Planktic foraminifera reveal differentiated relations with the physical environment which characterise the individual species. Only G. rubescens and G. tenella, and G. calida and G. siphonifera do not show clear differences in their adaptations. This may either suggest to include each pair in one taxonomic category, or the existence of unknown ecologic niches. These four species require taxonomic and biologic research.
Most species are widespread but are rare (relative abundance <1%) over at least 50% of their biogeographic range. More than half of the species does not exceed 5% in relative abundance in any sample. As a consequence, the number of counted specimens (494 ± 180) and the resultant counting error is close to the limits for reliable interpretations of much of the data. The present counting methods do not allow to characterise species at the fringes of their biogeographic range and to exploit their paleoceanographic potential in these areas.
For some species evidence emerged for reasons of their endemism in certain ocean basins. Species adapted to high salinity may be excluded from the Indian Ocean or may be rare because they exist at the margin of their ecologic range. Short-term changes in the biogeographic ranges of these species may relate to environmental change. On longer timescales migration may also result from evolutionary change in the adaptations of species.
The individual adaptations can also shed light on large-scale differentiation in planktic foraminifera. The limit between high latitude and low latitude assemblages in planktic foraminifera appears gradual when observed against sea surface water temperature and other parameters. In plots of relative abundances vs. vertical temperature gradients, a well defined biogeographic boundary becomes evident in regions where the vertical temperature gradient between the sea surface and 200 m is about 6 °C in summer.
The adaptations of individual species can be exloited in paleoenvironmental analyses with planktic foraminifera as tracers. It will be subject to future tests to include species in such analyses which are sensitive to certain parameters, and
to reduce the noise introduced by unsensitive species. New applications seem to be possible in the reconstruction of vertical temperature and density gradients. A number of species can characterise mainly winter conditions. They are probably
applicable in mapping polar to subtropical water masses, and some high latitude species (e.g. T. quinqueloba) may indicate areas of intermediate or deep water formation. Semiquantitative analyses are also possible when relative abundances of
species exclude certain intervals of conditions, e.g. when a species' relative abundance is only exceeded above a certain salinity. Any application of planktic foraminifera, however, needs to consider the multivariate character of their
adaptations. For most species the biological background of these adaptations is unknown.