Australia: The Land Where Time Began

A biography of the Australian continent 

Tropical Savanna - the Role of Insects

In Australia, the role of herbivorous insects has long been unrecognised and greatly underestimated, little interest being taken in researching their role. The comparatively small number of species of large native herbivores, most attention has been directed at cattle. Most of the scientific work on Australian tropical savannas has been directed at Kakadu and the surrounding region. The most important grazing insects in the tropical savannas are the grasshoppers and harvester termites, though the latter are mostly detritus feeders, as are other termites, concentrating mostly on dead plant material. The amount of grazing by grasshoppers in the Australian tropical savannas is unknown, though they are believed to probably be the major grazing anima in this ecosystem. It is known that in the African savannas their consumption rates can be comparable to that of large populations of mammalian herbivores.

Some work has been done on foliovorous insects in the southern parts of Australia in relation to eucalypts and Acacias, but their role in Australia's tropical savannas remains unstudied.

The main post dispersal seed herbivores are harvester ants, mainly Monomorium and Pheidole, mainly omnivores, and an endemic radiation of Meranoplus. The numbers of large native herbivores such as kangaroos and other macropods are low, mainly because of the low nutritional stratus of the tropical grasses. It has been claimed that grasshoppers are more important in the tropical savannas than all the native mammals combined, making them the main competitor of introduced livestock.

It has been found that there is an inverse relationship between the importance of grazing insects and mammalian grazers, that is believed to be associated with the soil fertility. In Kakadu National Park 30 sites were included in a study that found that the richness of termite species was correlated with the abundance and richness of grasshopper populations, but negatively correlated with the abundance of macropods and rodents, and also with soil fertility. As the soil fertility declines the dominance of insects becomes increasingly pronounced. It has been suggested that this correlation between increasing insect dominance and decreasing soil fertility is probably not just a function of the reduced presence of mammals, more likely being a positive response by the insects to low soil fertility. Much  more research is needed to elucidate the exact connection, but it has been proposed that as the soil fertility drops the plants have a harder time acquiring sufficient nutrients, the result is that resources are directed away from producing defensive chemicals, leaving the plants more susceptible to insect predation.

Sources & Further reading

  1. Mary E. White, Earth Alive, From Microbes to a Living Planet, Rosenberg Publishing Pty. Ltd., 2003
  2. Listen...Our Land is Crying
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                                                                                           Author: M.H.Monroe  Email:     Sources & Further reading