Lecture 5: Population dynamics of invader Flashcards
Explain the intentional release of the European Starling.
- released birds in central park to have birds from Shakespeare plays.
- all birds we see now are pretty much descendants from these
- 60 released in NYC 1880
- 40 more in 1891
- Present pop in NA = 200 million
Explain the intentional release of the European house sparrow.
- Initially 16 released in NYC 1851
- 100 more in 1852
- *initial 16 did not survive but the 100 did establish
Are all planned introductions successful?
- no
- most fail to become established
The probability of invasion increases with what?
- the number of attempted introductions and with the total number of colonizers
Do small or large populations have a higher extinction risk? Why?
- small
-bc of demographic stochasticity (i.e. bad luck) - minor glitches in reproduction or survival can wipe out a small population
Gamblers Ruin - ## if in small numbers, you do not have the numbers to buffer against fluctuations in the environment that are unfavourable etc – worse if you don’t have meta populations bc no rescue effect.
Give the reasons of why small populations have higher extinction risks.
- demographic stochasticity
L> glitches in reproduction or survival can wipe out a small population - small gene pool
L. insufficient genetic variability to adapt to environmental changes - population is spread too thinly
L> mate location becomes difficult
L> can be wiped out easily bc all in one close location - vulnerable to small scale environmental stresses
L> e.g. fire, storms, predation, disease
*** small populations need to be able to reproduce from small numbers to escape these fast to successfully establish
What is propagule pressure and what are the two types when involving only a single species .
- aka inoculation pressure/ introduction effort
- ** the quantity / rate of propagules (life stages) delivered to a site
1. Propagule size
2. Propagule number
What is propagule size?
- number of individuals in a given introduction event
What is propagule number?
- the number of introduction events
What are the two classes of propagule pressure?
- must introductions of propagules of a single species (propagule size and propagule number)
- multiple introduced species aka colonization pressure
Explain the relationship btwn propagule size and establishment for mammals introduced to Australia
- highlights when a large number are initially introduced there is a better chance of establishment
- also demonstrates you do not get a successful establishment on first introduction
Explain the proportional success of introducing different numbers of birds of a species in New Zealand
- if there are more than 50, establishment is likely
- there is a point where once you pass a certain threshold, it no longer matters how many you add, more so if they are aded in the right place
Explain the relationship of the number of introduced and established aquarium fish in Can and US as a function of popularity
- dumping depends on what ppl are buying
- some are more pop than others
- if something is popular there will be more of them in stores and diversity of stores to provide public demand
- how popular the fish is, is a proxy of propagule pressure. More popular = more being sold = more in tanks that eventually might be dumped
Explain the relationship btwn ship vectored invasions and shipping activity in the great lakes
- the more water being dumped out, the more propagules being pumped out THEREFORE a proxy of PP
- water release is a proxy of shipping activity too
- as shipping activity increases so does the number of species invasions
- could also reflect our increasingly better detection methods
Explain the spread of fire ants around an African oilfield through movement of oil rig platforms
- vector activity can be a proxy for propagule pressure
- oil rigs carried mud and insect around, invasive ants are an example
- small number of oil rig visits, small prob of establishment but AS it increases, prob of establishment increases
- eventually reaches an asymptote
- point is that it doesn’t go on forever
Explain the relationship between species richness and number of species added as seed
- number of seeds in plot and those coming out
- number of sp that become established are a direct function of the number of seeds added
- limited by recruitment and dispersal = for seeds
- colonization pressure is occurring: species numbers not number of individuals of one sp
- sp richness increasing with number of sp added as seeds increases
Explain the success of introduced salmonid fishes vs propagule supply
- both introduction attempts and number of individuals matters
- add a lot of fish and repeat
- by introducing many over diff time periods, you are opening windows of opportunity
Are there ever exceptions to the trend with propagule pressure?
- yes
- very small risk
- sometimes small numbers can lead to an invasion
Describe examples of when small numbers of sp can lead to invasions.
- Mitred parakeets colonized Maui from a single pair released by a resident
- muskrats invaded europe when five escaped from a fur farm
- a single pair of sheep released in Kerguelen islands resulted in a population as large as 700 in 30 years
- ** Noah Fallacy : assuming all you need is one breeding pair
What are the three hypothetical relationships between invasion success and propagule supply.
- Threshold effect
L> after while adding more individuals isn’t enough and will asymptote - Continous marginal benefit
L> direct linear relationship rarely happens bc usually other environmental factors will influence this
L>the more you add, the further the benefit and this will continue over time (don’t expect with asexual reproducing orgs) - Logistic
L> s shape
L> threshold where before you get little if anything, anything above it increases to a point. This threshold will vary with each context even for the same sp.
Explain the interactive effects of propagule size and number of experimental Daphnia populations.
- basically BOTH matter
- as propagule size and number increase, so does avg pop size
Explain why survivorship of propagules in ballast tanks decline over time
- propagule quality decreases via enviormenta; pressure bc of what is delivering them
- phytoplankton and zooplankton decline as the voyage goes longer
- if the voyage is shorter, the number of individuals will be more that are released
- physical condition will also be different
- organismal density decreased overtime in ballast water
Explain the relationship with species richness and time in ballast water
- the pathway chosen will determine the quality or nature of propagule pressure
- if ballast water has been there long the quality and quantity of individuals will be less
- this is more of an issue if quality of water is not replenished over time
- what happens to the vector determines the propagule pressure
- number of species decreases as the days increase since the last taking of ballast water
Explain Lonsdale’s model
E= I x S
E= number of exotic species in a region
I= number of species introduced (propagule pressure)
S= survival rate of introduced species (biological traits of the invader; habitat quality)
- colonization pressure = number of species introduced which depends on vectors
- survival rate depends on the relationship btwn the invader and the environment
- habitat quality it is also important upon introduction, which varies over time
- basic idea is that propagule pressure and environment matter BOTH of which vary over time
- it explains why the same sp can fail many times and invade in another situation
- *** SO even if it is introduced to a suitable habitat it does not sure establishment
