Food plant diversity as broad-scale determinant of avian frugivore richness

Latitudinal specificity of plant-avian frugivore interactions

Broad-scale assessments of plant-frugivore interactions indicate the existence of a latitudinal gradient in interaction specialization. The specificity (i.e. the similarity of the interacting partners) of plant-frugivore interactions could also change latitudinally given that differences in resource availability could favour species to become more or less specific in their interactions across latitudes. Species occurring in the tropics could be more taxonomically, phylogenetically and functionally specific in their interactions because of a wide range of resources that are constantly available in these regions that would allow these species to become more specialized in their resource usage. We used a data set on plant-avian frugivore interactions spanning a wide latitudinal range to examine these predictions, and we evaluated the relationship between latitude and taxonomic, phylogenetic and functional specificity of plant and frugivore interactions. These relationships were assessed using data on population interactions (population level), species means (species level) and community means (community level). We found that the specificity of plant-frugivore interactions is generally not different from null models. Although statistically significant relationships were often observed between latitude and the specificity of plant-frugivore interactions, the direction of these relationships was variable and they also were generally weak and had low explanatory power. These results were consistent across the three specificity measures and levels of organization, suggesting that there might be an interplay between different mechanisms driving the interactions between plants and frugivores across latitudes.

Food resource richness increases seed disperser visitations and seed rain richness

Within the context of global change, seed dispersal research often focuses on changes in disperser communities (i.e., seed dispersers, such as birds, in an area) resulting from habitat fragmentation. This approach may not be completely illustrative due to certain seed disperser communities being more robust to fragmentation. Additionally, this top-down approach overlooks how changing food resources on landscapes impacts resource tracking and, subsequently, seed dispersal. We hypothesized resource tracking may promote diffuse plant-animal dispersal mutualisms if resource richness is positively linked to disperser and seed rain richness. We predicted increasing food resource richness attracts more visits and species of avian dispersers, resulting in higher counts and greater species richness of seeds deposited at sites (i.e., seed rain). We tested this mechanism in two replicated field experiments using a model system with bird feeders positioned above seed traps. In the first experiment, we demonstrated resource presence skews seed rain. In the second experiment, we explored how species richness of food resources (0, 4, 8, or 12 species) affected the species richness and visitation of avian seed dispersers at feeders and in subsequent seed rain. Collectively, we observed a positive relationship between available food resources and seed rain, likely mediated by resource tracking behavior of avian dispersers. Our findings underscore a potential key mechanism that may facilitate ecological diversity, whereby accumulating species richness in the plant community attracts a more diverse seed disperser community and indirectly promotes more species in seed rain. Importantly, the resource tracking mechanism driving this potential positive feedback loop may also result in negative ecosystem effects if global change diminishes resource availability through homogenization processes, such as invasive species colonization. Future research should explore the bottom-up effects of global change on food resources and seed disperser behavior to complement the literature on changing disperser communities.

Species richness and endemism patterns of Sternorrhyncha (Insecta, Hemiptera) in China

One of the main goals in biogeography and ecology is the study of patterns of species diversity and the driving factors in these patterns. However, such studies have not focused on Sternorrhyncha in China, although this region hosts massive species distribution data. Here, based on the 15,450 distribution records of Sternorrhyncha species in China, we analyzed patterns in species richness and endemism at 1° × 1° grid size and determined the effects of environmental variables on these patterns using correlations analysis and the model averaging approach. We found that species richness and endemism of Sternorrhyncha species are unevenly distributed, with high values in the eastern and southeastern coastal regions of mainland China, as well as Taiwan Island. Furthermore, the key factors driving species richness and endemism patterns are inconsistent. Species richness patterns were strongly affected by the normalized difference vegetation index, which is closely related to the feeding habits of Sternorrhyncha, whereas endemism patterns were strongly affected by the elevation range. Therefore, our results indicate that the range size of species should be considered to understand the determinants of species diversity patterns.

Seasonal food preferences and group activity pattern of Blackbuck Antilope cervicapra (L., 1758) (Mammalia: Cetartiodactyla: Bovidae) in a semi-arid region of western Haryana, India

To evaluate food preferences and group activity patterns, a fragmented population of Blackbuck Antilope cervicapra was selected for observation in a semi-arid ecosystem of western Haryana. A field survey was conducted fortnightly, from dawn to dusk, between September 2019 and August 2020, covering every season. Scan sampling and quadrat methods were used to record data on group size and vegetation. Group sizes ranged from 3 to 72 individuals. Based on visual observation, blackbuck seasonally consumed 26 species belonging to 25 families with varied preferences, out of a total of 53 plant species documented from the study site. Some plant species with high medicinal and therapeutic values were preferred, including Artemisia scoparia, Cucumis callous, Ziziphus jujuba, and Ziziphus nummularia. Unlike most herbivores, Blackbuck also consumed the toxic and medicinally rich Calotropis procera. We suggest that zoos which house blackbuck include these preferred wild plant species in their diet. Observations on group activity were analyzed on hourly, monthly and seasonal bases, and converted into time percentages. Group foraging activity was at a maximum in the monsoon (62%) and minimum in winter (50%), followed by resting: maximum in winter (21%) and minimum (12%) in monsoon, largely influenced by food availability. Foraging/walking ratio was at a maximum (5.2) in monsoon and minimum (3.1) in winter, and was correlated with the number of group sightings (maximum in winter and minimum in monsoon) in nearby farmland, when the animals faced food scarcity in their natural habitat and fed on crops. 

Fruit Size and Structure of Zoochorous Trees: Identifying Drivers for the Foraging Preferences of Fruit-Eating Birds in a Mexican Successional Dry Forest

Simple Summary

Tropical dry forests are highly threatened by human activities such as agriculture, livestock, and selective logging. These activities have resulted in fragments of tropical dry forest under different successional stages that negatively affect the interaction between plants and fruit-eating birds. We analyzed the consumption of the fruits of zoochorous trees by birds during the dry season in a tropical dry forest and evaluated whether the horizontal and vertical structure of these trees explains fruit consumption. We also related the bird body mass and fruit size removed from zoochorous trees. We found that the tree structure can influence the visitation of fruit-eating birds, and therefore, the number of fruits consumed as the succession progresses. There was a relationship between fruit sizes and bird body mass in the successional gradient. Our results indicate that structural and fruit traits of zoochorous trees drive foraging preferences of fruit-eating birds, whose interactions in different successional stages can help to reverse the negative effects of fragmentation in tropical dry forests of the study area.

Abstract

Tropical dry forests (TDFs) are affected by land-use changes. These modifications impact their composition and arboreal structure, as well as the availability of food for several bird groups. In this study, we evaluated the foraging preferences in zoochorous trees of fruit-eating birds during the dry season of the year in three successional stages (early, intermediate, and mature) of TDFs in southern Mexico. The fruits of these trees are important in the diet of several birds during the dry season, a period during which food resources are significantly reduced in TDFs. We estimated foliar cover (FC) and foliage height diversity (FHD) of zoochorous trees in 123 circular plots. These variables were recognized as proxies of food availability and tree productivity. Foraging preferences were evaluated at the community level, by frugivore type, and by bird species. We evaluated the effect of the structural variables and the fruit size of zoochorous plants on fruit removal by birds and related the bird body mass and fruit size removed in the successional gradient. A total of 14 zoochorous tree species and 23 fruit-eating bird species were recorded along the successional gradient. Intermediate and mature stages showed greater fruit removal. The birds removed mainly B. longipes fruits across the three successional stages. The FHD and fruit size were important drivers in the selection of zoochorous trees and fruit removal by fruit-eating birds. Fruit size and bird body mass were positively related along the successional gradient. The results suggest that fruit removal by fruit-eating birds in the successional gradient can promote the demographic dynamics of several zoochorous tree species, especially of Bursera spp. along the TDFs.

Plant traits mediate the effects of climate on phytophagous beetle diversity on Mt. Kilimanjaro

Patterns of insect diversity along elevational gradients are well described in ecology. However, it remains little tested how variation in the quantity, quality, and diversity of food resources influence these patterns. Here we analyzed the direct and indirect effects of climate, food quantity (estimated by net primary productivity), quality (variation in the specific leaf area index, leaf nitrogen to phosphorus and leaf carbon to nitrogen ratio), and food diversity (diversity of leaf traits) on the species richness of phytophagous beetles along the broad elevation and land use gradients of Mt. Kilimanjaro, Tanzania. We sampled beetles at 65 study sites located in both natural and anthropogenic habitats, ranging from 866 to 4,550 m asl. We used path analysis to unravel the direct and indirect effects of predictor variables on species richness. In total, 3,154 phytophagous beetles representing 19 families and 304 morphospecies were collected. We found that the species richness of phytophagous beetles was bimodally distributed along the elevation gradient with peaks at the lowest (˜866 m asl) and upper mid-elevations (˜3,200 m asl) and sharply declined at higher elevations. Path analysis revealed temperature- and climate-driven changes in primary productivity and leaf trait diversity to be the best predictors of changes in the species richness of phytophagous beetles. Species richness increased with increases in mean annual temperature, primary productivity, and with increases in the diversity of leaf traits of local ecosystems. Our study demonstrates that, apart from temperature, the quantity and diversity of food resources play a major role in shaping diversity gradients of phytophagous insects. Drivers of global change, leading to a change of leaf traits and causing reductions in plant diversity and productivity, may consequently reduce the diversity of herbivore assemblages.

Quantitative estimates of glacial refugia for chimpanzees (Pan troglodytes) since the Last Interglacial (120,000 BP)

Paleoclimate reconstructions have enhanced our understanding of how past climates have shaped present-day biodiversity. We hypothesize that the geographic extent of Pleistocene forest refugia and suitable habitat fluctuated significantly in time during the late Quaternary for chimpanzees (Pan troglodytes). Using bioclimatic variables representing monthly temperature and precipitation estimates, past human population density data, and an extensive database of georeferenced presence points, we built a model of changing habitat suitability for chimpanzees at fine spatio-temporal scales dating back to the Last Interglacial (120,000 BP). Our models cover a spatial resolution of 0.0467° (approximately 5.19 km² grid cells) and a temporal resolution of between 1000 and 4000 years. Using our model, we mapped habitat stability over time using three approaches, comparing our modeled stability estimates to existing knowledge of Afrotropical refugia, as well as contemporary patterns of major keystone tropical food resources used by chimpanzees, figs (Moraceae), and palms (Arecacae). Results show habitat stability congruent with known glacial refugia across Africa, suggesting their extents may have been underestimated for chimpanzees, with potentially up to approximately 60,000 km² of previously unrecognized glacial refugia. The refugia we highlight coincide with higher species richness for figs and palms. Our results provide spatio-temporally explicit insights into the role of refugia across the chimpanzee range, forming the empirical foundation for developing and testing hypotheses about behavioral, ecological, and genetic diversity with additional data. This methodology can be applied to other species and geographic areas when sufficient data are available.

Ecological and evolutionary significance of primates' most consumed plant families

Angiosperms have been essential components of primate diets for millions of years, but the relative importance of different angiosperm families remains unclear. Here, we assess the contribution and ecological and evolutionary significance of plant families to diets of wild primates by compiling an unprecedented dataset of almost 9000 dietary records from 141 primary sources covering 112 primate species. Of the 205 angiosperm plant families recorded in primate diets, only 10 were consumed by more than half of primate species. Plants of the Moraceae and Fabaceae families were the most widely and frequently consumed, and they likely represent keystone resources for primates. Over 75% of species fed on these two families, and together they made up a median of approximately 13% of primate diets. By analysing the relative proportion of different plant parts consumed, we found that Moraceae was mainly eaten as fruit and Fabaceae as non-fruit parts, with the consumption of these two families not showing a significant phylogenetic signal across primate species. Moraceae consumption was associated with small home range sizes, even though more frugivorous primates tended to have larger home ranges compared to more folivorous species, possibly due to the year-round availability of moraceous fruits and the asynchrony in their phenology. Our results suggest that primates may be intricately and subtly shaped by the plant families that they have consumed over millions of years, and highlight the importance of detailed dietary studies to better understand primate ecology and evolution.

Disentangling the role of environment in cross-taxon congruence of species richness along elevational gradients

Spatial patterns of species richness have been found to be positively associated, a phenom called cross-taxon congruence. This may be explained by a common response to environment or by ecological interactions between taxa. Spatial changes in species richness are related to energy and environmental heterogeneity but their roles in cross-taxon congruence remain poorly explored. Elevational gradients provide a great opportunity to shed light on the underlying drivers of species richness patterns. We study the joint influence of environment and biotic interactions in shaping the cross-taxon congruence of plants and orthopterans species richness, along three elevational gradients in Sierras Grandes, central Argentina. Elevational patterns of species richness of orthopterans and plants were congruent, being temperature the best single predictor of both patterns supporting the energy-related hypotheses. Using a structural equation model, we found that temperature explained plant richness directly and orthopteran richness indirectly via orthopteran abundance. Cross-taxon congruence is likely due to a common response of both taxa to temperature although via different theoretical mechanisms, possibly, range limitations for plants and foraging activity for orthopterans. We disentangled the role of temperature in determining the cross-taxon congruence of plants and orthopterans by showing that a common response to the environment may mask different mechanisms driving the diversity of different taxonomic groups.

Microbiome and environment explain the absence of correlations between consumers and their diet in Bornean microsnails

Classical ecological theory posits that species partition resources such that each species occupies a unique resource niche. In general, the availability of more resources allows more species to co-occur. Thus, a strong relationship between communities of consumers and their resources is expected. However, correlations may be influenced by other layers in the food web, or by the environment. Here we show, by studying the relationship between communities of consumers (land snails) and individual diets (from seed plants), that there is in fact no direct, or at most a weak but negative, relationship. However, we found that the diversity of the individual microbiome positively correlates with both consumer community diversity and individual diet diversity in three target species. Moreover, these correlations were affected by various environmental variables, such as anthropogenic activity, habitat island size, and a possibly important nutrient source, guano runoff from nearby caves. Our results suggest that the microbiome and the environment explain the absence of correlations between diet and consumer community diversity. Hence, we advocate that microbiome inventories are routinely added to any community dietary analysis, which our study shows can be done with relatively little extra effort. Our approach presents the tools to quickly obtain an overview of the relationships between consumers and their resources. We anticipate our approach to be useful for ecologists and environmentalists studying different communities in a local food web.

Direct and plant-mediated effects of climate on bird diversity in tropical mountains

AIM

Although patterns of biodiversity across the globe are well studied, there is still a controversial debate about the underlying mechanisms and their generality across biogeographic scales. In particular, it is unclear to what extent diversity patterns along environmental gradients are directly driven by abiotic factors, such as climate, or indirectly mediated through biotic factors, such as resource effects on consumers.

LOCATION

Andes, Southern Ecuador; Mt. Kilimanjaro, Tanzania.

METHODS

We studied the diversity of fleshy-fruited plants and avian frugivores at the taxonomic level, that is, species richness and abundance, as well as at the level of functional traits, that is, functional richness and functional dispersion. We compared two important biodiversity hotspots in mountain systems of the Neotropics and Afrotropics. We used field data of plant and bird communities, including trait measurements of 367 plant and bird species. Using structural equation modeling, we disentangled direct and indirect effects of climate and the diversity of plant communities on the diversity of bird communities.

RESULTS

We found significant bottom-up effects of fruit diversity on frugivore diversity at the taxonomic level. In contrast, climate was more important for patterns of functional diversity, with plant communities being mostly related to precipitation, and bird communities being most strongly related to temperature.

MAIN CONCLUSIONS

Our results illustrate the general importance of bottom-up mechanisms for the taxonomic diversity of consumers, suggesting the importance of active resource tracking. Our results also suggest that it might be difficult to identify signals of ecological fitting between functional plant and animal traits across biogeographic regions, since different species groups may respond to different climatic drivers. This decoupling between resource and consumer communities could increase under future climate change if plant and animal communities are consistently related to distinct climatic drivers.

Tree diversity effects through a temporal lens: Implications for the abundance, diversity and stability of foraging birds

Tree diversity exerts a strong influence on consumer communities, but most work has involved single time point measurements over short time periods. Describing temporal variation associated with diversity effects over longer time periods is necessary to fully understand the effects of tree diversity on ecological function. We conducted a year-long study in an experimental system in southern Mexico assessing the effects of tree diversity on the abundance and diversity of foraging birds. To this end, we recorded bird visitation patterns in 32 tree plots (21 × 21 m; 12 tree species monocultures, 20 four-species polycultures) every 45 days (n = 8 surveys) and for each plot estimated bird abundance, richness, functional diversity (FD) and phylogenetic diversity (PD). In each case, we reported temporal (intra-annual) variation in the magnitude of tree diversity effects, and calculated the temporal stability of these bird responses. Across surveys, tree diversity noticeably affected bird responses, demonstrated by significantly higher abundance (43%), richness (32%), PD (25%) and FD (25%) of birds visiting polyculture plots compared to monoculture plots, as well as a distinct species composition between plot types. We also found intra-annual variation in tree diversity effects on these response variables, ranging from surveys for which the diversity effect was not significant to surveys where a significant 80% increase (e.g. for bird FD and PD) was observed in polyculture relative to monoculture plots. Notably, tree diversity increased the stability of all bird responses, with polycultures having a greater stability abundance (18%), richness (38%), PD (32%), and FD (35%) of birds visiting tree species polycultures compared to monocultures. These results show that tree diversity not only increases bird visitation to plots, but also stabilizes bird habitat usage over time in ways that could implicate insurance-related mechanisms. Such findings are highly relevant for understanding the long-term effects of plant diversity on vertebrates and the persistence of bird-related ecosystem functions. More work is needed to unveil the ecological mechanisms behind temporal variation in vertebrate responses to tree diversity and their consequences for community structure and function.

Ecological Limits as the Driver of Bird Species Richness Patterns along the East Himalayan Elevational Gradient

Variation in species richness across environmental gradients results from a combination of historical nonequilibrium processes (time, speciation, extinction) and present-day differences in environmental carrying capacities (i.e., ecological limits affected by species interactions and the abundance and diversity of resources). In a study of bird richness along the subtropical east Himalayan elevational gradient, we test the prediction that species richness patterns are consistent with ecological limits using data on morphology, phylogeny, elevational distribution, and arthropod resources. Species richness peaks at midelevations. Occupied morphological volume is roughly constant from low elevations to midelevations, implying that more species are packed into the same space at midelevations compared with low elevations. However, variance in beak length and differences in beak length between close relatives decline with elevation, which is a consequence of the addition of many small insectivores at midelevations. These patterns are predicted from resource distributions: arthropod size diversity declines from low elevations to midelevations, largely because many more small insects are present at midelevations. Weak correlations of species mean morphological traits with elevation also match predictions based on resources and habitats. Elevational transects in the tropical Andes, New Guinea, and Tanzania similarly show declines in mean arthropod size and mean beak length and, in these cases, likely contribute to declining numbers of insectivorous bird species richness along these gradients. The results imply that conditions for ecological limits are met, although historical nonequilibrium processes are likely to also contribute to the pattern of species richness.

Temperature-Dominated Driving Mechanisms of the Plant Diversity in Temperate Forests, Northeast China

Climate, topography, and tree structure have different effects on plant diversity that vary with spatial scale. In this study, we assessed the contribution of these drivers and how they affect the vascular plant richness of different functional groups in a temperate forest ecosystem in Northeast China. We investigated about 0.986 million plants from 3160 sites to quantify the impact of annual mean temperature, sunshine duration, annual precipitation, standard deviation of diameter at breast height, and forest type on richness of vascular plants (total species, tree, treelet, shrub, and herb, separately) using the gradient boosting model. The results show that annual mean temperature had the strongest impact on plant richness. The tree richness peaked at intermediate annual mean temperature and sunshine duration and increased with annual precipitation. The Shannon diversity index and Simpson dominance index increased with annual precipitation and standard deviation of diameter at breast height, decreased with sunshine duration, and peaked at intermediate annual mean temperature and forest type. The total richness and understory richness increased with annual mean temperature and standard deviation of diameter at breast height and peaked at intermediate sunshine duration and annual precipitation. A comprehensive mechanism was found to regulate the plant diversity in forest ecosystems. The relationship between tree richness and annual mean temperature with latitudinal effect could be affected by the differences in number and size of tree individuals, indicating that plant diversity varies with the utilization of energy. The force driving plant richness varied with the functional group due to the different environmental resource requirements and the life history strategies of plants layers.

Influence of phylogenetic structure and climate gradients on geographical variation in the morphology of Mexican flycatcher forests assemblages (Aves: Tyrannidae)

Morphological variation is strongly related to variation in the ecological characteristics and evolutionary history of each taxon. To explore how geographical variation in morphology is related to different climatic gradients and phylogenetic structure, we analyzed the variation of morphological traits (body size, bill, and wing) of 64 species of tyrant flycatchers (Tyrannidae) distributed in Mexico. We measured these morphological traits in specimens from biological collections and related them to the climatic and topographic data of each collection locality. We performed the analyses separately at two levels: (1) the regional level and (2) the assemblage level, which was split into (assemblage I) lowland forests and (assemblage II) highland forests and other vegetation types. We also calculated the phylogenetic structure of flycatchers of each locality in order to explore the influence of climatic variables and the phylogenetic structure on the morphological variation of tyrant flycatchers, by means of linear mixed-effects models. We mapped the spatial variation of the relationship between morphological traits and environmental gradients, taking into account the phylogenetic structure. Important climatic variables explaining the morphological variation were those of temperature ranges (seasonality) and the results suggest that the phylogenetic clustering increases towards the highlands of Sierra Madre Oriental and Sierra Madre del Sur, and the lowlands of Balsas Depression. For the regional level, the spatial distribution of body size showed a pattern coincident with Bergmann's rule, with increasing in size from south to north. In the tropical lowland forests assemblage, body size tend to increase in seasonally dry forests (western Mexico) and decrease in the humid ones (eastern Mexico). In the assemblage of highland forests and other types of vegetation, morphological trait values increased northeast to southwest. Phylogenetic structure helped to explain the variation of morphology at the assemblage level but not at the regional level. The patterns of trait variation in the lowland and highland assemblages suggest that parts of morphological variation are explained both by the climatic gradients and by the lineage relatedness of communities. Overall, our results suggest that morphological variation is best explained by a varied set of variables, and that regression models representing this variation, as well as integrating phylogenetic patterns at different community levels, provide a new understanding of the mechanisms underlying the links among biodiversity, its geographical setting, and environmental change.

Bird species diversity in Altai riparian landscapes: Wood cover plays a key role for avian abundance

AIMS

We aim to understand bird richness and variation in species composition (beta diversity) along a 630 km riparian landscape in the Altai Mountains of China and to test whether vegetation cover is the main explanation of species diversity.

METHODS

We selected nine regions along a gradient of natural vegetation change. Bird surveys and environmental measurements were conducted at 10 points in each of the nine regions. We collected environmental land cover variables such as wood cover (area proportion of trees and shrubs with saplings in habitats; here trees are woody plant with a single trunk and higher than 3 m, shrubs and saplings are distinguished from trees by their multiple trunks and shorter height) and tree cover, and two climate factors which were Annual Mean Temperature (AMT) and Annual Precipitation (AP). We used Liner Regression Models to explore the correlation between bird species richness and environmental variables. We used Sørensen's dissimilarity index to measure birds' beta diversity, and quantified the contribution of environmental variables to this pattern using a Canonical Correspondence Analysis (CCA).

RESULTS

Wood cover was the strongest predictor of overall, insectivore, and omnivore bird richness. Regions with wood cover contained more bird species. Beta diversity was overall high in the studied regions, and turnover components occupied a major part of beta diversity. Wood cover and AP were significant predictors of bird species composition explaining 33.24% of bird beta diversity together.

CONCLUSIONS

Wood vegetation including trees, shrubs, and saplings, rather than only trees, contains high bird richness. High beta diversity suggests that expansion of the existing nature reserves is needed in the riparian landscapes to capture the variation in bird species composition. Thus all wood cover in the overall riparian landscapes of Altai Mountains should be protected from farming and grazing to improve bird conservation outcomes.

OPEN RESEARCH BADGES

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at Raw bird data in this study: osf.io/78qcw; Raw environment data: osf.io/qr5cw.

Inferring processes of coevolutionary diversification in a community of Panamanian strangler figs and associated pollinating wasps

The fig and pollinator wasp obligate mutualism is diverse (∼750 described species), ecologically important, and ancient (∼80 Ma). Once thought to be an example of strict one-to-one cospeciation, current thinking suggests genera of pollinator wasps codiversify with corresponding sections of figs, but the degree to which cospeciation or other processes contribute to the association at finer scales is unclear. Here, we use genome-wide sequence data from a community of Panamanian strangler figs and associated wasp pollinators to estimate the relative contributions of four evolutionary processes generating cophylogenetic patterns in this mutualism: cospeciation, host switching, pollinator speciation, and pollinator extinction. Using a model-based approach adapted from the study of gene family evolution, our results demonstrate the importance of host switching of pollinator wasps at this fine phylogenetic and regional scale. Although we estimate a modest amount of cospeciation, simulations reveal the number of putative cospeciation events to be consistent with what would be expected by chance. Additionally, model selection tests identify host switching as a critical parameter for explaining cophylogenetic patterns in this system. Our study demonstrates a promising approach through which the history of evolutionary association between interacting lineages can be rigorously modeled and tested in a probabilistic phylogenetic framework.

How do fruit productivity, fruit traits and dietary specialization affect the role of birds in a mutualistic network?

Many plant traits might explain the different ecological and network roles of fruit-eating birds. We assessed the relationship of plant productivity, fruit traits (colour, seed size and nutritional quality) and dietary specialization, with the network roles of fruit-eating birds (number of partners, centrality and selectivity) in the Atlantic Forest, Brazil. We classified bird species according to their dietary specialization into three categories: obligate, partial and opportunistic fruit-eating birds. To test if network roles changed according to dietary specialization, fruit productivity and traits, we used a generalized linear model analysis. The selected 14 species of plant interacted with 52 bird species, which consumed 2199 fruits. The most central and generalist fruit-eating bird, Turdus albicolis, interacted with plants that produced more fruits, such as Miconia cinerascens, and had, on average, larger seeds, such as Myrcia splendens. The most selective birds interacted with fruits with a higher concentration of lipids and less intense colour, and plants that produced fewer fruits. Obligate fruit-eating birds, such as Patagioenas plumbea, were more selective than partial and opportunistic birds. Different plant traits are therefore related to the different network roles of fruit-eating birds in the Atlantic Forest, which are also dependent on bird dietary specialization.

Phylogeography and ecological niche modeling unravel the evolutionary history of the Yarkand hare, Lepus yarkandensis (Mammalia: Leporidae), through the Quaternary

Background

The Taklimakan Desert in China is characterized by unique geological and historical dynamics and endemic flora and fauna, but the influence of historical climate oscillations on the evolutionary history of endemic animals is poorly understood. Lepus yarkandensis is an oases-dependent Near Threatened species that lives in fragmented oasis habitats in the Taklimakan Desert, China. We investigated the geological and climatic impacts on its geographical differentiation, demographic history and influence of Pleistocene glacial-interglacial cycles on the evolutionary history of L. yarkandensis. Further, studied the impact of climatic oscillation based modification on phylogeography, distribution and diversification pattern of Yarkand hare by using Cytb (1140 bp), MGF (592 bp) and SPTBN1 (619 bp) markers. Ecological niche modeling (ENM) revealed the evolutionary history of this species in response to climate change during the Quaternary. Paleodistribution modeling was used to identify putative refugia and estimate their historical distributions.

Results

Both historical demographic analyses and climatic niche modeling revealed strong effects of glacial climate changes, suggesting recurrent range contractions and expansions. The EBSP results indicated clear population expansion of L. yarkandensis since the Pleistocene. In the “early Pleistocene”, the demographic expansion continued from 0.83 MYA to the last glacial period. The ENM analysis supported a wide distribution of Lepus yarkandensis at high altitudes during the last interglacial (LIG) period. During the last glacial maximum (LGM), the suitable climate was reduced and restricted to the western part of the Taklimakan Desert.

Conclusions

Inland aridification, oasis evolution and river flow played major roles in the population differentiation and demographic history of Yarkand hares. Historically, the large, continuous oases in the Taklimakan Desert contained a viable and unique population of L. yarkandensis. The fragmented desert environment might have caused low gene flow between individuals or groups, thus leading to predominant genetic differentiation. The Pleistocene climatic cycles triggered the diversification and expansion of this species during cold and warm periods, respectively, leading to multiple colonization events within the Taklimakan Desert. These events might be due to the expansion of the Taklimakan Desert during the Middle Pleistocene. Yarkand hare previously occupied vast areas at low and intermediate altitudes in Xinjiang, Gansu, Shanxi, Henan and Shaanxi Provinces in China. The past aridification, climate change-induced oasis modifications, changes in river volumes and flow directions, and human activities all affected the population demography and phylogeography of the Yarkand hare.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1426-z) contains supplementary material, which is available to authorized users.

Teamwork makes the dream work: Disentangling cross-taxon congruence across soil biota in black pine plantations

Soil plays a fundamental role in many ecological processes, throughout a complex network of above- and below-ground interactions. This has aroused increasing interest in the use of correlates for biodiversity assessment and has demonstrated their reliability with respect to proxies based on environmental data alone. Although co-variation of species richness and composition in forests has been discussed in the literature, only a few studies have explored these elements in forest plantations, which are generally thought to be poor in biodiversity, being aimed at timber production. Based on this premise our aims were 1) to test if cross-taxon congruence across different groups of organisms (bacteria, vascular plants, mushrooms, ectomycorrhizae, mycelium, carabids, microarthropods, nematodes) is consistent in artificial stands; 2) to evaluate the strength of relationships due to the existing environmental gradients as expressed by abiotic and biotic factors (soil, spatial-topographic, dendrometric variables). Correlations between groups were studied with Mantel and partial Mantel tests, while variance partition analysis was applied to assess the relative effect of environmental variables on the robustness of observed relationships. Significant cross-taxon congruence was observed across almost all taxonomic groups pairs. However, only bacteria/mycelium and mushrooms/mycelium correlations remained significant after removing the environmental effect, suggesting that a strong abiotic influence drives species composition. Considering variation partitioning, the results highlighted the importance of bacteria as a potential indicator: bacteria were the taxonomic group with the highest compositional variance explained by the predictors used; furthermore, they proved to be involved in the only cases where the variance attributed solely to the pure effect of biotic or abiotic predictors was significant. Remarkably, the co-dependent effect of all predictors always explained the highest portion of total variation in all dependent taxa, testifying the intricate and dynamic interplay of environmental factors and biotic interactions in explaining cross-taxon congruence in forest plantations.

Influence of Land-Use Type on Forest Bird Community Composition in Mount Kenya Forest

Few studies have explored how human land uses influence and support persistence of forest biodiversity in central Kenya. In the case of the Mount Kenya ecosystem, farmlands and plantation forests are significant land-use types. Using point counts, we assessed bird communities in natural forests, plantation forests, and farmlands in the Nanyuki Forest Block, Western Mount Kenya. Bird point counts were undertaken during two sampling periods (wet and dry season). Compared to farmlands and plantation forest, natural forest had the highest overall avian species richness and relative species richness of all except one forest-dependent foraging guild (granivores) and nonforest species, which occurred frequently only on farmlands. Plantation forest had the lowest relative richness of all avian habitat and foraging guilds. Conversely, specialist forest-dependent species mainly occurred in the structurally complex remnant natural forest. Our study underscores the importance of remnant natural forests for the persistence and conservation of forest biodiversity and risks posed by replacing them with plantation forests and farmlands.

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.

Bird species richness is associated with phylogenetic relatedness, plant species richness, and altitudinal range in Inner Mongolia

Bird species richness is mediated by local, regional, and historical factors, for example, competition, environmental heterogeneity, contemporary, and historical climate. Here, we related bird species richness with phylogenetic relatedness of bird assemblages, plant species richness, topography, contemporary climate, and glacial‐interglacial climate change to investigate the relative importance of these factors. This study was conducted in Inner Mongolia, an arid and semiarid region with diverse vegetation types and strong species richness gradients. The following associated variables were included as follows: phylogenetic relatedness of bird assemblages (Net Relatedness Index, NRI), plant species richness, altitudinal range, contemporary climate (mean annual temperature and precipitation, MAT and MAP), and contemporary‐Last Glacial Maximum (LGM) change in climate (change in MAT and change in MAP). Ordinary least squares linear, simultaneous autoregressive linear, and Random Forest models were used to assess the associations between these variables and bird species richness across this region. We found that bird species richness was correlated negatively with NRI and positively with plant species richness and altitudinal range, with no significant correlations with contemporary climate and glacial–interglacial climate change. The six best combinations of variables ranked by Random Forest models consistently included NRI, plant species richness, and contemporary‐LGM change in MAT. Our results suggest important roles of local ecological factors in shaping the distribution of bird species richness across this semiarid region. Our findings highlight the potential importance of these local ecological factors, for example, environmental heterogeneity, habitat filtering, and biotic interactions, in biodiversity maintenance.

Low Levels of Fruit Nitrogen as Drivers for the Evolution of Madagascar's Primate Communities

The uneven representation of frugivorous mammals and birds across tropical regions - high in the New World, low in Madagascar and intermediate in Africa and Asia - represents a long-standing enigma in ecology. Several hypotheses have been proposed to explain these differences but the ultimate drivers remain unclear. Here, we tested the hypothesis that fruits in Madagascar contain insufficient nitrogen to meet primate metabolic requirements, thus constraining the evolution of frugivory. We performed a global analysis of nitrogen in fruits consumed by primates, as collated from 79 studies. Our results showed that average frugivory among lemur communities was lower compared to New World and Asian-African primate communities. Fruits in Madagascar contain lower average nitrogen than those in the New World and Old World. Nitrogen content in the overall diets of primate species did not differ significantly between major taxonomic radiations. There is no relationship between fruit protein and the degree of frugivory among primates either globally or within regions, with the exception of Madagascar. This suggests that low protein availability in fruits influences current lemur communities to select for protein from other sources, whereas in the New World and Old World other factors are more significant in shaping primate communities.

Molecular genetic analysis of two native desert palm genera, Washingtonia and Brahea, from the Baja California Peninsula and Guadalupe Island

The complex geological and ecological processes that have generated high levels of biodiversity and endemism in the Baja California Peninsula have been the subject of intensive study. However, relatively little is known about phylogeography of the iconic endemic palm species of this region. We therefore analyzed a total of 2,294 bp of chloroplast and 738 bp of nuclear sequence data in 169 samples of five native palm species from Baja California, Sonora and Guadalupe Island. We found that Washingtonia and Brahea palms had low levels of genetic diversity and were highly structured, with the majority of species and major geographic regions being characterized by distinct haplotypes. We also found strong support for currently recognized species in Washingtonia, but our results were less clear cut for Brahea due to haplotype sharing. Furthermore, patterns of population structure were broadly consistent with historical vicariant events such as the inundation of the Isthmus of La Paz, the formation of the Sea of Cortez, and the more recent colonization and isolation of Guadalupe Island's palms. Our findings contribute toward a growing appreciation of the complexity of plant responses to past geological changes and also provide valuable baseline genetic data on relict American palm species.

Land use history and population dynamics of free-standing figs in a maturing forest

Figs (Ficus sp.) are often considered as keystone resources which strongly influence tropical forest ecosystems. We used long-term tree-census data to track the population dynamics of two abundant free-standing fig species, Ficus insipida and F. yoponensis, on Barro Colorado Island (BCI), a 15.6-km2 island in Lake Gatún, Panama. Vegetation cover on BCI consists of a mosaic of old growth (>400 years) and maturing (about 90-150 year old) secondary rainforest. Locations and conditions of fig trees have been mapped and monitored on BCI for more than 35 years (1973-2011), with a focus on the Lutz Catchment area (25 ha). The original distribution of the fig trees shortly after the construction of the Panama Canal was derived from an aerial photograph from 1927 and was compared with previous land use and forest status. The distribution of both fig species (~850 trees) is restricted to secondary forest. Of the original 119 trees observed in Lutz Catchment in 1973, >70% of F. insipida and >90% of F. yoponensis had died by 2011. Observations in other areas on BCI support the trend of declining free-standing figs. We interpret the decline of these figs on BCI as a natural process within a maturing tropical lowland forest. Senescence of the fig trees appears to have been accelerated by severe droughts such as the strong El Niño event in the year 1982/83. Because figs form such an important food resource for frugivores, this shift in resource availability is likely to have cascading effects on frugivore populations.

Functional traits reveal the expansion and packing of ecological niche space underlying an elevational diversity gradient in passerine birds

Variation in species richness across environmental gradients may be associated with an expanded volume or increased packing of ecological niche space. However, the relative importance of these alternative scenarios remains unknown, largely because standardized information on functional traits and their ecological relevance is lacking for major diversity gradients. Here, we combine data on morphological and ecological traits for 523 species of passerine birds distributed across an Andes-to-Amazon elevation gradient. We show that morphological traits capture substantial variation in species dietary (75%) and foraging niches (60%) when multiple independent trait dimensions are considered. Having established these relationships, we show that the 14-fold increase in species richness towards the lowlands is associated with both an increased volume and density of functional trait space. However, we find that increases in volume contribute little to changes in richness, with most (78%) lowland species occurring within the range of trait space occupied at high elevations. Taken together, our results suggest that high species richness is mainly associated with a denser occupation of functional trait space, implying an increased specialization or overlap of ecological niches, and supporting the view that niche packing is the dominant trend underlying gradients of increasing biodiversity towards the lowland tropics.

Modularity in ecological networks between frugivorous birds and congeneric plant species

Ecological and evolutionary factors influence the presence of modules in species interaction networks, and these modules usually cluster functional similar species. But whether closely related species form modules is still unknown. We tested whether the interaction networks formed by frugivorous birds and Miconia plants are modular and evaluated how modules were divided. To do so, we gathered from the literature data concerning four networks of Miconia and their frugivorous birds (three from Brazilian savanna and one from a rain forest in Panama). We quantified modularity using binary and weighted algorithms and also tested the relationship between bird traits (body mass, dietary specialization, migratory behaviour and phylogeny) in relation to within- and among-module connectivity indices (c and z values). If considering only binary information, networks did not present distinct modular structure. Nevertheless, by including interaction strength, modules can be detected in all four Miconia-bird networks. None of the bird traits, however, was related with the connectivity indices. The possible fluctuation of frugivorous bird abundance coupled with the asynchronic fruiting period of Miconia might favour the formation of temporal modules comprising birds and plant species with phenological overlap, ensuring seed dispersal and facilitating the coexistence in sympatry. Bird traits had little effect on the role that each species plays within the modular network, probably because the frugivorous assemblages were dominated by small-bodied and opportunistic species.

Disentangling effects of abiotic factors and biotic interactions on cross-taxon congruence in species turnover patterns of plants, moths and beetles

High cross-taxon congruence in species diversity patterns is essential for the use of surrogate taxa in biodiversity conservation, but presence and strength of congruence in species turnover patterns, and the relative contributions of abiotic environmental factors and biotic interaction towards this congruence, remain poorly understood. In our study, we used variation partitioning in multiple regressions to quantify cross-taxon congruence in community dissimilarities of vascular plants, geometrid and arciinid moths and carabid beetles, subsequently investigating their respective underpinning by abiotic factors and biotic interactions. Significant cross-taxon congruence observed across all taxon pairs was linked to their similar responses towards elevation change. Changes in the vegetation composition were closely linked to carabid turnover, with vegetation structure and associated microclimatic conditions proposed causes of this link. In contrast, moth assemblages appeared to be dominated by generalist species whose turnover was weakly associated with vegetation changes. Overall, abiotic factors exerted a stronger influence on cross-taxon congruence across our study sites than biotic interactions. The weak congruence in turnover observed particularly between plants and moths highlights the importance of multi-taxon approaches based on groupings of taxa with similar turnovers, rather than the use of single surrogate taxa or environmental proxies, in biodiversity assessments.