Revisiting florivory: an integrative review and global patterns of a neglected interaction.

Florivory is an ancient interaction which has rarely been quantified due to a lack of standardized protocols, thus impairing biogeographical and phylogenetic comparisons. We created a global, continuously updated, open-access database comprising 180 species and 64 families to compare floral damage between tropical and temperate plants, to examine the effects of plant traits on floral damage, and to explore the eco-evolutionary dynamics of flower-florivore interactions. Flower damage is widespread across angiosperms, but was two-fold higher in tropical vs temperate species, suggesting stronger fitness impacts in the tropics. Flowers were mostly damaged by chewers, but neither flower color nor symmetry explained differences in florivory. Herbivory and florivory levels were positively correlated within species, even though the richness of the florivore community does not affect florivory levels. We show that florivory impacts plant fitness via multiple pathways and that ignoring this interaction makes it more difficult to obtain a broad understanding of the ecology and evolution of angiosperms. Finally, we propose a standardized protocol for florivory measurements, and identify key research avenues that will help fill persistent knowledge gaps. Florivory is expected to be a central research topic in an epoch characterized by widespread decreases in insect populations that comprise both pollinators and florivores.

Ecosystem engineering in the arboreal realm: heterogeneity of wood-boring beetle cavities and their use by cavity-nesting ants.

Wood-boring beetle larvae act as ecosystem engineers by creating stem cavities that are used secondarily as nests by many arboreal ant species. Understanding the heterogeneity and distribution of available cavities and their use by ants is therefore key to understanding arboreal ant community assembly and diversity. Our goals were to quantify the abundance and diversity of beetle-produced cavity resources in a tropical canopy, reveal how ants use these resources, and determine which characteristics of the cavity resource contribute to ant use. We dissected branches from six common tree species in the Brazilian Cerrado savanna, measuring cavity characteristics and identifying the occupants. We sampled 2310 individual cavities, 576 of which were used as nests by 25 arboreal ant species. We found significant differences among tree species in the proportion of stem length bored by beetles, the number of cavities per stem length, average entrance-hole size, and the distribution of cavity volumes. The likelihood that a cavity was occupied was greater for cavities with larger entrance-hole sizes and larger volumes. In particular, there was a strong positive correlation between mean head diameters of ant species and the mean entrance-hole diameter of the cavities occupied by those ant species. Wood-boring beetles contribute to the structuring of the Cerrado ant community by differentially attacking the available tree species. In so doing, the beetles provide a wide range of entrance-hole sizes which ant species partition based on their body size, and large volume cavities that ants appear to prefer.

The effects of high-severity fires on the arboreal ant community of a Neotropical savanna.

Fire-suppression is of concern in fire-prone ecosystems because it can result in the loss of endemic species. Suppressing fires also causes a build-up of flammable biomass, increasing the risk of severe fires. Using a Before-After, Control-Impacted design, we assessed the consequences of high-severity fires on Neotropical savanna arboreal ant communities. Over a 9-year period, we sampled the ant fauna of the same trees before and after two severe fires that hit a savanna reserve in Brazil and the trees from an unburned savanna site that served as a temporal control. The ant community associated with the unburned trees was relatively stable, with no significant temporal variation in species richness and only a few species changing in abundance over time. In contrast, we found a strong decline in species richness and marked changes in species composition in the burned trees, with some species becoming more prevalent and many becoming rare or locally extinct. The dissimilarity in species richness and composition was significantly smaller between the two pre-fire surveys than between the pre- and post-fire surveys. Fire-induced changes were much more marked among species with strictly arboreal nesting habits, and therefore more susceptible to the direct effects of fire. The decline of some of the ecologically dominant arboreal ant species may be particularly important, as it opens substantial ecological space for cascading community-wide changes. In particular, severe fires appear to disrupt the typical vertical stratification between the arboreal and ground-dwelling faunas, which might lead to homogenization of the overall ant community.

Ant diversity in Neotropical savannas: Hierarchical processes acting at multiple spatial scales.

Understanding what creates and maintains macroscale biodiversity gradients is a central focus of ecological and evolutionary research. Spatial patterns in diversity are driven by a hierarchy of factors operating at multiple scales. Historical and climatic factors drive large-scale patterns of diversity by affecting the size of regional species pools, while habitat heterogeneity or microhabitat characteristics further influence species coexistence at small scales. We tested the degree to which the species-energy, historical factors, habitat heterogeneity and local environment hypotheses explain observed patterns of ant diversity across hierarchical spatial scales. We sampled ground-dwelling ants at 29 sites within a Neotropical savanna region, the Brazilian Cerrado. We measured species density - an abundance-dependent diversity metric - and rarefied species richness - an abundance-independent metric - at spatial scales with varying grain sizes. For each hypothesis, two correlates were used to predict ant diversity patterns: (a) species-energy: rainfall and productivity; (b) historical factors: historical variation in rainfall and refugial areas; (c) habitat heterogeneity: heterogeneity in greenness and diversity of land cover; and (d) local factors: contents of sand and coarse fragments in the soil. Ant diversity patterns correlated to net primary productivity and to the proportion of coarse fragments in the soil, corroborating the species-energy and local environment hypotheses, respectively. Soil negatively influenced species density, but not rarefied species richness, which was positively influenced by productivity. We found scale dependencies in the effects of soil/productivity on species density; productivity best predicted species density patterns at large scales, since sampling completeness offset the abundance-driven effects of soil. Considering abundance differences may help to discern the mechanisms underlying the relationship between macroscale diversity patterns and its ecological drivers. Plant productivity affected ant diversity independently of abundance, possibly by limiting the size of regional species pools. On the other hand, soil properties had an abundance-dependent effect on ant diversity, indicating a sampling mechanism. Our findings are consistent with predictions of the hierarchical theory of diversity. Large-scale patterns of productivity limit regional diversity, an effect that cascades down to finer spatial scales, where soil properties influence the number of coexisting species.

Revisiting ecological dominance in arboreal ants: how dominant usage of nesting resources shapes community assembly.

Ecologically dominant species can shape the assembly of ecological communities via altering competitive outcomes. Moreover, these effects may be amplified under limited niche differentiation. Nevertheless, the influences of ecological dominance and niche differentiation on assembly are rarely considered together. Here, we provide a novel examination of dominance in a diverse arboreal ant community, defining dominance by the prevalent usage of nesting resources and addressing how it influences community assembly. We first used a series of quantitative observational and experimental studies to address the natural nesting ecology, colony incidence on surveyed trees, and level of dominance over newly available nesting resources by our focal species, Cephalotes pusillus. The experimental studies were then used further to examine whether C. pusillus shapes assembly via an influence on cavity usage by co-occurring species. C. pusillus was confirmed as a dominant user of cavity nesting resources, with highly generalized nesting ecology, occupying about 50% of the trees within the focal system, and accounting for more than a third of new cavity occupation in experiments. Our experiments showed further that the presence of C. pusillus was associated with modest effects on species richness, but significant decreases in cavity-occupation levels and significant shifts in the entrance-size usage by co-occurring species. These results indicate that C. pusillus, as a dominant user of nesting resources, shapes assembly at multiple levels. Broadly, our findings highlight that complex interactions between a dominant species and the resource-usage patterns of other species can underlie species assembly in diverse ecological communities.

Global climate change increases risk of crop yield losses and food insecurity in the tropical Andes.

One of the greatest current challenges to human society is ensuring adequate food production and security for a rapidly growing population under changing climatic conditions. Climate change, and specifically rising temperatures, will alter the suitability of areas for specific crops and cultivation systems. In order to maintain yields, farmers may be forced to change cultivation practices, the timing of cultivation, or even the type of crops grown. Alternatively, farmers can change the location where crops are cultivated (e.g., to higher elevations) to track suitable climates (in which case the plants will have to grow in different soils), as cultivated plants will otherwise have to tolerate warmer temperatures and possibly face novel enemies. We simulated these two last possible scenarios (for temperature increases of 1.3°C and 2.6°C) in the Peruvian Andes through a field experiment in which several traditionally grown varieties of potato and maize were planted at different elevations (and thus temperatures) using either the local soil or soil translocated from higher elevations. Maize production declined by 21%-29% in response to new soil conditions. The production of maize and potatoes declined by >87% when plants were grown under warmer temperatures, mainly as a result of the greater incidence of novel pests. Crop quality and value also declined under simulated migration and warming scenarios. We estimated that local farmers may experience severe economic losses of up to 2,300 US$ ha-1  yr-1 . These findings reveal that climate change is a real and imminent threat to agriculture and that there is a pressing need to develop effective management strategies to reduce yield losses and prevent food insecurity. Importantly, such strategies should take into account the influences of non-climatic and/or biotic factors (e.g., novel pests) on plant development.

Dominance-diversity relationships in ant communities differ with invasion.

The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance-impoverishment rule states that high levels of dominance only occur in species-poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non-native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground-dwelling ants distributed across five continents to document the generality of the dominance-impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance-diversity relationship varies greatly, and depends on whether dominant species are native or non-native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance-impoverishment rule applies to invaded communities, we propose an alternative dominance-diversification rule for native communities.

Biogeography of mutualistic fungi cultivated by leafcutter ants.

Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov-Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.

The most relictual fungus-farming ant species cultivates the most recently evolved and highly domesticated fungal symbiont species.

Fungus-farming (attine) ant agriculture is made up of five known agricultural systems characterized by remarkable symbiont fidelity in which five phylogenetic groups of ants faithfully cultivate five phylogenetic groups of fungi. Here we describe the first case of a lower-attine ant cultivating a higher-attine fungus based on our discovery of a Brazilian population of the relictual fungus-farming ant Apterostigma megacephala, known previously from four stray specimens from Peru and Colombia. We find that A. megacephala is the sole surviving representative of an ancient lineage that diverged ∼39 million years ago, very early in the ∼55-million-year evolution of fungus-farming ants. Contrary to all previously known patterns of ant-fungus symbiont fidelity, A. megacephala cultivates Leucoagaricus gongylophorus, a highly domesticated fungal cultivar that originated only 2-8 million years ago in the gardens of the highly derived and recently evolved (∼12 million years ago) leaf-cutting ants. Because no other lower fungus-farming ant is known to cultivate any of the higher-attine fungi, let alone the leaf-cutter fungus, A. megacephala may provide important clues about the biological mechanisms constraining the otherwise seemingly obligate ant-fungus associations that characterize attine ant agriculture.

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.

Extrafloral nectaries have a limited effect on the structure of arboreal ant communities in a Neotropical savanna.

How environmental contexts shape the strength of species interactions, and their influence on community structure, remains a key focus for the field of community ecology. In particular, the extent to which local competitive interactions impact community structure, and whether this differs across contexts, persists as a general issue that is unresolved across a broad range of animal systems. Studies of arboreal ants have shown that competitive interactions over carbon-rich exudates from extrafloral nectaries (EFNs) and homopteran aggregations can have positive and negative effects on the local abundances of individual species. Nevertheless, it is still unclear the extent to which these local effects scale to community-level effects. Here we address the role of food from extrafloral nectaries on the structure of arboreal ant communities in a savanna of central Brazil. We did this with a combination of a diversity survey across tree species with and without EFNs, a repeated survey at times of peak EFN activity, and testing of our survey findings with two experimental manipulations of nectar availability that also provided supplementary nesting cavities. Species richness, but not composition, differed significantly between trees with and without EFNs. However, trees with EFNs had, on average, only 9% more species than those without EFNs. Furthermore, ant species richness did not differ significantly between periods of high and low EFN activity. Although nectar supplementation significantly affected nest occupation rates, this difference was seen solely in. the experiment with a massive supply of nectar and there was no effect on total ant richness or identity of the focal assemblages. Our findings suggest that the effects of extrafloral nectar on the abundances of arboreal ants at local scales do not scale to a strong structuring force at the community level. We suggest that this is most likely due to a lack of specificity of community members for EFN tree species, and the diffuse temporal and spatial nature of the availability of active EFNs. These properties mean that observable short-lived activity and competition over particular EFNs does not ultimately drive lasting changes in the associated assemblage of species, and therefore, the community as a whole.

Stability and phylogenetic correlation in gut microbiota: lessons from ants and apes.

Correlation between gut microbiota and host phylogeny could reflect codiversification over shared evolutionary history or a selective environment that is more similar in related hosts. These alternatives imply substantial differences in the relationship between host and symbiont, but can they be distinguished based on patterns in the community data themselves? We explored patterns of phylogenetic correlation in the distribution of gut bacteria among species of turtle ants (genus Cephalotes), which host a dense gut microbial community. We used 16S rRNA pyrosequencing from 25 Cephalotes species to show that their gut community is remarkably stable, from the colony to the genus level. Despite this overall similarity, the existing differences among species' microbiota significantly correlated with host phylogeny. We introduced a novel analytical technique to test whether these phylogenetic correlations are derived from recent bacterial evolution, as would be expected in the case of codiversification, or from broader shifts more likely to reflect environmental filters imposed by factors such as diet or habitat. We also tested this technique on a published data set of ape microbiota, confirming earlier results while revealing previously undescribed patterns of phylogenetic correlation. Our results indicated a high degree of partner fidelity in the Cephalotes microbiota, suggesting that vertical transmission of the entire community could play an important role in the evolution and maintenance of the association. As additional comparative microbiota data become available, the techniques presented here can be used to explore trends in the evolution of host-associated microbial communities.

Attack frequency and the tolerance to herbivory of Neotropical savanna trees.

Tolerance is the ability of a plant to regrow or reproduce following damage. While experimental studies typically measure tolerance in response to the intensity of herbivory (i.e., the amount of leaf tissue removed in one attack), the impact of how many times plants are attacked during a growing season (i.e., the frequency of damage) is virtually unexplored. Using experimental defoliations that mimicked patterns of attack by leaf-cutter ants (Atta spp.), we examined how the frequency of herbivory influenced plant tolerance traits in six tree species in Brazil's Cerrado. For 2 years we quantified how monthly and quarterly damage influenced individual survivorship, relative growth rate, plant architecture, flowering, and foliar chemistry. We found that the content of leaf nitrogen (N) increased among clipped individuals of most species, suggesting that Atta influences the allocation of resources in damaged plants. Furthermore, our clipping treatments affected tree architecture in ways thought to promote tolerance. However, none of our focal species exhibited a compensatory increase in growth (increment in trunk diameter) in response to herbivory as relative growth rates were significantly lower in clipped than in unclipped individuals. In addition, the probability of survival was much lower for clipped plants, and lower for plants clipped monthly than those clipped quarterly. For plants that did survive, simulated herbivory dramatically reduced the probability of flowering. Our results were similar across a phylogenetically distinct suite of species, suggesting a potential extendability of these findings to other plant species in this system.

Canopy connectivity and the availability of diverse nesting resources affect species coexistence in arboreal ants.

1. Arboreal ants are both diverse and ecologically dominant in the tropics. Such ecologically important groups are likely to be particularly useful in ongoing empirical efforts to understand the processes that regulate species diversity and coexistence. 2. Our study addresses how access to tree-based resources and the diversity of pre-existing nesting cavities affect species diversity and coexistence in tropical arboreal ant assemblages. We focus on assemblage-level responses to these variables at local scales. We first surveyed arboreal ant diversity across three naturally occurring levels of canopy connectivity and a gradient of tree size. We then conducted whole-tree experimental manipulations of canopy connectivity and the diversity of cavity entrance sizes. All work was conducted in the Brazilian savanna or 'cerrado'. 3. Our survey suggested that species richness was equivalent among levels of connectivity. However, there was a consistent trend of lower species density with low canopy connectivity. This was confirmed at the scale of individual trees, with low-connectivity trees having significantly fewer species across all tree sizes. Our experiment demonstrated directly that low canopy connectivity results in significantly fewer species coexisting per tree. 4. A diverse array of cavity entrance sizes did not significantly increase overall species per tree. Nevertheless, cavity diversity did significantly increase the species using new cavities on each tree, the species per tree unique to new cavities, total species using new cavities, and total cavity use. The populations of occupied cavities were consistent with newly founded colonies and new nests of established colonies from other trees. Cavity diversity thus appears to greatly affect new colony founding and colony growth. 5. These results contribute strong evidence that greater resource access and greater cavity diversity have positive effects on species coexistence in local arboreal ant assemblages. More generally, these positive effects are broadly consistent with niche differentiation promoting local species coexistence in diverse arboreal ant assemblages. The contributions of this study to the understanding of the processes of species coexistence are discussed, along with the potential of the focal system for future work on this issue.

Nesting biology and fungiculture of the fungus-growing ant, Mycetagroicus cerradensis: new light on the origin of higher attine agriculture.

The genus Mycetagroicus is perhaps the least known of all fungus-growing ant genera, having been first described in 2001 from museum specimens. A recent molecular phylogenetic analysis of the fungus-growing ants demonstrated that Mycetagroicus is the sister to all higher attine ants (Trachymyrmex, Sericomyrmex, Acromyrmex, Pseudoatta, and Atta), making it of extreme importance for understanding the transition between lower and higher attine agriculture. Four nests of Mycetagroicus cerradensis near Uberlândia, Minas Gerais, Brazil were excavated, and fungus chambers for one were located at a depth of 3.5 meters. Based on its lack of gongylidia (hyphal-tip swellings typical of higher attine cultivars), and a phylogenetic analysis of the ITS rDNA gene region, M. cerradensis cultivates a lower attine fungus in Clade 2 of lower attine (G3) fungi. This finding refines a previous estimate for the origin of higher attine agriculture, an event that can now be dated at approximately 21-25 mya in the ancestor of extant species of Trachymyrmex and Sericomyrmex.

How much leaf area do insects eat? A data set of insect herbivory sampled globally with a standardized protocol.

Herbivory is ubiquitous. Despite being a potential driver of plant distribution and performance, herbivory remains largely undocumented. Some early attempts have been made to review, globally, how much leaf area is removed through insect feeding. Kozlov et al., in one of the most comprehensive reviews regarding global patterns of herbivory, have compiled published studies regarding foliar removal and sampled data on global herbivory levels using a standardized protocol. However, in the review by Kozlov et al., only 15 sampling sites, comprising 33 plant species, were evaluated in tropical areas around the globe. In Brazil, which ranks first in terms of plant biodiversity, with a total of 46,097 species, almost half (43%) being endemic, a single data point was sampled, covering only two plant species. In an attempt to increase knowledge regarding herbivory in tropical plant species and to provide the raw data needed to test general hypotheses related to plant-herbivore interactions across large spatial scales, we proposed a joint, collaborative network to evaluate tropical herbivory. This network allowed us to update and expand the data on insect herbivory in tropical and temperate plant species. Our data set, collected with a standardized protocol, covers 45 sampling sites from nine countries and includes leaf herbivory measurements of 57,239 leaves from 209 species of vascular plants belonging to 65 families from tropical and temperate regions. They expand previous data sets by including a total of 32 sampling sites from tropical areas around the globe, comprising 152 species, 146 of them being sampled in Brazil. For temperate areas, it includes 13 sampling sites, comprising 59 species. Thus, when compared to the most recent comprehensive review of insect herbivory (Kozlov et al.), our data set has increased the base of available data for the tropical plants more than 460% (from 33 to 152 species) and the Brazilian sampling was increased 7,300% (from 2 to 146 species). Data on precise levels of herbivory are presented for more than 57,000 leaves worldwide. There are no copyright restrictions. Please cite this paper when using the current data in publications; the authors request to be informed how the data is used in the publications.

Canopy and litter ant assemblages share similar climate-species density relationships.

Tropical forest canopies house most of the globe's diversity, yet little is known about global patterns and drivers of canopy diversity. Here, we present models of ant species density, using climate, abundance and habitat (i.e. canopy versus litter) as predictors. Ant species density is positively associated with temperature and precipitation, and negatively (or non-significantly) associated with two metrics of seasonality, precipitation seasonality and temperature range. Ant species density was significantly higher in canopy samples, but this difference disappeared once abundance was considered. Thus, apparent differences in species density between canopy and litter samples are probably owing to differences in abundance-diversity relationships, and not differences in climate-diversity relationships. Thus, it appears that canopy and litter ant assemblages share a common abundance-diversity relationship influenced by similar but not identical climatic drivers.

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness.

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.

Long-term persistence of a neotropical ant-plant population in the absence of obligate plant-ants.

Interactions between ants and ant-plants are considered classic examples of obligate mutualisms. Previous studies have indicated that for many ant-plants the loss of ant colonies results in severe defoliation or mortality. Although individual plants can persist for some period of time without their mutualistic partners, to date populations of ant-free plants have only been recorded at high altitudes or on remote islands where herbivores are also scarce. We studied the interaction between ants, herbivores, and the ant-plant Tococa guianensis in the Cerrado region of central Brazil. Using a survey conducted across a large geographic region, we show that there is interpopulation variation in ant occupancy across sites and habitats. At most sites surveyed, plants were inhabited by Allomerus octoarticulatus, an obligate plant-ant. Plants with obligate ants had significantly lower standing levels of herbivore damage than plants with opportunistic ants and plants with no ant occupants. Furthermore, experimental removal of A. octoarticulatus resulted in increased levels of damage in both young and mature leaves. Despite the protection provided by obligate ants, populations of T. guianensis were found to persist without these ants in some areas. Plants without A. octoarticulatus had significantly greater leaf toughness and trichome density than those with A. octoarticulatus. Furthermore, trichome density in plants with A. octoarticulatus increased after ants were removed, probably as a response induced by increased levels of herbivore damage. To our knowledge, this is the first record of the occurrence of native myrmecophyte populations without their mutualistic ants in mainland low-elevation sites. Several factors may help to explain the long-term persistence of T. guianensis populations without plant-ants in some areas of the Brazilian Cerrado, including its potential for induced morphological defenses against insect herbivores and selection for increased levels of constitutive defenses. In addition, T. guianensis may be under lower herbivore pressure in the sites we studied than in other parts of its range because existing populations were small, isolated, and some were very close to the edge of this species' distribution.

Functional richness shows spatial scale dependency in Pheidole ant assemblages from Neotropical savannas.

There is a growing recognition that spatial scale is important for understanding ecological processes shaping community membership, but empirical evidence on this topic is still scarce. Ecological processes such as environmental filtering can decrease functional differences among species and promote functional clustering of species assemblages, whereas interspecific competition can do the opposite. These different ecological processes are expected to take place at different spatial scales, with competition being more likely at finer scales and environmental filtering most likely at coarser scales. We used a comprehensive dataset on species assemblages of a dominant ant genus, Pheidole, in the Cerrado (savanna) biodiversity hotspot to ask how functional richness relates to species richness gradients and whether such relationships vary across spatial scales. Functional richness of Pheidole assemblages decreased with increasing species richness, but such relationship did not vary across different spatial scales. Species were more functionally dissimilar at finer spatial scales, and functional richness increased less than expected with increasing species richness. Our results indicate a tighter packing of the functional volume as richness increases and point out to a primary role for environmental filtering in shaping membership of Pheidole assemblages in Neotropical savannas. OPEN RESEARCH BADGES: This article has been awarded Open Materials, Open Data, Preregistered Research Designs Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5061/dryad.31201jg.