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What is Biodiversity?

Biodiversity, or “biological diversity,” refers to the variety of plants, animals and other living things in a particular area or region. It includes genetic variety, species diversity, and variability in communities, ecosystems, and landscapes.

San Diego County is very rich in biodiversity. In fact, San Diego has more biodiversity than any other county in North America and, along with the rest of California, is among the top 10 biodiversity regions on earth. The mild, Mediterranean climate (hot dry summers and cool, wet winters) and varied landforms create a number of distinct habitats, including: beaches, salt marshes and lagoons, coastal sage scrub, grasslands, chaparral, oak woodlands, streamsides, mixed conifer forests, freshwater marshes and meadows, and desert.

Scientists describe our region as a conservation “hotspot” because of the vast numbers and variety of threatened and endangered species that reside here. Many of these species are endemic. “Endemic” means that a species is native to a specific geographical area, such as San Diego County, and found nowhere else in the world.

Some of the rare, threatened, and endangered species in San Diego County are listed below.

Rare, Threatend and Endangered San Diego Species


Orcutt's hazardia

San Diego thornmint San Diego ambrosia
  Brand's phacelia Peirson's milk-vetch Del Mar mazanita
  Tecate Cypress Encinitas baccharis coastal dunes milk-vetch
  Torrey Pine thread-leaved brodiaea Nevin's barberry
  Cuyamaca meadow foam Otay tarplant Orcutt's spineflower
  Cuyamaca larkspur spreading navarretia salt marsh bird's beak                    
  Cuyamaca downingia   San Diego button celery
  Parry’s tetracoccus   Mexican flannelbush
  Dehesa beargrass   willowy monardella                    
  Little mousetail   California Orcutt grass
  Otay lotus   San Bernardino bluegrass
  Otay manzanita   San Diego mesa mint 
  Otay ceanothus   Otay mesamint
  Gander’s pitcher sage   Gambel's watercress
  Cedros island oak    


Hermes copper butterfly   San Diego fairy shrimp
  Thorne’s hairstreak butterfly   Quino checkerspot butterfly
  Harbison dun skipper butterfly   Laguna Mountains skipper butterfly
      Riverside fairy shrimp
    desert pupfish
      tidewater goby
      unarmored threespine stickleback
    Southern steelhead     
    arroyo toad
      California red-legged frog
  none none
mountain plover Bald eagle Least Bell's vireo
  yellow-billed cuckoo California gnatcatcher Southwestern willow flycatcher
  Belding's savannah sparrow Western snowy plover brown pelican
      short-tailed albatross
      light-footed clapper rail
      California least tern
      peregrine falcon
  Southern sea otter Stephens' kangaroo rat

Peninsular bighorn sheep

      Pacific pocketmouse


According to biologists, human activities are the primary cause of ongoing species decline and extinctions. Because of the ever increasing size of the human population and its exponential rate of resource consumption, the environmental impacts of humans are quite significant and, in some cases, irreversible.

Human activities contribute directly to species loss through habitat degradation and destruction, pollution, introduction of non-native species into natural habitats, and overexploitation of wild plant and animal species. For exmple, urbanization and related habitat encroachment, expansion of large-scale agriculture, road construction, livestock grazing, logging, strip mining, and oil extraction have reduced California’s wetlands, riparian forests, and coastal sage scrublands to 10 percent of their original habitat area, and native grasslands and vernal pool habitats to 1 percent of their orginal habitat areas.  Human pollution, particularly, has now been linked to significant physical and biotic changes at all levels, from local ecosystems to the global climate change.  California is one of the four most ecologically degraded states in the United States and contains some of the country's most endangered ecosystems. More of California's plant and animals species (250) are protected under the U.S. Endangered Species Act than in any other state, and 180 more are proposed for listing.

Our everyday actions can have an impact – positive or negative – on the health of San Diego’s native habitats and the plants and animals found there.


Photos by Barbara Barnes

Hiking Vulcan Mountain near Julian                                  Clark Valley in Anza-Borrego State Park


Shore Gull near Encinitas                   Photo by Barbara Barnes


Why is Biodiversity Important?

The value of protecting and maintaining the biodiversity of our region is ecologic, economic, and esthetic.

Species of all types, no matter how small, play an important role in an ecosystem (a community of plants, animals, and microorganisms that are linked by energy and nutrient flows and that interact with each other and with the physical environment). It is this combination of species and the roles that they each play that enables an ecosystem to recover from a variety of disturbances, including fire. Some of the benefits of a healthy and vital ecosystem include:

•recycling and purification of water and air through the regional watershed system
•mitigation of climatic and weather extremes (e.g., floods and drought, winds

  and waves, fire)
•breakdown and detoxification of pollution
•cycling of nutrients
•re-generation of fertile soils
•pollination of crops and wild plants
•control of agricultural pests by natural predators and parasites
•and, the continual renewal of biological diversity that supports all of the above


 © D.L Green (2001)                                                              Photo By Douglas Aguilard

       Bee pollinating Horesmint                                      Santa Margarita River near Fallbrook

In short, biodiversity helps sustain the outstanding and unique environment in which we live. It also enables us to obtain direct benefits, such as, tangible materials (wood, paper, rubber, limestone, coral), genetic resources (used in agriculture and biotechnology), chemical discoveries (incorporated into medicines, chemical engineering), and food (local citrus, strawberries and other fruits, avocados, vegetables, eggs, honey, poultry and beef)

Clementine tangerines

The degree to which medicinal knowledge is based in biological diversity is particularly striking. For example, of the top 99 prescribed compounds (found in the top 150 prescription drugs), 53% have their origins in species of animals, plants, fungi, or bacteria. When estimates of discovery rates of medicinally active chemicals are combined with estimated extinction rates of species, scientists conclude that about three potential new medicines are being lost each year due to losses of biological diversity.


Julian apples                                                                                           Photo by Barbara Barnes


Finally, the variety in the natural world—plants, animals, terrain, habitats--is beautiful and serves as a source of wonderment and great enjoyment for many people.

      Hermes Copper butterfly (rare - found only in San Diego County )             Photo by Douglas Aguillard


What Can We Do To Conserve Biodiversity?

Learn about your entire community. For example, where does your water come from? ... How does food get to your table? … Where is your clothing made? Explore the natural places around you, such as, San Diego's wilderness areas. Take note of the diversity of the plants and animals where you live. By understanding and appreciating how your daily choices affect San Diego’s remarkable biodiversity, you can join with others in helping conserve it.

              Mission Trails Regional Park                                                                        Photo by Scott Streit

Sources: Adapted from

American Museum of Natural History, Center for Biodiversity and Conservation. (2005). Biodiversity. Retrieved January 27, 2005 from

California Department of Fish and Game. (2005). California's plants and animals. Retrieved January 26, 2005 from

Conservation International, Center for Applied Biodiversity Science. (2005). Biodiversity hotspots. Retrieved January 25, 2005 from

Reiser, C.H. (2005). Rare plants of San Diego County. Retrived January 25, 2005 from

San Diego Zoo. (2005). San Diego's habitats (PDF). Retrieved Janaury 21, 2005 from

World Wildlife Fund. (2005). Biodiversity 911 on the web; Biodiversity basics. Retrieved Jnauary 27, 2005 from

Photo Credits:

Aguillard, D. (2005). The birds, butterflies, & dragonflies. Retrieved January 29, 2005 from

Barnes B.E. (2004). Assorted photographs from San Diego County, 2004. WhiteSage

Green, D.L. (2005). Pollination homepage; bee pollinating horsemint (photo). Retrieved January 29, 2005 from

Streit, S. (2005). Bird friends of San Diego County. Retrieved January 29, 2005 from

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Copyright 2004 San Diego State University Foundation