Invasion Ecology

Question 1

Invasion Process

Answer 1

-Europeans hoped to make NA more like home, and introduced many new species

Introduce species then compete for what’s there and then others suffer in ecosystem

(Invasion in Hawaii correlate to spikes around post economic booms.. People brought lots of species over and introduced exotic plants or animals)

-Relationship between US imports and the accuulation of Non-Native species. Fitted line (models) for mollusks and plant pathogens show a sharp decreased

Even when not intending to bring in new spp - they may come in with imports/exports (with ships etc).. Ports are first to be hit with invasive spp (secondary invasion in smaller ports)

-Spp biodiversity is cut in half (less species) & (Less natives, leaves room for more invasive (both in population and species type)

Question 2

Salmon fishery

Answer 2

Many non-indigenous spp (fish, plants, invertabrates etc)

Four main causes of adverse impact on fish:

1. Habitat alteration
2. Harvest
3. Hatcheries (homogenize gene pool, enhancement in favour of salmon)
4. Hydro-systems
5. Invasive spp (has been recently acknowledged to be a part of this list)

-Results indicate that the effects of these non-indigenous spp on salmon could require proper management of the invasives in order for salmon recovery

Question 3

Correlation between invasive and native spp

Answer 3

The more invasives, the more likely you’ll have a longer list of endangered species

Question 4

Invasive plants and Salmon..

Answer 4

Invasive plants can drop the water table - and fill in the entire channel to make a terrestrial ecosystem - blocking salmon from spawning (ex purple loosestrife)

Also Eurasian water milfoil provides habitat for predatory fish that may feed on salmon young - also enroaches salmon spawning region

Question 5

Biodiversity questions

Answer 5

What is native? Ships may have been introducing new species for a long time

Question 6

Where is majority of introduced species?

Answer 6

Temperate regions

Currently most common between NA and Asia.. Previously Europe

Question 7

Invasability

Answer 7

E = I X S

E = number of exotics
I = number of species introductions
S = survival rate (establishment) of introduction

*The proportion of non-native species established in a given location is the site’s invasibility (E)

*Islands are thought to be more invasible than mainlands
e.g., Vancouver Island (VI) versus the mainland

*The higher number of invasive species on VI may be due to the number of species introductions (I) (many by hudson bay company) and not related to mechanisms related to the establishment stage (e.g., disturbance, competition, life history, climate)

Question 8

Global Patterns of Plant Invasion

Answer 8

*Non-native and native species richness are positively correlated

*This positive correlation occurs regardless of whether the area is an island or mainland

Question 9

Propagules

Answer 9

The set of non-native individuals released in the new environment are called propagules

Question 10

Propagule Pressure

Answer 10

*a composite measure of the number of individuals of a species released into a region to which they are not native.

*As the number of releases or the number of individuals released increases, propagule pressure also increases.

*Propagule pressure can be defined as the quality, quantity and frequency of invading organisms

*Propagule pressure is a key element to why some introduced species persist while others do not.

*Species introduced in large quantities and consistent quantities prove more likely to survive, whereas species introduced in small numbers with only a few release events are more likely to go extinct.

Propagule Pressure is composed of three elements:

1. number of individuals released per event
2. number of release events
3. health of the individuals released

Question 11

Number of Individuals Released per Event

Answer 11

The larger the number of individuals released the more likely it will establish with large populations

Question 12

Number of Release Events

Answer 12

The more frequent releases result in a greater proportion (%) of establishments

Question 13

Health of Released Individuals

Answer 13

Third thing that effects propagule pressure

Question 14

Propaguled animal species and their effect on terrestrial New Zealand

Answer 14

*New Zealand native forests grew and developed without browsing mammals.

*Their populations expanded rapidly and contributed to the destruction of forests and the initiation of erosion.

Question 15

Disturbance: Classification

Answer 15

Natural versus Anthropogenic
e.g., wild fire versus prescribed burn

Biotic versus Abiotic
e.g., praire dog versus deep plowed grasslands

Endogenous versus Exogenous
e.g., succession versus tree planting

Question 16

Disturbance: Definition

Answer 16

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 number per unit time)
*Duration (temporal extent of event – how long does it last)
*Predictability (regularity of the occurrence)
*Distribution (size and spatial extent)
*Synergism (does a disturbance precipitate or exacerbate further disturbances)

Question 17

Probability of community invasion

Answer 17

a) Within Community Resistance:

Abiotic Resistance: e.g., temperature, water, light, disturbance Level

Biotic Resistance: e.g., species richness, competition, predation
versus
b) Propagule Pressure (e.g., invasive seed supply)

Invasiveness will change depending on their invasion resistance and propagule supply (also previously effected are more likely to be hit harder the next time as the overall community resistance decreases AND

-All leading to the same high probability of invasion, but depending on their propagule supply , may get there faster. Highest getting to invasion faster.

*Hard to go back - try to fix the situation, but impossible once affected.

*extreme sloping indicates way to destruction - shifting into low resistance because propagules won’t stop

Question 18

Gary Oak and Probability of Invasion

Answer 18

Community resistance can decrease after an invasion making a community more susceptible.

Previous invasion can facilitate conditions necessary for later arrivals.
e.g., Victoria and Garry oak communities first invaded by Scotch broom and later by daphne.

Question 19

Allee Effect

Answer 19

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

(establishment stage: Impact)

Allee is the lag phase that occurs when

Question 20

Biogeoclimatic Ecological Classification

Answer 20

*Based on the concept of equilibrium-based population and community models developed during the 1930s – 70s

*All variation is directional, toward a stable equilibrial abundance of species

e.g., CDF forest is the climax (final) stage and Garry oak is merely a disturbance caused by anthropogenic fire (disclimax).

Question 21

Wrack disturbance

Answer 21

Wrack disturbance and the facilitation of seedling establishment of the invasive grass, common reed

Wrack: mats of dead plants deposited by storms, waves and tides.

Question 22

Theory of Fluctuating Resource Availability

Answer 22

Resource uptake vs supply

Resource Changes…

1. Pulse (ex eutrophication.. increase in nutrients) (b)
2. Decline (ex reduced herbivory - overgrazing) (c)
3. Both (ex eutrophication/over grazing) (d)

Invasibility is highest below the isocline

*Uptake loss - native don’t do luxury growth - so they can’t follow the isocline - which will allow invasives to fluorish.

*The theory of fluctuating resource availability holds that a community’s susceptibility to invasion increases as resource availability (the difference between gross resource supply and resource uptake) increases.
Resourse availability can increase due to a pulse in resource supply (A→B), a decline in resource uptake (A→C) or both (A→D).

*In the previous plot, resource availability, and hence invasibility increases as the trajectory moves further right and/or below the supply/uptake isocline (where resource uptake = gross resource supply).