Ant Diversity and Function in Disturbed and Changing Habitats

Abstract

Habitat transformation and disturbance are significant threats to biodiversity conservation and ecosystem function. Disturbance is generally defined as any event that removes biomass (Townsend and Hildrew 1994), and is distinguished from habitat transformation or stress, which reduces available resources or changes the microclimate or structure of the habitat (Andersen 2000; Pickett and White 1985). Habitat disturbance and transformation affect communities in many ways either by altering the balance of competitive interactions, often in effect resetting the process of competitive exclusion, or by clearing space for colonization of new organisms. The degree to which habitat disturbance and transformation affect animal communities in general, and ants in particular, depends largely on the frequency and intensity of disturbance, the permanence with which habitats are transformed, and the distance from which propagules travel to recolonize affected habitats. Ant habitats of all kinds are modified by natural disturbances, such as fire, forest gap formation, hurricanes, and flooding, which vary in their extent, magnitude, and frequency. Furthermore, many terrestrial ecosystems, especially in tropical regions, have been altered by human activities including deforestation, urbanization, agriculture, agricultural intensification, grazing, and mining. At the same time, ants themselves are also instigators of habitat modification via their roles as mound builders and ecosystem engineers (Decaens et al. 2002; Folgarait 1998). The impacts of habitat disturbance and transformation for ants arewidespread, yet theyvarywith region and ecosystem. Ants can be very sensitive to habitat transformation and disturbance, and for this reason have been extensively used as indicator species (Hoffmann and Andersen 2003; see Box 8.1). Because ants are colonial organisms, removal of individuals (mortality) caused by habitat disturbance or transformation may not translate to extirpation of the colony from the habitat (Andersen 2000). This may mean the responses of ants to disturbance may differ from other terrestrial animals and plants that may become locally extinct after disturbances. Disturbance effects on ant communities include loss of diversity, changes in species composition, alteration of interspecific interactions, changes in trophic interactions with ant-plants and honeydew-producing hemipterans, and modification of ant-provided ecosystem services such as seed dispersal, predation, and soil modification. Virtually all habitats are subject to some sort of disturbance, although the disturbance will obviously vary in origin (natural or human-induced), in scale, and in magnitude. Many insights to basic ecology are thus gained by investigating ecology in disturbed habitats. For example, seminal work examining predator-caused disturbance in intertidal zones has formed the basis for the field of disturbance ecology (e.g. Paine 1996). Similarly, research in tropical forests affected by hurricanes and tree-fall gaps has shaped our knowledge