L6 non-adaptive radiation 2 Flashcards
What concept explains that not all evolutionary radiations involve dramatic ecological divergence?
The idea that evolutionary radiations can occur without major ecological differences among species.
What pattern describes many species confined to a small geographic area?
Species-rich groups found within small regions.
What does “clustered speciation” look like on a phylogenetic tree?
Rapid bursts of speciation appearing as clusters of branching events.
How is the slowing of lineage accumulation through time visualized?
With lineage-through-time plots showing a deceleration in branching rates.
Why are these patterns (small region richness, clustered speciation, slow lineage accumulation) often seen as signs of adaptive radiation?
They’re interpreted as evidence of colonization of new resources or niches driving diversification.
What distinguishes non-adaptive radiation from adaptive radiation?
Non-adaptive radiation involves speciation without ecological divergence, often due to geographic factors.
How is non-adaptive radiation defined?
Diversification from a single ancestor without niche differentiation, yielding ecologically similar allopatric or parapatric replacements.
What role do multiple geographic barriers play in non-adaptive radiation?
Islands, mountains, or rivers isolate populations simultaneously, promoting speciation.
What is the mutation-order process?
Genetic divergence in similar environments due to different mutations accumulating in different isolated populations.
Why can current phylogenetic patterns mislead interpretations of past radiations?
Historical extinctions may have removed lineages, altering the apparent pattern of diversification.
Which methods are used to model speciation and extinction rates?
Phylogenetic trees calibrated with fossil evidence and molecular clocks, producing time-calibrated trees and lineage-through-time plots.
What challenge arises when two groups share similar branching patterns but different species counts?
Past extinction events can reduce observable species, decoupling branching pattern from current diversity.
How do Hawaiian landbirds illustrate non-adaptive radiation?
Sequential volcanic islands produced ecologically similar species via mutation-order divergence rather than niche shifts.
How do Californian salamanders exemplify non-adaptive radiation?
Geographically replacing sister species remain ecologically similar despite diverging over ~10 Ma.
What pattern is seen in island monarchs of Northern Melanesia?
Functionally equivalent species across islands replacing each other through vicariance.
What did mandible-landmark PCA reveal about Sigmodontine rodents?
Morphological variation was poorly explained by diet categories once phylogeny was accounted for, supporting non-adaptive radiation.
How do woodland salamanders demonstrate non-adaptive radiation?
A speciation burst ~8 Ma with modest lineage accumulation and limited phenotypic or niche disparity.
What role does dispersal capacity play in silvereye radiation?
High dispersal enabled colonization of remote islands, maintaining ecological roles and genetic diversity via founder events.
What comparative insight describes the adaptive vs. non-adaptive radiation dichotomy?
Radiations range from clearly adaptive with niche divergence to non-adaptive with minimal ecological change, with mixed cases in between.
Within the Hawaiian Tetragnatha spider radiation, what divergent ecological phases coexist?
A non-adaptive phase of genetically distinct green morphs with similar ecology, and an adaptive phase of sympatric brown and maroon morphs with different foraging behaviors.
How do green morphs in Tetragnatha illustrate non-adaptive divergence?
They are allopatric eco-morphs across islands that are genetically distinct species but share nearly identical ecological roles.
What ecological differences characterize the brown and maroon morphs in Tetragnatha?
Brown morphs roam twigs hunting small flying insects, while maroon morphs remain sedentary catching only weakly flying insects.
How can geographic context change over the course of speciation?
Lineages may diverge in allopatry and later come into secondary sympatry, altering interactions and evolutionary outcomes.
What is scenario 1 when allopatric ecological speciation is followed by secondary sympatry?
Persistent reproductive barriers allow both species to coexist in sympatry, producing an adaptive radiation.
What occurs in scenario 2 of secondary contact?
Weak reproductive isolation leads the two incipient species to collapse back into a single species.
What is scenario 3 following non-ecological allopatric speciation?
Secondary sympatry triggers competitive exclusion, causing one species to go extinct.
What defines scenario 4 in secondary contact after non-ecological speciation?
Character displacement evolves, permitting stable coexistence despite initial ecological similarity.
What is scenario 5 of non-ecological speciation followed by secondary sympatry?
Both species persist with similar niches due to mutation-order divergence, resulting in non-adaptive radiation.
How do repeated rounds of isolation and divergence contribute to adaptive radiation?
Successive allopatric divergence and secondary contact build up ecological differences and reproductive barriers, driving species into new adaptive peaks.
Why must ecological and reproductive divergence be coupled for true adaptive radiation?
Because novel phenotypes must confer fitness advantages in new niches and maintain barriers upon secondary contact.
How does geographic context influence whether a radiation is adaptive or non-adaptive?
The timing and pattern of barrier formation, dispersal, and secondary contact determine opportunities for niche differentiation versus non-adaptive speciation.
How is non-adaptive radiation recognized in empirical studies?
By finding reproductively incompatible but ecologically similar species distributions and by examining speciation/extinction rates and phylogenetic patterns.
