Plant-animal interactions

Abstract

The diversity, complexity and functional importance of interactions between plants and animals is illustrated by focussing on three case topics: nutrient cycling by termites, habitat selection by vertebrates, and seed predation by ants. Termites are a conspicuous component of the soil fauna of tropical savannas, and are the premier decomposer insects. Unlike other decomposers, termites fundamentally alter the distribution of carbon and other nutrients, enriching the soils associated with their nests and mounds, and depleting soils elsewhere. Termites might also play a significant role in the global budgets of the “greenhouse” gases carbon monoxide and methane. The key factors influencing habitat selection by vertebrates are considered to be moisture and nutrient availability, and fire. The responses of mammals, lizards and birds to a moisture gradient associated with seasonal creeklines is outlined. Fire typically occurs every 1–3 years at most sites, and is a powerful modifier of vegetation patterns. Some vertebrates, such as granivorous and scavenging birds, exploit the immediate post-fire habitat, whereas others respond to the longer-term effects of fire on vegetation structure. Ants are major seed-harvesters throughout the Kakadu region, as they are throughout most of Australia. Eighteen harvester species have been recorded from a single savanna site, with nest densities averaging over 1600 ha⁻¹. In general terms, insects are pre-eminent over mammals as primary consumers in the Kakadu region, and this is attributed to low soil fertility. The resulting faunal assemblages contrast sharply with the mammalian-dominated systems characteristic of eutrophic African savannas.