Bryophyte phytomass in tropical ecosystems

Knowledge about bryophyte production and phytomass in the tropics is poor and has been derived principally from studies of epiphytic bryophytes. Such work has been undertaken in Transvaal, Tanzania, Venezuela, Peru and Borneo. Except for the studies in Peru and Borneo, the vegetation types studied and the methods used have been too variable to allow many comparisons or generalizations to be made. However, in general it can be stated that phytomass of epiphytic bryophytes in equatorial latitudes increases from the tropical lowlands to the foreslline. This striking phenomenon has been hypothetically explained by gradients of factors such as precipitation, humidity, temperature and desiccation, or combinations of these. Recent experiments on the gas exchange of tropical-montane bryophytes have revealed that the rate of net assimilation decreases dramatically above 25^oC and that high temperature combined with low light intensities, as realized in the tropical lowland forest, results in high rates of respiration and insufficient net photosynthesis. Experiments with temperate bryophytes show the same results. If can be assumed that tropical lowland species have special physiological adaptations to survive these unfavourable conditions, such as a specialized phytochrome system or effective storage of photosynthetic products. Additional factors could include the relatively high nutrient supply provided by abundant precipitation in tropical montane forests, and damage to cells by strong desiccation in the tropical lowlands.     

Brains of Vespertilionids III. Comparative cytoarchitectonics of the hippocampus

The large size of the hippocampus in the papillose bat (Kerivoula papulosa) (see Part I) is paralleled by a structural differentiation of area CA 1 which is unique among Vespertilionids, and possibly Chiroptera in general. CA 1 of the papillose bat has a very thick band of cells which fills about ²/₃ of the whole thickness of CA 1, in contrast to a maximum of ¹/₃ in other Vespertilionids. As in primates, the cells are dispersed over the whole stratum oriens and reach the alveus. Unlike in primates, however, the cells seem to migrate also in the direction of the periphery, i. e. into the sub-stratum radiatum of the molecular layer. Only a relatively small outer cell-poor band remains (¹/₄ of the whole thickness versus more than ¹/₂ in primates; Table 2). In K. papulosa the cell band of CA 1 is clearly thicker than that of the adjacent neocortex, separated by the lateral ventricle (Fig. 4). So far we have no strong arguments to correlate this very specific structural character with any particular behavior in K. papulosa.     

Brains of Vespertilionids

Macromorphology and encephalization (EI) of brains were compared in 58 Vespertilionid species, brain composition in 36 species: 46 or 27 species of Vespertilioninae, 8 or 5 species of Miniopterinae, 2 species of Kerivoulinae, and 2 species of Nyctophilinae. Subfamily differences were found in the extent of the cover of the mesencephalon. It is nearly fully covered in Kerivoula papulosa (Kerivoulinae), at least half covered (by the cerebellum) in Miniopterinae, and free (completely or nearly so) in Nyctophilinae and Vespertilioninae. In relative brain size, the Kerivoulinae are highest (average EI = 130), followed by the Miniopterinae (111), Nyctophilinae (102) and Vespertilioninae (95). The higher encephalization of Kerivoulinae and Miniopterinae is accompanied by a marked increase of relative size in cerebellum and striatum, and in Kerivoulinae, in hippocampus and neocortex as well.     

Brains of Vespertilionids II. Vespertilioninae with special reference to Tylonycteris

As shown in Part I, the Vespertilioninae have on the average the lowest encephalization index (EI) of all the Vespertilionid subfamilies available, and the average size indices (Sis) of most of their brain parts are also lowest. There are, however, clear differences between the genera. The highest indices for the total brain and for many brain parts (OBL, DIE, TEL, PAL, SEP, STR, SCH) were found in Myotis, the highest Sis for NEG and MES in Scotophilus, for CER in Lasiurus, for BOL in Rhogeessa, and for HIP in Cbalinolobus. The lowest values for all brain parts except BOL were found in Tylonycteris (for BOL in Glauconycteris). The average EI of the flat-headed bamboo bats Tylonycteris pachypus and T. robustula was 60, i. e., ²/₅ less than that of the non-Tylonycteris Vespertilionids, which, as the reference group, have an average EI of 100. The brain size reduction may well be related to the adaptation to extreme flat-headedness. The amount of reduction in the various brain parts differs: it is strongest (about ¹/₂) in higher but more dispensable brain parts (STR, HIP, NEO) and distinctly lower (about ¹/₄) in structures closely involved in the fundamental vegetative functions (OBL, MES). Genera with conservative skull characteristics may have derivative characteristics of the brains, and vice versa.