling slender anoles will experience severely reduced locomotor performance, activity time, and energy budgets as the climate warms over the coming century. Conversely, the forest-edge-dwelling brown anoles may use behavioral compensation in the face of warming, maintaining population viability for many decades. Our results indicate that local habitat variation, through its effects on behavior and physiology, is a major determinant of vulnerability to climate change. When attempting to predict the impacts of climate change on a given population, broad-scale characteristics such as latitude may have limited predictive power.

Long‐term monitoring of seed dispersal by Asian elephants in a Sundaland rainforest

Abstract: Elephants have profound effects on the functioning of the ecosystems they inhabit. Little is known, however, about the role of Asian elephants (Elephas maximus) as agents of seed dispersal in tropical rainforests of Southeast Asia, particularly in the Sundaland region. Sundaic forests are peculiar in their phenology, with supra-annual and highly irregular episodes of mast fruiting. Here I present a long-term (73-month) monitoring of the seeds dispersed by elephants in dipterocarp forests of northern Peninsular Malaysia. I conducted monthly dung surveys in two mineral licks (11.3 km apart) frequently visited by elephants. Additionally, I recorded haphazard observations of seeds and seedlings in elephant dung. I recorded a minimum of 45 morphospecies from at least 25 plant families dispersed by elephants. Elephant seed dispersal varies spatially, with only 39.4% of the morphospecies dispersed at both sites (Jaccard dissimilarity index = 0.45). Temporally, elephants dispersed seeds in sporadic pulses in terms of abundance and diversity, without any apparent seasonality (seeds appeared in 19.1 % of 1,284 dung piles and 49.3 % of 73 months sampled). Around 14 morphospecies exhibited the two types of megafaunal syndrome traits defined by Guimaraes et al. (2008). However, another 11 morphospecies were found to conform to a Type 3 trait; species with large fruits and moderately large (> 1.5 cm) seeds in moderately large numbers (> 15). This makes the total of 24 morphospecies exhibiting megafaunal syndrome traits. However, the current definition is over simplified, and a new definition is needed that expands beyond physical fruit traits. Over half (53%) of the plants dispersed by elephants exhibit the megafaunal dispersal syndrome, suggesting a higher level of specialized elephant-plant seed dispersal interactions than previously assumed in Asia. Sundaland’s forests are undergoing a rapid loss of their rich megafaunal assemblages, with profound and long-term consequences for their function.

Detecting aquatic and terrestrial biodiversity in a tropical estuary using environmental DNA

Abstract: Estuaries are characterized by a tidal regime and are strongly influenced by hydrodynamics and host diverse and highly dynamic habitats, from fresh, brackish, or saltwater to terrestrial, whose biodiversity is especially difficult to monitor. Here, we investigated the potential of environmental DNA (eDNA) metabarcoding, with three primer sets targeting different regions of the mitochondrial DNA 12S ribosomal RNA gene, to detect vertebrate diversity in the estuary of the Don Diego River in Colombia. With eDNA, we detected not only aquatic organisms, including fishes, amphibians, and reptiles, but also a large diversity of terrestrial, arboreal, and flying vertebrates, including mammals and birds, living in the estuary surroundings. Further, the eDNA signal remained relatively localized along the watercourse. A transect from the deep outer section of the estuary, across the river mouth toward the inner section of the river, showed marked taxonomic turnover from typical marine to freshwater fishes, while eDNA of terrestrial and arboreal species was mainly found in the inner section of the estuary. Our results indicate that eDNA enables the detection of a large diversity of vertebrates and could become an important tool for biodiversity monitoring in estuaries, where water integrates information across the ecosystem. Abstract in Spanish is available with online material.

Upward shifts in elevational limits of forest and grassland for Mexican volcanoes over three decades

Abstract: Global climates have been warming over the past four decades, with many implications and effects on species and natural communities, in terms of shifts in geographic and elevational ranges. Nonetheless, major knowledge gaps exist, particularly for tropical regions, as regards the timescale and rate of range shifts. We used Landsat imagery to characterize the upper limits of forest and of bunch grassland on the 15 highest (>3500 m) volcanoes of central Mexico over three decades (1986–2018), and documented upward vegetation shifts averaging >490 m in elevation over this period. Treelines showed upward shifts averaging 17.3 m/year over 1986–2018; for one eastern Mexican volcano (Sierra Negra), the NDVI‐based rate (35.7 m/year) contrasts dramatically with a rate of 4.5 m/year measured over the preceding century for that volcano based on comparisons of photographs. These upward elevational shifts imply areal reductions for high‐elevation habitats, and particularly for the bunch grassland that is the focus of considerable local endemism. Abstract in Spanish is available with online material.

Phylogenetic and ecological correlates of pollen morphological diversity in a Neotropical rainforest

Abstract: Morphology varies enormously across clades, and the morphology of a trait may reflect ecological function or the retention of ancestral features. We examine the tension between ecological and phylogenetic correlates of morphological diversity through a case study of pollen grains produced by angiosperms in Barro Colorado Island, Panama (BCI). Using a molecular phylogeny of 730 taxa, we demonstrate a statistically significant association between morphological and genetic distance for these plants. However, the relationship is non‐linear, and while close relatives share more morphological features than distant relatives, above a genetic distance of ~ 0.7 increasingly distant relatives are not more divergent in phenotype. The pollen grains of biotically pollinated and abiotically pollinated plants overlap in morphological space, but certain pollen morphotypes and individual morphological traits are unique to these pollination ecologies. Our data show that the pollen grains of biotically pollinated plants are significantly more morphologically diverse than those of abiotically pollinated plants.

Functional redundancy of Amazonian dung beetles confers community-level resistance to primary forest disturbance

Abstract: Tropical forest biodiversity is being threatened by human activities, and species losses during forest disturbance can compromise important ecosystem functions and services. We assessed how species losses due to tropical forest disturbance affect community functional structure, using Amazonian dung beetles as a model group. We collected empirical data from 106 forest transects and used simulated extinction scenarios to determine how species loss influences community structure at regional and local scales. Although functional and taxonomic community metrics were largely unaffected by primary forest disturbance, they differed markedly between primary and secondary forests. However, our extinction scenarios demonstrated scale-dependence of species losses, whereby functional structure only eroded with species extinction at the local scale. Hence, we extend the spatial insurance hypothesis by demonstrating that landscape-scale functional redundancy offsets the impact of local species losses and confers community-level resistance to primary forest disturbance.

Fostering local involvement for biodiversity conservation in tropical regions: Lessons from Madagascar during the COVID-19 pandemic.

Abstract: Tropical ecosystems host a large proportion of global biodiversity and directly support the livelihoods of many of the world's poorest, and often marginalized, people through ecosystem goods and services and conservation employment. The coronavirus pandemic has challenged existing conservation structures and management but provides an opportunity to re-examine strategies and research approaches across the tropics to build resilience for future crises. Based on the personal experiences of conservation leaders, managers, and researchers from Madagascar during this period, we discuss the coping strategies of multiple biodiversity conservation organizations during the coronavirus pandemic. We highlight the vital role of local communities in building and maintaining resilient conservation practices that are robust to global disruptions such as the COVID-19 crisis. We argue that the integration of local experts and communities in conservation, research, and financial decision-making is essential to a strong foundation for biodiversity conservation in developing countries to stand up to future environmental, political, and health crises. This integration could be achieved through the support of training and capacity building of local researchers and community members and these actions would also enhance the development of strong, equitable long-term collaborations with international communities. Equipped with such capacity, conservationists and researchers from these regions could establish long-term biodiversity conservation strategies that are adapted to local context, and communities could flexibly balance biodiversity and livelihood needs as circumstances change, including weathering the isolation and financial challenges of local or global crises.

Arboreal monkeys facilitate foraging of terrestrial frugivores

Abstract: in Spanish is available with online material. K E Y W O R D S attraction, camera trapping, eavesdropping, GPS tracking, interspecific associations, Panama, tropical forest | 1687 HAVMØLLER Et AL. of semideciduous tropical lowland forest located in the Panama Canal (9°09’N, 79°51’W; for a full description see (Leigh, 1999). The study took place over two seasons from June 2015 to April 2016 and June 2017 to April 2018. During the period December– March a single tree species, Dipteryx oleifera (hereafter Dipteryx), produces the majority of the food resources available to the frugivore community (Wright & Calderón, 2006; De Steven and Putz 1984). Sixteen species of mammals have been recorded to eat Dipteryx fruits at this study site, with the majority being arboreal or aerial (Bonaccorso et al., 1980). Great fruiteating bats (Artibeus lituratus) and other large fruit bats are thought to be the main dispersers of Dipteryx, carrying fruits up to hundreds of meters away from the parent tree (Bonaccorso et al., 1980). Collared peccaries (Pecari tajacu) and several species of rodents (e.g., redtailed squirrel [Sciurus granatensis], Central American agouti [Dasyprocta punctata], and Tome's spiny rat [Proechimys semispinosus]) have been recorded feeding on Dipteryx seeds, primarily after they have fallen to the ground (Bonaccorso et al., 1980). In contrast, primates (whitefaced capuchins [Cebus capucinus], blackhanded spider monkeys [Ateles geoffroyi] and mantled howler monkeys [Alouatta palliata]) are arboreal and feed exclusively on the pulp of Dipteryx fruit (Bonaccorso et al., 1980). Kinkajous (Potus flavus) and whitenosed coati (Nasua narica) also only feed on the pulp, with kinkajous feeding arboreally (Bonaccorso et al., 1980) while coatis mainly feed on the ground (Kaufmann, 1962). In this study we focused on four species of frugivores that rely heavily on seasonally available Dipteryx fruit, which has been found to constitute more than 75% of feeding times for these four species during this period: two species of arboreal frugivores— capuchin and spider monkeys— and two species of terrestrial frugivores— agoutis and coatis (unpublished data from Davis, Crofoot, Kays, Hirsh; Gompper, 1996; Kaufmann, 1962). The importance of this resource is illustrated by the fact that they experience dieoffs during years where Dipteryx fails to produce fruit (De Steven and Putz 1984; Wright et al., 1999). Three of our study species are social with capuchin monkeys living in stable social groups that travel together as a cohesive unit. We tracked a single capuchin per group (eight groups over the two years, six unique groups) and considered the movements of these individuals as representative of their entire social unit following (Crofoot et al., 2008). A single community of spider monkeys inhabits our study site, and members of this community engage in highly dynamic and flexible patterns of subgrouping (Campbell, 2004). The movements of the eight spider monkeys we tracked were treated as independent, although due to their fissionfusion dynamics, these individuals sometimes travelled together. Finally, coati males and females differ in their social behavior with females travelling as part of stable and cohesive social groups and males living solitarily through most of the annual cycle, but joining groups during the mating season (Gompper & Krinsley, 1992; Hirsch & Gompper, 2017). We tracked 6 male and 10 female coatis belonging to seven unique groups. As with capuchins, the movements of collared female coatis were considered as representative of their group. Agoutis live in pairs with varying degrees of social interactions depending on season and food F I G U R E 1 Schematic of methods used (1) Fruit fall traps: What percentage of fruits are partially eaten by arboreal frugivores? (2) Camera traps: Do terrestrial frugivores stay longer at fruit trees when monkeys are overhead? (3) Acoustic playback experiments: Are terrestrial frugivores attracted to monkey sounds? (4) GPS collars: Who initiates interactions? Do coatis spend more time near fruit trees when monkeys present? Do monkeys and coatis meet more than expected by chance?