EUCALYPTS, ARTHROPODS AND BIRDS - ON THE RELATION BETWEEN FOLIAR NUTRIENTS AND SPECIES RICHNESS

Using chemical knockdown procedures, canopy arthropod communities on e ucalypts (Eucalyptus spp,) were found to be extraordinarily rich in sp ecies, Four seasonal samples from four species of eucalypts, two in ea stern Australia and two in Western Australia, yielded 976 species of c anopy arthropods from the eastern site and 683 species from the west, The richest and most abundant faunas occurred on the site with the gre atest soil fertility and on the tree species with highest levels of fo liage nutrients (i.e. nitrogen and phosphorous), High nutrient concent rations are taken as a measure of overall productivity, Seasonal and a nnual differences in arthropod abundances, biomass, and species richne ss are correlated with temporal changes in rainfall affecting tree phe nological events (e.g. growth of new leaves) and productivity, Species of insectivorous birds that are dependent on energy-rich source carbo hydrates (e.g. lerp, manna) select between plant species as foraging s ubstrates on the basis of the kinds of arthropods available and their abundance on each kind of plant. On the basis of our results from stud ies of avian and canopy arthropod communities, we propose a general mo del to explain patterns of species richness in eucalypt forest communi ties, In eucalypt forests, site productivity appears to shape faunal r ichness in two ways, First, productive forests tend to be structurally and floristically complex, This provides opportunities for a high deg ree of specialisation among animal species. Secondly, these levels of specialisation are possible only where there are high levels of produc tivity and resources that are abundant and equitable in their temporal distribution, The richness of eucalypt communities, the rarity of man y arthropod species, and the association of the richest communities wi th temperate, moist forests on the most productive soils suggests that eucalypt forest biodiversity will be sensitive to changes in forest s tructure, floristic composition, and changed levels of productivity as sociated with logging and broad area fuel reduction fires.