Biotic interactions and invasive species Flashcards
(14 cards)
What does the tens rule say?
It says that out of 1000 introductions only 1 will become invasive.
1000 introductions
100 survive
10 naturalize
1 invasive
Why will some species become successful in the new area?
Because of:
- Enemy release
- Novel weapons
- New traits
- New associations
- Genetic change/adaptability
What is an example of how a situation of enemy release was solved?
Giant salvinia (Salvinia molesta) escaped a botanical garden in Sri Lanka in 1939, and had then continued to spread across the world.
The problem had become so widespread that scientists looked into biological control as a potential solution.
By 1980 the first releases of a weevil species was done on a heavily infested lake in Queensland. And by mid 1981 the weevil had reduced the plant to a few small patches.
Briefly explain the following hypotheses for why species become successful in areas where they are introduced: (a) enemy release
(a) Enemy Release
Explanation: Introduced species leave behind their co-evolved natural enemies (predators, parasites, pathogens) in their native range. In the new environment, local enemies may not recognize or be adapted to effectively control the invader.
Result: The introduced species experiences reduced pressure, allowing it to reallocate resources from defense to growth and reproduction, leading to rapid population growth and competitive advantage.
Briefly explain the following hypotheses for why species become successful in areas where they are introduced: (b) novel weapons
(b) Novel Weapons
Explanation: Introduced species possess unique biochemicals or traits (e.g., allelopathic compounds released by plants, unique toxins) that are detrimental to the native species.
Result: Native species, lacking a shared evolutionary history, have no evolved defenses or tolerance to these “weapons.” This gives the invader a significant competitive edge, allowing it to suppress native populations and dominate resources.
Briefly explain the following hypotheses for why species become successful in areas where they are introduced: (c) new traits
(c) New Traits
Explanation: Introduced species develop entirely new adaptive characteristics (e.g., altered growth rates, broader physiological tolerances, changes in reproductive strategy, novel foraging behaviors) after introduction, often through mutation, hybridization, or rapid selection in the new environment.
Result: These newly acquired traits allow the species to better exploit resources, overcome local challenges, or interact more effectively (often detrimentally) with native species, leading to increased fitness and success.
Briefly explain the following hypotheses for why species become successful in areas where they are introduced: (d) genetic change.
(d) Genetic Change
Explanation: The introduced population undergoes rapid evolutionary change in its genetic makeup in response to selective pressures in the new environment. This can involve changes in gene frequencies, accumulation of beneficial mutations, or adaptation to local conditions.
Result: This rapid adaptation (evolution in action) allows the introduced species to become better suited to the new habitat, potentially overcoming initial establishment hurdles and enhancing its invasiveness by optimizing its phenotype for the new biotic and abiotic conditions.
What is Elton’s hypothesis of biotic resistance?
The hypothesis of biotic resistance (Elton 1958) stating that the complex world of biotic interactions makes communities resistant. Note the focus on long co-evolutionary history. Often phrased as: Organisms in communities not disturbed by man share a long evolutionary history.
Why do some introduced species fail to become invasive, despite the lack of natural enemies?
If the introduced species is somewhat related to the species in the native flora, it is likely to be more preferred by native generalist herbivores in the new area.
Why are some communities more sensitive to invasion?
Increased transoceanic communications in the 15th-16th century and human expansion disrupted the natural disturbance regimes, felled forests (land conversion), and introduced new agricultural techniques, crops, animals and diseases.
- This weakened the biotic resistance of the native ecosystems, left novel ecosystems or abandoned nisches (because native species were outcompeted/ reduced by the new conditions) that were open for opportunistic invasive species
Are some communities resistant to invasions?
Nutrient-limited ecosystems where the nutrients are monopolized by the treas and their mycorrhiza (coniferous/eucalypt forests), are generally considered resistant.
But with climate change and more adaptive invasive species that can create their preferred conditions or adapt to new conditions through new traits, as well as increased human interaction/ manipulation, maybe it’s only a matter of time before these ecosystems loose their resistence too.
What is propagule pressure?
It is a measurement in invasion biology that can be described as
- establishment probability of a non-native species
It estimates this by incorporating quantity, quality and frequency of introduced organisms. Higher propagule presssure means increased likelihood of establishment, keeping a low propagule pressure could therefore reduce establishment probability.
What is shifting baselines? and why does it become a problem in invasion biology?
Shifting baselines describe a gradual shift in what is percieved as normal or healthy for an ecosystem. This happens because each generation accepts the conditions of their youth as the baseline, rather then finding out the historical state of the ecosystem. (There is also not an abundance of historical data on pre-invaded ecosystems).
This becomes a problem in invasion biology because it is hard to know what to protect, what species that are considered native or alien, and what the end goal of the restoration effort is supposed to look like to resemble a natural state.
This leads to:
- Further acceptance of invasion-dominated ecosystems as the norm
- Inadequate restoration efforts
- Reduced public engagement and support of restoration actions
- Reduced funding for restoration efforts
Which then repeats in a negative feedback loop
Can native species become invasive?
Yes. The ongoing climate warming, habitat fragmentation and habitat loss due to land conversion, forces native species to migrate into habitats were they previously did not exist, which can lead to “invasive effects” on the species that were there first - even though they are both native species.
This becomes an issue on how to handle it. Do we let them invade the new habitat on the cost of the species that were there before? Or do we control their spread and risk losing the species?
