. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. Folivores; Forest ecology; Leaves; Mammals; Mammals. SOIL TEXTURAL COMPOSITION DOUALA-EDEA. D DOUALA-EDEA 1 CONTENTS OF EXCHANGEABLE BASES, IN M-EO'S/lOO G SOIL Figure 4. Comparison of Kibale and Douala-Edea soils. A, tex- tural composition; B. contents of exchangeable calcium, magne- sium, and potassium. the upper B horizon of 3 samples (1 from each of the major soil types) from Kibale and means of 7 samples from the Douala-E
. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. Folivores; Forest ecology; Leaves; Mammals; Mammals. SOIL TEXTURAL COMPOSITION DOUALA-EDEA. D DOUALA-EDEA 1 CONTENTS OF EXCHANGEABLE BASES, IN M-EO'S/lOO G SOIL Figure 4. Comparison of Kibale and Douala-Edea soils. A, tex- tural composition; B. contents of exchangeable calcium, magne- sium, and potassium. the upper B horizon of 3 samples (1 from each of the major soil types) from Kibale and means of 7 samples from the Douala-Edea site taken at comparable depths (just below the A horizon, about 10 cm-20 cm beneath the surface). As shown in the figure, the Douala-Edea soils have very small amounts of silt and clay, and average about 91 percent sand. Not sur- prisingly, given their low content of anything but sand, the contents of exchangeable bases in these soils are much lower than in the Kibale soils, up to 10 times lower in the case of calcium. The beach sands on which these soils are built were probably deficient in nutrients to begin with. The intensive leaching that should occur when heavy rainfall (about 4 m annually) percolates through a material with such a high percentage of sand and very poor ion retention properties has doubtless led to a further reduction in the amounts of nutrients available to plants. Other features of this soil appear inimical to plant growth. Preliminary results for an extensive series of soil profiles collected by J. S. Gartlan reveal that surface pH values can be as low as (Gartlan, personal communication). Vegetation In a habitat such as the Douala-Edea study area, where the availability of nutrients for plants is very low but the physical environment is favorable to animals, there should be selection for increased in- vestment in the chemical defense of leaves, since it costs the plant more to replace a leaf eaten by a herbivore (Janzen, 1974). There should al
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