Conservation Biology 55-437Lecture 3

Feb. 26, 2010

Temporal Radiations

Species radiations

The opposite of extinction is radiation – speciation diversifying a taxon.

Van Bocxlaer et l. 2010. Science 327: 679−682

Cape Leopard toad (South Africa)

Pebas stubfoot toad (South America)

American toad (North America

Toads: subcosmopolitan distribution

Traits Context

Adults(Semi-)terrestrial adult niche (according to IUCN data)*

No dependency on constant water or humidity

Large body size Higher relative water storage ability in bladder

Presence of parotoid glands* Enhanced toxicity and rehydration ability

Presence of inguinal fat bodies* Extra energy reserve (extra fat storage ability)

Reproduction and developmentAquatic, opportunistic oviposition site* Ability to use all kinds of water bodies, including

those in harsh habitatsLarge clutch size Typical feature of r-strategyExotrophous larvae* Limited maternal investment in larval nutrition

Case Study: The Cane Toad Bufo marinus

Galapagos Islands: Most islands are not occupied; Darwin visited the islands in 1830; Cocos Island is 600km NE

26 species of land birds occurred naturally on the Islands before human introductions; 13 of these are finches. The islands also support 4 mockingbird, 2 flycatcher, 2 owl, 1 hawk, 1 dove, 1 cuckoo, 1 warbler and 1 martin species (Pianka 1983)

The island finches belong to a distinct subfamily of finches, endemic to the Galapagos and Cocos Island (Costa Rica).  Cocos Island supports only 1 finch species, the Cocos Island finch Pinaroloxias inornata. 

• Warbler finch may be the ancestral species, not the Cocos finch, which groups with the tree finches.

Sato et al. 1999 PNAS 96:5101−5106

Phylogeny

On the Galapagos Islands, adaptive radiation has resulted from geographic isolation and reduced gene flow among islands. Three distinct genera (Geospiza, Camarhynchus and Certhidea) occur on the islands. 

Members of these genera differ in where they forage, how they forage, and what they eat.

Finch diversity by island

The 6 species of Camarhynchus finches forage in trees, have narrower beaks, and eat either vegetation (1 species) or different sizes of insects.  C. pallidus uses a stick or cactus spine to probe for insects.  

Tree finches

Ground finches (Geospiza)These species are similar in coloration -- adult males are black, and females streaked brown. They all have bills of the "crushing" variety,

useful for feeding on seeds.

The ‘Vampire Finch’ Geospiza difficilis septentrionalis

On islands where Geospiza fuliginosa and G. fortis occur sympatrically, they tend to have widely divergent beak depths.

Character Displacementdifferences among similar species are accentuated in regions

where the species co-occur but are minimized where the species’ distributions do not overlap.

Only one of these species is on each of Daphne and Crossman.  The beak morphologies are very similar when the species occur in isolation.

1) the change in mean character state in areas of overlap should not be predictable from variation within areas of isolation

2) sampling should occur at more than one set of locations to eliminate local variation effects

3) Heritability of the feature must be high if genetic variation is thought to underlie variation in the feature, and if it is to be passed to subsequent generations

4) Evidence must be presented to demonstrate that competition occurs and that the measured feature has relevance to competition among groups

Before it can be confirmed that character displacement has occurred, 4 conditions must be met:

1) the change in mean character state in areas of overlap should not be predictable from variation within areas of isolation

3) Heritability of the feature must be high if genetic variation is thought to underlie variation in the feature, and if it is to be passed to subsequent generations

G. fortis & G. scadens on Daphne Major (Grant & Grant 1993, Proc. R. Soc. Lon. B)

rainfall on Daphne Major seed size (white) and hardness (black)

fortis (top), scandens (bottom)

Strong selection for G. fortis, which feeds on small seeds, over G. scandens, which feeds on rare cactus seeds, following drought after 1983

G. fortis on Daphne Major (Boag & Grant 1981, Science)

•1500 birds banded and studied between 1975-78

•regular rainfall (large finch populations) until 1977, when only 24mm rain fell. G. fortis did not breed and 85% decline in population (A); seed abundance declined (B), big males survived best (C), corresponding with decline of small seeds (D)

Grant & Grant (2002) Science paper

• studied the same populations of G. fortis (medium ground finch) and G. scandens (cactus finch) on Daphne Major for 30 years

• survival of marked and measured individuals measured each year

• 6 traits studied were reduced by Principal Components Analysis, which break down as body size, beak size and beak shape

If species were not changing, each measures should have stayed within its original 95% confidence interval (horiz. lines). Clearly this is not happening. G. scandens converged on G. fortis' morphology

1. body & beak sizes selected more than beak shape

2. species differed in net selection direction on size traits

3. unidirectional selection (up to 3 yrs) occurred in both species

4. selection events in the species were not synchronized except in late '70s during a drought

5. each of these studied traits was highly heritable, so evolution followed for fortis (body size, beak size, beak shape) and for scandens (body size, beak size)

4. Evidence must be presented to demonstrate that competition occurs and that the measured feature has relevance to

competition among groups

There is, however, no way to deal with criterion 2 since there is only one

Daphne and one Crossman.  Satisfying this requirement would necessitate observing the same

pattern on other islands like Daphne and Crossman.

Large-beaked G. fortis (A) and G. magnirostris (B) can crack or tear the woody tissues of T. cistoides mericarps (D), whereas small-beaked G. fortis (C) cannot

P. R. Grant et al., Science 313, 224 -226 (2006)

G. fortis

Fleisher et al. (1998) Mol. Ecol.

Aging the Hawaiian Islands

Hawaiian honeycreepers

These birds experienced much greater adaptive radiation than Darwin's finches, though, sadly, many of the taxa have been driven extinct due to introduction of diseases, other passerine birds and mammals, and destruction of habitat. 

On Laysan Island introduced rabbits and a windstorm destroyed vegetation resulting in the extinction of the Laysan honeycreeper.

Bird pox virus and avian malaria (introduced to the Hawaiian islands by mosquitoes on ships in 1826) have caused sharp declines in Drepanidid species, including the honeycreeper.

wide diversity, some now extinct (E)

beak shape highly variable and highly adapted to feeding mode

Origin of the Honeycreepers

• Johnson et al. (1989) used starch gel electrophoresis to study 8 genera (9 species) of honeycreepers

• they are a monophyletic group (only one ancestor)

• the ancestral species colonized the Hawaiian archipelago 7-8 million yr ago

• this agrees with the emergence of Nihoa (now largely submerged) but predated the island of Kauai (5 MYBP)

• Oreomystis and Paroreomyza are the oldest and most diverse lineages

• youngest lineages are the nectar feeders and thick billed finch types

Time difference between island formation dictates genetic distance between species

Hawaiian Flycatchers: VanderWerf et l. Conservation Genetics 2009

• Currently, honeycreepers occur primarily at altitudes above 600 m on the main islands and on several smaller remote islands in the NW part of the archipelago.

• Mosquitoes, by contrast, occur primarily below 600 m, and overlap very little with the honeycreepers.

• At the lower altitudinal end of the honeycreeper species ranges, between 2 and 7% of individuals have avian malaria. 

• in total, 28 of 53 known species are extinct (34 known from historical records, 19 from fossil records)

• 18 of the remaining species are endangered

• 9 extinctions have occurred since introduction of malaria to the islands. Of these, 6 occurred on Lana'i, Moloka'i and O'ahu. These islands have been radically modified by humans, thus habitat destruction appears to have played a large role.

• Behaviour may have affected 2 large, nectar-feeding Drepanidid species driven extinct and 2 smaller ones extirpated ('akoekoe and 'i'iwi) on some islands.

• The rare 'akiapola'au, a specialized insectivore, has become endangered because it lives primarily in large koa trees; koa trees have been widely harvested for furniture lumber. 

• Another endangered species, the palila, a granivore, exploits seeds of one tree, the mamane. This tree has been adversely affected by introduced goats and sheep, thereby endangering the bird.

• Honeycreepers are endangered because of their extreme specialization (habitat or food), which itself is a result of dramatic adaptive radiation. This problem may be compounded by introduced diseases, mammals, and exotic birds.

What's the Honeycreeper's Future?Benning et al. (2002) PNAS

• habitat loss began with the Polynesian colonists (900-1000 yrs ago), who cleared low elevation and seasonally dry forest

• European colonists brought new agricultural technology, domesticated cattle

• hunting, beginning with Polynesians, and introduction of dogs and rats that preyed on nesting birds. These predators were followed by mongoose, cats and 2 more rat species

• introduction of mosquitoes and of avian pox, and more recently avian malaria, had the greatest consequences

Temp. <13°C is critical to prevent malaria infection. In Hanawi Forest (Maui), a 2°C increase would cut this zone area by half (665 to 285Ha).

low mosquito risk zone, Hanawi, Maui

low mosquito risk zone, Hakakau Refuge, Hawaii (low risk areas declines from 3120 to 130 HA)

Alakai Swamp, Kauai. No area currently below 13°C, area of possible high risk moves up 300m. Must focus on disease prevention in remaining honeycreeper populations.

Hawaiian Drosophila

More than 900 endemic species, each typically restricted to one island.

Speciation of these flies is also speculated to have occurred as a result of adaptive radiation. 

Each species has individual preference for mating ceremonies and territories which involve factors of light, temperature, and humidity

Differences in food sources-

herbaceous v. carnivorous

Body, wing size and shape

• Adaptive situations often cause plants to evolve the available pollinators, such as changing insect spp., to birds, etc.

• Point: Radiations can affect multiple levels – a waterfall

Cyrtandra

Flower Leaf Fruit