Invasive Species relocation of organisms across geographical boundaries occurs naturally by various means. Since humans began exploring the globe, however, the rate of new species being introduced into regions has greatly increased. humans have dispersed species on purpose; – plants transported from Europe to North America for agricultural and ornamental purposes Others were transported accidentally by ship, train, airplane - even on the shoes of hikers.

Local Examples Asian shore crab, Hemigrapsus sanguineus Pathway: introduced from Asia to eastern seaboard most likely by ballast water; reported in Long Island Sound in 1993 Current Distribution: Maine to North Carolina; prefers rocky cobble Impact: dominant rocky intertidal crab; consumes juvenile mussels and oysters, green crabs, snails, polychaetes, algae, hydroids, barnacles

Green crab, Carcinus maenas Omnivore - consumes barnacles, clams, hermit crabs, worms, algae, organic debris Pathway: introduced by end of 18th century from Europe, probably via ship hulls; reported in LIS in Current Distribution: Gulf of St. Lawrence to Delaware; lives on rocky shores, quiet backwaters, marshes, estuaries, brackish waters or coastal waters Impact: voracious predator and scavenger; consumes juvenile shellfish (may have caused decline of softshell clam industry in Maine and even Long Island Sound); competes with native crabs.

Mute swan, Cygnus olor Pathway: Introduced from Europe as decorative waterfowl in late 1800s or early 1900s Current Distribution: southern Ontario to North Carolina or Florida; reported in LIS by 1920s Impact: using long necks, the swans graze on vegetation by ripping important submerged aquatic vegetation such as eelgrass out by the roots, damaging marsh and shallow water habitats; overpopulated, displacing native swan

Some introduced species are not able to survive in their new habitat. Others may find optimal conditions for growing, reproducing, and adapting to the new environment, and their populations soar. – lack of predators – ability to outcompete other species (for ex, by surviving and growing on fewer resources) – Alter ecosystem function and services Invasive Species

Terminology "invasive", "exotic", "introduced“, “nonnative”, “alien” Introduced species that have profound effects on their new ecosystems have been termed invasive species. These effects include outcompeting native species, sometimes causing their extinction, and altering ecosystem functioning upon which we depend!

Growth of invaders in a new range Phases of proliferation and spread Lag phase makes early detection difficult Often no lag phase Lag phase Log phase

Very hard to predict Difficult to identify common characteristics shared among invasive species Difficult to ID characteristics among invaded communities Above problems could be partly solved if we knew more about EARLY STAGES of invasions Control sometimes feasible, often costly Are often hard/impossible to eradicate Invasive Species –Why such a problem?

Community Vulnerability to Invasion Current hypotheses: – Vacant niches – Escape from biotic constraints – Community species richness – Disturbance before or upon immigration

Zebra Mussels Dressena polymorpha widely known example of an aquatic invader in the U.S. native to southern Russia, introduced to the Great Lakes in 1985 or 1986 via ballast water now exist in many aquatic systems in the eastern US and expected to invade freshwaters throughout the nation in about 20 years Progression: USGS linkUSGS link

Effects of Zebra Mussels filter feeds unusually large amounts of phytoplankton outcompetes other filter feeders (esp. zooplankton, an important food for fish) can reach densities of up to 700,000 individuals/m2. smothers clams, native mussels and snails, clogs water intake and exit pipes for facilities such as electric generating plants. annual damage for U.S. utilities at about $100 million

Why are zebra mussels succesful? Lack of predators and parasites Availability of space; attach to hard substrates with byssal threads (pipes, boat hulls and motors, trailers, docks, anchors, and rocky beaches)

Why are zebra mussels succesful? free-swimming veliger larva can disperse widely Females are also extremely fecund (huge release of eggs; spawning events several times a year). Have a relatively long lifespan for an invertebrate (2- 5 y) early sexual maturity (can be within 1 year) eggs and sperm viable for several or more hours dispersal of all life stages tolerance of some salinity

Figure 2A. Changes in populations of animals that are thought to depend on phytoplankton for food in response to the arrival of zebra mussels in the Hudson River. (a) Macroplankton are microscopic floating animals that are visible to the eye; (b) Unionids are clams (c) Shaeriids are clams. The dashed line shows the point at which the zebra mussel became abundant. Data are yearly averages at one station during June-August; Strayer, et al. 1999

Figure 2B. Changes in concentrations of edible and inedible particles in water in response to the arrival of zebra mussels in the Hudson River. (a) phytoplankton; measurement is concentration of the pigment chlorophyll a (b) biomass of microscopic zooplankton (tiny floating animals (c) solids suspended in the water, units are milligrams per liter. The dashed line show the point at which the zebra mussel became abundant. Data are yearly averages at one station during June-August. Unusually heavy summer rains happened in 1996 (Strayer etal. 1999)

Figure 2C. Key variables in the Hudson River ecosystem. (a) freshwater discharge; units are cubic meters per second. (b) water temperature (c) estimated filtration rate of zebra mussels (grey bars) and all other filter feeding animals (white bars) averaged for the river. The dashed line shows the point at which the zebra mussel became abundant. Data are yearly averages at one station during June-August. (Strayer et al. 1999)