Biological Invasions

Definitions from the National Invasive Species Council: Native species = a species that, other than as a result of an introduction, historically occurred or currently occurs in an ecosystem. Syn: Indigenous Alien species = any species …that is not native to an ecosystem. Syn: Non-native, non-indigenous, exotic, immigrants, introduced Invasive species = an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.

Some characteristics of invaders High rate of reproduction “pioneer species” Short generation time Long-lived High dispersal rates Broad native range Abundant in native range Tolerant of a wide range of conditions Generalist BUT … even though we know a lot about invasive species, we are still unable to predict which non-native species will become invasive.

Why are people interested in invasive species? The National Invasive Species Council (NISC) was formed in 1999 “to prevent the introduction of invasive species and provide for their control and to minimize the economic, ecological, and human health impacts that invasive species cause”

Economic costs Estimates of total costs on industry and agriculture range from $27 to 137 billion per year. One estimate: Zebra mussels caused losses of $60.2 million dollars to industries in the Great Lakes between 1988 and (Approximately $800, 000/year for each power plant.)

Impact on native ecosystems Invasive species impact 30-50% of the species currently listed as Threatened or Endangered under the U.S Federal Endangered Species Act. (Second only to habitat destruction.)

Impact on human health

West Nile Virus in the United States as of September 12, 2003

(1)Primary Productivity (3) Decomposition (4) Nutrient and water cycles (5)Disturbances change the flow of matter and energy through ecosystems Sunlight (2) Populations of organisms Provides energy for Are linked with Create organic matter that is transformed by Is carried out by Creates organic matter that is transformed by Is carried out by Are used for Are used by

Impact on productivity and energy flow Non-native herbivores, like gypsy moth, directly affect the flow of energy captured by plants from the sun. Non-native earthworms can dramatically increase decomposition in soils.

Sea Lampreys are native to the Atlantic Ocean, but now impact fish in the Great Lakes. Purple loosestrife becomes dominant in wet areas, directly impacting other plant populations. Impacts on populations and food webs

Impact on nutrient and water cycles Invasive nitrogen fixers (like fayatree in Hawaii) increase nitrogen in soils. The high evapotranspiration rate of saltcedar draws down the local water table and can slow the flow of rivers and streams.

Impact on disturbances Forest Savanna or grassland FIRE land clearing introduction of non-native grasses grasses are favored by fire increased flammability microclimate change Disturbances often promote invasion, but invaders can change how frequently a disturbance occurs.

Methods of controlling invasive species 1) Chemical control Ex., using pesticides 2) Mechanical control Ex., physically removing the invasive species 3) Biological control Ex., Introducing a natural enemy 4) Ecological control Ex., Manipulating environmental factors

High Cost Low Low Impact of invader High Do nothing Do nothing?Control ?? How to decide whether to control an invasive species?

What more is needed? (From Mack et al. 2000) 1)Greater understanding of Movement of currently invasive species. Impact of invasive species on ecosystems. The likelihood that introduced species will become invasive. 2)Experiments that allow us to understand #1. 3)Better economic estimates of the true costs of invasions. 4)Greater public and governmental awareness of the effects of invasive species.