As humans traverse the globe in planes, trains, and automobiles they bring with them non-native plants and animals. Both intentional and unintentional introductions can spread uncontrollably throughout a new environment and fundamentally change an ecosystem. Although these changes are not always well understood, we do know that invasive species are the:
- Leading cause of avian extinctions
- Second leading cause of fish extinctions
- Second leading cause of mammalian extinctions
Migratory connectivity information of both native and invasive species is needed to facilitate effective eradication, protect habitat, and measure population level impacts.
- Knowing the movement and connectivity of species like the aggressive Asian carp can give us insights into how to control and minimize their harmful impacts
- Research on migratory patterns of seabirds has informed our understanding of how invasive brine shrimp disperse
Invasive plants such as kudzu and purple loosestrife dramatically alter the properties and functions of the landscapes they invade. We do not have a complete understanding of the stresses imposed by altered ecosystems or the associated carry-over effects.
- Birds that eat invasive plants during migration stop-over along the Gulf Coast of Mexico often have subpar nutrition and energy reserve. This reduces their ability to complete migration and fly thousands of miles over land and water.
- Tamarisks in the southwest outcompete and replace native willow trees. Because they take up more water than native plants, they have devastatingly drying effects on riparian ecosystems. The Federally protected southwestern willow flycatchers historically nested in willows but now use tamarisks. This makes tamarisk removal difficult.
- Nutria destroy wetlands that provide critical migratory, breeding, and wintering habitat for birds
- Mute swans devour grasses and aquatic vegetation in delicate marsh ecosystems
- Red deer and rabbits overgraze meadows and forests
- The 60-120 million cats in the United States are estimated to kill between ½ to one billon birds a year and are a serious threat to migratory species. At stop-over locations, migratory birds are hyper-occupied with refueling and are easy abundant prey for feral cats.
- In tropical regions, introduced black rats hunt birds while they roost, forcing them to alter normal roosting behavior.
- In Yellowstone National Park, native cutthroat trout are devoured by introduced lake trout as they migrate through mountain lakes.
Introduced competitors like the European starling are a serious threat to breeding birds. Starlings evict other cavity nesters and kill their young. Purple martins can be heavily impacted, with evicted birds being forced to re-nest or risk reproductive failure for the year. Migratory connectivity gives insight into the carry-over effects of attempting a second nest.
An invasive parasitic worm (carried by the invasive green crab) infects and kills eider ducks. The invasive fungus responsible for white-nose syndrome in bats is transferred through spores and affects bats during winter hibernation. We need more information to fully understand the long-term effects of invasive species throughout the annual cycle.
Spread of invasive species
The spread of many invasive species is facilitated by human movements and the biology of the introduced organism. However, native migratory animals also facilitate invasion.
- Invasive plants are ingestion by migratory species and transported along migratory corridors
- Invasive brine shrimp follows migration routes of seabirds
- Knowing migratory connectivity and migratory routes, we are able to determine patterns of migration-aided colonization
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