Ant Communities Research Articles

Disentangling the factors that shape bromeliad and ant communities in the canopies of cocoa agroforestry and preserved Atlantic Forest

AbstractIn tropical forest canopies, host tree characteristics shape epiphyte communities, and both host tree characteristics and epiphytes determine invertebrate communities, for example, ants. Tree height is among the factors most often mentioned as a strong predictor for both bromeliad and ant communities. However, many factors interact dynamically in shaping the tree–bromeliad–ant association. Here, we investigated the effects of the host tree and canopy structural characteristics on both bromeliads and ants. We sampled bromeliads on 180 trees and ants in 360 bromeliads living on a subset of 60 of those trees in a continuum of native forest fragments and agroforestry systems in the Atlantic Forest, a Brazilian biodiversity hotspot. We found that the host trees’ crown area had a positive effect on the abundance of bromeliads. Also, the introduced tree species had higher abundance of bromeliads than native tree species. Moreover, we found that the ant species composition was different between native and introduced trees. In addition, we observed a positive effect of the size of bromeliads and tree crown height on ant species richness on both bromeliad and tree scales, but there was no effect of tree height. Taken together, our findings highlight the importance of trees with large crowns for the maintenance of bromeliads, which are also associated with richer ant communities in both Atlantic Forest and agroforestry systems. These results emphasize the importance of trees with larger crowns for biodiversity conservation in both native forest fragments and agroforestry systems.Abstract in Portuguese is available with online material.

Invasive ant establishment, spread, and management with changing climate.

Ant invasions and climate change both pose globally widespread threats to the environment and economy. I highlight our current knowledge of how climate change will affect invasive ant distributions, population growth, spread, impact, and invasive ant management. Invasive ants often have traits that enable rapid colony growth in a range of habitats. Consequently, many invasive ant species will continue to have large global distributions as environmental conditions change. Distributions and impacts at community scales will depend on how resident ant communities respond to local abiotic conditions as well as availability of plant-based carbohydrate resources. Though target species may change under an altered climate, invasive ant impacts are unlikely to diminish, and novel control methods will be necessary.

Ant Communities and Ecosystem Services in Organic Versus Conventional Agriculture in the U.S. Corn Belt.

Reducing the use of synthetic fertilizers and pesticides can limit negative impacts of agriculture on insects and is a crucial step towards sustainable agriculture. In the United States, organic agriculture has the potential to reduce greenhouse gas emissions, pollutant runoff, and biodiversity loss in the Midwestern Corn Belt-an area extending over 500,000 km2 devoted to intensive production of corn Zea mays (Linnaeus 1753) (Poales: Poaceae), often in rotation with soy Glycine max (Linnaeus 1753) (Fabales: Fabaceae) or wheat Triticum aestivum (Linnaeus 1753) (Poales: Poaceae). Working in 30-yr-long landscape experiments in this region, we tested for impacts of conventional versus organic agriculture on ant communities (Hymenoptera: Formicidae) and potential ecosystem services they provide. Organic fields supported higher ant diversity and a slightly more species-rich ant assemblage than conventionally managed fields but did not otherwise differ in community composition. Despite similar community composition, organic and conventional fields differed in seasonal patterns of ant foraging activity and potential for natural pest suppression. Conventional plots experienced higher overall ant foraging activity, but with the timing skewed towards late in the growing season such that 75% of ant foraging occurred after crop harvest in a wheat year and was therefore unavailable for pest suppression. Organic fields, in contrast, experienced moderate levels of ant foraging activity throughout the growing season, with most foraging occurring during crop growth. Organic fields thus supported twice as much pest suppression potential as conventional fields. Our results highlight the importance of timing in mediating ecosystem services in croplands and emphasize the value of managing landscapes for multiple services rather than yield alone.

Ant diversity inhabited oil palm plantations in a peatland in Sumatra, Indonesia

Abstract. Johari A, Hermanto MA, Wulandari T. 2021. Ant diversity inhabited oil palm plantations in a peatland in Sumatra, Indonesia. Nusantara Bioscience 13: 158-163. Ant community is one of the soil biotic components with diverse roles, including pollinators, predators, decomposers, parasites, and herbivores. Changes in land use from natural habitats to plantations affect the diversity and composition of ants because these groups are very vulnerable to environmental changes. The purpose of the study was to analyze the diversity of ants (Formicidae) found in peatland planted with oil palm. The study was conducted on peatland in Gambut Jaya village, Sungai Gelam sub-district, Muaro Jambi district, Indonesia from October 2019 to May 2020. The research was conducted through surveys in two peatland locations (natural peatland and oil palm plantation) using the purposive sampling technique through the stages of transect making, field sampling, sample preparation, and identification. A total of 2636 individuals of ants were collected from natural peatland, while 3183 individuals were found in oil palm plantations. Eight ant species were identified from both study sites belong to four subfamilies, namely Dolichoderinae, Formicinae, Myrmicinae, and Ponerinae. Among the species, Dolichoderus thoracicus were most dominant, composed 63.6% in natural peat-land and 73.6% in oil palm plantation. The diversity index of ant species in natural peatland was higher (0.97) than that in oil palm plantations (0.88), indicate the change in the abundance and diversity of ant species in oil palm plantations. Therefore, efforts to preserve the habitat of ants by maintaining their microhabitat and resource, as well as conserving the important species such as natural enemies of pests, need to be taken into account in peatland management.

Ant Species Diversity, Distribution, and Community Composition in Different Forest Types in Papua New Guinea

Previous studies have provided important scientific information on ant species richness and composition relating to the effects of elevation, sampling approaches, stratification, and forest succession. Yet, they have primarily focused on single sites or regions. Knowledge of ant ecology should also include the impact of disturbance in various forest types. Tuna baiting and hand collection methods were used to investigate diversity and community composition of ants in 16 sites sampled across Papua New Guinea, in both disturbed and pristine forest, at heights ranging from 28 to 2,728 m above sea level. We found 176 species as a result of exposing 320 tuna baits and traversing 72 hand-searched plots. Baiting samples were strongly dominated by a few common species, while the hand-collecting captured more species per plot. The Chao 2 richness estimator for both methods predicted undersampling of the local community. As expected, ant species diversity and richness significantly decrease with increasing elevation. We observed, on average, greater species diversity of ground-dwelling ant communities in disturbed compared to undisturbed forests. The effect was not significant using multivariate randomisations, since the same species dominated both forest classes. The unexpected pattern of ant species richness being locally higher in the disturbed sites is driven by our sampling of undisturbed communities at all elevations, but sampling of the disturbed communities only up to 1,600 m above sea level. Hence, future studies should consider more locations, aiming ideally for an equal sampling effort to capture disturbance stage and elevation.

Multiyear drought exacerbates long-term effects of climate on an invasive ant species.

Invasive species threaten biodiversity, ecosystem function, and human health, but the long‐term drivers of invasion dynamics remain poorly understood. We use data from a 28‐yr ongoing survey of a Northern California ant community invaded by the Argentine ant (Linepithema humile) to investigate the influence of abiotic and biotic factors on invasion dynamics. We found that the distribution of L. humile retracted following an extreme drought that occurred in the region from 2012 to 2015. The distribution of several native ant species also contracted, but overall native ant diversity was higher after the drought and for some native ant species, distributions expanded over the 28‐yr survey period. Using structural equation models, we found the strongest impact on the distribution of L. humile was from direct effects of climate, namely, cumulative precipitation and summer maximum temperatures, with only a negligible role for biotic resistance and indirect effects of climate mediated by native ants. The increasing drought and high temperature extremes projected for northern California because of anthropogenic‐driven climate change may limit the spread, and possibly the impact, of L. humile in invaded regions. The outcome will depend on the response of native ant communities to these climatic stressors.

β diversity among ant communities on fragmented habitat islands: the roles of species trait, phylogeny and abundance

Habitat loss and fragmentation reduce biodiversity and alter species composition in local communities. β diversity describes the variation in species composition between or among communities in fragmented landscapes and has two components: species turnover and nestedness. In this study, we assessed β diversity of ant assemblages on 24 island fragments in the Thousand Island Lake, China. We constructed a species‐level phylogenetic tree and measured five morphological traits of all ant species captured. We then assessed taxonomic (both incidence‐based and abundance‐weighted), functional and phylogenetic β diversity and partitioned β diversity into turnover and nestedness (as well as the contributions of particular species and particular islands). Finally, we examined the relationships between β diversity and a suite of geographical variables (i.e. difference in island area, difference in isolation and inter‐island distance) using Mantel tests. We found taxonomic and phylogenetic turnover components dominated overall β diversity whereas the functional turnover and nestedness components contributed equally to overall β diversity. Overall β diversity increased with increasing difference in isolation and inter‐island distance; however, only abundance‐weighted overall β diversity decreased with increasing difference in island size. Our results indicate that species that were abundant on large islands were also abundant on small islands. We conclude that the dispersal limitation of ants likely shapes the pattern of β diversity along isolation and inter‐island distance gradients. Additionally, functional redundancy of species (i.e. different species share similar functional roles) could also explain β diversity patterns among fragmented habitat islands. Our results highlight the necessity of incorporating both incidence‐based and abundance‐weighted community data when examining β diversity in fragmented landscapes. By partitioning β diversity into the contributions of particular species and particular fragments, our study implies that small patches can be valuable for maintaining biodiversity among ant communities.

High Diversity in Urban Areas: How Comprehensive Sampling Reveals High Ant Species Richness within One of the Most Urbanized Regions of the World

The continuous increase in urbanization has been perceived as a major threat for biodiversity, particularly within tropical regions. Urban areas, however, may still provide opportunities for conservation. In this study focused on Macao (China), one of the most densely populated regions on Earth, we used a comprehensive approach, targeting all the vertical strata inhabited by ants, to document the diversity of both native and exotic species, and to produce an updated checklist. We then compared these results with 112 studies on urban ants to illustrate the dual roles of cities in sustaining ant diversity and supporting the spread of exotic species. Our study provides the first assessment on the vertical distribution of urban ant communities, allowing the detection of 55 new records in Macao, for a total of 155 ant species (11.5% being exotic); one of the highest species counts reported for a city globally. Overall, our results contrast with the dominant paradigm that urban landscapes have limited conservation value but supports the hypothesis that cities act as gateways for exotic species. Ultimately, we argue for a more comprehensive understanding of ants within cities around the world to understand native and exotic patterns of diversity.

Rainforest conversion to monocultures favors generalist ants with large colonies

AbstractThe conversion of natural ecosystems to agricultural land is one of the most important drivers of biodiversity decline worldwide, particularly in the tropics. Species loss is typically trait‐associated, leading to filtering of disturbance‐resistant species during community assembly, which affects ecosystem functioning and evolutionary potential of communities. To understand the ecological and phylogenetic impact of rainforest conversion to agricultural systems, we combine analysis of nesting habit, feeding habit, colony size, and body size of canopy ants (Formicidae) with a phylogenetic analysis of species collected in four land‐use systems in Sumatra, Indonesia: (1) lowland tropical rainforest, (2) jungle rubber (extensive rubber agroforest), and smallholder plantations of (3) rubber and (4) oil palm. Canopy ant communities in these land‐use systems differed in trait composition, with a larger proportion of generalist nesting and generalist‐omnivore feeding species in oil palm compared to rainforest and a larger proportion of generalist nesters and species with large colonies (>1000 individuals) in rubber than in rainforest. Traits of canopy ant communities in jungle rubber were more similar to those in rainforest than to those in rubber and oil palm plantations. In rainforest, mean pairwise phylogenetic distance was lower than expected for random community assembly, but did not differ from random in the other land‐use systems. Of the traits nesting habit, feeding habit, and colony size, only feeding habit exhibited phylogenetic signal. Our results show that rainforest conversion to agricultural systems is accompanied by shifts in trait composition of canopy ant communities. Further, our results argue against environmental filtering of closely related canopy ant species as the major community assembly mechanism in plantation systems, but suggest that the Sumatran lowland rainforests harbor recently diverged endemic ant species that are particularly vulnerable to rainforest conversion to agricultural systems. Given the importance of ants for tropical ecosystems, the ecological differences among ant communities along the land‐use gradient might have important consequences for ecosystem functioning and services in plantation systems.

A comparative assessment on ant communities in three vegetation types located at Mfou Suburban locality of Yaoundé (Cameroon)

Urban expansion in Cameroon and many other Congo basin countries, involves the destruction of natural habitat previously colonized by a rich and diversified invertebrate and vertebrate fauna. In order to understand the dynamic of transformation of natural landscape into urban area on ant communities, a study was conducted at Mfou, a suburban agglomeration of Yaoundé. We aimed to evaluate the variation in ant diversity and ant community structure in relation to the type of habitat. Ants were collected on the ground and trees in cocoa farms, secondary forests, and palm groves using visual catch, pitfall traps, quadrat, and baits. We recorded 144 species belonging to 39 genera and 6 subfamilies. Cocoa farms (S= 102; H’= 3.83; E=0.83) were richer and more diversified than secondary forests (S= 100; H’= 3.83; E=0.83) and palm groves (S= 70; H’= 3.61; E=0.85). Myrmicinae, Formicinae and Ponerinae were the richest subfamilies both at genus and species levels. Based on their frequency of occurrence, Myrmicaria opaciventris (18.6%), Crematogaster striatula (17.1%), Crematogaster gabonensis (14.9%) and Camponotus crawleyi Emery, 1920 (14.2%) species were numerically dominant. Strumigenys sp.1, Strumigenys sp.2, Strumigenys sp.3, and Strumigenys sp.4 species were found only in secondary forests, suggesting the relatively stability of this habitat despite anthropogenic disturbance. Camponotus brevicollis, Technomyrmex sp.2 and Tetramorium guineensis were the indicator species in cocoa farms. In the secondary forests, Camponotus wellmani, Hypoponera punctatissima and Pheidole pulchella were found as indicator species while in palm groves H. punctatissima was the only indicator species.

Temporal variation in ant community assemblages along a rural–urban gradient in the Yaoundé metropolis, Cameroon

Temporal variation in ant community assemblages along a rural–urban gradient in the Yaoundé metropolis, Cameroon

Discovery-defense strategy as a mechanism of social foraging of ants in tropical rainforest canopies

AbstractMany hypotheses have been proposed to explain the coexistence of ants sharing similar food resources, including ecological trade-offs, however, these hypotheses have mostly been tested in ground-dwelling ant communities. For instance, the discovery-dominance trade-off hypothesis states that species with overlapping food resources differ in their ability to find and dominate resources. However, ant species may use different strategies to share food resources, including discovery-defense, in which the first species to arrive at a food resource maintains control of it. Here, we evaluated whether the discovery-dominance trade-off hypothesis, or the discovery-defense strategy could be a mechanism that promotes coexistence of ant species in the canopy of highly diverse tropical forest canopies. We evaluated the succession of ant species on 72 baits exposed on 24 trees during 13 observation periods (15–195 min) in the canopy of a tropical rain forest in Mexico. In general, we observed little variation in ant species composition (i.e., low β-diversity values) during the 195 min of bait exposure. Moreover, we found that ant species with the greatest ability to discover new food resources were those that dominated them. These findings empirically show that the discovery-defense strategy can be a social foraging strategy in rain forest canopy ants and reject the discovery-dominance trade-off. In short, our results highlight the importance of the discovery of a food resource in the canopy of a tropical rain forest, allowing it to be dominated.

Tree Preference and Temporal Activity Patterns for a Native Ant Community in an Urbanized California Woodland

Anthropogenic disturbances, including land use change and exotic species, can alter the diversity and dynamics of ant communities. To examine foraging behavior in an urbanized habitat in northern California, we surveyed the presence of 9 ant species on 876 trees across 4 seasons during both day and night in a 9.5-hectare urbanized oak-exotic woodland. Ants were more likely to be observed on native, evergreen trees, suggesting that native evergreen species may help maintain ant diversity. Species showed clear patterns of temporal partitioning of foraging activity. Ant species varied in their use of native evergreen Quercus agrifolia trees across season and day/night axes. Of the 3 ant species most frequently observed, Camponotus semitestaceus was most active during spring and summer nights, Formica moki was most active during spring and summer days, and Prenolepis imparis was most active during both day and night during fall and winter. Liometopum occidentale was the second most active species during summer day and night, and winter day. Our findings demonstrate that an oak-exotic urban woodland in Northern California was able to maintain a native ant community, and strong temporal partitioning within that community.

Soil-litter ant (Hymenoptera: Formicidae) community response to reforested lands of Gishwati tropical montane forest, northern-western part of Rwanda

AbstractRecently, human activities have impacted biodiversity-rich forest in western Rwanda, creating a need to enhance restoration activities of degraded lands in the region. To evaluate the effects of reforestation activities on the community composition of soil-litter ants, research was conducted in Gishwati tropical montane forest, located in northern-western part of Rwanda. The ant fauna was studied in reforested lands dominated by regenerated native species and exotic tree species. Further, a primary forest made of native trees served as a reference. In each forest type, nine sampling points were used to sample ants. Ant specimens were collected using pitfalls, hand sampling and Winkler extractor. They were identified to subfamilies, genus and species levels using dichotomous keys, and also statistically analysed for species richness, diversity, evenness and community composition. We collected a total of 2,481 individuals from 5 subfamilies, 18 genera and 35 species. Higher abundance, diversity and species richness were found in soil-litter under natural primary and secondary forests dominated by regenerated native plant species compared to exotic tree forest. The ant community composition analysis indicated higher similarities in ant species sampled under primary native forest and secondary forest dominated by regenerated native species. Reforestation by regenerating native species may be given priority in restoration of degraded lands due to their importance in species richness and species diversity.

Thermal traits predict the winners and losers under climate change: an example from North American ant communities

AbstractAcross the globe, temperatures are predicted to increase with consequences for many taxonomic groups. Arthropods are particularly at risk as temperature imposes physiological constraints on growth, survival, and reproduction. Given that arthropods may be disproportionately affected in a warmer climate—the question becomes which taxa are vulnerable and can we predict the supposed winners and losers of climate change? To address this question, we resurveyed 33 ant communities, quantifying 20‐yr differences in the incidence of 28 genera. Each North American ant community was surveyed with 30 1‐m2 plots, and the incidence of each genus across the 30 plots was used to estimate change. From the original surveys in 1994–1997 to the resurveys in 2016–2017, temperature increased on average 1°C (range, −0.4°C to 2.5°C) and ~64% of ant genera increased in more than half of the sampled communities. To test Thermal Performance Theory's prediction that genera with higher average thermal limits will tend to accumulate at the expense of those with lower limits, we quantified critical thermal maxima (CTmax: the high temperatures at which they lose muscle control) and minima (CTmin: the low temperatures at which ants first become inactive) for common genera at each site. Consistent with prediction, we found a positive decelerating relationship between CTmax and the proportion of sites in which a genus had increased. CTmin, by contrast, was not a useful predictor of change. There was a strong positive correlation (r = 0.85) between the proportion of sites where a genus was found with higher incidence after 20 yr and the average difference in number of plots occupied per site, suggesting genera with high CTmax values tended to occupy more plots at more sites after 20 yr. Thermal functional traits like CTmax have thus proved useful in predicting patterns of long‐term community change in a dominant, diverse insect taxon.

Ants community structure in the urban and the city suburbs areas of Douala (Littoral-Cameroon)

The Douala harbour represents the main gateway through which human activities introduce invasive ants, so that Solenopsis geminata (Fabricius, 1804) originating from Neotropics has been reported in several areas of the Littoral region of Cameroon. But nothing is known about the ant community structure and composition of the coastal zone. We hypothesized that environmental perturbations around Douala have repercussions on the native litter-dwelling ants. Collections conducted in 33 houses, six gardens of 225 m² each, 41 plantations of one hectare each and 34 two-year old fallows of one hectare each suggested lowly even communities, low species richness, low diversity and low dominance by a few species. Among 28 species recorded four species were mostly represented: two foreign origin species [S. geminata (Fabricius, 1804) and Trichomyrmex destructor (Jerdon, 1851), from tropical America and India respectively], one native species [Pheidole megacephala (Fabricius, 1793)] and two ambiguous native range species [Paratrechina longicornis (Latreille, 1802) and Tapinoma melanocephalum (Fabricius, 1793)] since they have long been recorded as having a widespread distribution. Alien species were highly represented than native ones (52.9% and 47.1% respectively, p<0.001). Inside houses, gardens and plantations the ant species were distributed according to the geometrical progression (Motomura’s model) while in the old fallows abundance distribution suggested an evolved ecosystem (Mandelbrot’s model). Between the three dominant species [Pa. longicornis (Latreille, 1802), Ph. megacephala (Fabricius) and S. geminata (Fabricius)], the first species was positively correlated with the third one while other associations were not significant. These dominant species appeared influencing the abundance of the rare species. Dominance and high abundance of a few species indicated that areas were influenced mostly by interspecies competition and/or disturbance by human activities.

Similarity of ant communities increases with isolation from natural habitat and abundance of invasive ants in oil palm plantations of Central Borneo

Natural habitats can support insect diversity and shape their community structure in agroecosystems. The objective of this research was to investigate how proximity of natural habitat and invasive ant species influences the community structure of ants in oil palm plantations in Central Borneo, Indonesia. Twelve oil palm fields, at varying distances from areas of remaining forest or natural habitat, were selected as research plots. In each plot, insects were sampled using canopy knockdown fogging with a pyrethroid insecticide. In total, we found 62 canopy ant species belonging to six subfamilies. We found that Anoplolepis gracilipes (invasive species) and Oecophylla smaragdina were the most abundant ant species across all of our plots, and their abundances were not spatially correlated. Distance of oil palm fields to natural habitat did not affect species richness and abundance of ants, but affected ant community similarity. Based on the generalized linear models, the ant community similarity was not only affected by the distance to natural habitat but also affected by the abundance of A. gracilipes. A. gracilipes abundance also had a negative effect on other ant abundance especially O. smaragdina. In conclusion, the occurrence of natural habitats helps shape the similarity of ant community in oil palm plantations possibly via inhibits the abundance of invasive species.

Patterns of Ant Diversity in the Natural Grasslands of Southern Brazil.

In the south of Brazil, grasslands are naturally widespread over two different biomes, the Pampa in the southernmost region and within the Atlantic Forest in the northern portions. The natural grasslands of the state of Paraná comprise a very particular physiognomy composed of two distinct formations: the Campos Gerais and the grasslands of the southwest. The first is located in the edge of the second plateau of Paraná state, comprising a great diversity of environments. The grasslands of the southwest are more homogeneous, with a continuous herbaceous stratum dominating the landscape. In this context, the aim of this study was to evaluate the patterns of species richness and composition of ants, an ecologically prominent group, along the natural grasslands of Paraná. We also intended to compare the faunal similarity between the two different grassland formations. For that, four different Conservation Unities were sampled along a latitudinal gradient. A remarkable total of 245 ant species was recorded, and the results indicate that species richness decreases as latitude increases along the grasslands of Paraná. There were clear differences in species composition between these two grasslands formations, given the significative number of endemic species in each of these two grassland formations. Ten species were recorded for the first time in the state of Paraná, of which three also for the first time in the Southern Region of Brazil. Overall, our study contributes to a better understanding about the diversity and composition of ant communities in subtropical grasslands.

First record of Aphis lugentis in Australia, tended by native ants on Senecio odoratus

AbstractWe report the discovery of the invasive aphid Aphis lugentis for the first time in Australia. This aphid specialises on Compositae, particularly on Senecio species. Aphids were tended by several ant species at a site on Kangaroo Island, South Australia, which is unlikely to be the location of the original introduction. We recommend the investigation of the distribution of A. lugentis in Australia and its impacts on plant hosts including threatened species and associated native ant and aphid community structures.

Limited ant co-occurrence and defensive mutualism in Acacia plants in a West African savanna.

Our understanding of the role of fire and effect of ant species composition, beyond their diversity and abundance, on the effectiveness of mutualism defence is limited. Most of our knowledge of ant–plant defence in tropical Africa is biased towards East African savannas which have richer soil, higher primary productivity and a more diverse arthropods and mammal community than West African savannas. We assessed the diversity of ant species associated with Acacia species in the Pendjari Biosphere Reserve in the Dahomey Gap, and their impacts on elephant damage. Elephant damage, ant diversity and abundance were measured in stands of five Acacia species. Eleven ant species were identified in the Acacia stands. The composition of these ant communities varied across Acacia species. Pair of ant species co-occurred in only 2 % of sampled trees, suggesting a strong competitive exclusion. Within this annually burnt environment, ants were rare on small trees. The intensity of elephant-caused branch breaking did not vary between trees with ants and trees without ants, suggesting limited Acacia–ant mutualism. Such limited biotic defence may mask strong physical and chemical defence mechanisms of Acacia trees against elephant damage. Ant assemblages in West Africa, unlike those in the more productive East Africa, are particularly species-poor. However, there is a convergence between these two regions in low rate of ant co-occurrence which might indicate strong competitive exclusion. Our study suggests that such low ant species richness while limiting the efficacy of mutualism in controlling mega-herbivore damage may mask a strong defence syndrome.