Grazing and aridity have contrasting effects on the functional and taxonomic diversity of ants

Ants are one of the most abundant and ubiquitous organisms on Earth and play critical roles in multiple ecosystem services such as seed dispersal and nutrient cycling. Despite this, the effects of climatic and land use stressors on particular species or groups of ants are poorly known. We conducted a regional field survey across 108 locations in south-eastern Australia, using correlation network analysis and structural equation modelling to identify how ants respond to environmental stressors. We found contrasting relationships amongst ants, and aridity, and vertebrate grazing intensity and history. Increasing aridity was associated with reduced ant richness, whereas increasing grazing intensity was associated with greater ant richness directly, and indirectly, via reductions in litter depth and perennial grass density. However, these taxonomically diverse groups of ant species still shared contrasting responses to increasing aridity and grazing intensity. We found strong associations between grazing, aridity and the abundance of Seed Harvesters, weak indirect relationships with Generalist Foragers, but no relationships for Predators or Sugar Feeders. Taken together, our work identifies contrasting relationships amongst grazing, aridity and ants (ant ‘winners’ or ‘losers’) across contrasting ecological contexts. Given that increasing aridity is generally associated with lower grazing intensity, our results suggest that locations with more arid sites will have lower ant richness with fewer Seed Harvesters, whereas more mesic sites with high grazing intensity might increase ant richness, and the abundance of specific ant species. Such knowledge is important if we are to maintain critical ant-mediated functions as Earth becomes drier and grazing intensity increases.     

Experimental evidence for weak effects of fire ants in a naturally invaded pine‐savanna ecosystem in north Florida

1. Fire ants naturally invade some undisturbed ecosystems of high conservation value and may negatively impact co‐occurring ants. 2. Over 3 years, fire ants were added and removed from a longleaf pine savanna ecosystem that naturally supports a low density of fire ants. Impacts on co‐occurring ants were monitored using pitfall traps. 3. Treatments resulted in significant differences in average fire ant abundance across all plots only in the first year of the experiment. Fire ants had little discernible impact. The abundance and species richness of co‐occurring ants in removal plots never differed from unmanipulated control plots. The abundance of co‐occurring ants was very slightly lower and ant species richness was slightly higher where Solenopsis invicta Buren colonies were added, but neither contrast was significant. 4. The poor conditions in this habitat for many native ants may explain this outcome. More broadly, the impact of fire ants on ant assemblages still appears to be secondary and largely a consequence of human impacts on the environment.     

Climate-based model of spatial pattern of the species richness of ants in Georgia

For optimal planning of conservation and monitoring measures, it is important to know the spatial pattern of species richness and especially areas with high species richness. A spatial pattern of the species richness of ants in Georgia (Caucasus) was modeled, areas with the highest number of ant’s species were inferred, and climatic factors that influence the pattern of ant diversity were identified. A database was created by accumulating occurrences for 63 ant species, including 256 localities and 2,018 species/occurrences. Species richness was positively correlated with variables associated with temperature and negatively correlated with variables associated with precipitation. Species richness reaches a maximum at the elevations 800–1,200?m a.s.l. and declines at both lower and higher altitudes. The role of climatic variables and geography of the study area in determining the observed pattern of species richness is discussed.     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.     

Dominance and species co-occurrence in highly diverse ant communities: a test of the interstitial hypothesis and discovery of a three-tiered competition cascade

The role of competitive exclusion is problematic in highly diverse ant communities where exceptional species richness occurs in the face of exceptionally high levels of behavioural dominance. A possible non-niche–based explanation is that the abundance of behaviourally dominant ants is highly patchy at fine spatial scales, and subordinate species act as insinuators by preferentially occupying these gaps—we refer to this as the interstitial hypothesis. To test this hypothesis, we examined fine-scale patterns of ant abundance and richness according to a three-tiered competition hierarchy (dominants, subdominants and subordinates) in an Australian tropical savanna using pitfall traps spaced at 2 m intervals. Despite the presence of gaps in the fine-scale abundance of individual species, the combined abundance of dominant ants (species of Iridomyrmex, Papyirus and Oecophylla) was relatively uniform. There was therefore little or no opportunity for subordinate species to preferentially occupy gaps in the foraging ranges of dominant species, and we found no relationship between the abundance of dominant ants and nondominant species richness at fine spatial scales. However, we found a negative relationship between subdominant and subordinate ants, a negative relationship between dominant and subdominant ants, and a positive relationship between dominant and subordinate ants. These results suggest that dominant species actually promote species richness by neutralizing the effects of subdominant species on subordinate species. Such indirect interactions have very close parallels with three-tiered trophic cascades in food webs, and we propose a “competition cascade” where the interactions are through a competition rather than trophic hierarchy.     

Yellow crazy ant (<Emphasis Type="Italic">Anoplolepis gracilipes</Emphasis>) invasions within undisturbed mainland Australian habitats: no support for biotic resistance hypothesis

Ants are highly successful invaders, especially on islands, yet undisturbed mainland environments often do not contain invasive ants, and this observation is largely attributed to biotic resistance. An exception is the incursion of Yellow crazy ant Anoplolepis gracilipes within northeast Arnhem Land. The existence of A. gracilipes within this landscape’s intact environments containing highly competitive ant communities indicates that biotic resistance is not a terminally inhibitory factor mediating this ant’s distribution at the regional scale. We test whether biotic resistance may still operate at a more local scale by assessing whether ecological impacts are proportional to habitat suitability for A. gracilipes, as well as to the competitiveness of the invaded ant community. The abundance and species richness of native ants were consistently greater in uninfested than infested plots but the magnitude of the impacts did not differ between habitats. The abundance and ordinal richness of other macro-invertebrates were consistently lower in infested plots in all habitats. A significant negative relationship was found for native ant abundance and A. gracilipes abundance. No relationships were found between A. gracilipes abundance and any measure of other macro-invertebrates. The relative contribution of small ants (<2.5 mm) to total abundance and relative species richness was always greater in infested sites coinciding with a reduction of the contribution of the larger size classes. Differences in the relative abundance of ant functional groups between infested and uninfested sites reflected impacts according to ant size classes and ecology. The widespread scale of these incursions and non-differential level of impacts among the habitats, irrespective of native ant community competitiveness and abiotic suitability to A. gracilipes, does not support the biotic resistance hypothesis.     

Local and landscape drivers of biodiversity of four groups of ants in coffee landscapes

Agriculture of varying management intensity dominates fragmented tropical areas and differentially impacts organisms across and within taxa. We examined impacts of local and landscape characteristics on four groups of ants in an agricultural landscape in Chiapas, Mexico comprised of forest fragments and coffee agroecosystems varying in habitat quality. We sampled ground ants found in leaf litter and rotten logs and arboreal ants found in hollow coffee twigs and on tree trunks. Then using vegetation and agrochemical indices and conditional inference trees, we examined the relative importance of local (e.g. vegetation, elevation, agrochemical) and landscape variables (e.g. distance to and amount of nearby forest and rustic coffee) for predicting richness and abundance of ants. Leaf litter ant abundance increased with vegetation complexity; richness and abundance of ants from rotten logs, twig-nests, and tree trunks were not affected by vegetation complexity. Agrochemical use did not affect species richness or abundance of any ant group. Several local factors (including humus mass, degree of decay of logs, number of hollow twigs, tree circumference, and absence of fertilizers) were significant positive predictors of abundance and richness of some ant groups. Two landscape factors (forest within 200 m, and distance from forest) predicted richness and abundance of twig-nesting and leaf litter ants. Thus, different ant groups were influenced by different characteristics of agricultural landscapes, but all responded primarily to local characteristics. Given that ants provide ecosystem services (e.g. pest control) in coffee farms, understanding ant responses to local and landscape characteristics will likely inform farm management decisions.     

Influences on the structure of suburban ant (Hymenoptera: Formicidae) communities and the abundance of Tapinoma sessile

Urbanization can alter the organization of ant communities and affect populations of urban pest ants. In this study, we sampled ant communities in urban and suburban yards to understand the habitat factors that shape these communities and influence the abundance of a common pest species, Tapinoma sessile (Say). We used pitfall traps to sample ant communities and a combination of pitfall traps and baiting to collect T. sessile at 24 sites in Knoxville, TN. In total, we collected 46 ant species. Ant species richness ranged from seven to 24 species per yard. Ant species richness tended to be lowest near houses, whereas T. sessile abundance was highest near houses. The best predictors of ant species richness in yards were canopy cover and presence of leaf litter: ant species richness peaked at mid-levels of canopy cover and was negatively correlated with the presence of leaf litter. Tapinoma sessile abundance increased with presence of logs, boards, or landscaping timbers and leaf litter in yards. Our results indicate that ant communities and the abundance of particular pest species in these urban and suburban landscapes are shaped by many of the same factors that structure ant communities in less anthropogenically disturbed environments.     

Disentangling the Diversity of Arboreal Ant Communities in Tropical Forest Trees

Tropical canopies are known for their high abundance and diversity of ants. However, the factors which enable coexistence of so many species in trees, and in particular, the role of foragers in determining local diversity, are not well understood. We censused nesting and foraging arboreal ant communities in two 0.32 ha plots of primary and secondary lowland rainforest in New Guinea and explored their species diversity and composition. Null models were used to test if the records of species foraging (but not nesting) in a tree were dependent on the spatial distribution of nests in surrounding trees. In total, 102 ant species from 389 trees occurred in the primary plot compared with only 50 species from 295 trees in the secondary forest plot. However, there was only a small difference in mean ant richness per tree between primary and secondary forest (3.8 and 3.3 sp. respectively) and considerably lower richness per tree was found only when nests were considered (1.5 sp. in both forests). About half of foraging individuals collected in a tree belonged to species which were not nesting in that tree. Null models showed that the ants foraging but not nesting in a tree are more likely to nest in nearby trees than would be expected at random. The effects of both forest stage and tree size traits were similar regardless of whether only foragers, only nests, or both datasets combined were considered. However, relative abundance distributions of species differed between foraging and nesting communities. The primary forest plot was dominated by native ant species, whereas invasive species were common in secondary forest. This study demonstrates the high contribution of foragers to arboreal ant diversity, indicating an important role of connectivity between trees, and also highlights the importance of primary vegetation for the conservation of native ant communities.     

Contribution of cocoa plantations to the conservation of native ants (Insecta: Hymenoptera: Formicidae) with a special emphasis on the Atlantic Forest fauna of southern Bahia,Brazil

By maintaining a forest-like structure, shaded cocoa plantations contribute to the conservation of ants that usually live in the soil, leaf litter or canopy of tropical forests. Here we synthesize the available information on the diversity and community structure of ants in shaded cocoa plantations in the Atlantic forest region of Brazil, compare ant assemblages in cocoa agroforests with forests and other forms of agriculture, and discuss how these shaded plantations contribute to the conservation of the ants in the Atlantic Forest region. We also discuss ants of economical importance and of special interest, including Camponotus, Dolichoderus, Gnamptogenys, Pachycondyla, Pseudomyrmex and other litter dwelling genera. We discuss the situation of the tramp ant Wasmannia auropunctata in the Bahian cocoa-producing region where it is considered as native, and that of the two cryptobiotic genera Thaumatomyrmex and Typhlomyrmex, as well as that of proven and possible endangered army ant and Ponerini species. A total of 192 ant species from four strata were found in extensive sampling of a cocoa plantation with a relatively simple shade canopy (comprised primarily of Erythrina). Species richness in the cocoa plantations corresponded roughly to that of low diversity native forests, and species composition of cocoa plantations was most similar to native habitats (forest and mangroves) while ant composition in other agricultural habitats was most similar to that of urban areas. Although occurrences of Wasmannia auropunctata were similar in cocoa plantations and forests, abundance of Thaumatomyrmex and Typhlomyrmex, generally thought to be rare ants, was relatively high in cocoa plantations. These results, from cocoa plantations with relatively simple shade, demonstrate the importance of cocoa for ant conservation in the Atlantic forest region of Brazil. It is likely that cocoa plantations with a greater number of vegetation strata and higher tree species richness (such as traditional cabruca plantations) provide even more important habitat for ants generally and for ant species of conservation concern.     

Changes in Species Richness,Abundance, and Composition of Arboreal Twig‐nesting Ants Along an Elevational Gradient in Coffee Landscapes

The distribution, diversity, and assembly of tropical insects have long intrigued ecologists, and for tropical ants, can be affected by competitive interactions, microhabitat requirements, dispersal, and availability and diversity of nesting sites. Arboreal twig‐nesting ants are limited by the number of hollow twigs available, especially in intensive agricultural systems. Ant diversity and abundance may shift along elevation gradients, but no studies have examined if the proportion of occupied twigs or richness of arboreal twig‐nesting ants vary with elevation. In coffee agroecosystems, there are over 40 species of arboreal twig‐nesting ants. We examined communities of twig‐nesting ants in coffee plants along an elevational gradient to answer the following questions: (1) Do species richness and colony abundance decline with elevation or show a mid‐elevation peak? (2) Does community composition change with elevation? (3) Is elevation an important predictor of change in ant abundance, richness, and relative abundance of common species? We surveyed 42 10 × 10 m plots in 2013 from 450 to1550 m elevation across a coffee landscape in Chiapas, Mexico. We sampled a total of 2211 hollow coffee twigs, 77.1 percent of which were occupied by one of 28 species of ants. Pseudomyrmex simplex was more abundant in lower elevations, whereas Pseudomyrmex ejectus dominated in high elevations. Species richness and the percent of occupied hollow twigs both peaked at mid‐elevations (800–1050 m). In sum, we found that species richness, abundance, and composition of arboreal twig‐nesting ants shift with elevation. These findings may provide important insights for understanding ant communities in coffee agroecosystems.     

Wood-nesting ants and their parasites in forests and coffee agroecosystems

Agricultural intensification is linked to reduced species richness and may limit the effectiveness of predators in agricultural systems. We studied the abundance, diversity, and species composition of wood-nesting ants and frequency of parasitism of poneromorph ants in coffee agroeco systems and a forest fragment in Chiapas, Mexico. In three farms differing in shade management and in a nearby forest fragment, we surveyed ants nesting in rotten wood. We collected pupae of all poneromorph ants encountered, and incubated pupae for 15 d to recover emerging ant parasites. If no parasites emerged, we dissected pupae to examine for parasitism. Overall, we found 63 ant morphospecies, 29 genera, and 7 subfamilies from 520 colonies. There were no significant differences in ant richness or abundance between the different sites. However, there were significant differences in the species composition of ants sampled in the four different sites. The parasitism rates of ants differed according to site; in the forest 77.7% of species were parasitized, and this number declined with increasing intensification in traditional polyculture (40%),commercial polyculture (25%), and shade monoculture (16.6%). For three of four poneromorph species found in >1 habitat, parasitism rates were higher in the more vegetatively complex sites. The result that both ant species composition and ant parasitism differed among by site indicates that coffee management intensification affects wood-nesting ant communities. Further, coffee intensification may significantly alter interactions between ants and their parasites, with possible implications for biological control in coffee agroecosystems.     

Biodiversity on Broadway - Enigmatic Diversity of the Societies of Ants (Formicidae) on the Streets of New York City

Each year, a larger proportion of the Earth''s surface is urbanized, and a larger proportion of the people on Earth lives in those urban areas. The everyday nature, however, that humans encounter in cities remains poorly understood. Here, we consider perhaps the most urban green habitat, street medians. We sampled ants from forty-four medians along three boulevards in New York City and examined how median properties affect the abundance and species richness of native and introduced ants found on them. Ant species richness varied among streets and increased with area but was independent of the other median attributes measured. Ant assemblages were highly nested, with three numerically dominant species present at all medians and additional species present at a subset of medians. The most common ant species were the introduced Pavement ant (Tetramorium caespitum) and the native Thief ant (Solenopsis molesta) and Cornfield ant (Lasius neoniger). The common introduced species on the medians responded differently to natural and disturbed elements of medians. Tetramorium caespitum was most abundant in small medians, with the greatest edge/area ratio, particularly if those medians had few trees, whereas Nylanderia flavipes was most abundant in the largest medians, particularly if they had more trees. Many of the species encountered in Manhattan were similar to those found in other large North American cities, such that a relatively small subset of ant species probably represent most of the encounters humans have with ants in North America.     

Response of ants to human‐altered habitats with reference to seed dispersal of the myrmecochore Corydalis giraldii Fedde (Papaveraceae)

Anthropogenic habitat disturbance has potential consequences for ant communities. However, there is limited information on the effects of ant responses on associated ecological processes such as seed dispersal. We investigated the effect of disturbance on the abundance, richness, and composition of ant communities and the resulting seed‐dispersal services for a herbaceous myrmecochore, Corydalis giraldii (Papaveraceae), in an undisturbed habitat (forest understory), moderately disturbed habitat (abandoned arable field), and highly disturbed habitat (road verge) on Qinling Mountains, China. In total, we recorded 13 ant species, and five out of these were observed to transport seeds. The community composition of dispersers was significantly different amongst habitats. The richness of the dispersers did not differ among the habitats, but their total abundance varied significantly across habitats and was 21% lower in the road verge than in the abandoned arable fields. The major seed‐dispersing ant species in both the forest understory and the abandoned arable field were large‐bodied (Myrmica sp. and Formica fusca, respectively), whereas the major seed‐dispersing ants found in the road verge were the small‐bodied Lasius alienus. This difference resulted in lower seed removal rates and dispersal distances in the road verge than in the other two habitats. The different dispersal patterns were attributed primarily to differences in dispersing ant abundance and identity, most likely in response to habitats with different degree of anthropogenic disturbance. The possible influence of disturbance on the ecological specialization of ant‐seed dispersal interaction is also discussed.     

Ecological restoration following the local eradication of an invasive ant in northern Australia

There have been many management programs for invasive ants, yet few have achieved eradication. Of those that were successful, none have documented the subsequent recovery of the affected ecological system. Here I document the ecological impact and eradication of a 5 ha infestation of the African big headed ant Pheidole megacephala from an intact habitat in northern Australia, as well as the subsequent recovery of the native ant fauna. Pre-treatment, the impact of P. megacephala on the native ant fauna was clear. Native ant abundance and species richness were almost always significantly lower in infested compared to uninfested samples. Multivariate analysis statistically separated sample grids from infested and uninfested areas. Following treatment, no P. megacephala individuals were detected for 2 years and it was therefore declared eradicated. Ecological recovery post treatment was also clear. Twenty-one months post-treatment, native ant abundance and species richness within the treated (infested) area were always almost always significantly greater than in the pre-treatment sample, corresponding with no change in the control area (uninfested area). Total species richness from plots in the treated area was identical to that from plots in the control area. Multivariate analysis showed no statistical separation of the treated or control plots. Species richness within lure plots displayed no trend within the treated area relative to the treatment boundary or locations away from the treated area. This project demonstrates the feasibility of eradicating this ant, and that ecological systems are capable of recovering following removal of an exotic invader.     

The role of resource dispersion in promoting the co‐occurrence of dominant and subordinate ant species

Dominant competitors govern resource use in many communities, leading to predictions of local exclusion and lower species diversity where dominant species are abundant. However, subordinate and dominant species frequently co‐occur. One mechanism that could facilitate resource sharing and co‐occurrence of dominant and subordinate competitors is fine‐scale resource dispersion. Here, we distributed 6 g of a food resource into 1, 2, 8, 32 or 64 units in small 0.40 m² areas centred on nests of the dominant ant Monomorium sydneyense. We tested three hypotheses. First, we hypothesized that the species richness and abundance of foraging ants would increase with increasing resource dispersion. Accordingly, species richness doubled and total ant abundance was two orders of magnitude higher in high resource dispersion treatments. Secondly, we hypothesized that increasing resource dispersion would reduce competitive interactions such as resource turnover events and lower the probability of food resources being occupied. Substantial support for this hypothesis was observed. Finally, we tested the hypothesis that the foraging time of each species would be proportional to the relative abundance of each species solely in high resource dispersion treatments. Expected and observed foraging times were statistically similar for only the dominant ant M. sydneyense. The subdominant Pheidole rugosula increased its foraging time much more than was expected, while two subordinate ants showed no relationship between observed and expected times. Thus, while increasing resource dispersion significantly increased overall species richness, this increase in co‐occurrence did not correlate with a significant increase in foraging time for the two subordinate species. Rather, changes in resource dispersion appeared to benefit only the subdominant species. Inter‐site variation appeared more important for other subordinate species indetermining co‐occurrence and foraging time. Multiple mechanisms facilitate co‐occurrence and resource sharing in this community, and probably in most other communities.     

Invasive ants as back-seat drivers of native ant diversity decline in New Caledonia

Biological invasions are typically associated with disturbance, which often makes their impact on biodiversity unclear—biodiversity decline might be driven by disturbance, with the invader just being a ‘passenger’. Alternatively, an invader may act as a ‘back-seat driver’, being facilitated by disturbance that has already caused some biodiversity decline, but then causing further decline. Here we examine the interactive effects of anthropogenic fire and invasive ant species (Anoplolepis gracilipes or Wasmannia auropunctata) on native ant diversity in New Caledonia, a globally recognized biodiversity hotspot. We first examined native ant diversity at nine paired burnt and unburnt sites, with four pairs invaded by Anoplolepis, 5 years after an extensive fire. In the absence of invasion, native epigaeic ants were resilient to fire, but native ant richness and the abundance of Forest Opportunists were markedly lower in invaded burnt sites. Second, we examined native ant diversity along successional gradients from human-derived savanna to natural rainforest in the long-term absence of fire, where there was a disconnection between disturbance-mediated variation in microhabitat and the abundance of the disturbance specialist Wasmannia. All native ant diversity responses (total abundance, richness, species composition, functional group richness and the abundance of Forest Opportunists) declined independently of microhabitat variables but in direct association with high Wasmannia abundance. Our results indicate that invasive ants are acting as back-seat drivers of biodiversity decline in New Caledonia, with invasion facilitated by disturbance but then causing further biodiversity decline.     

Does Coastal Foredune Stabilization with Ammophila arenaria Restore Plant and Arthropod Communities in Southeastern Australia?

In this study we examine whether stabilization of denuded coastal foredunes in southeastern Australia with the exotic grass species Ammophila arenaria (marram grass) restores plant and ground‐active arthropod assemblages characteristic of undisturbed foredunes. Vascular plants and arthropods were sampled from foredunes that had been stabilized with marram grass in 1982, and from foredunes with no obvious anthropogenic disturbance (control dunes). All arthropods collected were sorted to Order, and ants (81.5% of all specimens) were further sorted to morphospecies. Abundance within arthropod Orders, as well as richness, composition, and structure of the plant and ant assemblages from control and stabilized dunes, were compared. The abundance of Diptera was significantly greater on stabilized dunes, while the abundance of Isopoda was significantly greater on control dunes. There were no significant differences in morphospecies richness or composition of ant assemblages on the two dunes types, although some differences in the abundances of individual morphospecies were observed. By contrast, stabilized dunes exhibited lower plant species richness and highly significant differences in plant species composition, due mainly to the large projected foliage cover of marram grass. The study revealed that after 12 years, the vegetation composition and structure of stabilized dunes was still dominated by marram grass and, as a result, invertebrate assemblages had not been restored to those characteristic of undisturbed foredunes.     

The Importance of Primary Tropical Rain Forest For Species Diversity: An Investigation Using Arboreal Ants as an example

The arboreal ant communities of a primary lowland rain forest and three differently disturbed forests that lie close together forming an anthropogenic disturbance gradient were collected with insecticide fogging. Combined samples from all trees (87 foggings) comprised 153,504 ants sorted to 331 morphospecies. The primary forest ant fauna was characterized by high species richness and 53 foggings were necessary to collect communities representatively. Another 63 species of ants were found in the disturbed forests indicating a large regional species pool that might exceed 420 species of arboreal ants. Anthropogenic disturbance caused a change in the taxonomic composition, diversity and structure of ant communities. Community size was a predictor of species richness in the severely disturbed forest types but not in the old secondary or primary forest. Ant abundance had declined significantly in the disturbed forests and only 10% of the primary forest’s species were collected in the most disturbed forest type. In each of the secondary forests a change in the frequency distribution of species was observed and a small number of species had gained numerical dominance. Analysis of species associations indicates that the strength of species interactions changed with the degree of forest disturbance. These changes were still clearly recognizable after 40 years of forest regeneration despite optimal conditions for colonization from the adjacent primary forest, demonstrating that the time scale needed for forest recovery after anthropogenic disturbance is very long.     

Direct and indirect effects of land‐use intensification on ant communities in temperate grasslands

Land‐use intensification is a major driver of local species extinction and homogenization. Temperate grasslands, managed at low intensities over centuries harbored a high species diversity, which is increasingly threatened by the management intensification over the last decades. This includes key taxa like ants. However, the underlying mechanisms leading to a decrease in ant abundance and species richness as well as changes in functional community composition are not well understood. We sampled ants on 110 grassland plots in three regions in Germany. The sampled grasslands are used as meadows or pastures, being mown, grazed or fertilized at different intensities. We analyzed the effect of the different aspects of land use on ant species richness, functional trait spaces, and community composition by using a multimodel inference approach and structural equation models. Overall, we found 31 ant species belonging to 8 genera, mostly open habitat specialists. Ant species richness, functional trait space of communities, and abundance of nests decreased with increasing land‐use intensity. The land‐use practice most harmful to ants was mowing, followed by heavy grazing by cattle. Fertilization did not strongly affect ant species richness. Grazing by sheep increased the ant species richness. The effect of mowing differed between species and was strongly negative for Formica species while Myrmica and common Lasius species were less affected. Rare species occurred mainly in plots managed at low intensity. Our results show that mowing less often or later in the season would retain a higher ant species richness—similarly to most other grassland taxa. The transformation from (sheep) pastures to intensively managed meadows and especially mowing directly affects ants via the destruction of nests and indirectly via loss of grassland heterogeneity (reduced plant species richness) and increased soil moisture by shading of fast‐growing plant species.