Invasive Species

What are invasive species? Invasive species, alien species, exotic pests, bio- pollution, non-indigenous species, or invasive alien species, are common names that categorize non-native animals, microbes, diseases, or plants that are pests.  These pests are not native in areas in which they cause problems and they are considered "invasive" because they invade and establish populations in new areas and the resulting uncontrolled population growth and spread causes economic or environmental problems.

Lake Tahoe Invasive species timeline

Where Do Invasive Species Come From? Invasive species are often native to a country or area different to that in which they have invaded and are now causing problems. On average, California acquires around six invasive species per year, this is a rate of one new species every 60 days. Hawaii and Florida acquire new species at a rate of around 15 per year.

Examples An example of invasive species that are not native to California are the persea mite and avocado thrips that attack avocados. Persea mite and avocado thrips are native to Mexico, one of the countries where avocados evolved. These two pests were accidentally introduced into California and because there are lots of commercially-grown and backyard avocados for them to feed and reproduce on, and California has such an agreeable climate where avocados are grown, they readily established and caused problems.

Examples Another example of a native American species causing problems in California are north American bullfrogs. These amphibians were likely introduced into California in the late 1890's where they are now threatening native California frog and fish species because of competition for resources

Why are invasive species a problem? Invasive species cause a wide diversity of economic and environmental problems which almost always arise fromuncontrolled population growth and spread in the area which has been invaded. Economic problems arise from the costs required to control invasive species, to reduce their rate of spread, or the need to inspect agricultural products that are being exported that may accidentally move the invasive pest to a new area.

problems Environmental problems caused by invasive species can be the extinction of native species. Invasive weeds are often responsible for the drastic modification of native ecosystems. For example, invasive weeds can choke out native plants thereby removing food and shelter for native animals. In California, there are a large number of invasive weeds which include thistles, giant cane, salt cedar trees, seaweeds, algae, floating and submerged freshwater weeds, and non-native mustards.

What economic impact do invasive species have on California? It has been estimated that in California alone, invasive pests cost at least $3 billion a year! A recent analysis by the California Invasive Plant Council (Spring 2009) indicates that weeds alone cost California at least $82 million per year. Some estimates suggest that invasive species cost the USA $138 billion per year, and that 42% of endangered US species have reached this status because of invasive species. Globally, 80% of endangered species are threatened primarily by invasive species, only habitat destruction causes greater endangerment of native species

How do invasive species move from place to place? Invasive species reach new areas outside of their home range in one of two ways: (1) self introduction on their own, or (2) with human assistance that may be deliberate or accidental.

Plane Flights in 24 hours http://www.youtube.com/watch?feature=player_embe dded&v=o4g930pm8Ms

How they move Humans have deliberately moved an incredible number of plant and animal species around the globe either for food, as part of international commerce (e.g., the pet and nursery trade), or for sport (e.g., hunting and fishing). Often, invasive species are moved accidentally by humans. This can occur through hitch-hiking unnoticed on plants that are being moved (e.g., tiny insects or diseases on leaves or in potting), in ballast water that is used to stabilize large transport ships, or inside other animals (e.g., diseases that kill birds have been spread by the commercial trade in exotic pet birds.)

How do invasive species establish? In relative terms very few non-native species that are introduced into a new area become invasive species. There is a generalization, referred to as the "Tens Rule," that suggests that of non-native species that enter a new ecosystem about 10% of these will survive, and of those survivors a further 10% (or just 1% of the original number) will become invasive pests. At least four different factors can affect the successful invasion, establishment, and spread of invasive species.

factors 1.Propagule pressure: This refers to the number and frequency of introductions of an organism (or propagules) into a new area. 2.Minimum viable population size: Should an introduction result in the establishment of a population of a new organism in a new area, a minimum number of individuals are needed to sustain the population and to help it grow. 3.Lag period: Often when a new species establishes in a new area its population is highly localized and the numbers of individuals is not particularly high. This situation may persist for a long time, sometimes years, before exponential growth is observed. Then, for reasons often not well understood, the lag or "incubation" period ends, and the population explodes in size and the area occupied. 4.Climate and environment: An introduced species is only going to survive and do well in an area in which the climate is suitable and if there are sufficient resources available for growth and reproduction.

Why do some species become invasive but other species do not? Not all non-native species become invasive pests when they are introduced into a new area. Why is this? Answers to this question are varied, and often unique to certain situations. Some species may become invasive because they lack control by natural enemies The way the invader breeds may enable it to establish easily and build up numbers quickly. Species that have wide tolerances for a variety of different climates or can utilize many different types of resources in the environment are more likely to become invasive.

How can invasive species be managed and controlled? Invasive species management and control falls into one of two broad categories: (1) Proactive management: In this approach potentially invasive species are not allowed to enter a new area. (2) Reactive management: In this situation the invasive species has successfully invaded and high populations are now spread over large areas making exclusion and eradication impossible. Chemical and biological approaches are typically employed.

What can you do about invasive species? We can all take some responsibility for reducing the problems caused by invasive species. Some very simple steps include careful selection of garden plants, use species that are not likely to be invasive. The release unwanted pets into the wild has resulted in the establishment of populations that have become invasive. Moving soil and firewood from one area to another can help invasive species move. Boats and boat trailers can move invasive water weeds, snails, and mussels from infested areas into clean uninfested waterways. Carefully cleaning boating equipment can help greatly in preventing the accidental spread of noxious aquatic organisms. When traveling notify customs officials at ports of entry if you are bringing in food, fruit, plants, wood and animal products, fishing, hiking, and camping equipment. These things can be quickly examined by experts and determined if they pose a risk or not.

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