1. General Ecology: EEOB 404

2. Evolutionary ecology: speciation and extinction
Topics for this class:
Species richness of communities depends on both speciation and extinction processes
Nature of speciation concepts, mechanisms
Example: beetle herbivores & speciation on angiosperm plants
Nature and impact of extinction on species richness
Impact of humans on contemporary rates of extinction

3. Species richness depends on both speciation and extinction
Species richness is another form of biological diversity than genetic diversity within a species
Species richness is a characteristic of evolutionary clades, and of ecological communities
High rates of speciation can boost species richness over time, just as high rates of extinction can decimate it

4. Species concepts
Evolutionary biologists still debate which of a number of species concepts apply most widely in nature
Ernst Mayr’s Biological Species Concept probably applies most widely (at least in animals): Accordingly species are reproductively isolated units
No one species concept applies to all organisms

5. Mechanisms of speciation
Similarly, mechanisms of speciation are still poorly understood by evolutionary biologists
Several are well documented:
Allopatric speciation (probably most vertebrates)
Sympatric speciation (especially insects)
Polyploidy and chromosome rearrangements in small peripheral populations (especially plants)
We need not concern ourselves in this class with particular species concepts or mechanisms to get the main points about the importance of evolutionary phenomena to understand ecological questions

6. Effect of speciation on species richness: an example
Outstanding question: “Why are there so many beetle species?”
Background:
Insects are overwhelmingly rich in species: 751,000 species, ca. 50% of all described species
Of insects, beetles are overwhelmingly dominant: >50% of all insects are beetles
Of beetles, leaf-eating families are dominant groups (e.g., Chrysomeloidea = leaf beetles, Curculionoidea = weevils)

7. Famous anecdote
J.B.S. Haldane is a well known evolutionary biologist, one of the architects of “The Modern Synthesis”
A theologian reputedly asked Haldane, late in life, “What can we conclude about the nature of the creator from looking at the creation?”
Haldane replied: The Creator has an inordinate fondness for beetles”

8. Question of beetle diversity was recently addressed by phylogenetic study
Study by Farrell,B.D Science 281:555. (copy on class reserve)
Study first devised phylogeny of 115 phytophagous beetles (representative families)
Sequenced entire 18s ribosomal subunit, 2117 nucleotide positions-->355 informative characters (i.e., those that varied among the species)
2nd data set,scored 212 morphological characters
Parsimony analysis-->most likely “tree” of evolutionary relationships (= cladistic analysis)

9. Adaptive radiations of beetles began in late Jurassic, continued to diversify up until today; Herbivores diversified disproportionately
20000
100
200
300
400
Herbivores
Number of beetle genera
10000
Carnivores
Saprophages
Permian
Triassic
Jurassic
Cretaceous
Tertiary
Recent

10. Next step in analysis...
Superimpose onto phylogeny feeding habitats of living species, timing at which groups show up in fossil record, number of extant species
Results (next slide):
Five independent cases in which phytophagous beetles became associated with angiosperm plants
Each of these cases associated with increased species richness
This pattern general, because we see it replicated 5 times, independently in beetles’ evolutionary history
These beetle radiations took place in Cretaceous & Tertiary, corresponding with adaptive radiation of angiosperms (flowering plants)

11. 1 2 3 4 5 Tr Ju Cr Ter Clytrinae(947) Nemonychidae(85)
Attelabinae(800)
Rhynchitinae(1200)
Antliarhininae(24)
Apioninae(1500) 1
Rhynchophoridae(1100)
Curculionidae(40502)
Oxycoryninae(10)
Allocoryninae(20) 2
Belinae(150)
Prioninae(770)
Aseminae(75)
Spondylinae(3) 3
Cerambycinae(10000)
Lamiinae(14000)
Lepturinae(1000)
Palophaginae(3) 4
Megalopodinae(350)
Zeugophorinae(50)
Orsodacninae(8)
Aulacoscelidinae(18)
Synetinae(11)
Eumolpinae(3200)
Megascelidinae(60)
Lamprosomatinae(190)
Cryptocephalinae(2290)
Clytrinae(947)
Chlamisinae(360) 5
Chrysomelinae(2000)
Galerucinae(5300)
Alticinae(8000)
Cassidinae(3000)
Hispinae(3000)
Donaciinae(165)
Criocerinae(1400)
Pachymerinae(77)
Amblycerinae(400)
Bruchinae(3000) Tr Ju Cr
Ter
early Oligocene

12. Interpretation of Farrell’s study?
Angiosperms diverged greatly in plant chemistry.
Each plant group provided new “island archipelago” with opportunities for colonization, diversification in how the insects could use these new plants (e.g., chew leaves, mine leaves, eat seeds, mine stems, chew flowers)
Basically flowering plant speciation appears to have triggered massive adaptive radiation of plant-feeding insects, i.e., co-evolutionary arms-race
Thus, we see evolutionary tools applied to addressing ecological question (distribution & abundance of species)

13. Extinction is the other evolutionary process that influences species richness
Rates of extinction have varied enormously in Earth’s history from negligible (background) rates to a number of mass extinctions (5--class overhead)
E.g., extinction of dinosaurs (and many other birds, mammals, marine reptiles, etc.) 65 MYA, response to asteroid impact
Extinctions opened opportunities for subsequent radiations, such as mammals and birds following dinosaur mass extinctions
Extinction is the rule, rather than the exception

14. Humans causing extinctions today, higher rate than mass-extinctions!
Increasing rate of extinction (e.g., birds, mammals) correlated with increasing human population
Disproportionate vulnerability of island populations
Entire clades wiped out by human over-hunting (e.g., Moas of New Zealand; native flightless birds of Hawaii)
Almost all islands world-wide are missing species due to human-caused extinctions (on order of 50% of spp.)
However mainland species also vulnerable--e.g., passenger pigeon, Carolina parakeet, ivory-billed woodpecker, Bachman’s warbler = U.S. birds extinct since 19th century

15. What are some lessons about extinction & its causes?
Causes of known animal extinctions (484 spp.):
Introduced animals (17%)--e.g., brown tree snake, Guam
Habitat destruction (16%)
Over-hunting (10%)
Other (1%) or unknown (56%) causes
Different causes of extinction in different taxa, different locations
E.g., Hawaiian organisms particularly affected by introduced organisms
Hawaiian birds particularly affected by disease (avian malaria)
Many island populations overexploited (e.g., hunted)

16. Conclusions
Understanding evolutionary processes (such as speciation, extinction) provides critical information on present-day patterns of organism distribution and abundance
Speciation and extinction processes have both had a profound impact on ecological patterns and processes observed today
Extinction and speciation processes affect taxa differently, and geographic locations differently
Humans today, and deep into our evolutionary past, have profound impacts on ecological systems...why?