Imprints of interactions Flashcards
Why are Ecological Opportunity (EO) and Ecological Character Displacement (ECD) described as 2 sides of the same story?
EO: Low competition → Expands trait diversity by allowing species to exploit new resources (niche expansion)
ECD: High competition → Reduces niche overlap by driving trait divergence to minimize competition.
Both describe how species evolve in response to resource availability and competition, but from opposite perspectives—EO focuses on opportunity, ECD on constraint.
How does character displacement affect evolution on a phenotypic landscape?
Phenotypic landscape: A theoretical adaptive landscape with fitness peaks (optimal traits) and fitness troughs (low survival traits).
- Without ECD: No competition → Slow evolution, possible incomplete speciation.
- With ECD: Competition drives evolution toward fitness peaks, increasing speciation rate until divergence is achieved.
How do Ecological Opportunity (EO) and Ecological Character Displacement (ECD) affect phenotypic evolution over time?
- Both EO and ECD drive early bursts of rapid phenotypic evolution.
- Over time, evolution slows as niche availability is finite
- Once most adaptive peaks are occupied, further divergence is constrained
What are phenotypic slowdowns?
A decline in the rate of phenotypic evolution over time.
- Often expected after an early burst of rapid evolution (e.g., after EO or ECD).
- Happens when niche space fills up, limiting further divergence.
How common are phenotypic slowdowns?
Support for early burst models appears rare; most data fit Brownian Motion or OU models.
How does competition and lineage diversity affect the evolution of body size and shape in Anolis lizards?
Study modeled evolution rate as a function of lineage diversity & time, accounting for sympatry (only considering species that interact).
Findings:
- Body size evolution fits a diversity-dependent model → More co-occurring species = slower evolution.
- Body shape evolution fits a time-dependent model → Shape changes slow over time, but lineage diversity had little effect.
Supports idea that niches fill up, constraining further evolution.
How do the Brownian, Early Burst, and Diversity-Dependent models differ in explaining trait evolution?
Brownian Motion Model:
- Random evolution over time, with no specific pattern or acceleration.
- Steady rate of change in traits over time, independent of niche availability or species interactions.
Early Burst Model:
- Rapid initial evolution followed by a slowdown.
- Ecological opportunity main driver = niches fill up
- Assumes slowdown due to time alone
- E.g Darwins Finches
Diversity-Dependent Model:
- Rate of evolution slows down as lineage diversity increases (more species = more competition).
- Driven by competition
- Assumes slowdown correlates with diversity
- E.g Anole lizards in Caribbean
How does trait evolution influence patterns of species diversity?
Global species distributions are affected by the Latitudinal Diversity Gradient:
- More resources and more species interactions (in tropics) = more divergence.
- Cyclical relationship
- But there are still upper limits to how much divergence can occur.
How does phylogenetic community structure relate to trait evolution?
- We often assume that more similar species are closely related, but this depends on the mode of trait evolution.
- Under Brownian motion, similarities match phylogenetic relatedness.
- Under competition models, closely related species are more similar due to shared evolutionary pressures.
- Under the OU model, similarities can break down, as traits are influenced by stabilizing selection that pushes species toward different adaptive peaks.
What are the challenges in measuring phenotypic slowdowns?
Why do early burst models assume slowdowns start at the tree root?
- EBMs are time-dependent = they assume rapid evolution occurs early in a clade’s history
- Based on adaptive radiation (where early lineages diversify quickly before slowing down due to niche saturation)
- Slowdowns expected to originate at the phylogenetic root as evolutionary opportunities decline over time.
What are the challenges in measuring phenotypic slowdowns?
How does high data noise bias results toward the Ornstein-Uhlenbeck (OU) model?
- Intraspecific variation and measurement error introduce noise into trait data.
- This noise can make traits appear to cluster around a mean, artificially supporting stabilizing selection (OU process).
- As a result, real evolutionary patterns may be misinterpreted, leading to overestimation of OU dynamics.
What are the challenges in measuring phenotypic slowdowns?
Why is it hard to track phenotypic slowdowns in evolution?
- Evolutionary rates can be decoupled from trait disparity
- A past burst of rapid evolution can maintain high trait disparity, even if the rate slows.
- OU models (stabilizing selection) cause slowdowns but keep disparity high, making slowdowns difficult to detect.
- Measuring trait disparity alone is not enough; direct estimates of evolutionary rates are needed.
