Annual fire resilience of ground‐dwelling ant communities in Hiraodai Karst Plateau grassland in Japan

The fire resilience of ground‐dwelling ant assemblages in grassland subjected to annual fire management was investigated. Study sites consisted of three burnt sites and three unburnt sites in grasslands on the Hiraodai Karst Plateau in Fukuoka Prefecture, Japan. Ground‐dwelling ants were sampled by Winkler extraction and collected at 10 days and 1, 2, 3 and 6 months post‐fire. In total 33 ant species belonging to 25 genera in six subfamilies were collected from the burnt and unburnt sites. Eight of the 29 ant species collected at burnt sites were restricted to burnt sites, while four of the 25 ant species collected at unburnt sites were restricted to unburnt sites. Non‐metric multidimensional scaling and analysis of similarities revealed that the ant assemblages in the burnt sites at 10 days and 1 month post‐fire were clearly separated from the assemblages observed at 2, 3 and 6 months post‐fire. The results suggested that the ground‐dwelling ant fauna in the study area were highly resilient to fire at 2 months post‐fire and that the annual fire regime did not have a marked effect on species richness.     

Environmental context alters ecological trade‐offs controlling ant coexistence in a spatially heterogeneous region

1. Ecological trade‐offs in ant (Hymenoptera: Formicidae) assemblages and their implications for coexistence boast a rich history in entomology. Yet investigations of trade‐offs have largely been limited to homogeneous environments. We examined how environmental context modifies trade‐off expression in an ant assemblage spanning a heterogeneous region in central Florida, U.S.A. 2. We examined how trade‐off expression is altered among two contrasting habitat types: open shrub and forest. We tested for the presence of the dominance‐discovery trade‐off and two dominance‐thermal tolerance trade‐offs by estimating behavioral dominance, discovery ability, and thermal tolerance (foraging thermal limit, lethal temperature, and maximal abundance temperature) for a wide range of interacting ant species. 3. We found significantly linear dominance hierarchies in both shrub and forest habitats, showing dominant species out‐compete subordinates for food resources. In thermally stressful shrub habitats, subordinates exhibit higher thermal tolerances, take greater thermal risks, and reach maximum forager abundances at higher temperatures than do dominant species. This suggests temperature mediated trade‐offs control coexistence in shrub habitat. In thermally moderate forest habitat, we found limited evidence for trade‐offs between competitive dominance and resource discovery or between dominance and thermal traits, implying other processes control coexistence. These results demonstrate that trade‐offs controlling ant coexistence may be contingent on environmental context.     

Response of ant and terrestrial spider assemblages to pastoral and military land use,and to landscape position,in a tropical savanna woodland in northern Australia

This study aims primarily to assess the response of two invertebrate groups to the effects of pastoralism and military training, at one site in the tropical savanna of north‐eastern Queensland. The richness and species composition of ants and terrestrial spiders were examined at two contrasting times of year across three land use treatments (pastoralism, military training and undisturbed) and four landscape positions (upper slope to riparian). Ant species richness was least in the grazed sites, and a high proportion of the ant species recorded varied significantly in frequency between the grazed and the two ungrazed land uses. This variation was generally greater than that associated with landscape position. Although variation in the richness of spiders was significantly related to land‐use type, this effect was less pronounced than for ants, was less marked than variation associated with landscape position and was confounded by a strong interaction between land use and landscape position. Quadrat‐scale variation in the composition of spider assemblages was influenced most by season of sampling. For both spiders and ants, there were few differences in richness or species composition between undisturbed land and that managed for military use.     

More long‐unburnt forest will benefit mammals in Australian sub‐alpine forests and woodlands

The composition of mammalian communities in Australia's Eucalyptus forests and woodlands is known to be affected by fire. However, there are few published studies that compare mammal assemblages in recently burnt and long‐unburnt forests because there are few areas with long‐term fire history data. Understanding the value of long‐unburnt forest is important because it is becoming rare in fire‐prone regions of the world, such as south‐eastern Australia, partly because of the widespread use of prescribed burning. We deployed wildlife cameras for 28 trap‐nights at each of 81 sites that ranged from 0.5 to at least 96 years since the last fire. We recorded a total of 15 native mammal species. At least one mammal species was recorded at 80 of the 81 sites. Significantly more species were detected at long‐unburnt sites (>96 years since fire) than sites 0.5–12 years since the last fire. Species composition varied significantly between sites 0.5–12 years and >96 years since the last fire but did not vary between sites 0.5–2 years and 6–12 years since the last fire. Although there was not one category of time since fire (i.e. 0.5–2 years, 6–12 years and >96 years) in which all 15 native mammal species were recorded, long‐unburnt sites were significantly more important for the occurrence of seven mammal species; intermediate and recently burnt sites were significantly more important for one species. Our results suggested that, while a diversity of fire ages is important for conserving mammalian diversity, long‐unburnt forests and woodlands (which comprised only 8% of our study area) are disproportionately important for mammal conservation. Our results add to a growing body of the literature from south‐eastern Australia, suggesting that remaining long‐unburnt forest should be afforded protection from fire and more forest should be transitioned to long unburnt.     

A comparison of foliar nutrient concentration in trees from monsoon rainforest and savanna in northern Australia

Abstract Analysis of foliar nutrient concentrations revealed that two mesophyllic monsoon rainforest trees had higher concentrations of most nutrients in leaves than eight savanna species. One of the tested monsoon rainforest species with sclerophyllous leaves had similar nutrient concentrations to the savanna tree species. There were positive or no significant correlations between live foliar nutrient concentration and the percentage of nutrients withdrawn prior to litterfall. The nutrient concentration of litter was similar for most nutrients among tree species of monsoon rainforest or savanna. The results of this study suggest that the relative fertility of surface soils of monsoon rainforest compared with savanna is not determined by contrasting nutrient cycling strategies whereby monsoon rainforest tree species enrich their soils with relatively nutrient rich leaf litter relative to savanna tree species.     

Structure of ground‐dwelling ant communities in burned and unburned areas in Brazilian subtropical grasslands

Fire is frequently used in the management of pastures in southern Brazil, but its effects on ground‐dwelling ant communities in Brazilian subtropical grasslands is still poorly understood. Here, we compared ant species richness and composition between periodically burned and unburned areas in native grasslands of the Atlantic Forest biome. In total, we found 35 epigeic ant species in burned and unburned areas. There was slightly higher species richness in burned than in unburned areas, independent of the sampling period (season). There was a significant difference in richness over the sampling period (season effect). Species composition varied significantly between the areas, in which nine species (26%) occurred only in burned areas, eight (23%) occurred only in unburned areas, and 18 (51%) occurred in both. Four species showed a significant preference for burned sites (Camponotus crassus, Linepithema humile and two undetermined species of Pheidole and Solenopsis). Although this study did not separate fire effects on ground‐dwelling ant communities (due to sampling design), it provides new information regarding subtropical native grasslands that can be used as a baseline for future studies.     

Assembly rules of ground-foraging ant assemblages are contingent on disturbance, habitat and spatial scale

Aim A major endeavour of community ecology is documenting non‐random patterns in the composition and body size of coexisting species, and inferring the processes, or assembly rules, that may have given rise to the observed patterns. Such assembly rules include species sorting resulting from interspecific competition, aggregation at patchily distributed resources, and co‐evolutionary dynamics. However, for any given taxon, relatively little is known about how these patterns and processes change through time and vary with habitat type, disturbance history, and spatial scale. Here, we tested for non‐random patterns of species co‐occurrence and body size in assemblages of ground‐foraging ants and asked whether those patterns varied with habitat type, disturbance history, and spatial scale. Location Burned and unburned forests and fens in the Siskiyou Mountains of southern Oregon and northern California, USA. Methods We describe ground‐foraging ant assemblages sampled over two years in two discrete habitat types, namely Darlingtonia fens and upland forests. Half of these sites had been subject to a large‐scale, discrete disturbance – a major fire – in the year prior to our first sample. We used null model analyses to compare observed species co‐occurrence patterns and body‐size distributions in these assemblages with randomly generated assemblages unstructured by competition both within (i.e. at a local spatial scale) and among (i.e. at a regional scale) sites. Results At local spatial scales, species co‐occurrence patterns and body‐size ratios did not differ from randomness. At regional scales, co‐occurrence patterns were random or aggregated, and there was evidence for constant body‐size ratios of forest ants. Although these patterns varied between habitats and years, they did not differ between burned and unburned sites. Main conclusions Our results suggest that the operation of assembly rules depends on spatial scale and habitat type, but that it was not affected by disturbance history from fire.     

Short‐term changes in the structure of termite assemblages associated with slash‐and‐burn agriculture in Côte d'Ivoire

Termites are major decomposers in tropical regions and play critical roles in many soil‐related processes. Studies conducted in Asia and the Neotropics suggest that habitat modification can strongly affect termite assemblages, but data on termite communities from forests in Africa, especially West Africa, are scarce. Here, we measured the short‐term impact of slash‐and‐burn agriculture on termite assemblages in an agricultural region of central Côte d'Ivoire. We assessed termite diversity and relative abundance in four habitat types: secondary forest, cleared forest, burned forest, and crop fields. The secondary forest had higher species richness compared with the other habitats, but all habitat types had similar assemblage structures. Fungus‐growing termites were the most abundant feeding group in all habitats. Soil feeders were most abundant in secondary forest, intermediately abundant in cleared and burned forests, and almost entirely absent in crop fields. Wood‐feeding species showed clear responses to burning; their abundances decreased after fire. We conclude that slash‐and‐burn agriculture does not appear to severely erode the diversity of termite assemblages. This could be due to the dominance of ecologically versatile fungus growers or to the relatively long time between clearing and burning. However, forest clearing negatively affects soil feeders, with the Apicotermitinae most affected by canopy loss.     

Effects of long‐term fire exclusion and frequent fire on plant community composition: A case study from semi‐arid shrublands

Time since last fire and fire frequency are strong determinants of plant community composition in fire‐prone landscapes. Our study aimed to establish the influence of time since last fire and fire frequency on plant community composition and diversity of a south‐west Australian semi‐arid shrubland. We employed a space‐for‐time approach using four fire age classes: ‘young’, 8–15 years since last fire; ‘medium’, 16–34; ‘old’, 35–50; and ‘very old’, 51–100; and three fire frequency classes: burnt once, twice and three times within the last 50 years. Species diversity was compared using one‐way ANOVA and species composition using PERMANOVA. Soil and climatic variables were included as covariables to partition underlying environmental drivers. We found that time since last fire influenced species richness, diversity and composition. Specifically, we recorded a late successional transition from woody seeders to long‐lived, arid‐zone, resprouting shrub species. Fire frequency did not influence species richness and diversity but did influence species composition via a reduction in cover of longer‐lived resprouter species – presumably because of a reduced ability to replenish epicormic buds and/or sufficient starch stores. The distinct floristic composition of old and very old habitat, and the vulnerability of these areas to wildfires, indicate that these areas are ecologically important and management should seek to preserve them.     

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.     

Major disturbances test resilience at a long‐term boreal forest monitoring site

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Not enough niches: non‐equilibrial processes promoting species coexistence in diverse ant communities

Abstract Explanations for species coexistence in ant communities have traditionally focused on niche partitioning, particularly relating to differences in diet, foraging times and nesting requirements. Although niche separation is undoubtedly important, it seems insufficient to account for the high levels of local species richness that are commonly observed. This paper explores alternative explanations for ant species coexistence, focusing on factors that prevent competitive exclusion in diverse ant communities experiencing high levels of behavioural dominance, such as characteristically occurs in Australia. Very high species densities require two conditions to be met: first, a large number of species must successfully establish; and second, there must be a high rate of species persistence once established. In this context I advance five propositions based around three sets of arguments. First, ant sociality and modularity confers a high level of persistence once colonies are established, so that species coexistence is determined to a significant extent by processes operating at the establishment phase, rather than just by interactions between established colonies. Second, competitive outcomes are highly conditioned by environmental variation, which severely limits competitive exclusion. Finally, dominant species are highly patchy in space, and cannot comprehensively monopolize resources, such that there will usually be room for low densities of subordinate species. These propositions have relevance to neutral theories of community ecology, and to understanding intercontinental differences in local species richness.     

Diel and seasonal patterns of foraging activity in the arboreal ant Crematogaster matsumurai Forel

The foraging habits of the arboreal ant Crematogaster matsumurai Forel were studied in natural and captive colonies in southern Kyushu, Japan. The nests of C. matsumurai are made mainly in the trunks of living trees. In the natural environment, the species mainly lives in decayed parts of relatively tall trees, such as Acer palmatum, Prunus jamasakura and Prunus yedoensis. Observation over a 24 h period showed that C. matsumurai foraged actively at night as well as during the day. The foraging of the workers out of the nest was seen from early spring to late autumn, both on the tree and on the ground. As protein sources, aphids were mainly collected by foragers from the tree, while small parts of dead insects or other arthropods were mainly collected from the ground surface. The foraging activity of workers is assumed to be influenced by the quantity and quality of food rather than seasonality.     

Simplifying the savanna: the trajectory of fire‐sensitive vegetation mosaics in northern Australia

Aim Fire is a key agent in savanna systems, yet the capacity to predict fine‐grained population phenomena under variable fire regime conditions at landscape scales is a daunting challenge. Given mounting evidence for significant impacts of fire on vulnerable biodiversity elements in north Australian savannas over recent decades, we assess: (1) the trajectory of fire‐sensitive vegetation elements within a particularly biodiverse savanna mosaic based on long‐term monitoring and spatial modelling; (2) the broader implications for northern Australia; and (3) the applicability of the methodological approach to other fire‐prone settings. Location Arnhem Plateau, northern Australia. Methods We apply data from long‐term vegetation monitoring plots included within Kakadu National Park to derive statistical models describing the responses of structure and floristic attributes to 15 years of ambient (non‐experimental) fire regime treatments. For a broader 28,000 km² region, we apply significant models to spatial assessment of the effects of modern fire regimes (1995–2009) on diagnostic closed forest, savanna and shrubland heath attributes. Results Significant models included the effects of severe fires on large stems of the closed forest dominant Allosyncarpia ternata, stem densities of the widespread savanna coniferous obligate seeder Callitris intratropica, and fire frequency and related fire interval parameters on numbers of obligate seeder taxa characteristic of shrubland heaths. No significant relationships were observed between fire regime and eucalypt and non‐eucalypt adult tree components of savanna. Spatial application of significant models illustrates that more than half of the regional closed forest perimeters, savanna and shrubland habitats experienced deleterious fire regimes over the study period, except in very dissected terrain. Main conclusions While north Australia’s relatively unmodified mesic savannas may appear structurally intact and healthy, this study provides compelling evidence that fire‐sensitive vegetation elements embedded within the savanna mosaic are in decline under present‐day fire regimes. These observations have broader implications for analogous savanna mosaics across northern Australia, and support complementary findings of the contributory role of fire regimes in the demise of small mammal fauna. The methodological approach has application in other fire‐prone settings, but is reliant on significant long‐term infrastructure resourcing.     

Effect of rainfall exclusion on ant assemblages in montane rainforests of Ecuador

Models of global climate change generally predict higher rainfall variability, with more intense rainfall events separated by extended dry periods. We experimentally studied the effects of prolonged droughts on diverse ant assemblages found at three elevations in an Ecuadorian montane rainforest. We hypothesized that most species will be negatively affected directly (physiological stress) or indirectly (less food or suitable nesting resources) by drought. We thus expected a decrease in species richness as well as changes in assemblage composition. As the decrease of moisture content was expected to be more marked above ground than in soil, its impact on ants should differ according to their nesting site (dead wood, leaf litter, soil). After 6-month treatments, dead wood, leaf litter and soil samples were on average 53%, 46% and 4% drier under tents than controls, respectively. The drought did not alter overall species richness in the three nesting situations. However, species composition was significantly modified, mostly in dead wood and in leaf litter. Camponotus in dead wood, Strumigenys in leaf litter and Solenopsis in all three microhabitats were more abundant under tents. In contrast, Pheidole in dead wood, and Pachycondyla in leaf litter, were less abundant than in controls. Similar trends were observed at the three study sites. To conclude, after 6-month droughts dominant ant genera in the assemblages were affected differently. In the longer term, alteration of the rainfall regime is therefore expected to have an important impact on ants, as well as on their ecosystem functions and services, through shifts in species dominance and composition.     

Fire rather than nitrogen addition affects understory plant communities in the short term in a coniferous‐broadleaf mixed forest

Increasing fire risk and atmospheric nitrogen (N) deposition have the potential to alter plant community structure and composition, with consequent impacts on biodiversity and ecosystem functioning. This study was conducted to examine short‐term responses of understory plant community to burning and N addition in a coniferous‐broadleaved mixed forest of the subtropical‐temperate transition zone in Central China. The experiment used a pair‐nested design, with four treatments (control, burning, N addition, and burning plus N addition) and five replicates. Species richness, cover, and density of woody and herbaceous plants were monitored for 3 years after a low‐severity fire in the spring of 2014. Burning, but not N addition, significantly stimulated the cover (+15.2%, absolute change) and density (+62.8%) of woody species as well as herb richness (+1.2 species/m², absolute change), cover (+25.5%, absolute change), and density (+602.4%) across the seven sampling dates from June 2014 to October 2016. Light availability, soil temperature, and prefire community composition could be primarily responsible for the understory community recovery after the low‐severity fire. The observations suggest that light availability and soil temperature are more important than nutrients in structuring understory plant community in the mixed forest of the subtropical‐temperate transition zone in Central China. Legacy woody and herb species dominated the understory vegetation over the 3 years after fire, indicating strong resistance and resilience of forest understory plant community and biodiversity to abrupt environmental perturbation.     

The immediate and long‐term effects of water drawdown on macrophyte assemblages in a large subtropical reservoir

1. Disturbances play a central role in determining the spatial and temporal dynamics of many plant communities. In our study of macrophyte assemblages at 150 sites in five arms of a large subtropical reservoir (Itaipu Reservoir, Brazil–Paraguay border), we used co‐occurrence null models and spatiotemporal analyses to describe the patterns in the assemblages during a historically large water drawdown in 2000, in comparison with the previous year (1999) and subsequent years (2001–07). A C‐Score co‐occurrence index tested the null hypothesis of random structure during the drawdown period. A detrended correspondence analysis and multiresponse permutation procedure were used to verify whether species composition differed before, during and after the disturbance. 2. In contrast to our expectations, the null models showed that the macrophyte assemblages were spatially structured during the drawdown (2000), although species composition was significantly different from the previous year (1999) and also changed in the following years (2001–07). Significant species co‐occurrence patterns were generated by the drawdown disturbance, with species extinctions and colonisation by new species from propagules and seed bank germination. 3. The randomness we expected in 2000 actually occurred in 2001, probably because the reestablishment of normal water level enabled both submersed and free‐floating species to recolonise the shore that emergent species had inhabited since the drawdown. Biotic interactions appeared to increase during the years after the disturbance and the habitat preferences of the aquatic macrophytes were re‐established, resulting in higher similarities in aquatic macrophyte species composition in the years after the drawdown.     

The effect of forest disturbance on the leaf litter ant fauna in Ghana

In order to observe the effect of forest loss on the leaf litter ant fauna in Ghana, West Africa, samples were taken in primary forest, secondary forest and in cocoa plots. Ants were extracted from the leaf litter by sieving followed by suspension in Winkler bags. The species composition and species richness in the three different habitats were compared and no significant difference was found between them. It was concluded that most primary forest leaf litter ant species continue to survive in parts of the agricultural landscape which has largely replaced their original habitat.     

Seasonal patterns in rainforest litterfall: Detecting endogenous and environmental influences from long‐term sampling

Tropical rainforests play an important role in the storage and cycling of global terrestrial carbon. In the carbon cycle, net primary productivity of forests is linked to soil respiration through the production and decomposition of forest litter. Climate seasonality appears to influence the production of litter although there is considerable variability within and across forests that makes accurate estimates challenging. We explored the effects of climate seasonality on litterfall dynamics in a lowland humid rainforest over a 7‐year period from 2007 to 2013, including an El Niño/La Niña cycle in 2010/2011. Litterfall was sampled fortnightly in 24 traps of 0.50 m diameter within a 1‐ha forest plot. Total mean litterfall was 10.48 ± 1.32 (±SD, dry weight) Mg ha^?1 year^?1 and seasonal in distribution. The different components of litterfall were divided into L_Leaf (63.5%), L_Wood (27.7%) and L_{FF[flowers & fruit]} (8.8%), which all demonstrated seasonal dynamics. Peak falls in L_Leaf and L_Wood were highly predictable, coinciding with maximum daily temperatures and 1 and 2 months prior to maximum monthly rainfall. The El Niño/La Niña cycle coincided with elevated local winter temperatures and peak falls of L_Leaf and L_Wood. Importantly, we establish how sampling length and generalized additive models eliminate the requirement for extensive within‐site sampling when the intention is to describe dynamics in litterfall patterns. Further, a greater understanding of seasonal cycles in litterfall allows us to distinguish between endogenous controls and environmental factors, such as El Niño events, which may have significant impacts on biochemical cycles.