World Biomes

Rationale for Hierarchical Organization of the World's Environments

Dennis Paulson, Director Emeritus

Life on Earth is extremely interesting, as most of us already know from television, if not from our own travels, and it becomes more so when each piece of the complex pattern fits understandably into the whole. One important goal of a biology curriculum should be to educate students about nature, in order to promote empathy and support for the natural world around us, and the interrelationship of all aspects of nature must be an integral part of the message delivered.

Biomes (bioclimatic zones) are appropriate divisions by which to organize the natural world, because the organisms that live in each of them possess common constellations of adaptations to them, in particular to the climate of each of the zones and to the characteristic vegetation types that develop in them. The primary elements to be dealt with under each zone were chosen because they are considered the basic elements at all levels, from the entire planet through each of its component physical environments to the species themselves.

The climate must be understood as perhaps the most important element in determining what kinds of organisms can live in an area and how they are modified to live under different conditions of temperature and precipitation and the seasonal distribution of these factors. Again, each spot on Earth has its own climate, influenced by both the macroclimate of the region and the microclimate of the particular site. But there are climatic commonalities on a grand scale that cause, for example, unrelated animals in the Sahara and Sonoran Deserts to have surprisingly much in common, and by effectively explaining these factors, an educational institution does much to fulfill its obligation to educate.

Soils are very important because they influence the types of plants (and thus plant communities) that will grow within a particular bioclimatic zone, and as substrates to animals as well. And soils in turn are much influenced by regional climates, as well as parent-rock geology.

The vegetation of an area is dependent on climate and soils and, in turn, influences very greatly both the plant and the animal species that can exist in a location. Vegetation varies in size and structure (physiognomy), in its seasonal manifestation, and in how it changes over time. Its importance is greater than the sum of its individual plant parts, as many species of animals, for example, are influenced greatly by the physical structure of the plant community, still others by the actual species of plants present.

A major component of the plants and animals in a region is their overall diversity, indicative of how many species can coexist there. This varies substantially both among and within bioclimatic zones, dependent on both climate and vegetation. In more diverse communities the degree and types of interactions among plants and animals are increased, with an increase in the number and complexity of stories to be told.

Plant and animal adaptations are the physical manifestations of organic evolution. Each individual is a collection of adaptations that allow it to function effectively in its environment, and these adaptations characterize the species to which it belongs. They are affected by all aspects of the environment, both physical (climate, water, substrate) and biological (other species as prey, predators, parasites, competitors or symbionts). Each species is unique, yet it shares particular types of adaptations with many other species. The generalities that can be expressed about these adaptations, if effectively presented, should reside in the brain as the conceptual file folders within which the individual species fact sheets can be stored.

Finally, as humans are significant in the world far out of proportion to being only one of millions of species in it, an interpretive element dealing with human effects seems necessary. No part of the world is unaffected by our presence, and we have the ability to modify environments on a massive scale. Our effects, which began in small ways millions of years ago and grew in proportion to the growth of the human population, can be considered positive or negative, depending on perspective.

Most basic principles of biology can be illustrated in the context of these elements, but those that are based on relationships among two or more species do not always clearly fall within features of the environment such as climate and soils or adaptations of individual species. These principles include the broad category of trophic relationships (food webs, productivity, decomposition, nutrient cycles) and interactions such as predator-prey relationships, competition, and symbiosis.