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Invasion Ecology

Not just invasive species
Whole new subject area studying the whole process of invasion
- Exponential increase in research and citations around early 1990's


Invasion Process

Transport: Death/captivity or Successful Introduction
Establishment: Fail or Establish Successfully (Japanese Knotweed)
Spread: Remain Local (Holly/English Daisy) or spread
Impact: Low or High(Scotch broom and Daphne) (can depend on human perception such as blackberries are yummy!)


What is currently happening in the Comox Valley regarding Introduction?

Saltmarsh Cordgrass has been introduced from California and is replacing native Distichilis. Cordgrass is very aggressive.


Guam Invasion

Pre 1945: 25 species with 18 native and 7 introduced
1965: Addition of brown tree snake brought total species to 28 with 18 native and 10 introduced, major impacts on food web
1995: Introduction of brown tree snake sent food web to hell after the only predator was eliminated (preyed on each other), Total 12 species with 4 native and 8 introduced


What is the most major anthropogenic cause of invasion?

Shipping routes and abundant trade
Either purposeful or accidental
Many caused by Europe


Hub and Spoke Invasion Theory

A hub port is at the center (eg Vancouver) with primary invasion
- From there, nearby ports can be invaded (Nanaimo, Victoria)
- Other Sites for secondary invasion can occur on export routes from the hub port


When did invasions really start to exponentially accumulate in most places?

Later 1800's as shipping significantly increased. Correlation.


4 main causes of adverse impact on native fish (ie salmon)
- What may surpass all of those traditional impacts?

- Habitat Alteration (largest impact)
- Harvest (over-harvest)
- Hatcheries (Reduce genetic diversity)
- Hydro-systems (small or large)
- Non-indigenous species may exceed or equal the previous impacts


What is the U.S. ESA?

Endangered Species Act
- A real Act that is enforced and has power in the courts
- Number of invasive species correlates to more native fish added to the ESA


How are non-indigenous fish introduced?
What are the main introduced species that affect aquatic habitat?

Often purposefully for sport fishing purposes (Yummy)
- Brook Trout
- Walleye
- American Shad
- Freshwater Bass
- Channel Catfish


Main problematic species that are not fish?

- NZ Mudsnail
- Siberian Freshwater Shrimp
- Eurasion water Milfoil (Transported by boaters)
- Purple Loosestrife (Shifts hydrology and plant composition, forming a monoculture)


Reconstruction of the 1500's exploration by Sir Francis Drake

- Easily transported marine inverts
- B/c ship sat on bottom of bay at low tide (picking up sedentary bottom dwellers)
- Most of these bays now have similar species composition - So which are the native ones? Most have naturalized


Where are the majority of invasive species found and why?

Temperate regions because there are more people (and potentially more land mass)
- Temperate regions are less extreme and easier to survive (introductions drop off as you go north from temperate areas)


Transportation routes and impacts

Most import routes are unidirectional
- Pacific Asia & NA frequently exchange species
- Areas around ports and islands are hit hardest b/c of the shipping


Hawaiian impacts

- Six import routes, no exports (no Hawaiian endemics found elsewhere)
- Most Hawaiian terrestrial endemics have disappeared


Modeling Invasibility

E = I x S
E - # exotics present (proportion of non-native species established is the sites invasibility, E)
I - # species introductions
S - Survival rate (establishment) of introductions


Components of # introductions

I = Ia + Ii
Ia - Accidental release (bilge waters)
Ii - Intentional release


Components of Survival rate of introductions

S = SvShScSm
S is establishment after accounting for:
Sv - Competition
Sh - Herbivory
Sc - Chance events
Sm - Maladaption


I vs. S on Van Isle

Sometimes the # of introductions is enough to support the Establishment even with significant mechanisms such as competition, disturbance, life history, and climate


Global patterns of Plant invasions

- Non-native and Native species richness are weakly positively correlated (regardless of whether it is a mainland or island)
- The plot is a list of species # and doesn't account for abundance
- Abundance is more important than list
- There is a tipping point where natives become outcompeted (abundance issue)



Set of non-native individuals released into a new environment
- Can be seeds or clones


What are the 3 components of propagule pressure?

- # of individuals released per event
- # of release events
- Health of individuals released


Propagule pressure: Health of individuals released

Ballast water Plankton
- Phytoplankton and zooplankton can survive for weeks on board a ship, but will die over time


Propagule pressure: # of individuals released per event

More released = higher likelihood of establishment
- Ex. The release of insect in NZ to control Broom, more intros = larger population establishment


Propagule pressure: # of release events

More frequent releases = greater proportion of establishments


Propagule pressure and biological traits of birds introduced worldwide

Bird Traits:
- Large body mass*
- High annual fecundity*
- Large geographic range*
- Diet generalist*
- Migratory tendency
- Sexual dicromatism
* indicates statistically significant correlation to intro success which may reflect human bias in choice release
- Correlated success of an intro to propagule size


Introductions to NZ

10th century: Polynesians brought 2 mammals (Maori Dog, Pacific Rat)
1769: Captain Cook brings goats
1792: Sealers and Whalers exhaust stocks over 20 year period. Introduced Norway Rat & Black Rat & mice
1840s: Large influx of European settlers brought the remaining terrestrial vertebrates (ex. Deer)
1851 - 1910: 26 recorded new introductions never found before


Rodent introductions to NZ

Each of the introduced rat species (Pacific, Norway, Black) has unique trophic niche and food preference
- The 3 species covered all and devastated bird populations for seabirds, ground-nesters and even tree-nesters


Deer introductions to NZ

Started in 1851 for sport hunting purposes
- No natural predator
- Forests evolved w/o deer, so introduction was devastating
- Deer population rapidly expanded exponentially
- Destruction of forests led to initiation of erosion problems


Why are islands more invasible?

Access to ports, smaller space to invade, More coastline, and more opportunities due to shipping


Disturbance Classifications

- Natural vs. Anthropogenic
eg. Wildfire vs Prescribed burn
- Biotic vs. Abiotic
eg. Prairie dog vs. deep plowed fields
- Endogenous vs. Exogenous
eg. Succession vs. Tree planting
ie. Occurs by itself vs. intentional


Definition of Disturbance

Any event in time that disrupts ecosystem community or population structure and changes resources, substrate availability or the physical environment


Range of events and processes

- Intensity (magnitude and severity
- Frequency (mean # per unit time
- Duration (temporal extent, how long does it last)
- Predictability (regularity of the occurrence)
- Distribution (size & spatial extent)
- Synergism (does a disturbance precipitate or exacerbate further disturbances)


Probability of community invasion

Within community resistance (Abiotic- Temp, water, light, disturbance level & Biotic- Species richness, competition, predation)
Propagule pressure (invasive supply eg. seeds)


Probability of community invasions
- Effect of increased propagule supply

- Probability of invasion increases w/ more propagule pressure (it only took 9 seeds for Broom to establish here)
- Lose the biotic and abiotic resistance


What happens post-invasion regarding probability of community invasion?

- Previous invasion can facilitate conditions necessary for future arrivals
- Eg. Broom facilitated Daphne
- Community resistance decreases after invasion making the community more susceptible
- Once the resistance decreases enough and probability increases the community is destroyed and can no longer fight back
- Even if introductions stop the community is so damaged it is significantly more susceptible


Allee effect

For smaller populations, the reproduction and survival rates of individuals increases with population density, although this effect usually disappears as increased intraspecific competition occurs


Theory of fluctuating resource availability

- Uptake/supply isocline (resistance to invasion isocline)(uptake=supply)
- Invasibility is highest w/ increase supply and under the isocline (less uptake)
- Pulse the system with increased nutrients, and natives will not respond in uptake so invasives move in to take advantage of nutrients


Resource uptake vs. supply plot

Gross resource supply vs. Resource uptake
- Pulse: Increase supply, no change to uptake = Run-off/eutrophication
- Decline: No change in supply w/ decreased uptake = Overgrazing/herbivory
- Both: Increase nutrients, decrease uptake = Agricultural problem from both overgrazing & over-fertilizing (biggest disturbance)


Theory of fluctuating resource availability cont.

- Community susceptibility to invasion increases as resource availability increases (the difference btwn gross resource supply and resource uptake)
- ie Competition for available resources is primary driver of vegetative succession
- Resource availability can increase due to a pulse in resource supply, a decline in resource uptake, or both may occur (highest disturbance)
- Resource availability increases invasability


Watershed disturbance example

- Many variables
- More disturbed the watershed was increased the # of non-natives
- Urban development, agriculture were the most important disturbance forces and correlated together