In light of these facts, it is likely that Earth's animal life - both terrestrial and aquatic - will experience population responses to rising levels of atmospheric CO2 that will parallel those of the plant kingdom; for the greater the plant food base, the greater the superstructure of animal life that can be supported. And with greater populations of individual organisms, greater biodiversity will likely abound, as each species of plant and animal must maintain a certain "critical biomass" to sustain its unique identity and insure its long-term viability.
When air temperatures and atmospheric CO2 concentrations rise concurrently, there is another CO2-induced phenomenon that also tends to increase ecosystem species richness. Driven by the unique ability of atmospheric CO2 enrichment to increase the ability of plants to withstand higher temperatures, this phenomenon leads to a stabilization of the low-latitude boundaries of the ranges of most plant species, even in the face of significant regional or global warming, while allowing them the opportunity to expand their high-latitude boundaries and thereby increase the sizes of their ranges. Herbivores that feed upon plants, and carnivores that eat herbivores and other animals, then have the opportunity to likewise increase the sizes of their ranges. And the increased overlapping of plant and animal habitats provided by this phenomenon tends to increase ecosystem biodiversity the world over, as is currently being observed in studies specifically designed to explore these phenomena.
Scheiner, S.M. and Rey-Benayas, J.M. 1994. Global patterns of plant diversity. Evolutionary Ecology 8: 331-347.
McNaughton, S.J., Oesterheld, M., Frank, D.A. and Williams, K.J. 1989. Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats. Nature 341: 142-144.
Cyr, H. and Pace, M.L. 1993. Magnitude and patterns of herbivory in aquatic and terrestrial ecosystems. Nature 361: 148-150.