Different burning intensities affect cavity utilization patterns by arboreal ants in a tropical savanna canopy
Introduction
Fire is an important natural disturbance in many ecosystems of the world, and some systems, such as tropical savannas, are a product of frequent fire events (Bowman et al., 2009, Pyne, 1997, Simon et al., 2009). In these biomes, fire influences patterns of biodiversity and drives population dynamics and community assembly of animals and plants (He et al., 2019, Koltz et al., 2018, Pausas and Keeley, 2019, Pausas and Parr, 2018). The effects of fire disturbance on species assembly patterns can operate at different levels. While it can affect population size by direct mortality, it can also have an indirect effect on population dynamics by impacting the availability of essential resources, and especially food and shelter resources (Andersen, 2018, Fagundes et al., 2015, Frizzo et al., 2012). In many cases, both direct and indirect effects can be acting at the same time, and identifying the main cause of changes in species assemblies after fire events is notoriously hard to track.
Some insects, like ants and termites, are responsible for a large portion of the animal biomass of tropical savannas (Dawes-Gromadzki, 2008) and can be used as biological indicators (Andersen et al., 2012, Cunha, 2006, Hoffmann and Andersen, 2003, Majer, 1983, Tiede et al., 2017) since these highly diverse organisms show fast responses to ecological disturbances (Andersen and Müller, 2000, Eggleton et al., 2002, Hoffmann and Andersen, 2003, Majer et al., 2007). Although fire can have crucial effects on the communities of these insects, the main effects are not through direct mortality, but rather through changes in the habitat, and consequently on resource availability (Costa et al., 2018, Fagundes et al., 2015, Kim and Holt, 2012, Swengel, 2001). Thus, it is expected that those animals that rely directly on arboreal resources may be especially sensitive to fire (Frizzo et al., 2012), and their responses may be idiosyncratic, depending on fire intensity, duration, and frequency (Vasconcelos et al., 2017).
The Cerrado is the largest South American savanna and is also the most diverse and threatened of all grassy biomes, and is considered a hotspot of biodiversity (Myers et al., 2000). Ants comprise a high proportion of the animal biomass in this ecosystem, and about one-third of the ant fauna of Cerrado actively forage on trees (Camacho and Vasconcelos, 2015). Cerrado arboreal ants feed on other arthropods and the sugar-rich liquid food resources produced by sap-sucking hemipterans and extrafloral-nectaries (Ribas et al., 2010, Rico-Gray and Oliveira, 2007). Arboreal ants also use trees as shelter, nesting almost exclusively in abandoned feeding tunnels of wood-boring beetles (Novais et al., 2017, Philpott and Foster, 2005, Powell et al., 2011). Indeed, recent research shows that shelter resources are very limited for arboreal ants, and may be much more important in determining arboreal ant species assembly patterns than previously thought (Debout et al., 2007, Jiménez-Soto and Philpott, 2015, McGlynn, 2006, Peeters and Molet, 2009, Philpott and Foster, 2005, Powell et al., 2011). Thus, Cerrado arboreal ants are ideal organisms to study the impacts of fire events on resource use and, ultimately, on arboreal ant species assembly patterns.
Here, we aimed to understand the impacts of fire on arboreal ant usage of essential and limited shelter resources. Moreover, we also assessed the potential influence of different fire intensities on arboreal ant shelter use. For this, we assessed the colonization rates of experimental cavities under four different burning intensities: ‘control,’ ‘low-intensity,’ ‘intermediate-intensity,’ and ‘high-intensity.’ We hypothesized that fire would have a detrimental effect on experimental cavity occupation by arboreal ants, with less occupied nests per tree and also a lower number of trees with occupied nests in the fire treatments. Importantly, this effect would be dependent on fire intensity, being stronger in higher intensity burns, once they can dramatically decrease the availability of natural cavities and, thus, the abundance and richness of arboreal ants. We also predicted that some ant species would be indicative of different fire intensities, due to differences in heat tolerance and colony size.
Section snippets
Study area
This study was conducted in the microregion of Chapada dos Veadeiros (13°33′ S, 47°31′ W), a 235,000-hectare reserve, located in the Northeast region of the state of Goiás, Brazil. This region is characterized by a tropical climate with two well defined seasons: a dry winter (May to September), and a rainy summer (October to April). The mean annual precipitation ranges between 1300 and 1500 mm, and the mean annual temperature is around 25 °C (Antonelli-Filho, 2011). The experiments were
Ant species richness
A total of 1,281 individuals belonging to 13 species, five genera, and three subfamilies of ants were recorded from the sampled cavities (Table 2). The different burning intensities had significantly different ant species richness (Estimate = 0.257, SE = 0.131, p = 0.049) (Fig. 2), increasing with the intensity of the fire, with the highest number of nesting ant species found in the high-intensity burn (nine species), and the lowest on the control area (four species).
Colonized trees
Nearly half of the
Discussion
Here, we have shown that fire has a significant positive effect on experimental cavity use by arboreal ants, with more ant species, more colonized trees, and higher cavity occupation under fire treatment. The positive effect of fire was modulated by its intensity, with higher species richness and number of overall trees colonized in the high-intensity fire. Moreover, there were higher cavity occupation rates under fire with intermediate intensity. In the absence of fire, ant species richness
CRediT authorship contribution statement
F.V. Arruda: Conceptualization, Methodology, Writing - original draft. T.J. Izzo: Methodology, Writing - review & editing. F.B. Teresa: Methodology, Writing - review & editing. F. Camarota: Conceptualization, Methodology, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank IBAMA, especially Diego Guimaraes de Sousa, and the fire brigade of the Kalunga community, in particular, Damião Moreira Dos Santos. The authors would also like to thank Micael Parreira Rosa, Werther Ramalho, and two anonymous reviewers for valuable insights. TJI and FBT were supported by CNPQ (grants 309552/2018-4 and 306912/2018-0, respectively), and FVA by CAPES (financing code-001) which provided his Ph.D. scholarship. The authors would like to thank João
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2022, Perspectives in Ecology and ConservationCitation Excerpt :This species richness increase soon after fire was accompanied by a marked difference in ant species composition between burned and unburned plots, with ten ant species found exclusively in the former ones. While fire can cause direct and indirect impacts on ant communities (Andersen, 2018; Arruda et al., 2020), the direct effects are often related to the death of colonies (Vasconcelos et al., 2017), which was probably not the case, due to the increase in ant species richness. Meanwhile, indirect effects are more likely to explain this rapid local increase in abundance and richness: ant colonies often increase their foraging activity after a fire due to habitat simplification and a decrease in ground-dwelling arthropod prey (Parr et al., 2007), which can be substantially affected by fires in the short-term (York, 1999).