Evolution and Biodiversity in California

by Robert L Bowman

Exerpt from California's Wild Heritage; Threatened and Endangered Animals in the Golden State, by Peter Steinhart, reproduced with permission.

CALIFORNIA IS ONE OF the most biologically diverse areas in the world. Within its 160,000 square miles, California harbors more unique plants and animals than any other state. The diversity of climates and landscapes, and all the barriers to migrations such as rivers, mountains, and deserts, have led over thousands of years to the evolution of a large number of isolated species and varieties of animals, many of which are found only here. For example, there are about 30,000 species of insects recorded from California, 63 freshwater fishes, 46 amphibians, 96 reptiles, 563 birds, 190 mammals, and about 8,000 plants.

Yet it is also true that today, California's extraordinary diversity is being lost in many important habitats throughout the state. On average, over 20 percent of the naturally occurring species of amphibians, reptiles, birds, and mammals are classified as endangered, threatened, or "of special concern" by agencies of the state and federal governments.

Why does California have more endangered species than any other state? Biologists believe that the basic cause is an ever-increasing human population that is degrading the environment at an ever-accelerating rate. Many of California's unique species live in restricted habitats, under special conditions to which they have been adapting for hundreds or thousands of years. As people change or destroy these habitats, their native inhabitants die or fail to reproduce.

The Nature of Biological Diversity

WHEN WE SPEAK 0F "biodiversity," we imply more than just the variety of life forms around us. Each species plays a distinct role in its own biotic community, and carries distinct genetic potential encoded in its genes. This legacy of organic evolution is the basis and foundation of Earth's wealth. An understanding of ecology, the study of ecosystems - the interrelationships between biotic communities and their physical environments - is basic to effective conservation.

Nature's creativity is evident in the delicate interrelations among organisms within natural communities. In the few remaining old-growth forests of the Sierra Nevada and other mountainous regions as far south as San Diego, the reclusive spotted owl nests in the tops of the oldest trees. The vernal pools of the Sacramento Valley are home to several species of ephemeral flowers, specially adapted to seasonal fluctuations between standing water and aridity. Through their feeding and burrowing habits, three common rodent grazers, the common ground squirrel, Valley pocket gopher, and the California vole - all widely regarded as "pests" - can make significant contributions to both the quantity and quality of the grassland vegetation of the Central Valley. Above-ground grazing by these animals encourages seed dispersal, while burrowing promotes soil turnover and aeration. The burrows provide retreats for many kinds of invertebrate animals, and the rodents themselves are food for larger predators such as black-shouldered kites, gopher and garter snakes, and great egrets. There are intricately woven patterns of support that integrate living things into a functional community. If any one of the threads is broken, the fabric of the entire system is threatened.

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