David A. Donoso

Higher predation risk for insect prey at low latitudes and elevations

Risky in the tropics It is well known that diversity increases toward the tropics. Whether this increase translates into differences in interaction rates among species, however, remains unclear. To simplify the problem, Roslin et al. tested for predation rates by using a single approach involving model caterpillars across six continents. Predator attack rates were higher toward the equator, but only for arthropod predators. Science, this issue p. 742 Like diversity, predation rates among insects increase toward the equator and at lower altitudes. Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution.

Trees as templates for tropical litter arthropod diversity.

Increased tree species diversity in the tropics is associated with even greater herbivore diversity, but few tests of tree effects on litter arthropod diversity exist. We studied whether tree species influence patchiness in diversity and abundance of three common soil arthropod taxa (ants, gamasid mites, and oribatid mites) in a Panama forest. The tree specialization hypothesis proposes that tree-driven habitat heterogeneity maintains litter arthropod diversity. We tested whether tree species differed in resource quality and quantity of their leaf litter and whether more heterogeneous litter supports more arthropod species. Alternatively, the abundance–extinction hypothesis states that arthropod diversity increases with arthropod abundance, which in turn tracks resource quantity (e.g., litter depth). We found little support for the hypothesis that tropical trees are templates for litter arthropod diversity. Ten tree species differed in litter depth, chemistry, and structural variability. However, the extent of specialization of invertebrates on particular tree taxa was low and the more heterogeneous litter between trees failed to support higher arthropod diversity. Furthermore, arthropod diversity did not track abundance or litter depth. The lack of association between tree species and litter arthropods suggests that factors other than tree species diversity may better explain the high arthropod diversity in tropical forests.

Climate mediates the effects of disturbance on ant assemblage structure

Many studies have focused on the impacts of climate change on biological assemblages, yet little is known about how climate interacts with other major anthropogenic influences on biodiversity, such as habitat disturbance. Using a unique global database of 1128 local ant assemblages, we examined whether climate mediates the effects of habitat disturbance on assemblage structure at a global scale. Species richness and evenness were associated positively with temperature, and negatively with disturbance. However, the interaction among temperature, precipitation and disturbance shaped species richness and evenness. The effect was manifested through a failure of species richness to increase substantially with temperature in transformed habitats at low precipitation. At low precipitation levels, evenness increased with temperature in undisturbed sites, peaked at medium temperatures in disturbed sites and remained low in transformed sites. In warmer climates with lower rainfall, the effects of increasing disturbance on species richness and evenness were akin to decreases in temperature of up to 9°C. Anthropogenic disturbance and ongoing climate change may interact in complicated ways to shape the structure of assemblages, with hot, arid environments likely to be at greatest risk.

Using nutritional ecology to predict community structure: a field test in Neotropical ants

Nutritional ecology predicts consumer behavior based on the biochemistry of species and biogeochemistry of the environment. It is thus well suited as a tool for predicting the effects of specific nutrients on consumer activity, abundance, and diversity across the landscape. We tested hypotheses from nutritional ecology in a Neotropical litter ant community by supplementing forest plots with carbohydrates (CHOs) and protein in a blocked factorial design. We tested the Compensation Hypothesis, which posits that consumers accumulate in patches of the rarest food type relative to demand, and the Economics Hypothesis, which assumes that species differ in nutrient based-functional traits, and that changes in nutrient availability will generate changes in species composition and community behavior. We found that CHO and protein had distinct effects on ant density, community composition, and per-worker activity. Ant density increased by 35% on +CHO plots but not +Protein plots, a result supporting the Compensation Hypothesis because CHO-rich plant exudates are uncommon and CHO-demanding microbial productivity is high in this brown food web. Consistent with the Economics Hypothesis, we found that +CHO plots had higher per-capita ant activity (the Metabolic Fuel Hypothesis) and attracted ants averaging 10% lower δ15N values. Species composition changed as well, with Wasmannia auropunctata, an invasive outside its native range, elsewhere, increasing five-fold on +CHO plots. Nutritional ecology can thus account for some of the patchiness and behavior of consumers in diverse communities.

The life history continuum hypothesis links traits of male ants with life outside the nest

An ant society, headed by a mated queen, can live for decades. Male ants, in contrast, are generally assumed to be ephemeral sperm delivery vessels programmed to die hours after leaving the nest to mate. However, the events from dispersal to mate location have rarely been studied, and the links between male traits and the ecological demands of diverse mating systems remain poorly understood. Here, we propose that interspecific variation in the length of mating flights has generated a life history continuum for male ants, and that the previously proposed ‘male aggregating’ and ‘female calling’ mating syndromes represent the endpoints. We also provide the first evidence for systematic divergence in pre‐mating traits between males that attract females to brief nuptial swarms (Male aggregation syndrome) and those that must survive while searching for patchily distributed females that signal with pheromones (Female calling syndrome). Specifically, female‐calling males tend to have larger eyes and mandibles, but the length of the basal antennal segment (scape) appears relatively constant across body sizes. After exploring these patterns, we review evidence that key components of fitness like mating frequency vary across a male life history continuum, and then explore links between male traits and a colonys per capita reproductive investment. Systematic variation in pre‐flight provisioning of males relative to mating systems may have important ecological implications, given that ants are dominant consumers on a global scale, and colonies ultimately use large fractions of harvested resources to fuel reproduction.

GlobalAnts: a new database on the geography of ant traits (Hymenoptera: Formicidae)

In recent years the focus in ecology has shifted from species to a greater emphasis on functional traits. In tandem with this shift, a number of trait databases have been developed covering a range of taxa. Here, we introduce the GlobalAnts database. Globally, ants are dominant, diverse and provide a range of ecosystem functions. The database represents a significant tool for ecology in that it (i) contributes to a global archive of ant traits (morphology, ecology and life history) which complements existing ant databases and (ii) promotes a trait‐based approach in ant and other insect ecology through a broad set of standardised traits. The GlobalAnts database is unique in that it represents the largest online database of functional traits with associated georeferenced assemblage‐level data (abundance and/or occupancy) for any animal group with 9056 ant species and morphospecies records for entire local assemblages across 4416 sites. We describe the structure of the database, types of traits included and present a summary of data coverage. The value of the database is demonstrated through an initial examination of trait distributions across subfamilies, continents and biomes. Striking biogeographic differences in ant traits are highlighted which raise intriguing questions as to the mechanisms generating them.

Timeless standards for species delimitation

Recently a new species of bombyliid fly, Marleyimyia xylocopae, was described by Marshall & Evenhuis (2015) based on two photographs taken during fieldwork in the Republic of South Africa. This species has no preserved holotype. The paper generated some buzz, especially among dipterists, because in most cases photographs taken in the field provide insufficient information for properly diagnosing and documenting species of Diptera.

Effects of climate change on Andean biodiversity: a synthesis of studies published until 2015

Understanding how GCC is affecting the biological diversity of the Andes is of utmost importance and timeliness given the relevance of the region for biological conservation. Our research questions were (1) what is the spatial (country-level) and temporal distribution of the scientific research exploring links between GCC and biodiversity in the Andean region? (2) What are the methodological approximations, areas of research and subjects of study most commonly considered? And (3) What are the trends in biodiversity responses most commonly found under different GCC stressors? We found that the first paper on GCC and biodiversity in the Andes was published in 2001. Since then the annual rate of publications, as well as the variety of areas of research, has risen steeply. The 65 published articles we found are likely to represent 1% of the scientific literature dealing with tropical ecology. Of those, more than half of the studies were conducted in a single country, used mostly observation rather than modelling or experimental methodological approaches, and focused mainly on plants. Studies dealing with birds, mammals and reptiles were notoriously underrepresented. The high number of GCC stressors and the great variety of responses found in this synthesis makes it difficult to draw general conclusions. However, we found that observational, modelling and experimental studies report negative GCC impacts on the biological diversity of the region. Most generally, observation and modelling studies report contractions of the distribution ranges of Andean species, and negative effects on species population densities and individual performance. We conclude our review suggesting that networking, recovering historic field data and conducting large-scale ecosystem experimental studies are critical to improve our knowledge on the effects of GCC on Andean biodiversity.

Coevolutionary arms race versus host defense chase in a tropical herbivore-plant system

Significance Although plants and their herbivores account for most of macroscopic, terrestrial biodiversity, we do not fully understand the evolutionary origins of this high diversity. Coevolutionary theory proposes that adaptations between plants and their herbivores are reciprocal and that their interactions might have driven diversification and community composition. Contrary to this scenario of defense and counterdefense, we find an apparent asymmetry in the interactions between plants and herbivores. Specifically, despite the evolutionary constraints of long lifetimes for trees, plant–antiherbivore defenses may be more evolutionarily labile than herbivore adaptations to their hosts, allowing long-lived plant species to persist in the arms race with their insect herbivores. In contrast, herbivores may be evolutionarily “chasing” plants, feeding on species for which they have preadaptations. Coevolutionary models suggest that herbivores drive diversification and community composition in plants. For herbivores, many questions remain regarding how plant defenses shape host choice and community structure. We addressed these questions using the tree genus Inga and its lepidopteran herbivores in the Amazon. We constructed phylogenies for both plants and insects and quantified host associations and plant defenses. We found that similarity in herbivore assemblages between Inga species was correlated with similarity in defenses. There was no correlation with phylogeny, a result consistent with our observations that the expression of defenses in Inga is independent of phylogeny. Furthermore, host defensive traits explained 40% of herbivore community similarity. Analyses at finer taxonomic scales showed that different lepidopteran clades select hosts based on different defenses, suggesting taxon-specific histories of herbivore–host plant interactions. Finally, we compared the phylogeny and defenses of Inga to phylogenies for the major lepidopteran clades. We found that closely related herbivores fed on Inga with similar defenses rather than on closely related plants. Together, these results suggest that plant defenses might be more evolutionarily labile than the herbivore traits related to host association. Hence, there is an apparent asymmetry in the evolutionary interactions between Inga and its herbivores. Although plants may evolve under selection by herbivores, we hypothesize that herbivores may not show coevolutionary adaptations, but instead “chase” hosts based on the herbivore’s own traits at the time that they encounter a new host, a pattern more consistent with resource tracking than with the arms race model of coevolution.

A global database of ant species abundances

What forces structure ecological assemblages? A key limitation to general insights about assemblage structure is the availability of data that are collected at a small spatial grain (local assemblages) and a large spatial extent (global coverage). Here, we present published and unpublished data from 51 ,388 ant abundance and occurrence records of more than 2,693 species and 7,953 morphospecies from local assemblages collected at 4,212 locations around the world. Ants were selected because they are diverse and abundant globally, comprise a large fraction of animal biomass in most terrestrial communities, and are key contributors to a range of ecosystem functions. Data were collected between 1949 and 2014, and include, for each geo-referenced sampling site, both the identity of the ants collected and details of sampling design, habitat type, and degree of disturbance. The aim of compiling this data set was to provide comprehensive species abundance data in order to test relationships between assemblage structure and environmental and biogeographic factors. Data were collected using a variety of standardized methods, such as pitfall and Winkler traps, and will be valuable for studies investigating large-scale forces structuring local assemblages. Understanding such relationships is particularly critical under current rates of global change. We encourage authors holding additional data on systematically collected ant assemblages, especially those in dry and cold, and remote areas, to contact us and contribute their data to this growing data set.