ABSTRACT
In eukaryotes, the role played by identified environmental factors and biological attributes that either accelerate or decelerate species diversity is elaborated. They consist of 2.6 million described species. At current description rate of 6,200 species/y, the number may go up to 2.7 or up to 3.0 million species. With 90% clonality decelerating diversity and slow description rate of 1,400 species/y, the fungal species number may not exceed 260,000 in the next 100 yr. Irrespective of covering 71% the Earth’s surface, the stable aquatic habitats support 402,262 species or 20% eukaryotes only, whereas the labile terrestrial habitats 80% eukaryotes. Hence, the former decelerates species diversity, but the latter accelerate it. The Earth (510 million km2) is divided into hot, humid, rainier (100 – 450 cm) tropics (36%), cool but less rainy (75 – 150 cm) temperate (58%) and the least raining (< 20 cm) polar zones (6%). Species diversity progressively decreases from the equator toward the poles. Precipitation is a causative factor, as species number of vascular plant grows with increasing net primary productivity caused by heavy precipitation. Scarcity of liquid water limits the diversity to 0.045 species/km2 in deserts and polar zones, in comparison to over 153 – 1,855 species/km2 in tropical evergreen forests. Unicellularity decelerates and limits diversity to 1.7% eukaryotes. So is the radial symmetry, which limits it to < 25%. Depending on random mutation alone, clonality decelerates the diversity to 15% eukaryotes. The costlier fragmenting clonals decelerates the diversity, while the cheaper budding clonality accelerates it. Clonality decreases from 100% in unicellular Protozoa to 90% seven tissue typed fungi, 24% in 60 tissue typed flowering plants, 1% in worms and 0% in 200 tissue typed vertebrates. Within eukaryotes, 1,980,109 species or 96% are sexualized and gametogenics. The 4% remain as clonals (e.g., Cyanophyta) or as unicellular Protozoa and structurally simpler fungi, which have secondarily lost sex. Of sexualized eukaryotes, 1,567,977 species or 79% are dioecious and the remaining 21% are monoecious. To minimize selfing in < 30% monoecy, protozoans and fungi have devised strategies limited to sexual systems; for example, mating groups and mating types in ciliates, and bipolarity and tetrapolarity in fungi. The 92% monoecious plants have developed the structural, i.e., sexual, floral and chemical systems. They have reduced selfing to 26%. The strategies in Metazoa includes the costlier sequential hermaphriditism and cheaper behavioral gonochorism, which have reduced selfing to 1%. In eukaryotes, evolution has proceeded from external fertilization to internal oogamic fertilization, which affords safety for immotile eggs and saving of their motility cost. Modality refers to modes of life. The trends for symbionts progressively increasing from Protozoa to plants but that for parasites decreases. Motility is measured in different units, varies at different ontogenetic stages and so on. Nevertheless, the diversity remains less in the flightless 200 speciose ratite birds, in comparison to 9,838 flying birds.
