Factors Determining the Success of an Exotic Species- not all invasive species succeed in becoming established- why not

1. Factors Determining the Success of an Exotic Species- not all invasive species succeed in becoming established- why not? Remember the rule of 10s from the previous PowerPoint lecture Leidy’s Comb Jelly- introduced into the Black Sea from the East Coast of North America in the ballast water of trans-oceanic cargo ships

2. 1. There must be available and suitable habitat which includes completely compatible ecological niches. House or English Sparrow- introduced into the United States from the U.K. This species thrives in habitats altered by humans, including almost all urban areas. It is one of the three most common bird species living in the Morgantown area, the other two are also introduced exotic species.

3. 2. Adequacy of the “introduction unit”, such units are referred to as propagules. a. Health- weak or diseased individuals have little chance of success Red squirrel that perished due to parapox virus, less than two weeks after contracting the disease

4. b. Simple numbers As few as a single individual may serve as an effective propagule. For example, based on genetic evidence it is believed that the Chinese Mitten Crab was established into the San Francisco Bay area from a single individual egg attached to a boat which arrived from overseas. However, it took multiple introductions of many individuals to generate a successful population of European Starlings. This species has spread throughout the U. S. several Provinces of Canada and States in Mexico.

5. c. Genetic make up of the propagule(Note: for a brief overview of the study of genetics as it relates to conservation/invasion issues, please take a look at the accompanying PowerPoint presentation on Genetic Diversity.) • Generally, it is difficult for populations with low numbers to survive in a new area or recover from severe reduction in numbers in their existing location. This is known as the “Small Population Paradigm”. • Small populations suffer from a variety of adverse factors including; • a. Increased risk to disease • Inbreeding depression • Founder effect • Difficulty in finding mates • Genetic drift • Random, catastrophic events such as hurricanes or volcanic eruptions • Unfamiliarity with local habitats and their associated predators and potential food resources • A unique suite of parasites and diseases

6. 3. Behavior- including social aspects- for example, some species have highly evolved behavioral characters that make survival alone or in low numbers extremely difficult. Examine the behavioral ecology of the gray wolf, which was re-introduced into the Greater Yellowstone Ecosystem. 1.) they hunt large prey items and need groups, including associated group strategies, to do so. 2.) their mating system requires the presence of multiple individuals and a hierarchical/matriarchal social structure.

7. The Darling Effect- named in honor of Frank Fraser Darling, this ecological phenomenon centers on the group behavior of animal populations. He specifically worked on sea birds but the theory has been expanded to many species and may be the fundamental reason that declining populations of Passenger Pigeons and Great Auks went extinct, even after it was discovered that they needed protection. Groups of animals congregate and show behavior based on the presence of other individuals. For example, sea birds nesting in a colony have a decided advantage if the majority of the offspring hatch and leave the nest at the same time, thus overwhelming potential predators. In essence they produce more young than the predators can consume. Any behavior that aids in synchronizing the group would have a selective advantage. A nesting colony of Gannets on the coast of Scotland

8. 4. Degree of escape from competitors- some invaders seem to be resistant to the effects of interspecific (between species) competition for resources. Or, in fact, they may be better competitors for resources than “native” species. A good example of this would be the Japanese White-eye that has successfully invaded the Hawaiian Island chain, at the expense of local species. Japanese White-eye foraging on an Ohia, a plant species formerly used by the extinct Bishop’s ‘O’o Bishop’s ‘O’o Last seenin 1915