The effect of fire on resource discovery in Mediterranean ant communities

Background/Question/Methods

Fire is an important natural disturbance force in many ecosystems that can affect community biodiversity. Ants are crucial members of ecosystems, altering the abiotic and biotic properties of their environment. While the effect of fire on ant community composition has been frequently examined, little is known about how fire impacts foraging dynamics. It has previously been hypothesized that ants may forage at faster rates and more efficiently in burned habitats, perhaps because of reduced vegetative complexity and the need to quickly discover limited, valuable food items. We tested this hypothesis by quantifying resource discovery patterns in a species-rich ant community in Catalonia, Spain. Data were collected from three pairs of burned and control plots in European black pine forest one year after a lightening-provoked canopy fire during peaks of ant activity. Using survivorship models, we examined the relationship of resource discovery with species presence, abundance, vegetative cover, and soil temperature. 

Results/Conclusions

In contrast to past predictions, discovery was twice as fast in unburned versus burned areas as a result of differences in forager abundance and soil temperature. First, forager abundance was higher in unburned areas and higher abundances led to faster discovery times. The higher forager abundance in unburned areas resulted both from greater species richness as well as some species having more numerous foragers. Second, the higher soil temperatures found in burned plots were associated with slower discovery times. Although vegetative complexity reduced soil temperatures, it did not independently affect discovery patterns. Only one species, Formica gerardi, responded positively to fire; although equally abundant in both areas, it foraged more efficiently in burned habitats. These results suggest ants in burned habitats may face harsh foraging conditions, such as hotter soil temperatures and diminished food, which may limit the occurrence of certain species. Those that persist may have to find less food with fewer foragers, perhaps because a negative feedback between food and forager numbers. This is one of the first studies to specifically address how fire changes foraging in an ant community. Our results highlight the importance of looking beyond species occurrence in order to understand fire’s impacts.