Spatial Distribution of Dominant Arboreal Ants in a Malagasy Coastal Rainforest: Gaps and Presence of an Invasive Species

We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species—a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression.     

The dynamics of ant mosaics in tropical rainforests characterized using the Self‐Organizing Map algorithm

Ants, the most abundant taxa among canopy‐dwelling animals in tropical rainforests, are mostly represented by territorially dominant arboreal ants (TDAs) whose territories are distributed in a mosaic pattern (arboreal ant mosaics). Large TDA colonies regulate insect herbivores, with implications for forestry and agronomy. What generates these mosaics in vegetal formations, which are dynamic, still needs to be better understood. So, from empirical research based on 3 Cameroonian tree species (Lophira alata, Ochnaceae; Anthocleista vogelii, Gentianaceae; and Barteria fistulosa, Passifloraceae), we used the Self‐Organizing Map (SOM, neural network) to illustrate the succession of TDAs as their host trees grow and age. The SOM separated the trees by species and by size for L. alata, which can reach 60 m in height and live several centuries. An ontogenic succession of TDAs from sapling to mature trees is shown, and some ecological traits are highlighted for certain TDAs. Also, because the SOM permits the analysis of data with many zeroes with no effect of outliers on the overall scatterplot distributions, we obtained ecological information on rare species. Finally, the SOM permitted us to show that functional groups cannot be selected at the genus level as congeneric species can have very different ecological niches, something particularly true for Crematogaster spp., which include a species specifically associated with B. fistulosa, nondominant species and TDAs. Therefore, the SOM permitted the complex relationships between TDAs and their growing host trees to be analyzed, while also providing new information on the ecological traits of the ant species involved.     

Inter-specific aggression generates ant mosaics in canopies of primary tropical rainforest

The ant mosaic is a concept of the non-random spatial distribution of individual ant species in trees built upon the assumption of interspecific behavioural associations. However, colony identity and environmental variance may also play a role in species distribution. Here we assess the presence of ant mosaics in a primary forest ecosystem and whether they are structured by species' aggressive behaviours or by habitat filtering. We sampled arboreal ants from vertically stratified baits exposed in 225 canopy trees in a 9-ha plot of primary lowland forest in Papua New Guinea, the largest forest area surveyed to detect ant mosaics. We performed behavioural tests on conspecific ants from adjacent trees to determine the territories of individual colonies. We explored the environmental effects on the ant communities using information on the plot vegetation structure and topography. Furthermore, we created a novel statistical method to test for the community non-random spatial structure across the plot via spatial randomisation of individual colony territories. Finally, we linked spatial segregation among the four most common species to experimentally assessed rates of interspecies aggression. The ant communities comprised 57 species of highly variable abundance and vertical stratification. Ant community composition was spatially dependent, but it was not affected by tree species composition or canopy connectivity. Only local elevation had a significant but rather small effect. Individual colony territories ranged from one tree to 0.7 ha. Species were significantly over-dispersed, with their territory overlap significantly reduced. The level of aggression between pairs of the four most common species was positively correlated with their spatial segregation. Our study demonstrates the presence of ant mosaics in tropical pristine forest, which are maintained by interspecific aggression rather than habitat filtering, with vegetation structure having a rather small and indirect effect, probably linked to microclimate variability.     

The invasive Yellow Crazy Ant and the decline of forest ant diversity in Indonesian cacao agroforests

Throughout the tropics, agroforests are often the only remaining habitat with a considerable tree cover. Agroforestry systems can support high numbers of species and are therefore frequently heralded as the future for tropical biodiversity conservation. However, anthropogenic habitat modification can facilitate species invasions that may suppress native fauna. We compared the ant fauna of lower canopy trees in natural rainforest sites with that of cacao trees in agroforests in Central Sulawesi, Indonesia in order to assess the effects of agroforestry on occurrence of the Yellow Crazy Ant Anoplolepis gracilipes, a common invasive species in the area, and its effects on overall ant richness. The agroforests differed in the type of shade-tree composition, tree density, canopy cover, and distance to the village. On average, 43% of the species in agroforests also occurred in the lower canopy of nearby primary forest and the number of forest ant species that occurred on cacao trees was not related to agroforestry characteristics. However, A. gracilipes was the most common non-forest ant species, and forest ant richness decreased significantly with the presence of this species. Our results indicate that agroforestry may have promoted the occurrence of A. gracilipes, possibly because tree management in agroforests negatively affects ant species that depend on trees for nesting and foraging, whereas A. gracilipes is a generalist when it comes to nesting sites and food preference. Thus, agroforestry management that includes the thinning of tree stands can facilitate ant invasions, thereby threatening the potential of cultivated land for the conservation of tropical ant diversity.     

Structure and Dynamics of the Arboreal Termite Community in New Guinean Coconut Plantations21

Whereas ant mosaics have been widely recognized and described in tropical ecosystems, data on space partitioning among arboreal termite colonies are rudimentary. During a long term field study in New Guinea, the distribution of arboreal termite species in coconut plantations as well as the extent and dynamics of competition between them were investigated. The three dominant species, Mirrocerotermes biroi, Nasutitermes princeps and N. novarumhebridarum, feed on the same items but never exploit the same tree. The resulting distribution pattern is a mosaic with two peculiarities. First, some extended areas around N. princeps colonies appear unexploited, as this species practices interference competition on a wide scale, defending large territories inter- and intra-specifically. Second, interspecific relations are asymmetrical. In some plantations, large colonies of N. princeps expand their territory by destroying colonies of M. biroi, but when the pressure of N. princeps is relaxed, dense populations of colonies of M. biroi can recolonize the trees in a few years’ time. Territorial boundaries may thus change relatively fast. N. novarumhebridarum often colonizes dead trees and interferes less with the other species. These facts are consistent with each species’ reproductive investment strategy. Hypotheses are proposed to explain how the dominant species can coexist, even in long established plantations.     

Effects of canopy connectivity on the arboreal ant community in coffee shade trees

Canopy connectivity influences foraging, movement, and competition in arboreal ant communities. Understanding how canopy connectivity affects arboreal ant communities could inform the development of management practices that maximize services from known biocontrol agents. We experimentally manipulated connectivity between the crowns of large shade trees to investigate the effects of canopy connectivity on arboreal ant species richness and composition in a coffee agroecosystem. A linear mixed-effects analysis showed that the number of species observed at baits set in tree crowns increased significantly after the crowns had been connected with nylon ropes. Crowns that were connected increased in similarity of ant species composition, particularly between adjacent connected crowns. Connectivity may increase the number of species present in tree crowns by allowing ants to move and forage in the canopy while bypassing trunks with more aggressive, territorial species such as Azteca sericeasur. Because twig-nesting species in the upper canopy have been shown to act as biocontrol agents of herbivores, an increase in species richness in tree crowns could have positive implications for agricultural pest-control services.     

Arboreal Ant Abundance and Leaf Miner Damage in Coffee Agroecosystems in Mexico

Shaded coffee agroecosystems traditionally have few pest problems potentially due to higher abundance and diversity of predators of herbivores. However, with coffee intensification (e.g., shade tree removal or pruning), some pest problems increase. For example, coffee leaf miner outbreaks have been linked to more intensive management and increased use of agrochemicals. Parasitic wasps control the coffee leaf miner, but few studies have examined the role of predators, such as ants, that are abundant and diverse in coffee plantations. Here, we examine linkages between arboreal ant communities and coffee leaf miner incidence in a coffee plantation in Mexico. We examined relationships between incidence and severity of leaf miner attack and: (1) variation in canopy cover, tree density, tree diversity, and relative abundance of Inga spp. shade trees; (2) presence of Azteca instabilis, an arboreal canopy dominant ant; and (3) the number of arboreal twig‐nesting ant species and nests in coffee plants. Differences in vegetation characteristics in study plots did not correlate with leaf miner damage perhaps because environmental factors act on pest populations at a larger spatial scale. Further, presence of A. instabilis did not influence presence or severity of leaf miner damage. The proportion of leaves with leaf miner damage was significantly lower where abundance of twig‐nesting ants was higher but not where twig‐nesting ant richness was higher. These results indicate that abundance of twig‐nesting ants in shaded coffee plantations may contribute to maintenance of low leaf miner populations and that ants provide important ecosystem services in coffee agroecosystems.     

The arboreal ants of a Neotropical rain forest show high species density and comprise one third of the ant fauna

In tropical rain forests, the ant community can be divided into ground and arboreal faunas. Here, we report a thorough sampling of the arboreal ant fauna of La Selva Biological Station, a Neotropical rain forest site. Forty-five canopy fogging samples were centered around large trees. Individual samples harbored an average of 35 ant species, with up to 55 species in a single sample. The fogging samples yielded 163 observed species total, out of a statistically estimated 199 species. We found no relationship between within-sample ant richness and focal tree species, nor were the ant faunas of nearby trees more similar to each other than the faunas of widely spaced trees. Species density was high, and beta diversity was low: A single column of vegetation typically harbors at least a fifth of the entire arboreal ant fauna. Considering the entire fauna, based on 23,326 species occurrence records using a wide variety of collecting methods, 182 of 539 observed species (196 of 605, estimated statistically) were entirely arboreal. The arboreal ant fauna is thus about a third of the total La Selva ant fauna, a robust result because inventory completeness was similar for ground and arboreal ants. The taxonomic history of discovery of the species that make up the La Selva fauna reveals no disproportionately large pool of undiscovered ant species in the canopy. The "last biotic frontier" for tropical ants has been the rotten wood, leaf litter, and soil of the forest floor.     

How plants shape the ant community in the Amazonian rainforest canopy: the key role of extrafloral nectaries and homopteran honeydew

Ant-plant interactions in the canopy of a lowland Amazonian rainforest of the upper Orinoco, Venezuela, were studied using a modified commercial crane on rails (Surumoni project). Our observations show a strong correlation between plant sap exudates and both abundance of ants and co-occurrence of ant species in tree canopies. Two types of plant sap sources were compared: extrafloral nectaries (EFNs) and honeydew secretions by homopterans. EFNs were a frequent food source for ants on epiphytes (Philodendron spp., Araceae) and lianas (Dioclea, Fabaceae), but rare on canopy trees in the study area, whereas the majority of trees were host to aggregations of homopterans tended by honeydew-seeking ants (on 62% of the trees examined). These aggregations rarely occurred on epiphytes. Baited ant traps were installed on plants with EFNs and in the crowns of trees from three common genera, including trees with and without ant-tended homopterans: Goupia glabra (Celastraceae), Vochysia spp. (Vochysiaceae), and Xylopia spp. (Annonaceae). The number of ant workers per trap was significantly higher on plants offering one of the two plant sap sources than on trees without such resources. Extrafloral nectaries were used by a much broader spectrum of ant species and genera than honeydew, and co-occurrence of ant species (in traps) was significantly higher on plants bearing EFNs than on trees. Homopteran honeydew (Coccidae and Membracidae), on the other hand, was mostly monopolised by a single ant colony per tree. Homopteran-tending ants were generally among the most dominant ants in the canopy. The most prominent genera were Azteca, Dolichoderus (both Dolichoderinae), Cephalotes, Pheidole, Crematogaster (all Myrmicinae), and Ectatomma (Ponerinae). Potential preferences were recorded between ant and homopteran species, and also between ant-homopteran associations and tree genera. We hypothesize that the high availability of homopteran honeydew provides a key resource for ant mosaics, where dominant ant colonies and species maintain mutually exclusive territories on trees. In turn, we propose that for nourishment of numerous ants of lower competitive capacity, Philodendron and other sources of EFNs might be particularly important.     

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.     

Effects of an Epiphytic Orchid on Arboreal Ant Community Structure in Panama

Epiphytes are conspicuous structural elements of tropical forest canopies. Individual tree crowns in lowland forests may support more than 30 ant species, yet we know little about the effects of epiphytes on ant diversity. We examined the composition of arboreal ant communities on Annona glabra trees and their interactions with the epiphytic orchid Caularthron bilamellatum in Panama. We surveyed the ants on 73 trees (45 with C. bilamellatum and 28 lacking epiphytes) and recorded their nest sites and behavioral dominance at baits. We found a total of 49 ant species (in 20 genera), ranging 1–9 species per tree. Trees with C. bilamellatum had higher average (±SD) ant species richness (4.2±2.28) than trees without epiphytes (2.7±1.21). Hollow pseudobulbs (PBs) of C. bilamellatum were used as nest sites by 32 ant species, but only 43 percent of suitable PBs were occupied. Ant species richness increased with PB abundance in trees, but nest sites did not appear to be a limiting resource on A. glabra. We detected no close association between ants and the orchid. We conclude that higher ant species richness in the presence of the orchid is due to bottom‐up effects, especially the year‐round supply of extrafloral nectar. The structure of ant communities on A. glabra partly reflects interference competition among behaviorally dominant species and stochastic factors, as observed in other forests.     

Territory defense by the ant Azteca trigona: maintenance of an arboreal ant mosaic

Mosaics of exclusive foraging territories, produced by intra-and interspecific competition, are commonly reported from arboreal ant communities throughout the tropics and appear to represent a recurring feature of community organization. This paper documents an ant mosaic within mangrove forests of Panama and examines the behavioral mechanisms by which one of the common species, Azteca trigona, maintains its territories. Most of the mangrove canopy is occupied by mutually exclusive territories of the ants A. trigona, A. velox, A. instabilis, and Crematogaster brevispinosa. When foraging workers of A. trigona detect workers of these territorial species, they organize an alarm recruitment response using pheromonal and tactile displays. Nestmates are attracted over short distances by an alarm pheromone originating in the pygidial gland and over longer distances by a trail pheromone produced by the Pavan's gland. Recruits are simultaneously alerted by a tactile display. No evidence was found for chemical marking of the territory. Major workers are proportionally more abundant at territory borders than on foraging trails in the interior of the colony. The mechanisms of territory defense in A. trigona are remarkably similar to those of ecologically analogous ants in the Old World tropics.     

An Ant Mosaic Revisited: Dominant Ant Species Disassemble Arboreal Ant Communities but Co-Occur Randomly

The spatial distributions of many tropical arboreal ant species are often arranged in a mosaic such that dominant species have mutually exclusive distributions among trees. These dominant species can also mediate the structure of the rest of the arboreal ant community. Little attention has been paid to how diet might shape the effects of dominant species on one another and the rest of the ant community. Here, we take advantage of new information on the diets of many tropical arboreal ant species to examine the intra- and inter-guild effects of dominant species on the spatial distribution of one another and the rest of the tropical arboreal ant community in a cocoa farm in Bahia, Brazil. Using null model analyses, we found that all ant species, regardless of dominance status or guild membership, co-occur much less than expected by chance. Surprisingly, the suite of five dominant species showed random co-occurrence patterns, suggesting that interspecific competition did not shape their distribution among cocoa trees. Across all species, there was no evidence that competition shaped co-occurrence patterns within guilds. Co-occurrence patterns of subordinant species were random on trees with dominant species, but highly nonrandom on trees without dominant species, suggesting that dominant species disassemble tropical arboreal ant communities. Taken together, our results highlight the often complex nature of interactions that structure species-rich tropical arboreal ant assemblages.     

Impact of Argentine ants (<Emphasis Type="Italic">Linepithema humile</Emphasis>) on an arboreal ant community in Doñana National Park,Spain

Due to the invasive character of the exotic Argentine ant (Linepithema humile), its use of aphids in trees, and the ecological importance of the Doñana National Park (Spain) that is invaded by this species, we designed a study to analyze the extent of the problem with native species of arboreal ants. By searching for de visu the species that inhabited 182 cork trees, we found out that the structure of the community of native arboreal ants has been greatly influenced by interspecific competition. The introduced species L. humile and the native species Crematogaster scutellaris and Lasius brunneus are dominant, while Camponotus lateralis and Camponotus truncatus are subordinate species associated with C. scutellaris. The distribution of the species in the trees depends on these relationships. Species richness is determined by tree size, thus, when a tree is large enough all native species may appear together. However, in areas colonized by L. humile, this is the only species occupying the tree, regardless of tree size. L. humile is displacing native arboreal ant species as shown by the fact that from 1992 to 2000 the exotic species occupied 23 new cork trees (of the 182 studied) previously inhabited by native species.     

Contrasting Effects of Fire on Arboreal and Ground‐Dwelling Ant Communities of a Neotropical Savanna

Ants are a dominant group in tropical savannas and here we examined the responses of the arboreal and ground‐dwelling ant fauna to a fire in a Neotropical savanna (cerrado) reserve in Central Brazil. Ants were collected using pitfall traps and baits placed in trees and on the ground beneath each tree. Of the 36 trees marked along two transects, half (from each transect) were burned and half not. The same trees were sampled 1 wk before and again 3 and 12 mo after the fire. Rarefaction curves and ordination analyses using data from all trees from each side of each transect indicated that overall ant species richness and composition did not change after fire. Fire, however, reduced the mean number of ant species per tree, and increased the mean number of species on the ground. Fire increased the average abundance of specialist predators, Camponotini, and opportunistic species, and decreased that of arboreal specialists. Changes in the ground‐dwelling fauna were only detected 12 mo after the fire, while those in the arboreal fauna occurred earlier and were no longer apparent 12 mo after the fire. We suggest that these contrasting results represent mainly an indirect response of the ant communities to fire‐induced changes in vegetation. Given the temporary and small scale nature of the effects detected and the overall resilience of the ant fauna, our results indicate that a single fire in the cerrado vegetation does not greatly impact the structure of ant communities in the short term.     

Extrafloral nectar as a driver of arboreal ant communities at the site‐scale in Brazilian savanna

Despite years of study, it remains unclear if and to what extent the effects of extra‐floral nectaries (EFNs) on arboreal ants observed on individual trees scale up to larger spatial scales. Here, we address this issue in Brazilian savanna and tested three predictions: (i) Trees with EFN have higher richness of arboreal ant species than trees without; (ii) Arboreal ant species richness increases with the proportion of total EFN‐bearing trees at the site scale, due to a higher occurrence of non‐core ant species; (iii) Ant species composition changes with the proportion of EFN‐bearing trees at the site scale. We sampled arboreal ants in 32 plots with EFN‐bearing trees ranging from 0% to 60% of all trees. We sampled 72 ant species, from which 17 (mostly belonging to Camponotus, Cephalotes and Crematogaster) were identified as core species in at least one of the ant‐EFN networks in the 32 plots. Ant species richness was significantly higher on EFN‐bearing trees. We identified 11 ant species that preferentially occurred on EFN‐bearing trees, all of which were core partners in networks. Species richness at the site scales increased with the proportion of EFN‐bearing trees, regardless of tree density and richness; this pattern was due to a higher occurrence of non‐core ant species. Finally, species composition also varied with the proportion of EFN‐bearing trees. Therefore, we found that the presence of EFNs not only influences arboreal ants on individual trees but also has a substantial effect on the ant‐EFN network on a broader community scale. The increase in non‐core species site scale reveals that this interaction is unlikely to result in substantially enhanced protection services for EFN‐bearing plants.     

Trees as islands: canopy ant species richness increases with the size of liana‐free trees in a Neotropical forest

The physical characteristics of habitats shape local community structure; a classic example is the positive relationship between the size of insular habitats and species richness. Despite the high density and proximity of tree crowns in forests, trees are insular habitats for some taxa. Specifically, crown isolation (i.e. crown shyness) prevents the movement of small cursorial animals among trees. Here, we tested the hypothesis that the species richness of ants (S_a) in individual, isolated trees embedded within tropical forest canopies increases with tree size. We predicted that this pattern disappears when trees are connected by lianas (woody vines) or when strong interactions among ant species determine tree occupancy. We surveyed the resident ants of 213 tree crowns in lowland tropical forest of Panama. On average, 9.2 (range = 2–20) ant species occupied a single tree crown. Average (± SE) S_a was ca 25% higher in trees with lianas (10.2 ± 0.26) than trees lacking lianas (8.0 ± 0.51). S_a increased with tree size in liana‐free trees (S_a = 10.99A^0.256), but not in trees with lianas. Ant species composition also differed between trees with and without lianas. Specifically, ant species with solitary foragers occurred more frequently in trees with lianas. The mosaic‐like pattern of species co‐occurrence observed in other arboreal ant communities was not found in this forest. Collectively, the results of this study indicate that lianas play an important role in shaping the local community structure of arboreal ants by overcoming the insular nature of tree crowns.     

Influence of forest type and tree species on canopy ants (Hymenoptera: Formicidae) in Budongo Forest, Uganda

The arboreal ant fauna was investigated in Budongo Forest, a seasonal rain forest in Uganda, using the insecticidal fogging technique. Ants were collected from 61 trees, between 7 and 33 m in height, belonging to four tree species. Trees were growing in adjacent plots of forests characterized by different use and structure: an old primary forest, a primary swamp forest along a small river, and a secondary forest where selective logging was carried out for 30 years. A total number of 37,065 ants, belonging to 161 species in 30 genera were collected. Considering the high number of species found only once, the completeness of the canopy ant fauna was relatively high and of relatively similar magnitude as samples from the Neotropics or the Oriental region. Up to 37 ant species on a single tree, with an average of 18.2 species per tree, were found. Forty-four ant species (28.1%) were found only once, less than ten individuals were found for each of 88 species (54.7%), but 64.0% of all individuals belonged to one of five species. Considering the high numerical dominance of a few ant species like a Pheidole sp., Tetramorium aculeatum (Mayr) and a Crematogaster sp., there is some evidence for an ant mosaic in the lower canopy of the Budongo Forest. Individual numbers of ants were strongly correlated with nests in the fogged tree, though the ants were not homogeneously distributed in the tree crowns. Diversity measures that strongly depend on individual numbers such as the Morisita-Horn index or rarefaction methods were calculated, but results were not concordant with those of incidence-based estimates such as jack-knife calculations. Differences in ant species richness and faunal composition between tree species were low, but more significant between forest types. The ant fauna in the secondary forest was less diverse with 12.6% fewer species compared to the primary forest sites. The average number of ant species per tree was significantly lower in the secondary forest (<20% of the species; F=8.03, df=59, P<0.01) than in the undisturbed forest types. Cataulacus, Leptothorax, Tetraponera, and Polyrhachis, which are typical canopy-dwelling ant genera, had a significantly higher diversity and frequency in the two primary forest types (F=4.17, df=53, P<0.05). Secondary forest trees are often younger, lacking dead branches and epiphytes which are important requisites for ant colonization on trees.     

Why are there more arboreal ant species in primary than in secondary tropical forests?

1.?Species diversity of arboreal arthropods tends to increase during rainforest succession so that primary forest communities comprise more species than those from secondary vegetation, but it is not well understood why. Primary forests differ from secondary forests in a wide array of factors whose relative impacts on arthropod diversity have not yet been quantified. 2.?We assessed the effects of succession-related determinants on a keystone ecological group, arboreal ants, by conducting a complete census of 1332 ant nests from all trees with diameter at breast height?≥?5?cm occurring within two (unreplicated) 0·32-ha plots, one in primary and one in secondary lowland forest in New Guinea. Specifically, we used a novel rarefaction-based approach to match number, size distribution and taxonomic structure of trees in primary forest communities to those in secondary forest and compared the resulting numbers of ant species. 3.?In total, we recorded 80 nesting ant species from 389 trees in primary forest but only 42 species from 295 trees in secondary forest. The two habitats did not differ in the mean number of ant species per tree or in the relationship between ant diversity and tree size. However, the between-tree similarity of ant communities was higher in secondary forest than in primary forest, as was the between-tree nest site similarity, suggesting that secondary trees were more uniform in providing nesting microhabitats. 4.?Using our rarefaction method, the difference in ant species richness between two forest types was partitioned according to the effects of higher tree density (22·6%), larger tree size (15·5%) and higher taxonomic diversity of trees (14·3%) in primary than in secondary forest. The remaining difference (47·6%) was because of higher beta diversity of ant communities between primary forest trees. In contrast, difference in nest density was explained solely by difference in tree density. 5.?Our study shows that reduction in plant taxonomic diversity in secondary forests is not the main driver of the reduction in canopy ant species richness. We suggest that the majority of arboreal species losses in secondary tropical forests are attributable to simpler vegetation structure, combined with lower turnover of nesting microhabitats between trees.     

A canopy dominant ant affects twig‐nesting ant assembly in coffee agroecosystems

One commonly studied driver of community assembly is the effect of dominant species on subordinate species. Dominant species may impact community assembly during competitive sorting, or recruitment. For ants, important and abundant species in the tropics, several factors may drive community assembly including competition, dispersal, priority effects, and environmental conditions. Although competition is a hallmark of ant ecology, few have examined the influence of patchily distributed dominant ants on other ant species and diversity, especially at the recruitment stage. Here, I consider the impacts of a canopy dominant ant species, Azteca instabilis, and changes in vegetation on twig‐nesting ant colony founding and ant community assembly in a coffee agroecosystem. I added artificial nests to coffee plants in areas with and without A. instabilis four times over a year, and then examined the occupation rate and identity of species colonizing nests. I also examined vegetation characteristics of sites where nests were added. The presence of A. instabilis on coffee plants drastically lowered colonization rates, but nest occupation increased with tree density, and with decreasing proportion of Inga spp. trees in the canopy. The presence of A. instabilis limited the number of nests occupied by six of the ten most common species; most rare species, however, were not affected by A. instabilis presence. Richness of colonizing ants in areas with A. instabilis was lower, but these effects did not significantly affect richness across broader scales. Despite large effects on individual species, species composition did not differ greatly in areas with and without A. instabilis, but some vegetation characteristics (basal area and tree richness) were predictive of ant composition. These results suggest that A. instabilis strongly affects founding events especially for common twig‐nesting species and that both vegetation and influences from this dominant species affect community assembly of twig‐nesting ants at the local scale.