Decay of interspecific avian flock networks along a disturbance gradient in Amazonia

Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.     

Forest structure predicts species richness and functional diversity in Amazonian mixed-species bird flocks

Secondary forest has the potential to act as an important habitat for biodiversity and restoring ecological benefits. Functional diversity, which includes morphological and behavioral traits that mediate species interactions with the surrounding environment, relates to the resilience of ecosystems. To assess the relationship between habitat structural differences in primary and secondary forest and the resultant differences in functional diversity of avian species, we followed 11 mixed-species flocks at the Biological Dynamics of Forest Fragments Project, near Manaus, Brazil. We used remote sensing LiDAR to assess which three-dimensional forest structural features are most closely associated with variation in species richness and functional diversity in secondary and primary tropical forest flocks. The species richness of flocks in primary forest increased in areas with higher elevation and higher leaf area density in the understory and subcanopy but was not correlated with habitat structure in secondary forest. Functional diversity increased at lower elevations and with a denser subcanopy in both primary forest and secondary forest but only increased with greater understory leaf area density in primary forest. Together, these results indicate that a dense subcanopy and understory can be important for mixed-species flocks and that flock richness and functional diversity can be predicted by vegetation structure.     

Edge effect and structure of mixed-species bird flocks in an Afrotropical lowland forest

Avian mixed-species flocks are a dominant feature of tropical moist forests, yet their cost–benefit balance and habitat dependence in Africa are not fully documented. We recorded the composition of mixed-species bird flocks in a pristine Afrotropical lowland forest site in Salonga NP, DRC. Our data showed that at least four types of flock existed, one of which specialized on edge habitats. We used multivariate analyses to further characterize edge effect on the most documented mixed-species flock type and found a significant effect on flock composition. While neither species guild nor preferential foraging stratum played an important role in flock participation, the nucleus role was played by a different species at the edge and in the interior, and both species abundance and associations were habitat-dependant, suggesting “domino effects” on the structure of mixed-species flocks.     

Elevation‐related climatic factors dominate soil free‐living nematode communities and their co‐occurrence patterns on Mt. Halla,South Korea

Nematodes play vital roles in soil ecosystems. To understand how their communities and coexistence patterns change along the elevation as well as to determine the best explanatory factors underlying these changes, we investigated free‐living soil nematodes on Mt. Halla, South Korea, using an amplicon sequencing approach targeting the 18S rRNA gene. Our results showed that there was significant variation in the community diversity and composition of soil nematodes in relation to elevation. The network interactions between soil nematodes were more intensive at the lower elevations. Climatic variables were responsible explaining the elevational variation in community composition and co‐occurrence pattern of the nematode community. Our study indicated that climatic factors served as the critical environmental filter that influenced not only the community structure but also the potential associations of soil nematodes in the mountain ecosystem of Mt. Halla. These findings enhance the understanding of the community structure and co‐occurrence network patterns and mechanisms of soil nematode along elevation, and the response of soil nematodes to climate change on the vertical scale of mountain ecosystems.     

Evaluating the sufficiency of protected lands for maintaining wildlife population connectivity in the U.S. northern Rocky Mountains

Aim The goal of this study was to evaluate the sufficiency of the network of protected lands in the U.S. northern Rocky Mountains in providing protection for habitat connectivity for 105 hypothetical organisms. A large proportion of the landscape falls into one of several categories of protected lands. However, protected lands in the region are primarily higher elevation forest and mountain habitats. Little is known about how the network of protected lands may maintain connectivity for a broad spectrum of species expressing different habitat requirements and dispersal abilities. Location The study was conducted across the states of Montana and northern Idaho, USA, comprising an area of 30.2 million hectares. Methods We used resistant kernel modelling to map the extent of the study area predicted to be connected by dispersal for each of 35 species groups with different ecological associations. We evaluated the effect of vagility on protected area sufficiency by varying dispersal ability across three levels for each species group. We evaluated the degree of vulnerability of each of the 105 hypothetical species (35 species groups × 3 dispersal abilities) in terms of the extent of the total study area predicted to be connected by dispersal. We defined nine categories of risk as the combination of species vulnerability because of the extent of connected habitat and the degree to which that habitat was protected. Results We found high variation in the vulnerability of species because of the extent of connected habitat, and the extent to which connected habitat overlapped protected lands. Species associated with high elevations and species associated with lower elevations were predicted to have limited extent of connected habitat. Species associated with high elevations were predicted to have the vast majority of their connected habitat protected by federal Forest Service and National Park Service lands. In contrast, species associated with lower elevations were poorly protected by the existing network of protected lands. Main conclusions Low elevation and non‐forest habitats are at highest risk of human‐induced habitat loss and fragmentation in the study area. Conservation efforts in the region may be most effective if they focus on expanding the network of lower elevation protected lands in such a way that maximizes connectivity across the landscape.     

Species and functional group composition of ant communities across an elevational gradient in the Eastern Himalaya

Elevational gradients in mountains show rapid changes in environmental conditions across a small geographic extent. This results in habitat specialization in animal communities which results in changes in species composition across space. We explore changes in species and functional group composition of ants using the first ever data on the distribution of ants across an elevational gradient in the Eastern Himalaya. Ants were sampled from 600 to 2400 m elevations at 200 m intervals using Winklers and pitfall traps. The sampling yielded 166 species of ants from 10,560 individuals, which were then classified into functional groups. We used redundancy analysis to test the effects of environmental factors (temperature, leaflitter volume, understory vegetation) and spatial predictors on species as well as functional group composition of communities at different elevations. Our results show that species diversity within all functional groups decreases towards higher elevations. The functional group composition of ant communities shows a gradient from high evenness at low elevations to being dominated by opportunist species at higher elevations. Redundancy analyses shows that most of the variation in species as well as functional group composition is driven by spatially structured environmental variation. This is most likely due to the high correlation between temperature and elevation. In summary, the changes in species as well as functional group composition are likely driven by a gradient in climate across the elevation gradient.     

Diversity patterns in savanna grassland communities: implications for conservation strategies in a biodiversity hotspot

For any conservation strategy to be effective, it must be preceded by knowledge of how diversity is configured within the area of interest. Here, data from 40 savanna-grassland sites were used to examine how plant biodiversity and species composition varied across spatial scales at the Kalakad-Mundanthurai Tiger Reserve (KMTR), south India. Grasslands surveyed contained 278 plant species, and were characterized by high spatial variability in species association patterns. Fourteen distinct community assemblages were identified, organized primarily along an elevation gradient in the reserve. Overall, grasslands at KMTR were characterized by the dominance of a few, widespread species. The bulk of species richness, however, resulted from subordinate species with fairly restricted distributions. At low elevations, grasslands had high species richness and species composition differed greatly between sites. Mid-elevation grasslands contained about half the number of species present at low elevations, but sites were more similar in species composition. Richness of high-elevation grasslands was a third of that found at low elevations, but different sites harbored unique sets of species. Herbivore use of grasslands varied between communities and showed patterns that coincided with elevation. Herbivore use of low-elevation communities was high albeit variable, of mid-elevation sites was consistently low, and increased at higher elevations. Tall grass communities were the least utilized by herbivores at all elevations. Most species surveyed were rare and restricted in their distribution suggesting that conservation efforts must, perforce, encompass the entire reserve. However, differences in the structuring of diversity across elevations, and in herbivore use of grasslands, suggest that conservation efforts can be partitioned differentially across locations, specifically targeting low and high elevation grasslands in the reserve.     

Changing ecological communities along an elevation gradient in seasonally dry tropical forest on Hispaniola (Sierra Martín García,Dominican Republic)

We report the results of systematic vascular plant and bird surveys in Seasonally Dry Tropical Forest (SDTF) across leeward and windward elevation gradients (31–884 masl) in the Sierra Martín García (SMG), Dominican Republic. We expected to see gradual, systematic changes in plant distributions with elevation owing to the strong effect of topoclimate. In contrast, we predicted bird community composition to be related only weakly to elevation, because we expected bird distributions to be more strongly related to vegetation structure than composition. Based on 48 vegetation transects, we identified seven groups that differed in their species composition, which was correlated with elevation and precipitation. The most distinctive vegetation community occurs in dry, warm, and low elevations on the leeward slope, featuring large numbers of non‐woody indicator species (those species found frequently within one group but not in other groups) even though most of its trees and shrubs represent species that are widespread. Low rainfall and shale bedrock (rather than limestone) may be the primary drivers of distinctiveness in the low‐elevation leeward plots. On the leeward slope, where we also surveyed the birds, the vegetation community changes gradually with elevation at mid‐ to high elevations. The most distinctive bird community also was associated with the low‐elevation forest on shale bedrock and was dominated by widespread species. At higher elevations, but still within leeward SDTF, the bird communities had a stronger component of species endemic either to Hispaniola or to Caribbean islands, and species turnover did not correspond to the elevation gradient. Abstract in Spanish is available with online material.     

Floral fungal-bacterial community structure and co-occurrence patterns in four sympatric island plant species

Flowers’ fungal and bacterial communities can exert great impacts on host plant wellness and reproductive success—both directly and indirectly through species interactions. However, information about community structure and co-occurrence patterns in floral microbiome remains scarce. Here, using culture-independent methods, we investigated fungal and bacterial communities associated with stamens and pistils of four plant species (Scaevola taccada, Ipomoea cairica, Ipomoea pes-caprae, and Mussaenda kwangtungensis) growing together under the same environment conditions in an island located in South China. Plant species identity significantly influenced community composition of floral fungi but not bacteria. Stamen and pistil microbiomes did not differ in community composition, but differed in co-occurrence network topological features. Compared with the stamen network, pistil counterpart had fewer links between bacteria and fungi and showed more modular but less concentrated and connected structure. In addition, degree distribution of microbial network in each host species and each microhabitat (stamen or pistil) followed a significant power-law pattern. These results enhance our understanding in the assembly principles and ecological interactions of floral microbial communities.     

Host functional and phylogenetic composition rather than host diversity structure plant–herbivore networks

Declining plant diversity alters ecological networks, such as plant–herbivore interactions. However, our knowledge of the potential mechanisms underlying effects of plant species loss on plant–herbivore network structure is still limited. We used DNA barcoding to identify herbivore–host plant associations along declining levels of tree diversity in a large‐scale, subtropical biodiversity experiment. We tested for effects of tree species richness, host functional and phylogenetic diversity, and host functional (leaf trait) and phylogenetic composition on species, phylogenetic and network composition of herbivore communities. We found that phylogenetic host composition and related palatability/defence traits but not tree species richness significantly affected herbivore communities and interaction network complexity at both the species and community levels. Our study indicates that evolutionary dependencies and functional traits of host plants determine the composition of higher trophic levels and corresponding interaction networks in species‐rich ecosystems. Our findings highlight that characteristics of the species lost have effects on ecosystem structure and functioning across trophic levels that cannot be predicted from mere reductions in species richness.     

Biofilm development and enhanced stress resistance of a model,mixed-species community biofilm

Most studies of biofilm biology have taken a reductionist approach, where single-species biofilms have been extensively investigated. However, biofilms in nature mostly comprise multiple species, where interspecies interactions can shape the development, structure and function of these communities differently from biofilm populations. Hence, a reproducible mixed-species biofilm comprising Pseudomonas aeruginosa, Pseudomonas protegens and Klebsiella pneumoniae was adapted to study how interspecies interactions affect biofilm development, structure and stress responses. Each species was fluorescently tagged to determine its abundance and spatial localization within the biofilm. The mixed-species biofilm exhibited distinct structures that were not observed in comparable single-species biofilms. In addition, development of the mixed-species biofilm was delayed 1–2 days compared with the single-species biofilms. Composition and spatial organization of the mixed-species biofilm also changed along the flow cell channel, where nutrient conditions and growth rate of each species could have a part in community assembly. Intriguingly, the mixed-species biofilm was more resistant to the antimicrobials sodium dodecyl sulfate and tobramycin than the single-species biofilms. Crucially, such community level resilience was found to be a protection offered by the resistant species to the whole community rather than selection for the resistant species. In contrast, community-level resilience was not observed for mixed-species planktonic cultures. These findings suggest that community-level interactions, such as sharing of public goods, are unique to the structured biofilm community, where the members are closely associated with each other.     

Positive interactions between alpine plant species and the nurse cushion plant Laretia acaulis do not increase with elevation in the Andes of central Chile

In alpine habitats, positive interactions among plants tend to increase with elevation as a result of altitudinal increase in environmental harshness. However, in mountains located in arid zones, lower elevations are also stressful because of scarce availability of water, suggesting that positive interactions may not necessarily increase with elevation. Here we analysed the spatial association of plant species with the nurse cushion plant Laretia acaulis at two contrasting elevations, and monitored the survival of seedlings of two species experimentally planted within and outside cushions in the semiarid Andes of central Chile. Positive spatial associations with cushions were more frequent at lower elevations. Species growing at the two elevations changed the nature of their association with cushions from neutral or negative at higher elevations to positive at lower elevations. Survival of seedlings was higher within cushions, particularly at lower elevations. The increased facilitation by cushions at lower elevations seems to be related to provision of moisture. This result suggests that cushion plants play a critical role in structuring alpine plant communities at lower elevations, and that climatic changes in rainfall could be very relevant for persistence of plant communities.     

Understanding the Linkage between Elevation and the Activated-Sludge Bacterial Community along a 3,600-Meter Elevation Gradient in China

To understand the relationship between elevation and bacterial communities in wastewater treatment plants (WWTPs), bacterial communities in 21 municipal WWTPs across China, located 9 to 3,660 m above sea level (masl), were investigated by 454 pyrosequencing. A threshold for the association of elevation with bacterial community richness and evenness was observed at approximately 1,200 masl. At lower elevations, both richness and evenness were not significantly associated with elevation. At higher elevations, significant declines with increased elevations were observed for community richness and evenness. The declining evenness trend at the phylum level was reflected by distinct trends in relative abundance for individual bacterial phyla. Betaproteobacteria, Bacteroidetes, and Firmicutes displayed significant increases, while most other phyla showed declines. Spearman correlation analysis indicated that the community richness and evenness at high elevations were more correlated with elevation than with any other single environmental variable. Redundancy analysis indicated that the contribution of elevation to community composition variances increased from 3% at lower elevations to 11% at higher elevations whereas the community composition variance at higher elevations remained much more explained by operational variables (39.2%) than by elevation. The influent total phosphorus concentration, food/microorganism ratio, and treatment process were the three shared dominant contributors to the community composition variance across the whole elevation gradient, followed by effluent ammonia nitrogen and temperature at higher elevations.     

Interspecific primate associations in Amazonian flooded and unflooded forests

Stable associations between two or more primate species are a prominent feature of neotropical forest vertebrate communities and many studies have addressed their prevalence, and their costs and benefits. However, little is known about the influence of different habitat types on the frequency, seasonality, and composition of mixed-species groups in Amazonian forest primates. Here we examine the features of interspecific primate groups in a large mosaic of flooded (várzea and igapó) and unflooded (terra firme) forest in central Amazonia. In total, 12 primate species occurred in the study area, nine of which were observed in mixed-species associations. Primates were more than twice as likely to form associations in várzea forest than in terra firme forest. Squirrel monkeys were most frequently found in mixed-species groups in all forest types, most commonly in association with brown capuchins. Another frequent member of interspecific associations was the buffy saki, which often formed mixed-species groups with tamarins or brown capuchins. There was no seasonality in the frequency of associations in terra firme forest whereas associations in várzea forest were twice as frequent during the late-dry and early-wet seasons than in the late-wet and early-dry seasons. Interspecific primate associations were common in all forest types, but the degrees to which different species associate varied between these environments. We suggest that the temporal variation of várzea forest associations is connected with seasonal changes in habitat structure and resource abundance. However, more work is needed to pinpoint the underlying causes of mixed-species associations in all forest types and their strong seasonality in várzea forest.     

Modularity and specialization in bat–fly interaction networks are remarkably consistent across patches within urbanized landscapes and spatial scales

Patterns of specialization and the structure of interactions between bats and ectoparasitic flies have been studied mostly on non-urban environments and at local scales. Thus, how anthropogenic disturbances influence species interactions and network structure in this system remain poorly understood. Here, we investigated patterns of interaction between Phyllostomidae bats and ectoparasitic Streblidae flies, and variations in network specialization and structure across Cerrado patches within urbanized landscapes in Brazil and between local and regional scales. We found high similarity in the richness and composition of bat and fly species across communities, associated with low turnover of interactions between networks. The high specialization of bat–streblid interactions resulted in little connected and modular networks, with the emergence of modules containing subsets of species that interact exclusively or primarily with each other. Such similarities in species and interaction composition and network structure across communities and scales suggest that bat–fly interactions within Cerrado patches are little affected by the degree of human modification in the surrounding matrix. This remarkable consistency is likely promoted by specific behaviors, the tolerance of Phyllostomidae bats to surrounding urbanized landscapes as well as by the specificity of the streblid–bat interactions shaped over evolutionary time.     

Microbial communities may modify how litter quality affects potential decomposition rates as tree species migrate

Background and aims

Climate change alters regional plant species distributions, creating new combinations of litter species and soil communities. Biogeographic patterns in microbial communities relate to dissimilarity in microbial community function, meaning novel litters to communities may decompose differently than predicted from their chemical composition. Therefore, the effect of a litter species in the biogeochemical cycle of its current environment may not predict patterns after migration. Under a tree migration sequence we test whether litter quality alone drives litter decomposition, or whether soil communities modify quality effects.

Methods

Litter and soils were sampled across an elevation gradient of different overstory species where lower elevation species are predicted to migrate upslope. We use a common garden, laboratory microcosm design (soil community x litter environment) with single and mixed-species litters.

Results

We find significant litter quality and microbial community effects (P?<?0.001), explaining 47 % of the variation in decomposition for mixed-litters.

Conclusion

Soil community effects are driven by the functional breadth, or historical exposure, of the microbial communities, resulting in lower decomposition of litters inoculated with upslope communities. The litter x soil community interaction suggests that litter decomposition rates in forests of changing tree species composition will be a product of both litter quality and the recipient soil community.     

Effect of livestock grazing in the partitions of a semiarid plant–plant spatial signed network

In recent times, network theory has become a useful tool to study the structure of the interactions in ecological communities. However, typically, these approaches focus on a particular kind of interaction while neglecting other possible interactions present in the ecosystem. Here, we present an ecological network for plant communities that consider simultaneously positive and negative interactions, which were derived from the spatial association and segregation between plant species. We employed this network to study the structure and the association strategies in a semiarid plant community of Cabo de Gata-Níjar Natural Park, SE Spain, and how they changed in 4 sites that differed in stocking rate. Association strategies were obtained from the partitions of the network, built based on a relaxed structural balance criterion. We found that grazing simplified the structure of the plant community. With increasing stocking rate species with no significant associations became dominant and the number of partitions decreased in the plant community. Independently of stocking rate, many species presented an associative strategy in the plant community because they benefit from the association to certain ‘nurse’ plants. These ‘nurses’ together with species that developed a segregating strategy, intervened in most of the interactions in the community. Ecological networks that combine links with different signs provide a new insight to analyze the structure of natural communities and identify the species which play a central role in them.     

Changes in Species Richness,Abundance, and Composition of Arboreal Twig‐nesting Ants Along an Elevational Gradient in Coffee Landscapes

The distribution, diversity, and assembly of tropical insects have long intrigued ecologists, and for tropical ants, can be affected by competitive interactions, microhabitat requirements, dispersal, and availability and diversity of nesting sites. Arboreal twig‐nesting ants are limited by the number of hollow twigs available, especially in intensive agricultural systems. Ant diversity and abundance may shift along elevation gradients, but no studies have examined if the proportion of occupied twigs or richness of arboreal twig‐nesting ants vary with elevation. In coffee agroecosystems, there are over 40 species of arboreal twig‐nesting ants. We examined communities of twig‐nesting ants in coffee plants along an elevational gradient to answer the following questions: (1) Do species richness and colony abundance decline with elevation or show a mid‐elevation peak? (2) Does community composition change with elevation? (3) Is elevation an important predictor of change in ant abundance, richness, and relative abundance of common species? We surveyed 42 10 × 10 m plots in 2013 from 450 to1550 m elevation across a coffee landscape in Chiapas, Mexico. We sampled a total of 2211 hollow coffee twigs, 77.1 percent of which were occupied by one of 28 species of ants. Pseudomyrmex simplex was more abundant in lower elevations, whereas Pseudomyrmex ejectus dominated in high elevations. Species richness and the percent of occupied hollow twigs both peaked at mid‐elevations (800–1050 m). In sum, we found that species richness, abundance, and composition of arboreal twig‐nesting ants shift with elevation. These findings may provide important insights for understanding ant communities in coffee agroecosystems.     

Subsidies mediate interactions between communities across space

Most spatial ecology focuses on how species dispersal affects community dynamics and coexistence. Ecosystems, however, are also commonly connected by flows of resources. We experimentally tested how neighbouring communities indirectly influence each other in absence of dispersal, via resource exchanges. Using two‐patch microcosm meta‐ecosystems, we manipulated community composition and dynamics, by varying separately species key functional traits (autotroph versus heterotroph species and size of consumer species) and trophic structure of aquatic communities (species growing alone or in presence of competitors or predators). We then analysed the effects of species functional traits and trophic structure on communities connected through spatial subsidies in the absence of actual dispersal. Both functional traits and trophic structure strongly affected dynamics across neighbouring communities. Heterotroph communities connected to autotroph neighbours developed better than with heterotroph neighbours, such that coexistence of competitors was determined by the functional traits of the neighbouring community. Densities in autotroph communities were also strikingly higher when receiving subsidies from heterotroph communities compared to their own subsidies when grown in isolated ecosystems. In contrast, communities connected to predator‐dominated ecosystems collapsed, without any direct contact with the predators. Our results demonstrate that because community composition and structure modify the distribution of biomass within a community, they may also affect communities connected through subsidies through quantitative and qualitative changes of detritus flows. This stresses that ecosystem management should account for such interdependencies mediated by spatial subsidies, given that local community alterations cascade across space onto other ecosystems even if species dispersal is completely absent.     

Twenty‐five years of plant community dynamics and invasion in New Zealand tussock grasslands

Understanding how plant communities respond to plant invasions is important both for understanding community structure and for predicting future ecosystem change. In a system undergoing intense plant invasion for 25 years, we investigated patterns of community change at a regional scale. Specifically, we sought to quantify how tussock grassland plant community structure had changed and whether changes were related to increases in plant invasion. Frequency data for all vascular plants were recorded on 124, permanent transects in tussock grasslands across the lower eastern South Island of New Zealand measured three times over a period of 25 years. Multivariate analyses of species richness were used to describe spatial and temporal patterns in the vegetation. Linear mixed‐effects models were used to relate temporal changes in community structure to the level and rate of invasion of three dominant invasive species in the genus Hieracium while accounting for relationships with other biotic and abiotic variables. There was a strong compositional gradient from exotic‐ to native‐dominated plant communities that correlated with increasing elevation. Over the 25 years, small‐scale species richness significantly decreased and then increased again; however, these changes differed in different plant communities. Exotic species frequency consistently increased on some transects and consistently declined on others. Species richness changes were correlated with the level of Hieracium invasion and abiotic factors, although the relationship with Hieracium changed from negative to positive over time. Compositional changes were not related to measured predictors. Our results suggest that observed broad‐scale fluctuations in species richness and community composition dynamics were not driven by Hieracium invasion. Given the relatively minor changes in community composition over time, we conclude that there is no evidence for widespread degradation of these grasslands over the last 25 years. However, because of continuing weed invasion, particularly at lower elevations, impacts may emerge in the longer term.