Eucalypts, arthropods and birds: on the relation between foliar nutrients and species richness
Recher, H.F., Majer, J.D. and Ganesh, S. (1996) Eucalypts, arthropods and birds: on the relation between foliar nutrients and species richness. Forest Ecology and Management, 85 (1-3). pp. 177-195.
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Using chemical knockdown procedures, canopy arthropod communities on eucalypts (Eucalyptus spp.) were found to be extraordinarily rich in species. Four seasonal samples from four species of eucalypts, two in eastern Australia and two in Western Australia, yielded 976 species of canopy arthropods from the eastern site and 683 species from the west. The richest and most abundant faunas occurred on the site with the greatest soil fertility and on the tree species with highest levels of foliage nutrients (i.e. nitrogen and phosphorous). High nutrient concentrations are taken as a measure of overall productivity. Seasonal and annual differences in arthropod abundances, biomass, and species richness are correlated with temporal changes in rainfall affecting tree phenological events (e.g. growth of new leaves) and productivity. Species of insectivorous birds that are dependent on energy-rich source carbohydrates (e.g. lerp, manna) select between plant species as foraging substrates on the basis of the kinds of arthropods available and their abundance on each kind of plant.
On the basis of our results from studies of avian and canopy arthropod communities, we propose a general model to explain patterns of species richness in eucalypt forest communities. In eucalypt forests, site productivity appears to shape faunal richness in two ways. First, productive forests tend to be structurally and floristically complex. This provides opportunities for a high degree of specialisation among animal species. Secondly, these levels of specialisation are possible only where there are high levels of productivity and resources that are abundant and equitable in their temporal distribution. The richness of eucalypt communities, the rarity of many arthropod species, and the association of the richest communities with temperate, moist forests on the most productive soils suggests that eucalypt forest biodiversity will be sensitive to changes in forest structure, floristic composition, and changed levels of productivity associated with logging and broad area fuel reduction fires.
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