Numerically dominant species drive patterns in resource use along a vertical gradient in tropical ant assemblages

Resource availability can influence the foraging strategy adopted by different ant species as they endeavor to meet nutrient demands of the colony. In tropical rain forests, environmental conditions including resource availability vary over a vertical gradient. Consequently, nitrogen is predicted to become more limiting than carbohydrates toward the canopy as food webs shift to become more reliant on plant‐based resources. We used a “bait‐choice” experiment in a tropical rain forest to examine differences in protein and carbohydrate use with height and determined whether there were differences in response between common (numerically dominant) and rare species. Additionally, we investigated the nutrient use at the species level. Using species co‐occurrence analysis, we examined interspecific competition by testing the co‐occurrence of ant species at the tree level. Over the 12 trees investigated, 124 morphospecies were identified with eight species comprising 90% of total ant abundance. Species richness and protein use increased with height of bait for all species pooled and for common species but not rare species. Correspondingly, relative carbohydrate use decreased with height. We found greater species richness of rare species on carbohydrate baits compared with protein baits. Ant species were randomly distributed among trees when all species were included in co‐occurrence analysis. However, when only common species were considered, segregation between species was evident among trees providing evidence for the presence of ant mosaics. Our results suggest that nitrogen limitation in the canopy may not be true for the whole ant assemblage but rather for the few common species.DATA AVAILABILITY STATEMENT: Data are archived with the Environmental Information Data Centre (EIDC)/NERC, https://doi.org/10.5285/62bf0 251-ca8d-4288-a274-0ff6e39b3a3c (Law & Parr, 2019). Voucher specimens are retained at the University of Liverpool and the Universiti Malaysia Sabah.This publication is a contribution from the UK NERC-funded Biodiversity and Land-use Impacts on Tropical Ecosystem Function (BALI) consortium (http://bali.hmtf.info) (NERC grant no. NE/L000016/1) and was supported by the South-East Asian Rainforest Research Partnership (SEARRP) with permission from the Maliau Basin Management Committee. SL was funded by the University of Liverpool.http://wileyonlinelibrary.com/journal/btphj2020Zoology and Entomolog

Termites and fire : current understanding and future research directions for improved savanna conservation

No abstract available.The Rufford Small Grants Innovation Award, the Trapnell Fund, University of Oxford as well as the University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-9993ab201

The effect of fire on ant assemblages does not depend on habitat openness but does select for large, gracile predators

Ecosystems can respond in a variety of ways to the same agent of disturbance. In some contexts, fire causes large and long-lasting changes to ecological communities. In others, fire has a limited or short-lived impact on assemblages of animals and plants. Understanding why this occurs is critical if we are to manage these kinds of disturbances across the globe. A recent synthesis proposed that these seemingly idiosyncratic responses to fire can be understood in the context of habitat openness pre-disturbance. Assemblages in open habitats should respond less to a single fire event that those in closed habitats. We provide a test of this hypothesis by examining the response of ant (Hymenoptera: Formicidae) communities to large-scale fire events in three habitats of different natural canopy openness on the Peloponnese peninsula in Greece. We also test the hypothesis that assemblage responses to fire are trait dependent. Fire simplifies the physical structure of the environment, increases insolation, and limits opportunities for ants to exploit herbivorous feeding strategies. Consequently, we predict that ants will face a strong environmental filter between unburnt and recently burnt plots, which will be reflected in their functional morphology. Our analysis shows that burnt plots have more individual ants, more species and an almost complete compositional change relative to unburnt plots. These changes do not depend on initial canopy openness. Rather, we suggest that openness must be interpreted relative to the study taxon; for ants, openness should be measured closer to the ground level. In our study, ground-level openness does not vary across the plots, which may explain the results. Furthermore, ants in burnt plots are significantly larger, have relatively longer legs, relatively longer mandibles, and more elongate heads. This morphotype fits with our prediction of ants that can move and feed successfully in the burnt micro-landscape. Ultimately, more work is needed to fully explore the relationship between habitat openness and the response to fire. Our results showing a filtered set of ant morphologies in burnt environments suggest that ant traits may offer a further way forward to understand the faunal response to fire and disturbance in general.http://www.esajournals.org/loi/ecspam2022Zoology and Entomolog

Resistance of mound-building termites to anthropogenic land-use change

Humans pose a major threat to many species through land-use change in virtually every habitat. However, the extent of this threat is largely unknown for invertebrates due to challenges with investigating their distributions at large scales. This knowledge gap is particularly troublesome for soil macrofauna because of the critical roles many of these organisms perform as ecosystem engineers. We used a combination of high-resolution airborne Light Detection and Ranging and deep learning models to map the distribution of the ecologically important termite genus Macrotermes across a South African savanna land-use gradient, quantifying the effects of land-use change on patterns of mound densities, heights and spatial patterning. Despite significant anthropogenic alteration to landscapes, termite mounds persisted and shared a number of similarities to mounds in untransformed areas. Mean mound height was not substantially reduced in transformed landscapes, and over-dispersion of mounds at localized scales was conserved. However, mound densities were partially reduced, and height distributions in transformed areas differed to those in protected areas. Our findings suggest that mound-building termites persist even in areas of relatively high human disturbance, but also highlight important differences in termite distributions that could lead to reductions in ecosystem services provided by termites in human-modified landscapes. The persistence of at least half of mounds in human-modified landscapes could serve as starting points for savanna restoration.http://iopscience.iop.org/1748-9326am2020Zoology and Entomolog

Termites have wider thermal limits to cope with environmental conditions in savannas

1. The most diverse and abundant family of termites, the Termitidae, evolved in African tropical forests. They have since colonised grassy biomes such as savannas. These open environments have more extreme conditions than tropical forests, notably wider extremes of temperature and lower precipitation levels and greater temporal fluctuations (of both annual and diurnal variation). These conditions are challenging for soft-bodied ectotherms, such as termites, to survive in, let alone become as ecologically dominant as termites have. 2. Here, we quantified termite thermal limits to test the hypothesis that these physiological limits are wider in savanna termite species to facilitate their existence in savanna environments. 3. We sampled termites directly from mound structures, across an environmental gradient in Ghana, ranging from wet tropical forest through to savanna. At each location, we quantified both the Critical Thermal Maxima (CTmax) and the Critical Thermal Minima (CTmin) of all the most abundant mound-building Termitidae species in the study areas. We modelled the thermal limits in two separate mixed-effects models against canopy cover at the mound, temperature and rainfall, as fixed effects, with sampling location as a random intercept. 4. For both CTmax and CTmin, savanna species had significantly more extreme thermal limits than forest species. Between and within environments, areas with higher amounts of canopy cover were significantly associated with lower CTmax values of the termite colonies. CTmin was significantly positively correlated with rainfall. Temperature was retained in both models; however, it did not have a significant relationship in either. Sampling location explained a large proportion of the residual variation, suggesting there are other environmental factors that could influence termite thermal limits. 5. Our results suggest that savanna termite species have wider thermal limits than forest species. These physiological differences, in conjunction with other behavioural adaptations, are likely to have enabled termites to cope with the more extreme environmental conditions found in savanna environments and facilitated their expansion into open tropical environments.Royal Society-DFID/FCDO Capacity Building Initiative; NERC ACCE DTP.http://wileyonlinelibrary.com/journal/janeZoology and Entomolog

A longitudinal study of nest occupancy, trail networks and foraging in a polydomous wood ant population

Most ant colonies live in a single nest (monodomy) or a group of nests (polydomy). However, the length of time for which nests are inhabited varies significantly between different species. Although colonies of some species frequently move nest sites, in others, colonies inhabit the same nest or group of nests for many years. Similarly, in some species foraging and resource-sharing trails are highly dynamic, while in other species trails are used for years. Wood ants are a group of keystone species that inhabit many northern hemisphere woodlands, where they are important predators of invertebrates and indirectly act as herbivores through the farming of aphids. Wood ant colonies exhibit both monodomy and polydomy, and can inhabit nests for many years. Trails in wood ant colonies are also thought to be relatively stable. However, information about colony dynamics is mostly anecdotal as, until now, no longitudinal datasets have been collected. In this study, we collected data from ten polydomous wood ant colonies annually for 8 years and a subset of four colonies 16 times over 2 years. We found that most polydomous wood ant nests are abandoned in the first 2 years after being constructed and are more likely to be abandoned in the latter part of the active season. However, the rate of nest abandonment decreases after 2 years and is lower in larger nests. We also found that wood ant trails are relatively static within an active season and become more static later in the season as trails become established.The NERC ACCE DTPhttp://link.springer.com/journal/40am2020Zoology and Entomolog

Agricultural expansion in African savannas : effects on diversity and composition of trees and mammals

Land use change (LUC) is the leading cause of biodiversity loss worldwide. However, the global understanding of LUC’s impact on biodiversity is mainly based on comparisons of land use endpoints (habitat vs non-habitat) in forest ecosystems. Hence, it may not generalise to savannas, which are ecologically distinct from forests, as they are inherently patchy, and disturbance adapted. Endpoint comparisons also cannot inform the management of intermediate mosaic landscapes. We aim to address these gaps by investigating speciesand community-level responses of mammals and trees along a gradient of small scale agricultural expansion in the miombo woodlands of northern Mozambique. Thus, the case study represents the most common pathway of LUC and biodiversity change in the world’s largest savanna. Tree abundance, mammal occupancy, and tree- and mammal-species richness showed a non-linear relationship with agricultural expansion (characterised by the Land Division Index, LDI). These occurrence and diversity metrics increased at intermediate LDI (0.3 to 0.7), started decreasing beyond LDI>0.7, and underwent high levels of decline at extreme levels of agricultural expansion (LDI>0.9). Despite similarities in species richness responses, the two taxonomic groups showed contrasting β-diversity patterns in response to increasing LDI: increased dissimilarity among tree communities (heterogenisation) and high similarity among mammals (homogenisation). Our analysis along a gradient of landscape-scale land use intensifcation allows a novel understanding of the impacts of diferent levels of land conversion, which can help guide land use and restoration policy. Biodiversity loss in this miombo landscape was lower than would be inferred from existing global syntheses of biodiversity-land use relations for Africa or the tropics, probably because such syntheses take a fully converted landscape as the endpoint. As, currently, most African savanna landscapes are a mosaic of savanna habitats and small scale agriculture, biodiversity loss is probably lower than in current global estimates, albeit with a trend towards further conversion. However, at extreme levels of land use change (LDI>0.9 or<15% habitat cover) miombo biodiversity appears to be more sensitive to LUC than inferred from the meta-analyses. To mitigate the worst efects of land use on biodiversity, our results suggest that miombo landscapes should retain>25% habitat cover and avoid LDI>0.75—after which species richness of both groups begin to decline. Our fndings indicate that tree diversity may be easier to restore from natural restoration than mammal diversity, which became spatially homogeneous.Rufford Small Grants Foundation; Abrupt Changes in Ecosystem Services project funded with support from the Ecosystem Services for Poverty Alleviation (ESPA) programme. The ESPA programme was funded by the Department for International Development (DFID), the Economic and Social Research Council (ESRC) and the Natural Environment Research Council (NERC).http://link.springer.com/journal/10531pm2021Zoology and Entomolog

Clarifying terrestrial recycling pathways

Pausas and Bond argue that there are three major pathways by which the carbon and nutrients assimilated by plants are recycled through ecosystems: microbial decomposition, vertebrate herbivory, and wildfires. This framework has three principles. First, that each pathway recycles nutrients into plant-available forms. Second, that each pathway is broadly equivalent in that they consume ‘biomass’. Third, that the dominance of each pathway varies under different environmental conditions. We welcome the reframing of terrestrial recycling pathways in this way, but have identified three areas where the ‘Three Pathways Framework’ could be built upon.http://www.cell.com/trends/ecology-evolution/homehj2022Zoology and Entomolog

Geographical variation in ant foraging activity and resource use is driven by climate and net primary productivity

AIM : Foraging activity is critical for animal survival. Comprehending how ecological drivers influence foraging behaviour would benefit our understanding of the link between animals and ecological processes. Here, we evaluated the influence of ecological drivers on ant foraging activity and relative resource use. LOCATION : Six Brazilian biomes: Amazon, Atlantic rainforest, Caatinga, Cerrado, Pampa and Pantanal. TAXON : Formicidae. METHODS : We assessed ant foraging activity and resource use by sampling across 60 sites. We placed baited tubes that contained one of five liquid resources (sugar, lipids, amino acid, sodium and distilled water). We used model selection to assess the influence of ecological drivers (temperature, precipitation, temperature seasonality and net primary productivity) on ant foraging activity and relative resource use. RESULTS : Foraging activity was higher in wetter, more productive and less thermally seasonal environments. The relative use of amino acids increased at higher temperatures while the relative use of lipids decreased. The relative use of sugar increased in drier and less productive environments with high-temperature seasonality while the relative use of amino acid and sodium decreased in those environments. The relative use of lipids was complex: increasing with increasing temperature seasonality and decreasing with increasing precipitation. Furthermore, the relative use of sodium was greater where the foraging activity was high. MAIN CONCLUSIONS : We demonstrate how ecological drivers are correlated with ant foraging activity and resource use in the field across large spatial scales. The search for resources encompasses different interactions involving ants with abiotic and biotic components in the ecosystem. Thus, we suggest that changes in climate and NPP, which influence the intensity and the way that ants search for resources, will result in changes in ant-mediated ecological processes.Chaim J. Lasmar is a Post-doctoral researcher at the Programa de Pós-Graduação em Ecologia Aplicada (Universidade Federal de Lavras, Brazil). This study was part of his Ph. D. work at the Universidade Federal de Lavras with an internship period at the University of Liverpool.DATA AVAILABILITY STATEMENT: All data have been uploaded to Dryad (https://doi.org/10.5061/dryad.6wwpzgmxc).Fundação de Amparo à Pesquisa do Estado de Minas Gerais and Rufford Foundation.http://wileyonlinelibrary.com/journal/jbiam2022Zoology and Entomolog

Spatial variability and abiotic determinants of termite mounds

Termite mounds contribute to the spatial heterogeneity of ecological processes in many savannas, but the underlying patterns and determinants of mound distributions remain poorly understood. Using the Carnegie Airborne Observatory (CAO), we mapped the distribution of termite mounds across a rainfall gradient within a river catchment ( ∼ 27 000 ha) of the Kruger National Park, South Africa. We assessed how diff erent factors were associated with the distribution and height of termite mounds at three spatial scales: the entire catchment, among three broad vegetation types, and on individual hillslope crests. Abiotic factors such as the underlying geology and mean annual precipitation shaped mound densities at broad scales, while local hillslope morphology strongly infl uenced mound distribution at fi ner scales, emphasising the importance of spatial scale when assessing mound densities. Fire return period had no apparent association with mound densities or height. Mound density averaged 0.46 mounds ha 1 , and exhibited a clustered pattern throughout the landscape, occurring at relatively high densities (up to 2 mounds ha 1 ) on crests, which are nutrient-poor elements of the landscape. Mounds exhibited signifi cant over-dispersion (even spacing) at scales below 60 m so that evenly spaced aggregations of termite mounds are embedded within a landscape of varying mound densities. Th e tallest mounds were found in dry savanna (500 mm yr 1 ) and were positively correlated with mound density, suggesting that dry granitic savannas are ideal habitat for mound-building termites. Mound activity status also varied signifi cantly across the rainfall gradient, with a higher proportion of active (live) mounds in the drier sites. Th e diff erential spacing of mounds across landscapes provides essential nutrient hotspots in crest locations, potentially sustaining species that would otherwise not persist. Th e contribution to biodiversity and ecosystem functioning that mounds provide is not uniform throughout landscapes, but varies considerably with spatial scale and context.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-05872015-06-30hb2014ab201