Invasive Species Ecol 6080 Fall 2009
Conservation concern is with species that are greatly expanding their range while reducing the populations of other species or degrading the ecosystem. They may be native species expanding their range or population (white-tailed deer). Most commonly they are non-native species that are colonizing a new disjunct range ( English Sparrow, fire ants, cogongrass, etc.)…and this is our primary focus. We will refer to these species as native invasives or non-native invasives. Note that this classification differs from your textbook. Generally, the use of the term “alien species” is no longer used because it carries too much political baggage.
The vast majority of species that arrive in a new habitat do not become established. (Rule of 10) Of those that do become established, most are not considered invasive in our sense of the term (teasel) Only a small fraction of species that arrive in a new habitat become invasives. But, they can cause major environmental problems (fire ants, cogon grass, tallow trees, hydrilla, etc)
Some problems caused by invasives • competitive exclusion (cogongrass) • disrupting pollination syndromes (chinese tallow) • lowers (increases) nutrient cycling • changes ecological function (zebra mussel) • severe predation rates (mongoose) • increase disease (pathogens are invasive species) Etc etc etc
Are invasives always “bad”? What if they are N-fixers and enrich low nutrient soils? Lespedeza enriches piedmont soils What if they provide resources for other species? Chinese tallow supports pollinators. What if they “jump start” restoration? Guava in tropical pastures Important to be specific about the ecological effects Of invasive species.
European Teasel An introduced non-native, non-invasive
Teasel seeds Note: elaiosome on seed Ant dispersed !
Red Imported Fire Ant Solenopsis invicta from seasonally flooded areas in southern Brazil and Paraguay Affects native ants, seed dispersal, wildlife, Soil mixing and structure Major natural biological control is S. (Diplorhoptrum) spp. Shift from single queen to multiple queen colonies
Fire ant mounds have radiating tunnels for foraging and water. They are adapted to disturbances such as floods. Now, many mounds may have hundreds of fertile queens.
Fire ants have hydrophobic cuticle allowing them to float during floods.
Fire ants eat the eggs of endangered Florida snails
Fire ants kill the nestlings of ground and shrub nesting birds.
Fire ants have invaded the dark blue and can invade the light blue areas of Australia
Phorid flies attack and decapitate ants. Possible biological control for fire ants???
Fire ants: some general lessons for invasive species • Evolution is important and small genetic changes can have big ecological effects • Chemical controls can have unforseen consequences • Biological control has to be integrated and can’t be recalled • Source areas can subsidize populations in sink areas • Large population and high dispersal rates mean that novel habitats are frequently “sampled” • Politics and human behavior can’t be ignored
What is a common characteristic of the species that persisted after the invasion of the Brown tree snake???
The Brown Tree Snake has become increasingly diurnal. Peak activity occurs during day and night time hours of minimal electrical demand. An evolutionary shift? Possible because native birds have no experience with snakes and so snakes are efficient predators day and night. Will this change?
Euphydryas editha ovipositing on native Collinsia parviflora vs. introduced Plantago lanceolata Evolutionary shift??
Bumblebee pollination of native Stachys palustris Impatiens Stachys
Impact of invasive depends on environmental context An example with comb jellys
Meniopsis • A comb jelly (Ctenophore) native to Atlantic of North America • Arrived in Black Sea in ballast water • Later arrival in brackish Caspian Sea • Decimated zooplankton • Predator Ctenophore Benoe arrives in Black and then Caspian Sea
Meniopsis: Lessons Learned • Meniopsis disrupted ecosystem processes from bottom up • Fishing collapsed in Black Sea • Arrival of predator Benoe controlled Meniopsis and fishing returned in Black Sea • Benoe did not control Meniopsis in Caspian Sea because couldn’t tolerate lower salinity