Invertebrates: Their effects on the properties and processes of desert ecosystems

TitleInvertebrates: Their effects on the properties and processes of desert ecosystems
Publication TypeBook Chapter
Year of Publication2001
AuthorsWhitford WG
EditorPrakash I.
Book TitleEcology of Desert Environments
PublisherScientific Publishers
CityJodhpur, India
ARIS Log Number150390
Keywordsarid lands, decomposition, ecosystem processes, invertebrates, macropores, properties
AbstractThis book chapter summarizes the role of invertebrate animals as regulators of ecosystem processes and their effects on the properties of ecosystem properties in arid lands. Several groups of invertebrates are key players in decomposition and nutrient cycling processes. Soil nematodes that feed on bacteria and fungi regulate the population growth of these soil microbes, thereby affecting the rates of decomposition, nitrogen mineralization, and rates of cycling of other nutrients. Soil nematode populations are regulated by predation by several taxa of mites. Fungal feeding mites are also directly involved in mineralization processes and are key invertebrates in nutrient cycling because they maintain activity in dry soils. Soil bacteria, protozoans and nematodes cease activity when soil water potentials fall below the wilting point for agronomic plants. The most important arid soil animals are termites. Termites supplant earthworms in arid soils as the animals that process dead plant material. Termites process between 30% and 70% of dead plants, depending upon the species, and also process much of the dung of large herbivores. Because of the efficiency of the microflora and microfauna in the hind gut of termites, most of the plant material they consume is converted to carbon dioxide and water. There is a strong negative correlation between termite abundance and soil organic matter in Chihuahuan Desert rangelands and African rangelands. Termites are primarily responsible for the low organic carbon content of desert rangeland soils.Pedogenesis (soil formation) in arid environments is significantly affected by invertebrate animals. Desert snails consume large quantities of soil algae, grind surfaces of exposed limestone and grind soil crusts. Their fecal material is chemically and physically different from the materials that are ingested, thereby contributing to soil formation. Burrowing and nest building by ants, isopods, and burrowing spiders results in soil turnover with subsoil deposited on the surface. This activity is functionally similar to plowing but over geological time periods. Termites build above-ground nests and foraging galleries and sheeting from subsurface soils, thereby contributing to soil turnover and pedogenesis.In arid rangeland soils invertebrates directly affect hydrological properties of soil by the production of macropores. Macropores are continuous tubes or spaces (voids) in the soil with diameters larger than spaces in which capillary water movement occurs. During rains, water moves down macropores by bulk flow. Bulk flow is rapid and quickly wets deep soil layers around macropores. Arthropods in order of relative importance for the production of macropores in arid rangelands are: termites, ants, isopods, burrowing spiders, cicadas, and beetles. Emperical measurements of the effects of subterranean termites on hydrology have shown that infiltration rates on plots with termites are more than double those on plots with termites eliminated.Several species of ants and termites have been documented to be responsible for producing fertile patches in arid rangelands and thereby affecting plant production and plant species composition of the patches. Insects not only affect plant production by changing soil fertility, some species of Cerambicid beetles and Bostrichid beetles stimulate productivity of mesquite (Prosopis glandulosa) by girdling or boring into stems to provide safe sites for larval development. Mesquite exhibits compensatory growth by producing a number of stem leaders at nodes below the girdle or bore entrance. The pruning of shrubs by girdling and boring insects exacerbates the problem of shrublands that resist control efforts and remain in a degraded state.