Patterns and mechanisms involved in a cerrado arboreal ant community structure

In this study, I evaluated some of the most important mechanisms structuring arboreal ant communities. For this I took advantage of the easy accessibility and high diversity of the arboreal ant fauna of the savannas of central Brazil (Cerrado). First, I assessed the co-occurrence patterns of the arboreal ant species and evaluated to which extent these patterns can be explained by interspecific competition or by habitat association. For that, I used a dataset of 240 trees and performed null model analyses, first accounting only for the species incidence in the community and later incorporating habitat attributes. I performed analyses with all the ant species in the community and then with only the most common species using both a matrix level and a pairwise approach. I found that competition is the most important factor behind the distribution of these arboreal ants, with a much smaller influence of habitat attributes. The effect of competition was detected when I accounted for the 14 most common ant species in the community, both in the matrix level and the pairwise analyses. The importance of competition is consistent with the observed differences in some important biological characteristics of the coexisting ant species. After that, I focused on the patterns of resource use and how they can influence the diversity of arboreal ants. First, I assessed how the heterogeneity of nesting resources and the presence of a dominant species can affect the nesting patterns of arboreal ants. For this, I performed an experimental manipulation in 80 trees belonging to the same species. On each tree I placed 27 cavities with different entrance holes divided in two treatments: high entrance diversity (HE), with 9 different entrance sizes (0.15 to 0.55 mm²) and low entrance diversity (LE), with only 3 different entrance sizes (0.15 to 0.25). I considered Cephalotes pusillus as the dominant species over shelter resources, since it was the species which occupied the highest number of cavities and was also the most common in the experimental trees. I found more nesting ant species nesting in the HE treatment trees, and also a change in the used entrance sizes with an increase in the range and diversity of entrance sizes. I also found significant effects of the presence of the dominant species in nesting patterns, with more ant species and colonized nests when it was absent. There were also changes in the mean entrance size used by the ants in the presence of C. pusillus. Finally, I assessed the competitive outcomes of arboreal ants at food baits. I quantified the differences in resource use by the different ant species and asked if there was a significant relationship between the ability to find resources and to dominate them. I further asked which aspects of the ant are responsible for the observed outcomes. I performed observations in 175 medium sized trees from several species during the day and in a subset of 44 trees at night. I placed a teaspoon of sardine bait in the main branch of each tree and observed the turnover of species at the baits. I found a positive relationship between the discovery ability and the dominance of the ant species, supporting a priority effect over food resources. Overall, I found that colony size was the most important characteristic determining the outcomes at the baits. The present works fits in the growing demand for empirical studies assessing the factor defining species coexistence, showing the importance of competition for the structure of an arboreal ant community.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorTese (Doutorado)In this study, I evaluated some of the most important mechanisms structuring arboreal ant communities. For this I took advantage of the easy accessibility and high diversity of the arboreal ant fauna of the savannas of central Brazil (Cerrado). First, I assessed the co-occurrence patterns of the arboreal ant species and evaluated to which extent these patterns can be explained by interspecific competition or by habitat association. For that, I used a dataset of 240 trees and performed null model analyses, first accounting only for the species incidence in the community and later incorporating habitat attributes. I performed analyses with all the ant species in the community and then with only the most common species using both a matrix level and a pairwise approach. I found that competition is the most important factor behind the distribution of these arboreal ants, with a much smaller influence of habitat attributes. The effect of competition was detected when I accounted for the 14 most common ant species in the community, both in the matrix level and the pairwise analyses. The importance of competition is consistent with the observed differences in some important biological characteristics of the coexisting ant species. After that, I focused on the patterns of resource use and how they can influence the diversity of arboreal ants. First, I assessed how the heterogeneity of nesting resources and the presence of a dominant species can affect the nesting patterns of arboreal ants. For this, I performed an experimental manipulation in 80 trees belonging to the same species. On each tree I placed 27 cavities with different entrance holes divided in two treatments: high entrance diversity (HE), with 9 different entrance sizes (0.15 to 0.55 mm²) and low entrance diversity (LE), with only 3 different entrance sizes (0.15 to 0.25). I considered Cephalotes pusillus as the dominant species over shelter resources, since it was the species which occupied the highest number of cavities and was also the most common in the experimental trees. I found more nesting ant species nesting in the HE treatment trees, and also a change in the used entrance sizes with an increase in the range and diversity of entrance sizes. I also found significant effects of the presence of the dominant species in nesting patterns, with more ant species and colonized nests when it was absent. There were also changes in the mean entrance size used by the ants in the presence of C. pusillus. Finally, I assessed the competitive outcomes of arboreal ants at food baits. I quantified the differences in resource use by the different ant species and asked if there was a significant relationship between the ability to find resources and to dominate them. I further asked which aspects of the ant are responsible for the observed outcomes. I performed observations in 175 medium sized trees from several species during the day and in a subset of 44 trees at night. I placed a teaspoon of sardine bait in the main branch of each tree and observed the turnover of species at the baits. I found a positive relationship between the discovery ability and the dominance of the ant species, supporting a priority effect over food resources. Overall, I found that colony size was the most important characteristic determining the outcomes at the baits. The present works fits in the growing demand for empirical studies assessing the factor defining species coexistence, showing the importance of competition for the structure of an arboreal ant community

The influence of extrafloral nectaries in the structure of the cerrado arboreal ant community

The extrafloral nectaries (EFN´s) are very important in ant plant interactions, being present in a big number of plant families, mainly in the tropics. However, little is known about the influence of this resource in the structure of the ant community that uses it, except for a few studies in wet tropical forests. The goal of this work was to test and evaluate the importance of nectar resources in the structure of the ant community in a unique and still understudied biome, the Brazilian cerrado, a neotropical savanna. For that, I made a natural experiment and an experimental manipulation in the field, in a reserve located near Uberlândia, Southeastern Brazil. The natural experiment aimed to evaluate the differences in the ant community and the influence of the seasonality of this resource in tree species with and without EFN´s in two periods of the year, one when the EFN´s were mostly inactive (between June and July of 2010) and one in the peak of extrafloral nectar production (between October and November of the same year). For that, I sampled six common species of trees in the cerrado, Caryocar brasiliense, Qualea grandiflora and Stryphnodendron polyphyllum, that have EFN´s and Sclerolobium aureum, Machaerium opacum e Kielmeyeria coriacea, that doesn´t have it. In total, ninety two trees were sampled, ranging from 12 to 18 individuals of each tree species. The sampling was done with the use of pitfall traps, left for 48 hours on the plants. I didn´t find neither any significant differences in ant species richness for plants with or without EFN´s nor any effect for different times of the year. However, at the individual level (plant by plant) there was a bigger species turnover between sampling times in plants with EFN´s than in those without it, the same not been observed when population level was considered. I did an experimental manipulation with the addition of artificial nectaries in two plant species, one that naturally have EFN´s (C. brasiliense) and one that naturally doesn´t have it (S. aureum). I measured the rates of occupation of artificial wood nests (20 nests per tree). The artificial nectaries were made of 2 ml eppendorfs, which were filled weekly with a solution of water, sugar and amino acids, resembling the natural extrafloral nectar constitution. I placed 40 eppendorfs in 20 trees of each plant species, being 10 treatments and 10 controls. The occupation rate was significantly bigger in plant with artificial nectar addition in S. aureum, the same not happening for C. brasiliense. This study shows the need of more studies focusing the importance of EFN´s at the ant community level, in search of direct and indirect factors that influence this importance, like the seasonality of this resource.Mestre em Ecologia e Conservação de Recursos NaturaisOs nectários extraflorais (NEF´s) têm uma grande importância nas interações entre formigas e plantas, estando presentes em um grande número de famílias vegetais, principalmente nos trópicos. Pouco se sabe, porém, sobre a influência deste recurso na estruturação das comunidades das formigas que dele se utilizam, exceto por alguns estudos em florestas tropicais úmidas. O objetivo deste trabalho foi o de avaliar e testar a importância de recursos de néctar na estrutura da comunidade de formigas em um bioma único e ainda pouco estudado, o cerrado brasileiro. Para isso, foram realizados um experimento natural e uma manipulação experimental no campo, realizados na Estação Ecológica do Panga, em Uberlândia, Minas Gerais. O experimento natural buscou avaliar as diferenças na comunidade de formigas e a influência da temporalidade na oferta deste recurso em espécies de árvores com ou sem a presença de NEF´s e em dois períodos do ano, um quando a maioria dos NEF´s estavam inativos (entre junho e julho de 2010) e outro quando os NEF´s estavam no auge da atividade (entre outubro e novembro de 2010). Para isto, foram amostradas seis espécies diferentes de árvores comuns no cerrado, Caryocar brasiliense, Qualea grandiflora e Stryphnodendron polyphyllum que possuem NEF´s e Sclerolobium aureum, Machaerium opacum e Kielmeyeria coriacea que não possuem NEF´s. Noventa e duas árvores foram amostradas no total, divididas entre 12 e 18 indivíduos de cada uma das 6 espécies de plantas. A amostragem foi feita com a utilização de armadilhas do tipo pitfall deixadas por 48 horas nas plantas. Não foram observadas diferenças significativas na riqueza de espécies de formigas tanto para plantas com ou sem NEF´s, como para os diferentes períodos amostrais. Porém, no nível individual (planta por planta) houve uma maior troca (turnover) de espécies entre os períodos amostrais nas plantas com NEF´s do que nas sem NEF´s, padrão este que não foi observado para o conjunto total de plantas de cada espécie. Uma manipulação experimental foi realizada, com a adição de nectários artificiais em duas espécies de plantas, uma que possui NEF (C. brasiliense) e outra que não os possui (S. aureum). Foram medidas as taxas de ocupação de ninhos artificiais de madeira (20 ninhos por árvore). Os nectários artificiais se constituíram de microtubos eppendorf de 2ml, que eram enchidos semanalmente com uma solução de água, açúcar e amionácidos, semelhante a que ocorre naturalmente nos NEF. Foram colocados 40 microtubos em 20 árvores de cada espécie de planta, sendo 10 tratamentos e 10 controles (eppendorf apenas com água). A taxa de ocupação foi significativamente maior em plantas com a adição de néctar em S. aureum, o que não ocorreu em C. brasiliense. Este trabalho demonstra que embora os NEF´s sejam importantes na estruturação das assembléias de formigas, é necessária uma visão mais ampla, de comunidades em busca de fatores que influenciem diretamente nesta importância, como a sazonalidade do recurso

Ant Rafting in an Extreme Ecosystem

Ants are among the most abundant organisms on Earth, being adapted for living on different solid surfaces. However, in some habitats, like riparian forests and flooded plains, water can be a constant obstacle, and overcoming this obstacle can be essential to determine the persistence of ants in such habitats. While most ant species avoid the water during a flood by foraging at higher elevations or climbing on trees, a few species developed ways to overcome this obstacle by swimming. Here, we report, for the first time, ants of the species Linepthema micans (Forel 1908) performing rafts. We observed 14 rafts in three consecutive days at approximately 1400 meters a.s.l. in Serra do Cipó, Brazil. Notably, this is the first record of ant rafting in tropical mountaintop grasslands, which are extreme habitats with shallow and sandy soils, and where small temporary water pools are extremely common in the wet season

Complex temporal dynamics of insect metacommunities along a tropical elevational gradient

Unraveling the spatiotemporal dynamics of communities is critical to understand how biodiversity responds to global changes. However, this task is not trivial, as these dynamics are quite complex, and most studies are limited to few taxa at small local and temporal scales. Tropical mountains are ideal indicators of biodiversity response since these endangered and complex ecosystems include many distinct habitats within small geographical areas, harboring a megadiverse fauna, especially insects. Indeed, while insects are particularly sensitive to environmental and climatic changes, the extent of the impact of climate variability on mountain tropical insect diversity remains poorly understood. Here we present time‐series data from a decade of studying the spatiotemporal dynamics of ants, butterflies and dung beetles. We assessed patterns of species richness change along the elevational gradient for each taxonomic group per sampling year and cumulatively over years. We then quantified community changes over time by measuring the variation in species richness across sampling years (temporal trends in α‐diversity), and the temporal variation in species composition (temporal β‐diversity) evaluating species gains and losses over time. We also evaluated the variation of air temperature and humidity through meteorological stations within the sampling years. We detected a classical pattern of species richness decline with elevation, albeit with a noticeable increase in species richness variation with increasing elevation. The temporal β‐diversity exhibited considerable variability across elevations, taxa, and time. Only dung beetles presented a positive relationship with humidity variation over the years. Critically, both rare and common species drove extirpations and colonizations, and we found no trend of temporal decline of insect species at local and regional scales. Our study shows that insect metacommunity responses to elevation and global changes are rather complex, and stresses the importance of long‐term studies that incorporate multiple sampling periods and different groups of organisms in tropical mountains

Differential response of fire on the community dynamics of five insect taxa in a tropical mountaintop forest archipelago

Abstract The Earth's most diverse group of organisms is facing an imminent crisis, as recent investigations suggest a remarkable decline in insect diversity. Within this context, altimontane forest islands might emerge as important refuges holding an invaluable diversity of species that would be doomed to disappear. Here, we aimed to examine the impact of fire on the temporal variation of ant, bee, butterfly, dung beetle, and wasp communities in natural and highly threatened altimontane forest islands. We predicted that fire incidence would increase the natural variation in the structure of these insects' communities over time. Furthermore, we predicted that each taxon would respond accordingly to their ability to move between forest islands (i.e., vagility). We sampled these five bioindicator taxa in the rainy seasons of 2014, 2015, 2018, and 2020 within 14 forest islands in southeast Brazil. We assessed the incidence (presence/absence) of fire occurrence on each forest island toward the end of the dry season in each sampling year. We found an influence of fire incidence on the species composition changes over time (temporal β‐diversity) in the less vagile insect groups: ants, and dung beetles. Nevertheless, we found no influence of fire incidence on shifts in species composition of highly vagile insects: bees, butterflies, and wasps. Importantly, species turnover was the primary component of temporal β‐diversity driving the interannual variation of all insect taxa examined in this study. Our results highlight the distinct responses of more‐or‐less vagile insect groups to fire in forested ecosystems and shed light on the drivers of vulnerability and resilience of these groups to this critical anthropogenic pressure. By understanding and elucidating the intricate responses of distinct insect communities to global stressors, we can strengthen our capacity to predict future trends in biodiversity decline and provide valuable insights for conservation efforts and environmental management strategies

Has climate change hijacked the environmental agenda?

Since the establishment of the Intergovernmental Panel on Climate Change (IPCC), decision-makers have realised that periodic assessments were needed to closely monitor climate change. Studies on it became widespread and include the science of greenhouse gas emissions, the composition of these gases and the extent to which humans have been responsible for climate change. In this sense, the United Nations summit has made significant progress since the Rio Conference (Eco 92), with the creation of the Conference of the Parties (COPs). However, governments should not solely focus on curbing greenhouse gas emissions into the atmosphere. In a society with broad and deep environmental problems, governments, the private sector and non-governmental organisations’ (NGOs) efforts should include biodiversity conservation in their agenda. Solving a single problem, the climate crisis is honourable and urgently needed, but to constrain our ever-increasing land-use footprints on the planet needs the tackling of another equally challenging problem, the loss of biodiversity. The destruction of ecosystems undermines nature’s ability to regulate greenhouse gas emissions and protect against extreme weather, thus accelerating climate change and increasing our vulnerability to it. Therefore, tackling environmental challenges means more than building electric cars, investing in “clean” energy and imposing fines on those who burn forests. To save the environment, scientists, industry, policy-makers and the wider society urgently need to look at other aspects of ecosystem conservation and restoration in the same way they look at the climate agenda