Is the notion that species interactions are stronger and more specialized in the tropics a zombie idea?

From the High Arctic to the Equator: Do Soil Metagenomes Differ According to Our Expectations?

Comparing the functional gene composition of soils at opposite extremes of environmental gradients may allow testing of hypotheses about community and ecosystem function. Here, we were interested in comparing how tropical microbial ecosystems differ from those of polar climates. We sampled several sites in the equatorial rainforest of Malaysia and Brunei, and the high Arctic of Svalbard, Canada, and Greenland, comparing the composition and the functional attributes of soil biota between the two extremes of latitude, using shotgun metagenomic Illumina HiSeq2000 sequencing. Based upon "classical" views of how tropical and higher latitude ecosystems differ, we made a series of predictions as to how various gene function categories would differ in relative abundance between tropical and polar environments. Results showed that in some respects our predictions were correct: the polar samples had higher relative abundance of dormancy related genes, and lower relative abundance of genes associated with respiration, and with metabolism of aromatic compounds. The network complexity of the Arctic was also lower than the tropics. However, in various other respects, the pattern was not as predicted; there were no differences in relative abundance of stress response genes or in genes associated with secondary metabolism. Conversely, CRISPR genes, phage-related genes, and virulence disease and defense genes, were unexpectedly more abundant in the Arctic, suggesting more intense biotic interaction. Also, eukaryote diversity and bacterial diversity were higher in the Arctic of Svalbard compared to tropical Brunei, which is consistent with what may expected from amplicon studies in terms of the higher pH of the Svalbard soil. Our results in some respects confirm expectations of how tropical versus polar nature may differ, and in other respects challenge them.

Latitudinal variation in soil biota: testing the biotic interaction hypothesis with an invasive plant and a native congener

Soil biota community structure can change with latitude, but the effects of changes on native plants, invasive plants, and their herbivores remain unclear. Here, we examined latitudinal variation in the soil biota community associated with the invasive plant Alternanthera philoxeroides and its native congener A. sessilis, and the effects of soil biota community variation on these plants and the beetle Agasicles hygrophila. We characterized the soil bacterial and fungal communities and root-knot nematodes of plant rhizospheres collected from 22 °N to 36.6 °N in China. Soil biota community structure changed with latitude as a function of climate and soil properties. Root-knot nematode abundance and potential soil fungal pathogen diversity (classified with FUNGuild) decreased with latitude, apparently due to higher soil pH and lower temperatures. A greenhouse experiment and lab bioassay showed native plant mass, seed production, and mass of beetles fed native foliage increased with soil collection latitude. However, there were no latitudinal patterns for the invasive plant. These results suggest that invasive and native plants and, consequently, their herbivores have different responses to latitudinal changes in soil-borne enemies, potentially creating spatial variation in enemy release or biotic resistance. This highlights the importance of linking above- and below-ground multitrophic interactions to explore the role of soil biota in non-native plant invasions with a biogeographic approach.

Testing for latitudinal gradients in defense at the macroevolutionary scale

Plant defenses against herbivores are predicted to evolve to be greater in warmer climates, such as lower latitudes where herbivore pressure is also thought to be higher. Instead, recent findings are often inconsistent with this expectation, suggesting alternative hypotheses are needed. We tested for latitudinal gradients in plant defense evolution at the macroevolutionary scale by characterizing plant chemical defenses across 80 species of the evening primroses, spanning both North and South America. We quantified phenolics in leaves, flowers, and fruits, using advanced analytical chemistry techniques. Dominant individual ellagitannin compounds, total concentrations of ellagitannins, flavonoids, total phenolics, and compound diversity were quantified. Variation in these compounds was predicted with latitude, temperature, precipitation, and continent using phylogenetic generalized least squares (PGLS) multiple regression models. Latitude did not strongly explain variation in chemical defenses. Instead, fruit total ellagitannins, oenothein A, and total phenolics were greater in species inhabiting regions with colder climates. Using analytical chemistry and 80 species in two continents, we show that contrary to classic predictions, concentrations of secondary metabolites are not greater at lower latitudes or in warmer regions. We propose higher herbivore pressure in colder climates and gradients in resource availability as potential drivers of the observed patterns in Oenothera.

The effect of multiple biotic interaction types on species persistence

No species can persist in isolation from other species, but how biotic interactions affect species persistence is still a matter of inquiry. Is persistence more likely in communities with higher proportion of competing species, or in communities with more positive interactions? How do different components of community structure mediate this relationship? We address these questions using a novel simulation framework that generates realistic communities with varying numbers of species and different proportions of biotic interaction types within and across trophic levels. We show that when communities have fewer species, persistence is more likely if positive interactions-such as mutualism and commensalism-are prevalent. In species-rich communities, the disproportionate effect of positive interactions on persistence is diluted and different combinations of biotic interaction types can coexist without affecting persistence significantly. We present the first theoretical examination of how multiple-interaction networks with varying architectures relate to local species persistence, and provide insight about the underlying causes of stability in communities.

Global reef fish richness gradients emerge from divergent and scale-dependent component changes

Biodiversity varies from place to place due to environmental and historical factors. To improve our understanding of how history and the environment influence observed patterns, we need to address the limitations of the most commonly used biodiversity metric, species richness. Here, we show that scale-dependent dissections of species richness into components of total abundance, species relative abundances and spatial aggregations of species reveal that two well-known biogeographic reef fish species richness gradients emerge from very different underlying component patterns. Latitudinal richness is underpinned by scale-independent patterns of total and relative abundances, suggesting ecological constraints scale up to determine abundances within communities. In contrast, the longitudinal gradient of species richness typically attributed to historical biogeography only emerges at the largest scale and is accompanied by a similar pattern of relative abundances, suggesting that site-to-site compositional variation leading to species aggregation (i.e. a component of β-diversity) underlies this gradient. Examining relationships among the components that underpin biodiversity gradients reveals new patterns that can better identify processes influencing patterns of biodiversity.

Bringing ecology blogging into the scientific fold: measuring reach and impact of science community blogs

The popularity of science blogging has increased in recent years, but the number of academic scientists who maintain regular blogs is limited. The role and impact of science communication blogs aimed at general audiences is often discussed, but the value of science community blogs aimed at the academic community has largely been overlooked. Here, we focus on our own experiences as bloggers to argue that science community blogs are valuable to the academic community. We use data from our own blogs (n = 7) to illustrate some of the factors influencing reach and impact of science community blogs. We then discuss the value of blogs as a standalone medium, where rapid communication of scholarly ideas, opinions and short observational notes can enhance scientific discourse, and discussion of personal experiences can provide indirect mentorship for junior researchers and scientists from underrepresented groups. Finally, we argue that science community blogs can be treated as a primary source and provide some key points to consider when citing blogs in peer-reviewed literature.

Accelerated body size evolution during cold climatic periods in the Cenozoic

How ecological and morphological diversity accumulates over geological time is much debated. Adaptive radiation theory has been successful in testing the effects of biotic interactions on the rapid divergence of phenotypes within a clade, but this theory ignores abiotic effects. The role of abiotic drivers on the tempo of phenotypic evolution has been tested only in a few lineages or small clades from the fossil record. Here, we develop a phylogenetic comparative framework for testing if and how clade-wide rates of phenotypic evolution vary with abiotic drivers. We apply this approach to comprehensive bird and mammal phylogenies, body size data for 9,465 extant species, and global average temperature trends over the Cenozoic. Across birds and mammals, we find that the rate of body size evolution is primarily driven by past climate. Unexpectedly, evolutionary rates are inferred to be higher during periods of cold rather than warm climates in most groups, suggesting that temperature influences evolutionary rates by modifying selective pressures rather than through its effect on energy availability and metabolism. The effect of climate on the rate of body size evolution seems to be a general feature of endotherm evolution, regardless of wide differences in species' ecology and evolutionary history. These results suggest that climatic changes played a major role in shaping species' evolution in the past and could also play a major role in shaping their evolution in the future.

Fungal-algal association patterns in lichen symbiosis linked to macroclimate

Both macroclimate and evolutionary events may influence symbiont association and diversity patterns. Here we assess how climatic factors and evolutionary events shape fungal-algal association patterns in the widely distributed lichen-forming fungal genus Protoparmelia. Multilocus phylogenies of fungal and algal partners were generated using 174 specimens. Coalescent-based species delimitation analysis suggested that 23 fungal hosts are associating with 20 algal species. Principal component analysis (PCA) was performed to infer how fungal-algal association patterns varied with climate. Fungi associated with one to three algal partners whereas algae accepted one to five fungal partners. Both fungi and algae were more specific, associating with fewer partners, in the warmer climates. Interaction with more than one partner was more frequent in cooler climates for both the partners. Cophylogenetic analyses suggest congruent fungal-algal phylogenies. Host switch was a more common event in warm climates, whereas failure of the photobiont to diverge with its fungal host was more frequent in cooler climates. We conclude that both environmental factors and evolutionary events drive fungal and algal evolution in Protoparmelia. The processes leading to phylogenetic congruence of fungi and algae are different in different macrohabitats in our study system. Hence, closely related species inhabiting diverse habitats may follow different evolutionary pathways.

The Overlooked Role of Facilitation in Biodiversity Experiments

Past research has demonstrated that decreased biodiversity often reduces ecosystem productivity, but variation in the shape of biodiversity-ecosystem function (BEF) relationships begets the need for a deeper mechanistic understanding of what drives these patterns. While mechanisms involving competition are often invoked, the role of facilitation is overlooked, or lumped within several less explicitly defined processes (e.g., complementarity effects). Here, we explore recent advances in understanding how facilitation affects BEF relationships and identify three categories of facilitative mechanisms that can drive variation in those relationships. Species interactions underlying BEF relationships are complex, but the framework we present provides a step toward understanding this complexity and predicting how facilitation contributes to the ecosystem role of biodiversity in a rapidly changing environment.

High richness of insect herbivory from the early Miocene Hindon Maar crater, Otago, New Zealand

Plants and insects are key components of terrestrial ecosystems and insect herbivory is the most important type of interaction in these ecosystems. This study presents the first analysis of associations between plants and insects for the early Miocene Hindon Maar fossil lagerstätte, Otago, New Zealand. A total of 584 fossil angiosperm leaves representing 24 morphotypes were examined to determine the presence or absence of insect damage types. Of these leaves, 73% show signs of insect damage; they comprise 821 occurrences of damage from 87 damage types representing all eight functional feeding groups. In comparison to other fossil localities, the Hindon leaves display a high abundance of insect damage and a high diversity of damage types. Leaves of Nothofagus(southern beech), the dominant angiosperm in the fossil assemblage, exhibit a similar leaf damage pattern to leaves from the nearby mid to late Miocene Dunedin Volcano Group sites but display a more diverse spectrum and much higher percentage of herbivory damage than a comparable dataset of leaves from Palaeocene and Eocene sites in the Antarctic Peninsula.

The influence of floral traits on specialization and modularity of plant-pollinator networks in a biodiversity hotspot in the Peruvian Andes

BACKGROUND AND AIMS

Modularity is a ubiquitous and important structural property of ecological networks which describes the relative strengths of sets of interacting species and gives insights into the dynamics of ecological communities. However, this has rarely been studied in species-rich, tropical plant-pollinator networks. Working in a biodiversity hotspot in the Peruvian Andes we assessed the structure of quantitative plant-pollinator networks in nine valleys, quantifying modularity among networks, defining the topological roles of species and the influence of floral traits on specialization.

METHODS

A total of 90 transects were surveyed for plants and pollinators at different altitudes and across different life zones. Quantitative modularity (QuanBiMo) was used to detect modularity and six indices were used to quantify specialization.

KEY RESULTS

All networks were highly structured, moderately specialized and significantly modular regardless of size. The strongest hubs were Baccharis plants, Apis mellifera, Bombus funebris and Diptera spp., which were the most ubiquitous and abundant species with the longest phenologies. Species strength showed a strong association with the modular structure of plant-pollinator networks. Hubs and connectors were the most centralized participants in the networks and were ranked highest (high generalization) when quantifying specialization with most indices. However, complementary specialization d' quantified hubs and connectors as moderately specialized. Specialization and topological roles of species were remarkably constant across some sites, but highly variable in others. Networks were dominated by ecologically and functionally generalist plant species with open access flowers which are closely related taxonomically with similar morphology and rewards. Plants associated with hummingbirds had the highest level of complementary specialization and exclusivity in modules (functional specialists) and the longest corollas.

CONCLUSIONS

We have demonstrated that the topology of networks in this tropical montane environment was non-random and highly organized. Our findings underline that specialization indices convey different concepts of specialization and hence quantify different aspects, and that measuring specialization requires careful consideration of what defines a specialist.

Latitudinal Gradients in Induced and Constitutive Resistance against Herbivores

Plants are hypothesized to evolve increased defense against herbivores at lower latitudes, but an increasing number of studies report evidence that contradicts this hypothesis. Few studies have examined the evolution of constitutive and induced resistance along latitudinal gradients. When induction is not considered, underlying patterns of latitudinal clines in resistance can be obscured because plant resistance represents a combination of induced and constitutive resistance, which may show contrasting patterns with latitude. Here, we asked if there are latitudinal gradients in constitutive versus induced resistance by using genotypes of Oenothera biennis (Onagraceae) sampled along an 18° latitudinal gradient. We conducted two bioassay experiments to compare the resistance of plant genotypes against one generalist (Spodoptera exigua) and one specialist (Acanthoscelidius acephalus) herbivore. These insects were assayed on: i) undamaged control plants, ii) plants that had been induced with jasmonic acid, and iii) plants induced with herbivore damage. Additionally, we examined latitudinal gradients of constitutive and induced chemical resistance by measuring the concentrations of total phenolics, the concentration of oxidized phenolics, and the percentage of phenolics that were oxidized. Spodoptera exigua showed lower performance on plants from lower latitudes, whereas A. acephalus showed no latitudinal pattern. Constitutive total phenolics were greater in plants from lower latitudes, but induced plants showed higher total phenolics at higher latitudes. Oxidative activity was greatest at higher latitudes regardless of induction. Overall, both latitude and induction have an impact on different metrics of plant resistance to herbivory. Further studies should consider the effect of induction and herbivore specialization more explicitly, which may help to resolve the controversy in latitudinal gradients in herbivory and defense.