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Week 4: Courtney Robichaud Guest Lecture (invasive phragmites)

Terms in this set (19)

Why are cycles of flooded and dry years important for wetland biodiversity?
High water level periods will kill off dry land plants, and increase emergent plants. These die off periods are important because plants can only deal with flooded conditions for so long before their density decreases. In the next dry period, the species will regrow from the seed banks.
What is an example of a transplant experiment involving native and invasive cattails that takes advantage of wetland zonation?
In an ecosystem where both native and invasive cattails are present, the native ones will grow in deeper water while the invasive ones grow in shallower water. However, if you transplant the native species into shallow water and remove all invasive competition, the native species does well. This shows that the native species is outcompeted by the invasive species in the shallow water zone.
What are the biotic and abiotic factors that constrain and define the "boundaries" of each wetland zone?
biotic: competition
abiotic: flooding/water levels
How does vegetation zonation lead to biodiversity?
More habitat types in one area mean that more species can coexist in a small area, due to niche partitioning (using different resources)
Why is phragmites australis australis called a cryptic invader?
It looks similar to the native phragmites species
What defines an invasive species? 3
1. Non native
2. Grow on it's own
3. spread outside of introduced range
What are the 4 stages of an invasion?
introduction --> colonization --> establishment --> spread (outside of introduced range)
What factor makes it difficult for non native species to colonize new areas?
Competitive exclusion: all niches are taken up by existing species, and two species can't coexist if they use the same resources/niche
What is the classical prediction for the effects of an invasive species based on the competitive exclusion principle?
high overlap => repelled OR complete takeover (since they can't coexist)
low overlap => get established, with few negative effects
What is niche differentiation?
Different species use different niches/resources, promoting them to coexist. Species will even self-limit their resource use in order to achieve this.

This process benefits rare species because it means less species are sharing it's niche.
What is fitness differentiation? how is it different from niche differentiation?
Differences between species that make some more fit than others, benefitting the more fit ones in any situation, regardless of the rarity of a species/nice. This promotes competitive dominance of the more fit species.
How does the modern coexistence theory of predicting invasive species impacts combine the ideas of niche differentiation and fitness differentiation? What situation based on this theory will cause the most damaging invasion?
Niche differentiation promotes coexistence while fitness differentiation promotes competitive dominance. These two ideas are combined to predict how an invasive species will interact with a community, based on a spectrum of how the invader compares to the native plants in niche differentiation and fitness differentiation.

The most damaging invasion is in section D, where there is high niche overlap (ie, low niche differentiation between invader and natives) and high fitness difference (ie, invader is more competitive than those it shares a niche with).
What are 8 traits that give invasive phragmites an advantage over native plants?
rapid clonal expansion
taller than most native plants (light competition)
more belowground biomass
perennial
more seeds produced per stem
multiple reproductive strategies (cloning and seeds)
wide environmental tolerance
no herbivores/competitors
long lived rhizomes and seeds
What is relative competition intensity index? What does it tell us about competition for light between phragmites and native species?
RCI = 1 --> maximal competition

RCI = 0 --> no competition

RCI = -1 --> maximal facilitation

Using this index, it was found that resident plants are more affected by phragmites than phragmites are affected by them (in terms of light competition)
What are the 2 metrics by which the success of an invasive species removal program is assesses?
1. Suppression of invasive plants
2. return of native vegetation
Why is glyphosate herbicide a good choice for targeting phragmites?
Phragmites transports the herbicides to the rhizomes, killing them, while other plants don't do this.
After the removal of phragmites at the study sites, what happened with European Frog Bit? Why is it less harmful than phragmites?
It took advantage of the less dense open water vegetation to become a secondary invasion. However, it is less harmful than phragmites because, since it is a floating plant, it is more limited in it's habitat.
Why did biodiversity decrease briefly in the 3 years following the phragmites treatment?
Due to natural fluctuations, there were high water levels, which was a natural process that temporarily reduce biodiversity.
What were the outcomes of the phragmites treatment project? 5
1. More open water and floating/submerged vegetation
2. Species richness decreasing (natural fluctuation of high water levels)
3. After 2 years, some sites look like reference (meadow/emergent marsh), others dominated by European frog bit
4. After 2 years, significant reduction of phragmites regrowth
5. Increase in native bird abundance
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