Eco-Evolutionary Dynamics Flashcards
Consider the following traits:
a. salinity tolerance in a grass species
b. body size of a rotifer
c. prey size preference of a Daphnia species
d. song complexity of a songbird species
e. biofilm formation in bacteria (individual bacteria “deciding” to cling to a surface) to avoid predation by
ciliates
Which of these traits could be involved in an eco‐evolutionary feedback loop? Describe for each
trait why / why not.
For a trait to be able to generate an eco-evolutionary feedback loop, there are a number of requirements it must meet:
1. it must be a trait that responds to ecological changes (e.g. changing abundances of prey, predators or competitors) – that is to say, a functional trait that determines how the species interacts with its environment and other species
2. there must be potential for rapid adaptation (most traits can do this if selective pressure is strong enough)
3. the rapid adaptation must feedback on the ecological dynamics: it must be a trait that responds to ecological changes but also causes ecological changes (e.g. a defensive trait in the prey, which responds to changes in predator abundance and also causes changes in predator abundance)
4. adaptation must be caused by evolution
With these requirements in mind, only trait b and c can be involved in an eco-evolutionary feedback.
Trait a (salinity tolerance) does not have the potential to cause a feedback: the trait may change in response to rising salinity, but it will not cause changes in salinity.
Trait d (song complexity) is not really a functional trait at all, even though it obviously affects interactions between individuals of the same species. But it is not a trait that determines the species’ position or role in the community, nor does it really affect its interaction with other species.
Trait e (biofilm formation) meets all requirements except the last one: it can adapt rapidly, and it can feedback on predator dynamics, but it is a phenotypically plastic trait, so the resulting feedback is not an eco-evolutionary feedback because there is no evolution involved.
Why are trade‐offs critical for eco‐evolutionary feedbacks? (In other words, why can there be no
feedback loop if there is no trade‐off?)
Eco-evolutionary feedbacks refers to the cyclical, or recurrent, interaction between
ecological and evolutionary (i.e. trait) changes. The famous example is a defensive trait in a
prey species, which responds to changes in predator abundance (and affects predator
abundance in turn): predators increase defense increases predator decreases defense
decreases predator increases …
For this to work, selection on the trait has to be context-dependent: in the above example,
selection favours either higher defense or lower defense at different points in time, depending
on the current predator abundance.
This can only happen if there is a trade-off. If defense did not come at a cost, it would simply
remain at a high level even after predator abundance has gone down, and then the feedback
loop would break. This same principle holds true for all eco-evolutionary feedback loops.
Some bacteria and fungi can produce toxins that negatively affect individuals of competing species
(but not conspecific individuals). These toxins are typically costly to produce, so that there is a
trade‐off between toxin production and growth rate.
Describe (in some detail) a hypothetical eco‐evolutionary feedback loop that involves the “level of
toxin production”‐trait. In this feedback loop, identify the “eco” and “evo” parts.
A hypothetical example would be very similar to the eco-evolutionary feedback loop
caused by prey defense:
High density of competitors from other species selection for increased toxin production
the elevated toxin levels cause heterospecific competitors to die off, thereby releasing the
toxin-producing species from competition
selection then turns against toxin production, because it doesn’t “pay off” to invest in
toxins if competitive pressure is low (there may of course still be competition from
conspecifics, even very strong competition, but conspecifics are not affected by the toxins)
competitors can increase again
…and so on
In this hypothetical feedback loop, the increase / decrease of heterospecific competitors is
the “eco” part, while the change in the level of toxin production is the “evo” part.
Define Eco-evolutionary feedbacks
Eco‐evolutionary feedbacks: the cyclical interaction between ecology and evolution in which changes in ecological interactions drive evolutionary change in organismal traits that, which in turn, alter the form of the ecological interaction (Post & Palkovacs 2009).
e.g. defense evolution in a prey species. Ability to form clumps. -> Trade-off between defense and growth
Under which circumstances can evolution be fast?
- …if standing genetic trait variation is already there
OR - …if new genetic variation can be generated very rapidly
- e.g. bacteria, viruses, unicellular organisms
- fast generation time, high population abundance - …if there is strong selective pressure on the trait
- traits that have a major impact on individual fitness
“fast evo.” means evo. change occurs within 100 generations
What is needed for eco-evolutionary feedback?
- Standing trait variation (or very rapid mutation)
- Rapid evolution (change in genotype frequencies)
- trait variation must be genetic!
- strong selective pressure
3.. Trait change must result in ecological change (e.g.
population dynamics)
- otherwise there is no feedback possible!
standing genetic trait variation: if there is already a broad variation in Genome of species
Name 2 different types of functional traits. Which one can only be involved in eco-evolutionary feedback? Why?
- Traits that determine response to the abiotic environment (e.g. sensitivity to temperature)
- Traits that determine interactions with environment and other species
- defence in prey (running / swimming speed, armour, toxin production, spines, body size, …)
- counter‐adaptations in predators
- nutrient uptake (competitiveness)
- life history traits, e.g. size/age at first reproduction
- feeding mode (generalist/specialist; chase vs. ambush hunting)
Only the second type of functional trait causes eco‐evolutionary feedbacks! They respond to ecological changes but also cause ecological changes (!).
Other types of feedbacks caused by trait changes
- Standing trait variation (in functional traits) can cause
feedbacks between ecological dynamics (e.g. changes in population densities) and trait dynamics genetic trait variation within a species: eco‐evolutionary feedbacks - Other types of trait variation: diversity of species with different traits in a community phenotypic plasticity (e.g. inducible defences)
Why are eco‐evolutionary feedbacks important?
- Standing genetic variation in functional traits is everywhere
potential for eco‐evolutionary feedbacks! - If we want to predict the future…
how will communities respond to climate change?
is a species at risk of extinction?
what can we do to help species avoid extinction?
how will community dynamics respond to loss of biodiversity?
how will communities respond to invasive species?
fast adaptation and trait changes, and resulting feedbacks, must be taken into account!
What can eco‐evolutionary feedbacks do?
- change the shape of predator‐prey dynamics
- affect stability
- promote species persistence / avoidance of extinction
- enable coexistence
Example of eco- ecolutionary feedback
defense evolution in prey species
Prey have the ability to form clumps
advantage: cannot be ingested
disadvantage: grow and reproduce slowly
- Ecological change: predator abundance increases
- Evolutionary change: prex becomes better defended
- Ecological change: predator abundance decreases
- Ecological change: prey becomes less defended
-> Eco change 1.
