Revisiting the ideas of trees as templates and the competition paradigm in pairwise analyses of ground-dwelling ant species occurrences in a tropical forest

Abstract A challenge for studies on the organization of ant assemblages in forest ecosystems is to disentangle the causal effects of species occurrences. The structural and functional attributes of trees can act as environmental filters for ground-dwelling ant species influencing resource availability and the microclimate. The biotic interactions, especially competition, can work together with plant characteristics influencing ant species occurrences. To test the importance of tree traits and species interactions on co-occurrence patterns of ants, we collected ground-dwelling ants, with pitfalls and litter sampling, beneath the canopies of four tree species during the rainy and dry seasons in a restored forest. We used five predictors (tree identity, crown size, trunk circumference, litter depth, and leaves density) to model the presence probabilities of ants . Hence, we applied habitat constrained null models in pairwise analyses to disentangle the causal effects of ants co-occurrences. The random pattern predominated in the assemblages, making up 96% of all possible species pairs combinations. Overall, 50% of the species pairs that showed nonrandomness in the ant occurrences were interpreted as resulting from environmental filters, 36% as negative associations and 14% as positive associations. Additionally, we found that the effects of season and the sampling technique on the ant assemblages were also important. We suggest that the ideas of the trees as templates and the paradigm of competition are both useful for understanding pairwise occurrence patterns in ant assemblages, and can be tested using tree traits as predictors in ant species distribution models for running constrained null models.

Parasitoids of the endangered leafcutter ant Atta robusta Borgmeier in urban and natural areas

Parasitoids of the endangered leafcutter ant Atta robusta Borgmeier in urban and natural areas. Hosts of parasitoids in urban areas may suffer from a double threat of habitat destruction by urbanization and parasitism pressure. Moreover, the parasitoids themselves might be at risk if they are specialists. Here, we studied whether Atta robusta (Hymenoptera, Formicidae), which is on the red list of Brazilian threatened species, suffers from higher parasitism pressure in an urban area compared to a natural one. In addition, we determined whether their specialist parasitoids, Eibesfeldtphora breviloba and Myrmosicarius exrobusta (Diptera, Phoridae), are in risk and evaluated whether they are influenced by habitat structure, temperature, humidity, ant traffic, and time of the day. The study was carried out in an urban park and in a natural protected area in the city of Rio de Janeiro. In each site we chose an open area and a closed area (forest) and sampled nine nests in each area. We found that parasitism pressure was similar in urban and natural areas, with the same two parasitoid species present in both areas. The main difference was related to habitat structure, since M. exrobusta was mainly present in open areas while E. breviloba was almost exclusively found in closed areas. Myrmosicarius exrobusta was not present during the hottest midday times, and its abundance was negatively correlated to vapor pressure deficit. These results suggest that green areas can be an important component in efforts to conserve diversity in urban areas. However, the complexity of the habitats in those areas is a fundamental issue in designing urban parks.

Teste da regra de equivalência energética para formigas de serapilheira: efeitos de diferentes métodos de estimativa de abundância em floresta ombrófila / Testing the energetic equivalence rule for litter ants: effects of different methods for abundance estimates in tropical rainforest

The Energetic Equivalence Rule (EER) states that species tend to consume energy independent of their body size. Here, the EER was tested for litter ants using body size and abundance data. Rainforest ants were obtained using pitfall traps and Winkler extractor. The abundance data from the Winkler extractions confirmed the EER, while the pitfall traps rejected it. Combination of abundance from pitfall catches and Winkler extractions either confirmed or rejected the EER. Further studies should focus on the interaction between sampling techniques and habitat types in the test of EER for ant communities.

A regra de equivalência energética (REE) propõe que o uso de energia independe do tamanho corporal da espécie. O tamanho e a abundância de formigas da serapilheira, coletadas em floresta ombrófila usando armadilhas pitfall e extrator de Winkler, foram usados no teste da REE. Os dados de abundância obtidos da extração de Winkler confirmaram a REE, enquanto os dados provenientes das armadilhas pitfall rejeitaram. A combinação das abundâncias estimadas pelas duas técnicas tanto aceitou quanto rejeitou a REE. Estudos posteriores deveriam focar a interação entre a técnica de coleta e o tipo de habitat no teste da REE para comunidades de formigas.

Efeitos de fatores ambientais sobre a mirmecofauna em comunidade de restinga no Rio de Janeiro, RJ / Effects of environmental factors on the ant fauna of restinga community in Rio de Janeiro, Brazil

A influência de fatores ambientais sobre a diversidade, riqueza e abundância de formigas em comunidade de restinga foi avaliada na Marambaia, litoral sul do estado do Rio de Janeiro. As amostras foram tomadas em agosto de 2004 (inverno) e março de 2005 (verão) em três fisionomias vegetais: (1) vegetação herbácea fechada de cordão arenoso (habitat homogeneo), (2) arbustiva fechada de cordão arenoso e (3) floresta de cordão arenoso (habitats heterogeneos). Em cada formação foram medidos os seguintes atributos ambientais: temperatura e umidade do solo, cobertura do solo por serapilheira e profundidade da serapilheira. Noventa e duas espécies distribuídas em 36 gêneros e oito subfamílias foram coletadas. A densidade de espécies e a abundância variaram significativamente com a fisionomia e época de coleta; a diversidade apenas com a fisionomia. O habitat homogêneo teve menor densidade de espécies, abundância e diversidade do que os habitats heterogêneos. As duas primeiras variáveis foram positivamente correlacionadas com a profundidade da serapilheira e ambas foram maiores na amostragem de verão do que na de inverno. Houve mais espécies de Ponerinae e Ectatomminae nos ambientes mais heterogêneos, enquanto que Formicinae foi mais abundante no ambiente homogêneo.

The effects of environmental factors on the richness, diversity and abundance of ants were studied in the Restinga da Marambaia, south coast of Rio de Janeiro State, Brazil. The samples were taken using pitfall traps in August/2004 (winter) and March/2005 (summer) in three different vegetation types: (1) herbaceous ridge palmoid (homogeneous habitat); (2) shrub dune thicket and (3) ridge forest (heterogeneous habitats). At each habitat a range of environmental attributes was recorded: soil temperature and humidity, percentage of soil covering by litter and litter depth. Ninety-two ant species belonging to 36 genera and eight subfamilies were recorded. Density of ant species and abundance varied significantly between habitats and seasons; ant diversity varied only between habitats. Homogeneous habitat had lower ant species density, abundance and diversity than heterogeneous habitats. The two first variables were positively correlated with litter depth and both were higher in summer than in winter samples. There were more species of Ponerinae and Ectatomminae in heterogeneous than in the homogeneous habitat, whereas the Formicinae species were more abundant in the later.