Population Extirpation

Local extinction occurs when a plant or animal once found in an area ceases to exist in that area but is still found elsewhere. This local extinction is referred to as extirpation.

Local extinctions often are caused by changes in a local ecology. For instance, when natural lands are developed into a housing development, gold course, or shopping area the local suite of species is often pushed out to make way for development. For proper building, changes must be made to level out the ground and sometimes amend the type of soil found there. Once a building is erected, parking areas and roads must be created and landscaping is often planted that does not reflect the plants that once existed in that area.

Larger scale versions of ecology change have occurred when humans have moved into an area en masse and the area has become urbanized. Cities and large towns take up vast amounts of space and can drastically reduce open areas for plants and animals. When ecology changes, local populations of plants and animals may no longer have conditions in which they will thrive which causes these species to become extinct in that local.

Extirpation of species, especially butterflies is very common in urban and developed areas. Butterflies are specialists and often have larvae that can eat only one or a very few species of host plant. When their host plant is no longer available, there is way that a butterfly population can sustain itself. Butterflies without a host plant will either travel in search of host plants elsewhere or will die without creating another generation.

Additional challenges may occur if habitats are fractured and butterflies cannot easily pass from one sustainable habitat to another, if butterflies are collected in large numbers for display by collectors or is widespread use of pesticides further reduces a population. There are many reasons why a species can become extirpated from a local area and once they are gone it becomes exceptionally difficult to make that area suitable for a species again. Even if new habitat is created, repopulating an area may be costly, difficult or even impossible.

San Francisco

In San Francisco, the native sand dune habitats were home to several unique species and sub-species of butterflies. First described in 1852, the Xerces Blue (Glaucopsyche xerces) population dwindled as the city of San Francisco spread and overtook the sand dunes. This species first disappeared from the San Francisco peninsula and then was last recorded in the wild in 1941.

Sthenele Satyr (Cercyonis sthenele sthenele) disappeared from the city’s westerly dunes by 1880 and the two small populations of Pheres Blue butterflies (Icaricia icarioides pheres) had disappeared from the San Francisco peninsula by 1950. The Myrtle's Silverspot (Speyeria zerene myrtleae), Quino Checkerspot (Euphydryas editha quino) and Bay Checkerspot (Euphydryas editha bayensis) are now mostly or entirely gone from the area.

Several species in the San Francisco peninsula are currently considered endangered including the Mission Blue (Aricia icarioides missionensis) and San Bruno Elfin butterfly (Callophrys mossii bayensis).

Florida

The peninsula of Florida and the Florida Keys contain a variety of unique habitats that contain vast numbers of species. Agriculture and development have shrunk available habitats for our native butterflies and have also reduced availability of host plants for these species. Pine Rockland and sand dune habitats continue to dwindle as land with higher elevations and beach front property is prized by development.

Due to habitat loss and scarcity of host plants, population of Miami Blue Butterfly (Cyclargus thomasi bethunebakeri) plummeted in recent years. In peninsular Florida and the Florida Keys populations decreased in size and range and many populations died out. Despite attempts at captive breeding and reintroduction to the wild, populations of the Miami Blue have not re-established in the wild. Now extirpated in most of it’s range, small populations of the Miami Blue can be found in the Key West National Wildlife Refuge.

The Zestos Skipper (Epargyteus zestos) is now considered to be entirely extirpated from the Florida Keys. Remaining populations of this species can now be found only in the West Indies. Many other species of imperiled Florida butterflies face extirpation from the Florida Peninsula and even the Florida Keys.

As populations of rare Florida butterflies continue to extirpate from portions of their former range, the overall numbers of their populations dwindle. Small numbers of live adults creates smaller pools of available breeding partners and populations become even more unstable. For each creature a Minimum Viable Population is needed to ensure survival of the species. When a population drops below this minimum only human intervention in the form of captive breeding and reintroduction programs are likely to keep a species from becoming globally extinct.

Learn more about current efforts in education, research and species recovery by the Butterfly Conservation Initiative.

Read more about research in Florida at the Florida Butterfly Monitoring Network website.